5th Annual ICPRB Water Conference

The 2026 Potomac River Conference, organized by the Interstate Commission on the Potomac River Basin (ICPRB) was held in Poolesville, Maryland September 9^th 2026- conveniently located near nothing. I attended and found comfort in that all the regional water utilities were in various stages of planning to address this critical need for a sustainable and resilient water supply in the region. Experts from various sectors gathered to discuss the impacts of population growth, aging infrastructure, and the significant water demands of data center development. The event highlighted the necessity of regional collaboration and innovative strategies like expanding  water reuse to navigate future environmental uncertainties. Additionally, the conference showcased advancements in forecasting technology though none of the models are as yet particularly good at forecasting river flow. Groundwater research intended to improve long-term resource management is just beginning. Here is some of what we learned.

Navigating Water Supply Challenges in the Potomac River Basin

The Potomac River serves as the primary drinking water source for about 5 million residents across the Washington metropolitan area, supplying major regional utilities including Loudoun Water, Fairfax Water, WSSC Water, DC Water, and the Washington Aqueduct. The  2026 Potomac River Conference was titled "A Dry Horizon: The Future of Water Supply in the Potomac River Basin."

Surging Demand: Population Growth and the Data Center Boom

Regional water demand is being reshaped by expanding communities and rapid industrial development across Northern Virginia, Maryland, and Washington, D.C.:

• Population Growth and Demographic Forecasting: Utilities rely on regional planning data, such as the Metropolitan Washington Council of Governments' (MWCOG) Cooperative Forecasts of population, employment, and households, to project long-term drinking water demand. As metropolitan populations and demand grow, balancing baseline residential water needs against finite seasonal river flows becomes increasingly complex.
• Data Center Expansion: The rapid development of data centers—particularly in Virginia—has introduced substantial new water and energy demands. Conference sessions highlighting the "water-energy nexus" and data center impacts noted that cooling infrastructure puts unique pressures on both surface water supply systems and groundwater sustainability. The need for water for cooling  occurs exactly at the same time when seasonal water flow is lowest. Organizations such as the Piedmont Environmental Council and the Montgomery Countryside Alliance emphasized the importance of groundwater to the overall water supply and  highlighted how high-density data center corridors require careful resource management to prevent aquifer stress and local infrastructure bottlenecks.

Julie Bolthouse, Director of Land Use Piedmont Environmental Council, had some interesting points on the growing use of water in data centers. Google is the ONLY hyperscaler reporting water withdrawal and consumption for individual data center facilities. Here is what they reported for their water use in their Virginia facilities in 2024. You will note that 74-80% of the water use is consumptive and lost from the system:

 

From PEC Presentation J. Bolthouse

In 2019 Loudoun County total average daily system demand was closer to 20–25 MGD. Maximum day water demand at that time was around 40 million gallons per day. As data centers come on-line the water use grows. By 2025 average daily system demand was 29 MGD and maximum day water consumption was 50 MGD. Though, population in Loudoun is growing in Loudoun, it’s not driving this increase in water consumption. In addition, data centers are using an average of 2.2 MGD and a Maximum of 5.5 MGD of reclaimed water that is not being returned to the Potomac. That is somewhere around a 50% increase in water use in Loudoun County in 6 years.

Supply Stressors: Climate Change and Land Use Shifts

While demand grows, environmental and land use factors are altering how water flows into and through the Potomac watershed:

• A Wetter but More Variable Climate: Hydrological research presented by the USGS indicates that the Potomac Basin is transitioning toward a wetter but more variable hydrological regime. This shift introduces greater unpredictable variability—bringing intense precipitation events alongside heightened risk of sudden seasonal droughts. To adapt, regional stakeholders are developing advanced forecasting tools, including probabilistic deep-learning  streamflow models and National Weather Service Middle Atlantic River Forecast Center (MARFC) products for water supply and drought management. Nonetheless, the frequency of whiplash events- going from drought to flood has increase and supply risk could grow despite general wetness of the future climate.
• Land Use and Watershed Health: Land use transformation across rural and suburban areas directly impacts groundwater recharge and increases stormwater and wastewater infrastructure challenges. Assessments in counties like Loudoun and Montgomery stress that protecting local groundwater supplies and managing land development are vital to preserving overall river basin resilience.

Regional Solutions and Collaborative Planning

To protect the region's drinking water future, regional water authorities are pursuing coordinated operational strategies:

• Water Reuse and Storage Strategies: Integrated approaches such as Fairfax Water's indirect water reuse program in the Occoquan reservoir system demonstrate how indirect potable reuse enhances overall system reliability during low-flow conditions. During dry summers, UOSA provides upto 90% of the flow into the Occoquan Reservoir.
• Shared Vision Planning and Source Protection: Water suppliers are engaging in USGS Shared Vision Planning frameworks, coordinated reservoir release operations, and ICPRB land prioritization mapping to protect critical source water parcels throughout the watershed. Unfortunately, the planning departments of many counties do not appear to be focused on protecting critical source water parcels.

