George Mason University
OP-27: Rainwater Management

The Storm Water Management Program at George Mason University (Mason) consists of minimizing the impacts of runoff associated with land disturbance such as flooding, erosion and water pollution. Due to current developmental expansion, Mason’s goal is to find cost-effective alternatives that provide water quantity and quality control while complying with laws and regulations. Moreover, as land disturbing activities take place, Mason continues to incorporate measures that protect and/or improve natural areas during and after construction. In addition to the ongoing efforts to preserve the natural landscape, Mason strives to reduce impervious areas as much as possible and create more vegetated regions.

The current strategies for campus operations of stormwater management include proper education on stormwater pollution prevention, spill prevention, and erosion and sediment control; routine inspections of current stormwater facilities; and necessary maintenance and repair of permanent stormwater management facilities.

The Childhood Development Center has a rainwater harvesting system that captures rainwater from the roof of the building and stores it in a cistern for irrigation purposes of the outside garden. Another system is located on the Arlington campus uses a stormwater detention tank to provide irrigation of the planter boxes on the plaza in front of the building.

There are two infiltration trenches on the Fairfax Campus. They are located near Potomac Heights as well as Piedmont. Infiltration practices use temporary surface or underground storage to allow incoming stormwater runoff to infiltrate into underlying soils. As the stormwater penetrates the underlying soil, chemical and physical absorption process remove pollutants. Infiltration practices have the greatest runoff reduction capability of any stormwater practice while also addressing water quality too. Prior to stormwater leaving portions of the Fairfax and Prince William campuses the water is treated using retention ponds that reduce the quantity of the flow and filter out pollutants to protect downstream waterways.

In 2006, George Mason University constructed its first vegetated roof located in Fairfax campus, outside of Research I building. The facility covers an area of approximately 64 X 16 square feet filled with a variety of hardy and aesthetically pleasant plants that seamlessly blend into landscaping. The filtration properties of this facility help to eliminate pollutants while reducing storm water runoff.

In the ongoing effort to reducing impervious areas, George Mason University (Mason)continues to enhance the implementation of porous pavement. Mason currently contains more than one acre of pervious pavement in Fairfax campus. Permeable pavement is mainly used in low-traffic areas such as back roads, housing facilities and bike racks. The use of pervious pavement not only reduces the runoff concentrations but also enhances the natural process of filtration.

There are several dormitories that utilize downspout disconnections by taking the stormwater from the roofs and turning it into overland flow, which eventually infiltrates into the ground.

There are five rain gardens currently in place around the Fairfax campus. Three are located within Masonvale (Faculty/Graduate Housing), while the other two are around the Piedmont dormitory. Each rain garden is composed of a variety of native perennial plant species, which require minimal maintenance. All of the rain gardens function as a regular BMP with the exception of the one rain garden between Piedmont and Tidewater; stormwater first undergoes the treatment processes of an infiltration trench prior to entering the rain garden.

George Mason University (Mason) has currently two retention (wet) ponds serving as both storm water management (SWM) and best management practice (BMP) facilities. The first retention pond is located on the south-east portion of Fairfax Campus (Mason Pond). Mason Pond treats approximately 125 acres, which is equivalent to more than a third of the total campus area. It retains nearly 8 acre-feet of storm water and it outfalls into an existing detention pond (Braddock Pond) located south-west of campus. The second pond (Prince William Pond) is located in the middle of Prince William campus and it treats close to 60 acres of the site. Prince William Pond discharges into an existing unnamed tributary.

At George Mason University (Mason) there are several vegetated swales which treat, convey and partially infiltrate storm water runoff at different locations of Fairfax and Prince William Campus. In some cases, these swales are implemented in conjunction with other structures such as check dams, which are used to slow runoff and enhance infiltration, where steep slopes are present. Such swales are vegetated with water-resistant plants. A variety of small grass swales can also be found on the west side of Fairfax Campus; these work essentially as drainage ditches, but they latently provide more infiltration and pollutant removal. All of Mason’s existing swales are used mostly as pre-treatment for other existing SWM/BMP facilities.

Other technologies used in storm water management at George Mason University (Mason) include: 1. Detention Ponds: There are 6 existing detention (dry) ponds used as both SWM and BMP facilities. a. Krasnow Pond: Located north-east on the Fairfax Campus. It treats a drainage area of 7.5 acres and outfalls into an existing unnamed tributary. b. FSH Pond: Located north-east on the Fairfax campus. It treats a drainage area of 14.7 acres and outfalls into an existing unnamed tributary. c. Roanoke Pond: Located on the south side of the Fairfax Campus. It treats the area of Roanoke River Road and a section of Braddock Road. d. West Campus Pond: There are 3 dry ponds on the west side of the Fairfax Campus that treat overland flow from the athletic and recreation fields. 2. Extended Detention Ponds: Braddock Pond: Located south-east on the Fairfax Campus. It treats a drainage area of 190 acres and serves as an outfall for Mason's East Fairfax Campus. 3. Rain Gardens: Mason has 5 rain gardens located on north-east portion of the Fairfax Campus. Each rain garden was carefully designed to allow for maximum water penetration with underground, gravel-filled reservoirs. The tops of these reservoirs were then filled with sand and then topsoil. Finally a variety of native perennial plant species were selected for each of the areas. These plants require minimal maintenance (wildflowers, shrubs and small trees). Rain gardens allow the storm water to penetrate into the ground and restore the water table, while simultaneously removing pollutants. 4. Grasscrete: A pre-fabricated structure made out of reinforced concrete with voids to be filled with grass. Grasscrete has been installed as an alternative to ordinary concrete in different locations within Fairfax and Prince William campuses, such as, fire access roads, low-traffic roads, and other areas where emergency traffic is required. Its drainage capabilities are roughly the same as regular grass; therefore, Grasscrete has been beneficial in Mason’s effort to reduce impervious areas. 5. Green Roof: There is a section of the lower level of Research Hall that is a green roof. The green roof consists of wildflowers and native grasses which absorb stormwater that hits that area of the roof. 6. Porous Pavement: All of the roads located behind the houses in Masonvale are made of porous asphalt, which allows for infiltration of stormwater. Additionally some of Mason’s bike and bus shelters on campus were all built on top of a porous platform. 7. Stream Restoration: Sections of the intermittent palustrine streams on the Fairfax Campus have been restored to provide a more natural and healthier environment. Stream restoration repairs erosion issues along the stream banks and reduces the amount of Total Suspended Solids in the water.

Data is for FY14