P.E. Eddie L. Thomason Two-thirds of Washington state's population. and virtually all of its rural residents depend on groundwater for their drinking water. Popular interest in public health and water's beneficial uses has led to state standards that forbid degrading groundwater quality and limit contaminant concentrations in drinking water. For example, public health standards limit nitrate in drinking water to 10 milligrams per liter, expressed as nitrogen, or 45 milligrams per liter as nitrate. A Vital Resource, EB1622, and other bulletins in the Clean Water for Washington series available at your county extension office.
Livestock wastes are a potential source of groundwater contamination.
Modern livestock production, confining larger herds in smaller spaces, has increased manure disposal problems. Collecting, storing, hauling, and applying manure to fields generally represents net production costs, but is usually the least-cost system for livestock waste disposal. Unpaved feedlots develop a compacted manure and soil seal 2 inches to 4 inches thick. Compacted manure above the manure-soil seal has almost no oxygen for aerobic decomposition. In this anaerobic condition, microorganisms reduce the amount of nitrate available to leach downward by converting the nitrate to nitrogen gas, which escapes to the atmosphere.