Sampling for Pesticide Residues in California Well Water
1995 Update of the Well Inventory Data Base. EH95-06.
For Sampling Results Reported From July 1, 1994 to June 30, 1995

D. Bartkowiak, K. Newhart, M. Pepple, J Troiano, D. Weaver

EXECUTIVE SUMMARY

About The 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 Well Inventory Database

What happens when detections are reported to DPR

General Information about Sampling Results in the Well Inventory Database

The Data In This Report

This is the tenth report, and the third update to the 1992 cumulative report on the entire contents of the database.

Summary of Data

Detections Referred to the SWRCB

Detections of eight chemiclas, including three chemicals where historical agricultural applications are considered by DPR to be the source of residues in ground water were reported the the SWRCB. The three chemicals and the number of wells with detections are:

1,2-dibromo-3-chloropropane (DBCP): 304 wells
1,2-dichloropropane (1,2-D): 11 wells, and
ethylene dibromide (EDB): 15 wells.

Summary of Verified Detections

      atrazine           diuron           prometon
      bromacil           hexazinone       simazine
      deethyl-atrazine          deisopropyl-atrazine (DIPA)
      2,3,5,6-tetrachloroterephthalic acid

private drinking-water wells (174)
public drinking water wells (18)
non-drinking-water wells (21)

First-time Verified Detections Were Made for the Following Chemicals and Counties:

First-time Verified Detections of Hexazinone in California Ground Water

Legal Agricultural Use Determinations

      atrazine          diuron          simazine
      bromacil          prometon        DIPA

     Fresno         Orange              Tehama
     Los Angeles    Riverside           Tulare
     Merced         San Bernardino      Yolo

Prometon in Los Angeles County.
Diuron in both Merced and Tehama counties.

Pesticide Management Zone (PMZ)

      Fresno         Orange       Tehama       Ventura
      Los Angeles    Riverside    Tulare       Yolo
      Merced         San Bernardino

One atrazine PMZ in Stanislaus County.
One bromacil PMZ in Tehama County.
One bromacil PMZ in Tulare 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 that prevent further ground water contamination. For the past several years, EHAP 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.

During the past year, EHAP scientists conducted well monitoring studies and field investigations in Fresno and Tulare counties as they continued to examine this method of identifying areas that are vulnerable to ground water pollution by the agricultural use of pesticides. This method may provide a basis for development of regional agricultural management practices to reduce ground water contamination by pesticides.

The State And Regional Water Boards

The SWRCB and nine RWQCBs 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 the SWRCB to prevent economic poisons from migrating to ground water include:

Table 1. Summary of well sampling results included in the Department of Pesticides Regulation's well inventory database, by report year, for data reported through June 30, 1995.

Figure 1. California counties with verified detections of pesticide residues in ground water that were reported to the Department of Pesticide Regulation during the period July 1, 1994 through June 30, 1995.

For a copy of this report, please contact:

Department of Pesticide Regulation
Environmental Monitoring and Pest Management Branch
1020 N Street, Room 161
Sacramento, CA 95814-5624

or phone (916) 324-4100

Please refer to the 1995 Well Inventory Report.