The Pesticide Contamination Prevention Act
The Pesticide Contamination Prevention Act (PCPA) was enacted in 1985 to prevent further pesticide pollution of the State's ground water. The PCPA requires:
The Department of Pesticide Regulation (DPR) to maintain a statewide database of wells sampled for active ingredients of pesticide products;
Agencies (government and private) to report to DPR the results of any well sampling for the active ingredients of pesticides;
DPR to review findings of pesticide contamination and undertake necessary mitigation;
DPR, in consultation with the California Department of Health Services (CDHS) and the State Water Resources Control Board (SWRCB), to annually make this report to the Legislature, CDHS, the State Office of Environmental Health Hazard Assessment, and SWRCB.
The Well Inventory Database
The well inventory database was developed by DPR (then a division of the California Department of Food and Agriculture) in 1983 before the passage of the PCPA.
The purposes of the database were to centralize information on the occurrence of nonpoint source contamination of ground water by the agricultural use of pesticides and to facilitate graphical, numerical, and spatial analyses of the data.
To meet the requirements of the PCPA, sampling results from both point source and nonpoint source contaimiation are included in the database.
What Happens When Detections are Reported to DPR
When a pesticide is found in ground water, a well-defined process established by the PCPA is triggered. This process allows for comprehensive review of the detection.
DPR refers detections to SWRCB if the pesticide is: not currently registered for use; registered for other than agricultural, outdoor industrial, or outdoor institutional uses; or found in ground water and determined not to be due to legal agricultural use.
DPR attempts to verify the detection of pesticides that are currently registered for agricultural use by conducting a well sampling study. There are specific criteria for verification of a detection. If a detection is verified, a determination is made as to whether the contamination occurred because of legal agricultural use of the chemical. Detections may not be verified for one of several reasons, including:
Follow-up sampling has not yet been completed by DPR, or sampling was not conducted by DPR. The detection may have been referred to SWRCB; there may be no wells available for sampling; or permission to sample could not be obtained from the well owner.
Analyses of all other samples taken by DPR in response to the positive sample were negative for the compound under investigation.
General Information about Sampling Results in the Well Inventory Database
A summary of the data in the database by report year is given in Table 1.
The data can be used to:
Display the geographic distribution of well sampling.
Display the geographic distribution of pesticide residues in sampled wells.
Identify areas potentially sensitive to contamination by the legal agricultural use of pesticides.
There are limitations on interpreting the data, including:
The data indicate which pesticides are present in well water among those pesticides for which analyses were performed. They do not represent a complete survey of ground water quality throughout the state nor do they represent sampling for all pesticides.
Sampling by agencies other than DPR is not necessarily related to suspected agricultural sources of contamination.
The Data in this Report
This is the eleventh report and the fourth update to the 1992 cumulative report on the entire contents of the database.
Data were submitted to DPR from July 1, 1995 to June 30, 1996.
Data are the results of six studies conducted by DPR and CDHS
Data are from studies that were conducted from 1994 to 1996.
Summary of Data in This Report
141,985 records (chemical analyses) were added to the database for this report.
3,564 wells were sampled in 48 counties.
121 pesticide active ingredients and breakdown products were analyzed.
22 compounds were reported with positive detections.
Detections Referred to SWRCB
Detections of 13 chemicals, including three chemicals where historical agricultural applications are considered by DPR to be the source of residues in ground water, were reported to SWRCB. The three chemicals and the number of wells with detections are:
1,2-dibromo-3-chloropropane (DBCP): 370 wells
1,2-dichloropropane (1,2-D): 8 wells, and
ethylene dibromide (EDB): 24 wells.
Summary of Verified Detections
Three herbicides had verified detections: atrazine, bromacil, and simazine.
Verified detections were made in six wells in five counties.
Counties with verified detections were: Butte, Kern, Monterey, San Joaquin, and Sutter.
All detections were in private drinking-water wells.
First-time Verified Detections Were Made for the Following Chemicals and Counties:
Bromacil in Monterey County and simazine in Sutter County.
Legal Agricultural Use Determinations
After well sampling and land use surveys are completed, a determination is made as to whether the detection of the pesticide residues in ground water could have been due to legal agricultural use. Specific criteria must be met for this determination to be made.
Four herbicides and one breakdown product were found in ground water as a result of legal agricultural use: atrazine, bromacil, diruon, simazine, and deisopropyl-atrazine.
Legal agricultural use was determined to be the source of pesticide residues in 20 Fresno County wells.
Pesticide Management Zone (PMZ)
A PMZ is a land area where a pesticide has been detected in ground water and where it has been determined that the contamination was due to legal agricultural use. PMZs are established in regulation to prevent further contamination of ground water. The use of certain chemicals is prohibited or restricted in these areas. PMZs have been established in various areas of the state for atrazine, bromacil, diuron, prometon, and simazine.
After evaluation of data, a total of 20 PMZs will be established in regulation in Fresno County.
