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HomeMy WebLinkAboutMINUTES - 12162003 - C13 TO: BOARD OF SUPERVISORS,AS GOVERNING BOARD OF CONTRA COSTA COUNTY AND CONTRA.COSTA COUNTY FLOOD CONTROL AND WATER CONSERVATION DISTRICT FROM: MAURICE M. SHIU, CHIEF ENGINEER DATE: DECEMBER 1 , 2003 SUBJECT: ADOPT the DA 67 Rossmoor Basin Expansion Project Mitigated Negative Declarationand Mitigation Monitoring Program in Compliance with the California Environmental Quality Act, APPROVE the project and AUTHORIZE the Chief Engineer to advertise the project,Walnut Creek area. [CDD-CP##03-451 (District II)Project No. 7539-6D8484 Specific Request(s)or Recornmendation(s) &Background &Justification 1. RECOMMENDED ACTION: FIND, on the basis of the DA 67 Rossmoor Detention Basin Expansion Project Mitigated Negative Declaration initial study and all comments received, that there is no substantial evidence the project will have a significant effect on the environment, and ADOPT the Mitigated Negative Declaration and Mitigation Monitoring Program in compliance with the California Environmental Quality Act,(the custodian of which is the Community Development Director who is located at 651 fine Street, Martinez), and DIRECT the Director of Community Development to file a Notice of Determination with the County Clerk, and ; CejWinued on Attachment: X SIGNATURE: jL L� ECOMMENDATION OF COUNTY ADMINISTRATOR _RECOMMENDATION OF BOARD COMMITTEE � �1'ROVE OTHER n SIGNATURE(S): ACTION OF BOA DECEMBER 16, 2003 APPROVED A RECOMMENDED OTHER VOTE OF SUPERVISORS X UNANIMOUS(ABSENT NONE ) AYES: NOES: ABSENT: ABSTAIN: I hereby certify that this is a true and correct copy of an action taken and entered on the minutes of the Board of LC:sr Supervisors on the date shown. G:\GrpData\EngSvc\Enviro\BO\2003\ (12-16-03)CEQA-Rossmoor Basin.doc Orig.Div: Public Works(Eng Sery Division) ATTESTED: DECEMBER 16, 2003 Contact: Leigh Chavez,Phone(925)313-23661 JOHN SWEETEN, Clerk of the Board of Supervisors cc: Administrator-Attn: E.Kuevor Auditor-Controller and County Administrator Community Development e K.Piona Public Works: Accounting Construction- By Deputy Flood Control—K.Emigh Engineering Services -T.Torres,Enviro -L.Chavez„Enviro L�t� SUBJECT: ADOPT the DA 67 Rossmoor Basin Expansion Project Mitigated Negative Declaration and Mitigation. Monitoring Program in Compliance with the California Environmental Quality Act; APPROVE the project and AUTHORIZE the Chief Engineer to advertise the project,Walnut Creek area[CDD-CP #03-45] (District R)Project No. 7539-6D8484 DATE: December 16, 2003 PAGE: 2 I, RECOMMENDED ACTION(continued): AUTHORIZE the Chief Engineer to arrange for payment of a $25 fee to Community Development for processing, and a$25 fee to the County Clerk for filing the Notice of Determination. DIRECT the Chief Engineer to arrange for the $1,250 Fish and Game filing fee to be transferred to the County Clerk, and APPROVE the DA 67 Rossmoor Basin Expansion Project, and AUTHORIZE the Chief Engineer to advertise the project. 11. FISCAL IMPACT: The estimated project cost is $1 million funded by Drainage Area 67 funds (70%) and the City of Walnut Creek(30%). 111. REASONS FOR RECOMl1IENDATIONCBACI GROUND: The project consists of four components: 1)acquisition of an adjacent property and excavation and removal of approximately 30,000 cubic yards ofmaterial from the property,2)removal of approximately 2,000 cubic yards of silt from the bottom of the existing basin,3)reconstruction of the existing outfall structure,and 4) long-term maintenance of the expanded detention basin. It is needed in order to expand the capacity of Rossmoor Detention Basin from 35-acre feet to 55-acre feet in order to protect residents in neighborhoods downstream of the detention basin from further periodic flooding. The project has been determined to be in compliance with the General Plan. A Mitigated Negative Declaration of environmental significance pertaining to this project was published on October 23,2003. The Board has considered the Mitigated Negative Declaration together with all comments received during the public review period. IV. CONSEQUENCES OF NEGATIVE ACTION: Delay in approving the project will result in a delay of design and construction and may jeopardize funding. e, J,3 Environmental Checklist Form 1. Project Title: Rossmoor Detention Basin Expansion Project' 2. Lead Agency Name and Address: Contra Costa County Community Development Department 651 Pine Street, North Wing - 4th Floor Martinez, CA 94553 3. Contact Person and Phone Number: Crystal Najera 4. Project Location: The project is located in the city of Walnut Creek near the corner of Tice Valley Boulevard and Rossmoor Parkway. 5. Project Sponsor's Name and Address: Contra Costa County Public Works Department 255 Glacier Drive Martinez, CA 94553 6. General Plan Designation: Public-Semi Public/Multi-Family Residential Low 7. Zoning: R-20 Single Family Residential District 8. Description of Project: Centra Costa County Flood Control and Water Conservation District proposes to expand the capacity of Rossmoor detention basin from 35 acre-feet to 55 acre-feet, The project consists of four components: 1) acquisition of an adjacent property and excavation and removal of approximately 30,000 cubic yards of material from the property, 2) removal of approximately 2,000 cubic yards of silt from the bottom of the existing basin, 3) reconstruction of the existing outfall structure, and 4) long-term maintenance of the expanded detention basin. Several standard Best Management Practices (BMPs) and mitigation measures will also be incorporated into the project in order to ensure that potential impacts are less than significant. 1) Excavation and Expansion: The area to be excavated is approximately 1.5 acres in area and 12 feet in depth and is located in the lower center of the existing basin (see Figure 1 and 2). The area consists of a vacant portable office building, parking lot and landscaping including approximately 70 mostly non-native trees (4 inches diameter breast height (DBH) or greater). Currently the vacant property is owned by UDC Homes, Inc. The Flood Control District will acquire the property prier to excavation of the basin. The vacant office, parking lot, and trees within the expansion area will all be removed. The existing low-flow channel to the North of the excavation area will not be disturbed during excavation of the expanded basin. Environmentally Sensitive Area (ESA)fencing and silt fencing will be placed at the base of the excavation area during construction. Once the basin has been excavated, an additional low flow channel will be constructed through the middle of the expanded basin. Construction of the new channel will abandon a portion of the existing creek just west of the drainage that enters from the North. Approximately 100 feet of the existing channel will be abandoned when flows are rerouted into the new low-flaw channel. However expansion of the basin and installation of the new low-flow channel will actually increase the amount of stream and riparian area existing within the basin. Upon completion of the excavation, all disturbed areas will be seeded with an appropriate mix of native grass seed. 2) Basin Resift_ Desilting of the existing basin will occur during the dry season (mid-April to October) so that flows in the creek are at a minimum. Approximately 2,000 cubic yards of silt will be removed. The low flow channel flowing through the basin may need to be dewatered in order to complete desilting operations. Measures will be taken in order to ensure that soil from construction operation does not eater the creek. if dewatering is necessary, a silt filtering area will be installed downstream of the work area. If dewatering is not necessary, the low-flow channel-will be isolated from the work area using ESA fencing and silt fencing materials. Habitat impacts will be temporary in nature. No trees will need to be removed in order to conduct desilt operations. Vegetation to be removed within the basin as a result of the desilt consists of wetland vegetation dominated by giant horsetail, kikuyu grass and salt grass. All heavy equipment used in the desilt process will operate from weight dissipating mats to minimize Rossmoor Detention Basin Expansion Project Page 1 compaction of soil when working in the wetland area. The sediment removed from the channel will be disposed at an off-site, upland location. Following completion of the desilt, all disturbed slopes will be seeded with a mix including native grasses prior to winter rains. 3) Outfall Reconstruction: The existing outfall structure at the downstream end of the basin will be modified for improved basin performance. The outfall will be designed such that it impacts the minimum amount of area possible. The new outfall will not have a larger footprint than the existing outfall. Measures will be taken to ensure that new concrete structures will not adversely modify the quality of ambient water. The new outfall will be constructed in the same location as the existing outfall; no additional concrete surface or other hard material will be installed along the creek. Construction of the outfall will occur during the dry season, however, Tice Creek is perennial so flows will be diverted around the outfall construction area. A bypass pipe system will be installed around the outfall construction area to allow creek flows to be maintained during construction. Sediment laden water will be treated prior to reintroduction into the creek to minimize sedimentation downstream. Several BMPs will be implemented during construction in order to minimize impacts to habitat within the project area. prior to any construction in the project area 'a qualified biologist will conduct pre-construction surveys for the sensitive species, if required by resource agencies. ESA fencing will be installed around all sensitive areas, including (but not limited to) sections of Tice Creek to the north of the excavation area and within the desilt area and any trees near the excavation area that will not be removed. In addition, sediment and erosion control measures will be placed to avoid and minimize soil that could potentially flow into the creek. All erosion control measures will be maintained as necessary throughout construction. All equipment will be fueled and maintained at a designated staging area. No heavy equipment will be operated in flowing water. Trash will be removed daily. 