Sunday, March 17, 2024

Prince William needs to Protect the Occoquan Watershed

With assistance from the PWCA ORPA workgroup.

The Occoquan Reservoir is a vital drinking water source for 800,000 residents in Northern Virginia including residents on the eastern end of Prince William County. The Occoquan Reservoir watershed spans less than 600 square miles and Prince William County has the largest portion of land area within the Occoquan Watershed in its jurisdiction (40%). Other jurisdictions comprising the watershed include Fauquier County (36%), Fairfax County (17%), and Loudoun County (5%). The City of Manassas and the City of Manassas Park comprise a total of about 2%.

As of the 2020 Census, there were approximately 574,000 people residing within the watershed. About 43% of the population in the Occoquan Watershed resides in Prince William County. As the most populous jurisdiction in the Occoquan watershed and the one with the largest land area, substantial changes in land use patterns in areas of Prince William County will impact water quality in the watershed which will impact the groundwater, the streams and rivers and the Occoquan Reservoir.

To protect the Occoquan Watershed, Fairfax County downzone 41,000 acres of land and protected another 5,000 along the Occoquan Reservoir during the 1980’s. Prince William County adopted a rural area called the Rural Crescent with the adoption of the 1998 Comprehensive Plan which served to protect the headwaters in the fragile Bull Run watershed and Occoquan Watershed by alleviating development pressure in the already heavily urbanized drinking water watershed.

When Prince William County approved their Comprehensive Plan pathway to 2040, the “Rural Area” designation was eliminated. It was replaced it with an "Agricultural Estate" designation covering 55,310 acres and with an "Agricultural and Forestal" designation covering 75,647 acres. These new designations allow for more development in the rural area. Recent rezonings have allowed even more intense development in what was once the rural area. The Comprehensive Plan update also established an Occoquan Reservoir Protection Area (ORPA), to protect the Occoquan Reservoir as a public water supply and meet the requirements of the Chesapeake Bay Watershed Implementation Plan that Virginia is using to meet the US EPA enforced Pollution Reductions mandates.

Protecting the Occoquan Reservoir requires protecting all the water resource in a region because all water on earth is connected. Precipitation moves into the water table (the hyporheic zone) down to groundwater or into rivers and streams. Disrupting the balance of water flow can have dire consequences. The available supply of fresh water is continually renewed by the hydrologic cycle and in the case of the Occoquan Reservoir the actions of mankind. The need for water is constant and grows with population and wealth and business activity. There is also a seasonality to water- we use more in summer.

Many activities of mankind interfere with the hydrologic cycle. Through land change we interrupt the recharge of groundwater which impacts stream flow. Changing the use of the land, covering it with buildings, driveways, roads, walkway and other impervious surfaces will change the hydrology of the site reducing groundwater recharge in the surrounding area increasing stormwater runoff velocity and quantity and reducing streamflow which is feed by groundwater.

As groundwater levels fall, perennial steams that feed the rivers become ephemeral. The groundwater becomes disconnected from the surface water network. Once the hydrology is destroyed by development, it cannot be easily restored, if at all.

The Occoquan Reservoir is fed by the Occoquan River which receives up to 40 million gallons a day of the treated discharge of the Upper Occoquan Sewage Authority treatment plant which discharges to the river 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 so you do not end up with constantly recycling and concentrating the same impurities into the Occoquan.

In addition, the reservoir receives stormwater runoff, precipitation from the Occoquan Watershed and feeds the streams and creeks that feed Bull Run and the Occoquan River. When generally open rural area is developed, stormwater runoff increases in quantity and velocity washing away stream banks, flooding roads and buildings carrying fertilizers, oil and grease, and road salt to the Occoquan Reservoir. The faster flow of storm water gouges the riverbeds picks up pollutants from impervious surfaces. The cumulative impact of these steps leads to flash floods, unstable banks, heavy pollution and waning life. This is why it is essential to have an ORPA, to ensure both public and private water users continue to have water to drink and use.

Geology, climate, weather, land use and many other factors determine the quality of the groundwater and in turn streamflow. Within Prince William County Virginia there are four distinct geologic provinces: (1) the Blue Ridge, (2) the Culpeper Basin, (3) the Piedmont, and (4) the Coastal Plain. The U.S. Geological Survey divides the four geologic provinces of the county into seven hydrogeologic groups based on the presence and movement of the ground water calling them groups: A, B, B1, C, D, E and F.

