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How DPR identified areas vulnerable
to pesticide movement to ground water
Pesticides have been found in a variety of climatic,
soil, and depth to ground water conditions. In the 1990’s
DPR scientists wondered whether there was a way to characterize
these various conditions so that pesticide movement to ground water
could be predicted, and thus prevented before contamination occurs.
The following sections describe the source of pesticide detection data, and the
various statistical techniques, the mathematical model, and depth to ground
water data that were used by DPR to identify vulnerable areas. These vulnerable areas are
where unmitigated use of certain pesticides is likely to contaminate ground water and were
adopted in regulation as “ground water protection areas.”
Source of pesticide detection data: Well inventory database
The Pesticide Contamination Prevention Act (PCPA)
requires DPR to sample wells for pesticides with the potential to
pollute ground water. The PCPA further requires all
local, county and state agencies to submit all results of well sampling
for pesticides to DPR. In addition, DPR encourages other entities, such as the
United States Geological Service, to submit results. DPR is also required to maintain
a database of these well sampling results. As a result, DPR has a large data set of
wells containing pesticide residues from legal agricultural use. DPR used this data set
to determine if there was a relationship between detections and local climate, soil,
and depth to ground water characteristics.
DPR’s well inventory
database and well sampling strategies are summarized in:
Statistical methods and modeling
Because of the wide range of climatic and
soil conditions associated with pesticide contamination of ground
water, an empirical statistical approach was devised to determine
whether vulnerable areas could be described. The empirical analysis
was conducted in two steps. In the first step, a cluster statistical
procedure was used to identify groups of contaminated wells with
similar soil properties. Initially, principal component analysis was used to associate
sections of land with those clusters. These procedures are described in the
following two publications - a DPR report available on the website,
and a journal article available from John Troiano at
.
- EH 92-09
Troiano, J., B. Johnson, S. Powell, and S. Schoenig.
1992. Profiling Areas Vulnerable to Ground Water Contamination
by Pesticides in California. (PDF, 1.8 mb).
- 1994 Troiano, J., B.R. Johnson, and S. Powell. 1994. Use of
Cluster and Principal Component Analyses to Profile Areas in California
Where Ground Water Has Been Contaminated by Pesticides. Environ.
Monitor. Assess. 32: 269-288.
Later, an alternative procedure (canonical variates analysis) was
used to improve characterization of vulnerable areas. The following
two publications describe how DPR tested that procedure
by sampling wells inside and outside of vulnerable areas, considering
depth to ground water as an additional factor. The statistical model
developed to identify vulnerable areas is called the CALVUL model.
Copies are available from John Troiano at
.
- 1997 Troiano, J., C. Nordmark, T. Barry, and B. Johnson. 1997.
Profiling areas of Ground Water Contamination by Pesticides in
California: Phase II - Evaluation and Modification of a Statistical
Model. Environ. Monitor. Assess. 45:301-318.
- 1998 Troiano, J., C. Nordmark, T. Barry, B. Johnson, and F.
Spurlock. 1998. Pesticide Movement to Groundwater: Application
of Areal Vulnerablility Assessments and Well Monitoring to Mitigation
Measures. p.239-251. In Ballatine et al. (ed.) Triazine Herbicides
Risk Assessment. ACS Symposium Series 683.
Application of the CALVUL model
Previously, DPR sampled for pesticides in ground water based on
pesticide use data only. However, in determining where to sample ground water for norflurazon residues,
DPR used the CALVUL model and pesticide use data. High norflurazon detection rates indicated
that the CALVUL model is an effective tool to identify areas where contamination is likely.
The norflurazon study also indicated that depth-to-ground water was another important variable
in determining vulnerable areas. These results are found in the following report:
The current method used to group and profile sections of land based
on soil data is explained in report EH 00-05 and the method to determine
depth-to-ground water estimates for sections of land in report EH
00-02. Both reports are listed below and are available on the website.
- EH 00-05 Troiano,
J., F. Spurlock, and J. Marade. 2000. Update of the California
Vulnerability Soil Analysis for Movement of Pesticides to Ground
Water: October 14, 1999. (PDF 1.8 mb)
- EH 00-02 Spurlock,
F. 2000. Procedures for Developing a Depth-to-Ground Water Database.
(PDF 1.4 mb)
Using this vulnerability analysis, studies
have been conducted to identify the pathways of contamination and
appropriate management practices.
For content questions contact:
Contact: John Troiano
phone: (916) 324-4115
e-mail:
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