4) Long-term Maintenance:_ The intent of the expansion of the Rossmoor detention basin is to detain creek flows during high flow events so that downstream neighborhoods and other urban areas are protected from flooding. As water is detained during the high flow events, the velocity of water flowing through the detention basin will slow and sediment will drop out of the water and accumulate within the detention basin, reducing the capacity of the basin and decreasing its ability to reduce flooding. In order to maintain flood capacity of the basin accumulated silt and vegetation will need to be routinely maintained. The basin will be desilted approximately every five years, or as necessary to maintain the flood capacity of the basin. In order to minimize impacts to adjacent riparian vegetation, access to the basin will be accomplished via one or more access ramp(s) that will be constructed as part of the expansion of the ;basin. Dewatering may be necessary in order to complete desilting operations. No work will occur within the live stream channel. A silt filter barrier will be placed downstream of the work area in order to ensure that dirt does not flow into the creek. ESA fencing will be installed to definethe limits of desilt work and protect existing vegetation. The sediment removed from the channel will be disposed of at an approved off-site location in uplands. Following completion of the desilt, all disturbed slopes will be seeded with a mix including native grasses prior to winter rains. Desilting operations will remain consistent with all existing state and federal water pollution control and environmental laws. Appropriate permits will be acquired as necessary from the Department of Fish and Game, U.S. Army Corps of Engineers and the Regional Water Quality Control Board. Vegetation within the basin area will be maintained on an annual basis as part of the County's Vegetation Management Program. All vegetation will be removed by hand and allowed to grow back throughout the year. 9. Surrounding Land Uses and Setting: Surrounding General Plan Land Use Designations: Multiple Family Residential, Open Space, Parks and Recreation, Commercial. The land surrounding the project consists' of a Rossrnoor Detention Basin Expansion Project Page 2 residential neighborhood, a commercial building and parking lot, open space and a church facility. 10. Other public agencies whose approval U.B. Army Corps of Engineers 404 Nationwide Permits 43 (e.g., permits, financing approval, or and 33, Regional Water Quality! Control Board 401 Water participation agreement). Quality Certification, and California Department of Fish and Game 1601 Streambed Alteration Agreement. ENVIRONMENTAL FACTORS POTENTIALLY AFFECTED. The environmental factors checked below would be potentially affected by this project, involving at least one impact that is a "Potentially Significant Impact" as indicated by the checklist on the following pages. Land Use& Planning TransportationlCirculation Public Services Population & Housing X Biological Resources Utilities&Service Systems Geological Problems Energy&Mineral Resources X Aesthetics X Water Quality Hazards X Cultural Resources Air Quality Noise Recreation Mandatary Findings of No Significant Impacts Significance Identified DETERMINATION On the basis of this initial evaluation: I find that the proposed project COULD NOT have a significant effect on the environment, and a NEGATIVE DECLARATION will be prepared. I find that although the proposed project could have a significant effect on the environment, there will not be a significant effect in this case because the mitigation measures described on an attached sheet have been X added to the project. A MITIGATED NEGATIVE DECLARATION will be prepared.. I find that the proposed project MAY have a significant effect on the environment, and an ENVIRONMENTAL IMPACT REPORT is required. I find that the proposed project MAY have a significant effect(s) on the environment, but at least one effect (1) has been adequately analyzed in an-earlier document pursuant to applicable legal standards, and (2) has been addressed by mitigation measures based on the earlier analysis as described on attached sheets, if the effect is a "potentially significant impact" or "potentially significant unless mitigated." An ENVIRONMENTAL IMPACT REPORT is required, but it must analyze only the effects that remain to be addressed. I find that although the proposed project could have a significant effect on the environment, there WILL NOT be a significant effect in this case because all potentially significant effects (a) have been analyzed adequately in an earlier EIR pursuant to applicable standards and (b) have been avoided or mitigated pursuant to that earlier �..� EIR, including revisions or mitigation measures that are imposed upon the proposed project. Signature Date Contra Costa County L i , 0 Ek E. I P,A Community Development Department Print Name SOURCES In the process of preparing the Checklist and conducting the evaluation, the following references (whichare available for review either at the Centra Costa County Community Development Department, 651 Pine Street 5th Floor-North Wing, Martinez or Contra Costa County Public Works Department, 255 Glacier Drive, Martinez)were consulted: 1. Contra Costa Resource Mapping System - Quad Sheet Panels, CA 2. The (Reconsolidated) County General Plan (July 1996) and EIR on the Genual Plan (January 1991) 3. Contra Costa County General Plan Map. Rossmoor Detention Basin Expansion Project Page 3 1 4. Contra Costa County Zoning Map. 5. Rossmoor Detention Basin Expansion Project Description, Contra Costa County Flood Control and Water Conservation District. 2003. 6. Important Farmland Map, Division of Land Resource Protection, Farmland Mapping and Monitoring Program. 2001. Centra Costa County, California. 7. Soil Survey of Contra Costa County, U.S. Department of Agriculture, Boil Conservation Service. 1977. California. 8. Wetland Delineation Report for the Rossmoor Basin Expansion Project, Essex Environmental. Half Moon Bay, California. 2003. 9. Habitat Assessment for the Rossmoor Basin Expansion Project, Essex Environmental. Half Moon Bay, California. 2003 10. Q3 Floodplains Map, Federal Emergency Management Agency. Contra Costa County, CA. 1996. 11. Major Faults of Contra Costa County Map. United States Geological Survey. 12. Cultural Resources Investigations for the Rossmoor Basin Expansion Project, Walnut Creek, Contra Costa County, California, David Chavez and Associates, Mill Valley, CA, 'September 2003. EVALUATION OF ENVIRONMENTAL IMPACTS: Potentially Significant Potentially Unless Less than Significant Mitigafion Significant Impact incorporation Impact Pio impact i. AESTHETICS. Would the proposal: a. Have a substantial adverse effect on a scenic vista? (Source#) X b. Substantially damage scenic resources, including,-but not limited to, trees, rock, outcroppings, and historic buildings within a state scenic highway? (Source#) X c. Substantially degrade the existing visual character or quality of the site and its surroundings: (Source #) X d. Create a new source of substantial light or glare, which would adversely affect day or nighttime views in the area? (Source#) -- X SUMMARY: Potentially significant unless mitigation is incorporated. The project area is not within a scenic vista since nor is it near a scenic highway. Construction activities will impact the minimum amount of vegetation feasible, however approximately 70 trees will need to be removed as a result of the project. All trees to be removed are within Department of Fish and Game jurisdiction. Mitigation will be implemented as part of the expansion project in order to minimize the impact of the loss of trees. Mitigation requirements and long-term success criteria will be determined through negotiations with Department of Fish and Game staff. Trees are likely to be replaced either on an established replacement ratio based on the number of trees removed or the total area of impact. The County will make every effort to incorporate on-site mitigation into the project design to the maximum extent feasible. However some off-site mitigation may be necessary. Implementation of mitigation will occur according to the schedule outlined in the attached Mitigation Monitoring and Reporting Plain in consultation with California Department of Fish and Game and San Francisco Bay Regional Water Quality Control Board. Efforts will be made to retain as many trees in place as possible. All trees to be removed will be flagged to avoid accidental removal of trees. Environmentally Sensitive Area (ESA) fencing will be placed where feasible to protect environmental resources. In order to minimize damage to any additional trees that will not require