There are numerous regulations that apply to water quality and use.
Federal: At the federal level, laws include the Clean Water Act and the Safe Drinking Water Act.
State: The Porter-Cologne Water Quality Control Act, the State Water Resources Control Board have regulations on the quality and quantity of surface water and groundwater.
Local: The MCWD, and Mono County all have regulations on the quality and quantity of surface water and groundwater.
Increased sediment loads and construction-related water quality pollutants including oils, greases, fuels, hydraulic fluid, paints, and cement washout may be released into the environment during construction. These could leach into stormwater and flow offsite, resulting in degradation of water quality downstream if a storm occurs.
Natural water sources could be impacted if drill cuttings, drilling mud, water/geothermal fluid, and additives are released from the drilling site. If geothermal fluids containing dissolved solid and minerals are released to surface waters, water quality will be affected. This could occur due to equipment failure.
Major well leaks will cause fluid to leak off-site and reach the tributary to Hot Creek, degrading water quality downstream.
If n-pentane used as a working fluid is released accidentally, it could combine with natural downstream waters and pollute groundwater if it reaches the subsurface.
There is the possibility for fluid leakages from equipment to combine with groundwater during run-off.
Drainage patterns will be altered as installation construction involves modifying topography which may lead to flooding and erosion.
Decommissioning could cause unwanted water pooling.
There are groundwater requirements for construction and decommissioning, possibly putting pressure on water resources.
Cumulative impacts
Potential construction-related water resources impacts through the accidental release of pollutants.
Accidental release of geothermal fluid may cause total dissolved solids (TDS) in lower portions of Mammoth Creek and could greatly increase the TDS in this region.
Mitigation
The drainage plan will evaluate potential changes in stormwater flow and determine measures needed to lessen or avoid the increase in stormwater runoff offsite.
Ensure sediment and other pollutants contained in well construction containment basins are not released into downstream waters by confirming that all basins are designed to contain expected flows.
All drill cuttings will be removed from each well site where on-site disposal is not available.
Ensure that storage tanks and piping for geothermal fluid storage are housed in temporary facilities able to contain spilled fluid.
The capacities of proposed containment facilities will be equal to at least twice the volume of the entire fluid contents of the power plant facility.
Equipment and vehicles will be maintained to prevent leaks from infiltrating water.
Residual Impacts
Residual degradation of water quality related to construction activities and operations are possible which could lead to contamination of surface water and groundwater.
Drainage and runoff may change due to the modification of on-site hydrology.
Based on the mitigation measures, it seems that many aspects of the project’s impact on water resources have been well represented. Strategies to prevent leakages were discussed, but more focus should be given to the increased sediment loads and construction-related water quality pollutants that are inevitable products of the project.