Mammoth's water district will appeal Casa Diablo geothermal plant expansion plan

Mammoth's local water district is filing an appeal of the environmental document outlining the plans for a sharp expansion of the Casa Diablo geothermal plant's electric power generation capacity. The plant is located east of Mammoth Lakes, off of Casa Diablo Road.

According to a news release issued Tuesday by the Mammoth Community Water District Board of Directors, "the district has authorized the filing of appeals to the decisions issued by the U.S. Bureau of Land Management and the U.S. Forest Service concerning the "Final Joint Environmental Impact Statement /Environmental Impact Report (Final EIS/EIR)" for the Casa Diablo IV Geothermal Development Project.

The district is holding a special meeting to inform the public about the consequences of the project’s potential impacts on Sept. 3 at 7 p.m. in the District Board Conference Room located at 1315 Meridian Blvd., the news release states. Water users and the general public are encouraged to attend.

Another geothermal-related meeting, this one with the local air pollution control district, will be held on Sept. 16 when the Great Basin Unified Air Pollution Control District (GBUAPCD) will be meeting to consider certification of the Final EIS/EIR under the California Environmental Quality Act (CEQA) at 10:30 a.m. in Suite Z in Mammoth Lakes.

"The Mammoth Community Water District (Water District) has serious concerns about the negative impacts the proposed Casa Diablo IV Geothermal Plant Expansion Project (CD IV) could have to local groundwater and surface water resources," the news release states. "To protect the water resources used by the community, the District will be filing appeals to the BLM and USFS decisions to approve the proposed CD IV expansion project.

"In order to protect the community’s water supply, the Water District is seeking a comprehensive, robust monitoring and mitigation plan with “trigger points.” The plan would protect the community’s water resources through the drilling of monitoring wells, aquifer stress tests ahead of project construction, inclusion of “trigger points” to reduce or cease CD IV operations if the project impacts the Water District’s groundwater and surface water supplies, collection of additional water chemistry data, and the implementation of a long-term monitoring program prior to construction and operation of the proposed project.

"Background: The proposed CD IV expansion project consists of up to 14 new geothermal wells for production of geothermal fluids (hot water from geothermal aquifers) in closer proximity to existing Water District groundwater supply wells than most of their existing wells.

"Geothermal fluid production will increase from 19,000 acre-feet/year to 29,000 acre-feet/year (12,000 gpm to 18,000 gpm). Such production dwarfs the 2,000 acre-feet/year or so of Water District groundwater extractions from the cold water aquifer above the geothermal aquifer.

"At present this groundwater supplies over 70% of the daily water use in Mammoth. The mining of heat in the hot water below the coldwater aquifer could reduce pressures and increase the likelihood of coldwater migrating downward through fractured rock into the geothermal zone. This could be catastrophic for Mammoth’s groundwater supplies.

"In addition, the project could negatively impact surface water flows in Mammoth Creek at a gauging station used to regulate the Water District’s surface water supply. These impacts could occur from pressure changes in the aquifers and alteration of the natural flow patterns of geothermal fluids.

" Long-time residents of the area have noted the disappearance of surface water ponds and hot springs in proximity to the existing Casa Diablo geothermal plant which started production in the 1980s.

"The Water District has maintained throughout the environmental review process that critically important data were missing, that large amounts of important data were being withheld as “proprietary” thereby stifling analysis, and that the hydrogeologic modeling process was flawed.

"These concerns were not adequately addressed in the process and there are no mitigation measures should the project hurt Mammoth’s water supply. With apparent pressure from the Secretary of Interior in Washington, the environmental document was pushed to rapid completion with decisions issued by both BLM and USFS within just a week after significant critical comments were submitted on the Final EIS/EIR and with no public hearings.

"Without the necessary scientific data, the Final EIR/EIS for the proposed project concludes that there will not be any significant impacts to the cold water system, stating there is no connection between the two aquifers even though some of the District’s wells have water temperatures over 90 degrees and water chemistry samples collected by the USGS show that the geothermal and coldwater aquifers are connected. Hydro-geologists reviewing the environmental documents and additional reports for the Water District have not found adequate scientific data to support the conclusion that the proposed project will not impact the community’s water supply.

"Currently, the proposed project does not include any provisions for avoiding potential impacts to the shallow cold water system through monitoring and mitigation actions. The project cannot proceed without the GBUAPCD approval.

"The project proponent, ORMAT, is now being asked to work with the Water District to thoroughly address all of the Water District’s concerns and develop an acceptable monitoring and mitigation plan."