General Guidelines

For all development having to comply with these guidelines, storm water treatment systems shall be designed to achieve average annual 85% Total Suspended Solids (TSS) removal.  Areas designated as open space that are not disturbed, and are not developed do not require storm water treatment.  Sites must employ one or more of the approved LID practices listed below to control and treat runoff from the first 1-inch of rainfall.  All designs must comply with the most recent version of the North Carolina Department of Environment and Natural Resources, Division of Water Quality, Storm Water Best Management Practices Manual and be approved on a plan submitted to the Mecklenburg County Land Use and Environmental Services Agency (LUESA).  A conceptual plan must be submitted and approved prior to formal engineering plan submittal.  Alternative BMP designs not listed below will be evaluated on a case-by-case basis.

• Bioretention (Rain Garden).  Bioretention BMPs are applicable as retention facilities for treatment of up to 5 acres.  Typically, they are designed to mimic forested BMPs that naturally control hydrology through infiltration and evapotranspiration.  They are especially suited to residential and commercial areas where additional landscaping can provide aesthetic benefits.  If necessary, bioretention systems can be modified in order to meet detention requirements.  Pollutant removal efficiency – 85% TSS.
  
  
• Infiltration Trench/Swale.  Infiltration trenches and swales are BMPs designed to fill with storm water runoff, and allow the water to infiltrate into the soil.  Some versions are filled with large crushed stone to create storage for the storm water in the voids between the stones.  Other versions use precast concrete chambers to provide a large storage volume to hold storm water for infiltration into the soil.  They are used to handle water from parking lots and buildings.  If necessary, infiltration trenches and swales can be modified in order to meet detention requirements.  Pollutant removal efficiency – 85% TSS.
  
  
• Vegetative Filter Strips and Buffers.  Filter strips are typically bands of close growing vegetation, planted between pollutant source areas and a downstream receiving water body.  They can also be used as outlet or pretreatment devices for other storm water control practices.  A filter strip should be viewed as only one component in a storm water management BMP.  Pollutant removal efficiency – 25% - 40% TSS.