Fairfax County Report on the Environmental 2024

At the end of the year the Environmental Quality Advisory Council (EQAC) of Fairfax County released its annual report. This report is intended to provide a big picture view of how environmental programs are working and identify areas that require attention. For 2024, they found that residents and businesses can expect clean water, and good air quality. They largely attributed the county’s clean water and good air quality to the county’s past environmental investments; however, they felt that the county will need to do more to address climate change and other environmental challenges to maintain a healthy environment and continue to improve our quality of life.

I would like to highlight some of the portions of the report that address water quality and availability and have excerpted them from the report.  The Potomac River and Occoquan Reservoir are the primary source water for Fairfax Water which supplies 85% of the drinking water in the county.  Fairfax Water draws water from the Potomac River near the James J. Corbalis Water Treatment Plant and from the Occoquan Reservoir at the Frederick F. Griffith Water Treatment Plant. The remaining drinking water is drawn from groundwater.

 Fairfax Water provides about 167 million gallons per day (mgd) of drinking water to nearly two million people in Northern Virginia, including most residents of Fairfax County. Fairfax Water also provides drinking water to the Prince William County Service Authority, Loudoun Water, Virginia America Water Company (City of Alexandria and Dale City), Town of Herndon, Town of Vienna, Fort Belvoir and Dulles Airport. As of 2014, both the City of Fairfax and the City of Falls Church systems were incorporated into Fairfax Water’s system. In addition, Fairfax Water purchases some treated water from the U.S. Army Corps of Engineers, Washington Aqueduct Division, treated at plants in Washington, D.C.

Fairfax Water provides highly advanced treatment for the water delivered to its customers, but those treatment systems cannot remove salt, PFAS and other emerging contaminants. Although Fairfax Water produces safe and high-quality drinking water that meets all current standards, some water-quality concerns are appearing at the National level. The U.S. Environmental Protection Agency (EPA) recently released final national primary drinking water standards for six types of poly- and perfluoroalkyl substances (PFAS). According to Fairfax Water’s Statement on EPA’s Final PFAS Standards for Drinking Water, released April 10, 2024, Potomac River water from the Corbalis plant currently meets the standards while the Occoquan Reservoir sourced water from the Griffith plant does not. The standards do not take immediate effect, but Fairfax Water is evaluating treatment processes to ensure that their water will meet these standards. Also, more studies are needed to determine the specific sources of PFAS in the Occoquan watershed.

Fairfax Water does not explicitly identify the Corbalis and Griffith service areas. The boundaries vary depending upon pumping and demand. (Fairfax has interconnections in the distribution system.) Nevertheless, if future concerns arise about either plant’s output, EQAC felt it may be necessary, in the interests of transparency, to provide a map of approximate service areas of water originating in the Occoquan Reservoir and from the Potomac River. There are no plans to differentiate the costs of the water in the service areas.

The Occoquan Reservoir obtains its water from the Occoquan Watershed and the Upper Occoquan Service Authority (UOSA) Wastewater Treatment Plant. The Occoquan Watershed covers about 590 square miles and includes the Occoquan Reservoir, which serves as the boundary between Fairfax and Prince William counties. Unlike the vastly larger Potomac Watershed, the Occoquan water supply is very susceptible to pollutants introduced in local jurisdictions and through the recycled water from UOSA.

According to a recent Wall Street Journal Report, roughly 250 existing data centers in Northern Virginia use about 4,000 MW of electric power, and another 7,000 MW could be added with the data centers approved and under construction. EQAC differentiates the water and power use of the older data centers from the newer projects just completed or under construction. Older data centers typically range from 10 MW to 50 MW in size and use conventional commercial air conditioners for heat dissipation. Newer data centers are larger, around 300 MW; requiring this much more cooling capacity to dissipate the heat from the energy use makes evaporative cooling, commonly used for power plants, an attractive option.

A 300 MW data center would need to evaporate about 3 million gallons per day (mgd)  of water to the atmosphere. Adding 7,000 MW of data center capacity using evaporative cooling would introduce about 70 mgd of consumptive water use, almost doubling existing consumptive water uses in the Potomac River Basin. None of this increased usage is included in the 2020 ICPRB estimates. All evaporative cooling systems concentrate any solids and other contaminants in the water and must discharge highly saline “blowdown” water. This is particularly worrisome in the Occoquan basin, where sodium levels already are of some concern. At present, it is not known if new data centers will actually request water for evaporative cooling, nor is it known if mitigation, such as interruptible water service, would be acceptable.

 Though the recycled water from UOSA is already part of the water supply for the Griffith plant, recycled water from the Noman M. Cole Jr., Wastewater Treatment Plant which currently treats about 40 mgd  may be an option for reuse for evaporative cooling. Clearly, any use of evaporative cooling for new data centers must be considered carefully as a regional issue and the type of cooling should be stated at approval. Considering their potential impacts to water supplies, EQAC recommends, if large data centers are approved with evaporative cooling, conditions must consider (1) Possible water cutoff during periods of drought; (2) Use of recycled wastewater where feasible; and (3) No return of any “blowdown” to the Occoquan Reservoir.

EQAC made three recommendations one from the 2023 report.

1. Continue and enhance the protection of the Occoquan Reservoir by developing a plan for managing threats such as PFAS and sodium. Fund monitoring and modeling of emerging contaminants such as PFAS and of the rising sodium levels in the Occoquan Reservoir. This effort should include an inventory of present and proposed pollution sources, such as data centers and other industrial facilities.
2. Continue to participate with the ICPRB in studying water supplies in the Potomac River. In particular, ecological studies of low flows in the Potomac Gorge.
3. If large data centers are approved with evaporative cooling, approval conditions must consider (1) Possible water cutoff during periods of drought; (2) Use of recycled wastewater where feasible; and (3) No return of any “blowdown” to the Occoquan Reservoir.