On Tuesday night, Mammoth Community Water District (MCWD) presented its case against the proposed Ormat, NV Casa Diablo IV Geothermal Development Project to the public. Mark Wildermuth of Wildermuth Environmental Inc., a specialized water resources consulting firm, guided the packed audience through an overview of the project and MCWD’s concerns regarding the effects of the project on Mammoth’s cold groundwater supply.
The Casa Diablo IV project will include the construction of a new, 40-megawatt geothermal power plant, up to 16 new production and injection wells, multiple pipelines, and an electric transmission line. Most troubling to MCWD is the fact that water use at the proposed Casa Diablo IV plant will increase from the current 19,000 acre-feet to about 29,000 acre feet per year. This water will be extracted from as many as 16 new production wells, 14 of which are located in the Basalt Canyon area, many in close proximity to MCWD groundwater supply wells.
MCWD currently extracts about 2,000 acre-feet of groundwater per year from the coldwater aquifer above the geothermal aquifer, which is enough to supply more than 70% of daily water use in Mammoth.
Wildermuth explained that MCWD had voiced its concerns about the potential effect of pumping so much water from the geothermal aquifer beneath the coldwater aquifer during the comment period on the project’s Draft Environmental Impact Statement (EIS) and Environmental Impact Report (EIR). “We didn’t feel we had enough information to make a decision [about whether the project would effect groundwater],” he said.
MCWD extracts cold groundwater from fractured rock known as an aquifer using wells that range from about 400-700 feet deep. Beneath the coldwater aquifer is an area of warm water, and beneath that an area of hot, geothermal water. The Casa Diablo IV geothermal wells, which will range between 1,500-2,000 feet deep, will tap into this geothermal aquifer. Because the condition of the rock between the two aquifers is not well understood, it is possible that extracting geothermal water below the coldwater could have a detrimental effect on coldwater supply, Wildermuth explained.
If Ormat extracts geothermal water from below the coldwater aquifer, this may reduce pressure created by the hotter water, allowing cold water to migrate down through the fractured, permeable rock into the geothermal zone. “If we lose 10-20 perfect supply through gradual draining down, that’s a huge impact to the District,” Wildermuth said.
Water District General Manager Pat Hayes pointed out that this process may already be occurring. According to Hayes, the two MCWD wells closest to the proposed geothermal wells, one at Sam’s Wood Site and one at the Water District headquarters, are heating up. The production well at Sam’s Wood Site is currently 70 degrees, he said, while the monitoring well near MCWD is 99 degrees. This could be evidence of a connectivity between coldwater and geothermal zones. “We just don’t know,” said Wildermuth.
The other potential effect of geothermal pumping to MCWD’s wells is a possible degradation in drinking water quality. Sufficient pressure in the geothermal zone, which may be released when Ormat begins drilling, could push the geothermal water upward. A migration of that water upward could decay the cold groundwater quality beyond MCWD’s ability to mitigate.
Yet the Final EIS/EIR, which both the BLM and USFS recently made separate Records of Decision to approve, “basically concludes that there will be no impact to the shallow groundwater system,” said Wildermuth. However, he added, geothermal well simulations included in the EIS/EIR “did not include coldwater.” Because of the lack of information, “There is no technical basis for the certainty of the [EIS/EIR] statement that the coldwater and geothermal systems are isolated,” he said.
Wildermuth noted that any impact to the Mammoth Community’s groundwater supply might not be seen for years or even decades, and possibly only in the case of drought. By then it would be too late, he said; “We need to create some certainty up front with a monitoring and mitigation plan.”
MCWD is proposing that Ormat first conduct aquifer stress tests to determine hydraulic connectivity between the coldwater and geothermal aquifer, and second create a new and continuous monitoring plan to determine whether the project has any negative impact on the Water District’s groundwater supply. Although Ormat has agreed to work on a monitoring plan with MCWD, MCWD still plans to appeal the BLM/USFS decisions to ensure that such a monitoring and mitigation plan will be part of the project before the Great Basin Unified Air Pollution Control Board (GBUAPD) gives final approval through CEQA (California Environmental Quality Act).
“I think this monitoring program is the way to go,” said GBUAPCD Board member Larry Johnston.
“I agree with monitoring; it’s in my decision,” said Steve Nelson, Acting Bishop Field Manager for the BLM. “Your concerns were heard, and it is a condition of approval for this project.”
“If in the end a plan is not arrived at through these discussions, will the project still go forward?” MCWD Attorney Steve Kronick asked Nelson. “Ultimately, I don’t know the answer to that,” Nelson replied. Kronick pressed, “So if the District remains concerned about this project, you still may allow this project to go forward?” Nelson answered, “If the project has an adverse impact on the Water District, no.”
But Kronick pointed out that the BLM wouldn’t know whether the project had an adverse impact if there was no monitoring and mitigation plan in place to collect the necessary data. Nelson concluded that he would not approve the project “without a monitoring plan of some sort.”
Charlene Wardlow, Ormat Environmental/Regulatory Affairs Administrator, gave her own brief presentation and requested that MCWD not appeal the BLM/USFS decisions. Instead, she invited MCWD “to work collaboratively and constructively to find solutions. Why waste money on legal recourse?” she asked.
One audience member agreed: “I’d rather see all my water money going toward a collaboration rather than a battle in court,” he said.
“Unfortunately, those Records of Decision set in place certain, very short timelines to appeal [the project],” replied Kronick. “The BLM and Forest Service have put the Water District in a very untenable position. It seems to me that if there was a real desire to work on an acceptable monitoring plan, those efforts would have been taken before the Records of Decision were issued. Now the Water District has to act as though with a gun to its head.”
MCWD had nothing to report from its closed session that followed the public presentations, but MCWD Environmental & Public Affairs Officer Irene Yamashita said, “We will [still] be appealing the Records of Decision.”
GBUAPCD will consider approval of the Casa Diablo IV project on Sept. 16.