BulkTransmission/Soils

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Transmission Soils

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.”

http://www.nrcs.usda.gov/wps/portal/nrcs/detail/national/technical/nra/?cid=nrcs143_014220

Sand, silt and clay are the three 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 along transmission line corridors and at construction sites can predict soil erosion, sedimentation and reclamation procedures.

https://www.soils.org/discover-soils/soil-basics/what-makes-soil-soil

Soils Impacts & Mitigation

Transmission line construction and land maintenance activities impact soil quality by causing soil compaction. This leads to low oxygen levels, which affects plants and seeds from obtaining optimal growing conditions. Typical impacts and mitigation measures include the following:

Soil Management Plans

  • These documents typically outline onsite management, proper handling techniques, sampling processes, and impacted soil disposal methods. Sample and evaluate any contaminated soil during construction and operating project phases. Certified agencies will determine if further assessment is warranted.

Reclamation

  • 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.
  • Use weed-free seed mix to meet reclamation standards and fence these areas to discourage livestock until final reclamation occurs.
  • Re-contour excavated areas to discourage water collection. Re-vegetate these areas and grade them to reflect a natural appearance.
  • Only use fertilizer, wood or straw mulches, tackifying agents, or soil stabilizing emulsions with landowner or land management agency approval.

Erosion

  • To mitigate erosion, add silt fencing, diversion ditches, and water bars.
  • Post speed limits to be 30 mph or less on unpaved access roads. Water these areas down.
  • In wet conditions, add extra gravel to mitigate rutting, compaction and road deformations. To ensure proper care and safety of vehicles in wet conditions, close the road if ruts are deeper than 4 inches. Reopen the road when 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 and gully formation, use road ripping, frequent water bars, and cross ditching (e.g., rolling dips). Conduct ripping patterns to follow a crossing, diagonal, or undulating sequence of tine paths.
  • Avoid unstable, steep, cut-and-fill excavation; site leveling slopes, and sensitive soils.

Construction

  • Design transmission tower footings and roads for specific soil conditions. Conduct soil assessments to determine tower and road placements. These assessments minimize soil impacts.
  • During site planning, conduct surveys to locate active and inactive landslides and bedrock hollows. Avoid tower placement in these areas.
  • Use existing access roads, limit road upgrades, and avoid widening trails to decrease vegetation and soil impacts.
  • Avoid construction near outstanding, stagnant or impaired water and streams. Decreased riparian area development not only enables biodiversity and un-compacted soils, but also limits erosion and sedimentation transport.
  • Follow the existing land contours and terrain, especially in areas with steep terrain.
  • Construct new roads on ridge tops; stable upper slopes, or wide valley terraces. Avoid slopes steeper than 70%.
  • Avoid project development in wet conditions. Enforce travel and work restrictions. If wet areas and conditions cannot be avoided, use wide-track or balloon tire vehicles and equipment, geotextile cushions, pre-fabricated equipment pads, and other weight dispersing materials to minimize soil damage.
  • Install contour berms and trenches around vehicle service and refueling areas, chemical storage and use areas, and waste dumps to fully contain spills. Use liners to prevent seepage into ground water.
  • Close inactive access roads to reduce long- term effects on sensitive resources.

Sedimentation

  • To protect wetlands and drainages, install silt fences where the road passes through poorly drained areas and where sediment drains into a wetland. In other areas, install straw bales and interceptor trenches prior to the rainy season. Monitor and maintain these structures throughout construction phases.
  • Dispose sediment accumulations offsite.

Storm water

  • Prepare a storm water pollution prevention plan.
  • Use culverts, ditches, and water bars to divert storm water from tower pads and substations. Soil types determine the appropriate ditch slopes and spacing.

Topsoil

  • 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.
  • Stabilize sub-soils onsite with weight dispersion mats, and erosion control measures, such as surface filling and back dragging. After construction is complete, re-grade and re-contour the area, replace topsoil, and reseed. End-haul soil if full-bench construction methods are used.
  • Stockpiles are not to exceed two feet in height to promote healthy ecosystems for organisms living in the soil. Cover the piles with plastic to mitigate wind erosion. Contour the stockpiles when placed atop filled areas during reclamation to allow restoration to occur. Avoid placing these materials near sensitive soils and habitats.