Loading...
HomeMy WebLinkAboutMINUTES - 02271990 - S.2 TO: BOARD OF SUPERVISORS Contra FROM: Supervisor Tom Torlakson Costa DATE, February 27, 1990 County SUBJECT: REPORT ON ALDICARB FROM THE STATE WATER RESOURCES CONTROL BOARD SPECIFIC REQUEST(S) OR RECOMMENDATION(S) & BACKGROUND AND JUSTIFICATION RECOMMENDED ACTION: (1) Refer the report on aldicarb from the State Water Resources Control Board to the Water Committee, the Health Department and the Agricultural Commissioner. Notify the Contra Costa Water District, the City of Brentwood, the Discovery Bay Property Owners Association, Sanitation District No. 19 Citizens Advisory Committee, agricultural groups and environmental groups of the date this matter is agendaed for the Water Committe. (2) Assess the state process for handling this report and determine if the state is likely to ban aldicarb. (3) If such a ban is not believed to be likely, then determine if the county can or should move ahead independently with a ban. An assessment of any county plan of action should include some well tests in areas like Brentwood, Byron and Discovery Bay. BACKGROUND: The Subcommittee of the Pesticide Registration and Evaluation Committee has submitted its findings on aldicarb, an insecticide/nematicide used largely on cotton in California. The subcommittee has concluded that agricultural use of aldicarb would carry a risk of ground water contamination. CONTINUED ON ATTACHMENT:- YES SIGNATURE: RECOMMENDATION OF COUNTY ADMINISTRATOR RECOMMENDATION OF BOARD COMMITTEE APPROVE OTHER SIGNATURE(S) ACTION OF BOARD ON February 27, 1990 APPROVED AS RECOMMENDED X OTHER VOTE OF SUPERVISORS X- UNANIMOUS (ABSENT I HEREBY CERTIFY THAT THIS IS A TRUE AYES: NOES: AND CORRECT COPY OF AN ACTION TAKEN ABSENT., ABSTAIN: AND ENTERED ON THE MINUTES OF THE BOARD OF SUPERVISORS ON THE DATE SHOWN. cc. Water Committee ATTESTED '44--46-t-�-4&,Ag a7- 19252 Health Services Director Phil Batchelor, Jerk of the Board of Agricultural Commissioner Supervisors and County Administrator County Administrator Roberta Goulart, CDD M382/7-83 BY DEPUTY 61 PESTICIDE CONTAMINATION PREVENTION ACT SUBCOMMITTEE REPORT ON FINDINGS AND CONCLUSIONS ON ALDICARB SEPTEMBER 27, 1989 I. Introduction The subcommittee established pursuant to Section 13150 of the Pesticide Contamination Prevention Act (the Act) has completed its deliberations on the pesticide aldicarb. This report contains the findings of the subcommittee as determined by vote of the subcommittee on September 13, 1989. In arriving at its findings, the subcommittee has carefully considered whether it could make any of the findings specified in subdivision (c) of Section 13150 of the Act. This question must be clearly addressed, because the Act provides that if none of the findings of subdivision (c) of Section. 13150 is made, the economic poison shall be canceled (Section 13151) . The subcommittee has determined that none of the findings specified in subdivision (c) of Section 13150 can be made. The findings of the subcommittee follow. II. Findings The subcommittee finds that: a) Aldicarb and its degradation products have polluted, and continue to threaten to pollute, the groundwaters of the State. b) No modified agricultural uses of aldicarb have been identified which would result in a high probability that aldicarb would not pollute the groundwaters of the State. c) Cancellation of aldicarb will not cause severe economic hardship on the State's agricultural industry. d) Aldicarb has failed to meet the conditions of Section 13150(c) of the Pesticide Contamination Prevention Act, as required in Sections 13150 and 13151 for continued registration. III. Discussion A. Determination of "Pollution Level" In making findings pursuant to the Act, the subcommittee must _ determine a level of "pollution" as defined in the Act. The subcommittee has determined, after consultation with the Department of Health Services, .that available data - do not support . establishment of a specific numerical "pollution level" for- aldicarb which would satisfy the definition of the Act. fi i -2- ( "Aldicarb" as used in this report means the parent compound aldicarb as well as its oxidation products aldicarb sulfoxide and aldicarb sulfone. ) Because of the extremely high toxicity of aldicarb and these oxidation products, it is not possible to assure "with an adequate margin of safety" that any given level of aldicarb in drinking water may be added to the existing residues in the average diet and "not cause adverse health effects. " Therefore, the subcommittee has determined that "pollution" shall mean the detectable presence of aldicarb, aldicarb sulfoxide, or aldicarb sulfone in groundwater. This determination is consistent with the Act's definition of "pollution, " and with the subcommittee's previous deliberations and findings on other economic poisons. The subcommittee's choice of this intentionally low "level of pollution" relates to uncertainties in the interpretation of toxicological data, as well as to concern for effects of total dietary exposure to aldicarb. In brief, the subcommittee considered the following points, among others. 