National Water-Quality Assessment (NAWQA) Project

   Home    Headlines    Featured Studies    Liaison Committee    Informing Decision Makers    Data    Modeling/Software    Publications    Maps

Featured Studies
Special studies on source-water and drinking-water quality
Surface-water intakes
General Information

Groundwater-Quality Trends

Home National Results and Maps Background Factors Affecting Trends Simulation and Forecasting Data Trends Publications

Central Columbia Plateau area of Washington (CCPT)

A total of 72 wells were sampled in 19931995 (Williamson and others, 1998) and again in 20022003 (Frans, 2008) in two monitoring well networks and one public supply well network. Twenty-nine pesticides were detected in the groundwater of the CCPT (Frans, 2008). The herbicide atrazine and its breakdown product, deethylatrazine (DEA), were detected far more frequently than any other pesticides. Because the majority of the pesticides were detected in an insufficient number of wells to detect a consistent change, the analysis was conducted only for atrazine and DEA.

Map showing the ocation of the Central Columbia Plateau area of Washington (CCPT) study area.

Location of the Central Columbia Plateau area of Washington (CCPT) study area (from Frans, 2008).

Concentrations of DEA had a statistically significant increase in groundwater sampled from a row crop monitoring well network, a regional aquifer well network, and for the data set as a whole. Atrazine concentrations did not change significantly. No statistically significant changes were found for nitrate concentrations in any of the three well networks. Despite the lack of changes within these three well networks, a previous USGS study with a larger 474-well data set found a statistically significant decrease from 19982002 for wells with nitrate concentrations greater than 10 mg/L (Frans and Helsel, 2005).

Return to Factors Affecting Groundwater-Quality Trends

Accessibility FOIA Privacy Policies and Notices

Take Pride in America home page. FirstGov button U.S. Department of the Interior | U.S. Geological Survey
Page Contact Information:
Page Last Modified: