The implications of UIC and NPDES regulations on selection of disposal options for spent geothermal brine

This document reviews and evaluates the various options for the disposal of geothermal wastewater with respect to the promulgated regulations for the protection of surface and groundwaters. The Clean Water Act of 1977 and the Safe Drinking Water Act Amendments are especially important when designing disposal systems for geothermal fluids. The former promulgates regulations concerning the discharge of wastewater into surface waters, while the latter is concerned with the protection of ground water aquifers through the establishment of underground injection control (UIC) programs. There is a specific category for geothermal fluid discharge if injection is to be used as a method of disposal. Prior to February 1982, the UIC regulations required geothermal power plant to use Class III wells and direct use plants to use Class V wells. More stringent regulatory requirements, including construction specification and monitoring, are imposed on the Class III wells. On February 3, 1982, the classification of geothermal injection wells was changed from a Class III to Class V on the basis that geothermal wells do not inject for the extraction of minerals or energy, but rather they are used to inject brines, from which heat has been extracted, into formations from which they were originally taken. This reclassification implies that a substantial cost reduction will be realized for geothermal fluid injection primarily because well monitoring is no longer mandatory. The Clean Water Act of 1977 provides the legal basis for regulating the discharge of liquid effluent into the nation's surface waters, through a permitting system called the National Pollution Discharge Elimination System (NPDES) Discharge quantities, rates, concentrations and temperatures are regulated by the NPDES permits. These permits systems are based upon effluent guidelines developed by EPA on an industry by industry basis. For geothermal energy industry, effluent guidelines have not been formulated and are not currently scheduled. There, are however, water quality standards that control the quantity and quality of wastewaters discharged into surface waters. These standards are established by the states in concert with EPA, and frequently result in NPDES conditions more restrictive than those based on effluent guidelines