Water quality constituents were analyzed in water samples from 281Treasure Valley wells. The constituents included common ions (calcium magnesium, chloride, sulftate, etc.), nutrients (nitrate, ammonia, etc.), trace elements (arsenic, copper, iron, zinc, etc.), radioactive elements, volatile organic compounds (benzene, perchloroethylene, etc), bacteria, and pesticides.
In 1997, 49 (17 percent) of 281 sampling sites (wells) had one or more constituents with concentrations greater than primary Maximum Contaminant Levels (MCLs) (Neely and Crockett, 1998) . The MCLs are established by the U.S. Environmental Protection Agency (EPA) for public dringing water supplies. Constituents exceeding these standards included arsenic, bacteria, fluoride, nitrate, and some volatile organic compounds.
Nitrate is often an indicator of aquifer vulnerability because higher concentrations are generally caused by land use activities. More recent data collected between 1997 and 2000 show that 35 percent of the Statewide Program wells in the Treasure Valley shallow system had nitrate levels equal to or greater than 5 milligrams per liter, and ten percent had concentrations over 10 mg/l (Neely, 2001) . Nitrate concentrations of two mg/l generally are considered to be above background in the Treasure Valley, and 10 mg/l nitrate is the drinking water standard. The map below shows the distribution of elevated nitrate concentrations in the Treasure Valley. More information on recent water quality measurements is available from http://www.idwr.state.id.us/planpol/techserv/gwmon/status_of_gwq_tv.pdf.
Neely, K.W. and Crockett, J.K., 1998. Ground water quality characterization and initial trend analysis for the Treasure Valley shallow and deep hydrologic subareas. No. 50 Part 3, Idaho Department of Water Resources.
Neely, K., 2001. Current status of ground water quality in the Treasure Valley - July, 2001, Idaho Department of Water Resources. http://www.idwr.state.id.us/planpol/techserv/gwmon/status_of_gwq_tv.pdf.