Sunday, April 9, 2023

PFAS in Prince William

Last month 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). 

  • PFOA and PFOS: EPA is proposing to regulate PFOA and PFOS at a level they can be reliably measured at 4 parts per trillion.
  • PFNA, PFHxS, PFBS, and GenX Chemicals: 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.

If finalized, the proposed regulation will require public water systems to monitor for these chemicals. It will also require systems to notify the public and reduce PFAS contamination if levels exceed the proposed regulatory standards.

In May 2021, the Prince William County Service Authority participated in a Virginia Department of Health (VDH) study to analyze for PFAS in water samples collected from the distribution systems of the 17 largest water utilities in the state. The Service Authority collected samples from its East and West systems and sent them to an independent laboratory selected by VDH for testing. What they found was:


The public water supply in eastern Prince William (blue) comes from the Occoquan Reservoir. PWSA purchases 15 million gallons of water a day from Fairfax Water which is all drawn from the Occoquan Reservoir. American Water also purchases the drinking water for Daily City from Fairfax Water and as you can see from the connector, that water, also comes from the Occoquan.

Fairfax Water also participated in the Virginia Department of Health (VDH) Occurrence Study that was completed in 2021. It is important to point out that the practical quantitative limit was 4 ppt just at the proposed regulatory limit. Some of Fairfax Water’s results for PFOS and PFAS were above the MRL and the regulatory limit. The ones below cannot be quantified, they might be just below the quantitative limit or lower. It is impossible to tell. It appears that based on the results from PWSA that the results above the detection limit were from the Occoquan Reservoir.

The water in the Occoquan Reservoir comes from the Occoquan Watershed. And yet our water supplies are connected to each other and the land. Two thirds of the Occoquan Watershed that supplies the Occoquan Reservoir is in Prince William County. The Rural Crescent allows rain water to flow gently over vegetation, feed the aquifers that provide water to the private wells and the Evergreen water system, but also feeds the tributaries to Bull Run and the Occoquan River assuring the base flow to the rivers and streams that feed the Reservoir.

There is no longer enough water in the rivers to meet the demand, the Upper Occoquan Service Authority, UOSA, -the waste water treatment plant also delivers 40 million/day of recycled water that originated in the Potomac River to the Occoquan Reservoir. Supplementing the supply.

There are thousands of PFAS chemicals, and they are found in many different consumer, commercial, and industrial products. This category of chemical has been widely used for over 80 years mainly for their ability to repel oil, grease, water, and heat. We are all exposed to PFAS in everyday life. Stain-resistant carpeting, old nonstick cookware, grease- and water-proof food packaging, fabric softeners, waterproof clothing, cosmetics, and through our diet and water.

These forever chemicals have gotten into our national soil. As documented in Maine, land applied biosolids have carried PFAS to the soil in some locations. These chemicals have remained in the soil, been taken up into plants, and made their way into animals who eat those plants. According to Fairfax Water diet is responsible for 66%-72% of exposures to PFOA and PFOS (the two chemicals that have been most widely studied). In some cases, they have also leached into both surface and groundwater. Water is responsible for 22%-25% of exposures.

Keeping PFAS out of the source water the real challenge when PFAS is in our diet and wastewater is reused in our drinking water supplies. To stay within the regulatory limit, Fairfax Water will have to identify the PFAS content in the various source of water and can mix them to minimize exposure or remove them. The sampling identified a difference between water from the Occoquan Reservoir and other sources (Potomac River and Lake Manassas). Two obvious potential causes are the water from UOSA added to the Occoquan Reservoir could contain PFAS in the waste water.

Another way PFAS could have reached the Occoquan Reservoir was from accidental release from Manassas Airport. The Manassas Airport is upstream from the Occoquan Reservoir along Cannon Branch which flows into Long Branch, and accidents do happen.  In February 2020, a malfunction released a large spill of PFAS-based firefighting foam from a hangar at Manassas Regional Airport, in the Occoquan River basin. Aqueous film-forming foam, which is known as AFFF, is a firefighting foam widely used in the aviation industry because it quickly extinguishes fuel fires by spreading across the surface, depriving the fire of oxygen. This also makes a spill hard to control. The foam contains chemicals known as per- and polyfluoroalkyl substances (PFAS).

This is a 2021 spill at Manassas Airport that was well contained

It is not known whether the spill contaminated water supplies, but that spill was not fully contained on site. At the time the Occoquan Watershed Monitoring Laboratory did not find “significant” PFAS contamination in the Reservoir, but it was not quantified and a part per trillion is very, very little. The 8.3 or so billion gallons would have diluted the PFAS present if it was carried to the Reservoir, but PFAS is known as the forever chemicals because they take hundreds if not thousands of years to degrade and accumulate in people and the environment.

Source water protection will also have to be part of the solution. With that in mind both Fairfax Water and the EPA have developed an analytic framework which provides information about PFAS across the environment. Fairfax Water plans to expand testing to fully identify (within measurement limits) the PFAS content in the various source water supplies. This information will help them develop a road map to complying with the regulation if it is finalized and providing safe drinking water to Northern Virginia.

The water quality of the Occoquan Reservoir is of concern. Last year, 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 determined that an overlay district was not necessary. According to Prince William County 9.8% of the Occoquan Watershed is covered by impervious surfaces. According to Dr. Stanley Grant, Director of the Occoquan Watershed Monitoring Laboratory watersheds with impervious surface cover 10 % or more of the land show clear signs of degradation. Until the recent Comprehensive Plan changes over half of the Occoquan Watershed in Prince William County was designated as rural and predominately zoned A-1. The rural and open land nature of the watershed had served to protect the Occoquan Reservoir from various kinds of contamination. The recent series of decision by the Board of County Supervisors has eliminated that protection.

In addition, when the Board of County Supervisors approved the new Comprehensive Plan they eliminated the protections to the Occoquan Reservoir that maintaining the Rural Crescent provided. The Comprehensive Plan Amendment approved for the development of the Digital Gateway will allow industrial development within 2,200 acres of the former Rural Crescent and provide for the development of 4 lane highways within that area bring truck traffic and introducing hundreds of sources of potential water contamination to the Occoquan Reservoir. There are other possible sources of contamination within the Occoquan Watershed that may have remained invisible when the detection limit for PFAS and other contaminants was higher.

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