The Quality of Our Nation's Waters
Pesticides in the Nation's Streams and Ground Water, 1992-2001

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How this table was made:

This table shows the number of public-supply, domestic, and observation wells sampled for agricultural and urban land-use studies and major-aquifer studies and the percentage of those samples for which one or more pesticide compounds were detected at concentrations that exceeded a drinking-water benchmark. Of the 83 pesticide compounds analyzed in water, 47 have drinking-water benchmarks.

Approximately one-third of the samples did not have pesticides analyzed by one of the two principal analytical methods used for the national assessment. The missing method, high performance liquid chromatography (HPLC), accounts for 36 of the 83 pesticides analyzed in water for the national assessment and 20 of the 47 pesticides with a drinking-water benchmark. The missing data were assumed to be nondetections. The expected effect of the missing HPLC analyses for table 6-1 is underestimation of the percentage of samples with an exceedance.

All wells in the public-supply and domestic categories are public-supply or domestic wells, respectively. The observation wells category includes (but is not limited to) wells used for monitoring, livestock, recreation, irrigation, institutions, industry, commercial properties, and aquaculture.

A single sample per well was used to characterize pesticides in ground water.

• For each of the three ground-water study and well types, the percentage of wells with one or more exceedances of a drinking-water benchmark was calculated as follows:

  (n / N) * 100

Where N is the number of samples with pesticide analyses and n is the number of wells with one or more exceedances of a drinking water benchmark. The percentage was rounded to the tenth’s place.

Pesticide names and analytical methods are presented in Appendix 1.

Information on sampling sites and their characteristics is presented in Appendix 5.

Downloadable concentration data are presented in Appendix 6.

Additional information on analytical approach is presented in Appendix 8.

For more information, contact:

Ground water:
Paul E. Stackelberg
U.S. Geological Survey
NAWQA Pesticide Synthesis Project
425 Jordan Road
Troy , NY 12180
voice: (518) 285-5652
fax: (518) 285-5601
email: pestack@usgs.gov