1. Aldicarb is a very potent cholinesterase (ChE) inhibitor, and one of the most acutely toxic pesticides known. Its dose-response relationship shows that toxicity rises rapidly with increasing dose, i.e. there is little margin between a. dose yielding no apparent toxic response and an acutely toxic dcse. This indicates that there is little room for error when considering margins of safety. 2. Some states have established drinking water or groundwater standards for aldicarb. Wisconsin has a current groundwater standard of 10 ug/l (micrograms per liter) , and a "Preventive Action Limit" of 2 ug/l. A groundwater standard of 1 ug/l has been proposed. New York has established a groundwater standard for aldicarb of 0.35 ug/l. 3. EPA has established a Reference Dose (RfD) of 1 ug/kg/day for aldicarb, and has proposed a Maximum Contaminant Level (MCL) of 10 ug/l, based on the RfD. The subcommittee is concerned about several uncertainties in the establishment of these levels. EPA has accepted as a "No Observed Effect Level" (NOEL) in .humans a dose (10 ug/kg/day) which was extrapolated to yield 30 percent whole blood ChE inhibition in the relevant test on human subjects. There is not convincing evidence that depression of ChE activity to this extent whould have no adverse human health impacts, particularly if repeated orprolonged. On the contrary, epidemiological evidence from poisoning incidents suggests that toxic effects may occur at doses as much as ten times lower than reported in the human study. EPA's calculation of a proposed MCL of 10 ug/l is based on _ 1 consumption of drinking water by adults. Consideration of consumption by infants and children could lead to an MCL of approximately one-third this value. If the RfD is also adjusted to account for the greater aldicarb toxicity indicated by epidemiological studies, a further lowering of the MCL by an order of magnitude may be appropriate. -3- 4 . Aldicarb residues occur in several foods, particularly potatoes and citrus crops. EPA has calculated that six vercent of infants and children in the United States are current y. being exposed to aldicarb in excess of the RfD, argely from potatoes and citrus . If drinking water contains the proposed MCL level of 10 ug/1, EPA calculates that 13 percent of infants would receive aldicarb doses in excess of the RfD in their diet, and 63 percent of infants would exceed an intake of half the current RfD. While "detectable presence" has been determined by the subcommittee to be the appropriate "pollution level" for aldicarb, the subcommittee has also determined that its findings would not be altered by the use of any definition of "pollution" up to and including EPA's proposed MCL of 10 ug/l. B. The Subcommittee's Finding "a" Sampling results from Humboldt and Del Norte counties, and from the Central Valley, show clearly that aldicarb has been detected in, and thus bas polluted, falifornials rou Based on evidence from fie 'Teaching tests, a subcommittee finds it likely that current use practices have polluted, and continue to pollute, extensive areas of California's groundwaters. Due to the lack of monitoring for aldicarb in areas of heavy use, it is not possible to define the full extent to which pollution by aldicarb has occurred. C. The Subcommittee's Finding "b" Nationwide monitoring has shown that aldicarb may leach to groundwater under widely varying conditions of soil and weather. The registrant's field tests in the Central Valley of California have demonstrated that aldicarb moves readily through these soils into groundwater, to depths of at least 50 feet. At each of these sites where groundwater was sampled (Livingston, Fresno, and Turlock) , it was found that a single small-plot application of aldicarb, with normal irrigation practices, resulted in groundwater pollution persisting for at least two to three years after the aldicarb use. While conditions of use which have resulted in leaching of aldicarb to groundwater have been amply