The reality is that an event like the Colonial Oil spill in 1993 which spilled 408,000 gallons of diesel/ fuel oil shut down the Fairfax Water Potomac Intake for two weeks could no longer be survived without disrupting water supply today. The Occoquan Reservoir/ Griffith Water Treatment plant and connection to the Aqueduct in Falls Church and Arlington could no longer supply their approximately 2 million customers.

17th Annual Upper Occoquan Cleanup

 

On Saturday, September 26, 2026, from 9 a.m. until 12 p.m. (rain date October 3, 2026), Prince William Trails and Streams Coalition (PWTSC) is conducting its 17th annual clean-up of the upper Occoquan River, from nine different sites along 25+ miles of the Occoquan River. The cleanup ranges from Cedar Run/Broad Run, through Lake Jackson, and from the base of Lake Jackson Dam to Hooes Run (south of Lake Ridge Marina) and Belmont Bay Community. Stormwater drainages and ponds are not left out during this community water quality awareness event.   

Homeowners’ associations, civic associations, businesses, environmental/cooperative organizations, and student organizations are encouraged to support these efforts to reduce trash  in local waterways and raise community awareness of water quality.

Experienced kayakers, canoeists, Jon boaters, and pontoon boaters are also requested for the on-the-water portion of this conservation effort.   Boaters are expected to put in and take out at the same access point. If you plan to put in and take out at another location, you must make transportation arrangements. No shuttle service is available this year. Interested participants should register at www.pwtsc.org for updates and cancellation information. 

Contact: Bill McCarty (wmccarty@manassaslawyers.com) and Veronica Tangiri at waterquality@pwswcd.org (571-379-7514). 

 For cleanup supplies, data sheets to report cleanup data, or to share pictures, contact: waterquality@pwswcd.org  (571-379-7514)

This massive collection of trash from the Occoquan River happens every year and on the river is the combined effort of the Prince William Trails and Streams Coalition, Trash Free Potomac Watershed, Penguin Paddling, Prince William County Parks and Recreation Department and the Prince William Soil and Water Conservation District Come on out and help our community. Trash bags, gloves, water and refreshments will be provided to all participants. This is a true on the river cleanup and is done primarily by boat – volunteers with canoes, kayaks or jon boats are needed. The signup has all the launch and take-out locations.

Unfortunately, it is necessary to hold these river cleanups annually. Year after year volunteers clean our roadways, streams, rivers, and streambeds of trash that started as litter and carried along by stormwater and wind into our waterways and parks. Volunteers also remove items that were illegally dumped in the woods or carried by off by storms. 

The ORPA Needs Strong Protections

The soils of the Occoquan Reservoir Protection Area (ORPA) are not ordinary land. They are part of the region’s drinking-water protection system. In this area, the thin layer of soil and saprolite above the bedrock stores rainfall, filters pollutants, slows runoff, and feeds groundwater and streams. Because the underlying crystalline bedrock provides little natural water storage, the soil layer does work that cannot be replaced once it is stripped, compacted, or regraded. Protecting ORPA soils is therefore not optional; it is essential to protecting private wells, stream baseflow, and the Occoquan Reservoir.

For that reason, the ORPA needs protections that are stronger than ordinary rural zoning and stronger than standard stormwater rules. In Hydrogeologic Group D crystalline igneous rock, water is not stored in the bedrock in any meaningful way. It is stored, slowed, filtered, and released by the soils above it. Those soils are the area’s natural water infrastructure. Any ordinance or rezoning that allows broad clearing, mass grading, heavy-equipment compaction, or large disturbed construction footprints in the ORPA allows the damage of the very system the ORPA was created to protect.

ORPA Soils Need Strong, Standalone Protection

1. ORPA Soil Loss Poses a Special Water-Supply Risk

The ORPA should not be regulated as if it were geologically the same as other rural areas. In sedimentary areas such as the Culpeper Basin, bedding planes and limited matrix storage may provide some additional capacity to absorb localized disturbance. That does not make disturbance harmless, but it does mean the risk is different.

In the ORPA, the risk is greater. The crystalline bedrock has little primary storage. Water depends on the soil and saprolite above the bedrock to infiltrate slowly, reach fractures, and recharge wells and streams. If that layer is removed, compacted, or cut off from the fracture system, the water-supply function can be lost on that site and may not be realistically restored.

A uniform rule is not scientifically fair when the risk is not uniform. The ORPA needs stricter rules because its soils perform the storage and filtration functions that deeper formations may perform elsewhere.

2. Mass Grading and Compaction Damage the ORPA’s Natural Water System

Construction in the ORPA can cause lasting hydrologic damage. Heavy equipment compresses soil, closes pore space, reduces infiltration, and increases runoff. Once that structure is lost, planting grass or adding landscaping does not restore the soil’s original ability to store and release water.