Factors That Contribute to Ground Water Contamination
DPR environmental scientists continue their work to understand the factors that contribute to ground water contamination by pesticides used in agriculture. They conduct field studies on pesticide movement, investigate contaminated wells, compile extensive databases, and review the work of other scientists. The knowledge gained from these activities is used to develop pesticide use practices designed to prevent further ground water contamination. For the past several years, DPR scientists have been developing an approach that integrates climatic, soil, and geographic data in analyses of their combined influence on the movement of pesticides to ground water. This method may provide a basis for development of regional agricultural management practices to reduce ground water contamination by pesticides.
DPR has begun a three-year program to prevent additional residues from reaching ground water. In cooperation with the University of California Cooperative Extension, DPR has been working with growers, pest control advisors, the agricultural industry, and herbicide registrants to identify practical farm management alternatives that can reduce or prevent off-site movement of herbicides used in grape and citrus production.
The State and Regional Water Boards
SWRCB and nine regional water quality control boards are responsible for protecting the beneficial uses of water in California and for controlling all discharges of waste into waters of the State. Actions taken by SWRCB to prevent pesticides from migrating to ground water are detailed in section IV of this report.
Table 1. Summary of well sampling results included in the Department of Pesticide Regulation's (DPR) well inventory database , by report year, for data reported through June 30, 1996.
| CATEGORY | 1986 | 1987 | 1988 | 1989 | 1990 | 1991 | 1992 | 1993 | 1994 | 1995 | 1996 | TOTAL
|
| Total wells sampled | 8987 | 574 | 3074 | 752 | 2784 | 1557 | 4741 | 2324 | 2839 | 3322 | 3564 | 20,042 |
| no detections | 6583 | 317 | 2791 | 543 | 2550 | 1351 | 3985 | 1945 | 2414 | 2769 | 3128 | 15,816 |
| detections (a) | 2404 | 257 | 283 | 209 | 234 | 206 | 756 | 379 | 425 | 552 | 436 | 4,226 |
| verified detections (b) | 44 | 29 | 4 | 140 | 93 | 133 | 67 | 80 | 37 | 213 | 6 | 794 |
| Total counties sampled | 53 | 20 | 41 | 33 | 53 | 30 | 52 | 46 | 50 | 47 | 48 | 58 |
| no detections | 30 | 6 | 24 | 11 | 27 | 11 | 24 | 25 | 30 | 19 | 20 | 11 |
| detections (a) | 23 | 14 | 17 | 22 | 26 | 19 | 28 | 21 | 20 | 28 | 28 | 47 |
| verified detections (b) | 5 | 3 | 3 | 16 | 8 | 14 | 9 | 17 | 10 | 17 | 5 | 31 |
| Total pesticides and related compounds | 160 | 79 | 167 | 96 | 191 | 186 | 125 | 112 | 114 | 166 | 121 | 293 |
| no detections | 144 | 64 | 142 | 81 | 164 | 166 | 85 | 83 | 95 | 139 | 99 | 199 |
| detections (a) | 16 | 15 | 25 | 15 | 27 | 20 | 40 | 29 | 19 | 27 | 22 | 94 |
| verified detections (b) | 8 | 6 | 5 | 9 | 6 | 9 | 5 | 10 | 6 | 9 | 3 | 22 |
(a) Includes verified and unverified detections.
(b) Detections are designated as verified if residues of a compound are detected in one sample as a result of an analytical method approved by DPR and verified, within 30 days in a second discrete sample taken from the well, by a second analytical method or a second analytical laboratory approved by DPR; or if an unequivocal detection is made in one sample.
(c) Legal, agricultural use is the application of a pesticide, according to its labeled directions and in accordance with all laws and regulations. Agricultural use is defined in Food and Agricultural Code section 11408.
(d) The total is not additive. A single well that had sampling data reported in the 1986, 1988, and 1990 reports is counted one time only.
(e) The 8 compounds are: 1,2-D, atrazine, bromacil, DBCP, deisopropyl-atrazine, diuron, EDB, and simazine.
(f) The 15 compounds are: 1,2-D, aldicarb, aldicarb sulfone, aldicarb sulfoxide, atrazine, bentazon, bromacil, DBCP, deethyl-atrazine, deisopropyl-atrazine, diuron, EDB, prometon, simazine, and 2,3,5,6-tetrachloroterephthalic acid. Aldicarb, atrazine, bentazon, bromacil, diuron, prometon, and simazine have been reviewed through the Pesticide Detection Response Process. DPR considers the remaining chemicals to have reached ground water as a result of legal, agricultural use.
For a copy of this report, please contact: Department of Pesticide Regulation, Environmental Monitoring and Pest Management, 1020 N Street, Room 161, Sacramento, California 95814-5624 , or phone (916)324-4100. Please refer to the 1996 Well Inventory Report.
If you have any questions regarding this report or the Well Inventory Data in general, please contact Jeff Schuette at jschuette@cdpr.ca.gov.