demonstrated, neither the registrant nor any other witness before the subcommittee has presented any conditions .of use where leaching has been shown not to occur. The registrant has in this hearing attempted to interpret positive finds of leaching as evidence that under other conditions this result would not have occurred. This interpretation constitutes the only evidence presented to the subcommittee to indicate that any agricultural use of aldicarb can be made without endangering groundwater. As a result, the subcommittee has concluded that neither. it, nor any witness before it, nor any source consulted by the subcommittee, has If f -4- knowledge of any current or modified agricultural use of aldicarb which can be employed with a high probability that groundwater would not be polluted. In this regard, the Department of Food and Agriculture (DFA) presented a proposed finding and recommendations to the subcommittee for its consideration. The subcommittee has declined to adopt DFA's proposal, for reasons which include those outlined below. DFA proposed that the subcommittee make a finding pursuant to paragraph 13150(c) (2) of the Act, i.e. a finding that agricultural use of aldicarb could be modified so that there would be a high probability that aldicarb would not pollute the groundwaters of the State. The recommendations offered by DFA as the proposed "modified use" to prevent groundwater pollution were essentially DFA's recently adopted "Pesticide Management Zone" (PMZ) regulations. Under these regulations, DFA will designate a "section" of land (roughly one square mile) as a PMZ for a given pesticide after pollution of groundwater by that pesticide has been found in that section. DFA may then require special permitting and reporting (in some cases banning) of the pesticide within the PMZ. The subcommittee concludes that DFA's proposed recommendations, and . the PMZ regulations in their current form, are not modified agricultural uses in the sense of the Act. A finding pursuant to paragraph 13150(c) (2) of the Act requires modified agricultural uses which will give "a high probability that the economic poison would not pollute" groundwater. Since a PMZ is designated in an area only after groundwater pollution by a pesticide has already occurred and been detected, the PMZ's will have no value in preventing groundwater pollution by aldicarb from occurring, and are not relevant to the preventive requirement of paragraph 13150(c) (2) . D. The Subcommittee's Finding "c" Aldicarb may be locally important to some growers, but no testimony has been presented to the subcommittee suggesting that its cancellation would cause a severe economic hardship on the State's agricultural industry. Its cancellation may affect some crop patterns, e.g. sugar beets, but in most cases alternative products are available or the impact on crop yield will be minimal. E. The Subcommittee's Finding "d" Section 13151 of the Act requires that any pesticide being considered by the subcommittee "which fails to meet any of the conditions of Section 13150 shall be canceled. " Aldicarb has failed to meet the conditions of Section 13150(c) , in that the subcommittee has declined to make any of the findings specified in paragraphs (1) , (2) , and (3) of that section. The subcommittee has in fact made directly contrary findings . It71 the subcommittee's understanding and intent that the California registration of aldicarb will now be canceled. i • -5- IV. Closing remarks The subcommittee wishes to thank all who participated in the hearing as witnesses, staff, or sources of technical information. The members representing the Department of Health Services and the State Water Resources Control Board wish to particularly acknowledge the fair and firm chairmanship of Mr. Lyndon Hawkins of the Department of Food and Agriculture, who guided the subcommittee's proceedings through to a timely conclusion. The' subcommittee also wishes to express concern over the lack of participation in the hearing process by potentially interested individuals or groups representing diverse viewpoints. Increased effort may be fruitful in future hearings to encourage broad public participation. Y)onald C. engle H. Paul Lillebo Department of Health S rvices State Water Resources . Control Board SUBCOMMITTEE OF THE PESTICIDE REGISTRATION AND EVALUATION COMMITTEE IMPLEMENTING OF THE PESTICIDE CONTAMINATION PREVENTION ACT\ ALDICARB: FINDINGS AND RECOMMENDATIONS OF THE DEPARTMENT OF FOOD AND AGRICULTURE MINORITY REPORT September 28, 1989 FINDINGS Finding One The