SS Credit 6.2: Stormwater Design—Quality Control
Value: 1 Point
Â
Intent- To limit disruption and pollution of natural water flows by managing stormwater runoff.
Multiple Sources of Stormwater Pollution
Stormwater runoff is a rush, or more appropriately a flush of water that is capable of conveying large quantities of contaminants to waterbodies in a short amount of time. Storm events are typically discrete and relatively short (hours to days) and produce exposures to contaminants potentially lasting from only minutes to hours. Pollutants, including sediment, trash and construction debris from development sites are picked up and washed into receiving streams and other aquatic resources during storm events. Pollutants that accumulate on impervious surfaces (auto fluids, chemical spills) and on compacted pervious surfaces, such as lawns, parks and athletic fields (Pesticide, fertilizer, pet waste) during dry weather are picked up and transported into receiving waters during rainfall events.
In addition to gathering pollutants as it moves through the developed landscape, stormwater runoff will also pick up a less obvious but still harmful additive, heat. Impervious surfaces, such as rooftops, roads and parking lots, tend to retain heat when exposed to sunlight. This is what is known as a heat island effect. As stormwater runoff moves over these impervious surfaces it absorbs the radiant heat and increases water temperature. Studies conducted by the Center for Watershed Protection and others have found that when this heated stormwater is conveyed into a river, stream, wetland or other aquatic resource, it can decrease the amount of dissolved oxygen contained within the water column, which reduces the amount of oxygen that is available to aquatic organisms causing damage even death to some.
To help prevent the flow of contaminants picked up by stormwater from reaching valuable natural habitats the USGBC requires that projects seeking certification implement a stormwater management plan that captures and treats the stormwater runoff from 90% of the average annual rainfall. The Best Management Practices (BMP’s) utilized for treatment must be designed in accordance with standards and specifications from a state or local stormwater management plan which is capable of removing 80% of the average annual post development total suspended solids (TSS) load (Dirt and other waste). For the project in Charles Town APUS is utilizing a BMP pond, designed by the Civil Engineering firm Dewberry, to capture and treat runoff from the site. Given that the project site is a capped Brownfield, this treatment pond plays a crucial role in containing and treating the runoff from the impervious site cap.
In a typical stormwater management (SWM) pond, a flow regulator is attached to the ponds drain pipe to reduce the size of the outlet. A smaller outlet causes the pond to collect excess flow and reduces the erosion potential of the initial pulse of water. These conventional stormwater retention ponds will release stormwater over 2-3 hours. In a BMP pond the flow regulator attached to the end of the pipe is even smaller. The smaller outlet forces the pond to hold the water for a longer period, allowing more time for the sediment and attached nutrients to settle out in a collection area. Whereas a conventional SWM pond will release stormwater over 2-3 hours, a stormwater management BMP pond may release the water over 2-3 day days allowing for optimum removal of sediment and nutrient loads.
The treatment approach APUS has selected will not only maintain the pre-development rate of runoff from the landscape, it will reduce the impact of the water on receiving ecosystems. This approach complies with the BMP’s of the state and the USGBC and will aide in improving water quality for the Ranson and Charles Town communities.
Images Provided by EPA Watersheds Site
Links of Interest
EPA Urban Stormwater BMP Performance Tool
EPA National Menu of Stormwater Best Management Practices
Center for Watershed Protection
West Virginia Stormwater Management Plan
Tags: apus, LEED, pollution, Stormwater, USGBC, watershed management
August 4th, 2010 at 4:15 pm
I am looking into what formulas are used to calculate this credit. Could you offer any device ?
Thanks,
Matt
August 5th, 2010 at 8:50 pm
According to the USGBC, to determine the volume that is treated the calculation is based on the area of the impervious paving and average annual rainfall. This would fall under the site engineers purview.
For treatment calculations, BMPs used to treat runoff must be capable of removing 80% of the average annual post-development total suspended
solids (TSS) load. The average TSS load is known from existing monitoring reports.
These calculations would all depend on the site in question and the best management standards and practices of the regulatory bodies overseeing that jurisdiction.