HomeMy WebLinkAboutMINUTES - 11022010 - C.06RECOMMENDATION(S):
APPROVE the Upper and Lower Sand Creek Basin Expansion Project and AUTHORIZE
the Public Works Director, or designee, to advertise the project [DCD-CP#09-52] Project
No.: 7589-6D8518, and
FIND on the basis of the Initial Study Mitigated Negative Declaration and all comments
received and staff responses contained herein, that there is no substantial evidence that the
project will have a significant effect on the environment, and
ADOPT the Mitigated Negative Declaration and Mitigation and Monitoring Reporting Plan
in compliance with the California Environmental Quality Act (CEQA) (the custodian of
which is the Department of Conservation and Development Director who is located at 651
Pine Street, Martinez), and
DIRECT the Director of Conservation and Development to file a Notice of Determination
with the County Clerk, and
AUTHORIZE the Chief Engineer to arrange for payment of a $25 fee to the Department of
APPROVE OTHER
RECOMMENDATION OF CNTY ADMINISTRATOR RECOMMENDATION OF BOARD COMMITTEE
Action of Board On: 11/02/2010 APPROVED AS RECOMMENDED OTHER
Clerks Notes:
VOTE OF SUPERVISORS
AYE:John Gioia, District I Supervisor
Gayle B. Uilkema, District II
Supervisor
Mary N. Piepho, District III
Supervisor
Susan A. Bonilla, District IV
Supervisor
Federal D. Glover, District V
Supervisor
Contact: Claudia Gemberling,
313-2192
I hereby certify that this is a true and correct copy of an action taken and entered on the minutes of the
Board of Supervisors on the date shown.
ATTESTED: November 2, 2010
David J. Twa, County Administrator and Clerk of the Board of Supervisors
By: EMY L. SHARP, Deputy
cc: S. Ybarra, Auditor Controller, H. Li, DCD, P. Denison, Finance, P. Detjens, Flood Control, C. Roner, Flood Control, L. Chavez, Environmental, M.
Parella, Environmental
C. 6
To:Board of Supervisors
From:Julia R. Bueren, Public Works Director/Chief Engineer
Date:November 2, 2010
Contra
Costa
County
Subject:APPROVE and AUTHORIZE the Public Works Director, or designee, to advertise the Sand Creek Basin
Expansion Project
Conservation and Development for processing, a $50 fee to the County Clerk for filing the
Notice of Determination, and payment of $2,010.25 for California Department of Fish and
Game fees.
RECOMMENDATION(S): (CONT'D)
FISCAL IMPACT:
There is no impact to the County General Fund. This project is funded by Drainage Area
130 (100%).
BACKGROUND:
Contra Costa County Flood Control and Water Conservation District (Flood Control
District) proposes to expand the interim flood control basins in the lower Marsh Creek
watershed to attenuate flows from the upper Marsh Creek watershed, which will help
provide flood protection for surrounding and downstream communities. The operation of
the Lower Sand Creek Basin (LSCB) is contingent upon the Upper Sand Creek Basin
(USCB) operating to meter peak flows.
Sand Creek is the largest tributary in the lower Marsh Creek Watershed as it contributes
approximately 15 square miles of watershed area to Marsh Creek. The primarily goal of
the improvements is to prevent flooding along the lower reach of Marsh Creek between
Sand Creek and the Marsh Creek outfall into the Sacramento-San Joaquin River at Big
Break in Oakley.
In 1990, the Contra Costa County Board of Supervisors approved an Environmental
Impact Report (EIR) that analyzed the environmental effects of establishing five (5)
drainage areas in the Marsh Creek Watershed, along with associated drainage
improvements. In 1992, the Flood Control District developed the Marsh Creek Watershed
Plan in order to address the deficiency of flood storage capacity in Marsh Creek. A
subsequent EIR evaluated eight (8) alternative sites and the Upper and Lower Sand Creek
Basins were selected for construction of regional flood control facilities in the lower
Marsh Creek Watershed. USCB was constructed in 1994 by funds from Assessment
District 27 in Antioch; LSCB was constructed in 1995 by funds from Subdivision 7950.
Both basins have each been constructed to an interim size and configuration large enough
to mitigate urban runoff from specific sites, and only local drainage enters each basin.
The regional goal for USCB and LSCB is to attenuate peak flows from Sand Creek into
Marsh Creek to 400 cubic feet per second for a 100-year storm event. Analyses of the
Sand Creek drainage area indicates that 900-acre feet and 300-acre feet of flood storage
capacity are ultimately required at the USCB and LSCB sites, respectively. The
stormwater generated in the watershed conveyed by Sand Creek and local urban
stormwater runoff will flow into the two basins where it will be stored and released
slowly through the basin outlets, reducing peak flows downstream and reducing the
potential for flooding downstream properties.
The USCB will be the first of the two basins to be expanded. The project will expand the
approximate 41-acre basin to approximately 62 acres, increasing its flood storage
capacity from 123-acre feet to 900-acre feet (35-foot maximum depth). The expansion
will consist of excavating the basin floor to create a deeper basin where water will be
held and slowly released downstream during major storm events. The basin will have
multiple levels of excavation. Excavation depths will range from 0 to approximately 37
feet below existing grade, resulting in proposed basin elevations ranging from 158 feet
above mean sea level in the lowest tier of the basin floor to 195 feet at the basin’s
perimeter. The basin expansion extends south of Sand Creek. The lowest (southern) tier
will include Sand Creek; approximately 3,876 feet of Sand Creek will be excavated 10
feet below its current elevation of which approximately 3,612 feet will be reconstructed
with a fluvial geomorphic (natural creek) design to restore and enhance Sand Creek
within the basin; the remaining 264 feet will be re-created on-site as wetland acreage.
Construction is planned to begin Spring 2011 and be completed by October 2011.
Following the USCB expansion, the LSCB portion of the project will expand the
approximate 19-acre interim basin to approximately 23 acres, increasing its flood storage
capacity from 40-acre feet to 300-acre feet (22-foot maximum depth). The expansion will
consist of excavating the basin floor to create a deeper basin where water will be held
slowly and released downstream during major storm events. Similar to USCB, the basin
will have multiple levels of excavation. Excavation depths will range from 4 to 23.5 feet
below existing grade resulting in basin elevations ranging from 88 feet above mean sea
level in the lowest tier of the basin floor to 110 feet at the basin’s perimeter. The basin
expansion extends north of Sand Creek. The lowest (northern) tier will include Sand
Creek; approximately 1,100 feet of Sand Creek will be excavated and reconstructed with
a wetland mitigation area within the expanded basin. Construction is anticipated for 2016
and will take approximately 6 months to complete.
No traffic impacts are anticipated as construction of the basins will occur off-road.
Traffic measures will be in place to minimize traffic impacts from construction-related
vehicles and trucks leaving and entering the project sites.
Real property transactions including, but not limited to, property acquisitions and
construction easements, will be required.
The project is located within the East Contra Costa County Habitat Conservation Plan
(HCP) inventory area. Therefore, in addition to on-site mitigation, the District will pay
fees to the HCP Conservancy. In addition, avoidance and minimization measures will be
implemented prior to and during construction to prevent direct and indirect impacts to
special-status species as well as other species that occur in the area.
CONSEQUENCE OF NEGATIVE ACTION:
The Flood Control District will not be able to construct the expansion of the USCB and
LSCB to their ultimate configurations and would not be able to provide regional flood
level protection for the surrounding communities.
CHILDREN'S IMPACT STATEMENT:
Not Applicable
Not Applicable
ATTACHMENTS
Initial Study
Comment & Response
NOD
INITIAL STUDY/MITIGATED NEGATIVE DECLARATION
UPPER AND LOWER SAND CREEK BASIN
EXPANSION PROJECT
ANTIOCH AND BRENTWOOD, CONTRA COSTA COUNTY
Contra Costa County Flood Control and Water Conservation District
255 Glacier Drive
Martinez, CA 94553
Project No.: 7589-6D8518
CP# 09-52
SEPTEMBER 2010
Upper Sand Creek Basin
Lower Sand Creek Basin
Initial Study/Mitigated Negative Declaration Upper and Lower Sand Creek Basin Expansion Project
Contra Costa County Flood Control and Water Conservation District September 2010
1
CALIFORNIA ENVIRONMENTAL QUALITY ACT
INITIAL STUDY/MITIGATED NEGATIVE DECLARATION
[Pursuant to Public Resources Code Section 21080(c) and California Code of Regulations, Title 14, Sections 15070-15071]
In compliance with the California Environmental Quality Act (CEQA) (California Public Resources
Code, Section 21000, et seq.), this Initial Study has been prepared to determine whether an
Environmental Impact Report (EIR) or a Negative Declaration needs to be prepared, or to identify
the significant environmental effects to be analyzed in an EIR.
PROJECT TITLE
Upper and Lower Sand Creek Basin Expansion Project
LEAD AGENCY NAME AND ADDRESS
Contra Costa County Department of Conservation and Development
651 Pine Street, North Wing – 4th Floor
Martinez, California 94553
CONTACT PERSON AND PHONE NUMBER
Claudia Gemberling (925) 313-2192
Environmental Analyst II
Contra Costa County Public Works Department
PROJECT LOCATION
The Upper Sand Creek Basin (USCB) is located in Antioch, approximately 1,500 feet east of
Deer Valley Road.
The Lower Sand Creek Basin (LSCB) is located in Brentwood north of Sand Creek Road and
west of Fairview Avenue, east of the Highway 4 Bypass.
PROJECT SPONSOR’S NAME AND ADDRESS
Contra Costa County Flood Control and Water Conservation District
255 Glacier Drive
Martinez, California 94553
GENERAL PLAN AND ZONING DESIGNATIONS
Upper Sand Creek Basin:
Contra Costa County: Public/Semi-Public (Contra Costa County 2005a)
City of Antioch: Public Facility (City of Antioch 2003a)
Lower Sand Creek Basin:
Contra Costa County: Public/Semi-Public (Contra Costa County 2005a)
City of Brentwood – Public Facility (City of Brentwood 2009a)
Contra Costa County Flood Control and Water Conservation District (Flood Control District)
proposes to expand the interim flood control basins in the lower Marsh Creek watershed to
attenuate flows from the upper Marsh Creek watershed, which will help provide flood protection for
surrounding and downstream communities. The operation of the LSCB is contingent upon the
USCB operating to meter peak flows.
Initial Study/Mitigated Negative Declaration Upper and Lower Sand Creek Basin Expansion Project
Contra Costa County Flood Control and Water Conservation District September 2010
2
BACKGROUND AND PURPOSE
Historically, the land use in the watershed has been predominantly cattle ranching and farming.
Since the early 1990s, the cities of Antioch and Brentwood have rapidly urbanized with a large
increase of residential and commercial developments. The Flood Control District is collaborating
with the cities on infrastructure needs associated with urbanization to improve flood protection for
the residents and businesses in this part of the County (Contra Costa County Flood Control and
Water Conservation District [Flood Control District] 2008).
In 1990, the Contra Costa County Board of Supervisors, in their capacity as Directors of the Flood
Control District, approved an Environmental Impact Report (EIR) that analyzed the environmental
effects of establishing five (5) drainage areas in the Marsh Creek watershed, along with associated
drainage improvements. In 1992, the Flood Control District developed the Marsh Creek Watershed
Plan in order to address the deficiency of flood storage capacity in Marsh Creek. The funding
mechanism to implement the Watershed Plan was the formation of Drainage Area 104 (DA 104).
New development within the DA 104 boundary is required to contribute to the DA 104 fund, which
is earmarked for construction of infrastructure improvements in the watershed. A subsequent EIR
evaluated the alternative sites for DA 104 and the Upper and Lower Sand Creek Basins were
selected for construction of regional flood control facilities (Flood Control District 1992).
Upper Sand Creek Basin (USCB) was constructed in 1994 by funds from Assessment District 27 in
Antioch; Lower Sand Creek Basin (LSCB) was constructed in 1995 b y funds from Subdivision
7950. Both basins have each been constructed to an interim size and configuration large enough
to mitigate urban runoff from specific sites, and only local drainage enters each basin. Ultimately,
the basins will become regional facilities when Sand Creek is routed through the basins to
substantially reduce peak flows and provide flood protection to regions around Sand Creek and
Marsh Creek (Flood Control District 1992).
Sand Creek is the largest tributary in the lower Marsh Creek Watershed as it contributes
approximately 15 square miles of watershed area to Marsh Creek (Flood Control District 2008).
The primarily goal of the improvements is to prevent flooding along the lower reach of Marsh Creek
between Sand Creek and the Marsh Creek outfall into the Sacramento-San Joaquin River at Big
Break in Oakley (Flood Control District 1992). The regional goal for USCB and LSCB is to
attenuate peak flows from Sand Creek into Marsh Creek to 400 cubic feet per second for a 100-
year storm event. Analyses of the Sand Creek drainage area indicates that 900-acre feet and 300-
acre feet of flood storage capacity are ultimately required at the USCB and LSCB sites,
respectively. The stormwater generated in the watershed will be conveyed by Sand Creek and
local stormwater runoff to the two basins where it will be stored and released slowly through the
basin outlets, reducing peak flows downstream and reducing the potential for flooding downstream
properties (Flood Control District 2008).
EXISTING SETTING/PROPOSED PROJECT DESCRIPTION
Contra Costa County has 31 major watersheds and sub-watersheds. Sand Creek Watershed is
located within the Marsh Creek Watershed, the second largest watershed in the County (Contra
Costa County 2003). Creek flows in the Marsh Creek Watershed originate in the Mount Diablo
foothills (Morgan Territory) and flow down the eastern flanks of the Mount Diablo foothills. The
terrain in the vicinity of USCB consists of rolling hills to its west, which slope to the east into flat
lands in the vicinity of LSCB.
Initial Study/Mitigated Negative Declaration Upper and Lower Sand Creek Basin Expansion Project
Contra Costa County Flood Control and Water Conservation District September 2010
3
Upper Sand Creek Basin
Existing Setting
The USCB interim basin is located approximately 1,500 feet east of Deer Valley Road in Antioch.
The natural terrain surrounding the site consists of rolling hills along the west and south that give
way to flat lands to the north and east. Ground elevations in the area range 200 feet in elevation
from the west to 180 feet in elevation to the east with a low of about 160 feet in elevation at the
creek bottom to a high of about 330 feet in elevation atop the hill south of the basin (USGS 1953,
1978). Sand Creek borders the basin along its southern and eastern boundaries; the relatively
steep banks are 15 to 20 feet high. Prior to construction of the interim basin, the elevation ranged
from 194 feet along the west side of the basin to 180 feet along the east side.
The existing basin elevation ranges from 176 feet above mean sea level at the basin floor to 194
feet along the perimeter of the elevated berms. The interim basin has a flood storage capacity of
123-acre feet (GEI 2009). It receives local urban runoff from nearby residential developments to
the north. The urban runoff flows into two 84-inch diameter inlet pipes at the northwest side of the
basin which drains into a low-flow channel within the basin’s floor and outfalls into Sand Creek via
outfall pipes at the southeast side of the basin (GEI 2009) (Figure 1).
The low-flow channel within the basin floor contains wetland vegetation surrounded by annual
grassland that has been used for cattle grazing.
Figure 1: Upper Sand Creek Basin
Basin
Inlet Pipes
Spillway
Outlet Pipes
Sand Creek
Old Homestead
Ranch Complex
Proposed
Basin
Boundary
Existing Basin
Boundary
Initial Study/Mitigated Negative Declaration Upper and Lower Sand Creek Basin Expansion Project
Contra Costa County Flood Control and Water Conservation District September 2010
4
Project Design
The USCB will be the first of the two basins to be expanded. The project will expand the
approximate 41-acre basin to approximately 62 acres, increasing its flood storage capacity from
123-acre feet to 900-acre feet (35-foot maximum depth). The expansion will consist of excavating
the basin floor to create a deeper basin where water will be held and slowly released downstream
during major storm events. The basin will have multiple levels of excavation. Excavation depths will
range from 0 to approximately 37 feet below existing grade, resulting in proposed basin elevations
ranging from 158 feet above mean sea level in the lowest tier of the basin floor to 195 feet at the
basin’s perimeter. The basin expansion extends south of Sand Creek. The lowest (southern) tier
will include Sand Creek; approximately 3,876 feet of Sand Creek will be excavated 10 feet below
its current elevation of which approximately 3,612 feet will be reconstructed with a fluvial
geomorphic (natural creek) design to restore and enhance Sand Creek within the basin; the
remaining 264 feet will be re-created on-site as wetland acreage. The basin will have a continuous
perimeter service road as well as ramps to the basin bottom and drainage structures for
maintenance access (GEI 2009).
Soil removed from the excavation will be used to construct an earthen dam on the northeast side of
the basin to impound flood waters from major storm events. Any remaining soil will be hauled off -
site, stockpiled in the basin, or placed on adjacent parcel(s) for future use by interested parties.
Three hydraulic structures will control stormwater flows: (1) basin inlets on the west side that
receive upstream flows from Sand Creek and local urban runoff; (2) primary spillway/outfall pipe on
the southeast side (under the dam) to drain low-flow or ponded water in the basin, and (3) an
emergency spillway on the east side of the dam to direct flows greater than the 100 -year storm
event. The basin inlet structures will consist of a concrete box structure with an energy dissipater .
Rock slope protection will be placed upstream and downstream of the inlet s to protect against
erosion. The primary spillway will consist of a headwall, an orifice and piping that will extend
underneath the dam and discharge into Sand Creek. A manually-operated secondary spillway will
also be constructed to allow the rapid drawdown of the basin in the event that large back -to-back
storms are expected. The outfall to the creek will be through an energy dissipat er located on the
downstream toe of the dam. The emergency spillway will consist of a 225-foot wide broad-crested
weir on the northeast side of the basin and an associated concrete -block chute that will direct
overflows to Sand Creek. The basin perimeter will have a maintenance service road and
associated access ramps into the basin (GEI 2009).
The basin will be a normally dry reservoir (except for low-flows) that will attenuate peak runoff by
containing stormwater flows up to the 100 -year storm event. During typical rains, the creek and
local stormwater runoff flows will be carried through a low-flow channel and will discharge through
the primary outlet pipe under the dam. It would release a maximum peak flow of 131 cubic feet per
second. Creek flows that exceed the inlet-controlled discharge capacity of the outlet works from
more severe storms will then pond in the basin and the basin stage will rise. After the peak of the
storm has passed, and once the creek flow becomes smaller than the outlet discharge, the water
stored in the basin will be passively released back to Sand Creek. For storms greater than the 100-
year storm event, flood flows will pass over the emergency spillway and follow a controlled route to
enter the creek downstream of the basin (GEI 2009).
Project construction will require real property transactions such as land acquisitions, permanent
easement rights, and temporary construction easements on adjacent parcels. Construction is
anticipated to start in spring 2011 and will take approximately 6 months to complete. However,
depending on available funding, the project may be phased or constructed in later years.
Initial Study/Mitigated Negative Declaration Upper and Lower Sand Creek Basin Expansion Project
Contra Costa County Flood Control and Water Conservation District September 2010
5
Lower Sand Creek Basin
Existing Setting
The LSCB interim basin is located in Brentwood approximately 2 miles east downstream of USCB.
The terrain surrounding the site is primarily flat with a topographic elevation ranging from 125 feet
elevation above mean sea level from the west to 100 feet elevation to the east. The abandoned
Old Sand Creek Road and the channelized Sand Creek parallel the northern side of the basin.
Vacant fields adjoin the site to the north and east; residential developments adjoin the site to the
south and west (Figure 2).
Figure 2: Lower Sand Creek Basin
The existing basin elevation ranges from approximately 98 feet elevation above mean sea level at
the basin floor to 110 feet elevation along the perimeter of the elevated berms . It has a flood
storage capacity of 40-acre feet. This interim basin receives local urban runoff from the adjacent
development to the south and west. An 84-inch diameter basin inlet pipe at the northwest side of
the basin drains the local urban runoff into a low flow channel within the basin’s floor which drains
into Sand Creek via outfall pipes at the northeast side of the basin (Figure 2).
Similar to USCB, the low flow channel contains wetland vegetation surrounded by nonnative
grasses and weedy plant species.
Project Design
Following the USCB expansion, the LSCB portion of the project will expand the approximate 19-
acre interim basin to approximately 23 acres, increasing its flood storage capacity from 40-acre
feet to 300-acre feet (22-foot maximum depth). The expansion will consist of excavating the basin
floor to create a deeper basin where water will be held slowly and released downstream during
Basin
Inlet Pipes
Spillway Outlet
Pipes
Sand Creek
Old (Abandoned)
Sand Creek Road
Drop
Structure
City of Brentwood –
Future Park
Existing Basin
Boundary
Proposed Basin
Boundary
Low-Flow
Channel
Initial Study/Mitigated Negative Declaration Upper and Lower Sand Creek Basin Expansion Project
Contra Costa County Flood Control and Water Conservation District September 2010
6
major storm events. Similar to USCB, the basin will have multiple levels of excavation. Excavation
depths will range from 4 to 23.5 feet below existing grade resulting in basin elevations ranging from
88 feet above mean sea level in the lowest tier of the basin floor to 110 feet at the basin’s
perimeter. The basin expansion extends north of Sand Creek. The lowest (northern) tier will
include Sand Creek; approximately 1,100 feet of Sand Creek will be excavated and reconstructed
with a wetland mitigation area within the expanded basin.
Soil removed from the excavation will be used on-site where necessary and either hauled off-site
or used for filling the adjacent City of Brentwood parcel that will be developed into a future park.
LSCB includes construction of wing walls and inlet weir in Sand Creek at the northwest corner of
the basin to direct upstream Sand Creek flows into the basin. During low flows, runoff that enters
the basin will continue downstream, unattenuated, through a 60-inch diameter primary
spillway/outfall pipe that will extend along the north side of the basin under a bench in the basin
embankment. The 60-inch diameter pipe will continue approximately 1,300 feet downstream where
it will discharge into the existing drop structure in Sand Creek at the northwest corner of Fairview
Avenue and Sand Creek Road (Figure 2).
During significant storm events, higher flows will create increasing head at the inlet to the 60 -inch
diameter primary spillway pipe. The head will continue to rise until stormwater spills over the weir
crest and into the basin. At peak operation (100-year storm), approximately 210 cubic feet per
second (cfs) will continue downstream, through the 60-inch diameter primary spillway pipe, while
approximately 1,050 cfs will spill over the weir into the basin. After the peak of the storm passes,
the basin will drain via flap-gated openings that are proposed within the wall of the inlet weir. A
perpetual pond will not occur in the basin as the low flow section will be graded to drain and an 18 -
inch diameter secondary drain pipe will be installed at the downstream side of the basin.
Project construction will require real property transactions such as land acquis itions, permanent
easement rights, and temporary construction easements on adjacent parcels. Construction is
anticipated to start in 2016 and will take approximately 6 months to complete.
SURROUNDING LAND USES AND SETTING
Upper Sand Creek Basin
The immediate surrounding area primarily consists of undeveloped grasslands. An old ranch
homestead complex, located within the proposed expansion area, and a formerly-occupied
residential building, now owned and utilized by the Antioch Unified School District as a conference
center, are located just southwest of the existing basin. A magnet school and Kaiser Hospital are
located approximately ¼ mile to the north followed by residential developments. Sand Creek Road
that will extend west from the planned Sand Creek Road/Highway 4 Bypass interchange in
Brentwood will border the basin’s north side. Developed areas in Brentwood are located
approximately 4 miles to the east and southeast, which include commercial retail centers and
residential neighborhoods located off of the Highway 4 Bypass.
Lower Sand Creek Basin
The surrounding area primarily consists of residential neighborhoods and commercial retail centers
to the west. The vacant land immediately adjacent to the north side of the basin is planned for
residential development; the vacant land immediately adjace nt to the east side of the basin is
owned by the City of Brentwood and is planned for a park.
