Evaluation of NDOT's Sediment Barrier Practices Using Performance Data

Construction activities involve heavy earth moving activities that typically disturb several acres of land. Due to the nature of construction activity, sediment is the predominant pollutant of concern during the clearing and grading stages, which typically exposes large un-vegetated and un-stabilized land areas to erosive elements. The lack of ground cover during construction results in land areas being susceptible to increased rates of soil erosion. As stormwater runoff flows over unprotected areas on construction sites, it can suspend and transport pollutants causing significant physical, chemical, and biological water quality impacts and impairments to nearby receiving surface waters. Furthermore, polluted surface waters can affect operations at water treatment plants, power stations, and other water-handling facilities. Sediment runoff rates from construction sites can be 10 to 20 times higher than those of agricultural lands and 1,000 to 2,000 times greater than those of forested lands. Construction sites have measured erosion rates of approximately 20 to 200 tons per acre (45 to 450 metric tons per ha) per year. Sediment emanating from slope and channel erosion are transported into existing stormwater conveyance systems. Other pollutants stemming from construction activities can also be introduced to the local environment through the improper use and disposal of chemicals and hydrocarbons. Erosion and the resulting sedimentation in waterways have become one of the nation’s largest water pollution problems. The United States Environmental Protection Agency (USEPA) identifies sediment along with nutrients and heavy metals, which typically sorb to soil particles, as the most widespread pollutants affecting the beneficial uses of the Nation’s rivers and streams. In addition to environmental implications, sedimentation can cause vast economic problems. The loss of aquatic habitat and diminished water quality is often difficult to quantify, however some impacts (i.e., cost of dredging and disposing of accumulated sediment) are easier to assess. Furthermore, the cost of eroded soil replacement comes at a high price. Eroded sediments may include the loss of soil nutrients necessary for plant growth. This nutrient loss can lead to topsoil replacement actions to satisfy proper vegetative growth. The creation of soil is a slow process, therefore better methods and practices for controlling erosion, sedimentation, and other pollutants from construction sites are needed to forestall these problems and meet the demands of increasing growth and development. Stormwater management has become an increasingly important aspect of construction activities in the state of Nebraska. The National Pollutant Discharge Elimination System Permit for Storm Water Discharges from Construction Sites (NPDES Permit) requires the Nebraska Department of Transportation (NDOT) to develop a stormwater pollution prevention plan (SWPPP) for all construction activities that are covered by the permit. The SWPPP includes the design, installation, and maintenance of erosion and sediment control practices to minimize downstream impact from stormwater discharges. Currently, NDOT has specifications, standard drawings, and guidance for the design of erosion and sediment control practices. Many of the practices included in these documents have not been formally evaluated for field performance. Furthermore, recent research performed by other state highway agencies has led to the development of new and improved erosion and sediment control practices. Opportunities exist to better understand the performance of standard NDOT erosion and sediment control practices, improve the design and performance of practices, and to develop additional design manual guidance for the proper selection and design of practices.