Wednesday, March 6, 2024

Looking for PFAS Sources in the Occoquan Watershed

 On March 14, 2023, EPA announced the proposed National Primary Drinking Water Regulation (NPDWR) for six Per- and Polyfluoroalkyl Substances (PFAS) including perfluorooctanoic acid (PFOA), perfluorooctane sulfonic acid (PFOS), perfluorononanoic acid (PFNA), hexafluoropropylene oxide dimer acid (HFPO-DA, commonly known as GenX Chemicals), perfluorohexane sulfonic acid (PFHxS), and perfluorobutane sulfonic acid (PFBS). When finalized, the proposed regulation will require public water systems to monitor for these chemicals.

In anticipation of the regulations, Fairfax Water hired an independent lab to test their water using current EPA-approved methods that can detect PFAS at much lower concentrations than previous methods. Fairfax Water also participated in the Virginia Department of Health (VDH) Occurrence Study that was completed in 2021. However, the practical quantitative limit was 4 ppt just at the proposed regulatory limit. Fairfax Water found that some of the results for the Occoquan Reservoir for PFOS and PFAS were above the MRL and the regulatory limit. Since that time the Occoquan Watershed Laboratory has upgraded their analytical equipment.

PFAS dissolves in water and combined with their chemical properties means that traditional drinking water treatment technologies used at water treatment plants are not designed to remove them, it is believed though, that carbon filtration does remove some. Activated carbon adsorption, ion exchange resins, and high-pressure membranes have been found to remove PFAS from drinking water, especially PFOA and PFOS, which have been the most studied of these chemicals and the PFAS substances with the lowest promulgated drinking water limit . Testing these technologies at the new regulatory limits is underway, but even if effective it could cost millions up to a billion dollars to remove PFAS from the Occoquan Reservoir, then the problem is how to dispose of the PFAS removed from the water. This would bring a whole new liability to the water utility.

The best strategy is to look for the sources of PFAS in the Occoquan watershed and prevent those from reaching the reservoir rather than removal by Fairfax Water. Source water protection  is the best solution if it can be done. With that in mind both Fairfax Water and the EPA have developed an analytic framework which provides information about PFAS across the environment. Now Fairfax Water has begun testing in the watershed to identify the sources of PFAS. 

Armed with $750,000 in new equipment for the purpose, the Occoquan Watershed Laboratory has begun to test samples from throughout the Occoquan watershed to determine where the PFAS in the reservoir is coming from. To start with there are several potential known sources: the reclaimed water from UOSA, accidental releases from Manassas airport,  and the old Vint Hill army base where the Fauquier Times reported that for the past several years, the U.S. Department of Defense has been monitoring PFAS contamination at Vint Hill that is believed to be tied to a former burn pit where soldiers practiced putting out fires with firefighting foam containing PFAS chemicals, which then leached into the soil and the groundwater.

There is no longer enough water in the rivers in the Occoquan watershed to consistently meet the demand during dry periods, so 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. 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.

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 spill was not entirely contained. The foam contains chemicals known as per- and polyfluoroalkyl substances (PFAS). There are likely to have been other spills over the years. So, soils and groundwater in that part of the watershed may be contaminated.

The Fauquier Times has reported that the area near Vint Hill army base gets its drinking water from Buckland Water and Sanitation, a private company, and that the water is  distributed by the Fauquier County Water and Sanitation Authority. Buckland apparently has been  testing Vint Hill wells for PFAS for years but failed to disclose it since it was not covered under the safe drinking water act. The level of contamination at the site was reported by the Fauquier Times and the Prince William Times was hundreds of times higher than the proposed drinking water standard.

There are other potential sites in the Occoquan Watershed to be studied and tested for PFAS. The old Atlantic Richfield superfund site recently acquired by Microsoft was never tested for PFAS though the groundwater has been monitored for solvents for years. There are likely to be other sites to test.

Related Reading and sources:,when%20the%20substances%20were%20detected.

Testing begins to find sources of 'forever chemicals' in the Occoquan Reservoir | News |

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