Snow has come this winter. Last week when I went to the grocery store, the entire asphalt parking lot for the strip mall was white with salt residue. I was grateful as an old woman not to be in danger of slipping, but the salt…The Potomac River and Occoquan Reservoir have become saltier over the decades. This is a problem for the drinking water supply of Northern Virginia and the customers of the local water companies who are eventually going to have to pay to reduce the salt content in the water supplies.
Analyses from three different studies at multiple locations
have found increasing freshwater salinization in Northern Virginia and the
Occoquan Reservoir. Increasing salt is from increased direct and indirect
potable reuse of wastewater, the changing land use, increased amount of pavement and the salting
of roads in the winter. Nearly all road salt is eventually washed into adjacent
rivers, streams, and groundwater aquifers - road salt is considered the largest
contributor to rising inland salt levels by many.
The Occoquan reservoir is a drinking water resource for up
to one million people in northern Virginia. The reservoir was the nation’s
first large-scale experiment in indirect potable water reuse- the practice of
deliberately introducing highly treated wastewater to surface water or
groundwater for potable supply (Grant et al. 2022). Because of this the
Occoquan Reservoir has been carefully and almost continually monitored and
studied for decades. They have found that: “approximately 15% (4.6 × 107 m³/yr)
of the reservoir’s average annual inflow is highly treated wastewater from the
Upper Occoquan Service Authority (UOSA), and the remaining 85% (7.1 × 108 m³/yr)
is baseflow and wet weather runoff from two local rivers, Bull Run and the
Occoquan River, and ungaged watershed flow (Bhide et al. 2021, Grant et al.
2022).”
The long-term monitoring data reveals that salinity in the
reservoir has been increasing over time and is reaching the critical point in
terms of taste. “The concentration of sodium ions occasionally exceeds U.S. EPA
guidance on taste and health thresholds for drinking water (EPA 2003b, Bhide
et al. 2021). Researchers have found that the primary source of sodium ions to
the reservoir depends on weather conditions (Bhide et al. 2021); namely, UOSA’s
discharges contribute 60–80% of sodium mass during dry weather, and watershed
discharges, particularly Bull Run, contribute 40–60% of sodium mass during wet
weather. On average, the total daily mass load of sodium to the reservoir is
42,000 kg/day.”
Watershed discharges are assumed to come primarily from road
salt. Road salt is applied to de-ice
roads in the winter for highway safety and public safety (like old ladies
carrying their groceries to the car). The more paved roads we build, the more
salt is used in the winter.
The ICPRB, the Virginia Department of Environmental Quality
(VDEQ) and the Northern Virginia Regional Commission joined together to develop
a voluntary Salt Management Strategy published in 2020 to reduce that source of
salt/ chloride to the Potomac, its tributaries and the Occoquan Watershed. Though
it was a first step, this policy alone is not enough to slow the increasing salinization
of our source water for drinking as road construction continues at an alarming
pace and business use salt and brine solutions to protect their customers and
employees. As we try to encourage the adoption of the voluntary salt management
strategy, we keep building roads and paving over the open wooded spaces.
Sodium and chloride the elements that make up salt and break
apart in water are washed off road by rain and melting snow and flow into local
waterways or seep through soils into groundwater systems with negative impacts
on water quality and the environment. Salts pollute drinking water sources and
are very costly to remove. The only available technology to remove salt from
the source water is reverse osmosis which could cost Fairfax Water alone $1-2
billion to install and requires a significant amount of energy to run in the
tens of millions of dollars a year.
There are significant other sources of salt in our watershed,
not a single source. The origin of salt is widespread in the watershed which spans
four counties, two cities, and three utilities. In addition, the salt content
of the UOSA seems also to be increasing. The Occoquan Reservoir watershed
cannot be easily regulated because all entities involved must agree and the
proposed solution for one entity may adversely affect that of another.
"Addressing salinization of the Occoquan Reservoir requires working across
many different water sectors, including the local drinking water utility
(Fairfax Water), the wastewater reclamation facility (Upper Occoquan Service
Authority), the state transportation agency (Virginia Department of
Transportation), and city and county departments in six jurisdictions
responsible for winter road maintenance, including the City of Manassas, City
of Manassas Park, Prince William County, Fairfax County, Loudoun County,
Fauquier County.”
In addition, current regulatory tools are not well suited to
address freshwater salinization in urban areas. The few federal regulations for
salt that do exist address acute and chronic limits for chloride intended to
protect aquatic freshwater species, as well as secondary (nonmandatory)
guidelines for drinking water. The U.S. Environmental Protection Agency (EPA) unregulated
contaminant program determined salt did not present a meaningful opportunity to
mitigate health risk and were therefore not regulated. Nonetheless, it is
a problem that continues to grow worse as time passes.
The Occoquan Watershed Monitoring Laboratory has obtained several
grants to study the potential effectiveness of utilizing Elinor Ostrom’s social-ecological systems (SESs) framework to address the problem (and other distributed
contamination problems that are emerging). This framework can be used to assess
the social and ecological dimensions that contribute to sustainable resource
management.
What the Occoquan Watershed Laboratory researchers did was
assemble stake holders from the local drinking water utility (Fairfax Water),
the wastewater reclamation facility (Upper Occoquan Service Authority), the
state transportation agency (Virginia Department of Transportation), and city
and county departments in six jurisdictions responsible for winter road
maintenance, including the City of Manassas, City of Manassas Park, Prince William
County, Fairfax County, Loudoun County, Fauquier County. The stakeholders were
prompted do develop frameworks or mental models for the salt problem using an
iterative process that began with co-production of a concept list featuring
causes of salinization, consequences of salinization, and actions that might be
taken to mitigate salinization.
The similarities and
differences across these groups, and the degree that pointed to actions that
could be taken to collectively manage
salinization in the region as well as other challenges to the sustainability of
our communities was explored. To increase the likelihood that actions could be
taken across a broad swath of stakeholders in the region, widespread
understanding of the problem and the interconnection of actions and
consequences needed to be communicated.
The Occoquan Watershed Laboratory has moved on to create the
first version of a simple to use model to provide stakeholders and decision
makers with the actionable information they need to manage cascading water
quality risks in more integrated and equitable ways, both now and under various
population growth and climate change scenarios. This tool could be used to
decision makers to gain an understanding of the consequences of their decisions
on the community as a whole. To see the overall impact of individual decisions made
over time on the community and ecology.
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| from OWML Grant et al |
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