Initial Study/Mitigated Negative Declaration Upper and Lower Sand Creek Basin Expansion Project
Contra Costa County Flood Control and Water Conservation District September 2010
7
OTHER PUBLIC AGENCIES WHOSE APPROVAL IS REQUIRED
The following agency approvals will be required for both basin expansion projects:
East Contra Costa County Habitat Conservancy
The East Contra Costa County Habitat Conservancy is a joint exercise of powers authority formed
by the cities of Brentwood, Clayton, Oakley, Pittsburg and Contra Costa County to implement the
East Contra Costa County Habitat Conservation Plan/Natural Community Conservation Plan
(HCP/NCCP). The HCP/NCCP provides a framework to protect natural resources in eastern
Contra Costa County, while improving and streamlining the environmental permitting process for
impacts on endangered species. The HCP/NCCP will allow the permittees (including the Contra
Costa County Flood Control and Water Conservation District, Contra Costa Water District, and
East Bay Regional Park District) to control endangered species permitting for activities and projects
in the region that they perform or approve. The HCP/NCCP also provides for comprehensive
species, wetlands, and ecosystem conservation and contributes to the recovery of endangered
species in northern California. The HCP/NCCP avoids project -by-project permitting that is generally
costly and time-consuming for applicants and often results in uncoordinated and biologically
ineffective mitigation (Contra Costa County 2006).
The HCP/NCCP has identified both basin expansions as covered activities. Therefore, the project
will comply with the HCP/NCCP.
U.S. Army Corps of Engineers – Sacramento District
Clean Water Act, Section 404 Permit
Section 404 of the Clean Water Act regulates permanent and temporary discharges of dredged or
fill material into jurisdictional waters of the United States, including wetlands. Sand Creek is
considered jurisdictional waters of the U.S. (U.S. Army Corps of Engineers [Corps] 2010a).
Therefore, a Section 404 permit will be obtained.
Regional Water Quality Control Board – Central Valley Region
Clean Water Act, Section 401, Water Quality Certification
Section 401 of the Clean Water Act also regulates permanent and temporary discharges of
dredged or fill material into jurisdictional waters of the United States, and waters of the state,
including wetlands (California Regional Water Quality Control Board [CRWQCB] 2010a). Sand
Creek is considered jurisdictional waters of the U.S. Therefore, the Flood Control District will obtain
a Water Quality Certification.
State Water Resources Control Board
National Pollution Discharge Elimination System (NPDES) General Permit for Storm Water
Discharges Associated with Construction Activity
Construction activities that disturb more than one acre of soil are required to obtain a NPDES
permit which will require the contractor prepare and implement plans to prevent construction -
related pollutants from contacting stormwater and keeping all products of erosion from moving off
site into receiving waters (CRWQCB 2010b). Each basin expansion project will result in
disturbance to more than one acre of soil. Therefore, coverage under the General Construction
Permit will be obtained. .
Initial Study/Mitigated Negative Declaration Upper and Lower Sand Creek Basin Expansion Project
Contra Costa County Flood Control and Water Conservation District September 2010
8
Department of Fish and Game – Region 3
Fish and Game Code, Section 1602, Lake and Streambed Alteration Agreement
Notification is required when an activity will substantially divert or obstruct the natural flow of any
river, stream or lake (California Department of Fish and Game [CDFG] 2010). Both basins include
disturbances to Sand Creek. Therefore, the Department of Fish and Game will be notified.
Department of Water Resources, Division of Safety of Dams
The Division of Safety of Dams (DSOD) has jurisdiction of reservoirs if the dam height is more than
6 feet and it impounds 50 acre-feet or more of water, or if the dam is 25 feet or higher and
impounds more than 15 acre-fee of water, unless it is federally-owned or exempted under special
provisions described in Sections 6004, 6025, or 6026 of the California Water Code. The DSOD
reviews and approves plans and specifications for the design of dams and oversees their
construction to ensure compliance with the approved plans and specifications. The DSOD requires
that an application be submitted for the construction, enlargement, repair, alteration or removal of a
dam (California Department of Water Resources [CDWR] 2010). Both basins fall under DSOD
jurisdiction.
City of Antioch, City of Brentwood
The City of Antioch and Brentwood may require grading permits and/or truck transportation permit
for haul trucks (City of Antioch 2003a, City of Brentwood 2010a).
Initial Study/Mitigated Negative Declaration Upper and Lower Sand Creek Basin Expansion Project
Contra Costa County Flood Control and Water Conservation District September 2010
10
Less Than
Significant
Potentially With Less Than
Significant Mitigation Significant No
ISSUES: Impact Incorporated Impact Impact
I. AESTHETICS
Would the project:
a) Have a substantial adverse effect on a
scenic vista?
b) Substantially damage scenic resources,
including, but not limited to, trees, rock
outcroppings, and historic buildings within
a state scenic highway?
c) Substantially degrade the existing visual
character or quality of the site and its
surroundings?
d) Create a new source of substantial light or
glare which would adversely affect day or
nighttime views in the area?
The USCB and LSCB are located northeast of Mount Diablo and south of the Sacramento-San
Joaquin River Delta in a low-lying valley at the northeastern edge of the Mount Diablo foothills.
This area provides a rural, small-town atmosphere and open space setting with expansive views of
natural features such as Mount Diablo and the foothills to the west and south (City of Brentwood
2009b). While views of Mount Diablo and foothill ridgelines in the distance reflect the ex isting rural
character, the visual context of the area is greatly influenced by surrounding development, creating
a mixed rural and urban environment.
USCB is primarily surrounded by undeveloped grasslands; nearby developed areas include a
magnet school, a Kaiser Hospital facility, and residential neighborhoods to the north. An old ranch
homestead complex is located in the southwestern portion of the project area, which will be
removed (Figure 1). The existing basin contains primarily grassland with the exception of seasonal
wetland vegetation associated with the low flow drainage. Scattered oak and willow trees are
scattered along the banks of Sand Creek. The project will result in removal of these trees.
LSCB is primarily surrounded by residential neighborhoods with commercial and retail centers to
the west at the State Route 4 Bypass interchange. The basin is generally dominated by nonnative
grasses and weedy plant species with the exception of seasonal wetland vegetation associated
with the low flow drainage. Several red willow trees are scattered throughout the basin along with a
Monterey pine and valley oak that occur just outside the fence line of the northern boundary
(Figure 2). The project will result in removal of these trees.
Initial Study/Mitigated Negative Declaration Upper and Lower Sand Creek Basin Expansion Project
Contra Costa County Flood Control and Water Conservation District September 2010
11
IMPACT DISCUSSION
a) Would the project have a substantial adverse effect on a scenic vista?
The ridgelines of Mount Diablo and foothills provide a scenic view from both basins. The project
will not have a substantial adverse effect as no structures will be constructed that would
compromise views of the surrounding hills visible from the nearby residential communities.
Therefore, the project will have no impact.
b) Would the project substantially damage scenic resources, including, but not limited to, trees,
rock outcroppings, and historic buildings within a state scenic highway?
Neither USCB nor LSCB are located on or adjacent to a state scenic highway. While Deer
Valley Road, located west of USCB, is considered a County scenic route, the basin expansion
will not negatively affect the scenic views from Deer Valley Road (Contra Costa County 2005b).
Therefore, the project will have no impact.
c) Would the project substantially degrade the existing visual character or quality of the site and
its surroundings?
The surrounding areas for USCB and LSCB are continually being developed with residential
communities transitioning the rural character of the area to a more suburban character. The
City of Antioch (2003b) and City of Brentwood (2009c) General Plans have designated the
areas surrounding both the USCB and LSCB as large-scale planned communities. While the
vacant old ranch homestead complex at USCB retains much of its original character in its
original setting, it is in an advanced state of disrepair with some of the structures so dilapidated
that they are no longer structurally sound and are gradually collapsing. Deer Valley Road, the
main corridor in the area of USCB, provides views of the rural setting of the area. While the old
ranch homestead complex is currently visible from Deer Valley Road, views toward this
complex are limited due to the narrow and somewhat winding roadway that is frequently
travelled at higher speeds than its design speed. Further, views toward the ranch complex from
the surrounding residential communities are limited due to distance and other obstructions
associated with urban development.
The project would not substantially degrade the existing visual character or quality of the site
and its surroundings at either basin as project features would primarily be located at grade and
at sub-grade levels out of view of the surrounding area. In addition, disturbed areas and creek
realignment will be re-planted and re-seeded with vegetation appropriate to the area which will
re-establish the disturbed areas and enhance the visual setting. While construction of the
basins will be visible from surrounding areas, it will be temporary ending upon completion of the
project. Therefore, project impacts will be less than significant.
d) Would the project create a new source of substantial light or glare that would adversely affect
day or nighttime views in the area?
The projects and construction of the projects will not create a new source of permanent or
temporary substantial light or glare. Therefore, the projects will have no impact.
Initial Study/Mitigated Negative Declaration Upper and Lower Sand Creek Basin Expansion Project
Contra Costa County Flood Control and Water Conservation District September 2010
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Less Than
Significant
Potentially With Less Than
Significant Mitigation Significant No
ISSUES: Impact Incorporated Impact Impact
II. AGRICULTURE AND FOREST RESOURCES
Would the project:
a) Convert Prime Farmland, Unique Farmland,
or Farmland of Statewide Importance
(Farmland), as shown on the maps prepared
pursuant to the Farmland Mapping and
Monitoring Program of the California
Resources Agency, to non-agricultural use?
b) Conflict with existing zoning for agriculture use,
or a Williamson Act contract?
c) Conflict with existing zoning for, or cause
rezoning of, forest land (as defined in
Public Resources Code section 12220(g),
Timberland (as defined by Public Resources
Code section 4526), or timberland zoned
Timberland Production (as defined by
Government Code section 51104(g)?
d) Result in the loss of forest land or conversion
of forest land to non-forest use?
e) Involve other changes in the existing
environment which, due to their location
or nature, could result in conversion of
Farmland, to non-agricultural use?
The California Farmland Mapping and Monitoring Program (FMMP) was established in 1982 in
response to a critical need for assessing the location, quality, and quantity of agricultural lands and
conversion of these lands over time. FMMP is a non-regulatory program and provides a consistent
and impartial analysis of agricultural land use and land use changes throughout California.
Creation of the FMMP was supported by the Legislature and a broad coalition of building,
business, government, and conservation interests (California Department of Conservation [CDC]
2010a).
Prime Farmland has the best combination of physical and chemical features able to sustain long
term agricultural production. This land has the soil quality, growing season, and moisture supply
needed to produce sustained high yields. Farmland of Statewide Importance is similar to Prime
Farmland but with minor shortcomings, such as greater slopes or less ability to store soil moisture.
Unique Farmland is of lesser quality soils used for the production of the state's leading agricultural
crops. This land is usually irrigated, but may include non-irrigated orchards or vineyards as found
in some climatic zones in California (CDC 2010a).
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The California Land Conservation Act of 1965, better known as the Williamson Act (Act), created a
program to help counties preserve agricultural land and open space by offering a tax incentive to
property owners. The Act provides an arrangement where private landowners voluntarily restrict
their land to agricultural and compatible open space uses under a contract with the County, known
as a Land Conservation Contract. Contra Costa County has been implementing the Williamson Act
since 1968 when the Board of Supervisors adopted Ordinance 68-53, which authorized the
creation of Agricultural Preserves and the execution of Land Conserv ation Contracts pursuant to
state law (CDC 2010b, Contra Costa County Department of Conservation and Development
[CCCDCD] 2010).
Assembly Bill 32 (California Global Warming Solutions Act of 2006) recognizes that California is
the source of substantial amounts of GHG emissions. Therefore, Senate Bill 97 amended the
CEQA Guidelines, effective January 1, 2010, to establish that greenhouse gas (GHG) emissions
and the effects of GHG are appropriate subjects for CEQA analysis (OP R 2008). There is a
renewed attention on California forests and the role they play in the carbon cycle. The forest sector
is the second largest global source of human-caused carbon dioxide emissions largely due to
deforestation (California Climate Action Registry 2010). There is a need to understand how much
carbon dioxide California forests are currently producing and sequestering, and how much they
could sequester in the future (California Air Resource Board [CARB] 2010).
IMPACT DISCUSSION
a) Would the project convert Prime Farmland, Unique Farmland, or Farmland of Statewide
Importance (Farmland), as shown on the maps prepared pursuant to the Farmland Mapping
and Monitoring Program of the California Resources Agency, to non -agricultural use?
Prime Farmland, Unique Farmland, or Farmland of Statewide Importance lands do not occur
within or immediately adjacent to USCB or LSCB (CDC 2009a). While the lands within and
surrounding both basins are designated as Farmland of Local Importance, which is typically
used for livestock grazing and dryland grain production, their respective cities have designated
both areas as public facilities within large-planned communities. Therefore, project impacts will
be less than significant.
b) Would the project conflict with existing zoning for agricultural use, or a Williamson Act contract?
As discussed above, both basins are designated as Farmland of Local Importance, but neither
are Williamson Act contract lands. In addition, both basins are designated as public facility use
within large-planned communities. Therefore, the project will have no impact.
c) Conflict with existing zoning for, or cause rezoning of, forest land (as defined in Public
Resources Code section 12220(g), Timberland (as defined by Public Resources Code section
4526), or timberland zoned Timberland Production (as defined by Government Code section
51104(g)?
Forest land is land that can support 10 percent native tree cover of any species, including
hardwoods, under natural conditions, and that allows for management of one or more forest
resources, including timber, aesthetics, fish and wildlife, biodiversity, water quality, recreation,
and other public benefits. Timberland is non-federal government-owned land and designated
as experimental forest land which is available for and capable of growing a crop of trees of any
commercial species used to produce lumber and other forest products, including Christmas
trees (California Public Resources Code 2010). Timberland Production is the area that has
Initial Study/Mitigated Negative Declaration Upper and Lower Sand Creek Basin Expansion Project
Contra Costa County Flood Control and Water Conservation District September 2010
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been zoned and is devoted to and used for growing and harvesting timber, or for growing and
harvesting timber and compatible uses (California Government Code 2010).
Neither basin is zoned as forest land, timberland, or Timberland Production as they are both
designated for public facility use within large-planned communities. Therefore, the project will
have no impact.
d) Result in the loss of forest land or conversion of forest land to non-forest use?
Neither basin is zoned as forest land, timberland, or Timberland Production as they are both
designated for public facility use within large -planned communities. Therefore, the project will
have no impact.
e) Would the project involve other changes in the existing environment, which due to their location
or nature, could result in conversion of Farmland to non-agricultural use?
No cattle grazing occurs within the LSCB. Cattle grazing currently occurs within the USCB and
adjacent parcels. However, cattle grazing will no longer continue at USCB after project
completion in order to minimize erosion and protect re-vegetated areas. While cattle grazing
will no longer occur at USCB, the basin has already been designated as a public facility within
a large-planned community (City of Brentwood 2009c). Therefore, project impacts will be less
than significant.
Initial Study/Mitigated Negative Declaration Upper and Lower Sand Creek Basin Expansion Project
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Less Than
Significant
Potentially With Less Than
Significant Mitigation Significant No
ISSUES: Impact Incorporated Impact Impact
III. AIR QUALITY
Would the project:
a) Conflict with or obstruct implementation of
the applicable air quality plan?
b) Violate any air quality standard or contribute
substantially to an existing or projected air
quality violation?
c) Result in a cumulatively considerable net
increase of any criteria pollutant for which
the project region is non-attainment under
an applicable federal or state ambient air
quality standard (including releasing
emissions which exceed quantitative
thresholds for ozone precursors)?
d) Expose sensitive receptors to substantial
pollutant concentrations?
e) Create objectionable odors affecting a
substantial number of people?
Air quality is affected by the rate, amount, and location of pollutant emissions, and the associated
meterological conditions that influence pollutant movement and dispersal. Atmos pheric conditions,
including wind speed, wind direction, and air temperature, in combination with local surface
topography (i.e., geographic features such as mountains and valleys), determine the effect of air
pollutant emissions on local air quality. The combination of low wind speeds and low inversions
produces the greatest concentration of air pollutants. On days without inversions, or on days of
winds averaging over 15 miles per hour, smog potential is greatly reduced (CCTA 2009).
Both basins are located in the eastern portion of Contra Costa County which is generally well
ventilated by winds flowing through the Carquinez Strait and Delta. While the terrain does not
restrict ventilation, temperatures are quite warm, promoting the formation of ozone (Contra Costa
County 2005d).
Regulatory Setting
Air pollution can cause long-term health effects such as cancer, birth defects, neurological
damage, asthma, bronchitis, or genetic damage; or short -term acute effects such as eye watering,
respiratory irritation, and headaches (Bay Area Air Quality Management District [BAAQMD] 2010a).
The 1970 federal Clean Air Act established national ambient air quality standards for six criteria
pollutants: ozone, carbon monoxide, nitrogen dioxide, sulfur dioxide, particulate matter, and lead;
to protect public health and welfare. Amendments to the federal Clean Air Act require the U.S.
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Environmental Protection Agency to classify air basins or portions of thereof, as either “attainment”
or “nonattainment” for each criteria pollutant, based on whether or not the national standards have
been achieved. The California Clean Air Act also requires areas to be designated as “attainment”
or “nonattainment” based on whether or not state standards have been achieved. Under the
federal and state Clean Air Acts, air basin jurisdictions with “nonattainment” areas are required to
prepare air quality plans that include strategies for achieving attainment (CCTA 2009). The Bay
Area Air Quality Management District (BAAQMD) is the primary agency responsible for assuring
that the National and California Air Ambient Standards are attained and maintained in the San
Francisco Bay Area Air Basin (SFBAAB). The SFBAAB is currently designated as a nonattainment
area for state and national ozone standards, and national particulate matter (PM 10, PM 2.5)
standards. The Bay Area 2010 Clean Air Plan (BAAQMD 2010a) includes strategies that are
implemented through various BAAQMD programs and rules and regulations. Since the Bay Area
was recently designated as non-attainment for the national PM 2.5 standard, the BAAQMD is
required to prepare a PM 2.5 State Implementation Plan pursuant to federal air quality guidelines
by December 2012 (BAAQMD 2010b).
In order to address global climate change associated with air quality impacts, CEQA statutes were
amended to require evaluation of greenhouse gas (GHG) emissions (global pollutants) (discussed
further in section VII) which includes criteria air pollutants (regional pollutants) and toxic air
contaminants (local pollutants). As a result, the BAAQMD adopted CEQA thresholds of
significance for criteria air pollutants and GHGs, and issued updated CEQA guidelines to assist
lead agencies in evaluating air quality impacts to determine if a project’s individual emissions
would be cumulatively considerable. Various modeling tools are used to estimate emissions based
on the type of project (i.e., land use developments, linear transportation and utility projects)
(BAAQMD 2010a).
In addition to criteria air pollutants, naturally-occurring asbestos (NOA), a toxic air contaminant, is
also an air pollutant of concern. It can cause lung cancer and mesothelioma which is dependent
upon the type of asbestos fibers inhaled and exposure levels. NOA is typically associated with
serpentinite and ultramafic rocks formed in high-temperature environments below the surface of
the earth when metamorphic conditions are right for the formation of asbestos. The BAAQMD
requires that projects where NOA is likely to be found implement t he best available dust mitigation
measures in order to reduce and control dust emissions as well as notification to the BAAQMD
(BAAQMD 2010a). Neither basin is located within an area identified as having rocks associated
with NOA (CDC 2010c).
IMPACT DISCUSSION
a) Would the project conflict with or obstruct implementation of the applicable air quality plan?
The expanded flood control basins would not generate an increase of air pollutant
concentrations. However, construction of the basin expansions would result in temporary
increases of air pollutant concentrations from construction equipment and off-haul truck
exhaust (criteria air pollutants) and soil excavations (PM dust). The project consists of
excavating approximately 62 acres of the existing and expansion areas at USCB which would
require the movement of approximately 420,000 cubic yards of soil. Approximately 105,000
cubic yards will be used on-site for construction of the “fill” dam; 40,000 cubic yards will be left
on-site or on adjacent properties, and 110,200 cubic yards will be hauled away to nearby
projects within a 10-mile radius (i.e., Highway 4/Loveridge Road Expansion in Antioch, Sand
Creek Interchange in Brentwood, EBART in Antioch). Construction is currently planned for
2011 and will take approximately six months to complete.
Initial Study/Mitigated Negative Declaration Upper and Lower Sand Creek Basin Expansion Project
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Approximately 249,000 cubic yards of soil will be excavated from LSCB of which approximately
47,000 cubic yards will be used on-site, leaving approximately 202,000 cubic yards that will be
hauled away or used for the adjacent City of Brentwood parcel that is planned for a future park
and/or to nearby projects in need of soil within a 20-mile radius. Construction is currently
planned for 2016 and will take approximately six months to complete.
The project did not meet the BAAQMD preliminary screening criteria due to the extent of soil
movement and transport. Therefore, estimated construction emissions were quantified using
the URBEMIS model (2007 version 9.2.4) to determine if project-related construction emissions
exceed the BAAQMD daily significance thresholds (LSA 2010). Since specific types of
construction equipment and vehicles are not known at this time, the following estimates are
based on URBEMIS defaults based on acres to be disturbed and off-site hauls within a six-
month period.
Table 1: URBEMIS Model Estimates
Basin
Total
Area to
be
Disturbed
Maximum
Daily Acreage
to be
Disturbed
Daily
Onsite
Cut/Fill
Daily
Offsite
Cut/Fill
Daily On-
Road Truck
Travel
Off-Road Equipment
(Operating 8 hrs/day)
USCB
(2011) 62 acres 15.5 acres
1208
cubic
yards
918
cubic
yards
420.61
(vehicle
miles
traveled
using 20-
cubic yard
truck within
10-mile
round trip)
1 Excavator (168
horsepower [hp])
(0.57 load factor)
1 Grader (174 hp)
( 0.61 load factor)
1 Rubber Tired Dozer
(357 hp)
(0.59 load factor)
3 Tractors/Loaders/
Backhoes (108 hp)
(0.55 load factor)
1 Water Truck (189 hp)
(0.5 load factor)
LSCB
(2016) 21 acres 5.25 acres
391
cubic
yards
1683
cubic
yards
1870.37
(vehicle
miles
traveled
using 20-
cubic yard
truck within
20-mile
round trip)
1 Grader (174 hp)
(0.61 load factor)
1 Rubber Tired Dozer
(357 hp)
(0.59 load factor)
2 Tractors/Loaders/
Backhoes (108 hp)
(0.55 load factor)
1 Water Truck (189 hp)
(0.5 load factor)
As shown in Table 2 on the following page, neither basin expansions will exceed the daily
significance thresholds.
Initial Study/Mitigated Negative Declaration Upper and Lower Sand Creek Basin Expansion Project
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Table 2: BAAQMD Significance CEQA Threshold Levels for Construction-Related
Emissions
Criteria Air
Pollutant/Precursor
Daily Average
Emissions
(lb s/day)
USCB
Project Emissions
(lbs/day)
LSCB
Project Emissions
(lbs/day)
Reactive organic gas
(ROG) 54 5.98 4.95
Carbon monoxide (CO) N/A 28.26 24.69
Nitrogen oxides (NOx) 54 51.68 48.15
Particulate Matter 10
(PM10)
82
(exhaust) 2.76 1.99
Particulate Matter 2.5
(PM2.5)
54
(exhaust) 2.5 1.83
Greenhouse gases
(GHGs)
N/A*
1,100 metric tons/year**
379.32
metric tons/year
575.93
metric tons/year)
* Significance threshold levels have not been determined at this time.
** Significance threshold level for operational-related sources.
Based on the BAAQMD CEQA Guidelines, if daily average construction -related criteria air
pollutants or precursors would not exceed any of the BAAQMD thresholds of significance, the
project would result in a less-than-significant impact to air quality. However, the BAAQMD
recommends the implementation of all Basic Construction Mitigation Measures as listed in
Table 8-2 of the BAAQMD CEQA Guidelines whether or not construction-related emissions
exceed applicable thresholds of significance. Therefore, the proje ct will implement the following
applicable air pollution control measures:
All exposed surfaces (e.g., parking areas, staging areas, soil piles, graded areas, and
unpaved access roads) will be watered two times per day.
All haul trucks transporting soil, sand, or other loose material off-site will be covered.
All visible mud or dirt track-out onto adjacent public roads will be removed using wet
power vacuum street sweepers at least once per day. Dry power sweeping will not be
used.
All vehicle speeds on unpaved roads will be limited to 15 mph.
Idling times will be minimized by either shutting equipment off when not in use or
reducing the maximum idling time to 5 minutes. Clear signage will be provided for
construction workers at all access points.
