ABSTRACT
Underground injection for the disposal of hazardous substances is based on simple hydrogeologic principles. Sedimentary basins are characterized by thousands of feet of relatively undisturbed, layered, water-bearing sedimentary rocks. Monitoring wells are also required in aquifers that serve as a source of drinking water, to detect fluid movement or pressure from the injection. Monitoring may also be required in the first aquifer overlying the confining zone, as well as quarterly sampling for groundwater quality. The siting of an underground injection well initiates at the regional level, is followed by localized studies, and then focuses upon the immediate well location. Siting must include the fulfillment of certain general geologic and hydrogeologic requirements. Aquifer exemptions are intended to apply to cases where an aquifer or portion of an aquifer is so inaccessible or disrupted by mining, energy production, or contamination that it would make little sense to develop the aquifer as a source of drinking water.