removal, but may be impacted by construction, contract specifications will include protective measures such as clean trimming of roots and limbs. With protective measures and tree replacement on site, removal of trees will not significantly alter the visual quality of the project area. Rossmoor Detention Basin Expansion Project Page 4 Construction equipment will be visible temporarily during construction of the outfail, excavation of the expanded basin and desilting of the existing basin, however the impact will be minor and short-term, ending upon completion of the project. In addition, most of the construction!,will not be directly visible from the roadway due to the line of trees along the road that will shield the view of the project'from the road. Building the project will not create a permanent source of significant new light or glare. Potentially Significant Potentially Unless Fess than Significant Mitigation Significant Impact Incorporation Impact No Impact 11. AGRICULTURAL RESOURCES. In determining whether impacts to agricultural resources are significant environmental effects, lead agencies may refer to the California Agricultural Land Evaluation and Site Assessment Model (1997) prepared by the California Dept. of Conservation as an optional model to use in assessing impacts on agricultural and farmland. Would the project: a. Convert Prime Farmland, Unique Farmland, or Farmland of Statewide, Importance (Farmland), as shown can the maps prepared pursuant to the Farmland Mapping and Monitoring Program of the California resources Agency, to non- agricultural use? - — X b. Conflict with existing zoning for agricultural use, or a Williamson Act contract? X c. Involve other changes in the existing environment, which, due to their location or nature, could result in conversion of Farmland, to non-agricultural use? _- - -- X SUMMARY: No Impact. The project will not impact any locally or statewide important farmland. According to the Division Of Land Resource Protection, Farmland Mapping and Monitoring Program, Important Farmland Map (2001) the project area is within urban and built-upland. No agricultural preserves are located in the immediate vicinity of the project. Potentially Significant Potentially Unless Less than Significant Mitigation Significant Impact Incorporation Impact No Impact Ill. AIR QUALITY. Where available, the significance criteria established by the applicable air quality management or air pollution control district may be relied upon to make the following determinations. Would the project: a. Conflict with or obstruct implementation of the applicable air duality plan? X b. Violate any air quality standard or contribute to an existing or projected'air quality violation? X 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 X Rossmoor Detention Basin Expansion Project Page 5 Potentially Significant Potentially Unless Less than Significant Mitigation Significant Impact Incorporation Impact --NO IgIL ct precursors)? - -- d. Expose sensitive receptors to substantial pollutant concentrations? X e. Create objectionable odors affecting a substantial number of people? X SUMMARY: Less than Significant. Grading, excavation and other work will necessitate the use of heavy construction equipment. Emissions from construction equipment and objectionable odors may be generated during construction; however, they will be minor and temporary. In order to minimize impacts due to construction activities, contract specifications will stipulate the use of properly tuned and muffled equipment and the elimination of unnecessary idling of equipment when not in use. Implementation of dust control practices including general.watering of exposed areas and/or use of chemical stabilizers will also minimize air quality impacts. The minor temporary deterioration of ambient air quality at the construction site will have no potentially adverse long-term impacts to air quality. Approximately 750 truck loads will be required to remove material over a period of approximately 3 weeps (15 days); therefore, truck trips generated along Rossmoor Parkway are expected to be approximately 50 trips a day over the 15 day period. Based on the relatively small number of truck trips generated and the limited number of days over which the trips will occur, the air quality impact due to the transportation of fill is less than significant. The project will not create any adverse change in air movement, winds, temperature or other climactic conditions. Potentially Significant Potentially Unless Less than Significant Mitigation Significant Impact Incorporations Impact No 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, polices, or regulations, or by the California Department of Fish and Game or U.S. Fish and Wildlife Service? X b. Have a substantial adverse effect on any - - riparian habitat or other sensitive natural communityidentified in local or regional plans, policies, regulations or by the California Department of Fish and Game or US Fish and Wildlife Service? X c. Have a substantial adverse effect on federally - protected wetlands as defined by Section 404 of the Gleans Water Act (including, but not limited to, marsh, vernal pool, coastal, etc.) through direct removal,'filling, hydrological interruption, or other means? X 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? X e. Conflict with any local policies or ordinances X Rossmoor Detention Basin Expansion Project Page 6 Potentially L • Significant Potentially Unless Less than Significant Mitigation Significant Impact Incorporation Impact No impact protecting biological resources, such as tree preservation policy or ordinance? -- f. Conflict with the provisions of an adopted Habitat Conservation Plan, Natural Community Conservation Plan, or other approved local, regional, or state habitat conservation plan? X SUMMARY: Potentially less than significant unless mitigation incorporated. Contra Costa County staff reviewed the site and Essex Environmental, a qualified biological consulting firm, conducted a habitat assessment of the project area. Based on the limited available habitat and the proximity to the surrounding urban area, Essex identified three species that have potential of occurrence in the project area: California red-legged frog (Rana aurora draytonii), Western pond turtle (Clemmys marmorata), and California tiger salamander (Ambystoma califorrliense). The likelihood of occurrence of these three species is low to moderate. Red-legged frog (RLF) is listed as federally threatened by the US Fish and Wildlife Service (USFWS) and considered e species of special concern by the Califomia Department of Fish and Game (DFC) RLF was not observed during the survey, however the California Natural Diversity Database (CNDDB) reports five occurrences of RLF within 5 miles of the project. Tide Creek provides some suitable habitat features for the species, including open space, aquatic habitat with emergentand submerged vegetation, overhanging banks, and relatively deep, still water. However, the immediate surrounding upland areas beyond the Tice Creek corridor provide little to no habitat for the RLF. Based on this habitat assessment, Red-legged frog are not likely to occupy the project area. However, the U.S. Array Corp of Engineers may require formal or informal Section 7 consultation'with the U.S. Fish and Wildlife Service. Any mitigation for loss of RLF habitat due to the basin expansion project will be purchased at an cuff-site RLF certified mitigation bank, prior to construction. California tiger salamander (CTS) is proposed as threatened by the USFWS and as a species of concern by the CDFG. No CTS were observed during Essex field surveys, and the closest occurrence of the species on the CNDDB is 2.5 miles away. Habitat within the project area is marginal for CTS. Marginal breeding habitat (aquatic habitat with relatively deep, open water) is available within the project area however the area lacks the necessary upland habitat (there are no burrows or underground refuges). Thus the CTS is not expected to occur within the project area particularly outside of breeding season. Western pored turtle is listed as a California species of special concern. No Western pond turtle were observed within the project area during Essex field surveys. Suitable aquatic habitat including open water, shallow water and dense emergent and submerged vegetation, exists at the project site for western pond turtle. However, marginal upland habitat exists for the western pond turtle with the project area or in surrounding areas. In addition, no western pond turtle have been observed within 5 miles of the project according to the CNDDB. Thus, the species is not expected to occur within the project area. Anadromous fish do not exist within the project area. As water flows downstream from Tice creek through Walnut Creek, it must travel through approximately 2 miles of continuous concrete channel, a 1500-foot enclosed underground culvert, and several drop structures. These barriers to upstream migration downstream from the project site are such that anadromous fish species cannot reach' the creek at the project site. Measures will be taken in order to ensure that no impact to any sensitive species occurs a result of this project. The measures include: 1) a qualified biologist will survey the project site and adjacent areas within 75 meters (246 feet) upstream and downstream prior to the start of construction, 2) if Rossmoor Detention Basin Expansion Project Page 7 any sensitive species is present, the County will notify the appropriate resources agency or agencies and obtain any