All construction equipment will be maintained and properly tuned in accordance with
manufacturer’s specifications. All equipment will be checked by a certified mechanic
and determined to be running in proper condition prior to operation.
Signs will be posted with the telephone number and person to contact regarding dust
complaints. Complaints will be corrected within 48 hours. The sign will also include the
BAAQMD phone number to ensure compliance.
The project will also require demolition of the old homestead ranch at USCB. Demolition of
existing buildings and structures are subject to BAAQMD Regulation 11, Rule 2 (Asbestos
Demolition, Renovation, and Manufacturing). This Rule is intended to limit as bestos emissions
associated with disturbance of asbestos-containing materials. It requires that lead agencies
and their contractors notify BAAQMD of renovation or demolition activities. All asbestos-
containing material found on the site must be removed prior to demolition or renovation activity
and disposed of appropriately and safely (BAAQMD 2010a). The on-site buildings have the
potential to contain asbestos-containing building materials and therefore, could result in
airborne asbestos emissions during demolition activities. In accordance to the BAAQMD
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Regulation 11, Rule 2, the Flood Control District or its contractor will notify the BAAQMD. All
asbestos-containing materials will be removed and properly disposed of prior to demolition
activities.
Implementation of the above-listed air pollution control measures is consistent with the air
quality plans. Therefore, project impacts will be less than significant.
b) Would the project violate any air quality standard or contribute substantially to an existing or
projected air quality violation?
The project would not violate any air quality standard or contribute substantially to an existing
project air quality violation with implementation of the air pollution control measures described
above. Therefore, project impacts will be less than significant.
c) Would the project result in a cumulatively considerable net increase of any criteria pollutant for
which the project region is non-attainment under an applicable federal or state ambient air
quality standard (including releasing emissions which exceed quantitative thresholds for ozone
precursors)?
The project would not result in a cumulatively considerable net increase of ozone with
implementation of the air pollution control measures described above. Therefore, project
impacts will be less than significant.
d) Would the project expose sensitive receptors to substantial pollutant concentrations?
Sensitive receptors include those segments of the population most susceptible to poor air
quality such as children, the elderly, and those with pre-existing serious health problems
affected by air quality which are those places such as schools/schoolyards, parks and
playgrounds, day care centers, nursing homes, hospitals, and residential communities
(BAAQMD 2010a).
The expanded flood control basins would not generate permanent air pollutant concentrations.
However, construction of the basin expansions would temporarily generate an increase in air
pollutant concentrations from construction equipment exhaust and from soil excavations
(particulate matter). The BAAQMD issued guidelines for estimating air quality health risk
impacts to sensitive receptors associated with construction activity. Construction-related
impacts can expose sensitive receptors to toxic air contaminants, including diesel particulate
matter (BAAQMD 2010c). The guidelines are based on minimum distance between the project
area boundary and the sensitive receptor. Based on the acreages of impact of USCB and
LSCB, the offset required from sensitive receptors to avoid significant health risks is
approximately 1,000 feet for USCB and 225 feet for LSCB. The closest sensitive receptor to
USCB is the Kaiser Hospital facility which is approximately 2,400 feet from the project area. For
LSCB, while there are residential developments that are within 225 feet along the west side of
the project area, the project would not result in substantial pollutant concentrations with
implementation of the air pollution control measures described above. Therefore, project
impacts will be less than significant.
e) Would the project create objectionable odors affecting a substantial number of people?
The expanded flood control basins would not generate permanent objectionable odors.
However, construction of the basin expansions has the potential to generate an increase in
objectionable odors from diesel exhaust of construction equipment. The USCB and surrounding
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parcels are primarily undeveloped and not occupied by people; while LSCB is primarily
surrounded by residential development, implementation of the air pollution control measures
described above will minimize objectionable odors to nearby residences. In addition,
construction will occur during the weekday hours when most residents are at work or school.
Therefore, project impacts will be less than significant.
Initial Study/Mitigated Negative Declaration Upper and Lower Sand Creek Basin Expansion Project
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Less Than
Significant
Potentially With Less Than
Significant Mitigation Significant No
ISSUES: Impact Incorporated Impact Impact
IV. BIOLOGICAL RESOURCES
Would the project:
a) Have a substantial adverse effect, either
directly or through habitat modifications,
on any species identified as a candidate,
sensitive, or special status species in local
or regional plans, policies, or regulations, or
by the California Department of Fish and
Game or U.S. Fish and Wildlife Service?
b) Have a substantial adverse effect on any
riparian habitat or other sensitive natural
community identified in local or regional
plans, policies, regulations or by the
California Department of Fish and Game
or U.S. Fish and Wildlife Service?
c) Have a substantial adverse effect on
federally protected wetlands as defined
(including, but limited to, marsh, vernal
pool, coastal, etc.) through direct removal,
filling, hydrological interruption, or other
means?
d) Interfere substantially with the movement
of any native resident or migratory fish or
wildlife species or with established native
resident or migratory wildlife corridors, or
impede the use of native wildlife nursery sites?
e) Conflict with any local policies or
ordinances protecting biological
resources, such as a tree preservation
policy or ordinance?
f) Conflict with the provisions of an
adopted Habitat Conservation Plan,
or other approved local, regional, or
state habitat conservation plan?
Regulatory Setting
In 1973, the federal Endangered Species Act (ESA) was passed by Congress to protect
ecosystems supporting special-status species to be administered by the U.S. Fish and Wildlife
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Service (USFWS). The California Endangered Species Act (CESA) was passed as a parallel act to
be administered by the California Department of Fish and Game (CDFG). Special-status species
include:
USFWS-designated listing of threatened or endangered species as well as candidate species;
CDFG-designated listing of rare, threatened, or endangered species as well as candidate
species;
Species considered to be rare or endangered under the conditions of Section 15380 of the
CEQA Guidelines such as those identified in the Inventory of Rare and Endangered Vascular
Plants of California by the California Native Plant Society; and
Other species that are considered sensitive or of special concern due to limited distribution or
lack of adequate information to permit listing, or rejection for state or federal status such as
Species of Special Concern designated by the CDFG.
The USFWS and CDFG both publish lists of special-status species, which satisfy criteria
classifying them as endangered. Species that have been proposed for listing but have not yet been
accepted are classified as candidate species. Generally, the term endangered (federal, state)
refers to a species that is in danger of becoming extinct throughout all or a significant portion of its
range, while a threatened (federal, state) or rare (state) species is one that could become
endangered in the foreseeable future (CDFG 2010, USFWS 2010).
East Contra Costa County Habitat Conservation Plan/Natural Community Conservation Plan
The USCB and LSCB are located within the East Contra Costa County Habitat Conservation
Plan/Natural Community Conservation Plan (HCP/NCCP) inventory area (J SA 2006). The
HCP/NCCP identifies various development and maintenance activities (covered activities) that
have the potential to impact special-status species as well as sensitive habitats, natural
communities, and federal and state jurisdictional waters and wetlands in eastern Contra Costa
County. Activities not covered by the HCP/NCCP require direct consultation with the USFWS and
CDFG. The HCP/NCCP covers 28 special-status species.
Table 3: HCP/NCCP Covered Species
Plants Mount Diablo manzanita, Brittlescale, San Joaquin spearscale, Big tarplant,
Mount Diablo fairy lantern, Recurved larkspur, Round-leaved filaree, Diablo
helianthella, Brewer’s dwarf flax, Showy madia, Adobe navarretia
Invertebrates Longhorn fairy shrimp, Vernal pool fairy shrimp, Midvalley fairy shrimp, Vernal
pool tadpole shrimp
Amphibians California tiger salamander, California red-legged frog, Foothill yellow-legged frog
Reptiles Silvery legless lizard, Alameda whipsnake, Giant garter snake, Western pond
turtle
Birds/Raptors Tricolored blackbird, Golden eagle, Western burrowing owl, Swainson’s hawk
Mammals Townsend’s western big-eared bat, San Joaquin kit fox
The HCP/NCCP utilizes a variety of development-based fees to fund mitigation that will offset
losses of various types of land cover, covered species habitat, and other biological values. The
HCP/NCCP identifies measures to avoid or minimize impacts to special-status species. The
avoidance and minimization measures are consistent with the USFWS and CDFG guidelines for
the individual species. Special-status species not covered by the HCP/NCCP are also addressed
in this document.
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Qualified biologists reviewed federal, state, and local databases of special -status wildlife and plant
species and conducted habitat assessments and wetland delineations (Nomad 200 9a, RCL
Ecology 2009). The habitat assessment meets the HCP/NCCP planning survey guidelines. The
results of the habitat assessment and wetland delineation and the level of impacts to natural
resources present in the project area are presented in the appropriate discussions below.
Environmental Setting
Upper Sand Creek Basin
Habitat assessments and a wetland delineation were conducted in spring and fall 2008 (Nomad
2009a,b). In addition, habitat assessments were also conducted of the adjacent Av iano-Williamson
(LSA 2007) property on which a portion of the project will occur. The basin floor and slopes
primarily contain annual and ruderal grassland that is grazed by cattle; the low-flow channel
contains permanent and seasonal wetland vegetation (Photo 1).
Photo 1: Southeast view from basin inlet pipes in Photo 2: Sand Creek upstream of outfall pipes.
northwest portion of the basin.
Sand Creek borders the existing basin’s southern boundary. This portion of Sand Creek is a
narrow, incised channel with steep, eroded banks exhibiting high sinuosity. The low-flow channel
(ordinary high water mark) ranges from 2 to 8 feet in width. It is characterized as an intermittent
stream upstream of the basin outfall pipes, with generally low quality runs and pools, and is
typically dry by June in most years. Few scattered riparian woodland and scrub trees such as
valley oak, blue oak, and red willow occur on the banks of this portion of the creek (Nomad 2009a)
(Photos 2 and 3). Habitat quality in this portion of the reach is poor based on the low water flow,
high turbidity, relatively high water temperatures, and minimal emergent or aquatic vegetation
required by many sensitive aquatic species as well as cattle grazing and human disturbances
(refuse, stream crossings) within and along the creek (Photo 4). Aquatic species observed include
western mosquitofish and red swamp crayfish. (Nomad 2009a).
11/8/08 12/3/09
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Photo 3: Sand Creek with flow. Photo 4: Cattle grazing impacts.
Downstream of the basin outfall pipes, the habitat quality of Sand Creek increases due to the
perennial water flow from urban runoff (2 to 4 cubic feet per second), increased emergent and
aquatic vegetation, trees, muddy to rocky substrate, and alternating run/pools (Photo 5). The
shallow, rocky areas exhibited an overgrowth of algae inhabited by fish species threespine
stickleback. Willow trees are present 300 to 400 feet downstream of the outfall near a deep pool
with a stand of tules (Photo 6). East of the existing basin, a 200-foot section of Sand Creek has
been used as a dump site for refuse, old appliances, and concrete. At the beginning of this
disturbed area is a dirt road crossing that overlays three corrugated pipe culverts. Sand Creek
narrows as it continues northeast and is characterized by steep, heavily vegetated streambanks
and a moderate overstory of valley oak and blue oak trees. Sand Creek exits the proposed
expansion area to the east in a moderately incised channel through non -native grasslands and
agricultural lands with scattered riparian trees.
Photo 5: Outfall pipes. Photo 6: Flows downstream of outfall pipes.
Lower Sand Creek Basin
Habitat assessments and a wetland delineation were conducted in fall 2008 and spring 2009 (RCL
Ecology 2009). Similar to USCB, LSCB contains a depressed basin with a low-flow channel. The
basin floor and slopes primarily contain annual grassland; the low-flow channel contains wetland
vegetation (cattails, tule, nutgrass, Baltic rush, cheeseweed, prickly lettuce, bristly ox -tongue, tall
fescue) (Photo 7). Few scattered willow trees border the low flow channel of the basin.
7/13/10
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Photo 7: Low-flow channel within basin. Photo 8: Upstream view of Sand Creek.
Approximately 590 feet of Sand Creek borders the basin’s northern boundary. This portion of Sand
Creek is approximately 20 feet wide and is channelized with steep slopes. It contains a mixture of
rock slope protection in some areas and vegetation in others, and a drop structure (Photo 8). Prior
to stream channelization, it was an ephemeral stream, but is now characterized as a perennial
stream due to urban runoff. The vegetation within Sand Creek is sparse, brushy, and dominated by
non-native grasses. The creek habitat quality for fish and wildlife is compromised due to poor water
quality from urban runoff and lack of shade and overhanging vegetation due to routine vegetation
maintenance.
IMPACT DISCUSSION
a) Would the project have a substantial adverse effect, either directly or through habitat
modifications, on any species identified as a candidate, sensitive, or special status species in
local or regional plans, policies, or regulations, or by the California Department of Fish and
Game or U.S. Fish and Wildlife Service?
A total of twenty-six (26) listed wildlife species have the potential to occur between both basins.
Seven (7) of them are federal or state-listed as threatened or endangered, or designated as
fully protected, and 19 are considered to be rare, sensitive or declining by agency or non -
governmental watchlists.
Table 4: Special-Status Species That Have the Potential to be Present
Invertebrates Bridge’s coast range shoulderband snail9, Curved-foot hygrotus diving beetle9,
Fish None
Amphibians California red-legged frog2,8,10, California tiger salamander2,8,10
Reptiles None
Birds of Prey
and Migratory
Birds
Allen’s hummingbird9, California horned lark10,11, Cooper’s hawk10,11, ferruginous
hawk4,11,12, golden eagle7,10,12, grasshopper sparrow8, loggerhead shrike4,8,
merlin9,12, Nuttall’s woodpecker9, oak titmouse9, Swainson’s hawk5,10, tricolored
blackbird8,10, western burrowing owl8,10, white-tailed kite7
Mammals American badger8, pallid bat8, San Joaquin kit fox1,6,10, San Joaquin pocket
mouse9, western red bat8
1Federal-listed endangered; 2federal-listed threatened; 3Critical Habitat; 4USFWS Bird Conservation Concern List; 5state-listed
endangered; 6state-listed threatened; 7California Fully Protected; 8California Species of Special Concern; 9California Department of
Fish and Game Special Animal List; 10HCP/NCCP Covered Species; 11California Watch List; 12Audobon Watch List; 13California
Native Plant Society List 1B.1 (seriously endangered in California) 14U.S. Migratory Bird Treaty Act
5/1/010 5/1/10
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Both basin expansions are covered by the HCP/NCCP. Therefore, potential project impacts will
have a less than significant impact with implementation of required compensatory mitigation
and species-specific avoidance and minimization measures as described below.
IMPACT BIO-1: The project will result in permanent and temporary impacts to suitable habitat
for the above-listed species. Permanent impacts include removing natural habitat for the
construction of the basin dam and hydraulic structures and temporary impacts from excavation
and construction-related activities. Construction of the project may result in incidental take of
these species.
MITIGATION MEASURE BIO-1:
The Flood Control District will pay the applicable HCP/NCCP development and wetland
fees, including a temporary impact fee. These fees will be based on the acreage of land
impacted by the project according to the HCP/NCCP fee calculator and will be paid to the
East Contra Costa County Habitat Conservancy at award of the construction contract.
Implementation of this measure and the following species avoidance and minimization
measures in accordance to the HCP/NCCP will reduce project impacts to less than
significant.
AVOIDANCE AND MINIMIZATION MEASURE BIO-1A:
CALIFORNIA RED-LEGGED FROG AND CALIFORNIA TIGER SALAMANDER
No preconstruction surveys are required by the HCP/NCCP.
Written notification to USFWS, CDFG, and the HCP/NCCP Implementing Entity,
including photos and breeding habitat assessment, is required prior to disturbance of
any suitable breeding habitat. The project proponent will also notify these parties of the
approximate date of removal of the breeding habitat at least 30 days prior to this
removal to allow USFWS or CDFG staff to translocate individuals, if requested. USFWS
or CDFG must notify the project proponent of their intent to translocate CTS within 14
days of receiving notice from the project proponent. The applicant must allow USFWS
or CDFG access to the site prior to construction if they request it.
There are no restrictions under this HCP/NCCP on the nature of the disturbance or the
date of the disturbance unless CDFG or USFWS notify the project proponent of their
intent to translocate individuals within the required time period. In this case, the project
proponent must coordinate the timing of disturbance of the breeding habitat to allow
USFWS or CDFG to translocate the individuals. USFWS and CDFG shall be allowed 45
days to translocate individuals from the date the first written notification was submitted
by the project proponent (or a longer period agreed to by the project proponent,
USFWS, and CDFG).
No construction monitoring is required by the HCP/NCCP.
AVOIDANCE AND MINIMIZATION MEASURE BIO-1B:
SAN JOAQUIN KIT FOX (SJKF)
Prior to any ground disturbance related to covered activities, a USFWS/CDFG-
approved biologist will conduct a preconstruction survey in areas identified in the
planning surveys as supporting suitable breeding or denning habitat for SJKF. The
surveys will establish the presence or absence of SJKF and/or suitable dens and
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evaluate use by kit foxes in accordance with USFWS survey guidelines (U.S. Fish and
Wildlife Service 1999). Preconstruction surveys will be conducted within 30 days of
ground disturbance. On the parcel where the activity is proposed, the biologist will
survey the proposed disturbance footprint and a 250-foot radius from the perimeter of
the proposed footprint to identify SJKF and/or suitable dens. Adjacent parcels under
different land ownership will not be surveyed. The status of all dens will be determined
and mapped. Written results of preconstruction surveys will be submitted to USFWS
within 5 working days after survey completion and before the start of ground
disturbance. Concurrence is not required prior to initiation of covered activities. If San
Joaquin kit foxes and/or suitable dens are identified in the surve y area, the measures
described below will be implemented.
If a SJKF den is discovered in the proposed project footprint, the den will be monitored
for 3 days by a USFWS/CDFG-approved biologist using a tracking medium or an
infrared beam camera to determine if the den is currently being used.
Unoccupied dens will be destroyed immediately to prevent subsequent use.
If a natal or pupping den is found, USFWS and CDFG will be notified immediately. The
den will not be destroyed until the pups and adults have v acated and then only after
further consultation with USFWS and CDFG.
If kit fox activity is observed at the den during the initial monitoring period, the den will
be monitored for an additional 5 consecutive days from the time of the first observation
to allow any resident animals to move to another den while den use is act ively
discouraged. For dens other than natal or pupping dens, use of the den can be
discouraged by partially plugging the entrance with soil such that any resident animal
can easily escape. Once the den is determined to be unoccupied it may be excavated
under the direction of the biologist. Alternatively, if the animal is still present after 5 or
more consecutive days of plugging and monitoring, the den may have to be excavated
when, in the judgment of a biologist, it is temporarily vacant (i.e., during the animal’s
normal foraging activities).
If dens are identified in the survey area outside the proposed disturbance footprint,
exclusion zones around each den entrance or cluster of entrances will be demarcated.
The configuration of exclusion zones should be circular, with a radius measured
outward from the den entrance(s). No covered activities will occur within the exclusion
zones. Exclusion zone radii for potential dens will be at least 50 feet and will be
demarcated with four to five flagged stakes. Exclusion zone radii for known dens will be
at least 100 feet and will be demarcated with staking and flagging that encircles each
den or cluster of dens but does not prevent access to the den by kit fox.
AVOIDANCE AND MINIMIZATION MEASURE BIO-1C:
SWAINSON’S HAWK
Trees will be removed during the non-nesting season (September 16 - March 14). However,
if removal occurs during the nesting season (March 15 – September 15), the following
measures will be implemented:
Prior to any ground disturbance related to covered activities that occurs during the
nesting season (March 15–September 15), a qualified biologist will conduct a
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preconstruction survey no more than 1 month prior to construction to establish whether
Swainson’s hawk nests within 1,000 feet of the project site are occupied. If potentially
occupied nests within 1,000 feet are off the project site, then their occupancy will be
determined by observation from public roads or by observations of Swainson’s hawk
activity (e.g., foraging) near the project site. If nests are occupied, minimization
measures and construction monitoring are required (see below).
During the nesting season (March 15–September 15), covered activities within 1,000
feet of occupied nests or nests under construction will be prohibited to prevent nest
abandonment. If site-specific conditions or the nature of the covered activity (e.g., steep
topography, dense vegetation, limited activities) indicate that a smaller buffer could be
used, the East Contra Costa County Habitat Conservancy (Implementing Entity) will
coordinate with CDFG/USFWS to determine the appropriate buffer size.
If young fledge prior to September 15, covered activities can proceed normally. If the
active nest site is shielded from view and noise from the project site by other
development, topography, or other features, the project applicant can apply to the
Implementing Entity for a waiver of this avoidance measure. Any waiver must also be
approved by USFWS and CDFG. While the nest is occupied, activities outside the
buffer can take place.
All active nest trees will be preserved on-site, if feasible. Nest trees, including non-
native trees, lost to covered activities will be mitigated by the project proponent
according to the requirements below.
If preconstruction surveys identify Swainson’s hawk nest trees that cannot be avoided by
construction, the loss of these trees will be mitigated by the Flood Control District by:
a) If feasible on-site, planting 15 saplings for every tree lost with the objective of having at
least 5 mature trees established for every tree lost according to the requirements listed
below.
AND either:
1. Pay the Implementing Entity (East Contra Costa County Habitat Conservancy) an
additional fee to purchase, plant, maintain, and monitor 15 saplings on the HCP/NCCP
Preserve System for every tree lost according to the requirements listed below, OR
2. The project proponent will plant, maintain, and monitor 15 saplings for every tree lost at
a site to be approved by the Implementing Entity (e.g., within an HCP/NCCP Preserve
or existing open space linked to HCP/NCCP preserves), according to the requiremen ts
listed below.
The following requirements will be met for all planting options:
b) Tree survival shall be monitored at least annually for 5 years, then every other year until
year 12. All trees lost during the first 5 years will be replaced. Success will be reached
at the end of 12 years if at least 5 trees per tree lost survive without supplemental
irrigation or protection from herbivory. Trees must also survive for at least three years
without irrigation.
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c) Irrigation and fencing to protect from deer and other herbivores may be needed for the
first several years to ensure maximum tree survival.
d) Native trees suitable for this site should be planted. When site conditions permit, a
variety of native trees will be planted for each tree lost to provide trees with different
growth rates, maturation, and life span, and to provide a variety of tree canopy
structures for Swainson’s hawk. This variety will help to ensure that nest trees will be
available in the short term (5-10 years for cottonwoods and willows) and in the long
term (e.g., Valley oak, sycamore). This will also minimize the temporal loss of nest
trees.
e) Riparian woodland restoration conducted as a result of covered activities (i.e., loss of
riparian woodland) can be used to offset the nest tree planting requirement above, if the
nest trees are riparian species.
f) Whenever feasible and when site conditions permit, trees should be planted in clumps
together or with existing trees to provide larger areas of suitable nesting habitat and to
create a natural buffer between nest trees and adjacent development (if plantings occur
on the development site).
g) Whenever feasible, plantings on the site should occur closest to suitable foraging
habitat outside the undeveloped area (UDA).
h) Trees planted in the HCP/NCCP preserves or other approved offsite location will occur
within the known range of Swainson’s hawk in the inventory area and as close as
possible to high-quality foraging habitat.
AVOIDANCE AND MINIMIZATION MEASURE BIO-1D:
WESTERN BURROWING OWL
Prior to any ground disturbance related to covered activities, a USFWS/CDFG-
approved biologist will conduct a preconstruction survey in areas identified in the
planning surveys as having potential burrowing owl habitat. The surveys will establish
the presence or absence of western burrowing owl and/or habitat features and evaluate
use by owls in accordance with CDFG survey guidelines.
On the parcel where the activity is proposed, the biologist will survey the proposed
disturbance footprint and a 500-foot radius from the perimeter of the proposed footprint
to identify burrows and owls. Adjacent parcels under different land ownership will not be
surveyed.
Surveys will take place near sunrise or sunset in accordance with CDFG guidelines.
All burrows or burrowing owls will be identified and mapped.
Surveys will take place no more than 30 days prior to construction.
During the breeding season (February 1 – August 31), surveys will document whether
burrowing owls are nesting in or directly adjacent to disturbance areas. During the
nonbreeding season (September 1 – January 31), surveys will document whether
burrowing owls are using habitat in or directly adjacent to any disturbance area. Survey
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results will be valid only for the season (breeding or nonbreeding) during which the
survey is conducted.
