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Geothermal Soils

Present, Potentially Affected

The Soil and Water Resources Conservation Act (SWRCA) (16 U.S.C. 2001 et seq.) allows for these three actions to occur:

  • “Appraises the status and trends of soil, water, and related resources on non-Federal land and assesses their capability to meet present and future demands;
  • Evaluates current and needed programs, policies, and authorities; and
  • Develops a national soil and water conservation program to give direction to USDA soil and water conservation activities.”

Natural Resources Conservation Service-Soil and Water Resources Conservation Act

Sand, silt and clay are the 3 common types of soil. Most often, the soil type is a hybrid of 2 or 3 categories. Sand has the largest particles, while clay has the smallest. These 3 categories are consequently broken up into 12 different soil types that are classified by their physical, chemical or biological properties. Soil types are measured by how much water they can hold. Soil identification at the geothermal site can predict soil erosion, sedimentation and reclamation procedures.

Soil Basics-What makes soil, a soil?

Soils Impacts & Mitigation

Geothermal construction and land maintenance activities have significant impacts to soils. Typical impacts and mitigation measures include the following:


  • To mitigate erosion after construction, add silt fencing, diversion ditches, and water bars.
  • Speed limit will be 30 mph on unpaved access roads and will be watered down.
  • In wet conditions, add extra gravel to mitigate rutting, compaction and road deformations. To ensure proper care and safety of vehicles, if ruts are deeper than 4 inches in wet conditions, close the road until conditions improve.
  • Along transmission lines, use existing roads to mitigate unnecessary soil erosion. If access roads need to be constructed, follow the existing contour and slopes. Site drainage and runoff management plan compliance reduces erosion and off‐site sedimentation.
  • To mitigate soil compaction, use existing compacted sites such as landings, skid-trails, truck turn-arounds, or road surfaces for drilling sites.
  • Avoid unstable, steep, cut-and-fill excavation and site leveling slopes and sensitive soils.

High Erodible Soils:

  • To stabilize road slopes, minimize the surface area and keep cut slopes as steep as possible. Do not lay the slopes back and use aggregate, asphalt concrete, penetration oil treatment to mitigate erosion.
  • For increased mechanical stabilization, use geotechnical materials such as jute netting and punched straw. Clear any debris at the base of the fill slopes and on the perimeter, use a sheeps-foot type roller to mitigate erosion. Use these methods for roads that require stream crossings adjacent to streams, exceed 6% grades and areas with 30% or more side slope. Do not use fills with 55% or more side slope grade.
  • Use up to three feet of aggregate to terrace compact fill slopes between 40% and 55% grade. This reduces land slides and soil erosion


  • To protect wetlands and drainages, install silt fences where the road passes through poorly drained areas and where sediment drains into a wetland.
  • Dispose of sediment offsite

Storm water:

  • Prepare a storm water pollution prevention plan
  • Use culverts, ditches, and water bars to divert storm water from well pads and power plant. Ditch slopes and spacing depend on soil types.
  • Before constructing rigs, install a berm to capture rainwater and spilled geothermal fluids. This decreases excess liquids on site.

Top Soil:

  • Save and store topsoils on an approved site in stockpiles for reclamation use. In moist, clay soils, removing topsoils and vegetation decreases soil compaction during construction.
  • Stockpiles are not to exceed two feet in height to promote healthy ecosystems for organisms living in the soil. Cover the piles to mitigate wind erosion. Contour the stockpiles when placed atop filled areas during reclamation to allow restoration to occur.


  • Reclaim disturbed areas soon after completing project work.
  • Storm water management actions for pre-interim reclamation can occur before the final wells are built. These actions happen early in the process to stabilize surface water flow and to mitigate disturbed and adjacent areas from erosion and siltation. All equipment and personnel vehicles will be parked on site to decrease widespread degradation. If restored and reclaimed areas need to be inspected or accessed for operation, adverse restoration affects will occur. Begin the restoration process after the area has become dormant.
  • To reclaim reserve pits, the pits must be at least 50% underground to mitigate dike failures and all fill dikes are to be compacted in the lifts.
  • On Bureau of Land Management (BLM) managed lands, use weed-free seed mix to meet reclamation standards and fence these areas to discourage livestock until final reclamation occurs.


  • Cultivate seedbed areas four to six inches 24 hours before seeding will occur. Loosen the soil with dozer tracking to make seed germination micro-sites.


  • Temporary mulching controls erosion, creates vegetation micro-sites, and retains soil moisture. It is contrived of hay, small-grain straw, wood fiber, live mulch, cotton, jute, or synthetic netting. To mitigate diseases and invasive organisms, mulch will be free from mold, fungi, noxious or invasive weed seeds.
  • If straw mulch is used, the fibers will be long enough to provide crimping and best coverage.