The soil profile also acts as the first filter for sediment, nutrients, hydrocarbons, metals, and other pollutants. When soil is stripped, thinned, or compacted, pollutants have a faster and less filtered path to fractures, groundwater, streams, and ultimately the reservoir.

That is why ORPA soils should be treated in law as protected water-resource infrastructure. Rules that permit broad clearing, mass grading, and unrestricted construction access are not compatible with the ORPA’s drinking-water purpose.

3. Disturbed ORPA Soils Increase the Risk to Wells, Streams, and the Reservoir

Where shallow soils sit above fractured crystalline bedrock, disturbance can create a direct pathway for contamination. Once the soil filter is damaged, contaminants can move more quickly toward groundwater and connected surface waters.

A spill, sediment release, fuel leak, or industrial discharge on a disturbed site may not remain on that site. It can move through fractures, drainage paths, or streams toward neighboring wells and tributaries. Because the ORPA helps protect the Occoquan Reservoir, that level of risk should not be accepted as a routine cost of development.

For this reason, uses that require extensive impervious cover, large grading footprints, heavy industrial or electrical infrastructure, high-volume water use, or large inventories of fuel or chemicals should either be prohibited in the ORPA.

4. Protecting ORPA Soils Protects the Region’s Drinking-Water Supply

The ORPA is not just a rural landscape. Its streams and shallow groundwater help sustain the Bull Run and Occoquan River system, which supports a major public drinking-water supply for Northern Virginia. Soil disturbance in this area can therefore affect more than one property owner; it can affect a regional water supply.

During dry periods, streams depend on slow groundwater discharge. If the ORPA’s soil sponge is compacted or removed, less water infiltrates, more water runs off quickly, and dry-weather streamflow declines. That means more erosion, more concentrated pollutants, greater stress on streams, and greater vulnerability for the reservoir.

Because the ORPA protects both private wells and a regional reservoir, the burden should be on development applicants to prove that their projects will not harm soil function, recharge, filtration, or baseflow. If that proof cannot be made, the answer should be no.

Recommended Requirements for an ORPA Soil Protection Overlay

A meaningful ORPA overlay should start with a simple rule: keep the natural soil profile intact unless disturbance is unavoidable and tightly limited. These protections should be enforceable requirements, not voluntary practices:

• Strict disturbance caps: Prohibit mass grading and sharply limit the area that may be cleared, stripped, compacted, or crossed by heavy machinery. The cap should apply to the full construction footprint, not only to final impervious surface.
• Protected soil conservation areas: Require fenced construction-exclusion zones where native soils, vegetation, and root systems remain undisturbed. These areas should be protected as seriously as wetlands and stream buffers.
• No net loss of infiltration capacity: Require applicants to show that post-development infiltration, recharge, and baseflow support will be maintained. Detention ponds should not be treated as substitutes for intact soils.
• Low-impact site design: Require development to preserve forest cover, maintain sheet flow, minimize grading, and use distributed practices such as rain gardens, bioswales, amended soils, and small-scale infiltration features that mimic natural recharge.
•  Limits on groundwater extraction: Prohibit or severely restrict high-volume groundwater withdrawals because fractured crystalline-rock systems cannot reliably absorb heavy pumping stress.
• Exclusion of incompatible uses: Ban or strictly limit uses that require large grading footprints, extensive impervious cover, heavy industrial infrastructure, hazardous materials, or water-intensive operations that conflict with reservoir protection.

Conclusion: The ORPA’s soils are the first line of defense for private wells, streams, and the Occoquan Reservoir. Once they are stripped or compacted, their function cannot be replaced by stormwater ponds, landscaping, or later mitigation. The law should therefore presume preservation, strictly limit disturbance, and require every proposed project to protect the soil system as essential public water infrastructure. If the ORPA is meant to protect the reservoir, then protecting its soils must be the starting point.

The Geology of Prince William County is not uniform

I know that lately I have focused on the highly fragile headwaters of the Occoquan and Bull Run Rivers, but from a hydrogeologic standpoint, the Occoquan Reservoir Protection Area (ORPA) represents the most fragile geology in all of Prince William County.

While other regions of the county face severe environmental pressures from the growing impacts of land use change, the Hydrogeologic Group D crystalline igneous rock underlying the Piedmont portion of the ORPA possesses a unique set of structural vulnerabilities that make its groundwater supply far more precarious than any other formation in the county. 

Comparative Fragility Across Prince William County's Three Geological Zones

To understand why the ORPA is uniquely fragile, it must be compared to the county's other two primary geological regions. Understand that I am talking about the impact on groundwater well users and baseflow flow to streams, not the long term limitation and renewed drawdown of the Coastal Plain Aquifer.