If burrowing owls are found during the breeding season (February 1 – August 31), the
project proponent will avoid all nest sites that could be disturbed by project construction
during the remainder of the breeding season or while the nest is occupied by adults or
young. Avoidance will include establishment of a non-disturbance buffer zone.
Construction may occur during the breeding season if a qualified biologist monitors the
nest and determines that the birds have not begun egg-laying and incubation or that the
juveniles from the occupied burrows have fledged. During the nonbreeding season
(September 1 – January 31), the project proponent will avoid the owls and the burrows
they are using, if possible. Avoidance will include the establishment of a buffer zone.
If occupied burrows cannot be avoided, passive relocation will be implemented. Owls
will be excluded from burrows in the immediate impact zone and within a 160 -foot buffer
zone by installing one-way doors in burrow entrances. These doors will be in place for
48 hours prior to excavation. The project area will be monitored daily for 1 week to
confirm that the owl has abandoned the burrow. Whenever possible, burrows will be
excavated using hand tools and refilled to prevent reoccupation. Plastic tubing or a
similar structure will be inserted in the tunnels during excavation to maintain an escape
route for any owls inside the burrow.
AVOIDANCE AND MINIMIZATION MEASURE BIO-1E:
OTHER BIRDS/RAPTORS PROTECTED BY THE U.S. MIGRATORY BIRD TREATY ACT
Fish and Game Code 3503.5 protects all birds of prey which include raptors, falcons, and
owls. Migratory birds are protected under the federal Migratory Bird Treaty Act (MBTA) of
1918 (16 U.S.C. 703-712). The MBTA makes it unlawful to take, possess, buy, sell,
purchase, or barter any migratory bird listed in 50 CFR Part 10 including feathers or other
parts, nests, eggs, or products, except as allowed by implementing regulations (50 CFR
21). Under the MBTA, nests of migratory birds that contain eggs are not to be disturbed
during the breeding season.
The nesting season varies depending on the bird species; the general nesting season is
February 1 to August 31. Trees will be removed at both basins. These trees could provide
suitable habitat for nesting birds. To avoid the potential for impacts to active nests the
following measures will be followed:
If feasible, the trees will be removed during the general non-nesting season (September
1 – January 31). Otherwise, a preconstruction survey for active nests will be conducted
by a qualified biologist no more than 30 days prior to construction. If no active nests are
found, then no additional avoidance and minimization measures are necessary.
If an active nest is located within 250 feet of the construction area, the qualified biologist
will:
Record the location(s) on a site map.
Establish a minimum 250 feet buffer zone to be delineated with Environmentally
Sensitive Area [ESA] fencing around the nest tree or nest location. The buffer zone
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will be maintained until the end of the breeding season. No construction activities
will occur within 250 feet of a nest tree or nest location while young a re in the nest.
A biologist will monitor the nest weekly during construction to evaluate potential
disturbance caused by construction activities. Once the biologist has determined that
nestlings have fledged, the nest will be removed.
If establishment of a buffer is not practical, DFG and/or USFWS will be contacted for
further avoidance and minimization guidelines.
Preconstruction surveys conducted and avoidance and minimization measures for the above-
listed species will also address other special-status species not covered by HCP/NCCP (i.e.,
Bridge’s coast range shoulderband snail, Curved-foot hygrotus diving beetle, American badger,
pallid bat, San Joaquin pocket mouse, western red bat). If species are found and they cannot
be avoided, avoidance and minimization measures outlined in the Biological Resources
Assessment report (Nomand 2009a) will be implemented.
b) Would the project have a substantial adverse effect on any riparian habitat or other sensitive
natural community identified in local or regional plans, policies, regulations or by the California
Department of Fish and Game or U.S. Fish and Wildlife Service?
Many of the riparian areas and streams in the lowlands of east Contra Costa County have been
severely affected by development. Streams including Sand Creek have either been devoid of
vegetation or contain only narrow bands of remnant vegetation. In the upland portions,
especially in the open grasslands, livestock grazing practices have resulted in heavily degraded
or denuded riparian areas (JSA 2006).
Four sensitive natural communities are present within USCB: permanent wetland, seasonal
wetland, riparian woodland/scrub, and stream. Two natural communities are present within
LSCB: seasonal wetland and stream. These sensitive natural communities are important for a
wide variety of wildlife species as they provide breeding, resting, and/or foraging habitat.
Permanent Wetland
Permanent wetlands (also referred to as perennial wetlands) are characterized by a year -round
water source. They are typically dominated by erect, rooted, herbaceous hydrophytic plant
species adapted to growing in conditions of prolonged inundation. Common plant species
present in this land cover type include cattails and tules. Common wildlife species include
waterfowl (great blue heron, great egret, ducks, killdeer), amphibians (red -legged frog, western
pond turtle, garter snakes, and mammals (mule deer).
The USCB contains approximately 0.47 acre of permanent wetland in the man-made drainage
channel in the existing basin and along a portion of the banks within the channel of Sand
Creek. These wetlands are dominated by narrow-leafed cattail and water cress, and also
include American tule, salt rush, Baltic rush, water bentgrass, spiny buttercup, cursed
crowsfoot, whorled marsh pennywort, brass-buttons, and rabbitsfoot grass.
Seasonal Wetland
Seasonal wetlands are freshwater wetlands that support ponded or saturated soil conditions
during winter and spring and are dry through the summer and fall until the first substantial
rainfall. The vegetation is composed of wetland generalist plants such a s hyssop loosestrife,
cocklebur, and Italian ryegrass that typically occur frequently along streams. During the wet
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season, these wetlands are commonly used by a variety of wildlife, including various
amphibians (western spadefoot toad, Pacific chorus frog, western toad, California tiger
salamander), waterfowl (killdeer, black-necked stilt, and American avocet); and birds (Brewer’s
blackbird, red-winged blackbird, brown-headed cowbird, American pipit). During the dry
season, a variety of small mammals use the areas, including deer mouse, California vole, and
long-tailed weasel. Raptors such as white-tailed kites, northern harrier, and red-tailed hawk
may forage in this land cover type (JSA 2006).
The USCB contains approximately 2.18 acres of seasonal wetlands within the basin along the
margins of the man-made drainage channel and one adjacent to and above the basin inlet.
Seasonal wetland species present in the drainage channel include California semaphore grass,
rabbitsfoot grass, brass-buttons, water cress, green dock, spiny buttercup, cursed crowsfoot,
Italian ryegrass, meadow barley, hyssop loosestrife, and strawberry clover; species present
above the basin inlet include stalked popcorn flower, dwarf allocarya, green dock, and toad
rush.
The LSCB contains approximately 1.03 acres of seasonal wetlands within the basin towards
the end of the man-made drainage channel. The seasonal wetland is dominated by native and
non-native forbs with a few willow trees. Dominant species are Baltic rush, tall fescue, curly
dock, and sow thistle.
Stream
A stream is defined as a long, narrow body of flowing water that occupies a channel with
defined bed and bank and moves to lower elevations under the force of gravity. A stream is
either perennial (flowing water year-round), intermittent (flowing water during certain times of
the year, when groundwater provides water for stream flow), or ephemeral (flowing water only
during and for a short duration after precipitation events in a typical year) (JSA 2006). Streams
provide essential habitat for terrestrial and aquatic species; many upland species rely on
streams as water sources. In summer and early fall, perennial streams provide the only
available water in an otherwise dry landscape. In addition, all stream types provide habitat for
aquatic macroinvertebrates, which are an important food source for local and downstream
populations of fish, birds, and other wildlife (JSA 2006).
Sand Creek at USCB is an intermittent stream upstream of the basin outfall pipes and
perennial downstream of the pipes due to yearly urban runoff into the basin . Approximately
3,876 feet of Sand Creek occurs within the expansion area. The entire creek length within the
expansion area will be permanently impacted for the placement of earthen material for the dam
and basin slopes, basin inlet and outlet structures and associated erosion control materials,
and excavation and realignment of the remaining creek. The remaining creek will be excavated
10 feet below the existing grade and recreated with a fluvial geomorphic (natural creek) design
and restored with a revegetation planting plan that will provide an enhanced creek corridor. The
loss of 264 feet of creek will be mitigated on-site with the creation of wetlands.
Sand Creek at LSCB is a perennial stream. Approximately 1,100 feet of Sand Creek occurs
within the expansion area. Approximately 1,060 feet of Sand Creek will be permanently
impacted for the basin embankment, drain inlet and outlet structures and associated erosion
control materials, and creation of a low-flow drainage and wetland mitigation area for the loss of
the creek.
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Riparian Woodland/Scrub
The riparian/woodland scrub land cover type is dominated by phreatophytic woody vegetation
associated with streams and permanent water sources. Riparian woodland is dominated by
trees and contains an understory of shrubs and forbs. Riparian scrub is dominated by young
trees and shrubs, typically representing an early successional stage of riparian woodland. This
land cover type is dominated by a mixture of trees and shrubs adapted to saturated and/or
flooded soil conditions such as Fremont cottonwood, western sycamore, and red willow. The
understory may also include woody shrubs such as arroyo willow and mule fat. This natural
community provides habitat for a wide diversity of wildlife. Some intermittent and ephemeral
streams in this part of the County are dominated by a narrow corridor of oaks, California bay, or
California buckeye with only scattered riparian tree species (e.g. willows and cottonwoods).
The presence of flowing water within these communities attracts numerous mammals,
amphibians, and reptiles. Riparian corridors are also important for deer migration. Common
mammals found in this community include mule deer, raccoon, gray fox, striped skunk, deer
mouse, harvest mouse, broad-handed mole, and dusky-footed woodrat. Because of their
proximity to rangelands, many riparian areas are grazed by livestock. Birds typically found in
this community include yello w warbler, northern flicker, white-tailed kite, Cooper’s hawk, red-
shouldered hawk, song sparrow, and grosbeak (JSA 2006).
USCB contains riparian woodland/scrub along Sand Creek at the downstream end of the
project area, which consists of an open canopy overstory of red willow trees and further
downstream, the overstory is composed of willow and oak trees. Other tree and shrub species
include California rose, blue elderberry, blue witch, and tree tobacco. The understory includes
herbaceous species such as California man-root, broad-leaved pepperweed, Bermuda
buttercup, white fiesta flower, miner’s lettuce, and common chickweed . LSCB contains a few
willow trees within the low-flow drainage area of the basin and an oak and a pine tree along the
northern boundary of the basin.
Most of the trees that occur along Sand Creek within USCB will be removed; the trees within
the LSCB basin and along its northern boundary will be removed.
IMPACT BIO-2:
Construction of these basins will remove portions of the natural communities identified above.
MITIGATION MEASURE BIO-2:
Permanent and temporary impacts will be mitigated through payment of fees to the East
Contra Costa County Habitat Conservancy as identified in the Development Fee Table 9-4
and Wetland Mitigation Fee Table 9-5 in Chapter 9 of the HCP/NCCP which are updated
annually (East Contra Costa County Habitat Conservancy 2010). In addition, impacts will
also be mitigated on-site with the creation of an enhanced creek corridor at USCB and a
wetland mitigation area at LSCB. These restoration activities will be consistent with the
restoration plan requirements outlined in the HCP/NCCP.
c) Would the project have a substantial adverse effect on federally protected wetlands as defined
(including, but limited to, marsh, vernal pool, coastal, etc.) through direct removal, filling,
hydrological interruption, or other means?
As discussed above, both basin expansion areas contain streams and wetlands that will be
permanently and temporarily impacted. Wetland delineations were conducted at both sites. The
wetland delineation conducted at USCB was verified by the U.S. Army Corps of Engineers
(Corps), the federal agency that has jurisdiction on most waterways and associated wetlands.
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Sand Creek and associated wetlands at USCB were determined to be under the Corps
jurisdiction whereas the manmade drainage channel and associated wetlands located within
the existing basin was determined to not be in Corps jurisdiction as it was created in uplands
and was never part of a natural waterway. One seasonal wetland located adjacent and above
the basin inlet structure was determined to be under Corps jurisdiction (U.S. Army Corps of
Engineers 2010). While the man-made drainage channel and its associated wetlands are not
federally-protected, they are state-protected under the State Water Resources Control Board.
The wetland delineation for LSCB has not been verified by the Corps . It is similar to the USCB
as the man-made drainage channel and associated wetlands within the existing basin were
also constructed in uplands and were not part of natural waterway. Therefore, the Corps will
likely not take jurisdiction over these features; however the Corps will likely take jurisdiction
over the adjacent Sand Creek.
Permit applications will be submitted to the Corps and the Central Valley Regional Water
Quality Control Board detailing the areas of permanent and temporary impacts and planned on-
site mitigation efforts and HCP/NCCP fees.
At USCB, approximately 3,876 feet of Sand Creek occurs within the expansion area of which
approximately 264 feet of the creek will be permanently lost. Approximately 3,612 feet of the
creek will be re-created on-site with a fluvial geomorphic (natural creek) design that will be
restored with a vegetation planting plan that will provide an enhanced creek corridor ; the
remaining 264 feet lost will be mitigated on-site with wetlands as out-of-kind mitigation. At
LSCB, approximately 1,100 feet of Sand Creek occurs within the expansion area of which
approximately 1,060 feet will be permanently impacted for the embankment, inlet and outlet
structures and associated erosion control materials. A low-flow drainage area and wetlands will
be re-created in the basin to offset the loss of Sand Creek.
IMPACT BIO-3:
Construction of these basins will permanently and temporarily impact waters of the U.S. and
seasonal wetlands.
MITIGATION MEASURE BIO-3:
Permanent and temporary impacts for the basin structures will be mitigated through
payment of fees to the East Contra Costa County Habitat Conservancy as identified in the
Development Fee Table 9-4 and Wetland Mitigation Fee Table 9-5 in Chapter 9 of the
HCP/NCCP which are updated annually (East Contra Costa County Habitat Conservancy
2010). In addition, impacts will also be mitigated on-site with the creation of an enhanced
creek corridor at USCB and a wetland mitigation area at LSCB. These restoration activities
will be consistent with the restoration plan requirements outlined in the HCP/NCCP.
d) Would the project interfere substantially with the movement of any native resident or migratory
fish or wildlife species or with established native resident or migratory wildlife corridors, or
impede the use of native wildlife nursery sites?
Habitat loss, fragmentation, and degradation resulting from land use changes or habitat
conservation can alter the use and viability of wildlife movement corridors (i.e., linear habitats
that naturally connect and provide passage between two or more otherwise disjunct larger
habitats or habitat fragments) (Nomad 2009a).
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Both basins lie within Lone Tree Valley with largely unrestricted access to the northwestern-
most extent of the Diablo Mountain Range, which functions as a regional movement corridor.
This regional corridor extends from the eastern foothills of Mt. Diablo and Black Diamond Mines
Regional Park southeast toward the Altamont Pass. This land tract promotes the dispersal and
gene flow between a variety of plant and animal subpopulations occurring within the region.
Sand Creek drains the Lone Tree and Horse Valleys and provides connectivity to upper and
lower portions of the watershed occupied by several federally and state listed and locally
sensitive wildlife species (Nomad 2009a). USCB provides connectivity to adjacent habitats to
the east, west, and south whereas LSCB is largely surrounded by adjacent urbanization.
While the basin expansions will not result in permanent disruption to movement of wildlife
species, construction of the project and subsequent recovery of restored areas may temporarily
inhibit dispersal, migration, and daily movement of common, listed and rare wildlife. However,
the restoration and enhancement of the portions of Sand Creek impacted at USCB and LSCB
will result in a net benefit to wildlife by increasing the value of the stream corridors for
movement and dispersal of wildlife. In addition, permanent impacts that cannot be restored will
be offset by payment to the East Contra Costa County Habitat Conservancy as discussed
above. Therefore, project impacts will be less than significant with incorporation of Mitigation
Measures BIO-1 to BIO-3.
e) Would the project conflict with any local policies or ordinances protecting biological resources,
such as a tree preservation policy or ordinance?
Both basins will require removal of trees. While both basins are located within the cities of
Antioch (USCB) and Brentwood (LSCB), the basins are owned by the Flood Control District
which falls within the jurisdiction of Contra Costa County. While the Flood Control District is not
subject to the County Tree Ordinance, tree removals will be mitigated through payment of fees
to the East Contra Costa County Habitat Conservancy as well as on-site mitigation as
discussed above. Therefore, project impacts will be less than significant with incorporation of
Mitigation Measures BIO-1 to BIO-3.
f) Would the project conflict with the provisions of an adopted Habitat Conservation Plan, or other
approved local, regional, or state habitat conservation plan?
As discussed above, the HCP/NCCP provides specific avoidance and mitigation measures for
direct and cumulative impacts to covered special-status species and habitats and jurisdictional
wetlands and other waters in eastern Contra Costa County. Both basins are listed as a covered
activity (Construction and Expansion of Flood Control Basins) in the HCP/NCCP (Table 2-5).
The Flood Control District will implement the applicable restoration plan measures for the
restoration of Sand Creek within the basins as outlined in section 5.3.2 of the HCP, and will pay
the applicable mitigation fees as summarized in this section. Therefore, the project will have no
impact as it will not conflict with the provisions of the HCP/NCCP.
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Less Than
Significant
Potentially With Less Than
Significant Mitigation Significant No
ISSUES: Impact Incorporated Impact Impact
V. CULTURAL RESOURCES
Would the project:
a) Cause a substantial adverse change in
the significance of a historical resource
as defined in §15064.5?
b) Cause a substantial adverse change in
the significance of an archaeological
resource pursuant to §15064.5?
c) Directly or indirectly destroy a unique
paleontological resource or site or
unique geological feature?
d) Disturb any human remains, including
those interred outside of formal cemeteries?
Regulatory Background
Cultural resources in California are protected by a number of federal, state, and local regulations
and ordinances. The most frequently applied legislation consists of the provisions of CEQA that
provide for the documentation and protection of significant prehistoric and historic resources. Prior
to the approval of discretionary projects and the commencement of agency undertakings, the
potential impacts of the project on archaeological and historical resources must be co nsidered
(Public Resources Code Sections 21083.2 and 21084.1 and the CEQA Guidelines [California Code
of Regulations Title 14, Section 15064.5]).
The CEQA Guidelines define a significant historical resource as “a resource listed or considered
eligible for listing on the California Register of Historical Resources” (CRHR) (Public Resources
Code Section 5024.1). A cultural resource may be eligible for listing on the CRHR if it:
1. is associated with events that have made a significant contribution to the b road patterns of
California’s history and cultural heritage;
2. is associated with the lives of persons important in our past;
3. embodies the distinctive characteristics of a type, period, region, or method of construction or
represents the work of an important creative individual, or possesses high artistic values; or
4. has yielded, or may be likely to yield, information important in prehistory or history.
In order to determine if the area contains potential significant cultural and/or historical resources,
qualified archaeologists and historians reviewed records from the Northwest Information Center
(NWIC) at California State University, Sonoma in Rohnert Park, California and conducted field
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investigations (David Chavez & Associates 2004, William Self Associates 2008, 2010). In addition,
the Native American Heritage Commission (NAHC) and local Native American representatives
were contacted for information of unrecorded Native American cultural sites (NAHC 2003, 2009,
2010).
Previous Investigations
Multiple field surveys and investigations have been conducted for both basins. Field surveys for the
LSCB did not indicate the presence of archaeological or historical resources. However, USCB
contains a deteriorated homestead ranch complex, formerly occupied by the Sullenger Family, in
the southwest portion of the project area (Photos 9 and 10, Figure 1). The homestead ranch
consists of a two-story ranch house that was built sometime in the 1880s, a shed, carriage house
or garage, 80-year old barn, a blacksmith’s shop, and a privy; the barn, carriage house, and privy
have collapsed.
Photo 9: Two-story Sullenger ranch house Photo 10: Blacksmith shop building in front with
built ca. 1880. Sullenger ranch house in background.
In 1993, when the Flood Control District acquired the property for construction of the interim basin,
the entire project area was surveyed and no prehistoric sites were located. The Sullenger Ranch
complex, an example of a historic homestead dating from the late 19th to the mid-20th century, was
evaluated in accordance to criteria of importance as defined by California Environmental Quality
Act (CEQA) and determined potentially significant under CEQA. Further investigations in 2008
included archaeological testing and data recovery of the complex to assess and document historic
structures and subsurface features associated with the complex. The archaeological testing and
data recovery revealed five subsurface features (primarily domestic items associated with food
preparation, tableware, clothing, building materials as well as farming items) that were evaluated
and determined not eligible for listing in the CRHR, but the historic structures were recommended
as eligible for listing in the CRHR, as the site met two of the eligibility criteria.
Further evaluations were conducted in 2010, which included an updated records search,
consultations with the NAHC and interested Native American representatives, preparation of a
geoarchaeological assessment of potential buried resources, additional historic research and the
preparation of a historic context and recordation of the Sullenger Ranch, and CRHR eligibility
assessment of archaeological potential and structures that constitute the Sullenger Ranch.
The geoarchaeological assessment evaluated the potential for buried cultural resources which
included evaluation of data obtained from previous soil borings and test pit excavations. The
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assessment revealed that based on the soils and buried sediments within the project area there is
low or moderate-low sensitivity for prehistoric archaeological deposits over most of the project
area. The area of the existing basin has already been excavated to depths below the possibility for
any archaeological deposits and this area was determined to have low archaeological sensitivity.
Although, the soil types in proximity to the creek, are considered to have moderate archaeological
sensitivity, and in part lie on top of “younger terrace deposits” that could yield archaeolog ical
deposits. Therefore, the creek area is considered to have moderate archaeological sensitivity from
the surface to the base of the “younger terrace deposits” and to the top of the underlying “older
terrace deposits” or the bedrock, depending on location.
IMPACT DISCUSSION
a) Would the project cause a substantial adverse change in the significance of a historical
resource as defined in §15064.5?
No evidence of an earlier farmhouse or other historical structures were discovered during the
field survey of LSCB. USCB contains a deteriorated homestead ranch complex, formerly
occupied by the Sullenger Family. Re-evaluation of the Sullenger Ranch complex structures
determined that the Sullenger Ranch does not meet the eligibility criteria for listing on the
California Register as neither the buildings or the recovered archaeological deposits retain
sufficient integrity to be eligible for listing. While the Sullenger Ranch buildings are not
considered eligible for listing on the CRHR, the collected artifacts will be offered to interested
local historical societies to expand their existing collection of the local history. Therefore,
project impacts will be less than significant.
b) Would the project cause a substantial adverse change in the significance of an archaeological
resource pursuant to §15064.5?
No surface evidence of prehistoric archaeological resources was encou ntered during the field
survey of LSCB. In addition, no evidence of an earlier farmhouse, other structures or historic
archaeological features and resources was observed.
The geoarchaeological assessment at USCB concluded that areas within the existing basin are
not likely to reveal archaeological resources as the area of the existing basin has already been
excavated to depths below the possibility for any archaeological deposits and therefore this
area was determined to have low archaeological sensitivity. However, the creek area, including
the Sullenger Ranch, has a moderate sensitivity for archaeological resources. The proposed
plan for cutting and filling within and around the creek area is complex due to the e xisting
topography and the plan to recreate a natural looking creek through the expanded basin. Much
of the creek area will be cut to depths over 11 feet below ground surface , removing all of the
soil types that yield moderately sensitive deposits, and in some of the areas where the cut will
be less than 11 feet, the excavation will still be deep enough to remove all of the moderately
sensitive deposits. Although there is no evidence for prehistoric archaeological deposits either
on the surface or in the large number of geotechnical pits and bore holes that have been
excavated within the project area (including the creek area), there is some possibility that
buried prehistoric archaeological resources might be encountered in the vicinity of the creek.
While no archaeological resources were identified during surveys of both basins, there is the
possibility of encountering cultural resources during subsurface activities. Based on the
geoarchaeological assessment results for USCB, subsurface activities in the creek area will be
monitored by a qualified archaeologist. In the event that archaeological resources are
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discovered at either basin, project specifications direct the contractor to halt subsurface
activities in the general vicinity and to immediately notify the Flood Control District. The Flood
Control District will immediately consult with a qualified archaeologist to evaluate the
resource(s) and provide a management plan consistent with CEQA and Contra Costa County
cultural resources protection requirements. Therefore, project impacts will be less than
significant.
c) Would the project directly or indirectly destroy a unique paleontological resource or site or
unique geological feature?
