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Idaho

Groundwater quality and nitrate priority areas

Agency Idaho Department of Environmental Quality

Idaho groundwater quality and nitrate priority areas

The Idaho Department of Environmental Quality (DEQ) says Idaho Code § 39-120 designates it as the primary agency to coordinate and administer groundwater quality protection programs for the state. DEQ monitors groundwater, ranks the areas degraded by nitrate, and publishes its data on interactive maps and in reports. DEQ says groundwater supplies drinking water to 95% of Idaho citizens.

In a Phase I ESA

ASTM E1527-21 does not name groundwater quality maps or reports among its standard record sources. They are not lists of sites. They describe the groundwater setting a property sits in, which matters most where the property or its neighbors use a private well.

  • Degradation is local, and three constituents lead. DEQ says Idaho's groundwater quality is generally good, but that monitoring shows water has been significantly degraded in specific areas. It names nitrate, arsenic and uranium as three of the more commonly found constituents. DEQ describes arsenic and uranium as naturally occurring, though it also lists human sources of arsenic such as pesticide application, mining and smelting. It lists septic systems, animal feedlot waste and nitrogen-based fertilizers among the sources of nitrate. Check DEQ's data for the area before attributing one of these to the property.
  • Nitrate priority areas are ranked and mapped. DEQ keeps a list of nitrate-degraded groundwater areas, which it calls nitrate priority areas, ranked by the severity of the degradation. DEQ's mapping page describes the areas as places where nitrate concentrations potentially degrade drinking water quality, with 25% of sampled wells exceeding 5 milligrams per liter.
  • The state standard and the drinking water standard can differ. For nitrate, DEQ gives 10 milligrams per liter as both the Idaho groundwater quality standard and the EPA drinking water standard for public water systems. For arsenic, DEQ gives a drinking water standard of 10 parts per billion and says the Idaho groundwater quality standard is currently 50 parts per billion. For uranium, it gives a drinking water standard of 30 parts per billion and says there is currently no Idaho groundwater quality standard. Say which standard a result is being compared with.
  • Aquifers are in categories. DEQ says the Groundwater Quality Rule (IDAPA 58.01.11) defines three aquifer categories, each with a different level of protection: sensitive resource, general resource and other resource. It says the Spokane Valley-Rathdrum Prairie Aquifer is the only aquifer designated as a sensitive resource aquifer, and that standards stricter than those in the rule can be applied to sensitive resource aquifers.
  • Private wells are the owner's job. DEQ says private wells are not regulated under the Safe Drinking Water Act and that well owners are responsible for ensuring their water is safe. It says logs for wells drilled since 1987 are on file with the Idaho Department of Water Resources.

Where to look a site up

  • DEQ's Interactive Mapping and GIS Data page links the Idaho Nitrate Priority Areas map and the DEQ Groundwater Quality Data map. DEQ describes the second as a map-based source of groundwater quality analytical data collected by DEQ or its contractors, and says it investigates groundwater quality in regional and local areas where contamination is known or suspected to have occurred.
  • DEQ's Groundwater Reports and Data page carries annual monitoring summaries, technical reports and reports listed by county.
  • For the groundwater constituents of concern in an area, DEQ points to its regional offices and the public health districts.

Getting the file

The maps and reports are public on DEQ's pages. For records that are not posted, DEQ takes requests under the Idaho Public Records Act through its Public Records Request page, which lists the groundwater quality map among the resources that can often answer a question without a formal request.

Sources

Idaho Department of Environmental Quality pages, read October 1, 2026:

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