 Why the ORPA Group D Geology Wins the "Fragility Index"

1. Absolute Absence of Bedrock Storage: In the Culpeper Basin, if the topsoil is damaged, the underlying sandstones still hold millions of gallons of water within their layered sedimentary bedding planes. In the ORPA's Group D rock, there is no backup storage. If the shallow overburden sponge is stripped or compacted by land-use changes, the underlying water storage is effectively reduced to zero.
2. Immediate "Straw" Drawdown: Because water is tightly confined to narrow vertical fractures, a single high-volume well or an up-gradient disruption can instantly drain a localized rock fracture. The system lacks the horizontal hydrologic connectivity found in the Eastern Coastal Plain to dynamically "re-level" or distribute water pressure.
3. No Safety Net for Private Users: Unlike the eastern Urban Growth Boundary where residents are hooked up to municipal water lines, thousands of ORPA residents rely entirely on individual, private wells tapping these exact Group D fractures. They are isolated on a hyper-local supply that can fail with zero regional warning.

Google’s Water-Stewardship Claim vs. Water Sustainability

 Just last week Google announced a  $10 million water-stewardship commitment in Virginia.  Google’s public message is that this fund will address community concerns about data-center water use and support its goal of becoming water positive by 2030. The proposal emphasizes stormwater filtration, replenishment projects, agricultural conservation funding, and facility-efficiency measures.

That framing is useful as public relations, but it is superficial when compared with the permanent conversion of forests, soils, headwaters, and recharge areas into industrial campuses of concrete, asphalt, substations, server halls, and continuous heat exhaust. Filtration grants and offset accounting cannot replace the natural watershed functions and cooling capacity lost on site.

Google’s Proposed PR Claim

Google presents the funding as proof that data-center growth can continue while water impacts are managed through engineered projects and offset-style investments. The claim rests on three ideas: filter stormwater, replenish water elsewhere, and reduce facility water demand.

• Install 400 Stormwater Filtration Systems. The initial phase rolls out $4.4 million to install roughly 400 filtration units.  
• Target Urban Runoff. The projects focus heavily on capturing and cleaning stormwater, starting with communities near major operations, though exact area recipients are still being finalized.  (It will be in the Richmond they are building in Midlothian hydrologically upstream of Richmond.)
• Fund Watershed Replenishment. The remaining portion of the $10 million is part of a broader $60 million national expansion to co-fund early-concept infrastructure, nature-based solutions, and agricultural water-saving projects.

Why the Claim Is Superficial

The central problem is that Google treats water as an accounting exercise rather than as part of a living watershed and local climate system. Gallons funded or filtered in one place do not restore the recharge area, stream network, shade canopy, soils, and source-water protections destroyed somewhere else.

Agricultural BMP funding is not new. Virginia already has an Agricultural Best Management Practices Cost-Share Program administered through the Department of Conservation and Recreation and local soil and water conservation districts. Google’s reliance on that framework should not be described as a new solution to data-center impacts.

The Core Contradiction

Google’s narrative asks the public to focus on voluntary stewardship projects while overlooking the scale and permanence of the underlying land-use conversions. Data-center construction clears vegetation, compacts soils, and replaces permeable ground with roofs, roads, pads, and substations. These impervious land cover generate more stormwater runoff and mobilize more sediment before, during, and after construction. The company can fund filters, report replenishment volumes, and tout water-positive goals, but those measures do not restore destroyed headwaters, rebuild forested recharge areas, cool overheated industrial landscapes, or prevent source-water impairment from sediment, thermal loading, chemicals, and high-velocity runoff.

1. The Volumetric vs. Ecological Fallacy

Google and other hyperscalers claim they will become "water positive" by returning more gallons of clean water to the environment than they withdraw for cooling operations. However, water stewardship is not a simple ledger balance. Withdrawing millions of gallons of cool, treated potable water from an aquifer or municipal reservoir and replacing it with downstream stormwater runoff or agricultural savings at a different location creates severe localized hydrologic deficits.

Water extracted during heatwaves (when peak cooling demand occurs) reduces stream flows and aquifer levels when ecosystems are under maximum drought stress, while downstream stormwater replenishment during winter or wet seasons cannot revive depleted headwaters or dried-up vernal pools.

2. Paving Over Natural Hydrology

Constructing a hyperscale campus requires clearing hundreds of acres of mature forests, pastures, and permeable soils to install the hundreds of thousands of square feet of concrete server buildings, massive high-voltage electrical substations, and heavy-duty asphalt access roads and parking lots.

Forested soils absorb nearly 90% to 100% of standard rainfall, recharging local aquifers gradually. Impervious surfaces convert over 80% of rainfall directly into high-velocity surface runoff. Data-center construction therefore creates the very stormwater volume and velocity problem that downstream filtration systems are later marketed as solving.

Stormwater filters trap particulate matter (trash, oil, some heavy metals), but they do not reduce the volume or velocity of water. High-velocity storm surges blow out natural stream banks, cause severe downstream erosion, wash away riparian buffers, and destroy benthic (aquatic bottom-dwelling) ecosystems.