representative of CDFA on the subcommittee cannot make Finding One (Food and Agricultural Code [FAC) Section 13150[c]( 1]) because in the absence of a pollution level it cannot be determined whether or not aldicarb pollutes ground water, and based on its detection in ground water and the uncertainties of the impact of continued unmodified use of aldicarb in sensitive areas, it cannot be determined that. aldicarb does not threaten to pollute ground water. Finding Two The CDFA representative on the subcommittee finds that the agricultural use of aldicarb can be modified so -that there is a high probability that aldicarb would not pollute the ground waters of the state. The justification for this recommendation is attached. Also attached are recommendations for modifying use and for monitoring of soil and ground water are attached. Under these conditions the minority finding is Finding Two specified in FAC Section 13150(c)(2). Finding Three The CDFA representative on the subcommittee cannot determine whether modified use of aldicarb would cause severe economic hardship on the agricultural industry of the state because available information is not conclusive. Furthermore, no recommendation is made of a level of aldicarb that does not significantly diminish the margin of safety not to cause adverse health effects because the health data are not complete. Therefore, Finding Three specified in FAC Section 13150(c)(3) cannot be made. Lyn%tah S. Hawkins Chair, Subcommittee of the Pesticide Registration Evaluation Committee Attachment 1 JUSTIFICATION FOR FINDING TWO I.: The PREC Subcommittee has reviewed the detection of five other pesticides (atrazine, simazine, bromacil, diuron, and prometon) found in ground water due to legal agricultural use and in each case has recommended finding two: that their agricultural use could be modified so that there is a high probability that these pesticides would not pollute the ground waters of the State. II . The agricultural use of aldicarb can be similarly modified because the characteristics and detection history of aldicarb fall within the range of characteristics and detection history of atrazine, simazine, bromacil, diuron, and prometon as follows: A. Modeling Studies Modeling studies show that aldicarb is a potential leacher similar to other pesticides that have been found in California ground water. Models are developed to represent or approximate complex systems and can be classified as research, management/educational, or screening models (Wagenet, 1986) . Screening models are mathematical or experimental procedures designed to discriminate between the performance of defined elements (such as pesticides) in an idealized scenario (Jury et al. , 1988) . Screening models have been developed to give a comparison of the relative potential of pesticides to leach and can be used to select chemicals for actual ground water monitoring (Rao et al. , 1985) . These models cannot be used to predict pesticide movement under actual field conditions (Wagenet, 1986) . The screening model developed by Jury et al. ( 1987) ranked five pesticides found in California ground water in order of increasing leaching potential as follows: atrazine, simazine, diuron, aldicarb, and bromacil. The model by Rao et al. ( 1985) ranked the same pesticides in order of increasing potential as atrazine, simazine, aldicarb, diuron, and bromacil. In both cases, aldicarb is rated as having a lower leaching potential than pesticides which the subcommittee has previously recommended that use can be modified so that there is a high probability that pollution would not occur. B. Physical and Chemical Factors Physical and chemical factors indicate that aldicarb is a potential. leacher similar to other pesticides that have been found in California ground water. Physical and chemical factors that have been determined to affect the leaching of chemicals have been used to compare the relative mobility of agricultural chemicals applied to soil (Rao et al. , 1985; Jury et al. , 1987) . These factors include water solubility, soil adsorption coefficient (Koo) , hydrolysis, and aerobic metabolism. In AB 2021 , these factors are grouped as either mobility factors (water solubility, Koo) or persistence factors (hydrolysis, aerobic metabolism) . Pesticides which are determined to be both mobile and persistent based on at least one factor in each group are designated as potential leachers. The following table shows values of these factors for atrazine, simazine, bromacil, diuron, prometon, and aldicarb (Johnson, 1988). 