required permits prior to initiating construction, 3) sediment erosion control will be placed to prevent soil from entering the creek during construction, and 4) heavy equipment working near the water will be properly maintained such that oils and other fluids do not leak and enter the creek. Construction activities associated with the project will impact the minimum amount of riparian vegetation feasible. However, tree removal will be necessary in order to excavate and enlarge the basin. Approximately 70 trees greater than 4 inches diameter breast height (DBH) will be removed from the project area, approximately 25 of which are native species. Tree removal is planned to occur outside of the nesting season in order to minimize impacts to nesting birds. If trees need to be downed during the nesting season, a qualified biologist will conduct raptor nest surveys prior to tree removal to ensure that raptor impacts are avoided. Any trees occupied by nesting birds will not be removed until all young have fledged. All trees to be removed are within Department of Fish and Game jurisdiction. Mitigation will be implemented as part of the expansion project in order to minimize the impact of the loss of trees. Mitigation requirements and long-term success criteria will be determined through negotiationswith Department of Fish and Game staff. Trees are likely to be replaced either on a replacement ratio based on the number of trees removed or by the total area of impact. Implementation of these mitigation measures will occur according to the schedule outlined in the attached Mitigation Monitoring and Reporting Plan in consultation with California Department of Fish and Game and San Francisco Bay Regional Water Quality Control Board. The County will make every effort to incorporate on-site mitigation into the project design to the maximum extent feasible. However some off-site mitigation may be necessary. Efforts will be made to retain as many trees in place as possible. All trees to be removed will be flagged to avoid accidental removal of trees. Environmentally Sensitive Area (ESA) fencing will be placed where feasible to protect environmental resources. In order to minimize damage to any additional trees that may be impacted by construction, contract specifications will include protective measures such as clean trimming of roots and limbs. Areas exposed as a result of the project, will be seeded with a mix including native grasses and wildflowers. Wetlands Essex Environmental delineated wetlands using the technical standards developed by the USACE Wetlands Delineation Manual (Army Corps of Engineers, Environmental Laboratory, Technical Report Y-87-1, U.S. Army Engineer Waterways Experiment Station, Vicksburg, Miss., 1987 ["Delineation Manual"]). Approximately 0.91 acres of wet meadow wetlands and 9.18 acres of open water were found on-site. The desilt operations will temporarily impact the wetlands. These wetlands are within US Army Corps of Engineer's jurisdiction, thus mitigation for the temporal loss of wetland habitat will be required. County staff will apply for coverage under Corps` Nationwide permit program under Section 404 of the Clean Water Act. County staff will coordinate with Corps staff in order to determine appropriate mitigation measures for the temporal loss of wetland habitat. Efforts will be made to design the project such that on-site mitigation will be feasible, however some off'-site mitigation may be necessary. Implementation of these mitigation measures will occur according to the schedule outlined in the attached Mitigation Monitoring and Reporting Flan in coordination with the Army Corps of Engineers and San Francisco Bay Regional Water Quality;Control Board. Orange construction fencing will be installed to delineate the limits of construction impact for all operations including the outfall reconstruct, excavation of the expanded basin, and desilting of the existing basin. The fencing will serve to isolate environmentally sensitive areas (ESAs) from construction activities. The ESA fencing will be installed at the expected limits of construction impact Rossmoor Detention Basin Expansion Project 'age 8 as delineated on the construction plaits. In addition, sediment and erosion measures will be installed to reduce the potential for sediment to reacts the creek. Activities associated with construction of the expanded basin will occur within California Department of Fish and Game, U.S. Army Corps of Engineers and the San Francisco Regional Water Quality Control Board jurisdiction. The County will apply for a 1601 Streambed Alteration Agreement with the Fish and Game. Since the project is within Corps jurisdiction, the County will apply for appropriate Nationwide permits under Section 404 of the Clean Water Act and acquire Water Quality Certification from the Regional Water Quality Control Board. In addition, the Corps may require Section 7 consultation with the US Fish and Wildlife Service for Red Legged Frog. All necessary permits will be obtained prior to implementation of the project and theCounty will comply with all permit conditions negotiated. Potentially Significant Potentially Unless Less than Significant Mitigation Significant Impact incorporation Impact No Impact V. CULTURAL RESOURCES. Would the project: a. Cause a substantial adverse change in the significance of a historical resource as defined in §151364.5? - X b. Cause a substantial adverse change in the significance of an archaeological resource pursuant to;15064.5? X c. Directly or indirectly destroy a unique paleontological resource or site or unique geologic feature? X d. Disturb any human remains, including those interred outside of formal cemeteries? X SUMMARY: Potentially significant unless mitigation incorporated. A records search conducted by the Northwest Information Center (KWIC) at Sonoma State University found one recorded Native American cultural resources site and no historic cultural resources listed with the System that are within % mule of the project area. NWIC noted that there is a high potential for identifying resources in the area due to the location of the Native American resources site. Portions of the archaeology site are within the project area just southeast of the proposed desilt area. Based on the conclusion derived from Sonoma State, a Cultural Resources Investigation for the Rossmoor Basin Expansion area was conducted by David Chavez and Associates. This report confirmed the existence of a Native American cultural resource site within the project area and noted that the site is on the list of California Points of Historical Interest. The site consists of a ]dative American Saklan Village, which was once home to approximately 10 households and consisted of various types of domed, thatched houses and storage structures. Over the past 115 years, the site has been disturbed by the construction of a railroad spur line, a barn, Rossmoor parkway and the Rossmoor Detention Basin. Human remains and other cultural artifacts were recovered during tate excavation of the existing Rossmoor basin. Based on the research and site assessment conducted by David Chavez and Associates, the exact extent of the cultural resources sites is unknown and there is potential for undisturbed cultural resources to exist within the proposed project area. Furthermore, it is likely that the site is eligible for inclusion in the California Register of Historic Resources. In order to reduce the potential for cultural resources impacts to less than significant, a comprehensive mitigation strategy has been established. Before construction begins, a qualified archaeologist will conduct a subsurface testing program within the basin expansion area to determine whether cultural resources occur within the soil disturbance area and the approximate extent of the site. If cultural deposits are discovered, a professional level archaeological excavation will be performed in order to collect data for scientific study. A qualified archaeologist will conduct training Rossmoor Detention Basin Expansion Project Page 9 for the construction contractor, crew and County personnel. During construction, a qualified archaeologist will monitor all basin excavation activities. if remains are uncovered during construction, work will be temporarily stopped while the archaeologist makes an evaluation. if human remains are discovered at any time during the pre-construction evaluation or during construction, the County Coroner and any local tribal representative will be contacted. The Native American Heritage Commission (NAHC) has been contacted !regarding the proposed project. Follow up letters to Native American tribal representatives have been sent and follow-up phone calls will also be made. The County will consult with the NAHC prig to subsurface testing. The NAHC will be given the opportunity to negotiate the fate of any materials found on-site. The County will have a tribal representative on-site during the subsurface testing program, any archaeology investigation and construction of the expanded detention basin in addition to the qualified archaeologist. Potentially Significant Potentially Unless Less than Significant Mitigation Significant Impact Incorporation Impact No 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: 1. Rupture of a known earthquake fault, as delineated on the most recent Alquist-Paolo Earthquake Fault Zoning Map issued by the State Geologist for the area or based on other substantial evidence of a known fault? Refer to Division of Mines and Geology Special Publication 42. X 2. Strong seismic ground shaking? X 3. Seismic-related ground failure, including liquefaction? X 4. Landslides? X b. Result in substantial soil erosion or the loss of - topsoil? X c. 