Based on field surveys and subsurface investigations conducted by qualified archaeologists, no
unique paleontological resources or geologic feature were discovered at USCB or LSCB. As
indicated above, while no paleontological or unique geological feature was identified, there is
the possibility of encountering these resources during subsurface activities. In the event that
either of these resources is discovered, project specifications direct the contractor to halt
subsurface activities in the general vicinity and to immediately notify the Flood Control District.
The Flood Control District will immediately consult with a qualified archaeologist to evaluate the
resource(s) and provide a management plan consistent with CEQA Therefore, project impacts
will be less than significant.
d) Would the project disturb any human remains, including those interred outside of formal
cemeteries?
No formal cemeteries are present within or adjacent to either the USCB or LSCB. The NAHC
was contacted to determine if there are any recorded Native American burial grounds and/or
sacred land sites in the project vicinity. The NAHC reported that no recorded sites occur in the
vicinity of the basins. In order to determine if there are any unrecorded burial grounds and/or
sacred land sites in the vicinity of either basin, a list of Native American representatives for the
region was provided. The listed Native American representatives were notified of the project via
certified mail and follow up emails and/or phone calls. Responses were received from the local
Native American representatives who did not have specific knowledge of Native American sites
within or near the basins, however, they requested that subsurface activities within the creek
areas be monitored by a qualified archaeologist due to a higher potential of encountering
Native American resources. Because there is a potential for cultural resources to be
encountered during subsurface activities in the vicinity of the creek, an archaeological monitor
will be present during subsurface activities that occur in the creek area.
In the event Native American resources are discovered, project specifications direct the
contractor to halt subsurface activities in the general vicinity and to immediately notify the Flood
Control District. The Flood Control District will immediately consult with a qualified
archaeologist to evaluate the resource(s) and provide a management plan consistent with
CEQA. Further, if human remains are discovered, the Flood Control District will notify the
County Coroner, NAHC, and local Native American representatives to determine the extent of
the remains in accordance to the California Health and Safety Code (Health and Safety Code
Section 7050.5[b]). Therefore, project impacts will be less than significant.
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Less Than
Significant
Potentially With Less Than
Significant Mitigation Significant No
ISSUES: Impact Incorporated Impact Impact
VI. GEOLOGY AND SOILS
Would the project:
a) Expose people or structures to potential
substantial adverse effects, including the
risk of loss, injury, or death involving:
i) Rupture of a known earthquake fault,
as delineated on the most recent
Alquist-Priolo Earthquake Fault Zoning
Map issued by the State Geologist for
the area or based on other substantial
evidence of a known fault?
ii) Strong seismic ground shaking?
iii) Seismic-related ground failure,
including liquefaction?
iv) Landslides?
b) Result in substantial soil erosion or the
loss of topsoil?
c) Be located on a geological unit or soil
that is unstable, or that would become
unstable as a result of the project, and
potentially result in on- or off-site landslide,
lateral spreading, subsidence, liquefaction,
or collapse?
d) Be located on expansive soil, as defined in
Table 18-1-B of the Uniform Building Code
(1994), creating substantial risks to life or
property?
e) Have soils incapable of adequately
supporting the use of septic tanks or
alternative waste water disposal systems
where sewers are not available for the
disposal of waste water?
Environmental Setting
A geotechnical investigation was conducted of both basins to document subsurface geotechnical
conditions, provide analysis of anticipated site conditions as they pertain to the project, and to
recommend design and construction criteria as well as to establish a geotechnical baseline that
may be used to assess changed conditions that may be encountered during construction.
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Seismic Hazards
Contra Costa County is located within a region of high seismicity; the San Francisco Bay Region
has been impacted by severe earthquakes during historic time. In order to provide safety of
structures for human occupancy, the Alquist-Priolo Earthquake Fault Zoning Act was passed in
1972 to mitigate the hazards. This state law was a direct result of the 1971 San Fernando
Earthquake, which was associated with extensive surface fault ruptures that damaged numerous
homes, commercial buildings, and other structures. Surface rupture is the most easily avoided
seismic hazard. The law requires the State Geologist to establish regulatory zones (known as
Earthquake Fault Zones) around the surface traces of active faults and to issue appropriate maps.
The maps are distributed to all affected cities, counties, and state agencies for their use in planning
and controlling new or renewed construction (Contra Costa County 2005e).
For design of non-critical structures, active faults are defined those with Holocene seismic activity
(past 10,000 years). This definition is used to 1) establish the Alquist -Priolo Special Study Zone for
fault rupture hazard studies, and 2) develop seismic design criteria for dynamic analysis and
seismic design of structures (Fugro West 2003, 2004).
Approval of the design and operation of the basin falls under the jurisdiction of the California
Department of Water Resources, Division of Safety of Dams (DSOD) (Fugro West 2004). The
DSOD defines active faults as those with late Pleistocene seismic activity (past 35,000 years).
DSOD defines quaternary active faults (faults with activity within the last 1.6 millio n years) with
insufficient proof of inactivity within the late Pleistocene activity as potentially (conditionally) active
faults. According to DSOD’s guidelines, all active or potentially (conditionally) active faults should
be considered during seismic studies related to dams safety (Fugro West 2003, 2004).
Two local potentially seismic faults occur in the Antioch and Brentwood area. T he Antioch-Davis
fault is mapped as crossing the western portion of the USCB site. This fault was originally classified
as an Alquist-Priolo Earthquake Fault Zoning Act fault by the California Geologic Survey; however
the fault has been re-evaluated and dezoned on the basis of a lack of evidence for Holocene
activity (GEI 2009). The Antioch-Davis fault is not considered an active structure that could pose a
surface rupture or earthquake source hazard to the basins. However, other possible issues related
to the fault which will be considered in the design are the potential for differential settlement or
localized weak foundation materials within the fault zone, and possible seepage or piping along
bedrock faults and fractures (GEI 2009). The Antioch-Davis fault is located approximately 1.2 miles
west of the LSCB site. The Brentwood-Sherman Island Fault is located closer to the LSCB,
approximately 2 miles east of the Antioch-Davis fault and is considered potentially active for
planning purposes (City of Brentwood 2009d).
Other known nearby mapped major faults include the Great Valley fault located approximately 8
miles to the southwest, the Greenville fault located approximately 6 miles to the southwest, the Mt.
Diablo Blind Thrust located approximately 7 miles to the sout hwest, the Concord-Green Valley fault
located approximately 12 miles to the east, the Calaveras fault located approximately 7 miles to the
south, the Hayward fault located approximately 25 miles to the southwest, and the San Andreas
fault located approximately 43 miles to the southwest. Each of these faults ha s had a maximum
magnitude episode over 6.0 (Fugro 2004).
Geology
The general geology of both basins consist s of Quaternary Alluvium, consolidated and
unconsolidated sediments. Localized problems for construction include expansive clays, hillside
earthflows, and unstable cut slopes (Contra Costa County 2005e, Figure 10-1). From the
perspective of seismic safety planning, the older, coarser, and well-drained geological materials
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tend to be stable during earthquakes, while the younger, fine-grained and water-saturated deposits
tend to be less stable (Contra Costa County 2005d).
Specifically, the USCB is located in Lone Valley which consists of quaternary alluvial fan deposits
and recent alluvium overlying Markley Sandstone. Most of the project area will be excavated in the
alluvial fan deposits. Other geological features mapped in the project vicinity include landslide
deposits within the sandstone ridge near the southeast corner of the basin. The groundwater table
ranges between 21 and 26 feet below ground surface (Fugro West 2004).
The LSCB site is located east of Lone Tree Valley which also consists of quaternary alluvial fan
deposits. Subsurface conditions consists of up to 200 feet of Quaternary alluvium (clay, sand, and
gravel) overlying Pliocene Non-Marine Sediments. The groundwater table occurs between 10 to 25
feet below ground surface (Fugro West 2003).
Soils
At USCB there are four mapped soil units in and adjacent to the project area: Altamont-Fontana
Complex, 30 to 50 percent slopes; Capay Clay, 0 to 2 percent slopes; Pescadero clay loam; and
Rincon clay loam, 0 to 2 percent slopes. The Altamont Series consists of well -drained soils
underlain by shale and soft, fine-grained sandstone. These soils are on foothills north and east of
Mount Diablo. Slopes are 9 to 75 percent. Permeability is slow. Where the soil is bare, runoff is
medium to rapid and the hazard of erosion is moderat e to high. The Capay Series consists of
moderately well-drained soils formed in alluvium from sedimentary rock. These soils are on lower
edges of valley fill and on old benches that have been slowly dissected. Slopes are 0 -9 percent.
Permeability is slow with very slow surface water runoff, minimal hazard of erosion, and high
shrink-well potential. Pescadero Series consists of poorly-drained soils that formed in alluvium from
sedimentary rock. These soils are in small inland valleys on rims of basins. Slopes are 0 to 2
percent. Permeability is slow with very slow surface water runoff. There is no hazard of erosion
where the soil is tilted and exposed. Rincon Series consists of well -drained soils mainly on
benches. These soils formed in alluvial valley fill from sedimentary rock. Slopes are 0 to 15
percent. Permeability is slow with slow surface water runoff. The hazard of erosion is none to slight
where the soil is tilled and exposed (NRCS 1977).
On-site subsurface explorations at USCB indicate that subsurface conditions generally consist of
lean clay and sandy lean clay with interbedded layers of clayey and silty sand. Isolated lenses of
poorly graded sand, and poorly graded sand with silt and clay were encountered. The different soil
layers were grouped into three units: 1) lean clay, 2) interbedded sandy clay/sandy silt, and 3)
clayey and silty sands. In general, the upper lean clay consists of stiff to hard sandy lean clay and
lean clay within the upper 15 feet. The interbedded layers of sandy clay/sandy si lt underlie the
upper lean clay and consists of medium dense to dense clayey sand and medium stiff to stiff lean
clay that extends to a depth of approximately 35 feet. Discontinuous lenses of loose sand, silty
sand, and sandy silt are found within the interbedded unit. The lower lean clay underlies the
interbedded sandy clay/sandy silt layer and generally consists of very stiff to hard lean clay and
sandy lean clay and extends to the depths explored. Sandstone bedrock is anticipated to be
located at a depth of approximately 8 to 25 feet below the proposed basin bottom (Fugro West
2004).
The LSCB site is underlain by Sycamore silty clay loam. This soil type consists of grayish-brown
silty, clayey, loam extending to a depth of 15 inches. These soils are characterized as having
moderately slow permeability; risk of soil blowing and water erosion is slight (NRCS 1977).
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On-site subsurface explorations at LSCB indicate that the subsurface conditions generally consists
of lean clay, sandy lean clay, clayey sand, and interbedded layers of sandy clay and sandy silt.
Isolated lenses of poorly graded sand, silty sand, and poorly graded sand with silt and clay were
encountered. The different soil layers were grouped into four units: 1) upper lean clay, 2)
interbedded sandy clay/sandy silt, 3) sand, and 4) lower lean clay. In general, the upper lean clay
consists of stiff to hard sandy lean clay and lean clay within the upper 15 feet of the basin. The
interbedded layers of sandy clay/sandy silt underlies the upper lean clay and consist s of medium
dense to dense clayey sand and medium stiff to stiff lean clay that extends to a depth of
approximately 35 feet. Discontinuous lenses of loose sand, silty sand, and sandy silt (sand unit)
are found within the interbedded unit. The lower lean cl ay underlies the interbedded sandy
clay/sandy silt layer and generally consists of very stiff to hard lean clay and sandy lean clay and
extends to the depths explored (Fugro West 2003).
USCB will be expanded from approximately 41 acres to 62 acres, increasing its flood storage
capacity from 123-acre feet to approximately 900-acre feet (35-foot maximum depth). The basin
floor is at approximately 175 feet elevation. The basin will have multiple levels of excavation.
Excavation depths will range from 0 to approximately 60 feet below existing grade resulting in
basin elevations ranging from 158 feet above mean sea level in the lowest tier of the basin floor to
195 feet at the basin’s perimeter. The lowest (southern) tier will include Sand Creek; approximately
3,876 feet of Sand Creek will be excavated 10 feet below its current elevation and reconstructed
with a geomorphic creek design to restore and enhance Sand Creek within the basin.
The LSCB will be expanded from approximately 19 acres to 23 acres, increasing its flood storage
capacity from 40-acre feet to 300-acre feet (22-foot maximum depth). The basin floor is at
approximately 98 feet elevation. Similar to USCB, the basin will have multioplelevels of excavation.
Excavation depths will range from 4 to 23.5 feet below existing grade resulting in basin elevations
ranging from 88 feet in the lowest (northern) tier of the basin floor to 110 feet at the basin’s
perimeter. The basin expansion extends north of Sand Creek. The lowest (northern) tier will
include Sand Creek; approximately 1,100 feet of Sand Creek will be excavated and reconstructed
with a mitigation wetland area within the expanded basin.
IMPACT DISCUSSION
a) Would the project expose people or structures to potential substantial adverse effects, including
the risk of loss, injury or death, involving:
i) Rupture of a known earthquake fault, as delineated on the most recent Alquist-Priolo
Earthquake Fault Zoning Map issued by the State Geologist for the area or based on other
substantial evidence of a known fault?
Both basins are located in a seismically active area of the San Francisco Bay Area . While
the Antioch-Davis fault has been determined as an inactive fault and the Brentwood-
Sherman fault is considered as potentially active for planning purposes, nearby faults
associated with the San Andreas Fault system have the potential to affect the integrity of
the basins. Recommendations from the geotechnical investigations in accordance with the
DSOD design guidelines and local design practice will be incorporated into the project
contract specifications to ensure that the expanded basins will withstand seismic activity to
prevent flooding of downstream communities. Therefore, project impacts will be less than
significant.
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ii) Strong seismic ground shaking?
While the project area is located within an area of moderately low damage suscep tibility to
seismic ground shaking (Contra Costa County 2005e, Figure 10-4), as discussed above,
the project area is located in a seismically active region of California and therefore
earthquakes occurring along the other faults in the region have the potential to produce
strong groundshaking at both sites. For this reason, the outlet structures and earth
embankments will be designed to resist the forces generated by earthquake shaking, in
accordance with DSOD design guidelines and local design practice to ensure that the
expanded basins will withstand seismic activity to prevent flooding of downstream
communities (Fugro West 2004). Therefore, project impacts will be less than significant.
iii) Seismic-related ground failure, including liquefaction?
Soil liquefaction is a phenomenon primarily associated with saturated, cohesionless soils
located close to the ground surface, normally within the upper 50 feet. These soils lose
strength during cyclic loading, such as that induced by earthquakes. During the loss of
strength, the soil acquires “mobility” sufficient to permit both horizon tal and vertical
movements. Clean, loose, uniformly-graded, saturated, fine-grained sand is most
susceptible to soil liquefaction (Fugro West 2004).
Soils in both basins have generally a moderate to low susceptibility for seismic-related
ground failure including liquefaction (Contra Costa County 2005e, Figure 10-5; Fugro West
2003, 2004). The subsurface soil data within both basins consist of alternating layers of
lean clay, sandy lean clay, and clayey sand. In general, clayey soils are typically not
susceptible to soil liquefaction. The sandier soils are typically loose to medium dense and
are susceptible to soil liquefaction. The liquefiable layers within the project area are typically
interbedded with non-liquefiable soils and appear to be confined to former channels of
Sand Creek. Therefore, the risk of occurrence of widespread liquefaction is judged to be
low. However, localized soil liquefaction may occur, but the magnitude of liquefaction-
induced settlement is anticipated to be low, likely less than 5 inches for both basins (Fugro
West 2003, 2004).
The project design and construction will incorporate recommended measures in
accordance with local design practice and DSOD design guidelines to ensure that the
expanded basins will withstand seismic activity to prevent flooding of downstream
communities. Therefore, project impacts will be less than significant.
iv) Landslides?
The major geological hazards aside from earthquake rupture and direct effects of ground
shaking are unstable slopes, reclaimed wetlands, and marsh fill areas. Slopes may suffer
landslides, slumping, soil slips, and rockslides. Reclaimed wetlands, whether filled or not,
experience amplified lateral and vertical movements which can be damaging to structures,
utilities, and transportation routes and facilities (Contra Costa County 2005 e, page 10-21).
General Plans historically have recognized that major slope areas in excess of 26 percent
are “not readily developable” and “undevelopable”, recognizing the cost and engineering
difficulties of grading steep slopes as well as their inherit unsuitability (Contra Costa Count y
2005e, page 10-22).
The LSCB site does not contain geomorphic expressions of landslides and subsurface
explorations did not encounter loose and/or disturbed materials or distinct planes that would
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45
indicate presence of a landslide (Fugro West 2003). However, the USCB site contains a
deep-seated ancient bedrock landslide that exists on the hillslope above the east (right)
abutment of the proposed main dam. This slide has been substantially modified by erosion,
and the toe has been cut and buttressed by a portion of the alluvial terrace. The terrace is
undeformed by the slide, and shows that this slide has not been active for many thousands
of years. Further investigation of the ancient landslide did not show evidence of recent-
appearing movement and is partly “healed” and probably less susceptible to sliding
displacements than at the time of initial movement. In addition, numerous smaller and
shallower, more active landslides are present in the hillslope above Sand Creek in the area
of the proposed cut slopes bounding the margin of the basin. These slides include shallow
gullies, rotational slumps, and transitional slides in colluvial soils and stream terrace
deposits that are about 5 to 15 feet deep, slumps/slides in weathered bedrock that a re
about 15 to 25 feet deep and typically toe-out in the creek channel, and areas of shallow
raveling in steep bedrock cuts and slopes adjacent to the creek channel, partly in response
to creek incision (GEI 2009).
As part of the final design, further investigations will be made of the slide area to confirm or
refine the findings (GEI 2009). The project design and construction will incorporate
recommended measures in accordance with DSOD guidelines and local design practice to
ensure that the expanded basins will withstand seismic activity to prevent flooding of
downstream communities. Therefore, project impacts will be less than significant.
b) Would the project result in substantial soil erosion or the loss of topsoil?
Major grading and excavation will result in some changes in topography associated with the
basin expansion which will include temporary loss of topsoil and the potential for soil erosion
from wind and stream flows. The Flood Control District will notify the cities of Antioch and
Brentwood to determine if a grading permit is required. Standard project contract specifications
will require adherence to standard dust control and erosion control practices during
construction, including, but not limited to, general watering of exposed areas and/or use of
chemical stabilizers during construction. In order to minimize potential erosion due to general
watering during construction activities, project contract specifications will also require the
contractor to implement appropriate watering levels and duration. Permanent rock slope
protection will be placed at the inlets and outfalls to minimize exposure of bare soils to stream
flows. Upon project completion, all areas left exposed will be re-seeded and re-vegetated with
native species appropriate to the area in order to stabilize exposed soil. In addition, because
the disturbed area will exceed one acre, the Flood Control District will obtain a Stormwater
Construction General Permit from the State Water Resources Control Board which requires
that the contractor prepare a Storm Water Pollution Prevent Plan (SWPPP) which will identify
appropriate erosion control measures that will be implemented, after the Flood Control District’s
approval. Therefore, project impacts will be less than significant.
c) Would the project be located on a geologic unit or soil that is unstable, or that would become
unstable as a result of the project, and potentially result in on - or off-site landslide, lateral
spreading, subsidence, liquefaction or collapse?
See discussion under item a above. Project impacts will be less than significant.
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46
d) Would the project be located on expansive soil, as defined in Table 18-1-B of the Uniform
Building Code (1994), creating substantial risks to life or property?
Expansive soils swell when they absorb water and shrink as they dry. The basic cause of
expansion is the attraction and absorption of water in the expandable crystal structures of
clays. These areas must be recognized because they can cause cracking to foundations during
wet or dry periods. Moreover, various portions of a structure may become distorted, such that
doors and windows do not function properly. These hazards can be avoided through proper
drainage and foundation design. The California Uniform Building Code (UBC) has incorporated
standard response spectra as a basis for structural design and established minimum
standards. The UBC considers primary lateral seismic forces and general soil type (City of
Antioch 2003). If expansive soils are recognized through appropriate soils testing, corrective
measures can be designed into the foundations.
Both basins are located on alluvial soils primarily consisting of stiff to hard clay of medium to
high plasticity, which are likely to have moderate to high shrink-swell potential (GEI 2009). The
project design and construction will incorporate recommended measures in accordance with
DSOD design guidelines and local design practice to ensure that the embankments of the
expanded basins are constructed with soil types that are not susceptible to cracking caused by
differential settlement. Therefore, project impacts will be less than significant.
e) Have soils incapable of adequately supporting the use of septic tanks or alternative wastewater
disposal systems where sewers are not available for the disposal of wastewater?
Septic tanks and alternative wastewater disposal systems are not part of the project. Therefore,
the project will have no impact.
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Less Than
Significant
Potentially With Less Than
Significant Mitigation Significant No
ISSUES: Impact Incorporated Impact Impact
VII. GREENHOUSE GAS EMISSIONS
Would the project:
a) Generate greenhouse gas emissions,
either directly or indirectly, that may
have a significant impact on the
environment?
b) Conflict with an applicable plan, policy or
regulation adopted for the purpose of
reducing the emissions of greenhouse
gases?
Climate change refers to any significant change in measures of climate, such as average
temperature, precipitation, or wind patterns over a period of time (Office of Planning and Research
[OPR] 2008). There is a general scientific consensus that global climate change is occurring,
caused in whole or in part by increased emissions of greenhouse gases (GHGs) that ke ep the
earth’s surface warm by trapping heat in the atmosphere. Climate change may result from natural
factors, natural processes, and human activities that change the composition of the atmosphere
and alter the surface and features of the land (OPR 2008). GHGs are global pollutants, unlike
criteria air pollutants and toxic air contaminants, which are pollutants of regional and local concern,
respectively (LSA 2009). The major GHGs that are released from human activity include carbon
dioxide (CO2), methane (CH4), and nitrous oxides (NOx). The primary sources of GHGs are
vehicles (including planes and trains), energy plants, and industrial and agricultural activities (such
as dairies) (OPR 2008).
Assembly Bill 32 (AB 32), the California Global Warming Soluti ons Act of 2006, recognized that
California is the source of substantial amounts of GHG emissions which poses a serious threat to
the economic well-being, public health, natural resources, and the environment of California (OPR
2008). Potential adverse impacts of global warming include severe air quality problems, a
reduction in the quality and supply of water from the Sierra snowpack, a rise in sea levels causing
the displacement of coastal businesses and residences, damage to marine ecosystems and the
natural environment, and an increase in the incidences of infectious diseases, asthma, and other
human health-related problems (Health and Safety Code, section 38501) (OPR 2008). Other
potential threats include increased heat and ozone days, forest fires, and droughts (LSA 2009). In
order to avoid these consequences, AB 32 established a state goal of reducing GHG emissions to
1990 levels by the year 2020 (a reduction of approximately 25 percent from forecast emission
levels) with further reductions to follow.
In order to address global climate change associated with air quality impacts, CEQA statutes were
amended to require evaluation of greenhouse gas (GHG) emissions (global pollutants) which
includes criteria air pollutants (regional pollutants) and toxic air contaminants (local pollutants). As
a result, the BAAQMD adopted CEQA thresholds of significance for criteria air pollutants and
GHGs, and issued updated CEQA guidelines to assist lead agencies in evaluating air quality
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48
impacts to determine if a project’s individual emissions would be cumulatively considerable.
Various modeling tools are used to estimate emissions based on the type of project (i.e., land use
developments, linear transportation and utility projects) (BAAQMD 2010a).
a) Would the project generate greenhouse gas emissions either directly or indirectly, that may
have a significant impact on the environment?
The expanded flood control basins would not generate an increase of air pollutant
concentrations. However, construction of the basins would result in temporary increases of air
pollutant concentrations from construction equipment and off-haul truck exhaust (criteria air
pollutants) and soil excavations (PM dust). The project consists of excavating approximately 62
acres of the existing and expansion areas at USCB which would require the movement of
approximately 420,000 cubic yards of soil. Approximately 105,000 cubic yards will be used on -
site for construction of the “fill” dam; 40,000 cubic yards will be left on-site or on adjacent
properties, and 110,200 cubic yards will be hauled away to nearby projects within a 10-mile
radius (i.e., Highway 4/Loveridge Road Expansion in Antioch, Sand Creek Interchange in
Brentwood). Construction is currently planned for 2011 and will take approximately six months
to complete.
