Construction Site Pollution Prevention
Construction site runoff has been identified as a significant source of sediment loading within the urban environment, potentially contributing 25% of the entering Walnut Creek. Many strides have been made over the past two decades in the development and implementation of stormwater pollution prevention plans (SWPPPs). While most sites are applying for required permits and preparing SWPPPs, there appears to be room for improvement in installation and maintenance of adequate erosion and sediment best management practices (BMPs).
What is the Difference Between Erosion and Sediment Control?
Erosion control practices protect the surface of the ground from being displaced by the force of falling precipitation or flowing water. Sediment control practices are intended to collect polluted runoff for a period of time, allowing suspended pollutants to settle out of runoff before it is allowed to leave a construction site.
Why is Pollution from Construction Sites a Problem?
Construction activities create new development from farmland or other open spaces. These activities strip off any vegetation that is reducing the potential for surface erosion. Once this vegetation is gone, the surface of the soil is easily washed away by rainfall and flowing water. Soil can also be tracked onto roads and highways or dumped into waterways. All of these actions make it likely that soil will be carried off site and washed into downstream storm sewers, creeks and rivers. This eroded soil (sediment) can plug up storm sewers and fill in waterways, affecting their ability to convey runoff. Other impacts of sediment are listed in detail in Chapter 6 of the plan.
Without effective controls, sediment discharge from construction sites often will range between 35–45 tons per acre. Compare this with farmland areas which usually have loading rates of less than two tons per acre. Lawns and other stabilized areas have far lower erosion rates.
Construction sites can also be sources of other pollutants such as fuels, oils, paints, concrete washout, construction debris and human waste (collected in temporary toilet facilities from workers).
Recommended improvements to SWPPPs:
- The plan should be a “living document.” The plan should be amended in some fashion so that the site map reflects current site conditions. Inspection records and changes to the sequence of construction events should be made part of the SWPPP document.
- The SWPPP and all site controls are to be maintained as necessary until full establishment of vegetation across all disturbed areas. Site inspections and maintenance of controls should continue until all areas are stabilized with permanent vegetation and the Notice of Discontinuation (NOD) has been filed with the Iowa Department of Natural Resources.