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? X d. Be located on expansive soil, as defined in `Cable 18-1-B of the Uniform Building Code (1994), creating substantial risks to life or property? X — - e. Have soils incapable of adequately supporting the use of septic tanks or alternative waste disposal systems where sewers are not available for the disposal of wastewater? X SUMMARY: Less Than Significant Impact. The terrain surrounding the project site consists of gently and moderately sloping hills. According to the Soil Survey of Contra Costa County (Soil Conservation Service, 1977), the soils found in the area include Zamora silty clay loam (0-2% slope). These soils tend to have relatively low potential for erosion and are mostly used for home sites and less often used for various other uses like tree orchards, row crops, pasture and dryland pasture. The soils immediately adjacent to the proposed project area consist of Cut and Fill land-Millsholm complex (30-50% slopes). These areas are highly disturbed urban areas in which the slopes were Rossmoor Detention Basin Expansion Project Page 10 cut or filled for a road to the south and home sites to the north. The erosion hazard of these soils is high to very high. There are some minor faults located in the vicinity of the project area, however there are no faults located in the immediate vicinity of the project area. Based on the USGS Major Faults of Contra Costa County Map, there is a certain/concealed fault located approximately one mile to the west and a concealed fault located approximately 3l of a mile to the east. Activities associated with the project, including grading, will not result in an increase of exposure to geologic hazards, nor will they result in unstable earth conditions or changes to the geologic substructure. All sail excavation, detention basin construction and the new outfall will be designed and constructed to, account for site-specific soils conditions and potential geologic hazards. Grading and excavation associated with the project will result in some changes in topography within the immediate vicinity of the detention basin and a temporarily increase the exposure of soils to stream erosion. To address the exposure of bare soils to stream flows, contract specifications will require the installation of erosion control measures (seeding, soil stabilization, and revegetation) to prevent soil from leaving the project area or impacting the adjacent creek. These measures will be incorporated into the construction design and contract specifications. Because the disturbed area will exceed one acre, the County will obtain a General Stormwater Construction Permit from the State Water Resources Control Board. The Contractor shall prepare and implement, after County approval, a Storm Water Pollution Prevention Plan (SWPPP). Grading of the project area is not expected to result in unstable earth conditions or change geographical substructures. Exposure of people or property to geologic hazards is not expected to increase as a result of the project. All areas left exposed due to construction will be seeded with a mix including native grasses and wildflowers upon completion of the project in order to stabilize exposed soil. Potentially Significant Potentially Unless Less than Significant Mitigation Significant Impact Incorporation Impact No Impact Vii. 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? X 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? X c. Emit hazardous emissions or handle hazardous or acutely hazardous materials, substances, or waste within one-quarter mile of an existing or proposed school? X d. Be located on a site that is included on a list of hazardous materials sites compiled pursuant to Government Code Section 65862.5 and, as a result, would it create a significant hazard to the public or the environment? _ X 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 X Rossmoor Detention Basin Expansion Project Page 11 Potentially Significant Potentially Unless Less than Significant Mitigation Significant Impact Incorporation Impact No Impact 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? X g. Impair implementation of or physically interferes with an adopted emergency response plan or emergency evacuation plan? X h. Expose people or structures to a significant risk of loss, injury or death involving wildiand fires, including where wildlands are adjacent to urbanized areas or where residences are intermixed with wildlands? X SUMMARY: Less Than Significant Impact. The potential for a release of hazardous substances (e.g., accidental petroleum spills) exists at the project site during construction. Contract specifications will require that standard safety practices and standard best management practices be followed during construction to ensure no accidental release of hazardous substances and no increase in the potential for exposure to these substances. The SWPPP will also include a sampling and analysis plan for non-visual pollutants. Contract specifications will require the contractor to contact Underground Service Alert (USA) prior to conducting any work that could potentially impact utilities. The project site is located more than one- quarter mile from the nearest school and is not within two miles of any public airport or any private airstrip. No interference with an emergency evacuation or response is expected to result from the project. The majority of the work will occur within the project area. Traffic control measures will be implemented as necessary around the work area in order to minimize the potential for accidents. Standard specifications for the project will require installation of sufficient warning signs regarding the construction and associated work hours. Potentially Significant Potentially Unless Less than Significant Mitigation Significant Impact Incorporation Impact No Impact Vill. HYDROLOGY AND WATER. QUALITY. Would the project: a. Violate any water quality standards or waste discharge requirements? X 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)? X 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 X Rossmor Detention Basin Expansion Project Page 12 Potentially Significant Potentially Unless Less than Significant Mitigation Significant Impact incorporation impact No Em act . mariner, 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 ort- or cuff-site? X e. Create or contribute runoff water which would exceed the capacity of existing or planned storm water drainage systems or provide substantial additional sources of polluted runoff? X f. Otherwise substantially degrade water quality"? X g. 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? - X h. Place within a 900-year flood hazard area structures, which would impede or redirect flood flows? X L Expose people or structures to a significant risk of loss, injury or deathinvolving flooding, including flooding as a result of the failure of a levee or dam? X - j. Inundation by seiche, tsunami, or mudflow? -- - - X SUMMARY: Less than significant impact. During project-related construction, the potential exists for spills of gasoline, oil or other pollutants that may have a significant impact on water quality. Standard safety practices and best management practices will be followed in order td reduce the possibility of spills and minimize the potential for water quality impacts to a level that is less than significant. The expansion of the detention basin will realign a portion of the low flow channel and abandon approximately 100 feet of the existing low flow channel. However the new low-flow channel will',at a minimum be the same length as the existing channel. In addition, the riparian area within the basin will actually increase as a result of the expansion of the basin. During rainfall events when peak flows are high, the expanded basin will detain water for a limited amount of time in order to minimize flooding downstream, however this will not Significantly affect the existing drainage pattern. Construction activities at the project site may temporarily increase the potential for erosion of newly exposed soils. Runoff and discharges from construction areas could potentially be transported into nearby storm drains. These potential temporary impacts will be addressed through the implementation of best management practices and erosion control measures required by contract specifications. In order to comply with the State Water Resources Control Board National Pollutant Discharge Elimination System (NPDES) General Construction Permit requirements, -a Stormwater Pollution Prevention Plan (SWPPP) will be prepared and implemented for the project site to ensure erosion and sediment control is adequately addressed. According to the FEMA Flood insurance Rate Map the project is located within Zone X, an area that is determined to be outside the 1% (100 yr) and 0.2% (500 yr) annual chance floodplains. Project Rossmoor Detention Basin Expansion Project Page 13 construction will not affect this designation and will actually reduce the flooding potential in the lower areas of the watershed. Potentially Significant Potentially Unless Less than Significant Mitigation Significant Impact incorporation Impact No Impact IX. LAND USE AND PLANNING. Would the project: a. Physically divide an established community? X 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? X c. Conflict with any applicable habitat conservation plan or natural community conservation plan? X SUMMARY: Less Than Significant Impact. The County General Plan defines the project as located within a land use area including Multi family residential-low and public/semi-public. Land uses surrounding the project site include open space, a residential neighborhood, and a church located on land designated as parks and recreation, These land use characteristics will not change as a result of the proposed detention basin expansion. The detention basin expansion will allow the Flood Control District to more adequately project residents downstream of the basin from flooding. The project is not intended to increase capacity of the detention basin in anticipation of any future development. Rather expansion of the basin will add additional protect existing residents from potential flooding. Therefore, land use will not be impacted by the project. Property will be purchased in order to remove the abandoned building and parking lot and excavate for the expansion. Purchase of right of way will occur immediately adjacent to the existing detention basin and will not lead to a modification in the land use in the area surrounding the project. Additional real property transactions may be needed in support of this overall'project. Potentially Significant Potentially Unless Less than Significant Mitigation Significant Impact Incorporation Impact No Impact X. 