Approximately 249,000 cubic yards of soil will be excavated from LSCB of which approximately
47,000 cubic yards will be used on-site, leaving approximately 202,000 cubic yards that will be
hauled away or used for the adjacent City of Brentwood parcel that is planned for a future park
and/or nearby projects in need of soil within a 20-mile radius. Construction is currently planned
for 2016 and will take approximately six months to complete.
While the BAAQMD does not have an adopted threshold of significance for construction-related
GHG emissions, the Lead Agency should quantify and disclose GHG emissions that would
occur during construction. Sources of construction-related GHGs only include exhaust (carbon
dioxide, nitrous oxide) for which the same detailed guidance as described for criteria air
pollutants and precursors should be followed. As discussed in the Air Quality section, t he
project did not meet the BAAQMD preliminary screening criteria due to the extent o f soil
movement and transport. Therefore, estimated construction emissions were quantified using
the URBEMIS model (2007 version 9.2.4) to determine if project-related construction emissions
exceed the BAAQMD daily significance thresholds (LSA 2010). As shown in Table 2 in the Air
Quality section, neither basin expansions will exceed the daily significance thresholds.
However, the BAAQMD recommends the implementation of all Basic Construction Mitigation
Measures as listed in Table 8-2 of the BAAQMD CEQA Guidelines whether not construction-
related emissions exceed applicable thresholds of significance. Therefore, the project will
implement the following applicable air pollution control measures:
All exposed surfaces (e.g., parking areas, staging areas, soil piles, graded areas, and
unpaved access roads) will be watered two times per day.
All haul trucks transporting soil, sand, or other loose material off-site will be covered.
All visible mud or dirt track-out onto adjacent public roads will be removed using wet
power vacuum street sweepers at least once per day. Dry power sweeping will not be
used.
All vehicle speeds on unpaved roads will be limited to 15 mph.
Idling times will be minimized by either shutting equipment off when not in use or
reducing the maximum idling time to 5 minutes. Clear signage will be provided for
construction workers at all access points.
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All construction equipment will be maintained and properly tuned in accordance with
manufacturer’s specifications. All equipment will be checked by a certified mechanic
and determined to be running in proper condition prior to operation.
Signs will be posted with the telephone number and person to contact regarding dust
complaints. Complaints will be corrected within 48 hours. The sign will also include the
BAAQMD phone number to ensure compliance.
Implementation of the above-listed air pollution control measures will not generate direct or
indirect significant GHG emissions. Therefore, project impacts will be less than significant.
b) Would the project conflict with an applicable plan, policy or regulation adopted for the purpose
of reducing the emissions of greenhouse gases?
As discussed above and in the Air Quality section, implementation of the air pollution control
measures will minimize air quality impacts which are consistent with the BAAQMD air quality
plans on achieving GHG reductions. Therefore, project impacts will be less than significant.
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Less Than
Significant
Potentially With Less Than
Significant Mitigation Significant No
ISSUES: Impact Incorporated Impact Impact
VIII. HAZARDS AND HAZARDOUS MATERIALS
Would the project:
a) Create a significant hazard to the public or
the environment through the routine
transport, use, or disposal of hazardous
materials?
b) Create a significant hazard to the public
or the environment through reasonably
foreseeable upset and accident conditions
involving the release of hazardous materials
into the environment?
c) Emit hazardous emissions or handle
hazardous or acutely hazardous materials,
substances, or waste within one-quarter mile
of an existing or proposed school?
d) Be located on a site which is included on a
list of hazardous materials sites compiled
pursuant to Government Code Section
65962.5 and, as a result, would it create
a significant hazard to the public or the
environment?
e) For a project located within an airport
land use plan or, where such a plan
has not been adopted, within two miles
of a public airport or public use airport,
would the project result in a safety hazard
for people residing or working in the project
area?
f) For a project within the vicinity of a private
airstrip, would the project result in a safety
hazard for people residing or working in the
project area?
g) Impair implementation of or physically
interfere with an adopted emergency
response plan or emergency evacuation
plan?
Initial Study/Mitigated Negative Declaration Upper and Lower Sand Creek Basin Expansion Project
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51
Less Than
Significant
Potentially With Less Than
Significant Mitigation Significant No
ISSUES: Impact Incorporated Impact Impact
h) Expose people or structures to a significant
risk of loss, injury or death involving
wildland fires, including where wildlands
are adjacent to urbanized areas or where
residences are intermixed with wildlands?
Regulatory Background
A material is considered hazardous if it appears on a list of hazardous materials prepared by a
Federal, State, or local agency, or if it has characteristics defined as hazardous by such an
agency. A hazardous material is defined in Section 66261.10, Title 2 2 of the California Code of
Regulations (CCR) as follows:
A substance or combination of substances which, because of its quantity, concentration, or
physical, chemical or infectious characteristics, may either (1) cause, or significantly contribute to,
an increase in mortality or an increase in serious irreversible, or incapacitating reversible, illness; or
(2) pose a substantial present or potential hazard to human health or environment when improperly
treated, stored, transported or disposed of or otherwise managed.
Chemical and physical properties cause a substance to be considered hazardous. Such properties
include toxicity, ignitability, corrosivity, and reactivity. CCR, Title 22, Sections 66261.20 -66261.24
define the aforementioned properties. The rel ease of hazardous materials into the environment
could potentially contaminate soils, surface water, and groundwater supplies. Under Government
Code Section 65962.5, the California Department of Toxic Substances Control (DTSC) maintains a
list of hazardous substance sites. This list, referred to as the "Cortese List," includes CALSITE
hazardous material sites, sites with leaking underground storage tanks, and landfills with evidence
of groundwater contamination.
Numerous Federal and State agencies regulate hazardous materials and waste such as the
Environmental Protection Agency, DTSC, and California Department of Health Services. However,
depending on the waste, the California Air Resources Board or the State Water Resources Control
Board or another agency may also be involved. Locally, the Contra Costa Health Services,
Hazardous Materials Program (CCHS-HMP) serves area residents by responding to emergencies
and monitoring hazardous materials.
Environmental Setting
USCB and surrounding vicinity has been used for cultivation of grain and production of hay since
the late 1800s (Leighton 2001). However, in recent years the project area vicinity has been left
vacant and used only for cattle grazing. An abandoned gas well was present on the northern side
of the existing basin (SCI 2000). A CALPINE natural gas line and associated easement extends in
an east-west direction along the northern boundary of the project area.
LSCB and surrounding vicinity has been used for agricultural production since at least 1917. In
1917, an agreement was signed providing right-of-way to the East Contra Costa Irrigation
Company along Sand Creek, an area including LSCB. At that time, LSCB was a small portion of
the “Brentwood Irrigated Farms”. Historic aerial photographs showed a house and garage within
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LSCB adjacent to Sand Creek surrounded by orchards from 1957 to 1980s when the orchards
were removed and replaced with row crops and remained until at least the 1990s. A second house
and an agricultural building were situated approximately 700 feet west of LSCB (SCI 2002).
USCB contained one oil and gas exploration well along the northern boundary of the proposed
expansion area that was closed in 1993. While LSCB did not contain oil and gas exploration wells,
there were two wells near the western boundary of LSCB, but these wells did not encounter oil or
gas and have been plugged and abandoned (SCI 2000).
Previous Investigations
Due to the agricultural historic use of both basins, chemicals such as fungicides, insecticides, and
herbicides have the potential to be present within the soils on -site as some of the chemicals can
leave residues that persist in soils for 30 years or more (Baseline 1995). Subsurface investigations
were conducted prior to construction of the interim basins to determine if agricultural chemicals as
well as hydrocarbons within the diesel and motor ranges are present within the soils on-site.
Subsurface investigations of both basins consisted of collecting a range of soil samples from 0 to
15 feet below ground surface. No groundwater was encountered in any of the soil borings.
Analytical results indicated low levels of hydrocarbons, metals, and pesticides. Based on these
results, it does not appear that soils within the proposed basin expansion areas have been
significantly impacted from previous uses (SCI 2000, SCI 2002).
IMPACT DISCUSSION
a) Would the project create a significant hazard to the public or the environment through the
routine transport, use or disposal of hazardous materials?
Once constructed, the expanded flood control basins would not result in routine transport, use
or disposal of hazardous materials. However, there is the potential for a release of hazardous
substances from construction equipment operations (e.g., accidental petroleum spills) during
construction. Project contract specifications will require that the contractor prepare a site-
specific Stormwater Pollution Prevention Plan (SWPPP) as required by the Stormwater
Construction General Permit to identify safety and best management practices (e.g., placement
of drip pans under stationary equipment, routine equipment inspections, and having on-site spill
cleanup materials) to prevent accidental releases of hazardous substances and potential
worker exposure. In addition, project contract specifications will also require the contractor to
contact Underground Service Alert (USA) prior to conducting any work that could potentially
impact utilities. Therefore, project impacts will be less than significant.
b) Would the project create a significant hazard to the public or the environment through
reasonably foreseeable upset and accident conditions involving the release of hazardous
materials into the environment?
As discussed above, once constructed, the expanded flood control basins would not use or
store hazardous materials that would create a significant hazard to the public or the
environment. However, there is the potential for a release of hazardous substances from
construction equipment operations (e.g., accidental petroleum sp ills) during construction. The
required preventative measures discussed above will minimize potential impacts to the
environment and worker exposure. The CALPINE-owned natural gas line that borders the
northern boundary will be identified by Underground Service Alert (USA) and avoided.
Therefore, project impacts will be less than significant.
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c) Would the project emit hazardous emissions or handle hazardous or acutely hazardous
materials, substances or waste within one-quarter mile of an existing or proposed school?
Schools are located within one-quarter mile for both USCB and LSCB. There is one school
located approximately one-quarter mile north of USCB and an elementary school located within
one-quarter mile south of LSCB. The expanded flood control basins would not emit hazardous
emissions or handle hazardous materials, substances, or waste. While construction equipment
exhaust would generate an increase in air pollutant concentrations, it would be temporary and
effects would be negligible due to implementation of air pollution control measures and wind
patterns in this area of East County (see Air Quality section). Therefore, project impacts will be
less than significant.
d) Would the project be located on a site which is included on a list of hazardous materials sites
compiled pursuant to Government Code § 65962.5 and, as a result, would it create a significant
hazard to the public or the environment?
The project area and surrounding properties were not identified on any lists maintained by the
California Environmental Protection Agency (EPA), California Department of Toxic Substance
Control (DTSC), or Contra Costa Health Services, Hazardous Materials Program (CCHS-HMP)
databases available on their websites (DTSC, EPA, CCHS-HMP 2010). As previously
discussed in this section, soil sampling analysis results indicate that the residual petroleum
hydrocarbon, metals, and agricultural chemical constituents within the soil at both basins have
not been significantly impacted and would not pose an unacceptable human health or
ecological risk (SCI 2000, 2002). The deteriorated Sullenger Ranch buildings at USCB contain
trash which could contain unknown hazardous substances. The buildings will be removed prior
to start of excavation activities. During removal of the buildings, any hazardous substances
found will be handled and disposed of properly. Further, any evidence of soil staining or
presence of hazardous substance storage will be investigated by a qualified contractor to
determine the extent of contamination. Appropriate local and state agencies will be notified of
the results and will be remediated under their direction. Therefore, project impacts will be less
than significant.
e) For a project located within an airport land use plan area or, where such a plan has not been
adopted, within two miles of a public airport or a public use airport, would the project result in a
safety hazard for people residing or working in the project area?
Neither the USCB nor LSCB is located within two miles of a public airport. Therefore, the
project will have no impact.
f) For a project within the vicinity of a private airstrip, would the project result in a safety hazard
for people residing or working in the project area?
Neither the USCB nor LSCB is located in the vicinity of a private airstrip. Therefore, the project
will have no impact.
g) Would the project impair implementation of, or physically interfere with, an adopted emergency
response plan or emergency evacuation plan?
The majority of the work would occur within the existing flood control basins during
construction. Access to and from both basins would be properly maintained with appropriate
traffic control measures and would not require street closures to ensure that moving emergency
vehicles are not impacted. Therefore, project impacts will be less than significant.
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54
h) Would the project expose people or structures to a significant risk of loss, injury or death
involving wildland fires, including where wildlands are adjacent to urbanized areas or where
residences are intermixed with wildlands?
The surrounding area consists of undeveloped grasslands at USCB and residential
developments at LSCB. While the California Department of Forestry Hazard Severity Zones
map (2006) identifies both basins within a moderate fire hazard zone, the project does not
consist of development of structures that would expose people or structures to a significant
loss, injury, or death from wildland fires as the purpose of the project is to provide flood control
improvements to existing flood control basins. Further, safety and best management practices
required for construction of the project will identify proper protocol should a fire occur.
Therefore, project impacts will be less than significant.
Initial Study/Mitigated Negative Declaration Upper and Lower Sand Creek Basin Expansion Project
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Less Than
Significant
Potentially With Less Than
Significant Mitigation Significant No
ISSUES: Impact Incorporated Impact Impact
IX. HYDROLOGY AND WATER QUALITY
Would the project:
a) Violate any water quality standards or
waste discharge requirements?
b) Substantially deplete groundwater supplies
or interfere substantially with groundwater
recharge such that there would be a net
deficit in aquifer volume or a lowering of the
local groundwater table level (e.g., the
production rate of pre-existing nearby wells
would drop to a level which would not support
existing land uses or planned uses for which
permits have been granted)?
c) Substantially alter the existing drainage
pattern of the site or area, including
through the alteration of the course of a
stream or river, in a manner which would
result in substantial erosion or siltation on-
or off-site?
d) Substantially alter the existing drainage
pattern of the site or area, including
through the alteration of the course of
a stream or river, or substantially increase
the rate or amount of surface runoff in a
manner which would result in flooding
on- or off-site?
e) Create or contribute runoff water which
would exceed the capacity of existing
or planned stormwater drainage systems
or provide substantial additional sources of
polluted runoff?
f) Otherwise substantially degrade water
quality?
g) Place housing within a 100-year floodplain
hazard area as mapped on a federal Flood
Hazard Boundary or Flood Insurance Rate
Map or other flood hazard delineation map?
Initial Study/Mitigated Negative Declaration Upper and Lower Sand Creek Basin Expansion Project
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Less Than
Significant
Potentially With Less Than
Significant Mitigation Significant No
ISSUES: Impact Incorporated Impact Impact
h) Place within a 100-year flood hazard area
structures which would impede or redirect
flood flows?
i) Expose people or structures to a significant
risk of loss, injury or death involving flooding,
including flooding as a result of the failure
of a levee or dam?
j) Inundation by seiche, tsunami, or mudflow?
Environmental Setting
Hydrology
Hydrology within the basin is influenced by many factors such as precipitation, run -off, geologic
stratigraphy, topography, soil permeability, and plant cover. The mean annual rainfall varies from
20 inches a year at the higher elevation to 12 inches a year at the lowest elevation (Flood Control
District 2008). Sand Creek is the largest tributary in the lower Marsh Creek Watershed as it
contributes approximately 15 square miles of drainage to Marsh Creek (Flood Control District
2008). The primary goal of both basins is to prevent flooding along the lower reach of Marsh Creek
between Sand Creek and the Marsh Creek outfall point into the Sacramento-San Joaquin River at
Big Break in Oakley (Flood Control District 1992). The regional goal for USCB and LSCB is to
attenuate peak flows from Sand Creek into Marsh Creek to 400 cubic feet per second for a 100 -
year storm event. Analyses of the Sand Creek drainage area indicate that 900-acre feet and 300-
acre feet of flood storage capacity are ultimately required at the USCB and LSCB sites,
respectively. The stormwater generated in the watershed will be conveyed by Sand Creek to the
two basins where it will be stored and released slowly through the basin outlet pipes, reducing
peak flows downstream and reducing the potential for flooding downstream properties (Flood
Control District 2008).
Sand Creek is primarily an intermittent stream with the exception of segments within urbanized
areas that receive urban runoff from nearby developments primarily throughout the year.
Water Quality
The quality of surface water and groundwater in the vicinity of the project area is affected by past
and current land uses at the site and within the watershed, and the composition of geologic
materials in the vicinity. The State Water Resources Control Board and the Regional Water Quality
Control Boards regulate water quality in surf ace and groundwater bodies. Both basins are under
the jurisdiction of the Central Valley Regional Water Quality Control Board (RWQCB), which is
responsible for the implementation of state and federal water quality protection statutes and
regulations in the Delta area. The RWQCB implements the Water Quality Control Plan (Basin
Plan), a policy document for managing water quality issues in the region (RWQCB 2007). The
Basin Plan establishes beneficial water uses for waterways and water bodies within the region.
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The water quality in the Marsh Creek watershed has been historically degraded by merc ury and
coal mining, extensive agriculture operations, oil and gas production, and urbanization. Marsh
Creek Reservoir (located approximately 2 miles south of the project area) has been closed to
fishing since the mid-1980s due to high concentrations of mercury found in fish both in and
upstream of the reservoir. Discharges of wastewater from oil/water separation processes, as part
of production oil fields, to Sand Creek have commonly occurred. Historic coal mining to the west at
the Black Diamond Mines Regional Preserves, an East Bay Regional Parks District facility,
includes mine tunnels and shafts below the regional groundwater table that has been discharging
acid mine leachate into a tributary of Sand Creek. Efforts have been made to seal up the seep.
These past activities have likely affected water quality in many of the creeks within the watershed
(City of Antioch 2002).
Flood Hazard Areas
100-year Floodplains
The Federal Emergency Management Agency (FEMA) records are maintained as a means of
determining flood insurance rates through the National Flood Insurance Program (NFIP) (Contra
Costa County 2005e). Both basins are immediately adjacent to a designated 100-year floodplain
zone (Sand Creek) as shown on the FEMA NFIP Flood Insurance Rate Map (FEMA 2009).
Levees and Dams
Levee and dam failure can also cause flooding. Neither basin is located within nor in the vicinity of
levee systems (Contra Costa County 2005f) or dams (ABAG 1995). However, construction of the
basin expansions falls under the Division of Safety of Dams (DSOD) and therefore, will need to
comply with DSOD dam construction guidelines. The Division of Safety of Dams (DSOD) was
created in 1929 as a result of a catastrophic dam failure in southern California that killed more than
450 people, destroyed 900 houses and many bridges and roads, and swept away 24,000 acres of
farmland. A state commission reported that the two-year old dam failed because it was ill-built in a
geologically unstable site. A reservoir falls under the DSOD jurisdiction if the dam height is more
than 6 feet and it impounds 50 acre-feet or more of water, or if the dam is 25 feet or higher and
impounds more than 15 acre-fee of water, unless it is federally-owned or exempted under special
provisions described in Sections 6004, 6025, or 6026 of the California Water Code. The DSOD
reviews and approves plans and specifications for the design of dams and oversees their
construction to insure compliance with the approved plans and specifications. In addition, DSOD
engineers inspect over 1,200 dams on a yearly schedule to insure they are performing and are
being maintained in a safe manner (California Department of Water Resources 2010). The Office
of Emergency Services approves the maps and distributes them to local governments who in turn
adopt emergency procedures for the evacuation and control of areas in the event of a dam failure
(ABAG 2010).
IMPACT DISCUSSION
a) Would the project violate any water quality standards or waste discharge requirements?
The expanded basins will function to treat stormwater runoff by facilitating the settling of
sediment associated with stormwater runoff before it enters into Sand Creek. The basins will be
normally dry reservoirs (except for low-flows) that will attenuate peak runoff by containing
stormwater flows up to the 100-year storm event. During typical rains, the creek and local
stormwater runoff flows will be carried through a low-flow channel and will discharge through
the primary outlets. Creek flows that exceed the inlet-controlled discharge capacity of the outlet
works from more severe storms will then pond in the basin and the basin stage will rise. After
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the peak of the storm has passed, and once the creek flow becomes smaller than the outlet
discharge, the water stored in the basin will be passively released back to Sand Creek.
Construction will occur during the dry season (May 1 to October 15) when the creek is usually
dry or has low flows. Water quality objectives will be met through adherence to construction
provisions, precautions, and stipulations as described in the National Pollution Discharge
Elimination System (NPDES) permit that will be obtained under the Statewide General Permit
for Discharges of Storm Water Associated with Construction Activity (Order No. 2009-0009
DWQ) (Stormwater Construction General Permit). In accordance with the provisions of the
Stormwater Construction General Permit, the Flood Control District will require the contractor to
prepare a Storm Water Pollution Prevention Plan (SWPPP) which will identify applicable water
quality and erosion control best management practices (BMPs) that will reduce or minimize
discharge of pollutants from construction activities as well as a revegetation and erosion control
plan to ensure that all graded areas are revegetated prior to the onset of winter rains. The
graded areas will be revegetated with native grasses appropriate to the area, and rock slope
protection will be placed at the inlet and outlet structures.
The Flood Control District will also obtain permits from the Army Corps of Engineers (Corps)
(Section 404 of the Clean Water Act) (U.S. Army Corps of Engineers 2010) , Central Valley
Regional Water Quality Control Board (RWQCB) (Section 401 of the Clean Water Act)
(CRWQCB 2010), California Department of Fish and Game (CDFG) (Section 1600 of the
California Fish and Game Code) (CDFG 2010) for permanent and temporary impacts within
Sand Creek). In addition, a dewatering plan will be prepared to identify the appropriate method
of water diversion and will be provided to the CDFG for their review and approval if it differs
from the typical upstream and downstream cofferdam design. As discussed in the Biological
Resources section, permanent and temporary impacts to the creek and associated wetlands
will be mitigated by payment of development and wetland impact fees to the East Contra Costa
County HCP Conservancy and a plan to restore the creek within the basins in accordance to
the HCP/NCCP to ensure that the impacted areas provide beneficial values than what currently
exists. Therefore, project impacts will be less than significant.
b) Would the project substantially deplete groundwater supplies or interfere substantially with
groundwater recharge such that there would be a net deficit in aquifer volume or a lowering of
the local groundwater table level (e.g., the production rate of pre-existing nearby wells would
drop to a level which would not support existing land uses or planned uses for which permits
have been granted)?
Based on previous field explorations, the groundwater table was measured at a depth of 21 to
26 feet below existing ground surface (160 to 165 feet elevation) at USCB. The existing basin
floor is at approximately 175 feet elevation and will be excavated to 158 feet elevation (Fugro
2003). Therefore, excavation will extend to a depth roughly 1 to 5 feet above the groundwater
table.
Groundwater occurs at a depth of 18 to 20 feet below ground surface (85.5 feet to 92 feet
elevation) at LSCB. The existing basin floor is at approximately 98 feet elevation and will be
excavated to 88 feet elevation (Fugro 2003). Therefore, excavation will extend to a depth of
roughly 8 to 10 feet above the groundwater table.
While the basin expansions will not involve withdrawals from an aquifer or groundwater table,
minor withdrawals may occur during construction as groundwater and/or saturated conditions
may be encountered during excavation activities of the basin floor. Project contract
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specifications will require the contractor to prepare a groundwater control plan to address how
the groundwater will be removed from the work area and released. Dewatering may be
accomplished with sumps or a more advanced groundwater control system, which will be
designed by an experienced specialty contractor with experience in similar subsurface
conditions. Therefore, project impacts will be less than significant.
c) Would the project substantially alter the existing drainage pattern of the site or area, including
through the alteration of the course of a stream or river, in a manner, which would result in
substantial erosion or siltation on- or off-site?
As discussed in the Biological Resources section, both basin expansions will involve removal of
portions of Sand Creek which will be recreated within each basin expansion area with the
appropriate geomorphic and restoration design, which will also include wetland mitigation
areas.