3. Construction Sediment and Source-Water Impairment

Mass grading for data-center campuses exposes vast acreage of clay and silt while removing vegetation that would otherwise hold soil in place, absorb rainfall, and slow runoff. The result is a construction-phase surge in stormwater runoff and sediment loading. Even with silt fencing and sediment basins, intense Virginia downpours can overwhelm controls and carry disturbed soil into tributaries.

This has a significant impact on the source water for our drinking water supplies. Silt and sediment wash directly into tributaries of major drinking water sources (such as the Potomac River, Occoquan Reservoir, and the Swift Creek Reservoir, Lake Chesdin, and the James River. Hydrologically, Midlothian is located upstream of downtown Richmond.

Suspended sediment smothers fish spawning beds, blocks sunlight from submerged aquatic vegetation, and clogs municipal water treatment intake filters, driving up treatment costs for residents. Grants to install 400 municipal filtration units downriver in RIchmond do nothing to restore the headwater streams permanently altered by construction silt.

4. Thermal Pollution and Data Heat Islands

The same land conversion that increases stormwater volume also increases heat. Wide roofs, asphalt lots, concrete pads, transformers, generators, and substations absorb and re-radiate heat, while servers discharge waste heat continuously.

This creates a specialized data heat island which has been measured in recent studies. It is an industrial microclimate layered on top of ordinary urban heat-island effects. Heat from paved surfaces and server operations can increase local temperatures, intensify hot runoff, and add thermal stress to nearby streams.

Air-cooling shifts rather than eliminates the heat burden. It can reduce direct water withdrawals, but it pushes more waste heat into the surrounding air through fans and radiator systems, worsening local heat stress while leaving the industrial footprint in place. The result is the double burden of less natural land available to absorb rainfall and recharge groundwater, and more built infrastructure generating heat that can worsen stormwater and source-water impacts.

5. The Scale Imbalance: Offset PR vs. Watershed Loss

Virginia’s data-center buildout involves large, permanent land conversions across watersheds there are thousands of acres with millions of square feet of data centers. A $10 million local fund is small compared with the capital cost and ecological footprint of hyperscale campuses.

Even more significant is the scale of the impact.  Retention basins, filters, and agricultural cost-share dollars do not counteract the permanent loss of watershed sponge capacity, shade canopy, groundwater recharge, or local cooling function.

Corporate Commitments vs. Watershed Realities

Corporate Grant Focus	Actual Ecological Issue on the Ground	Resulting Ecological Outcome
Volumetric Gallons Replenished	Localized extraction during peak drought/heat spikes	Aquifer drawdowns and reduced baseflow in local streams
Downstream Stormwater Filters	Clearing, grading, soil compaction, and expansion of impervious surface area	More stormwater runoff, sediment loading, flash flooding, and downstream stream-bank erosion
Repackaged Agricultural BMP Cost-Share Funding	Virginia already operates a public agricultural BMP cost-share program through DCR and local soil and water conservation districts	Corporate funding is presented as innovation even though it relies on an existing conservation mechanism that does not repair data-center land conversion
Voluntary Stewardship Reports	Permanent conversion of forests to concrete/asphalt	Permanent loss of natural aquifer recharge, shade canopy, and landscape cooling capacity
Claims About Air-Cooling Efficiency*	Waste heat is discharged into the surrounding air instead of being reduced at the source	Localized heat islands, hotter stormwater, greater heat stress, and intensified thermal pollution of nearby streams

* We are not even addressing the water cost of the electricity and the additional power needed to "air cool."

Bottom Line

Google’s proposal may create discrete water-quality benefits, but it does not answer the central question of whether Virginia should accept permanent watershed conversion, impaired source waters, degraded stream systems, and intensified local heat islands in exchange for voluntary offset projects.

A more honest assessment would compare the public claim against the full ecological cost.  The total impact including forest loss, impervious-cover expansion, soil compaction, altered runoff, sediment pollution, thermal loading, data heat islands, and reduced resilience of drinking-water sources needs to be examined. This for the moment totally ignores the need to build more dispatchable power generation that also has a large water footprint.

2026 Dead Zone Update

 

from VIMS

The2026  “Dead Zone” began to build in May and rose steadily until early July when the peak in summer dead zone occurred. However, the size of the “Dead Zone” in the Bay has steadily declined since the peak in July. As of early August both the model-based and data-based estimates of hypoxia are point toward a relatively mild year for deep-water hypoxia in the Bay. This aligns with the forecast issued in the spring.

This year’s mild outlook was largely due to region wide drought with low river flows and reduced nitrogen pollution entering the Bay from earlier in the year. From January through April 2026, the amount of water entering the Bay from rivers was 32% below the long-term average, while the amount of nitrogen was 39% lower than average, totaling about 59 million pounds of nitrogen, according to estimates from U.S. Geological Survey (USGS) monitoring stations.

