The Idaho Department of Environmental Quality seeks owners of private wells in Twin Falls County to participate in a program that will sample for nitrates and other compounds.

Nitrates, arsenic, bacteria and common ions are sought through sampling, to occur in September and October. Participants in the free program will receive a copy of the results.

Groundwater provides more than 95% of the state’s drinking water, and nitrate is the most widespread groundwater contaminant, according to the department. Long-term exposure to high nitrate levels can cause adverse health effects.

Plants and other organic matter return nitrate to the soil as they decompose. Septic sewer systems, waste from feedlots and nitrogen fertilizers also release nitrate.

Amounts not used by plants can build up and move through soil, according to DEQ. Rain and snow, irrigation water, and sandy soils allow nitrate to percolate down into groundwater.

The study will help the department reassess sites in the Twin Falls County nitrate priority area sampled by other agencies before 2010 and will include new locations as part of an update to nitrate concentration data, according to a department news release. Results will help identify nitrate levels in the Snake River Plain Aquifer and inform decisions concerning future development.

The department maintains a list of nitrate priority areas. Eight are ranked high, 17 moderate-high and 10 moderate. On the most recent list, based on 2020 data, Twin Falls ranks highest in the moderate-high priority category.

The moderate-high classification is based on population, water quality — the percentage of sites over drinking-water standards — number of public water systems, water quality trend, and other beneficial uses, Nick Howell, department source water protection analyst, told Capital Press.

Upcoming work with private well owners is part of a DEQ Twin Falls regional effort to maintain current trends on nitrate priority areas, which are reassessed through follow-up sampling periodically, he said.

In the 2020 nitrate priority area ranking process, Twin Falls County was found to not show a current trend, and “more sampling is needed to identify potential trends,” Howell said.

Understanding nitrate trends will provide water quality data to private well owners and local decision makers, he said. The data can be used to “address potential contaminants and implement best management practices for future beneficial uses of groundwater,” and for continued public outreach.

For participation details, contact Howell at 208-726-3870 or Nicholas.Howell@deq.idaho.gov by Aug. 16.