As construction of both basins will occur during the dry season (May 1-October 15), it may
have a short-term impact on the turbidity of runoff in Sand Creek and the downstream reaches
of Marsh Creek during the rainy season. The effects of sediment on the beneficial uses of Sand
and Marsh Creeks could interfere with the activities of and physiological damage to aquatic
species. In addition, construction-related pollutants such as oils, greases, and coatings from
equipment operation and maintenance could enter the creek system, especially if large
quantities are spilled near the creek. A dewatering plan will be prepared to identify the
appropriate method of water diversion and will be provided to the CDFG for their review and
approval if it differs from the typical upstream and downstream cofferdam design . Project
contract specifications will direct the contractor to implement applicable BMPs to minimize
water quality impacts. Therefore, project impacts will be less than significant.
d) Would the project substantially alter the existing drainage pattern of the site or area, including
through the alteration of the course of a stream or river, or substantially increase the rate or
amount of surface runoff in a manner that would result in flooding on- or off-site?
As discussed above, both basin expansions will involve removal of portions of Sand Creek
which will be recreated within each expansion area with the appropriate geomorphic and
restoration design, including a wetland mitigation area. However, the drainage pattern for each
basin would not be substantially altered in that it would not result in on-site or off-site flooding
as the basin expansions will store and release flows slowly through the basin outlet pipes,
reducing peak flows downstream and reducing the potential for flooding downstream
properties. Therefore, project impacts will be less than significant.
e) Would the project create or contribute runoff water, which would exceed the capacity of existing
or planned stormwater drainage systems or provide substantial additional sources of polluted
runoff?
The purpose of the basin expansions is to control increased urban runoff and reduce peak
flows in Marsh Creek. As discussed above, the stormwater runoff will be stored and released
slowly through basin outlets, reducing peak flows downstream. Pollutants associated with
stormwater runoff would settle out prior to being discharged downstream into Sand Creek.
However, as discussed in item a above, construction of the basin expansions may impact
downstream water quality. Project contract specifications will direct the Contractor to implement
applicable BMPs to minimize water quality impacts. Therefore, project impacts will be less
than significant.
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f) Would the project otherwise substantially degrade water quality?
No additional impacts other than those discussed under Items a, c and e above are anticipated.
Therefore, project impacts will be less than significant.
g) Would the project place housing within a 100-year flood hazard area as mapped on a federal
Flood Hazard Boundary or Flood Insurance Rate Map or other flood hazard delineation map?
While both basins will be located within a 100-year flood hazard zone (Sand Creek) (FEMA
2009), the project does not include the construction of housing. Therefore, the project will have
no impact.
h) Would the project place within a 100-year flood hazard area structures that would impede or
redirect flood flows?
The existing basins are located adjacent to Sand Creek which is designated as a 100-year
flood hazard zone (FEMA 2009). The basin expansions will include portions of Sand Creek and
redirect flows for the purposes of providing flood protection for nearby and downstream
communities.
The USCB expansion will include a basin inlet on the southwest side to receive upstream flows
from Sand Creek, a primary spillway outfall on the southeast side (under the dam) to drain low-
flow or ponded water in the basin, and an emergency spillway on the east side of the dam to
direct flows greater than the 100-year storm event downstream to Sand Creek. The two
existing 84-inch diameter basin inlet pipes at the northwest side of the existing basin that
currently drain local stormwater runoff will remain; a drainage ditch will be created to re-direct
local stormwater runoff flows to Sand Creek. The basin will be a normally dry reservoir (except
for low-flows) that will attenuate peak runoff by containing stormwater flows up to t he 100-year
storm event. During typical rains, the creek and local stormwater runoff flows will be carried
through a low-flow channel and will discharge through the primary outlet pipe under the dam.
Creek flows that exceed the inlet-controlled discharge capacity of the outlet works from more
severe storms will then pond in the basin and the basin stage will rise. After the peak of the
storm has passed, and once the creek flow becomes smaller than the outlet discharge, the
water stored in the basin will be passively released back to Sand Creek. For storms greater
than the 100-year storm event, flood flows will pass over the emergency spillway and follow a
controlled route to enter the creek downstream of the basin.
Expansion of LSCB includes the construction of wing walls and inlet weir in Sand Creek at the
northwest corner of the basin to direct upstream Sand Creek flows into the basin. During low
flows, runoff that enters the basin will continue downstream, unattenuated, through a 60 -inch
diameter primary spillway/outfall pipe that will extend along the north side of the basin under a
bench in the basin embankment. The basin will be a normally dry reservoir (except for low-
flows) that will attenuate peak runoff by containing stormwater flows up to the 100-year storm
event. The 60-inch diameter pipe will continue approximately 1,300 feet downstream of the
basin under the basin embankment where it will discharge into the drop structure in Sand
Creek at the northwest corner of Fairview Avenue and Sand Creek Road. During significant
storm events, higher flows will create increasing head at the inlet to the 60 -inch diameter
primary spillway pipe. The head will continue to rise until stormwater spills over the weir crest
and into the basin. After the peak of the storm passes, the basin will drain back via flap-gated
openings that are proposed within the wall of the inlet weir. A perpetual pond will not occur in
the basin as the low flow section will be graded to drain and an 18-inch diameter secondary
drain pipe will be installed at the downstream side of the basin.
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IMPACT HYD-1:
After project completion, the flood hazard would be eliminated. However, unless the official
FEMA maps are updated, the owners of the properties within the designated flood prone areas
would be required to purchase flood insurance, and property values could be impact ed (Flood
Control District 1992).
MITIGATION MEASURE HYD-1:
The Flood Control District will petition FEMA to re-evaluate the Flood Insurance Rate Maps
upon completion of the flood control improvements. Project impacts will be less than
significant with implementation of this measure.
i) Would the project expose people or structures to a significant risk of loss, injury or death
involving flooding, including flooding as a result of a failure of a levee or dam?
While the purpose of the project is to provide increased flood control protection, failure of either
basins could flood surrounding communities. The basin expansions have incorporated design
features to prevent flooding and dam failure. The regional goal for USCB and LSCB is to
attenuate peak flows from Sand Creek into Marsh Creek to 400 cubic feet per second (cfs) for
a 100-year storm event. Analyses of the Sand Creek drainage area indicate that 900-acre feet
and 300-acre feet of flood storage capacity are ultimately required at the USCB and LSCB
sites, respectively.
For the USCB, it has been determined that a reservoir capacity of approximately 900-acre feet
is needed to route the flow from the 100 -year storm event through the outlet works and limit the
peak reservoir stage below the emergency spillway crest at 191 feet elevation. The peak
outflow from the outlet works would be approximately 134 cubic feet per second (cfs). The peak
outflow from the emergency spillway resulting from the 1,000-year storm event is approximately
2,500 cfs with maximum reservoir level at 193.5 feet elevation which is 1.5 feet below the crest
of the dam. These calculations were based on an empty reservoir at the beginning of the storm
(GEI 2009).
For the LSCB, it has been determined that a reservoir capacity of approximately 300 acre-feet
is needed to route the flow from the 100 -year storm event through the outlet works and limit the
peak reservoir stage below weir crest at 110 feet elevation. The peak outflow would be
approximately 210 cfs through the 60-inch diameter primary spillway pipe while approximately
1,050 cfs will spill into the basin (Fugro West 2003).
IMPACT HYD-2:
While the basins will be designed and constructed to withstand major storm events in
accordance to applicable state and local guidelines, unforeseen basin failure could impact
surrounding communities.
MITIGATON MEASURE HYD-2:
Both basins will be under the jurisdiction of the DSOD and therefore a dam failure
inundation map will be submitted to the Office of Emergency Services who in turn will adopt
emergency procedures for the evacuation and control of areas in the event of a dam failure
(DSOD 2010, ABAG 2010). Project impacts will be less than significant with
implementation of this measure.
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j) Would the project be subject to inundation by seiche, tsunami or mudflow?
The basins are not in an area subject to seiche, tsunami, or mudflow. Therefore, the project will
have no impact.
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Less Than
Significant
Potentially With Less Than
Significant Mitigation Significant No
ISSUES: Impact Incorporated Impact Impact
X. LAND USE AND PLANNING
Would the project:
a) Physically divide an established community?
b) Conflict with any applicable land use plan,
policy, or regulation of an agency with
jurisdiction over the project (including, but
not limited to the general plan, specific plan,
local coastal program, or zoning ordinance)
adopted for the purpose of avoiding or
mitigating an environmental effect?
c) Conflict with any applicable habitat
conservation plan or natural community
conservation plan?
IMPACT DISCUSSION
a) Would the project physically divide an established community?
Expansion of the existing flood control basins will not physically divide an established
community as the purpose of the project is to provide adequate flood control protection for the
surrounding communities. Therefore, the project will have no impact.
b) Would the project conflict with any applicable land use plan policy, or regulation of an agency
with jurisdiction over the project (including, but not limited to the general plan, specific plan,
local coastal program, or zoning ordinance) adopted for the purpose of avoiding or mitigating
an environmental effect?
The County General Plan designates both the USCB and LSCB as public/semi-public which
identify lands owned by public governmental agencies to provide public use such as libraries,
fire stations, schools as well as public transportation corridors and privately-owned
transportation and utility corridors (i.e., PG&E, railroads, pipelines). The USCB is located within
the City of Antioch’s Sand Creek Focus Area and has been designated as Public/Quasi Public
for public and institutional activities. The LSCB is located within City of Brentwood’s Special
Planning Area D and has been designated Public Facility.
The basin expansions will not conflict with the County or cities’ land use designations as both
cities have identified adjacent parcels as planned park developments. While portions of
adjacent parcels at USCB will be purchased to accommodate the expansion, the land
acquisitions will not lead to modification of the existing land use designations of these parcels.
Therefore, project will not conflict with any local plans.
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c) Would the project conflict with any applicable habitat conservation plan or natural community
conservation plan?
As discussed in section IV, both basins are located within the East Contra Costa County
Habitat Conservation Plan (HCP) inventory area. USCB and LSCB have been identified in the
HCP as covered activities. The project will comply with the requirements of the HCP as
described in section IV. Therefore, project will not conflict with the HCP.
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Less Than
Significant
Potentially With Less Than
Significant Mitigation Significant No
ISSUES: Impact Incorporated Impact Impact
XI. MINERAL RESOURCES
Would the project:
a) Result in the loss of availability of a known
mineral resource that would be of value
to the region and the residents of the state?
b) Result in the loss of availability of a locally-
important mineral resource recovery site
delineated on a local general plan, specific
plan or other land use plan?
Mineral resources are important in Contra Costa County as in other counties because minerals
such as crushed rock, sand, among others supply the necessary components for construction
materials such as asphalt and concrete for current and future development which provides
significant employment within the County. The most important mineral resources that are currently
mined in the County include diabase near Mt. Zion on the north side of Mt. Diablo, which provides
crushed rock primarily for roadbase and streambank stabilizations; domegine sandstone, located
just south of Camino Diablo and east of Vasco Road in the Byron area, which is the sole deposit in
the State of California and an important resource nationally, primarily used by Pacific Gas &
Electric Company as trench backfill and is a primary ingredient in the manufacture of heat -resistant
glass used in the national space program; and shale in the Port Costa area, which has been
designated for protection by the County General Plan (Contra Costa County 2005g).
IMPACT DISCUSSION
a) Would the project result in the loss of availability of a known mineral resource that would be of
value to the region and the residents of the state?
There are no mapped mineral resource areas in the vicinity of either basin (Contra Costa
County 2005g, Figure 8-4). The project will not impact the availability of mineral resources that
would be of value to the state or region. Therefore, the project will have no impact.
b) Would the project result in the loss of availability of a locally important mineral resource
recovery site delineated on a local general plan, specific plan or other land use plan?
There are no mapped mineral resource areas in the vicinity of either basin (Contra Costa
County 2005g, Figure 8-4). The project will not adversely affect the availability of a locally
important mineral resource recovery site delineated on a local general plan, specific plan or
other land use plan. Therefore, the project will have no impact.
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Less Than
Significant
Potentially With Less Than
Significant Mitigation Significant No
ISSUES: Impact Incorporated Impact Impact
XII. NOISE
Would the project result in:
a) Exposure of persons to or generation of
noise levels in excess of standards
established in the local general plan or
noise ordinance, or applicable standards
of other agencies?
b) Exposure of persons to or generation of
excessive groundbourne vibration or
groundborne noise levels?
c) A substantial permanent increase in ambient
noise levels in the project vicinity above
levels existing without the project?
d) A substantial temporary or periodic increase
in ambient noise levels in the project vicinity
above levels existing without the project?
e) For a project located within an airport land
use plan or, where such a plan has not been
adopted, within two miles of a public
airport or public use airport, would the
project expose people residing or working
in the project area to excessive noise levels?
f) For a project within the vicinity of a private
airstrip, would the project expose people
residing or working in the project area
to excessive noise levels?
The traditional definition of noise is “unwanted or disturbing sound”. Sound becomes unwanted
when it either interferes with normal activities such as sleeping, conversation, or disrupts or
diminishes one’s quality of life. Persistent and escalating sources of sound can often be considered
an annoyance which can have major consequences, primarily to one’s overall health. Problems
related to constant or high levels of noise include stress related illnesses, high blood pressure,
speech interference, hearing loss, sleep disruption, and lost productivity (USEPA 2010).
The main contributors to a community noise problem are transportation sources such as highways,
railroads, and airport as they are the most pervasive and continual. Other temporary noise sources
can add to the noise problem such as a jackhammer at a construction site. The dynamic of the
noise problem are based on the relationship between the noise source, the person or place
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exposed to the noise (receiver or sensitive receptor) and the path the noise will travel from the
noise source to the receiver/sensitive receptor. Since the ear is not as sensitive at some
frequencies and sound pressure level as at others, several methods of expressing average noise
levels over a period of time have been developed(HUD 2010) .
Sound intensity is typically measured in decibels (dB) from a range of 0 (threshold of hearing) to
140 (threshold of pain); the higher the decibels, the greater the intensity. For example, a decibel
level of 10 is the sound of leaves rustling, a decibel level of 30 is a whisper, a decibel level of 60 is
freeway traffic, a decibel of 90 is a noisy urban street, and a decibel level of 140 is a nearby jet
engine (HUD 2010). Prolonged exposure from at least 75 dB increases tension affecting blood
pressure, heart function, and nervous system; prolonged exposure from at least 85 dB causes
physical damage to human hearing; above 90 dB results in permanent cell damage, at 140 dB
feeling of pain, and 190 dB will rupture the eardrum and permanently damage the inner ear (City of
Antioch 1992).
The Noise Control Act of 1972 directed EPA to promote an environment for all Americans free from
noise that jeopardizes their health and welfare. The Quiet Communities Act of 1978 amended the
Noise Control Act to encourage noise control programs at the State and community level (HUD
2010). Section 65302(f) of the California Government Code requires that a noise element be
prepared as a part of all city and county general plans. The Noise Element of a General Plan
provides a basis for comprehensive local programs to control and abate environmental noise and
to protect citizens from excessive exposure. The California Department of Health Services
prepared Noise Element Guidelines which defines noise metrics, discusses the process of noise
element development, and present land use compatibility guidelines based on various noise levels
(California Environmental Resources Evaluation System 2010).
Since both basins are owned and operated by the Flood Control District, the Contra Costa County
General Plan was reviewed as well as the cities of Antioch and Brentwood General Plans. Each
respective General Plan provides goals and policies to protect new and existing noise-sensitive
areas by identifying maximum allowable exterior and interior noise exposure levels from
transportation noise sources and non-transportation noise sources.
Land uses in the vicinity of USCB consist of open grazing land followed by residential communities
to the north, east, and south, including a magnet school (Antioch Unified School District Medical
High School) and Kaiser Hospital approximately ¼ mile to the north. A formerly-occupied
residential dwelling immediately adjoins the USCB to the southwest, which is now owned by the
Antioch Unified School District and used as a teacher-training facility. The LSCB site is immediately
adjoined by a residential development to the west, a vacant field and a residential development to
the north, a vacant field and Fairview Avenue and residential development to the east, and Sand
Creek Road and residential development to the south. An elementary school is located
approximately ¼ mile south of Sand Creek Road.
IMPACT DISCUSSION
a) Would the project result in exposure of persons to or generation of noise levels in excess of
standards established in the local general plan or noise ordinance or of applicable standards of
other agencies?
The expanded basins will not generate noise. However construction of both basins will
temporarily generate noise from construction equipment. In general, construction equipment
generates noise levels ranging from about 76 to 88 decibels at 50 feet from the noise source,
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with slightly higher levels of about 88 to 91 decibels for certain types of earthmoving and impact
equipment (USEPA 1971). Construction activities for this project will have comparable noise
levels. The County General Plan provides a general guideline of conducting construction
activities during the hours of the day that are not noise-sensitive for adjacent land uses and
should occur during normal work hours of the day to provide relative quiet during the more
sensitive evening and early morning periods whereas the cities of Antioch and Brentwood
provide more specific guidelines as follows:
USCB is located within the City of Antioch. The City of Antioch General Plan regulates
construction activity operations from 7:00 a.m. to 7:00 p.m. Monday through Saturday and no
construction on Sundays or holidays, Antioch’s zoning ordinance provides different time
periods of 7:00 a.m. to 6:00 p.m. week days and on weekends and holidays between 9:00 a.m.
to 5:00 p.m. However, if construction activities occur within 300 feet of occupied dwelling
space, hours should be 8:00 a.m. to 5:00 p.m. weekdays (City of Antioch Zoning Ordinance
2010b).
LSCB is located within the City of Brentwood and is adjoined by residential developments
which may be impacted by noise associated with construction of the basin expansion.
Brentwood’s General Plan states that construction activities near sensitive land uses should be
limited to the hours of 9 a.m. to 7 p.m. on weekdays and 8 a.m. to 7 p.m. on Saturday with no
construction allowed on Sundays; Brentwood’s zoning ordinance provides different time
periods of 8 a.m. to 5 p.m. during the weekdays and 9 a.m. to 4:00 p.m. on Saturdays, and no
construction on Sundays or city holidays (City of Brentwood Zoning Ordinance 2010b)). The
zoning ordinance hours of operation should be referred to over the General Plan (pers. comm.
Zilm). However, grading activities that occur within residential zones, or within 1,000 feet of any
residential occupancy, hotel, motel, or other hospital, the hours shall be limited to 8:00 a.m. to
5:30 p.m. (City of Brentwood Zoning Ordinance 2010c).
Project contract specifications will require the contractor to comply with each city’s respective
hours of operation to minimize impacts to nearby sensitive receptors (residences, schools,
hospitals, etc.). In general, project contract specifications require the contractor ensure that
stationary and mobile construction equipment are properly tuned and maintained to minimize
noise impacts as well as eliminating unnecessary equipment idling and placement of
equipment such that emitted noise is directed away from sensitive noise receptors, if feasible.
Therefore, project impacts will be less than significant.
b) Would the project result in exposure of persons to or generation of excessive groundborne
vibration or groundborne noise levels?
The project will not result in generation of excessive groundbourne vibration or noise levels
than what exists currently. While construction activities include operation of large pieces of
equipment (e.g., graders, excavators) that may result in the periodic temporary generation of
groundborne vibration, the County and City General Plans provide a general guideline of
conducting construction activities during the hours of the day that are not noise -sensitive for
adjacent land uses and should occur during normal work hours of the day to provide relative
quiet during the more sensitive evening and early morning periods. Therefore, project impacts
will be less than significant.
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c) Would the project result in a substantial permanent increase in ambient noise levels in the
project vicinity above levels existing without the project?
Neither basin will result in a permanent increase in ambient noise levels above current
conditions. Therefore, the project will have no impact.
d) Would the project result in a substantial temporary or periodic increase in ambient noise levels
in the project vicinity above levels existing without the project?
See discussion under Item (a) above. Therefore, project impacts will be less than significant.
e) For a project located within an airport land use plan area or, where such a plan has not been
adopted, within two miles of a public airport or a public use airport, would the project expose
people residing or working in the project area to excessive noise levels?
Neither basin is located within two miles of an airport. Therefore, the project will have no
impact.
f) For a project located within the vicinity of a private airstrip, would the project expose people
residing or working in the project area to excessive noise levels?
Neither basin is located in the vicinity of a private airstrip. Therefore, the project will have no
impact.
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Less Than
Significant
Potentially With Less Than
Significant Mitigation Significant No
ISSUES: Impact Incorporated Impact Impact
XIII. POPULATION AND HOUSING
Would the project:
a) induce substantial population growth in an
area, either directly (for example, by
proposing new homes and businesses) or
indirectly (for example, through extension
of roads or other infrastructure)?
b) Displace substantial numbers of existing
housing, necessitating the construction of
replacement housing elsewhere?
c) Displace substantial numbers of people,
necessitating the construction of
replacement housing elsewhere?
The 2000 census indicates that Contra Costa County is home to approximately 949,000 residents,
making it the ninth most populous county in California. In general, the County can be divided into
three primary subregions – West, Central, and East. West County is urbanized with a developed
industrial base; Central County is a rapidly urbanizing area with much new office and light industrial
development; and East County has historically been primarily agricultural but has been
experiencing considerable residential development. Single-family homes are the predominant
housing type in the County, especially in the unincorporated areas. An important goal for the
County is to maintain and enhance the quality of the housing stock and residential neighborhoods
(Contra Costa County 2005i).
IMPACT DISCUSSION:
a) Would the project induce substantial population growth in an area, either directly (e.g., by
proposing new homes and businesses) or indirectly (e.g., through extension of roads or other
infrastructure)?
The proposed project is located within an existing flood control facilities and lands owned by
the Flood Control District. The existing basins currently receive local runoff from adjacent
subdivisions. The project will not induce substantial population growth as the purpose of this
expansion project is to provide increased flood control protection for recent and planned
communities in the cities of Antioch, Brentwood, and Oakley. Therefore, the project would have
no impact.
b) Would the project displace substantial numbers of existing housing, necessitating the
construction of replacement housing elsewhere?
The project will not displace substantial numbers of existing housing, necessitating the
construction of replacement elsewhere as the project is to expand an existing flood control
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71
basin to provide increased flood control protection for the communities in the cities of Antioch,
Brentwood, and Oakley. Therefore, the project would have no impact.
c) Would the project displace substantial numbers of people, necessitating the construction of
replacement housing elsewhere?
The project will not displace substantial numbers of people, necessitating the construction of
replacement housing elsewhere as the project is to expand an existing flood control basin to
provide increased flood control protection for the communities in th e cities of Antioch,
Brentwood, and Oakley. Therefore, the project would have no impact.
Initial Study/Mitigated Negative Declaration Upper and Lower Sand Creek Basin Expansion Project
Contra Costa County Flood Control and Water Conservation District September 2010
72
Less Than
Significant
Potentially With Less Than
Significant Mitigation Significant No
ISSUES: Impact Incorporated Impact Impact
XIV. PUBLIC SERVICES
a) Would the project result in substantial
adverse physical impacts associated with
the provision of new or physically altered
governmental facilities, the construction of
which could cause significant environmental
impacts, in order to maintain acceptable
service ratios, response times or other
performance objectives for any of the public
services:
Fire protection?
Police protection?
Schools?
Parks?
Other public facilities?
IMPACT DISCUSSION
a) Would the project result in substantial adverse physical impacts associated with the provision
of new or physically altered governmental facilities, need for new or physically altered
governmental facilities, the construction of which could cause significant environmental
impacts, in order to maintain acceptable service ratios, response times or other performance
objectives for any of the following public services:
Fire protection?
The Contra Costa County Fire Protection District provides fire protection and emergency
services to Antioch; the East Diablo Fire Protection District and Oakley Fire Prevention District
provide services to Brentwood (Contra Costa County 2005j). The project would not result in the
need for increased fire protection services. The majority of the work would occur within the
basins during construction. Access to and from the facility would be maintained to ensure
proper site access if fire protection vehicles needed to access the site. Further, traffic control
will be implemented for construction trucks accessing and leaving the site to ensure no
interference to moving emergency vehicles. Therefore, project impacts will be less than
significant.
Police protection?
The City of Antioch and City of Brentwood Police Department services areas within their
respective city limits and the Contra Costa County Sheriff’s Department services the
unincorporated areas of the cities’ planning areas (Contra Costa County 2005j). The project
would not result in the need for increased police protection services. The majority of the work
would occur within the basins during construction. Access to and from the facility would be
maintained to ensure proper site access if law enforcement vehicles needed to access the site.
Further, traffic control will be implemented for construction trucks accessing and leaving the
Initial Study/Mitigated Negative Declaration Upper and Lower Sand Creek Basin Expansion Project
Contra Costa County Flood Control and Water Conservation District September 2010
73
site to ensure no interference to moving emergency vehicles. Therefore, project impacts will be
less than significant.
