PROTECTING our environment, especially streams and wetlands, is a responsibility that Commonwealth and our clients take seriously. During the design development phase of our energy projects, Commonwealth’s environmental staff are working with the utility engineers, right-of-way personnel, and contractors to plan for soil erosion control and to minimize the impacts caused by construction, including off road access and installation of structures.
On developing land, erosion frequently presents in the form of gully erosion on land disturbed for a year or less. Gully erosion, the result of concentrated flows of surface runoff, generates high sediment volumes requiring costly clean-up and the continual need for site stabilization during development. A construction site typically erodes at a rate of 50 tons/acre/year. This erosion rate is 5 times greater than cropland erosion, and 250 times greater than woodland erosion. These land changes are the source of much of the sediment that pollutes our streams, rivers, lakes, ponds, and reservoirs.
In 1972, the Federal Water Pollution Control Act, PL 92-500 and Amendments, were passed. Section 208 of PL 92-500 required that area-wide plans be prepared to control pollution from all sources, including urban-industrial areas. The goal of PL 92-500 was to “restore and maintain the chemical, physical, and biological integrity of the nation’s waterways.” In 1992, the Federal Environmental Protection Agency (EPA) mandated that states, that had been given the authority to administer provisions of the Federal Water Pollution Control Act (33 U.S.C. Section 466 et seq.) and issue National Pollution Discharge Elimination System (NPDES) permits, make provisions for the regulation of discharges of stormwater and dewatering waste waters from construction activities.
Commonwealth has been expanding our services in providing Storm Water Pollution Prevention Plans (SWPPP) for transmission line construction projects. On route map drawings, we are incorporating access routes and storm water pollution prevention plan (SWPPP) measures per U.S. EPA and State standards. These plans include a narrative, location, and details of the controls. For transmission projects, this includes: drainage patterns and final slopes (in most cases the existing and final will be the same); areas of soil disturbance; location and details of controls to be used on the site; best management practices (BMPs); and the method for stabilization of disturbed areas, both temporary and permanent. BMPs include such things as: vegetative buffers, tracking surfaces, check dams, silt fence, temporary fords, treatment and release for dewatering, and site restoration and stabilization. The intent of these drawings is to show how sediment will be kept out of the streams and wetlands; prevent any off-site accumulations, including tracking onto public roads; and restore the site once construction is complete.
Soil erosion involves the wearing away of the surface of the land by the action of wind, water, ice, and gravity. Once worn away, the detached soil particles are transported and ultimately deposited, resulting in sedimentation. Geologic or "natural" erosion and sedimentation occur over long periods of geologic time, resulting in the wearing away of highlands and the building up of lowlands. In general, natural erosion and sedimentation occur at a very slow rate. Erosion and sedimentation become a problem when they are accelerated beyond natural rates. Accelerated erosion is primarily the result of the influence of human activities on the environment. Once exposed, unprotected soil is subject to rapid erosion by the action of wind, water, ice or gravity. In many parts of the US, sediment produced by uncontrolled erosion is the greatest pollutant by volume impacting our lakes, streams, and wetlands. Everyone in these areas is affected by erosion and off-site sedimentation. Erosion and sedimentation result in: loss of fertile topsoil, filling of lakes and streams, increased flooding, damage to plant and animal life, and structural damage to buildings and roads.
One period of higher erosion potential exists during the spring thaw. It is a time when the coastal storm track increases rainfall potential. Additionally, because the ground is still partially frozen, the absorptive capacity is reduced. While frozen soils are relatively erosion resistant, they melt from the top down, creating a soft erodible surface over a hard impervious sub-surface. In northern climates, thawing of the soils often occurs in conjunction with the early spring rains combined with snow melt. Additionally, soils with high moisture content are subject to frost heaving and can be very easily eroded upon thawing. Wind and water are the main agents of soil erosion. The amount of soil they can carry away is influenced by two related factors:
1. Speed - the faster either moves, the more soil it can erode; and
2. Cover - mulch, organic litter, plants, and hardscape protect the soil and, in their absence, wind and water can do much more damage. Vegetative cover plays an important role in controlling erosion by protecting soil surface from the impact of falling rain, holding soil particles in place, enhancing the soil’s capacity to absorb water, slowing the velocity of runoff, removing subsurface water between rain falls through the process of evapo-transporation, and improving infiltration rates.
By limiting and/or staging the removal of existing vegetation, and by decreasing the area and duration of exposure, soil erosion and sedimentation can be significantly reduced. Give special consideration to the maintenance of existing vegetative cover on areas of high erosion potential such as erodible soils, steep slopes, ditches, and the banks of streams.
The contribution of water pollutants from your property may be small; however, when hundreds of small inputs are added together or aimed at sensitive areas, the impact is significant. There are a number of things that homeowners can do that are simple and, in the end, will be very cost effective:
1. Become familiar with the natural drainage patterns of your property. Try not to alter them. Proper site design will help you avoid costly erosion control measures.
2. Contact your town, county, or state offices to find out whether permits will be needed from them and, if so, secure any necessary permits and applications.
3. Plan to preserve existing vegetation as much as possible. Vegetation will naturally take up water, trap sediment, curb erosion, and improve the appearance and the value of your property. Mark the trees and shrubs that you want to protect. The root systems of grasses, shrubs, and trees help keep sloped surfaces in place. Less erosion will occur on a vegetated hillside than on one without vegetation. This is extremely important near water. A vegetated buffer area can stabilize stream banks and be a last line of defense to absorb pollutants before they reach a river or lake. An ideal buffer area is 25 to 50 feet of uncut grasses, shrubs and trees, but even a smaller strip can be beneficial. Remember that heavy machinery must be kept well away from trees to avoid compacting their roots.
4. For construction projects, discuss all aspects of the job with your contractor, including what erosion control measures will be used, such as installing silt fence on the down slope sides of exposed soil or around soil stock piles. This is very important because there are laws concerning non-point source pollution and sediment is considered a non-point source pollutant.
5. Locate soil piles away from any roads or waterways.
6. Plan earth disturbing activities early in the year so that you can re-vegetate the site before the end of the growing season. Grass and vegetation help curb erosion. Plan to mulch disturbed sites if construction is delayed past the growing season. This will protect bare soil during the winter and from spring runoff.
7. Use temporary seed, such as an annual rye, to stabilize bare areas, including stockpiles, until removed or re-graded. Mulch can also be used when temporary seeding is not feasible.