Feds OK Expanded Geothermal Plant Near Mammoth Lakes

The site of the Casa Diablo IV geothermal plant | Photo: BLM

A 33-megawatt geothermal plant proposed for a spot along Route 395 near Mammoth Lakes cleared a hurdle this week, as two federal agencies signed off on the project. The project must still win approval from a regional air quality board.

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The 33-megawatt Casa Diablo IV Geothermal Development project got the thumbs-up Tuesday from the Bureau of Land Management and the U.S. Forest Service in the form of a positive Record of Decision from each agency. The project, which would be built and operated by the geothermal company Ormat, now awaits approval of its joint state and federal Environmental Impact Report/Environmental Impact Statement (EIR/EIS) by the Great Basin Unified Air Pollution Control District, which nod is expected later this summer.

Casa Diablo IV would tap into the region's abundant volcanic heat to generate power by way of a number of deep wells in the area. Brine heated in those geothermal reservoirs would be piped to a generating plant east of the Mammoth Lakes turnoff on Route 395. The plant would more than double Casa Diablo's current generating capacity. Casa Diablo Units I through III have a total maximum output of 29 megawatts: Casa Diablo IV would up that to 62 in total. The power would be sold to Southern California Edison for use by local customers.

The federal approval comes despite concern expressed by locals that as many as 16 new geothermal wells in the Shady Rest Park area east of Mammoth would pose some risk of releases of hydrogen sulfide gas, a toxic gas that smells like rotten eggs. Commenters during both the scoping process and the formal comment period on the EIR/EIS expressed concern about the project's impacts on the region's abundant cultural resources, the effect of geothermal pumping on local aquifers, creeks, and hot springs, and environmental effects on the plant's East Sierra-Great Basin desert surroundings, characterized mainly by wild sagebrush steppe and Jeffrey pine forest as shown in the photo here.

The EIR/EIS authors' overall response too those comments was rather startlingly dismissive:

Many of the individual comments reflect a selective use of information, ignore overall data trends, and reflect an incomplete understanding of the geologic setting, the Long Valley geothermal system, the findings of historic monitoring, and geothermal development and operation.

The positive Record of Decision from the BLM and U.S. Forest Service, said Inyo National Forest Supervisor Ed Armenta in a press release, is "the culmination of an outstanding cooperative interagency effort that involved extensive public involvement and participation."

About the Author

Chris Clarke is a natural history writer and environmental journalist currently at work on a book about the Joshua tree. He lives in Joshua Tree.
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