Staff Recommends No Overlay District for the Occoquan

Last fall, the Prince William County Board of Supervisors issued Directive No. 20-86 for county staff to develop a protection overlay district for the Occoquan Reservoir. County Staff has completed their study and according to a memo from Thomas Smith, Director of Public Works department, They recommend that an overlay district NOT be considered at this time.

The Occoquan Reservoir is essential to our drinking water supply. Fairfax Water supplies drinking water to around two million people in Fairfax County, Loudoun County and Prince William County. The Occoquan Reservoir supplies the source water to the Griffith water treatment plant which provides about 40% of the drinking water from Fairfax Water and serves eastern Fairfax County and the East System of Prince William County which serves Woodbridge, Occoquan, Dumfries, Triangle and Hoadly Manor.

The Occoquan Watershed encompasses 248 square miles of Prince William County- 66% of the land area of the county. According to Mr. Smith, currently, 9.8% of the watershed is covered in impervious surface and over half is designated as rural and predominately zoned A-1. The rural and open land nature of the watershed has served to protect the Occoquan Reservoir from contamination.

 Development in the watershed triggers a number of problems that begin with storm water runoff as the primary driver, though wastewater from the Upper Occoquan Service Authority and septic systems also contribute to the deterioration of the water quality. Pollution from runoff, called non-point source pollution is the most imminent threat to the health of the Occoquan Reservoir and our drinking water supply. An overlay district could have been used to limit the types and amount of development on land within the watershed to continue to protect the Occoquan Reservoir.

According to Mr. Smith; non-point source pollution is addressed by stormwater management , erosion and sediment controls and implementation of the Chesapeake Bay Resource Protection Areas. In 2014 the County stormwater management requirements were replaced with the more stringent Virginia Stormwater Management Program. This coming year County will be updating its Chesapeake Bay Preservation Area regulations to comply with the recent changes in the State regulations. In addition, the municipal stormwater management permit for the discharge of stormwater into waterways is scheduled for renewal in June 2022. 

Mr. Smith says: “Most of the traditional pollutants of concern are being addressed by the Upper Occoquan Sewage Authority Regional water Reclamation Plant and the existing non-point source programs and regulations. Today, the main concern for the reservoir is the increasing salinity…” Studies at multiple locations have found increasing freshwater salinization in Northern Virginia. Sewage contains salt from water softeners and our diets, but the main source of salt is believed to be from roads and paved surfaces.

Salts are very effective at deicing roads; however, after application, the salts are washed off into local waterways or seep through soils into groundwater systems. Salts pollute drinking water sources and are very costly to remove. The only available technology to remove salt from the source water is reverse osmosis which according to Mr. Smith would cost $1 billion to implement at Fairfax Water and requires a significant amount of energy to run. This would increase water rates for all customers. 

Road salting during snow and ice storms is now also considered the largest source of salt to the Potomac and its tributaries in the Washington, D.C. region (e.g., Porter et al. 2020). The ICPRB has been working with the Virginia Department of Environmental Quality (VDEQ) and the Northern Virginia Regional Commission to decrease salt levels in area streams. The plan is to implement a voluntary management of the use of salts for roadways and walkways through the implementation of the Salt Management Strategy published last year by the ICPRB and VDEQ.

Mr. Smith concludes his memo to the Board of Supervisors with the statement that “Many of the original pollutants of concern for the reservoir have been addressed through point source controls and …stormwater management requirements, erosion and sediment controls, Chesapeake Bay Resource Protection Areas, illicit discharge monitoring and enforcement and public education programs."

The  current pollutant problems identified in the memo are endocrine disrupting compounds, PFAS and salinity which he states need to be addressed on a regional basis. Virginia Tech is currently engaged in a study of the source of the salinity in the Occoquan Reservoir. Mr. Smith recommends waiting until the salinity study is completed, the Chesapeake Bay ordinance updated and the implementation of the Salt Management Strategy be completed before considering an Occoquan Overlay District.   However, the importance to the protection to the Occoquan Reservoir that only 9.8% of the watershed is covered in impervious surface and remains predominately open land and rural was ignored. The comprehensive plan amendments currently under consideration will  impact the Occoquan Watershed.