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Description
The Steamboat Springs geothermal area is part of the discharge area for a regional groundwater flow system near Reno, Nevada. Historic hot spring and geyser activity there was second only in concentration to Yellowstone National Park in the continental United States. Hot spring and geyser activity began to decline in early 1987, shortly after a binary-type geothermal power plant began operating nearby, and coincident with well testing at a second, primary flash-type, geothermal power plant. By early 1988, shortly after the primary flash-type power plant began operating, none of the numerous spring and geyser vents contained visible water. The two power plants use production and injection wells to supply and dispose of high temperature groundwater, but there is no net production (consumptive use) of water at the binary-type facility. Comparison of the results of this study with previous studies at Steamboat Springs indicates that spring water level fluctuations caused by earth tidal stresses, changing barometric pressure or other factors (e.g., earthquakes or local precipitation events) are small, short lived, or random when compared to those caused by discharging geothermal wells. Therefore, it is unlikely that these influences have contributed to the decline in spring water levels since early 1987. The recent spring water level fluctuations and decline are not the result of seasonal variations and are not consistent with spring discharge-annual precipitation relationships noted from previous studies. Comparison of recent spring activity (e.g., discharge rates) with that during previous droughts suggests that the recent drought in western Nevada is not the principal cause of the decline in spring and geyser water levels. Though the general spring and geyser decline began before the start of the current drought, it is not clear whether or not consecutive below-normal precipitation years have contributed to the spring and geyser decline There is no evidence to suggest that the springs are influenced by a nearby therapeutic spa well. However, the results of this study suggest that discharging geothermal wells in the primary flash-type and, to a much lesser extent, the binary-type power plant well fields have been the principal cause of the decline in water levels in the springs and geysers. This conclusion is supported by: (1) observations of spring water level declines during intervals of geothermal production and water level recoveries during non-production intervals, (2) the uncharacteristically parallel behavior of many of the springs in response to geothermal production, (3) observations of increased rates of water level decline in some springs upon interruption of injection during geothermal production, (4) spring hydrographs which mimic hydrographs from observation wells whose hydraulic connection to geothermal production wells has been established, (5) the consistency between short and long-term responses of springs to geothermal production and responses predicted by well hydraulics theory, and (6) the decline in the rate of natural thermal water discharge (as springs and inflow to nearby Steamboat Creek) as compared to previous estimates, which is consistent with net production of thermal water from the primary flash-type power plant well field.