1 Water Aerobic Solubility Koc Hydrolysis Metabolism Atrazine 33 180 160 190 Simazine 4.9 220 110 110 Bromacil 820 60 110 300 Diuron 42 460 110 NA Prometon 720 79 NA 280 Aldicarb 6000 79 1330* 46* Specific Numerical Values >4 <2400 >9 >730 * CDFA Registrant Data Water Solubility: Values greater than 4 indicate a potential leaching pesticide. Water solubility for aldicarb is almost an order of magnitude greater than the next highest pesticide, bromacil. Greater water solubility might indicate greater potential for leaching. However, the differences between bromacil and aldicarb may be minimized when the amounts of irrigation or rainfall ar= considered. For example, at an application rate of 15 lbs active ingredient;/acre which is greater than any crop label application rate, either pesticide theoretically would be completely solubilized in an irrigation or rainfall of . 10 inches. Since irrigation rates are normally much greater than .10 inches, water solubility probably does not distinguish between the leaching potential of bromacil and aldicarb. It should also be noted that oxymayl and dicamba, both found in ground water due to agricultural use in other States, have higher water solubility values (280,000 and 6100, respectively) than aldicarb, but have not been found in California ground water. Koc: Values less than 2400 indicate a potential leaching pesticide. The Koc for bromacil is lower than aldicarb indicating a higher leaching potential for bromacil. The Koc for prometon is the same as aldicarb. Hydrolysis Values greater than 9 indicate a potential leaching pesticide. Aldicarb is s.;gnificantly more stable in water at pH 7 than the other five pesticides. Aerobic . Metabolism: Values for aerobic metabolism cannot be used to distinguish leaching pesticides from non-leaching pesticides. However, the aerobic metabolism value (at 25° C) for aldicarb is less by almost an order of magnitude than the other pesticides found in ground water indicating a significantly greater degradation rate for aldicarb. Thus, regarding mobility (water solubility, Koc) , aldicarb is more soluble than the other, five leaching pesticides but falls in the range of Koc values for the other five. Under irrigated conditions in California, differences in j solubility are minimized because of the high amount of residues solubilized. in a single irrigation. r Regarding persistence (hydrolysis, aerobic metabolism) , aldicarb is .stable in water at pH 7 but has a shorter aerobic metabolism half-life than the other leaching pesticides. This simply reflects the different pathways of degradation of these compounds. Atrazine, simazine, bromacil, diuron, and prometon are degraded hydrolysis whereas aldicarb is degraded mainly by oxidation (Rhone Poulenc, 1989) . 2 C. Sampling The locations of sampling and numbers of samples analyzed for aldicarb residues are similar to other pesticides found in California ground water. AB 2021 requires that the CDFA maintain a statewide data base of wells sampled for pesticide active ingredients (Food and Agricultural Code [FAC] § 13152[c)) . In consultation with the California Department of. Health Services and the State Water Resources Control Board, the contents of this data base are annually reported to the Legislature (FAC 513152[e)) . Cumulatively, the well inventory data (Well Inventory Data Base, 1979-89 sampling period) show that between 1984 and 1987 aldicarb was extensively sampled for in California wells. A total of 558 wells were sampled in 34 counties, resulting in the detection of aldicarb in 34 wells located in Del Norte and Humboldt Counties. To date, aldicarb has not been found in any of the remaining 32 counties that have been sampled (County Summary of Aldicarb Information: Sampling and Use Data submitted to the subcommittee) . Most of the sampling was conducted as part of the statewide well survey mar::'ated by AB 1803 and carried out by , the • CDHS. AB 1803 requires sampling for many chemicals, including pesticides, from both large and small municipal water systems that may draw from shallow cr deep wells. The following table shows the number of counties sampled, the number of positive counties, and the number of total samples analyzed based on reports submitted between 1986-1988 for atrazine, simazine, bromacil, diuron, prometon, and aldicarb (Brown et al. , 1986; Ames et al. , 1987; Cardozo et al. , 1988) . Number of Number of Number of Total Counties Sampled Positive Counties Samples Taken Atrazine 37 7 1691 Simazine 39 8 1952 Bromacil 21 2 917 Diuron 29 1 1233 Prometon 