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Coso completes first year of Hay Ranch pumping

January 10, 2011

Coso Operating Company has completed its first year of pumping water from its Hay Ranch site to its geothermal power plant, and it’s time to check the numbers.
Coso started pumping 1,860 gallons per minute of water on Dec. 25, 2009 and as part of the Conditional Use Permit allowing it to do so, the project has to be monitored, recalibrated and potentially changed due to any harmful environmental impacts. The CUP issued by Inyo County stated that the project would have to be evaluated and recalibrated prior to the one-year benchmark before further pumping would be allowed.
The Hay Ranch property is near Coso Junction and sits atop the Rose Valley aquifer nearly nine miles from the geothermal plant. The pumped water will be added to the geothermal reservoir that is drying up, due to evaporation and other factors. This geothermal reservoir is basically the hot water that is turned into steam, pressurized and used to turn turbines, which in turn create electricity.
The initial CUP allowed for 1.2 years of pumping at a rate of 3,000 acre-feet per year. This was a trial period of sorts where the source of the pumped water, the Rose Valley aquifer, would be stressed by the pumping and measurements would be taken in that full year. The point was to be able to gain a more accurate picture of the aquifer and how it would react to the pumping.
One of the key components and contentious issues of the project was the model of the Rose Valley aquifer – its size and flow. The property has been left fallow for decades with little record existing of how past water extraction had affected the aquifer or how the water extraction would affect the ecosystems downstream from Hay Ranch, specifically Little Lake and surrounding riparian areas.
A third-party consultant, Daniel B. Stephens and Associates, was hired at cost to Coso, as per the CUP, to evaluate and recalibrate the model.
According to a memo from the Inyo County Water Department, the initial model for the project “was generally sound and gave a reasonably accurate picture of how the Rose Valley aquifer system would respond.”
According to Stephens, “the recalibrated model indicates that pumping at the full proposed rate (4,839 acre-feet per year) could continue for 2.4 years past the end of the first year of pumping. According to the recalibrated model, the currently permitted rate of pumping of 3,000 Continued from front page
acre-feet per year could continue for 4.1 years before significant impacts to Little Lake would occur.”
The CUP states that any mitigation must “meet the criteria that Little Lake surface waters will not ever experience a greater than 10 percent reduction in inflow as a result of the proposed project.”
Manager of the geothermal plant Chris Ellis said Friday that the project is working and Coso is considering it a success.
Ellis added that the modeling by Stephens is not yet complete and Coso will pump at the current rate of 3,000 acre-feet per year until the Inyo County Water Department proposes to up the amount.
“We’ll be working with the Water Department to see what the best operations will be for business and the environment,” Ellis said.
The model by Stephens should be completed by March and made scrutiny to a 30-day public review and comment period.

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