Last month the Bureau of Land Management (BLM), U.S. Forest Service (USFS), and Great Basin Unified Air Pollution Control District (GBUAPCD) released the final joint environmental impact statement (EIS) and environmental impact report (EIR) for the proposed Ormat NV Casa Diablo IV Geothermal Development Project.
The project has been in the works, as well as in the public eye, since Mammoth Pacific, LP (MPLP) filed its original application in February 2010. Ormat NV, Inc. subsequently acquired Mammoth Pacific, and continued the application process to build a new, 33-megawatt (MW) geothermal power generating facility located within the vicinity of the existing geothermal complex off Highway 395 near Mammoth Lakes.
In addition to constructing a new, binary power plant, the proposal also includes a pipeline to bring geothermal “brine” to and from the injection wells, with up to 16 geothermal resource wells total, as well as an overhead electric transmission line to interconnect to the Southern California Edison substation at Substation Road.
The current three-plant Casa Diablo complex produces 29 MW, sold to Southern California Edison and used by, among others, customers in the Eastern Sierra. At 33 MW, the new Casa Diablo project would generate enough electricity to power 10,000 additional homes.
However, in 27 comment letters received during the public comment period earlier this year, some residents expressed concern about the impact of the new wells to the adjacent community. As many as 14 of the wells would be located in the Basalt Canyon area near Shady Rest, although that number may be reduced if a smaller number of wells produce sufficient geothermal energy to power the Casa Diablo IV plant.
Residential concern stems from the toxic gases, particularly hydrogen sulfide, released by the wells. According to a January letter addressed to the BLM, retired petroleum engineer and geologist Brigitte Berman expressed concern that, “With increased geothermal hot water or steam production in the area, the emitted gases which are heavier than air will accumulate over the recreational fields since these are structurally lower than the new wells.”
The only time hydrogen sulfide will be released from the well areas is during drilling and well testing while the wells are being constructed, Collin Reinhardt, Project manager for the BLM, explained. Nevertheless, he agreed with Berman’s evaluation that such emissions are cause for concern. If the project is accepted, GBUAPCD will create an abatement and monitoring plan for the wells, “And if the levels of hydrogen sulfide exceed state and federal standards, construction must either pursue an abatement plan to capture the gas, or stop construction altogether,” he said. Once the wells are operational, he assured, “there will be no venting of gases.”
Berman’s letter alleged that a USGS observation well, RD8, was abandoned in the past because gas emissions were considered too dangerous to continue use. Reinhardt confirmed that the well was abandoned, an official term for ceasing operation, but that was “because it wasn’t useful as a monitoring well anymore,” he said. “From what I know, I don’t think [emissions] were the reason the well was closed.”
As for the dangers associated with a geothermal plant in an area known for seismic activity, Reinhardt said that “all facilities will be held to Seismic Code D standards, the most stringent standards available, to accommodate maximum credible earthquakes in the area.” BLM requires thorough geotechnical surveys before construction, Reinhardt said, to identify any potential for movement in fault zones. So, in addition to Code D standards, “[Ormat] might even have additional conditions that would apply to the project,” Reinhardt said.
Coordinating agencies BLM, USFS and GBUAPCD are expected to issue their decisions regarding the Casa Diablo IV Geothermal Development Project in early August. The public may appeal the decision; depending on whether or not there is an appeal, construction on the new plant may begin next summer.