12 1 498 Aldicarb 34 2 982 Generally, sampling for aldicarb took place in major agricultural counties where the pesticide has been used. Of the 34 counties sampled for aldicarb, 27 have reported that the pesticide was used during 1987, the most recent data available. Sampling was conducted in 7 counties where no aldicarb use was reported and no sampling was done in 11 counties where some aldicarb use was reported. Sampling for the other five leaching pesticides occurred in the major agricultural counties of the State. Aldicarb was found in only 2 counties compared to atrazine which was found in 7, and simazine which was found in 8. In addition, more samples have been taken for aldicarb than for bromacil and diuron, both of which the subcommittee recommended could be used under modifications to prevent pollution. D. Levels detected in pumping wells and drinking water health levels. The levels detected and health level for aldicarb are similar to other pesticides detected in California ground water. The following table shows the range of detections and drinking water health levels for aldicarb and the other five pesticides found in ground water: 3 Range of Median of Posi- Residue Levels tive Detections Health Level Detected (ppb) (Range) (ppb) (ppb) Atrazine .8 - 8.5a .20 3b Simazine .02 - 1 .4 .29 10b Bromacil . 1 - 6.7 ( .5 - .99) 90c Diuron .05 - 2.8 ( .05 - .49) 10c Prometon . 1 - 5.9 .25 100c Aldicarb .2 - 13.2a 1 . 15 10d a. One well exceeded the Department of Health Services (DHS) action level. Range for aldicarb is from Humboldt County sampling. b. Maximum contaminant level c. EPA lifetime health advisory d. DHS Action Level Except for one well in which it was found at a higher level than the other leaching pesticides, aldicarb has been found at the same range of residue levels as the other leaching pesticides. The median positive level detected for all six chemicals falls close to 1 ppb or below, and the aldicarb drinking water health level is higher (safer) than atrazine and the same as simazine and diuron. III. The US EPA has not yet adopted a program to prevent aldicarb contamination of ground water. The EPA has issued for public comment a Preliminary Determination of aldicarb (PD 2/3) and a Special Review Technical Support Document (June 1988) that are part of a special review process that will culminate in a final document (PD4) . The PD 2/3 is a draft plan for protecting ground water from contamination by the registered uses of aldicarb through label requirements, monitoring, and state management plans. Following a 90-day comment period, the EPA is in the process of reviewing comments and issuing a final plan to prevent aldicarb contamination of ground water. Although the Department is developing a state management plan, it will receive no guidance for .modifying aldicarb use from the EPA until the final PD 4 document is issued. IV. Since the characteristics of aldicarb and its detection history are similar to one or ,more of the other five pesticides found in California ground water and regulated under the Department's Ground Water Protection Program, it is appropriate to adopt similar regulations to prevent aldicarb movement to ground water. Under this program, the Department adopts regulations to modify the use of pesticides found in ground water or soil under certain conditions to prevent pollution of California ground water. These regulations ( 1) identify leaching pesticides, (2) designate such pesticides as restricted materials, (3) establish areas (Pesticide Management Zones-PMZs) sensitive to ground water contamination, (4) specify uses prohibited in PMZs, (5) require growers to submit ground water protection advisories in order: to :, get permits to use leachers inside PMZs when allowed, (6) provide that advisories can only be written by Pest Control Advisers who have completed the Department's Ground Water Protection Training Program, and (7) require use and sales reporting of leaching pesticides. 4 Attachment 2 RECOMMENDATIONS A. To assure current use of aldicarb does not threaten ground water, conduct soil and ground water monitoring in areas of highest aldicarb use with particular emphasis in areas of shallow ground water. B. Establish aldicarb Pesticide Management Zones (PMZs) as follows: 1. All sections of land in Humboldt County where rainfall in relation to the monthly crop evapotranspiration and to application timing of aldicarb to any crop listed on the label of products containing aldicarb, result in a potential threat to ground water. This recommendation is based on ( 1) the registrants decision in 1984 to not register aldicarb for use in Del Norte County where such rainfall conditions appear to cause agricultural areas similar to those in Humboldt County to be sensitive to aldicarb contamination of ground water and (2) the Humboldt County Agricultural Commissioner's decision in 1985 to not issue permits for outdoor use of aldicarb in Humboldt County because of similarity of conditions to those in Del Norte County. 