The “Dead Zone” of the Chesapeake Bay refers to a volume of hypoxic water that is characterized by dissolved oxygen concentrations less than 2 mg/L, which is too low for aquatic organisms such as fish and blue crabs to thrive. Within the hypoxic area life of the bay dies and a “Dead Zone” forms. The Chesapeake Bay experiences hypoxic conditions every year, with the severity varying from year to year, depending on nutrient and freshwater flows into the bay, wind, and temperature.

Each year the Maryland Department of Natural Resources measures the actual dissolved oxygen in the Maryland portion of the Chesapeake Bay main stem and the size of the Dead Zone. While the Virginia Institute of Marine Science (VIMS), Anchor QEA and collaborators at UMCES, operate a real-time three-dimensional hypoxia forecast model using measured inputs that predicts daily dissolved oxygen concentrations throughout the Bay (www.vims.edu/hypoxia) using the National Weather Service wind monitoring data.

The peak of oxygen depletion occurs in July or August when water temperatures are highest and the days are longest accelerating the growth of phytoplankton that ultimately consumes all the dissolved oxygen. The dead zone is typically gone by late fall. Cooler air temperatures at that time of year chill the surface waters, while the deeper water remains warm and allows more mixing of the layers during storms. Cooler water also will hold more oxygen. The size and shape of the dead zone is variable from month to month during the summer. So far this year is looking like a very promising year.

Real-time Estimates of Hypoxic Water Volume | Virginia Institute of Marine Science

At the end of the season the Virginia Institute of Marine Science (VIMS), Anchor QEA and collaborators at UMCES compile all the collected data to report the actual results.The report they prepared at the end of last year,  2025 Chesapeake Bay dead zone near long-term average | Virginia Institute of Marine Science says“… Similar to past years, the Bay’s dead zone expanded through June and peaked in July. However, it remained consistently high throughout July in comparison to past, more variable years. Elevated winds and cooler temperatures in early August helped reduce hypoxia in the Bay before the passage of Hurricane Erin in mid-August triggered a rapid decline. Hypoxia lingered at low levels through September before dissipating as temperatures cooled in the fall.”

“Even in what we classify as an average year, the Bay can experience periods of prolonged stress,” said Batten School of Coastal & Marine Sciences & VIMS Professor Marjorie Friedrichs. “July’s persistent hypoxia illustrates how sensitive the ecosystem is to subtle shifts in wind, temperature and river flow. Those changes can have real implications for the distribution and behavior of fish, crabs and other species that rely on well-oxygenated habitat.”

2025 Chesapeake Bay dead zone near long-term average | Virginia Institute of Marine Science

What We Know about Toxic Algae Blooms

from Maryland Department of Natural Resources

Local water systems, such as the WSSC Water Rocky Goege Reservoir in Maryland and Lake Anna in Virginia, have experienced a dramatic rise in frequency and intensity of Harmful Algal Blooms (HABs) over the last two decades. Let’s take a look at the current science on Hazardous Algae Blooms, HAB’s. Science evolves, but this is what we know, or believe we know now. Cyanobacteria (blue-green algae) has proliferated in Maryland and Virginia reservoirs in the last few decades due to a combination of factors.  While we know of many factors that contribute to HABs, how these factors come together to create a “bloom” of algae is not well understood. HABs occur naturally, but human activities that disturb ecosystems seem to play a role in their more frequent occurrence and intensity. 

The U.S. Geological Survey (USGS), the U.S. Environmental Protection Agency (EPA) and several Universities have studied the phenonium. When you dive into the data from the U.S. Geological Survey (USGS) HAB Research, and others it becomes clear that Harmful Algal Blooms (HABs) are primarily driven by mankind. Human-engineered landscapes, severe nutrient imbalances, and altered water physics, rather than being a vague byproduct of global climate change. The true, measurable causes of these toxic outbreaks break down into four distinct structural pillars:

1. Artificial Hydrological Engineering (Stagnation)

Natural, undisturbed river systems feature high turbulence and rapid flushing speeds that prevent single-celled organisms from accumulating.

When mankind dams rivers to construct drinking water reservoirs we create massive, slow-moving pools with extended water residence times. The result of this is that the water column naturally stratifies in the summer. This rewards the unique evolutionary architecture of cyanobacteria, which use internal gas vesicles to float to the sunny surface while harmless native algae sink and starve in the dark. This is exacerbated by the presence of microplastics which the cyanobacteria exploit .

2. Saturated Phosphorus "Batteries" (Biomass Reserves)

The raw physical volume of a bloom is dictated by phosphorus, which functions as the primary growth limiter in freshwater. Decades of heavy agricultural fertilization, livestock operations, and suburban lawn management have overloaded watershed soils with phosphorus.  This historic surplus creates internal sediment loading. When summer stagnation depletes oxygen at the reservoir bottom, chemical bonds in the mud break, releasing decades of "legacy phosphorus" back into the water to fuel massive blooms from the bottom up—even during dry years with zero active farming runoff.

