Stormwater Information for Businesses



Stormwater runoff is rain that falls on streets, parking areas, sports fields, gravel lots, rooftops or other developed land and flows directly into nearby creeks and rivers.


The drizzling or pounding rain picks up and mixes with what's on the ground:

- Oil, grease, metals and coolants from vehicles;

- Fertilizers, pesticides and other chemicals from gardens and homes;

- Bacteria from pet wastes and failing septic systems;

- Soil from construction sites and other bare ground;

- Soaps from car or equipment washing; and

- Accidental spills, leaky storage containers, tobacco spit and whatever else ends up on the ground.


The polluted runoff then rushes into nearby gutters and storm drains and into streams, lakes and rivers.




Stormwater Best Management Practices (BMPs)


A Best Management Practice (BMP) is method or activity (constructed or natural) that mitigates the negative impacts of stormwater runoff. These can vary from elaborate underground storage units, permeable pavements, or a bioretention basin. Below is a brief description of common BMPs.


Dry Detention Pond: Detain water for 36-72 hours after a storm. After this period, the water drains out slowly depending on the size of the structure. In most cases, if water persists, maintanence is required. However, some dry detention ponds may include a wetland marsh area to reduce the pollutants in the stormwater before it is released (Enhanced-Extended Detention Basin). 


Wet Detention Pond: Contain a permanent pool of water throughout the year. Stormwater is added to this and released at a controlled rate, much like the dry detention pond. These may be favored due to their aesthetic value. However, wet detention ponds must be carefully monitored and maintained to ensure that the pond is healthy and insect populations are under control. An algal bloom caused from excessive nutrients (nitrogen & phosphorus) can destroy the entire pond ecosystem if left unchecked.


Infiltration Practices: Most common infiltration practices are trenches filled with gravel or other media. The stormwater is held in the space between the rocks and slowly infiltrate into the surrounding soil. Not all soils will absorb the water (clay, compacted, or waterlogged), so drains may be incorporated into the design. Infiltration practices need to be maintained often as loose dirt and sediment may cause clogging and failure.


Biorentention Practices: Soil and plants are used to absorb stormwater as well as pollutants in this filtration method. They contain a grass buffer, sand bed, ponding area, organic or mulch layer, planting soil, and plants. Stormwater drains into the ponding area where it is slowly absorbed through the other layers. Landscaping & vector (mosquito) maintenance is required as well as sediment and trash removal.


Sand Filter Treatment: Sand acts as an underground, physical strainer to remove suspended solids and particulate nutrients. These can be very costly to repair when they are failing so maintenance is extremely important. The sand, when replaced, needs to be disposed of at a landfill.


Constructed Wetlands: Man-made shallow pools that contain emergent and aquatic vegetation. The vegetation is able to improve the quality of the stormwater run-off by absorbing excess nutrients and pollutants. Landscaping and vector control are two important maintenance concerns along with sediment and trash removal.


Vegetated Filter Strips: Buffer areas that filter pollutants and suspended sediment and reduce velocity of runoff in flat areas.


Grassed Swales: Broad, shallow drainage channels with check-dams to create ponds that detain initial runoff. Grassed swales filter pollution and increase natural soil infiltration.


Water Quality Swales: Broad, shallow drainage channels that are utilized to control peak flows during storms. The main difference between water quality swales and grassed swales is that the water quality

swales contain a bio-engineered soil bed mixture which removes more pollutants.


Pervious & Permeable Pavement: Allows the stormwater to be retained until it can infiltrate into the soil or underground drain system. Traditionally paved surfaces such as concrete and asphault do not allow water to reach soil so it becomes stormwater runoff. Frequent maintenance is required to ensure permeability.


Keep in mind that there are many BMPs available and researching which one best suits your business is key to a successful BMP. For more information: Maintaining Your Stormwater Pond or BPM: Roanoke County 

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