2. All sections of land outside Humboldt County where aldicarb is registered for use and has been found in soil as specified in the Pesticide Contamination Prevention Act or ground water due to legal agricultural use. C. To protect ground water, establish the following use requirements for use of aldicarb inside PMZs: 1 . Prohibit use in all PMZs in Humboldt .County. 2. Modify use of aldicarb in PMZs outside Humboldt County as .specified in Title 3 of the California Code of Regulations Section 6416, and emphasizing the critical role of irrigating using a water budget method to prevent aldicarb leaching. D. Monitor soil in PMZs outside Humboldt County to evaluate the effectiveness of modification of use of aldicarb. E. Develop a well head protection program to prevent direct point source contamination of ground water. F. Continue field studies to identify factors influencing pesticide leaching and incorporate findings into the ground water protection training program. i REFERENCES Ames, M. , C. Cardozo, S. Nicosia, J. Troiano, S. Monk, S. Ali and S. Brown. December, 1987. Sampling for pesticide residues in California well water: 1987 update - well inventory data base. California Department of Food and Agriculture, Environmental Hazards Assessment Program. - Sacramento, California. Brown, M. , C. Cardozo, S. Nicosia, J. Troiano and S. Ali. December, 1986. Sampling for pesticide residues in California well water: 1986 well inventory data base. California Department of Food and Agriculture, Environmental- Hazards Assessment Program. Sacramento, California. Cardozo, C. , M. Pepple, J. Troiano, D. Weaver, B. Fabre, S. Ali .and S. Brown. December, 1988. Sampling for pesticide residues in California well water: 1988 update - well inventory data base. California Department of Food and Agriculture, Environmental Hazards Assessment Program. Sacramento, California. Johnson, B. 1988. Setting revised specific numerical values. Environmental Hazards Assessment Program. California Department of Food and Agriculture, EH 88-14. . Jury, William A. Dennis D. Focht, and Water J. Farmer. 1987. Evaluation of pesticide groundwater pollution potential from standard indices of soil-chemical adsorption and biodegradation. J. Environ. Qual. , 16(4) :422-428. Jury, William A. and Masoud Ghodrati. 1988. Overview of organic chemical environmental fate and transport modeling approaches. p. 271-304. IN: Reactions and movement of -organic chemicals in soils. Soil Science Society of America and American Society of Agronomy, Special Publication - No. 22. Rao, P.S.C. , A.G. Hornsby, and R.E. Jessup. 1985. Indices for ranking the potential for pesticide contamination of groundwater. Proceedings of the Soil and Crop Science Society of Florida 44:1-24. Rhone Poulenc Ag Company. 1989. Report submitted. to the Pesticide Registration and Evaluation Committee Subcommittee. Wagenet, R.J. 1986. Principles of modeling pesticide movement in the unsaturated zone. P. 330-341 . IN: Willa J. Garner, Richard C. Honeycutt and Herbert N. Nigg (eds) . Evaluation of pesticides in ground water. ACS Symposium Series 315. American Chemical Society, Washington D.C. Wyman, J.A. , J.O. Jensen, D. Curwen, R.L. Jones, and T.E. Marquardt. 1985. Effects of application procedures and irrigation on degradation and movement of aldicarb residues in soil. Environmental Toxicology and Chemistry, 4:641-651. 6 REFERENCES Anonymous. April, 1987. Present and Potential Drainage Problem Areas Map. Department of Water Resources, San Joaquin District, California. Vibrant, Dan. April 9, 1989. Float device makes well monitoring easy. California Arizona Farm Press. Page 14, 15. Butchert, Jerald R. , General Manager. May, 1987. 1985-86 Water Conversation and Management Program. Review and Evaluation. Westlands Water District. 1- 41pp. Gonzalez, D. A. and D. J. Weaver. March, 1986. Monitoring concentrations or aldicarb and its breakdown products in irrigation water runoff and soil from agricultural fields in Kern County, 1985. California Department or Food and 'Agriculture, Environmental Hazards Assessment Program. 1-9pp.