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Soils and Geological Resources Mitigation Measures

Mitigation measures to avoid or reduce impacts to soils and geological resources from low-head hydropower development.

The following are examples of mitigation measures that could be applied to reduce impacts of a project on soils and geological resources depending upon site- and project-specific conditions. Impacts to soils and geological resources are related to the project activities (e.g., land disturbance, erosion) and the extraction of raw materials for project use. Many impacts can be reduced or avoided when taken into account during the siting and design phase.

Develop a final set of mitigation measures for any project in consultation with the appropriate federal resource management agencies and with stakeholders. Conduct these consultations as part of the project development process and preferably prior to final project siting and design.

Siting and Design Mitigation Measures

Siting and design considerations that mitigate impacts include:

  • Identify and avoid unstable slopes and local factors that can cause slope instability (groundwater conditions, precipitation, seismic activity, slope angles, and geologic structure).
  • Identify soil properties, engineering constraints, corrosive potential, and facility design criteria.
  • Develop a site grading and management plan to identify areas of disturbance, areas of cut and fill, slope during and after grading, existing vegetation, and measures to protect slope, drainages, and existing vegetation in the project area.
  • Develop an erosion control and revegetation plan to delineate measures to minimize soil loss and reduce sedimentation to protect water quality.
  • Minimize the amount of land disturbed as much as possible, using existing roads, disturbed areas, and borrow pits and quarries when possible. Minimize vegetation removal.
  • Stage construction to limit the exposed area at any one time.
  • Place access roads to follow natural topography and avoid or minimize side hill cuts. New roads should avoid going straight up grades steeper than 10%. Design roads with eventual reclamation in mind.
  • Use paved roads for construction traffic, if feasible.
  • Locate facility structures to comply with the setback requirements of the site grading and drainage plan to avoid disturbing natural watercourses.
  • Design runoff control features to minimize soil erosion.
  • Construct drainage ditches only where necessary. Use appropriate structures at culvert outlets to prevent erosion.
  • Use special construction techniques in areas of steep slopes, erodible soils, and stream crossings.

General Mitigation Measures

General mitigation practices and principles that could apply to any or all phases of a low-head hydropower project include:

  • Use fugitive dust abatement techniques on unpaved, unvegetated surfaces to minimize windblown erosion.
  • Provide temporary stabilization of disturbed areas that are not actively under construction.
  • Apply erosion controls such as jute netting, silt fences, and check dams to prevent/minimize soil erosion from vehicular traffic and during construction activities.
  • Maintain vegetative cover within road rights-of-way (ROWs) to prevent erosion and periodically monitor ROWs to assess erosion.
  • Clean and maintain catch basins, drainage ditches, and culverts regularly.
  • Keep equipment and vehicles within the limits of the initially disturbed areas.
  • Conduct routine site inspections to assess the effectiveness of and the maintenance requirements for erosion and sediment control systems.

Project Phase-Specific Mitigation Measures

Mitigation measures specific to a particular phase of a low-head hydropower project include:

Construction

  • Avoid creation of excessive slopes during excavation and blasting operations.
  • Obtain borrow material from authorized and permitted sites.
  • Dispose of excess excavation materials in approved areas to control erosion and minimize leaching of hazardous materials.
  • Save topsoil removed during construction to use in reclaiming disturbed areas.
  • Stabilize soils during final landscaping of the project site.

Decommissioning/Site Reclamation

  • Backfill any foundations and trenches, preferably with excess excavation material generated during the construction phase.
  • Use topsoil removed during the beginning of the project or during decommissioning activities to reclaim disturbed areas.
  • Reestablish the original grade and drainage pattern to the extent practicable.
  • Stabilize all areas of disturbed soil using weed-free native shrubs, grasses, and forbs.