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Transmission Geology and Minerals

Geology and Minerals
Present, Potentially Affected

Before transmission corridors and substations can be constructed, a geologic hazard and technical survey must be conducted. The United States Geological Survey (USGS) agency houses geological overviews of the United States, however for a specific area evaluation, each state has a geological survey agency to conduct site reviews and access historical maps. This comprehensive survey gathers data on several categories.

These surveys determine the compatible engineering approaches for the area’s geologic properties. Surface conditions are assessed for landslides, slope instability, earth and debris flows, and ground disturbances by reviewing geologic and aerial maps. To obtain subsurface information, data is collected from water well logs, soil samples, and existing data from nearby transmission projects. Each proposed tower location is independently evaluated to determine slope stability.

Geology and Minerals Impacts & Mitigation

Geologic properties determine geologic hazards and avoidance areas to enable the project’s corridor. Some areas may be more susceptible to landslides, unstable slopes, or subsistence than other areas. Historic or active mines pose safety hazards and impact transmission line site selection. Mines may also be discovered after construction has begun.

The following outlines typical impacts and mitigation measures:

Geologic hazards

  • To mitigate site hazards, avoid areas where ground shaking, liquefaction, landslides, karst subsistence, groundwater withdrawal, underground mining, historic mining, and active mining occur. The technical and hazardous geological survey identifies these areas.
  • If active mines cannot be avoided, review whether or not project facilities will obstruct mineral resource access or pose safety threats to employees or private landowners.
  • Relocate towers and roads if they are proposed within active landslides, bedrock hollows, or other geologic hazard areas.
  • Identify unstable slopes or local factors that could induce slope instability to mitigate unforeseen project consequences.
  • Develop a contingency plan for unavoidable geologic hazard areas to decrease potential pipeline spill impacts or project failure when connected to the grid.


  • To decrease landslide hazards, refrain from constructing towers and substations in these areas. If construction is unavoidable, mitigate landslides by excavating unstable material to even the slope, removing driving forces near the landslide’s top, constructing retaining walls, adding stabilization fills, and installing rock bolts or wire mesh along the rock face.
  • Control runoff and erosion by installing ditches, water bars, cross drainages, or roadside berms
  • Follow the natural topography and land contour to mitigate large cut and fill slopes.
  • Avoid sand dune areas to mitigate erosion and potential tower relocation.
  • Utilize existing access roads to decrease surface disturbance and total number of acres needed to undergo the geologic survey.
  • To decrease erosion, equip new access roads with appropriate drainage dips, side ditches, slope drains, and velocity reducers.
  • Stabilize excess soil or disperse it around tower construction sites. During grading operations, minimize soil side casting.
  • Design tower foundations to reduce the potential for soil settlement and compaction.


  • During construction, coordinate with mine owners and operators to avoid peak mining season and high volume, earth-moving periods. Operational mitigation includes spanning the mine.
  • To mitigate subsistence, review tower and substation final locations with mine owners and operators.