USGS FS-122-96: Pesticides in Public Supply Wells of Washington State

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Central Columbia Plateau - Yakima River Basin NAWQA Study - Publications

Pesticides in Public Supply Wells of Washington State

USGS Fact Sheet 122-96


The Safe Drinking Water Act requires quarterly pesticide monitoring of Washington State's 5,400 Class A* public water supply wells, beginning in 1995. In a 3-year sampling period, the cost of monitoring is estimated to be about $3,300 per well. For the 40% of Washington's Class A public water systems that have 15 to 100 connections, the cost per household could reach $70 per year for each well in the system.

In 1994 the Washington State Department of Health (WDOH) created a program, approved by the U.S. Environmental Protection Agency (EPA), enabling public water systems to apply for waivers from quarterly monitoring. Wells for which waivers are granted must be at low risk of contamination from 25 pesticides specified by the EPA Phase II-5 Rule.

In cooperation with the WDOH, the U.S. Geological Survey (USGS) began a statewide sampling program in 1994 to assess the vulnerability of Washington State public water systems to pesticides. 1,326 Class A public supply wells were selected for sampling-1,103 using USGS geographic information systems (GIS) data and random selection software, and 223 as a high-risk group based on nitrate concentration and well depth. The WDOH used three contract laboratories to collect and analyze samples from across the state. The USGS National Water Quality Laboratory analyzed 220 duplicate samples-80 from wells in the Puget Sound Basin and 140 in the Central Columbia Plateau. Because the USGS lab can detect pesticides at very low concentrations, USGS data were used to validate contract lab results and to provide additional low-level pesticide data. Study costs ($1.4 million) were recovered by waiver fees.

*Class A: Generally, community water systems with 15 or more connections


Statewide Sampling Results* and Waiver Program

Map showing public supply wells sampled by WDOH contract labs, and pesticide detections

Sampling results for 1,326 public supply wells


Risk assessment

Factors that correlated with pesticide detection were:


Waivers

On the basis of this sampling and risk assessment:


Savings

    Annual monitoring savings
       resulting from waivers : $ 6.0 million

    Study cost                : $ 1.4 million


    1994 Lab Comparisons     Contract labs      USGS lab
    ---------------------- ----------------- ---------------
           Cost per sample      $375-500         $370

           Number of               27             48
              pesticides
              analyzed

           Schedules           EPA 515.1       USGS 2001
              analyzed             525.1
    ---------------------- ----------------- ---------------

USGS Sampling Results Highlight Other Issues

Map showing duplicate samples analyzed by USGS, and pesticide detections

USGS results for 220 duplicate samples


Why does the USGS detect more pesticides?


Why are low detection limits needed?

Graph showing results of duplicate samples analyzed for atrazine by both USGS and a contract lab
Duplicate samples analyzed for atrazine by both USGS and a contract lab


USGS Fact Sheet FS-122-96 by Sarah J. Ryker and Alex K. Williamson

References:

Washington State Department of Health, Spring 1995, Preliminary Results of the Areawide Groundwater Monitoring Project: Washington State Department of Health, 9 p.

Wagner, R.J., Ebbert, J.C., Roberts, L.M., and Ryker, S.J., 1995, Agricultural pesticide applications and observed concentrations in surface waters from four drainage basins in the Central Columbia Plateau, Washington and Idaho, 1993-94: U.S. Geological Survey Water-Resources Investigations Report 95-4285, 50 p.


For health information, contact your water utility or county health agency, or the Washington State Department of Health: 1 (800) 521-0323.

For further technical information contact:

May 1996

Suggested citation:
Ryker, S.J., and Williamson, A.K., 1996, Pesticides in public supply wells of Washington State: U.S. Geological Survey Fact Sheet 122-96, on line at <URL: https://wa.water.usgs.gov/ccyk/fs-122-96.html>, last updated March 16, 1998


For a paper copy of this report, email: rwblack@usgs.gov


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Last modified: Mon Mar 16 08:37:22 1998
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