Don’t give free ride to geothermal energy

A drill bores deeper to tap into geothermal geysers underneath the mountains of southern Lake County near Anderson Springs.
A drill bores deeper to tap into geothermal geysers underneath the mountains of southern Lake County near Anderson Springs. Sacramento Bee file

California’s landmark legislation calling for 50 percent renewable energy by 2030 is helping the state grapple with clean energy needs in the face of climate change and population growth. Geothermal energy – using heated water and steam from deep below the earth’s surface to produce electricity – is a viable source of clean energy from the north state to the Sierra Nevada to Southern California.

But at what cost to the environment and local water supplies?

Unfortunately, the impacts of geothermal operations on California’s groundwater supplies are largely unstudied and unknown. The potential impacts of geothermal pumping on limited water supplies remain a very real and unquantified threat.

The town of Mammoth Lakes serves as a worrisome example of geothermal energy production in conflict with local water supplies and the environment. Analysis of its groundwater basin suggests that geothermal reservoirs could be connected to regional water aquifers, potentially affecting the quality and quantity of local supplies.

The Mammoth Community Water District has wells that record hotter temperatures the closer they are to geothermal production wells; one includes trace geothermal water quality elements. The findings indicate that geologic layers between the deep geothermal zones and the shallower groundwater basins above them may be connected.

If fractured rock allows flows between the two zones, then groundwater supplies could be reduced, degraded or both as geothermal pumping increases. This is a potentially serious problem, considering that Mammoth Lakes and many other regions across the state are almost entirely dependent on groundwater as surface water diminishes.

To make matters worse, recent analysis by the U.S. Geological Survey has revealed an increase of tree deaths in the area, rising soil temperatures and hydrogen sulfide concentrations that can be attributed to geothermal production.

Clean energy must not come at the cost of the water supplies that serve our communities, or negatively impact other environmental resources. When projects do impact the environment and natural resources, the law requires that those impacts be mitigated.

Agencies responsible for reviewing and approving geothermal projects must not simply expedite project approval, but instead must carefully evaluate their potential effects. For this reason, state and federal elected officials, community groups and water agencies like ours are calling on geothermal companies and their project proponents to investigate groundwater and environmental resources, and to provide adequate mitigation measures to ensure sustainable and safe water supplies for surrounding communities.

There is a right way and a wrong way to develop clean energy sources. As California seeks to expand geothermal projects, they must ensure the long-term availability of essential groundwater resources.

Patrick Hayes is general manager of the Mammoth Community Water District.