The quantity and quality of ground water in Prince William County varies across the county depending on the geologic and hydrogeologic group you are in. The rocks in the Blue Ridge, Piedmont, and Coastal Plain contain minerals that are resistant to weathering, and the ground water tends to be acidic having low concentrations of dissolved constituents. Generally speaking, the groundwater in the county is recharged in elevated areas between stream valleys and channels and discharges to streams and estuaries. However, the paths and duration of groundwater flow are different between consolidated rocks and unconsolidated material. Groundwater in the consolidated rocks flows through the system of fractures following a circuitous path before discharging to a stream or estuary. In unconsolidated material, ground water generally follows a direct path from the recharge area to the discharge area.

In the area of the proposed ORPA is beyond the Culpeper Basin in the Piedmont region. This area of the ORPA is primarily hydrogeologic group D composed of igneous rock formations with limited lenses of hydrogeologic group E that transition at the bounds of the ORPA to group E and then to the Coastal Plain.

Hydrogeologic group D is located within the Piedmont formation and consists of three igneous plutons in the eastern part of Prince William County: the Goldvein, Lake Jackson, and Occoquan Plutons. Rocks within hydrogeologic group D tend to have moderate water-bearing potential and ground-water storage tends to be predominantly in the overburden, which is the soils above the bedrock. Wells in this area are most susceptible to drought and tend to be slightly acidic. The igneous rocks have subhorizontal sheeting and near vertical joints overlain by thick overburden. Groundwater wells in the area tend to have yields range from 1.2 to 100 gal/min which has resulted in the development of homes with wells in the area due to the thickness of the water storing overburden.

Hydrogeologic group E is also in the Piedmont formation in the eastern part of the county, and consists of metasedimentary, metavolcanic, and other metamorphic rocks. Rocks within hydrogeologic group E tend to have poor water-bearing potential, and thin- to thick cover of overburden. Similar to the rocks of hydrogeologic group D, ground-water storage tends to be predominantly in the overburden. Some of the poorest yielding wells in Prince William County are located in this hydrogeologic group and can be as low a 0.25 gallons per minute upto 70 gallons per minute-, but tending towards the low end because of the thinness of the overburden beyond the limits of what is the proposed ORPA. Homes and businesses in this area have depended on public water supply due to the limitations on well development and that water comes from the Occoquan Reservoir.

Protecting groundwater serves to protect all of the water resources in the watershed. Today, the Occoquan watershed is often described as the most urbanized watershed in the nation. Certainly there are far more urbanized areas in the United States, but they do not have functioning watersheds. We need to effectively protect ours.

Wednesday, March 13, 2024

Death Valley Ephemeral Lake

Death Valley is the driest place in North America, with some areas receiving less than two inches of rain per year, and is the location of the highest temperature (134 °F on July 10, 1913) ever recorded in the United States. The valley is not dead, it is a below-sea-level basin, surrounded by towering peaks that are often frosted with winter snow. Rare rainstorms bring vast fields of wildflowers. Lush oases harbor tiny fish and serve as a refuge for wildlife and human life.

Usually Death Valley visitors see a vast salt flat at Badwater Basin. However heavy rain from Hurricane Hillary in August 2023 brought 2.2 inches if rain that filled the valley floor with a vast, shallow lake. At its largest, it was about 7 miles long, 4 miles wide, and two feet deep. Imagine only 2.2 inches of rain doing that!

By late January it had shrunk to about half that size, and was inches deep. Then an atmospheric river brought another 1.5 inches in early February, 2024 and after the atmospheric river moved through, the lake continue to expand as water drained into the basin from the Amargosa River, which feeds the basin from the south.  The Amargosa is usually an intermittent river was observed to be flowing by park rangers.

Badwater Basin is endorheic, meaning that water flows into but not out of it. Typically, evaporation far outpaces inputs from rain and the Amargosa, rendering the lake ephemeral. But in the past six months, the unusual atmospheric rivers have changed the equation. As of mid February, the lake is 1 foot deep in places, and it is uncertain how long it will last. Past appearances of the lake are rare- appearing in 2005 and 2015 and none on record have lasted as long as this one.

The satellite image below is from NASA Earth Observatory images by Wanmei Liang, using Landsat data from the U.S. Geological Survey. Photo by K. Skilling/National Park Service.



