Protecting the Occoquan Reservoir - ORPA

The Occoquan Reservoir watershed, primarily (40%) within Prince William County, is crucial for the water quality of our drinking water. Land use decisions in the county significantly influence the health of the watershed and thus the reservoir.

While Fairfax County implemented protective measures, such as downzoning, to protect the reservoir, Prince William County adopted the Rural Crescent in 1998 to limit sewer access and curb development pressure. However, recent changes in the Comprehensive Plan have blurred the line between rural and development areas.

Although the headwaters are experiencing development pressure, the updated Comprehensive Plan introduced an Occoquan Reservoir Protection Area (ORPA) in Midcounty, which was established to protect the Occoquan Reservoir as a public water supply, reduce nutrient & sediment loadings to the Chesapeake Bay watershed, and minimize land disturbance on one of the most environmentally sensitive areas in the county.

ORPA largely follows the Occoquan watershed line except where more intense development already exists. It also geologically follows the ground-water-flow system of the Piedmont. More intense development within the ORPA would mean more impervious surface, therefore, more runoff into the reservoir and less groundwater recharge. Residents on well water rely on the groundwater recharge for their drinking water supply, and wells in this area are more susceptible to drought due to the soil type.

Despite current regulatory efforts such as point-source controls, stormwater management requirements, erosion and sediment controls, Chesapeake Bay Preservation Area regulations (i.e. RPAs), and the County’s Municipal Separate Storm Sewer System (MS4) permit system, salt, sedimentation, and other pollutants continue to be present (and in some cases are rising) in the reservoir.

The establishment of ORPA could serve as a pilot study area for measures that may be essential to implement throughout the county or at least throughout the Bull Run basin to adequately protect both surface water and groundwater that enters the reservoir. 

Pending studies such as the groundwater study and the Occoquan Watershed Model, as well as additional studies carried out by the Occoquan Monitoring Lab, will be critical in developing sound policies that ensure the sustainability of both groundwater and the Occoquan Reservoir as reliable and affordable drinking water sources now and in the future.