Rising Salinity in the Occoquan Reservoir
Blog Post by Normand Goulet, Director, Division of Environmental and Resiliency Planning - Northern Virginia Regional Commission
Rising salinity in freshwater reservoirs is not unique to Northern Virginia. The nationwide issue is known as “Freshwater Salinization Syndrome” and is the increase of salt ions (e.g., sodium, chloride) concentrations originating from human activity and human-accelerated weathering of natural and manmade substrates (think concrete) to freshwater bodies.
Recently I received a very simple email from one of NVRC's jurisdictional watershed managers:
Salinity in the Occoquan Reservoir
-what is the fix and how much? Who pays for it?
Now if only the answer was so simple. I will preface my answer with almost everything the Region now knows about salinity in the Occoquan Reservoir is a direct result of the past and ongoing research being performed by Dr. Stanley Grant of the Occoquan Watershed Monitoring Laboratory (OWML).
Let’s start with the sources.
Salinity or increases in salt ions in the reservoir result from some very diffuse sources within the watershed. The episodic increases, which most people associate as the problem (wrongly), result from winter deicing operations. However, chronic salinization is primarily a result of a steadily increasing population within the watershed using household products that contain salt ions. It is even possible that these product uses have shifted over the years (e.g. powered detergents vs liquid detergents) resulting in even more changes to the ion concentrations within the products. Approximately 64% of the salt ions in the Reservoir come directly from the population through the sanitary sewer collection system. Yes, there are commercial/industrial discharges of the ions to the Upper Occoquan Sewage Authority (UOSA) but that is only a fraction of the inflows.
Following along with the increased watershed population is the increased use of products to treat the increased wastewater inflows and drinking water withdrawals. This increased population has produced water quality impacts, principally through the associated increase in impervious surfaces on the Occoquan Reservoir. UOSA’s management of its wastewater discharge to prevent additional releases of phosphorus from the reservoir sediments during the summer months has also had an impact on the reservoir's pH and alkalinity. From Dr. Grant’s research, he’s found that approximately 32% of the sodium mass in Griffith’s finished drinking water is from the water treatment plant itself as a result of chemical feeds needed to buffer the finished water pH to prevent lead and copper issues.
What is the fix and how much?
Source reduction clearly is the best and cheapest fix, but how, again gets complicated. Both UOSA and Fairfax Water are looking at their internal operations to see if alternative treatment operations might be possible to reduce their contributions and the Occoquan Lab will be working with UOSA to see if there is anything that might be accomplished with respect to changes with the reservoir management. Again though, those would only represent a fraction of the needed changes.
VDOT has made it pretty clear that their road deicing operations take priority for safety regions. They are also looking at their operations to tighten up salt and brine use and are employing best management practices to existing deicing operations. They are also looking at alternative chemicals but from what was learned during the SaMS Study is that the alternative treatment chemicals are much more expensive. Increases in VDOT budget therefore are a tax issue. We still don’t have a good handle on how much private deicing operations contribute to the problem but we suspect that number is significant. Short of regulatory changes, public outreach and education will be the key to reductions in the public sector.
NVRC’s Clean Water Partners have agreed to a small increase in winter public outreach and education and based on conversations around the 2019 salt survey, the Commission will plan to add a few questions to this year's Clean Water Partners stormwater survey that can help gauge residents' knowledge and behaviors around salt use. Thankfully the region is using a layered outreach approach with several entities such as the Clean Water Partners, the Metropolitan Washington Council of Governments, and the Interstate Commission on the Potomac River Basin all having some form of public messaging.
As for the lion's share that’s coming through the sanitary sewers, the region's experts are still searching for an answer. Personally, I suspect there will be a need for a combination of public outreach to force the use of alternative products within the household and/or regulatory changes to force that. We can draw on several examples of similar situations in the past such as the banning of phosphate-containing detergents in the Region during the mid-80’s and the more recent ban of phosphorus in fertilizer. While industry did put up a fight, it was not an all-out war because the public was already pressing the issue for changes and the science behind the need to do so was solid. Unfortunately, that kind of outreach and public messaging is currently extremely limited. The social dynamic research being undertaken by Dr. Grant’s team is just getting underway.
What happens if source reduction doesn’t work or is insufficient? Unfortunately, that will probably result in Fairfax Water having to implement some form of physical treatment. They’ve publicly put out a very rough guestimate of about $1 Billion in capital expenditures would be necessary. That cost would of course be borne by the ratepayers. Fairfax Water is currently working on refining that number and looking into what kind of operations would be necessary but nonetheless, that route is going to be very expensive to all the residents of Northern Virginia.
About the Northern Virginia Regional Commission
NVRC is a consortium of thirteen local governments representing more than 2.5 million residents. While only 3% of Virginia's land mass, Northern Virginia has a GDP of $276 Billion which is 41.6% of the GDP of the Commonwealth of Virginia. Northern Virginia’s GDP is larger than 24 states and the District of Columbia and if a country would be the 48th largest economy in the world. You can learn more about NVRC’s Occoquan Program on our website.