 

Sunday, March 10, 2024

Total Eclipse of the Sun

NASA


On Monday, April 8, 2024 a total solar eclipse will cross North America, passing over Mexico, the United States, and Canada. Weather permitting the total solar eclipse will begin over the South Pacific Ocean and hit Mexico’s Pacific coast at around 11:07 a.m. PDT. This is probably the last solar eclipse to cross North America in my lifetime. The last eclipse I saw was in July 1963, and this is my last shot to see another. I live under 200 miles from the path of totality and should be able to see much of the eclipse from home, but we are in a solar maximum and a few hours drive could yield quite a show! You can watch along with NASA.

The path of this eclipse will move from Mexico, entering the United States in Texas, and traveling through Oklahoma, Arkansas, Missouri, Illinois, Kentucky, Indiana, Ohio, Pennsylvania, New York, Vermont, New Hampshire, and Maine. Small parts of Tennessee and Michigan will also experience the total solar eclipse. The eclipse will enter Canada in Southern Ontario, and continue through Quebec, New Brunswick, Prince Edward Island, and Cape Breton. The eclipse will exit continental North America on the Atlantic coast of Newfoundland, Canada, at 5:16 p.m. NDT. We are close enough to drive to see it full on, but the eclipse will be visible all along the northeast corridor. 

NASA

The path of totality is where the moon will completely cover the sun making the sun’s corona visible. Viewing of partial eclipse will be possible from a much wider geographic area. This area is about 115 miles wide, In this area looking directly at the sun is unsafe except during the brief total phase of a solar eclipse (“totality”), when the moon entirely blocks the sun’s bright face, which will happen only within the narrow path of totality and only during the window of complete coverage which is about 4 and a half minutes. Otherwise you must protect your eyes and vision. The only safe way to look directly at a partially eclipsed sun is through special-purpose solar filters, such as “eclipse glasses or hand-held solar viewers.

Homemade filters or ordinary sunglasses, even  dark ones, are NOT SAFE for looking at the sun; they transmit thousands of times too much sunlight. Eclipse glasses and handheld solar viewers must be verified to be compliant with the ISO 12312-2 international safety standard for such products. Make sure you have real solar glasses. It's not enough today to just look for the ISO 12312-2  certification, because in 2017 many unscrupulous vendors on Amazon were printing fake glasses with ISO 12312-2  certifications. Only buy glasses made in the United States from a vendor on the approved list of the American Academy of Ophthalmology.  You can also view the eclipse on NASA’s web site or through a pinhole projector as we did when we were kids. NASA’s has a diagram on how to make a pinhole projector.

Most of the ‘beauty shot’ photographs you will see of the eclipse will be taken with professional digital cameras on tripods, or shot through a telescope, but the most common photos you will probably see will be taken by the millions of smartphones used by ordinary people to capture this event. Read NASA’s tips and precautions and remember to protect your eyes.

Do NOT use eclipse glasses or handheld viewers with cameras, binoculars, or telescopes. Those require different types of solar filters. When viewing the partial phases of the eclipse through cameras, binoculars, or telescopes equipped with proper solar filters, you do not need to wear eclipse glasses. (The solar filters do the same job as the eclipse glasses to protect your eyes.)

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:

https://www.asdwa.org/2023/07/11/usgs-releases-new-study-on-pfas-in-us-tapwater/#:~:text=The%20study%20notes%20that%20the,when%20the%20substances%20were%20detected.

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

https://www.sciencedirect.com/science/article/pii/S0160412023003069?via%3Dihub


Sunday, March 3, 2024

We’re Sinking and Sea Level is Rising

This article is excerpted from the article cited below,  the Virginia Tech news release, the NOAA 2022 update to the Sea Level Rise Technical Report and a previous blog post. 

Leonard O Ohenhen, Manoochehr Shirzaei, Patrick L Barnard, Slowly but surely: Exposure of communities and infrastructure to subsidence on the US east coast, PNAS Nexus, Volume 3, Issue 1, January 2024, pgad426, https://doi.org/10.1093/pnasnexus/pgad426

In 2022 NOAA Released an update to the Sea Level Rise Technical Report. The report project sea level along the U.S. coastline to rise, on average, 10 - 12 inches (0.25 - 0.30 meters) in the next 30 years (2020 - 2050), matching the rise measured over the last 100 years (1920 - 2020). Sea level rise will vary along U.S. coasts because of changes in both land and ocean height.

The east coast is expected to be the relative sea level hot spot over the next three decades projected to rise on average: 10 - 14 inches (0.25 - 0.35 meters). This hot spot along the east coast extends from Cape Hatteras, North Carolina to Boston, Massachusetts with the Southern Chesapeake Bay region will experiencing the most significant rise.

