Grant County Groundwater Study


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Grant County Groundwater Study

During routine testing of public water supply systems by the Washington State Department of Health, both the herbicide DCPA and increased nitrate were found in municipal wells in Quincy, Washington. Because both of these chemicals can be harmful to human health, WSDA, the Department of Health, the Columbia Basin Conservation District, and the City of Quincy worked together to collect more samples from wells in the region to find out if other wells had amounts of pesticides and nutrients that could be harmful to human health.


Water Sampling and Study Region

  • WSDA and Department of Health staff took samples from 7 municipal wells in Quincy and 11 residential wells in the surrounding area (sampling locations are shown in the map below).
  • We collected samples in the spring and fall of 2021 and a lab tested them for more than 150 pesticides, related chemicals, and nutrients (including nitrate).
  • We compared these samples to drinking water criteria set by the Environmental Protection Agency.


map of agriculture regions in Grant county by commodity, sampling, and canals

Pesticides

We found several pesticides and pesticide breakdown products in groundwater samples (details are in the table). All of them were at trace levels below the Environmental Protection Agency drinking water criteria for human health.
 
Active Ingredient Usage Type Brand Name Examples Use Examples % of Drinking Water Standard
Atrazine and atrazine breakdown products Herbicide Aatrex, Atrazine Corn, conifer, fallow land, industrial site, right-of-way, sorghum, turf 3.7
Dichlobenil or fluopicolide breakdown product Herbicide or fungicide Barrier, Casoron Apple, berry, cherry, conifer, fencerow, grape, ornamental, pear, right-of-way <1
Total DCPA and DCPA breakdown products Herbicide Dacthal Brassica, conifer, melon, ornamental, onion, strawberry, turf 13.9
Hexazinone Herbicide Velpar, Westar Alfalfa, blueberry, industrial site, pasture, right-of-way, turf <1
Simazine Herbicide Princep, Sum-Trol Apple, berry, cherry, corn, grape, ornamental, pear, turf <1


Nitrate

Drinking water contaminated with too much nitrate can reduce how much oxygen the body’s red blood cells can carry and cause health problems, especially for infants. The drinking water standard for nitrate is 10 ppm*, which is low enough to protect infants.
  • We found some nitrate in all of the samples, and three samples were above the drinking water standard.
  • In the spring sampling, nitrate in samples ranged from 0.63 ppm to 9.13 ppm.
  • In the fall sampling, nitrate in samples ranged from 0.61 ppm to 16.0 ppm.