Schools?
The Antioch Unified School District serves the majority of Antioch; a small area in the
southeastern portion of Antioch is served by the Brentwood Unified School District (grades K-8)
and the Liberty Union High School District (grades 9-12) (City of Antioch 2003). Schools
serving the Brentwood area include: Brentwood Union School District, Liberty Union School
District, Knightsen School District, Byron Union School District, Oakley Union School District,
and Contra Community College District (City of Brentwood 2009). Expansion of the basins
would not result in the need for construction of a new school facility or expansion of an existing
facility. Therefore, the project will have no impact.
Parks?
The project would not result in the need for construction of parks. The expanded basins would
not conflict with the proposed sports complex parks being considered at each site by the City of
Antioch and City of Brentwood. All improvements associated with the sports complex parks at
the basins will be evaluated in a separate CEQA document by each of the respective cities.
Therefore, the project will have no impact.
Other public facilities?
No other public facilities would be impacted. Therefore, the project will have no impact.
Initial Study/Mitigated Negative Declaration Upper and Lower Sand Creek Basin Expansion Project
Contra Costa County Flood Control and Water Conservation District September 2010
74
Less Than
Significant
Potentially With Less Than
Significant Mitigation Significant No
ISSUES: Impact Incorporated Impact Impact
XV. RECREATION
a) Would the project increase the use of
existing neighborhood and regional parks
or other recreational facilities such that
substantial physical deterioration of the
facility would occur or be accelerated?
b) Does the project include recreational
facilities or require the construction or
expansion of recreational facilities which
might have an adverse physical effect on
the environment?
IMPACT DISCUSSION
a) Would the project increase the use of existing neighborhood and regional parks or other
recreational facilities such that substantial physical deterioration of the facility would occur or be
accelerated?
Expansion of the existing flood control basins would not result in the use of existing recreational
facilities. Therefore, the project will have no impact.
b) Does the project include recreational facilities, or require the construction or expansion of
existing facilities, which might have an adverse physical effect on the environment?
While the project would not generate the need to create new or expand existing recreational
facilities, the cities of Antioch and Brentwood have considered multi-use of the expanded flood
control basins for sports and recreational facilities which is consistent with their General Plans .
The respective city would evaluate their proposal in a separate CEQA document. Therefore,
project impacts will be less than significant.
Initial Study/Mitigated Negative Declaration Upper and Lower Sand Creek Basin Expansion Project
Contra Costa County Flood Control and Water Conservation District September 2010
75
Less Than
Significant
Potentially With Less Than
Significant Mitigation Significant No
ISSUES: Impact Incorporated Impact Impact
XVI. TRANSPORTATION/TRAFFIC
Would the project:
a) Conflict with an applicable plan, ordinance
or policy establishing measures of effective-
ness for the performance of the circulation
system, taking into account all modes of
transportation including mass transit and
non-motorized travel and relevant com-
ponents of the circulation system, including
by not limited to intersection, streets, highways,
and freeways, pedestrian and bicycle paths,
and mass transit?
b) Conflict with an applicable congestion
management program, including, but not
limited to level of service standards and
travel demand measures, or other standards
established by the county congestion
management agency for designated roads or
highways?
c) Result in a change in air traffic patterns,
including either an increase in traffic levels
or a change in location that results in
substantial safety risks?
d) Substantially increase hazards due to a
design feature (e.g., sharp curves or
dangerous intersections) or incompatible
uses (e.g., farm equipment)?
e) Result in inadequate emergency access?
f) Conflict with adopted policies, plans, or
programs regarding public transit, bicycle,
or pedestrian facilities, or otherwise decrease
the performance or safety of such facilities?
Traffic circulation is of local and regional nature as it includes the movement of people and goods
using all modes of transportation and it affects land use, community design, growth management,
economic development, air quality, energy consumption, infrastructure, and emergency services
(City of Antioch 2003d).
Initial Study/Mitigated Negative Declaration Upper and Lower Sand Creek Basin Expansion Project
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76
The Circulation Element of General Plans describes the services, facilities, and capital
improvements that are needed to facilitate vehicle, pedestrian, transit, bicycle, and emergency
transportation. It also describes methods for promoting and encouraging the use of alternative
transportation modes, accommodating growth in travel demand, and preserving safety. It is
important to plan for future circulation facilities and services in conjunction with planned population
growth and future land use patterns (City of Brentwood 2009e).
Both the Cities of Antioch and Brentwood have identified major arterial roads for transportation
access and mobility which provide through-traffic within the urbanized sections and access to
freeways and expressways. Both basins are accessed by major arterial roads; USCB is accessed
from Deer Valley Road and LSCB is accessed from Sand Creek Road.
IMPACT DISCUSSION
a) Would the project conflict with an applicable plan, ordinance or policy establishing measures of
effectiveness for the performance of the circulation system, taking into account all modes of
transportation including mass transit and non-motorized travel and relevant components of the
circulation system, including by not limited to intersection, streets, highways, and freeways,
pedestrian and bicycle paths, and mass transit?
The expansion and operation of the flood control basins will not create new or increase existing
transportation. However, construction of the project would cause a temporary increase in
existing traffic of nearby roads from construction vehicles and haul trucks. Approximately
110,000 cubic yards of soil will be hauled away from USCB which would result in approximately
5,500 truck load trips (using a 20-cubic yard truck) over a six-month period resulting in
approximately 35 trips per work day. The average daily traffic on Deer Valley Road from 500
feet north of Empire Road to Lone Tree Way is 12,059 (2007 data) (pers. comm. City of
Antioch).
At LSCB, approximately 202,000 cubic yards will need to be hauled away which would result in
approximately 10,100 truck load trips (using a 20-cubic yard truck) over a six-month period
resulting in approximately 65 trips a day. The average daily traffic on Sand Creek Road
between Fairview Avenue and Highway 4 Bypass is 7,651 for westbound traffic and 10,034 for
eastbound traffic (2007 data) (pers. comm. City of Brentwood).
Efforts will be made to provide soil to nearby projects in need of soil (i.e., Highway 4/Loveridge
Road Expansion, Sand Creek interchange, EBART).
The Cities of Antioch and Brentwood require truck permits for use of city streets (Brentwood
Ord. 592, Section 1 (Exhibit 1 (part)), 1998; Antioch, Article 14, Section 4 -5.1405). In addition,
the City of Brentwood enforces special hours of 9:00 a.m. to 3:00 p.m. Monday through Friday
on work affecting traffic on various roads including Sand Creek Road and F airview Avenue to
minimize impacts to commuter and school traffic. The City of Brentwood also requires a traffic
control plan.
These traffic measures are expected to minimize significant congestion and delays. Therefore,
project impacts will be less than significant.
Initial Study/Mitigated Negative Declaration Upper and Lower Sand Creek Basin Expansion Project
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77
b) Conflict with an applicable congestion management program, including, but not limited to level
of service standards and travel demand measures, or other standards established by the
county congestion management agency for designated roads or highways?
As described above, the expanded flood control basins would not cause a substantial increase
of existing traffic that would exceed the level of service standard for the nearby roadways.
Construction of the project will result in a temporary increase in off-haul truck traffic however
measures outlined above will be incorporated into the project specifications which will minimize
impacts to existing traffic. Therefore, project impacts will be less than significant.
c) Would the project result in a change in air traffic patterns, including either an increase in traffic
levels or a change in location that results in substantial safety risks?
Neither basin would result in a change in air traffic patterns as there will be no increase in traffic
levels or change in location that would pose a substantial safety risk. Further, neither basin is
located within a vicinity of an airport. Therefore, the project will have no impact.
d) Would the project substantially increase hazards due to a design feature (e.g., sharp curves or
dangerous intersections) or incompatible uses (e.g., farm equipment)?
The project would not increase design feature hazards as these basins are located off the
roadway system and would not result in changes to existing roads in the area. Therefore, the
project will have no impact.
e) Would the project result in inadequate emergency access?
The majority of the work will occur within the flood control basins during construction. Traffic
control measures for off-haul truck traffic on Deer Valley Road for USCB and Sand Creek Road
for LSCB will ensure that there is no interference with passing emergency vehicles. In addition,
a traffic control plan will be submitted to the respective cities for approval. Therefore, project
impacts will be less than significant.
f) Conflict with adopted policies, plans, or programs regarding public transit, bicycle, or pedestrian
facilities, or otherwise decrease the performance or safety of such facilities?
Expansion of the basins will not conflict with adopted policies, plans or programs supporting
alternative transportation. The USCB site is located in Antioch’s Sand Creek Focus Area which
has identified a goal of developing a sports complex (City of Antioch General Plan 2002, page
4-56). Upon completion, USCB will be suitable for this use which will also provide an
opportunity for a recreational trail system. The LSCB site is located in Brentwood’s Special
Planning Area D, which has planned for a community park adjacent to the LSCB site. The
abandoned old Sand Creek Road that adjoins the LSCB site is planned as a future Class I
bikeway/trail (City of Brentwood 2009, Page III.3-15, Figure 11). The expansion will move the
trail to the north side of the basin upon project completion and will be compatible with the city of
Brentwood’s future park and trail plans. Therefore, project impacts will be less than
significant.
Initial Study/Mitigated Negative Declaration Upper and Lower Sand Creek Basin Expansion Project
Contra Costa County Flood Control and Water Conservation District September 2010
78
Less Than
Significant
Potentially With Less Than
Significant Mitigation Significant No
ISSUES: Impact Incorporated Impact Impact
XVII. UTILITIES AND SERVICE SYSTEMS
Would the project:
a) Exceed wastewater treatment requirements
of the applicable Regional Water Quality
Control Board?
b) Require or result in the construction of
new water or wastewater treatment facilities
or expansion of existing facilities, the
construction of which could cause significant
environmental effects?
c) Require or result in the construction of new
new storm water drainage facilities or
expansion of existing facilities, the construction
of which could cause significant environmental
effects?
d) Have sufficient water supplies available to
serve the project from existing entitlements
and resources, or are new or expanded
entitlements needed?
e) Result in a determination by the wastewater
treatment provider which serves or may serve
the project that it has adequate capacity to
serve the project’s projected demand in
addition to the provider’s existing commitments?
f) Be served by a landfill with sufficient permitted
capacity to accommodate the project’s solid
waste disposal needs?
g) Comply with federal, state, and local statutes
and regulations related to solid waste?
Wastewater Treatment
Delta Diablo Sanitation District (DDSD) is responsible for conveyance of wastewater from city of
Antioch pipelines to interceptor sewers, which convey sewage to the Bridgehead and Antioch
pump stations located in southeast Antioch and at Fulton Shipyard Road, respectively. The
wastewater is treated at the DDSD plant located near the border of Antioch and Pittsburgh (City of
Antioch 1993e). The City of Brentwood Wastewater Treatment Plant receives and treats
wastewater and discharges into Marsh Creek.
Initial Study/Mitigated Negative Declaration Upper and Lower Sand Creek Basin Expansion Project
Contra Costa County Flood Control and Water Conservation District September 2010
79
City of Brentwood 2009d)
Storm Drainage
Storm drainage in both the Antioch and Brentwood areas are largely provided by surface drainage
facilities, including roadside ditches, surface collection, and shallow drain pipes. The Contra Costa
County Flood Control and Water Conservation District oversees stormwater collection and flood
control of which discharge into channels and detention basins owned and maintained by both cities
and the Flood Control District (City of Antioch 1993f, City of Brentwood 2009f).
Water Supply
The City of Antioch supplies the entire city as well as unincorporated areas within the city’s sphere
of influence. The city purchases the water from Contra Costa Water District, which obtains the
water from the San Joaquin River, and distributes it to their wa ter treatment and storage plants
(City of Antioch 1993g). The City of Brentwood provides water supply to its residents. The primary
water is groundwater, supplemented by treated surface water (City of Brentwood 2009f).
Solid Waste
Pleasant Hill Bayshore Disposal provides solid waste collection, disposal, recycling and yard waste
services for Antioch which are taken to the Contra Costa Transfer and Recovery Station located in
Martinez where recyclables are separated out and stored before shipment to recycling markets. In
Antioch, solid waste is collected by Brentwood Disposal Service and disposed of in the Contra
Costa County landfill at Keller Canyon (City of Antioch 1993h). Solid waste in Brentwood is
collected by Brentwood Disposal Service and disposed of in the Contra Costa landfill at Keller
Canyon (City of Brentwood 2009f).
IMPACT DISCUSSION
a) Would the project exceed wastewater treatment requirements of the applicable Regional Water
Quality Control Board?
Neither basin would result in the need for wastewater treatment. Waste from portable toilets
used during construction would not exceed the requirements. Therefore, the project will have
no impact.
b) Would the project require or result in the construction of new water or wastewater treatment
facilities or expansion of existing facilities, the construction of which could cause significant
environmental effects?
Neither basin would require or result in the construction of new water or wastewater treatment
facilities or expansion of existing facilities. Therefore, the project will have no impact.
c) Would the project require or result in the construction of new construction of new storm water
drainage facilities or expansion of existing facilities, the construction of which could cause
significant environmental effects?
Expansion of both basins will not cause significant environmental effects. However, during
construction, sensitive natural communities that provide suitable habitat for special-status
species will be disturbed (Sand Creek, wetlands, riparian oak woodland/scrub). As discussed in
the Biological Resources section, permanent and temporary impacts will be mitigated on-site
and development and wetland impact fees will be paid to the East Contra Costa County Habitat
Conservancy. Therefore, project impacts will be mitigated to less than significant with
incorporation of these mitigation measures.
Initial Study/Mitigated Negative Declaration Upper and Lower Sand Creek Basin Expansion Project
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80
d) Would the project have sufficient water supplies available to serve the project from existing
entitlements and resources, or are new or expanded entitlements needed?
Neither basin would require water supply service. Therefore, the project will have no impact.
e) Would the project result in a determination by the wastewater treatment provider that serves or
may serve the project that it has adequate capacity to serve the project’s projected demand, in
addition to the provider’s existing commitments?
Neither basin requires wastewater treatment services. Therefore, the project will have no
impact.
f) Would the project be served by a landfill with sufficient permitted capacity to accommodate the
project’s solid waste disposal needs?
The expanded basins would not generate solid waste disposal needs. However, construction of
the project would generate some waste from removal of the historic homestead buildings at
USCB which is an insignificant amount and therefore, would not exceed the permitted capacity.
Further, appropriate building materials would be offered to salvage companies for re -use.
Excavated soil would be used on-site and for fill at other sites. Therefore, project impacts will
be less than significant.
g) Comply with federal, state and local statutes and regulations related to solid waste?
Project specifications will require that the contractor dispose of solid waste generated from
construction in accordance with federal, state and local regulations. Therefore, the project will
have no impact.
Initial Study/Mitigated Negative Declaration Upper and Lower Sand Creek Basin Expansion Project
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81
Less Than
Significant
Potentially With Less Than
Significant Mitigation Significant No
ISSUES: Impact Incorporated Impact Impact
XVIII. MANDATORY FINDINGS OF SIGNIFICANCE
a) Does the project have the potential to degrade
the quality of the environment, substantially
reduce the habitat of fish and wildlife species,
cause a fish or wildlife population to drop below
self-sustaining levels, threaten to eliminate a
plant or animal community, reduce the number
or restrict the range of a rare or endangered plant
or animal or eliminate important examples of the
major periods of California history or prehistory?
b) Does the project have impacts that are
individually limited, but cumulatively
considerable? (“Cumulatively considerable”
means that the incremental effects of a
project are considerable when viewed in
connection with the effects of past projects,
the effects of other current projects, and
the effects of probable future projects)?
c) Does the project have environmental effects
which will cause substantial adverse effects
on human beings, either directly or indirectly?
a) Does the project have the potential to degrade the quality of the environment, substantially
reduce the habitat of a fish or wildlife species, cause a fish or wildlife population to drop below
self-sustaining levels, threaten to eliminate a plant or animal community, reduce the number or
restrict the range of rare or endangered plants or animals, or eliminate important examples of
the major periods of California history or prehistory?
Construction of the basins initially will temporarily degrade the quality of the local habitat at
each site during construction, but subsequent to restoration of impacted areas will eventually
increase the value of the natural communities and associated wildlife species (see Section IV).
While the project will remove an old historic ranch homestead of lo cal significance, the on-site
buildings are in a state of disrepair and determined not to be of historic significance to
California. However, collected artifacts will be offered to interested local historical societies to
expand their existing collection of the local history. Implementation of the mitigation measures
will reduce project impacts to less than significant.
Initial Study/Mitigated Negative Declaration Upper and Lower Sand Creek Basin Expansion Project
Contra Costa County Flood Control and Water Conservation District September 2010
82
b) Does the project have impacts that are individually limited, but cumulatively considerable?
"Cumulatively considerable" means that the incremental effects of a project are considerable
when viewed in connection with the effects of past projects, the effects of other current
projects, and the effects of probable future projects?
The project will not have cumulative impacts as there are no other flood control projects
planned for the Sand Creek Drainage Area. Therefore, the project will have no impact.
c) Does the project have environmental effects that will cause substantial adverse effects on
human beings, either directly or indirectly?
The project is intended to provide flood control protection to surrounding and downstream
communities. After completion, the flood hazard would be eliminated. However, unless the
official FEMA maps are updated, the owners of the properties within the designated flood -prone
areas would be required to purchase flood insurance, and property values could be impacted.
Therefore, the Flood Control District will petition FEMA to re-evaluate the Flood Insurance Rate
Maps. In addition, while the basins will be designed and constructed to withstand major storm
events in accordance to applicable state and local guidelines, unforeseen basin failure could
impact surrounding communities. Since both basins are under the jurisdiction of the DSOD, a
dam inundation map will be submitted to the Office of Emergency Services who in turn will
adopt emergency procedures for the evacuation and control of areas in the event of a dam
failure. Implementation of these measures will reduce project impacts to less than significant.
Initial Study/Mitigated Negative Declaration Upper and Lower Sand Creek Basin Expansion Project
Contra Costa County Flood Control and Water Conservation District September 2010
83
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Contra Costa County Flood Control and Water Conservation District September 2010
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23.; Open Space Elements, 9.6 Scenic Resources, pages 9-4 – 9-8.
2005c: Agricultural Resources: 8. Conservation Element: 8.7: Agricultural Resources; pages 8-
19 – 8-30, Figure 8-2.
2005d: Air Quality: 8. Conservation Element, 8.14 Air Resources, page 8-51.
2005e: Geology: 10. Safety Element, Figure 10-1; Section 10.6: Seismic Hazards, page 10-14,
Figures 10-4, 10-5; 10.7: Ground Failure and Landslide Hazards, pages 10-21 – 22.
2005f: Hydrology/Water Quality: 10. Safety Element, 10.8 Flood Hazards, 10-26 – 10-30
2005g: Mineral Resources: 8. Conservation Element, 8.9-Mineral Resource Areas; page 8-33,
Figure 8-4
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Initial Study/Mitigated Negative Declaration Upper and Lower Sand Creek Basin Expansion Project
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2005j: Public Services: 7: Public Facilities/Services Element: 7.10 Fire Protection, page 7-25;
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CALIFORNIA ENVIRONMENTAL QUALITY ACT
NOTICE OF DETERMINATION
CONTRA COSTA COUNTY DEPARTMENT OF CONSERVATION AND DEVELOPMENT
651 PINE STREET NORTH WING, 4TH FLOOR MARTINEZ, CALIFORNIA 94553-0095
Contact Person: Claudia Gemberling, Environmental Analyst II Telephone: (925) 313-2192
Project Title: Upper and Lower Sand Creek Basin Expansion Project (WO#: 7589-6D8518)
Project Location: Upper Sand Creek Basin is located approximately 1,500 east of Deer Valley Road in Antioch; Lower
Sand Creek Basin is located on the north side of Sand Creek Road in Brentwood, approximately ¼
mile east of the Highway 4 Bypass in east Contra Costa County
County File #: CP# 09-52
Project Description: Contra Costa County Flood Control and Water Conservation District (Flood Control District) proposes to
expand the interim flood control basins in the lower Marsh Creek watershed to attenuate flows from the upper Marsh Creek
watershed, which will help provide flood protection for surrounding and downstream communities. The operation of the LSCB is
contingent upon the USCB operating to meter peak flows.
The USCB will be the first of the two basins to be expanded. The project will expand the approximate 41-acre basin to
approximately 62 acres, increasing its flood storage capacity from 123-acre feet to 900-acre feet (35-foot maximum depth). The
expansion will consist of excavating the basin floor to create a deeper basin where water will be held and slowly released
downstream during major storm events. The basin will have multiple levels of excavation. Excavation depths will range from 0
to approximately 37 feet below existing grade, resulting in proposed basin elevations ranging from 158 feet above mean sea
level in the lowest tier of the basin floor to 195 feet at the basin’s perimeter. The basin expansion extends south of Sand Creek.
The lowest (southern) tier will include Sand Creek; approximately 3,876 feet of Sand Creek will be excavated 10 feet below its
current elevation of which approximately 3,612 feet will be reconstructed with a fluvial geomorphic (natural creek) design to
restore and enhance Sand Creek within the basin; the remaining 264 feet will be re-created on-site as wetland acreage.
Construction is planned to begin spring 2011 and be completed by October 2011.
Following the USCB expansion, the LSCB portion of the project will expand the approximate 19-acre interim basin to
approximately 23 acres, increasing its flood storage capacity from 40-acre feet to 300-acre feet (22-foot maximum depth). The
expansion will consist of excavating the basin floor to create a deeper basin where water will be held slowly and released
downstream during major storm events. Similar to USCB, the basin will have multiple levels of excavation. Excavation depths
will range from 4 to 23.5 feet below existing grade resulting in basin elevations ranging from 88 feet above mean sea level in
the lowest tier of the basin floor to 110 feet at the basin’s perimeter. The basin expansion extends north of Sand Creek. The
lowest (northern) tier will include Sand Creek; approximately 1,100 feet of Sand Creek will be excavated and reconstructed with
a wetland mitigation area within the expanded basin. Construction is anticipated for 2016 and will take approximately 6 months
to complete.
No traffic impacts are anticipated as construction of the basins will occur off-road. Traffic measures will be in place to minimize
traffic impacts from construction-related vehicles and trucks leaving and entering the project sites.
Real property transactions including, but not lim ited to, property acquisitions and construction easements, will be required.
The project is located within the East Contra Costa County Habitat Conservation Plan (HCP) inventory area. Therefore, in
addition to on-site mitigation, the District will pay fees to the HCP Conservancy. In addition, avoidance and minimization
measures will be implemented prior to and during construction to prevent direct and indirect impacts to special-status species
as well as other species that occur in the area.
The project was approved on .
Pursuant to the provisions of the California Environmental Quality Act:
An Environmental Impact Report was prepared and filed with the State Clearinghouse (# ).
The Project was encompassed by an Environmental Impact Report previously prepared for ______(SCH#____).
A (Mitigated) Negative Declaration was prepared.
Copies of the record of project approval and the Negative Declaration or the final Environmental Impact Report may be
examined at the office of the Contra Costa County Public Works Department.
The Project will not have a significant environmental effect.
The Project will have a significant environmental effect.
Mitigation measures were made a condition of approval of the project.
A mitigation reporting or monitoring plan was adopted for this project.
A statement of Overriding Considerations was adopted.
Findings were adopted pursuant to Section 15091 of the State CEQA Guidelines.
Date: By:
Conservation and Development Department Representative
Applicant: Department of Fish and Game Fees Due
Public Works Department EIR - $2,768.25 Total Due: $
255 Glacier Drive Neg. Dec. - $2,010.25 Total Paid $
Martinez, CA 94553 DeMinimis Findings - $0
Attn: Claudia Gemberling County Clerk - $50 Receipt #:
Environmental Section Community Development Dept. - $25
G:\EngSvc\ENVIRO\Flood Control\Upper Sand Creek (DA 104)\Expansion WO# 8518\CEQA\NOD-1.doc
Form Updated: July 21, 2006
AFFIDAVIT OF FILING AND POSTING
I declare that on I received and posted this notice as required by California
Public Resources Code Section 21152(c). Said notice will remain posted for 30 days from the filing date.
Signature Title