Our Water Supply and Fairfax Water

Fairfax Water is the largest drinking water provider in the Commonwealth of Virginia and one of the largest in the nation. They supply drinking water to 2 million residents (1.13 million retail customers and 988,000 people through their wholesale customers - Prince William Service Authority, American Water and Loudoun Water). Fairfax Water owns and operates the two largest water treatment facilities in Virginia with an average daily water production of 167 million gallons and a combined maximum capacity of 376 million gallons per day. The James J. Corbalis Jr. treatment plant is at the northern tip of Fairfax County and the Frederick P. Griffith Jr. treatment plant is on the northern edge of the Occoquan Reservoir in the southeast part of Fairfax County.

from Fairfax Water

Within Fairfax, Prince William and Loudoun Counties are a number of residents who still obtain their water from private wells tapping the groundwater. However, most residents are served by pubic water and that water comes from two sources: the Potomac River and the Occoquan Reservoir. The Occoquan Reservoir is fed by the Occoquan River which receives up to 30 million gallons a day of the treated discharge of the Upper Occoquan Sewage Authority treatment plant. The Upper Occoquan Sewage Authority treatment plant is located south of Centreville and west of Route 123 with its discharge pipe upstream of the Occoquan Reservoir so, a significant portion of the flow (especially during dry periods) into the reservoir is recycled sewage. This treated wastewater is from areas supplied by the Corbalis plant or lake Manassas. In addition, the reservoir receives stormwater runoff, precipitation from the Occoquan Watershed which covers portions of Loudoun, Fairfax, Fauquier, and Prince William counties and feeds the streams and creeks that feed Bull Run and the Occoquan River.

from Fairfax Water

Fairfax Water provides most of their customers with water treated at either the Corbalis or the Griffith Treatment Plants, but a small area receives water from the Dalecarlia and McMillan Treatment Plants, part of the Washington Aqueduct.  The U.S. Army Corps of Engineers owns and operates those plans and provides water to the City of Falls Church. The Corbalis Treatment Plant and the Dalecarlia and McMillan Treatment Plants treat water from the Potomac River. The Frederick P. Griffith Jr. Treatment Plant treats water from the Occoquan Reservoir. Most of the county is served by the Fairfax Water owned water treatment plants-as you can see by the extent of the blue area in the map below. 

from Fairfax Water

After World War II Fairfax County had over 20 small water systems that primarily operated water distribution systems. In 1957, the county supervisors created the Fairfax County Water Authority (now called Fairfax Water), to centralize the water supply, but the county did not yet have a reliable water supply and distribution system. The City of Falls Church was supplied water by the Washington Aqueduct and an independent water system.

Over the years as the county grew Fairfax Water expanded its infrastructure. They built the James J. Corbalis Jr. and the Frederick P. Griffith Jr. Treatment Plants and expanded their distribution system. Falls Church which had remained independent, buying its treated water from the Washington Aqueduct, was acquired by Fairfax Water in 2013.

The result is that now Fairfax Water provides water to county residents from their two water treatment plants and buys water from the Washington Aqueduct to supply residents in and around the City of Falls Church. They did not build new water mains to supply the city. The newer developments around Merrifield and the Dunn Loring Metro Station are supplied water from the Fairfax Water owned plants.

from Fairfax Water

The most important things Fairfax Water does is to treat the raw water of the Potomac and Occoquan to make sure it is safe to drink, make sure the water supply is adequate and then deliver safe drinking water to the homes and businesses whenever they want it.   In order to ensure that tap water is safe to drink, the EPA limits the amount of certain contaminants (a list of more than 90 contaminants) that can be in the water provided by public water systems under the Safe Drinking Water Act. Last March the U.S. Environmental Protection Agency (EPA) announced its long awaited proposal for the national drinking water standard for six per- and polyfluoroalkyl substances (PFAS) . The comment period closed on May 30th 2023 and the EPA intends to have a final rule in place by year end.

• EPA is proposing to regulate PFOA and PFOS at 4 parts per trillion.
• EPA is also proposing a regulation to limit any mixture containing one or more of PFNA, PFHxS, PFBS, and/or GenX Chemicals. For these PFAS, water systems would use a hazard index calculation, defined in the proposed rule, to determine if the combined levels of these PFAS pose a potential risk.

Fairfax Water found PFAS above the proposed limit

As you can see above, independent testing by Fairfax Water found PFOA and PFOS above the proposed regulatory limit. As EPA finalizes this rule, Fairfax Water is looking for a solution because the test results for the Occoquan Reservoir for PFOS and PFOA were above the new proposed regulatory limit. Nanofiltration or reverse osmosis have been found to be extremely effective at removing PFAS because these technologies depends on membrane permeability and at this time look like the main options for removal. Reverse osmosis membranes are tighter than nanofiltration membranes. A standard difference between the two is that a nanofiltration membrane will reject hardness to a high degree, but pass salts; whereas reverse osmosis membrane will reject hardness and salts to a high degree (which is why it’s used for desalinization) and could aid in the inland salinization that has increasingly impacted the raw water sources.  

Reverse osmosis, the more effective method, has a high capital cost (estimated to be $3 billion when all the other fixed assets of Fairfax Water are $2 billion) and is very energy intensive (has a high operating cost in the form of energy necessary to push the water through the membranes). In addition, about 20-25% of water would be lost as a waste stream. That would be up to 55 million gallons a day in a future where water supply needs to be augmented to meet projected demand. In addition, the waste stream containing the PFAS would have to be disposed of in a way that does not contribute to the problem. 

Right now when untreated water enters the treatment plants, coagulants are added to cause small particles to adhere to one another and settle in a sedimentation basin. The water is then filtered through activated carbon and sand to remove remaining fine particles. This produces water with extremely low turbidity and provides an excellent barrier against pathogens such as Cryptosporidium and Giardia. Next, the water is disinfected with chlorine to kill harmful bacteria and viruses. A corrosion inhibitor is added to help prevent leaching of lead and copper that might be in household plumbing or service laterals. Fluoride is added to protect teeth. Powdered activated carbon and potassium permanganate may also be added to the treatment process to remove taste or odor-causing compounds. In addition to these treatment steps, the Corbalis and Griffith plants use ozone to further reduce odors and organic material.

The water quality report released in June 2023 found that there were no violations of the current U.S. EPA’s Safe Drinking Water Act. You can view the report at this link. Fairfax Water states that they will continue to evaluate their treatment processes and options before the US EPA's finalizes the regulation.  Fairfax Water is also working with the Virginia Department of Environmental Quality and other agencies to identify possible sources of PFAS in the Occoquan watershed to eliminate PFAS from the source water. Fairfax Water does not produce or manufacture PFAS.  Instead, these chemicals are present in source waters that are treated to produce drinking water.  However, if they need to dispose of PFAS removed from water they could be responsible for future contamination, so it is always preferable to eliminate the source of the PFAS. 

Keeping PFAS out of the source water is the real challenge when PFAS is in our diet and wastewater is reused in our drinking water supplies. Source water protection will have to part of the solution. With that in mind Fairfax Water has developed an analytic framework which provides information about PFAS across the environment.