Construction stormwater best management practice – Stormwater Inlet Protection
Stormwater Inlet Protection
The goal of stormwater inlet protection is to trap sediment from a construction site before it enters a storm sewer. This will keep sediment from being transported to lakes or streams and can also prevent clogging of the storm sewer caused by heavy sediment loads. A stormwater inlet refers to manholes, catch basins, curb inlets and other drop-type structures constructed to direct stormwater into storm sewers or other underground drainage systems. Inlet protection best management practices (BMPs) are fairly inexpensive, easy to construct, and if maintained properly can successfully reduce sediments from entering our waterways.
What is required by the NPDES/SDS construction stormwater permit?
The NPDES/SDS construction stormwater permit requires that sediment control practices be utilized to minimize sediment from entering surface waters, curb and gutter systems and storm sewer inlets. The permit states that all storm drain inlets must be protected by appropriate BMPs throughout construction and until all sources with potential for discharging to the inlet have been stabilized.
The permit also requires that the inlet protection BMPs be inspected at least once every seven days and within 24 hours after a rainfall event greater than 0.5 inches in 24 hours. All nonfunctioning inlet protection BMPs must be replaced or repaired within 24 hours of discovery. For full details of the permit requirements, a copy of the NPDES/SDS construction stormwater permit is available online: www.pca.state.mn.us/water/stormwater/stormwater-c Stormwater inlet protection BMPs can be inserted into a catch basin to trap sediment from a construction site before it enters a storm sewer.
Planning considerations
Inlet protection BMPs should be installed prior to any soil disturbance on a construction site where stormsewer systems are in place or BMPs should be installed as stormsewer systems are constructed and inlets begin collecting stormwater. The basic approach to inlet protection BMPs is to install a barrier around the inlet that ponds or filters the flow of stormwater resulting in the settling or filtration of sediment. It is important to note that ponding will occur behind the inlet protection BMPs and that regular maintenance is needed to remove sediment and prevent a safety hazard. Many different types of inlet protection BMPs exist and can be utilized depending on the field conditions and type of inlet.