In the last century this area experienced the highest rate of sea level rise in the nation and is forecast to continue to have the highest sea level rise in the next 30 years due to glacial rebound, land subsidence and the rising sea levels. In the most recent study Ohenhen et al, looked at the contribution of land subsidence on the relative sea level rise. They found that the major cities on the U.S. Atlantic coast are sinking, in some cases as much as 5 millimeters per year – a decline at the ocean’s edge that well outpaces global sea level rise. The land subsidence is due to compaction from groundwater pumping. When you withdraw the groundwater from fine-grained compressible confining beds of sediments which are typical of the coastal regions (and other areas)  and do not replace it, the land subsides. 

To examine the phenomena the scientist used space-based radar satellites to build digital terrain maps that show exactly where sinking landscapes present risks to the health of vital infrastructure within 62 miles of the coastline. Using the publicly available satellite imagery, Ohenhen et al measured millions of occurrences of land subsidence spanning multiple years. They then created some of the world's first high resolution depictions of the land subsidence.

The scientists found that New York City, Long Island, Baltimore, Virginia Beach and Norfolk are seeing areas of rapid “subsidence,” or sinking land, alongside more slowly sinking or relatively stable ground. This differential subsidence  increase the risk of damage and failure to roadways, bridges runways, building foundations, rail lines, and pipelines,

In Virginia our local land subsidence is due to glacial rebound after the Laurentide ice sheet melted, excessive groundwater extraction from the coastal aquifers, as well as the effects of the meteor impact near Cape Charles, Virginia (about 35.5 million years ago). Combined, they are all causing the relative sea level rise that is the highest along the coastline. The Aquifer-system compaction from non-sustainable groundwater extraction accounts for more than 50% of the land subsidence observed in the coastal region. 

Land subsidence barely registers as an issue of concern in public policy. However, this slow, gradual, and unapparent land sinking motion magnifies the exposure of coastal residents to the increases in sea levels due to climate change.  Subsidence increases the threat to coastal communities from sea level rise and may even triple estimates of potential flooding areas over the next few decades. Even if current climate measures successfully curb rising sea levels, continuous land subsidence may result in irreversible inundation, more frequent flooding and damage to infrastructure in these coastal regions.

Subsidence of more than a few millimeters per year are a cause for concern, particularly in densely populated areas because subsidence can undermine building foundations; damage roads, gas, and water lines; cause building and bridge collapse. Differential subsidence is most damaging especially in areas with essential facilities like hospitals, schools, or transportation hubs.

These groundbreaking new maps generated by Ohenhen et al show that a large area of the East Coast is sinking at least 2 mm per year, with several areas along the mid-Atlantic coast (Virginia) of up to 1,400 square miles, sinking more than 5 mm per year. This is more than the current 4 mm per year global rate of sea level rise. These coastal regions, where most large cities are located  are on the front lines of climate change impacts and associated uncertainties due to the combined effect of subsidence and sea level rise.  

Over the past century population migrated to the low-elevation coastal areas.  Continued accelerating sea-level rise and land subsidence will increase the future vulnerability of coastal communities worldwide. The impact of sea level rise-amplified hazards on coastal communities, such as flooding and erosion, dominates discussion and planning  in global climate change discussions, with land subsidence (due to unstainable groundwater use) relegated to the background. Land subsidence, however, is a pernicious and growing problem on a global scale with more immediate hazards to coastal areas and often presents more pressing and localized challenges. Policy changes to better manage groundwater withdrawal could slow relative sea level rise.

The lead author of this study is Leonard Ohenhen, a graduate student working with Associate Professor Manoochehr Shirzaei at Virginia Tech’s Earth Observation and Innovation Lab. This work provides important quantitative data for coastal disaster resilience planning.


 

Leonard Ohenhen

Manoochehr Shirzaei



Wednesday, February 28, 2024

Do You Know What's in your Well Water?


Public water supplies are tested daily for contaminants.  Private wells are tested when you do it, and you should do it every year. Prince William County Extension will be having a test your well water clinic next week.  Sign up now online BSE-VAHWQP-PW 2023 Prince William County Virginia Household Water Quality Program | Virginia Cooperative Extension (vt.edu)

Water samples will be tested for: iron, manganese, nitrate, lead, arsenic, fluoride, sulfate, pH, total dissolved solids, hardness, sodium, copper, total coliform bacteria and E. Coli bacteria. Sample kits will be $65  this year. Registration and pre-payment must be online by going to https://tinyurl.com/VCE-PW-VAHWQP before March 16th 2024. I had no trouble following the link and prepaying. Be aware they will send  a receipt and confirmation of registration from the VCEPrograms  and a payment receipt from the Bursar at VA Tech.

