Program Upper Snake River Basin Study Unit Ground Water Ground-water discharge into the middle Snake reach, from Milner Dam to King Hill, contributes a large percentage of the nitrate transported from the upper Snake River Basin at King Hill. The highest concentrations of nitrate in ground water are found in areas of urban and irrigated agricultural land use and where the water table is relatively shallow. Nitrate concentrations exceeded the drinking water standard of 10 milligrams per liter in ground-water samples collected from the Idaho National Engineering Laboratory, the Fort Hall area north of Pocatello, and agricultural areas surrounding Burley. Feedlots, dairies, fish hatcheries, and municipal and industrial discharges are the principal sources of nitrogen to ground and surface water in the basin. Water from domestic wells contained the highest nitrate concentrations compared to water from industrial and public-supply wells.
Nitrate concentrations are lower in deeper wells and higher in shallow wells.
Nitrogen from domestic septic systems is less than one percent and from precipitation is 6 percent of the total nitrogen input in the basin. Bingham, Cassia, Gooding, and Twin Falls counties had the highest amounts of excess nitrogen input in the basin.