Under the Virginia Stormwater Management Program (VSMP) permit regulations, the City of Alexandria is required to control stormwater pollution to the maximum extent practicable and to develop a pollution prevention plan – known as a Municipal Separate Storm Sewer System (MS4) Program Plan. The City’s initial plan was developed in 2003, was revised in 2008 and revised again in 2014 to reflect changes to the City's latest state permit. The permit contains Six Minimum Control Measures (MCMs). The City has developed appropriate and effective Best Management Practices (BMPs) to control stormwater pollution to the maximum extent practicable.
The MS4 Program Plan contains the BMPs that address the MCMs, which are discussed in some detail.
Post-construction runoff control in areas that have undergone development or redevelopment is necessary because runoff from these areas has been shown to significantly impact receiving streams.
Stormwater management regulations are designed to reduce pollution from development. As runoff flows over areas altered by development, it picks up harmful sediment and chemicals such as oil and grease, pesticides, heavy metals, and nutrients (e.g., nitrogen and phosphorus). These pollutants often become suspended in runoff and are carried to streams. In addition, areas undergoing development or redevelopment often result in increased impervious surfaces. Impervious surfaces, such as roofs, parking lots, and roads, increase the quantity of runoff generated by preventing water from filtering through vegetation and soil. This can result in stream bank erosion and downstream flooding, which often lead to a loss of aquatic life and damage to property.
The City has long required that development and redevelopment projects implement stormwater facility Best Management Practices (BMPs) to minimize the increase of pollutants and runoff to the City's streams. Examples of BMPs and stormwater controls include stormwater wet/dry detention ponds, vegetative buffers, bioretention areas, hydrodynamic structures, sand filters, cluster development to retain open space, and design standards that promote stream buffers and reduce impervious surfaces. The City also encourages a "tool box" approach to stormwater quality when site conditions and circumstances permit. This approach includes stream restoration, vegetated buffer enhancement, and constructing green roofs.
Ongoing maintenance of BMPs is required to ensure that they continue to function as designed. Detention ponds lose capacity as sediment and pollutants are captured and accumulate in the pond. Sand filters can clog with sediment, oil, and organic matter such as leaves and lawn clippings. Bioretention areas can lose their capacity to infiltrate stormwater. After a development is complete, the responsibility for maintenance is passed on to the owners of the development through the BMP Maintenance agreement. Frequently, the owners, be it a business or homeowners association, are unaware of their obligation to provide maintenance and/or unaware of the proper procedures to inspect and maintain BMPs. The City can assist in helping BMP owners / operators understand their maintenance obligations and can provide technical guidance for inspecting and maintaining BMPs.
BMP maintenance is VITAL to the proper functioning of each BMP and failure to properly maintain BMPs can even degrade water quality further. Failure to properly maintain BMPs can result in fines of up to $32,500 per day per violation. It is very important that property owners understand their obligations for the maintenance and inspection of BMPs.