 The Prince William Drinking Water Clinic has 3 parts:

1. Attend a Kick-Off Meeting and Collect Testing Kit Materials, the online registration lets you select from 3 Kick-Off Options:

Option 1: In Person, Woodbridge: Board Chambers, McCoart Administration Building (1 County Complex Ct, Woodbridge, VA 22192):  Saturday, March 23rd 10:00am - 11:00am. 
Option 2: In Person, Manassas: Jean McCoy Conference Room (Sudley Government Center, 7987 Ashton Ave, Manassas, VA 20109): Tuesday, March 19th 6:00pm - 7:00pm.
Option 3: 
Online, through ZoomWednesday, March 20th 11:00am - 12:00pm. If you choose this option, you must also register for the Zoom meeting through this link: https://bit.ly/PWCVAHWQP
*Test kits for Option 3 (Zoom meeting) must be picked up at VCE-PW Office (8033 Ashton Ave., Suite 105, Manassas, VA 20109): March 21st - 22nd or March 25th - 26th, 9:00am - 4:00pm

2. The Sample Drop Off: Wednesday, March 27th from 6:00am - 10:00am ONLY at the VCE-PW Office, 8033 Ashton Ave., Suite 105, Manassas 20109.

3. Results Interpretation Meeting through (Zoom) on Tuesday, May 7th, 6:00pm - 7:00pm. There will be a live Zoom interpretation meeting co-hosted by VCE Household Water QualityCoordinator Erin Ling and VCE-PW staff to explain the report, include a discussion, and questions and answers. Zoom link and details will be emailed to all registrants.

The number of kits is limited. Pre-payment online is the only way to pay and guarantee you will get a kit. You must pay and register by March 16th 2024. No refunds will be available. Household water quality is driven by geology, well construction and condition, nearby sources of groundwater contamination, and any water treatment devices and the condition and materials of construction of the household plumbing. To ensure safe drinking water it is important to maintain your well, test it regularly and understand your system and geology. If you have water treatment equipment in your home you might want to get two test kits to test the water before and after the treatment equipment to make sure you have the right equipment for your water and that it is working properly. All participant information is kept strictly confidential

The chart below shows what was found in the  private wells tested test of testing  in Prince William County in 2023 (kindly ignore the error in my column titles).

 


Sunday, February 25, 2024

Salt in the Reservoir

This article is excerpted from the article cited below and the Virginia Tech news release.  

Bhide, Shantanu & Grant, Stanley & Parker, Emily & Rippy, Megan & Godrej, Adil & Kaushal, Sujay & Prelewicz, Greg & Saji, Niffy & Curtis, Shannon & Vikesland, Peter & Maile-Moskowitz, Ayella & Edwards, Marc & Lopez, Kathryn & Birkland, Thomas & Schenk, Todd. (2021). Addressing the contribution of indirect potable reuse to inland freshwater salinization. Nature Sustainability. 10.1038/s41893-021-00713-7.

Inland freshwater salinization historically was once thought to be a problem only in areas with arid and semi-arid climates, poor agricultural drainage practices, sodic soils and saline shallow groundwater. However, today we know that inland freshwater salinization is on the rise across many cold and temperate regions of the United States.  Inland freshwater salinization is particularly notable in the densely populated Northeast and Mid-Atlantic and agricultural Midwest regions of the country like here in Northern Virginia.

Freshwater salinization threatens freshwater ecosystem health and human water security. Chloride enrichment of streams is associated with declines in pollution sensitive benthic invertebrates and loss of critical freshwater habitat. Stream-borne salts can mobilize, nutrients and heavy metals that were previously sequestered into sensitive ecosystems and drinking-water supplies. Salinization of drinking-water supplies can mobilize lead, copper and other heavy metals from ageing drinking-water infrastructure through cation exchange and corrosion. It can also alter the perception of the quality of the water, a high enough concentrations, sodium and other salts degrade the taste of drinking water (coffee and tea).