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? X b. Result in the loss of availability of a locally important mineral resource recovery site delineated on a locals general plan, specific pian or other land use plan? _ X SUMMARY: No impact. During construction, the project will use concrete, wood products, and other material's derived from natural resources; however, the project will not significantly impact these resources. The use of oil and gasoline to operate the machinery for construction purposes is negligible and of a short-term, temporary nature. In order to minimize impacts due to construction Rossmoor Detention Basin Expansion Project Page 14 ¢/ activities, contract specifications will stipulate the elimination of unnecessary idling of equipment when not in use. Potentially Significant Potentially Unless Lass than Significant Mitigation Significant Impact Incorporation impact No impact XI. NODE. 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? -- X b. Exposure of persons to or generation of excessive ground borne vibration or ground borne noise levels? _ X_ _ c. A substantial permanent increase in ambient noise lever in the project vicinity above levels existing without the project? X d. A substantial temporary or periodic increase in ambient noise levels in the project vicinity above levels existing without the project? X e. For a project located within an airport lurid 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? X 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? X SUMMARY: Less than significant. The dominant source of noise in the project area is the vehicles currently using Rossmoor Parkway adjacent to Rossmoor detention basin. The existing road is the main access to the homes beyond the project area. Construction of the project will not increase the capacity of the road, therefore the ambient noise levels associated with routine use of the roadwill remain the same. Construction of the project will increase the noise level temporarily; however, there are no sensitive receptors in the vicinity of the project. In general, construction activities produce noise levels of 86 dBA at 50 feet, which is well below the threshold of pain of 120-140 dBA. Contract specifications will require the use of properly tuned and muffled equipment to minimize Cather noise die to construction. Working hours will be limited to 7:30 a.m. to 7:00 p.m. Monday through Friday, unless modified upon written approval by the resident engineer, to reduce construction noise levels. These working hours will be incorporated as part of the construction contract. Potentially Significant Potentially Unless Less than Significant Mitigation Significant Impact Incorporation Impact No Impact X11. POPULATION AND HOUSING. Would the project: a. Induce substantial population growth in an area, either directly (for example, by proposing new X Rossmoor Detention Basin Expansion Project Page 15 Potentially, Significant' Potentially Unless Less than Significant Mitigation Significant Impact Incorporation impact No Impact 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? _ X c. Displace substantial numbers of people, necessitating the construction of replacement housing elsewhere? X SUMMARY: No Impact. The proposed project is located along an existing flood control facility. Installation of the project will not induce population growth. The project will not result in the displacement of any homes or residents. The project will not result in a change in the location, distribution, density or growth rate of human papulation in the area. The project will not affect existing housing, or create a demand for additional houses. The project will not require the removal of any homes or the displacement of any people. Potentially Significant Potentially Unless Less than Significant Mitigation Significant Impact incorporation impact No Impact All. PUBLIC SERVICES a. Would the project result in substantial adverse physical impacts associated with the prevision 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 public services: 1. Fire Protection? X 2. Police Protection? X 3. Schools? 4. Parks? - - _ X 5. Other Public facilities? X SUMMARY: Less than significant. The project consists of expanding the capacity of an existing public facility, a Contra Costa County Flood Control detention basin. although the project will physically alter an existing government facility, the project will actually enhance the performance of the facility. Once constructed, the project will not increase the need for fire or police protection, schools, parks or other governmental services. In addition, it will not increase the need for public services. During construction, access will be maintained to all nearby homes at all times. The majority of the work will be within the detention basin itself; therefore, heavy equipment will not black the adjacent roadway. Residents and emergency service vehicles will be able to drive around the construction areas at all times. Construction-related traffic would have a negligible impact on traffic flows associated with the adjacent road. Potentially Significant Potentially Unless Less than Significant Mitigation Significant Impact Incorporation impact No Impact Eossmoor Detention Basin Expansion Project Page 16 Potentially " Significant Potentially Unless Less than Significant Mitigation Significant Impact Incorporation Impact No Impact Xllll. 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? _ X 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? _ X SUMMARY: Less than significant. Field reviews did not identify any recreational opportunities in the immediate project area. Surrounding land uses in the immediate vicinity of,the project consist of, a residential neighborhood, a church, and undeveloped land. Potentially Significant Potentially Unless Less than Significant Mitigation Significant Impact Incorporation Impact No impact XV. TRANSPORTATION/TRAFFIC. Would the project: a. Cause an increase in traffic, which is substantial in relation to the existing traffic load and capacity of the street system (i.e., result in a substantial increase in either the number of vehicle trips, the volume to capacity ratio on roads, or congestion at intersections)? X b. Exceed, either individually or cumulatively, a level of service standard established by the county congestion management agency for designated roads or highways? X 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? X d. Substantially increase hazards due to a design - - feature (e.g., sharp curves or dangerous inter- sections) or incompatible uses (e.g., farm equipment)? X e. Result in inadequate emergency access? X f. Result in inadequate parking capacity? X g. Conflict with adopted policies, plans, or programs supporting alternative transportation (e.g., bus turnouts, bicycle racks)? X SUMMARY; less than significant. Approximately 32,000 cubic yards of material will be generated by excavation of the basin, about 750 truck loads will be required to remove this material. The material will be exported over a period of approximately 3 weeks (15 days), therefore, truck trips generated along Rossmoor Parkway are expected to be approximately 50 trips a day over the 15'day Rossmoor Detention Basin Expansion Project Page 17 period. Based on the relatively small number of truck trips generated and the limited number of days over which the trips will occur, the impact due to the transportation of fill is less than significant. Traffic may need to be temporarily stopped in order to allow dump trucks and other deliveries to enter and exit the work site, however impacts to traffic will be temporary and miner. The project will not alter waterborne, rail or air traffic as no water or air transportation facilities are located in the immediate vicinity of the project area, and the project will not impact the railroad. Potentially Significant Potentially Unless fess than Significant Mitigation Significant Impact Incorporation impact No impact XVI, UTILITIES AND SERVICE SYSTEMS. Would the,project a. Exceed wastewater treatment requirements of the applicable Regional Water Quality Control Board? X b. Require or result in the construction of new water or wastewater treatment facilities or expansion of