3. Elevated Nitrogen Inputs (The Toxicity Trigger)

While phosphorus controls how much algae grows, dissolved inorganic nitrogen directly dictates how dangerous the bloom becomes.  Municipal wastewater plants, urban stormwater networks, and failing residential septic infrastructure continuously release nitrates and ammonium directly into local tributaries.  Microcystin and other dangerous cyanotoxins are peptide molecules structurally packed with nitrogen. When human infrastructure floods a system with nitrogen, it alters the water's chemical ratios and acts as a genetic switch, forcing the algae to aggressively synthesize toxins.

4. Microplastic and Chemical "Plastispheres" (Incubation Hubs)

The modern, 21st-century chemical footprint has introduced synthetic materials that alter the physical and biological dynamics of reservoir water. Trillions of microscopic plastic fragments from synthetic clothing, consumer waste, and urban runoff settle into regional water basins.  Floating microplastics absorb organic pollutants and trace metals like iron. Cyanobacteria attach to these particles to form highly resilient biological communities called plastispheres. These plastic rafts keep the colonies floating in the optimal sunlight zone and physically shield them from natural zooplankton predators.

Additional reading can be found at the links below:

• Spatial heterogeneity in mechanisms of internal phosphorus loading from sediments in a subtropical plateau lake - ScienceDirect
• What is a harmful algal bloom? | National Oceanic and Atmospheric Administration
• A REVIEW OF WATER QUALITY RESPONSES TO AIR TEMPERATURE AND PRECIPITATION CHANGES 2: NUTRIENTS, ALGAL BLOOMS, SEDIMENT, PATHOGENS - PMC
• Decoding Harmful Algal Blooms: Unraveling the Mystery | U.S. Geological Survey

Toxic Algae Warning in Maryland

WSSC Water has detected high concentrations of blue-green algae (or cyanobacteria), known as a Harmful Algal Blooms (HAB), in the Triadelphia Reservoir. These HABs can cause adverse health effects. The water contact health advisory will remain in effect for at least one month. The reservoir, located along the Patuxent River in Montgomery and Howard counties, serves as a drinking water source for WSSC Water and a recreational area for hiking, fishing and boating. 

The water contact health advisory issued on July 21, 2026, for the T. Howard Duckett Reservoir also remains in effect. This reservoir is located along the Patuxent River in Montgomery, Prince George’s and Howard counties.

Toxic blue green algae also know as a harmful algal bloom (HAB)  has been increasingly found in the warmer months. WSSC Water monitors both treated and untreated water for cyanotoxins during the warmer months to ensure these toxins do not enter the water system.  Because boiling algae-affected water does not remove toxins, municipal water treatment plants rely on highly technical physical, chemical, and biological processes to ensure the finished tap water is completely safe. WSSC treats algae-impacted reservoir water using a multi-layered approach that physically removes intact algae cells and chemically neutralizes dissolved cyanotoxins to keep the drinking water safe.

WSSC also monitors the reservoirs used for recreation. Accidentally consuming water containing HAB can cause harmful health effects. Signs will be placed around each recreation area when water contact is unsafe. Please adhere to these signs. WSSC Water watershed regulations prohibit pets from being in the water at any time.  

Algae blooms also called harmful algal bloom (HAB) or dead zones form in summers when higher temperatures reduce the oxygen holding capacity of the water, the air is still and especially in years of heavy rains that carry excess nutrient pollution from cities, suburban lawns and farms. The excess nutrient pollution combined with mild weather encourages the explosive growth of algae fed by excessive nutrient pollution.

Not all algal blooms are toxic or hazardous. Only certain species of blue-green algae form the toxin, for reasons that aren't fully understood. Toxic bacteria were not a problem until the 21st century, though algae blooms have been a problem on Lake Erie, the Gulf of Mexico, the Chesapeake Bay and other areas for over half a century. Only algae that contains microcystine or cyanobacteria, a toxin produced by microcystis, a type of blue-green algae that spreads in the summer algae bloom are hazardous.

In the 21st century toxic or hazardous algal blooms have become a global concern in lakes, rivers and oceans, but rising water temperatures caused by climate change, increased nutrient runoff, and altered precipitation patterns are thought to be the contributing factors. They occur when algae grow out of control when there are favorable environmental conditions. Hazardous algal blooms, the ones that contain microcystis a type of blue-green algae produce Microcystine or cyanobacteria toxins, that can lead to the poisoning of fish, shellfish, birds, livestock, domestic pets and other aquatic organisms that can lead to human health impact from eating fish or shellfish exposed to toxins as well as drinking water contaminated by toxins.

The Department of Health advises:

• Avoid contact with any area of a lake or pond where water is green or an advisory sign is posted. WHEN IN DOUBT, STAY OUT!
• Waters that are discolored or have foam, scums or mats that are green or blueish-green should be avoided because they likely contain toxins.  Harmful algae can also be brown or red, and can resemble paint floating on the water.  Toxic algae can stink, smelling nauseating to people, but can be attractive to animals like dogs.
• Do not allow children or pets to drink from natural bodies of water.
• Keep children and pets out of the areas experiencing harmful algae bloom and quickly wash them off with plenty of fresh, clean water after coming into contact with algae scum or bloom water.
• If you, your kids or your animals experience symptoms after swimming in or near an algal bloom, seek immediate medical/veterinarian care.

