Single copies of the report can be obtained free of charge from:
Environmental Monitoring and Pest Management Branch, Department of
Pesticide Regulation, 1020 N Street, Sacramento 95814, phone (916)
324-4100. The executive summary, including a county breakdown of results
and a summary of findings from 1986 through 1995, can be downloaded from
DPR's Internet web page (http://www.cdpr.ca.gov).
Environmental Monitoring and Pest Management
California Department of Pesticide Regulation
Release No. 96-06
Date: March 13, 1996
DPR RELEASES ANNUAL REPORT ON GROUNDWATER TESTING FOR PESTICIDES
SACRAMENTO -- Cal/EPA's Department of Pesticide Regulation (DPR) today
released its annual 1995 report on the results of groundwater testing for
The report, required by the Pesticide Contamination Prevention Act
of 1985 (AB 2021, Connelly), was delivered to the Legislature this week.
It summarizes groundwater monitoring in 49 well sampling surveys submitted
to DPR between July 1, 1994 through June 30, 1995. The monitoring was
conducted by three state and local government agencies between 1993 through
1995. Among other provisions of AB 2021, government agencies that test
well water for pesticide residues must report the results to DPR.
Altogether, samples were taken from 3,322 wells in 47 of
California's 58 counties. Pesticide residues were detected and verified in
213 wells in 17 counties. This is an increase from previous years because
DPR conducted two extensive field studies in parts of Fresno and Tulare
Counties that are particularly susceptible to groundwater contamination.
Working in areas that are known to contain pesticide residues, DPR
scientists can expand scientific understanding of how climatic, soil, and
geographic data combine to influence the movement of pesticides to
groundwater. With this information, DPR plans to continue development of
pesticide use practices designed to prevent further groundwater
Of the 213 wells where pesticide residues were detected, 174 were
private drinking water wells, 18 were public drinking water wells, and 21
were nondrinking water wells.
In most cases, the levels of contamination found were well below
levels of health concern. However, in seven domestic water wells, residues
exceeded health advisory levels. Those findings were referred to the State
Department of Health Services, which can take immediate corrective action
when residues in community water wells exceed levels of health concern. In
addition, DPR may take regulatory action regardless of the level of
Most samples were analyzed for multiple chemicals. Overall, the
tests targeted a total of 166 pesticide active ingredients and breakdown
products. Of those, verified detections of nine different compounds were
made. Six of the chemicals detected were herbicides -- atrazine, bromacil,
diuron, prometon, simazine, and hexazinone. The remaining three chemicals
were pesticide breakdown products (deethyl-atrazine, deisopropyl-atrazine,
and 2,3,5,6 tetrachloroterephthalic acid). Five of the six chemicals have
been found in previous years. The sixth herbicide -- hexazinone -- was
detected and verified for the first time in California groundwater.
Hexazinone was found in four wells located in Tulare County and one well in
There were unconfirmed detections of nine other pesticides: 1,2-D,
DBCP, EDB, coumaphos, demeton, merphos, napthalene, ortho-dichlorobenzene,
and xylene. However, DPR did not conduct followup sampling to verify these
detections because the compounds are no longer registered in California or
no longer registered for agricultural or outdoor institutional use, and
therefore not subject to regulatory controls under AB 2021.
When pesticides are registered for agricultural or outdoor
institutional uses, and they are detected in groundwater, DPR investigates
to determine if the source of the residue is the result of routine
agricultural use (application to crops, for example), or a "point source"
of pollution (such as a pesticide spill into a well). In its
investigations, DPR first attempts to verify the detection by analyzing new
samples from the positive wells. Nearby wells are also tested to determine
the extent of any contamination.
After a detection is verified, the investigation focuses on whether
the pesticide reached groundwater because of routine agricultural use. If
a pesticide is only registered for nonagricultural uses, or no longer
registered, the detection is referred to the State Water Resources Control
Board for further investigation. Point sources of pollution are also
referred to the Water Board for further action.
If it is determined that routine agricultural use is the source,
DPR may establish a pesticide management zone (PMZ) around the location of
the detection. A PMZ is a geographic surveying unit of approximately one
square mile in size, designating the area as sensitive to groundwater
pollution. Once a PMZ is established, DPR initiates special restrictions
on the use of the detected chemical in the area. Actions in the past have
included revocation of permits to use pesticides, modification of use
practices to prevent groundwater contamination, or suspension of a
chemical's registration in California.
Routine agricultural use of currently registered pesticides was
determined to be the cause of pesticide residues found in groundwater for
the first time in three counties: Los Angeles, Merced, and Tehama.
Routine use was also determined to be the source of pesticides detected in
six counties where they had been found previously: Fresno, Orange,
Riverside, Los Angeles, Merced, Tehama, San Bernardino, Tulare, and Yolo.
Factors that contribute to groundwater contamination by pesticides
include amounts used and method of application, irrigation practices, the
physicochemical characteristics of the pesticide, soil type and climate.