existing facilities, the construction or which could cause significant environmental effects? X c. Require or result in the construction of new storm water drainage facilities or expansion of existing facilities, the construction of which could cause significant environmental effects? X d. Have sufficient water supplies available to serve the project from existing entitlement and resources, or are new or expanded entitlement needed? X 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? _ X f. Be served by a landfill with sufficient permitted capacity to accommodate the project's solid waste disposal needs? X g. Comply with federal, state and local statutes and regulations related to solid waste? X SUMMARY: Less than significant impact. The project will not result in a wasteful or inefficient use of energy for construction. Unnecessary idling of construction equipment when not in use will be avoided and equipment will be properly tuned. The expansion of the Rossmoor detention basin would not be expected to exceed any wastewater treatment requirements and would not require construction of any new water'treatment or wastewater treatment facilities or the expansion of any existing water treatment or wastewater'treatment facilities. No new or expanded water supply would be needed to serve the project, and the expansion of detention basin as proposed would not exceed the capacity of the existing wastewater treatment facilities which serve development in the area. Curing construction and operation of the expanded detention basin, more solid waste would be generated than is currently generated at the project site. However, disposal of project-related solid Rossmoor Retention Basin Expansion Project Page 18 waste would be accomplished in compliance with federal, state and local statutes and regulations, and would not be expected to exceed the permitted capacity of the landfill serving the local area. Potentially Significant. Potentially Unless Less than Significant Mitigation Significant Impact Incorporation Impact No Impact XVII. MANDATORY FINDINGS OF SIGNIFICANCE a. Dees the project have the potential to degrade the quality of the environment, substantially reduce the habitat of a 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? _ X 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)? X c. Goes the project have environmental effects, which will cause substantial adverse effects on human beings, either directly or indirectly? -- X SUMMARY: The project does have the potential to temporarily degrade the environment during the construction phase. This potential will be reduced considerably by the implementation of Best Management Practices during the course of construction. A representative of Contra Costa County will be onsite to ensure compliance with all environmental conditions imposed by either the regulatory agencies or County policies. Potential aesthetic impacts, primarily through the potential loss of trees, have been Addressed through avoidance and minimization of impacts to tree root systems. Potential biological impacts are limited and will be mitigated as required by associated resource agencies. The project may have geologic (sediment production) and hydrologic impacts, however these will be minimized through the application of Best Management Practices and the implementation of various erosion control measures (as discussed in Section VI (Geology and Soils) and Section VIII Hydrology and Water Quality. GAGrpDataiEngSvc\ENVIR012003 ProjectslRossmoor Basin%Rossmoor Neg Dec.doc 3118/03 Rossmoor Detention Basin Expansion Project Page 19 w � vy ca r °r u �r SZ.IM ,w t 8 ~� u ' �-�-� m p CL. 1 Vf d t k u 91 4 ��k 7 t fNf4 E kit x i" a• _ f s 6 M a �a 3 " �N Cy u s a" a`vs s� #' t ( t a' iQ N cL �.> �#`-Y$ B F„' y 't r F- a t3 CD m Y f }b45, Er t �"� t 3i ,a t �'i "# °' s'.;`• zC t9' F V� V � 4. t h E � �' � s��. 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CALIFORNIA ENVIRONMENTAL QUALITY ACT NOTICE OF DETERMINATION CONTRA COSTA COUNTY COMMUNITY DEVELOPMENT DEPARTMENT 651 PINE STREET 4TH FLOOR NORTH WING MARTINEZ,CALIFORNIA,94553-0095 Telephone: (925)313-2296 Contact Person: Cece Sellgren, Environmental Planner Project Description, Common Name(if any)and Location: DA 67 Rossmoor Detention Basin Expansion Project.County File#CP 03-45,Project Description-, Contra Costa County Flood Control District (District)proposes to expand the capacity of Rossmoor detention basin from 35 to 55 acre-feet. The project consists of four components: 1)Excavation and Expansion: Approximately 30,000 cubic years of soil will be excavated(1.5 acres, 12 feet deep)(see Figs. 142). A vacant portable office building, parking lot and landscaping including approximately 70 trees(4 inches diameter breast height(DBH)or greater)will also be removed. An additional low flow channel will be constructed through the middle of the expanded basin. A portion of the existing creek channel(approximately 100 feet)will be abandoned,however the project will increase the amount of stream and riparian area in the basin. The District will acquire the property from the current owner prior to construction. 2)ga_sjnDesiIt. Desilting of the existing basin(approx.2,000cubic yards)will occur during the dry season so that creek flows are minimal. The low flow channel may need to be dewatered in order to complete desilting operations. The sediment removed from the channel will be disposed at an off-site, upland location. 3)Outfall Reconstruction: The existing outfall structure will be modified for improved basin performance. The new outfall will be constructed in the same location at the existing outfall;no additional hard material will be installed. Construction of the outfall will occur during the dry season;however flows will be diverted around the construction area. 4)Long-term Maintenance: The basin will be desilted approximately every five years,or as necessary to maintain the flood capacity of the basin. Dewatering may be necessary in order to complete desilting operations. Vegetation within the basin will be maintained on an annual basis as part of the County's Vegetation Management Program. Appropriate environmental permits will be acquired as necessary. Several BMPs will be implemented during construction and long-term maintenance to minimize impacts to habitat in the project area. A qualified biologist will conduct pre-construction surveys for sensitive species. ESA fencing will be installed around all sensitive areas. Sediment and erosion control measures will be placed to avoid and minimize soil entering the creek. All equipment will be fueled and maintained at a designated staging area. No heavy equipment will be operated in flowing water. Upon completion of the project, all disturbed areas will be seeded with a mix including native grasses. Project Location: The project area is located %mile south of the Rossmoor Pkwy and Tice Valley Blvd intersection along Rossmoor Pkwy. The existing detention basin is located on Tice Creek, a tributary to Walnut Creek. (Fig. I and 2) The project was approved on Pursuant to the provisions of the California Environmental Quality Act. An Environmental Impact Report was prepared and certified(SCH# The Project was encompassed by an Environmental Impact Report previously prepared for_(SCH# A Mitigated Negative Declaration was prepared following identification of a potentially significant impact Copies of the record of project approval and the Negative Declaration or the final EIR may be examined at the office of the Contra Costa County Public Works Department. The Project will not have a significant environmental effect with incorporated mitigation measures The Project will have a significant environmental affect. Mitigation measures were made a condition of approval of the project. A statement of overriding considerations was adopted. Findings were adopted pursuant to Section 15091 of the State CEQA Guidelines. Date: By: Community Development Department Representative 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 Applicant: Filing Fees:$50,00 Public Works Departrnent EIR-$850 Total Due: $ 255 Glacier Drive,Martinez,CA 94553 X_ Neg.Dec.-$1,250 Total Paid Attn:Cece Sellgren DeMinimis Findings-$0 Contra Costa County Maurice M. shlu ex officio Chief Engineer -FLOOD CONTROL 255 Glacier Drive, Martinez, CA 94553-4825 & Water Conservation District Telephone: (925) 313-2000 FAX {925) 313-2333 . December 1, 2003 Janice Stern Senior Planner City of Walnut Creek P.O. Box 8039 Walnut Creek, CA 94896 Our File:. DA 67 Rossmoor Detention Basin Expansion Project Number: 7539-6D8484 Dear Ms. Stern: The Contra Costa County Flood Control and Water Conservation District (District) has received your comments regarding the Rossmoor Detention Basin Expansion Project, Following are responses to your comments (the numbering below corresponds to the numbering indicated in the margins of your attached comment letter): 1. Comment noted - the tree removals necessary to implement the project are subject to the City's Tree Preservation Ordinance. The District will submit an application for a Tree Removal Permit for the project from the City of Walnut Creek as soon as possible. 