When soil disturbance and vegetation removal occurs during construction projects, there is a drastic increase in water and wind erosion. When rain events take place, water flows through those unprotected, eroded soil surfaces and have the potential to transport sediment into waterways. This sediment-laden water is referred to as, "stormwater." As that "stormwater" flows over construction and industrial sites, it can also carry pollutants ranging from pesticides, chemicals and asphalt, to petroleum, and other debris collected from the soil surface and deposit those materials into water sources that serve as drinking water and aquatic habitats.
The Clean Water Act and other relevant mandates require that all federal and state regulated construction sites, Municipal Separate Storm Sewer Systems (MS4) communities and industrial sites be covered under a National Pollutant Discharge Elimination System (NPDES) stormwater permit to have the ability to legally discharge stormwater into waters of the United States of America. Most, if not all, of the mandatory stormwater permits require that the implementation of erosion and sediment control (ESC) Best Management Practices (BMPs) are applied to curtail and minimize pollutant discharges entering surface waters, MS4s and other bodies of water such as lakes, streams, rivers and oceans.
Best Management Practices (BMPs) for construction sites include:
- Erosion Control: Minimize exposure time of disturbed areas. Slopes, lots, and other areas where erosion can occur should not be left bare for long periods of time (2 weeks max). Immediately re-vegetate bare areas or provide temporary protection to the site using mulch, straw matting, or fiber bonded matrix. Sandbags, gravel, hay bales, silt fences, fiber roll, and temporary detention basins can also help to control erosion, but are not long-term solutions.
- Perimeter Controls: Surround the entire site with perimeter controls, such as gravel bags, silt fences and/or straw wattles (weighted down).
- Tracking Control: Prevent tracking dirt offsite. Use gravel and corrugated steel plates to provide a stabilized entrance and exit for vehicles. Clean plates regularly and replace gravel when no longer effective. Maintain dust control and implement street sweeping and vacuuming, as needed.
- Portable Bathrooms: Provide secondary containment underneath all portable restrooms and sinks and locate them at least 50 feet away from drainage inlets, whenever feasible. Always provide perimeter controls around portable restrooms and sinks.
- Building Material/Staging Areas: Store building and construction materials, such as paint and stucco, on-site at all times. Elevate materials off the ground and cover when not in use to prevent runoff caused by wind or rain. Mix all materials within secondary containment. Keep a spill kit on-site at all times.
- Concrete Trucks/Pumpers/Finishers: Provide perimeter controls, such as tarps and gravel bags, around work areas to contain materials and residue. Do not wash out concrete, stucco and paint from equipment or trucks onto the ground or streets.
- Washout Area: Provide a washout area, such as a lined pit or container, for the disposal of "wet" construction materials (concrete, paint, stucco, oils, etc.) or for cleaning tools and equipment. Washout areas should be lined and maintained to ensure wash water and residues are contained and do not leak.
- Dirt/Stockpiles: Cover temporary piles of soil/dirt with tarps and contain them using berms to prevent sediment from escaping. It is illegal to pile dirt or other materials (gravel, sand, etc.) in the street or on a driveway or sidewalk where it could run off into the storm drain. Dispose of permanently removed dirt at a legal dumping site.
- Earthmoving Equipment: Store all earthmoving equipment on-site, not in the right-of-way. Immediately clean up mud tracks and dirt trails left by equipment leading to and from the site. Place drip pans under all equipment while not in use.
- Dumpsters/Waste: Always cover dumpsters with rollback tarp. Sweep areas around dumpsters daily. Provide perimeter controls around dumpster areas to contain pollutants. Do not place liquid chemicals or waste in dumpsters.
- Storm Drain Inlets: Protect storm drains at all times with perimeter controls. Do not use sandbags for inlet protection, as they do not permit flow through. Immediately replace damaged gravel bags and remove all debris from the street, sidewalk and gutters. It is illegal to dump chemicals or wash out into the street or curb gutters.