Inland freshwater salinity is rising worldwide and is now called the freshwater salinization syndrome (FSS). Though increasing salinization is commonly attributed to winter deicing operations, winter application of brine and salt are only a part of the problem. Chronic salinization is primarily a result of increasing population and indirect potable reuse of wastewater-the practice of augmenting water supplies through the addition of highly treated wastewater and down river use of our freshwater resources. Releasing treated wastewater to surface waters and groundwaters has been growing and is encouraged by the EPA along with other forms of water reuse in their Water Reuse Action Plan.

In our own region, both indirect potable reuse of waste water from the Upper Occoquan Service Authority (UOSA) and human activities in the Bull Run and Occoquan River watersheds contribute to salinization of the Occoquan Reservoir in Northern Virginia. More than 95% of freshwater inflow to the reservoir is from the Occoquan River and Bull Run, which drain mixed undeveloped, agriculture, ex urban and urban and increasingly industrial landscapes.

Water from Bull Run includes baseflow (including from groundwater) and storm water runoff from the Bull Run watershed (34% of annual flow) together with highly treated wastewater discharged from UOSA (6% of annual flow) located just over a mile upstream of Bull Run’s confluence with the reservoir. Conceived and built in the 1970s, UOSA was the United States’ first planned application of indirect potable reuse and a model for the design and construction of similar reclamation facilities worldwide. Water discharged from the Occoquan River comes primarily from baseflow and stormwater runoff from the Occoquan River watershed (60% of annual flow).

The scientists found that possible sources of rising sodium concentration in the reservoir include deicer use in the rapidly urbanizing Occoquan River and Bull Run watersheds. Over the past 20 years salt has been added to UOSA’s sewer water from its >350,000 residential and commercial connections. Possible sources of sodium within UOSA’s sewershed include the down-drain disposal of sodium-containing drinking water and sodium-containing household products, use of water softeners in commercial and residential locations, and permitted and non-permitted sodium discharges from industrial and commercial customers.

from Bhide et al

The sodium concentration in UOSA’s effluent are consistently higher than sodium concentrations measured in Bull Run and the Occoquan Reservoir. Using probability analysis of the sodium mass load for the period 2010–2018 confirms that UOSA’s reclaimed water though small in volume dominates the sodium mass load entering the reservoir from the Occoquan River and Bull Run during dry and median weather conditions. UOSA’s contributes 60% to 80% of the sodium loading during dry periods, 30% to 50% during median and 5% to 25% during wet conditions. The Occoquan River and Bull Run watersheds exhibit the opposite pattern, contributing a greater percentage of the overall sodium load during wet weather periods. During wet weather, sodium mass loading from the Bull Run watershed is, on average, higher than sodium mass loading from the Occoquan River watershed, but both are dwarfed by UOSA. Across all timescales evaluated, sodium concentration in the treated wastewater is higher than in outflow from the two watersheds.

from Bhide et al
It begs the question, where does the sodium in UOSA’s reclaimed water come from? The scientists believe that the sodium in UOSA’s water comes from a variety of sources -watershed deicers, water treatment processes, household products, commercial and industrial discharges, drinking water treatment, and wastewater treatment. On the basis of data provided by UOSA they estimate that, on an annual average, 46.5% of the daily sodium mass load in UOSA’s reclaimed water is from chemicals used in water and wastewater treatment (for pH adjustment, chlorination, dechlorination and odor control), a single permitted discharge from the Micron Semiconductor facility and human excretion (our diets are salty). The source of the remaining 53.5% is unknown but the scientist believe it  includes contributions from the down-drain disposal of sodium-containing drinking water from Lake Manassas, the Potomac River and the Occoquan Reservoir, as well as sodium-containing house hold products that eventually end up in the sanitary sewer system.

Fairfax water has been exploring options to address the slowly rising sodium concentration in the reservoir, including the possible construction of a reverse osmosis treatment upgrade. Desalinating fresh water was estimated cost at least $1 billion, not including operating and maintenance costs and a vastly higher carbon footprint. This would include a tremendous loss of volume. Reverse osmosis looses about three quarters of the water. Which is the real problem.

The researchers envision at least four ways in which salt pollution can be reduced: limit watershed sources of sodium that enter the water supply (such as from deicer use), enforce more stringent pre-treatment requirements on industrial and commercial dischargers, switch to low-sodium water and wastewater treatment methods, and encourage households to adopt low-sodium products. 

"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," said Dr. Stanley Grant  the director of the Occoquan Waster Quality Laboratory and one of the paper’s authors.