2. Comment noted 3. Comment noted 4. Comment noted. Thank you for confirming that the Rossmoor Basin Expansion Project is consistent with the City of Walnut Creek General Plan. You may contact me at (925) 313-2366 or Ichavez@pw.co.contra-costa.ca.us or Kevin Emigh, Flood Control District Senior Engineer, at (925) 313-2233 or kemigh@pw.co.contra-costa.ca,us if you have questions regarding the project. Thank you. Sincerely, Le Chavez Planner 111 Engineering Services LC:sr GAGrpData\EngSvb\ENVlR0\2003 Projects\ Rossmoor BasinlResponseComrnentsCityotWalnutCreek.doe cc. K. Emigh,Flood Control J. Pulliam, Design C.Sellgren,Engineering Services E.W han, Engineering Services OCT 2 9 2003 f MENTAL c r y o F WALNUT E t K October 22, 2003 Trina Torres, Environmental Assistant Engineering Services Contra Costa County Flood Control 255 Glacier Drive Martinez, CA 94553-4825 Dear Ms. T orres: Re: Rossmoor BasinlDA67 Expansion Project (Prof. No.: 7539-6D8484) Thank you for your letter of October 9, 2003, addressed to Sandy Meyer,planning Manager, which was passed to me for response. You requested review of the CEQA documentation for this project (Negative Declaration) and confirmation of conformance with the City of Walnut Creek's General Plan. Regarding the proposed Negative Declaration and Initial Study, Section I.Aesthetics, and Section IV Biological Resources should be amended to note that any proposed tree removals will require the approval of a Tree Removal Permit from the City of Walnut Creek, and that such removals are subject to the City's Tree Preservation Ordinance. In addition, Section IX of the Initial Study(Land Use) should be corrected to read"City's General Plan" rather than "County General Plan", and in the second paragraph "project" should be changed to "protect". Regarding the matter of General Plan conformity, it is a policy of the City's General Plan to minimize the risk of property damage and personal injury due to flooding (Chapter 6, Public Safety, Policy 3), and to work with the County Flood Control District to provide mitigation for flooding problems (Program 3.2). The expansion of the capacity of the Rossmoor detention basin would be consistent with that policy. Thank you for the opportunity to review this project. If you have any questions or comments, please contact me at (925) 943-5899 x. 213, or stem(c walnut-creek.org Cordially an ce Stern or..Planner c. Steve Waymire CIP Engineering Past Office Box 8039, 1666 North N-lain Street,Walnut Creek,CA 94596 tel 925.943.5800 www.ci.walnut-creek.ca.us printed on recycled paper Contra Costa County Maurice M. shiu j # ex officio Chief Engineer ' I 11-400D CONTROL 255 glacier Drive, Martinez, CA 94553-4825 9 a + & Water Conservation ]district Telephone: (925) 333-2000 FAX (925) 313-2333 December 1, 2003 Dan Schrantz, Director Trust Operations Golders Rain Foundation 800 Rockview Drive Walnut Creek, CA 94595 Our File: Rossmoor Detention Basin Expansion Project Project Number: 7539-6D8484 Dear Mr. Schrantz: The Contra Costa County Flood Control and Water Conservation District has received your comments regarding the Rossmoor Detention Basin Expansion Project. Following are responses to your comments (the numbering below corresponds to the numbering on your comment letter): 1. Comment noted. Although tree stumps may be left in place temporarily following tree removal, they will be removed during the excavation activities at the basin. The trees will be cut as low to the ground as feasible to minimize unsightliness until basin excavation activities are initiated. 2. Comment noted. Project design will pay close attention to the protection of all excavated slopes. Slopes will be designed at the appropriate slope to ensure slope stability based on the soil characteristics in the area. In addition, following construction, exposed slopes will be stabilized with one or more of the following methods as appropriate: hydroseeding, erosion control blanketing, and/or turf- reinforcement matting. 3. It is our expectation that most (if not all) of the existing buffer landscaping will be unaffected by the construction operations. Any proposed modifications to the existing buffer landscaping will be discussed with Golden Rain Foundation (GRF) during the design phase of the project, and as requested, GRF will have the opportunity to review and comment on the final landscaping design. 4. Comment noted. Initiating work with heavy equipment at 8:00 a.m. is acceptable to the District. Contract specifications will note this heavy equipment start time. 5. Although it will be difficult to regulate the Contractor's exact break times, the project specifications will include language that encourages the Contractor to limit operations during these high traffic times. In addition, contract specifications will make it clear that pedestrians must be allowed to continue to utilize the sidewalk along the basin in a safe and unobstructed fashion. Dan Schrantz, Director "frust Operations Golden Rain Foundation December 1, 2003 Page 2 Your input on the project is appreciated, and the District recognizes that the Golden Rain Foundation will be involved in the review of project plans and specifications at review milestones. You may contact me at (925) 313-2355 or lchavez a pw.co.contra- costa.ca.us or Kevin Emigh, Flood Control District Senior Engineer, at kemigh@pw.co.contra-costa.ca.us if you have questions regarding the project. Thank you. Sincerely, A I JLChavez Planner 111 Engineering Services LC:sr GAGrpData\EngSvc\EnvirM2003 Projects\ Rossmoor Basin\ResponsetoCommentsRossmoor.doc cc. K.Emigh,Flood Control J.Pulliam,Design C.Sellgren,Engineering Services E.whan,Engineering Services FR eIVED�. SSM �. V 1 3 200WV E,WALNUT CREEK �3, .�... Lµ, November 12, 2003 Ms. Cece Sei'igren, Environmental Planner Centra Costa County Public Warks Department 255 Glacier Drive Martinez, CA 94553 Subject; Rossmoor Detention Basin Expansion Project Review Comments Dear Ms. Seligren. We have reviewed the documents comprising the proposed mitigated negative declaration for the subject project and are in general agreement with the proposal. We understand the basin will expand from 35 acre-feet to 55 acre-fleet involving the removal of approximately 30,000 cubic yards of material, removal of approximately 2,000 cubic yards of silt from the existing basin, reconstruction of the outfall structure, and long-term maintenance of the expanded basin. Our review comments are as follows: 1. Page 1, regarding the removal of 70 trees, no stumps should be left or visible at completion. 2. Wage 1, regarding protection of excavated slopes, pay special attention to protecting the base of the Rite Aid access road slope, west end, at its intersection with Rossmoor Parkway and where it curves to be more perpendicular to the direction of flow. 3. Page 4, Aesthetics, regarding mitigation of removed trees and replacement trees, refer to R. Mitch Avalon's letter of May 8, 2003 (attached), Items`3 & 4, where buffer landscaping, irrigation and short-term maintenance are discussed. If an 8 to 10 foot buffer strip from back of sidewalk is provided, it appears most of the existing trees fall outside this zone, meaning new trees and turf will have to be planted as part of the buffer landscaping design. We wish to have a chance to review and comment on this landscaping design at the appropriate time. 4. Fuge 15, Noise, regarding the working hours starting at 7:30 AM, this is about a half hour early in such close proximity to our retirement neighborhoods for the use of heavy earth--moving equipment and trucks. Starting work at 7:30 AM would be'acceptabI6 if the heavy equipment did not actually start operating until 8:00 AM. Trust Operations Division—Golden Rain Foundation 800 Rockview[give • walnut Creek, CA 94595 • (925) 988-7600 * Fax (925) 988-7679 r 5. Page 18, Transportation/Traffic, regarding the stopping of traffic on Rossmoor Parkway for construction vehicles, there are two very busy times of traffic flaw into Rossmoor, from 7:45 AM to 8:15 AM and from 12:45 PM to 1:00 PM during which the stopping of traffic should be avoided if possible. Perhaps the contractor could be directed to schedule breaks or other activities to accommodate these peak traffic flows. Also, if pedestrians will be allowed to continue to use the sidewalk on the basin side as their route to and from shopping, then security fencing, constant cleanup, and construction traffic control should be thoroughly addressed in the construction contract provisions. Thank you for your consideration of these matters. Sincerely, Dan Schrantz, Director Trust Operations Cc: Ralph Van Orsdel, Mutual 65 Keri Clark, Mutual 58 � R STATE OF CALIFORNIA h , O Governor's Office of Planning and Research 1 -4 1R6A l� State Clearinghouse and Planning Unit }R' 09rat.,f�"� Arnold .Ian Boel Schwarzenegger Interim Deputy Governor Director November 25,2003 [EN71VIRONMENTAL m v E D 1 2003 Cece Sellgren Contra Costa County Flood Control District 255 Glacier Dr. Martinez, CA 94553-0095 Subject: Rossmoor Detention Basin Expansion Project SCH#: 2003102116 Dear Cece Sellgren: The State Clearinghouse submitted the above named Negative Declaration to selected state agencies for review. The review period closed on November 24,2403, and no state agencies submitted comments by that date. This letter acknowledges that you have complied with the State Clearinghouse review requirements for draft environmental documents,pursuant to the California Environmental Quality Act. Please call the State Clearinghouse at(916)445-0613 if you have any questions regarding the environmental review process. If you have a question about the above-named project,please refer to the ten-digit State Clearinghouse number when contacting this office. Sincerely, r `7,1 errRoberts Director, State Clearinghouse 1400 TENTH STREET P.O.BOX 3044 SACRAMENTO,CALIFORNIA 95812-3044 (916)445-0613 FAX(916)323-3018 www.opr.ca.gov ................................................................. .. ..........................................................