Geothermal/Wetlands and Riparian Zones

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Geothermal Wetlands and Riparian Zones

Wetlands and Riparian Zones
Present, Potentially Affected

The Clean Water Act(CWA) (33 U.S.C. 1251-1387) sets standards for the chemical, physical and biological properties of all bodies of water in the United States. It mandates a permitting system and is responsible for programs to mitigate the impacts of certain pollutants.

CWA Section 404 defines “discharge of dredged material" to narrow wetland drainage exemptions. Allowable actions that degrade or destroy wetlands include, “redeposit, of dredged material, including excavated material, into waters of the United States which is incidental to any activity, including mechanized land clearing, ditching, channelization, or other excavation.” While section 404 regulates discharge into wetlands and riparian zones, it does not regulate groundwater depletion or wetland loss.

Water quality standards (WQS) uphold wetland integrity through specific scientific guidelines and carry out (CWA) requirements. Wetland (WQS)’s include case-by-case narrative standards opposed to quantitative standards to account for geographic and geologic variability when comparing water flow rates.

Wetlands and Riparian Zones Impacts & Mitigation

Shallow water and abundant plants supply nutrients to, “microbes, plants, insects, amphibians, reptiles, birds, fish and mammals”, making wetlands a diverse ecosystem. Wetland habitats become ideal for bird nesting, breeding, and migration. Mitigation to these areas includes operational and construction methods to reduce impacts. However, limiting wetland surface disturbance may have the biggest positive impact to these ecosystems. Wetland mitigation aims to repair natural wetland degradation from geothermal construction or operational activities. Typical impacts and mitigation measures include:

Construction:

  • Infrastructure development is limited near wetlands, playas, riparian zones, 100-year floodplains and other surface waters. All exceptions are case-by-case.
  • Improve existing seeps, springs and/or meadows access and install piping to maintain water flow from the wetland and riparian zones. Use pipe and rail fencing for the wetlands perimeter to discourage wildlife and unauthorized access. Fencing encourages riparian restoration. Install trough guzzlers to water wildlife and livestock. In dry months, monitor the trough’s water levels to ensure water presence.
  • To mitigate low spring flows, install a spring box and piping to direct water to a discharge point. In the event of excessive pumping, this mitigation measure will not revive dry groundwater supplies.
  • To mitigate soil impacts and decrease indigenous aquatic species impacts, place heavy equipment on mats when near wetlands and riparian zones.

Monitoring:

  • Conduct surveys before, during and after drilling activities to measure geothermal and well temperature, flow, stage or equivalent, and basic thermal water chemistry. Increase monitoring if land and reservoir adverse effects are found.
  • Landscape, rapid and intensive site assessments evaluate biological and hydrogeomorphic aspects using geographic information system (GIS). These assessments establish riparian functionalities and ecosystem impacts. This information is used to forecast and track geothermal development impacts on the area.

Environmental Protection Agency-Wetlands Monitoring and Assessment

Geothermal Reservoirs:

  • To mitigate surface water effects, alter geothermal fluid pressure and volume inside injection fluid and production wells, terminate one or more production wells, alter the geothermal fluid injection depth, or relocate production wells.
  • If wetland or other surface water effects persist, site relocation may occur.

Restoration:

  • Recharge, rebuild, repair, or re-establish wetland and riparian functions.
  • These functions include enabling erosion and flood control, regulating groundwater levels and flow rates, protecting drinking water, acting as storm surge buffers, and replenishing soil nutrients.