Erosion is the process by which water and wind change the natural surface of Earth and can occur on varying scales. For example, on a large scale the flow of the Colorado River cut the Grand Canyon from the surrounding rock over many millennia, and on a much smaller scale a quick breeze can blow soil across a dry street in an instant. Human operations can accelerate erosion by disrupting the natural balance that keeps natural erosion in check.
There are two main types of erosion: chemical and physical. Removal of rock or soil as clastic sediment is referred to as physical erosion; this contrasts with chemical erosion, where soil or rock material is removed from an area by dissolution. These direct effects can often lead to broader consequences, including shrinking habitats for animals, accumulation of sediments, the removal of nutrients and other negative effects.
The initial construction phase of an oil and gas construction project is considered an environmentally dangerous period of development because the land is cleared of vegetation and graded to create a proper surface for construction. The removal of natural vegetation and topsoil makes the exposed area particularly susceptible to erosion, causing transformation of existing drainage areas and disturbance of sensitive areas. To protect the minimize and mitigate the damages from erosion, Erosion Control Regulations have been established locally. Violations that affect water quality can compromise regulatory compliance and overall project costs, leading to the suspension or total shutdown of projects as well as substantial fines to the operator. For example, the Pennsylvania Department of Environmental Protection recently fined a natural gas production company $565,000 in civil penalties and reimbursement costs, in part because of erosion and sediment control violations1. The agency requires that the operators develop an erosion and sedimentation control (E&SC) plan that meets local the standards and specifications.
An effective E&SC starts in design phase of an oil and gas construction project, the first step is to assess the site and identify aspects of the topography and soil conditions that might accelerate soil erosion. For example, steep slopes are more prone to soil erosion than flat areas, and some soil types are more prone to erosion than others. Any bodies of water near the site are also at risk of increased sedimentation, the process by which soil eroded from a production site settles into water nearby through surface runoff. Sedimentation can affect quality and aquatic life. In some cases, surface runoff from production sites can also contain chemicals or other fluids, so a robust soil erosion management strategy is related to the spill prevention strategy.
To prevent unchecked erosion and sedimentation on large construction sites, operators may dig out a sediment basin as a temporary man-made pond to collect disturbed soil washed away by rainwater. In practice, surface runoff washes soil into the basin where it settles and the water is discharged or evaporated back into the atmosphere. Smaller construction sites where a large-scale basin may not be appropriate due to space constraints may employ a sediment trap to capture eroded soil before it enters a waterway. Porous sediment traps form an embankment between the construction site and the waterway allowing water to flow through, but trapping sediment. In some cases, sediment traps must be cleaned or replaced after every rain event.
Operators may install water bars to reduce erosion by runoff for road and pipeline construction projects. These channels that run diagonally across roads or pipelines divert the flow of water through the cleared area. The diversion reduces the overall length of unimpeded flow of water and reduces overall erosion. In some circumstances, where slopes are extremely long and steep with poor vegetative conditions, water bars alone may not be effective in minimizing erosion and resulting sedimentation. In this case water bars can be combined with sediment traps. Erosion control may also include installation of vegetated concrete block mats2.
One of the balances against the continuous force of erosion is plant life. Root systems anchor soil in place and minimize the amount of soil that wind or water can carry away. Many beach municipalities protect their natural sand dune systems with boardwalks and constructed paths. This protects the delicate root system of beach grasses from damage by human interaction and in turn protects the dunes. The removal of plant life as a phase of pad construction eliminates the root systems that protected that soil from erosion. To counteract soil stabilization issues due to land clearing, operators can reduce the amount of land cleared and they can also introduce temporary reseeding and mulching for cleared land that has not been permanently stabilized. Temporary reseeding is different from permanent reseeding that occurs as part of reclamation. The reclamation is another critical item for long-term erosion control. The reclamation plan should consider the segregation and proper storage of topsoil for future use.
- Pennsylvania Fines Natural Gas Producer for Fracking Violation http://ens-newswire.com/2012/02/14/pennsylvania-fines-natural-gas-producer-for-fracking-violation/
- Oil and Gas Drill Site Erosion Control https://www.flexamat.com/Products/19/Oil-38-Gas-Erosion-Control
Images: “Erosion” by Aaron licensed under CC BY 2.0