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Geothermal Energy Production Wastes
TENORM
Using geothermal energy requires drilling deep holes (boreholes) and inserting pipes for pumping high-temperature fluids from the ground. The rocks that contain the high-temperature fluids may also contain minerals, which tend to form a scale inside the pipes and production equipment. If the rocks also contain radionuclides, such as radium, the mineral scale, production sludges, and waste water will contain TENORM. The primary radionuclides produced with the geothermal fluids are radium-226 and radium-228.
Waste Generation
Geothermal energy currently makes a relatively minor contribution to total U.S. energy production. The primary geothermal development sites in the U.S. are the Geysers, in Sonoma County in northern California, and the Imperial Valley in southern California. The only significant TENORM wastes from geothermal power production are the solid wastes originating from the treatment of spent brines such as in Imperial Valley. The hot saline fluids from geothermal reservoirs in that area may have a dissolved solids content approaching 30 percent by weight. The estimated annual generation rate of geothermal energy production waste is 54,000 metric tons (MT).
The table below shows the estimated average activity in geothermal wastes, based on data from southern California geothermal power production facilities:
| Wastes | Radiation Level [pCi/g] | ||
|---|---|---|---|
| low | average | high | |
| Geothermal Energy Waste Scales |
10 | 132 | 254 |
The Radiation in TENORM Summary Table provides a range of reported concentrations, and average concentration measurements of NORM associated with various waste types and materials.
Disposal and Reuse
Because of unsuitable physical characteristics, solid geothermal wastes are not reused, but disposed of in solid waste landfills. A few facilities are also considering process of these wastes to extract valuable minerals (gold, sliver, and platinum).
About 96 percent of the national geothermal electric generating capacity is in the State of California and the southern sites generate the most solid geothermal waste. In addition, the disposal site associated with the Imperial County facilities is useful for characterizing a generic facility.
This facility contains 400,000 m3 of geothermal solid waste (about 740,000 MT), approximately 20 years of geothermal waste filter cake from plants operating in Imperial County. The disposal area occupies 100,000 square meters, with a waste depth of 4 meters. (Closed (full) sites have about 2.4 m of soil added to reduce radon emissions to within regulatory limits.)
This site is much larger than disposal sites needed to accommodate the geothermal waste produced in other states, where geothermal energy production is much less.