Symptoms: Human contact with HABs can cause rashes, stomach upset, diarrhea and vomiting.  Dogs can show symptoms including staggering, drooling, breathing difficulty, convulsions or seizures.

To ensure fish fillets are safe to eat, properly clean fish by removing skin and discarding all internal organs, rinse thoroughly with drinking water and cooking fish to the proper temperature.

If you, your pet, or someone you know has come in contact with or ingested water at the reservoir, call your local health department:  

• Montgomery County: 240-777-0311 (Montgomery County 311) 
• Prince George’s County: 301-883-4748 (Prince George’s County 311) 
• Howard County: 410-313-1773 (Environmental Health Department)  

Takeaways from the DEQ Report

When the Virginia Department of Environmental Quality’s (DEQ) finally released their  report on groundwater availability last month it was shocking to many in the groundwater management area.

The Major Takeaways from the Report:

• Groundwater levels across the vital Potomac aquifer are projected to enter a sharp, renewed decline within the next 5 to 10 years under existing conditions.
• Just the two paper mills (located in Franklin and West Point) account for 43% of all reported groundwater withdrawals, creating massive underground "cones of depression".
• Decades of falling water levels have caused land subsidence (sinking) that is accelerating. The land has subsided below sea level, causing irreversible saltwater intrusion into the fresh drinking aquifer.
• Private domestic wells  which need neither a permit or have monitoring make up 34% of groundwater withdrawals (estimated). They are believed to be the fastest-growing drain on the aquifer that DEQ completely lacks the authority to regulate. These numbers are all estimated since there is not data on use for private wells. ** (see note below)
• Due to these constraints, any new water-intensive industry like  a data center using evaporative cooling cannot be accommodated by the available groundwater supply.

However, the most shocking disclosure was that DEQ’s historical regulatory oversight via the groundwater  management area has essentially been irrelevant to active conservation of the Coastal Plain Aquifers. The factual timeline of the Potomac Aquifer demonstrates this point perfectly:

• When the Franklin mill closed in 2010 due to the recession, groundwater levels in the Potomac Aquifer rose to levels not seen since the 1960s. This dramatic rebound was entirely an economic accident, not a result of DEQ regulatory prowess. 
• As soon as economic activity picked up and the mill reopened at a lower production rate in 2012, that entire rebound vanished. Other regional users had quickly consumed the temporary surplus, and by 2021, the aquifer began a renewed steady decline. 
• Even when the DEQ swooped inmoved to aggressively renegotiate and "slash" the permitted limits of the 14 largest industrial users, the cuts reductions were mostly cosmetic. Regulators scaled the permitted caps down to match what the manufactures were already actually using, changing virtually nothing about the real-world volume of water leaving the ground. 

The report fundamentally exposes the Eastern Virginia Groundwater Management Area as a bureaucratic boundary rather than an effective ecological shield. Because the DEQ cannot mandate alternative surface-water switches or stop private well drilling, the declaration of a "management area" has done nothing to alter the water use math dictating the aquifer's decline. 

The global data on aquifer interventions validates this point that labeling a boundary on a map is irrelevant if it does not enforce physical changes in water demand. A landmark 2026 global study published in Science by Dr. Scott Jasechko analyzed 67 successful groundwater recovery stories across six continents and found that mere administrative oversight lacks ecological impact.

The global data reveals why the DEQ’s approach failed and how real recovery actually happens:

The Illusion of "Paper" Management

The Science study notes that 81% of true groundwater success stories relied on introducing an alternative water source to physically offset pumping demands. In contrast, the DEQ’s management area strategy focused on rewriting permit levels on paper. Because those cuts only matched what industries were already pumping, the intervention required zero behavioral change and resulted in zero actual water savings.

Why the Franklin Rebound was a False Success

The study highlights the "impermanence of groundwater recovery," explicitly warning that economic shifts can instantly erase temporary aquifer gains. The 2010 Potomac aquifer rebound occurred purely because the Franklin mill shut down during a recession. Because the DEQ's management area failed to permanently retire that water allocation or legally mandate a switch to surface water, regional users quickly swallowed up the temporary surplus the moment economic activity picked up.

The Cost of Inaction is Irreversible Sinking

The global assessment confirms a harsh geologic reality for the Virginia Coastal Plain while proper interventions can slow down or stall land subsidence (sinking) caused by excessive pumping, the ground sinking (subsidence) is entirely irreversible. Every year the DEQ operates an "irrelevant management area without enforcement teeth that actually limit groundwater use, the regional infrastructure and coastal topography suffer permanent, unfixable structural compression. The compressed land that has subsided will never hold water again.

To move past symbolic boundaries and fix the regulatory loopholes, the Virginia DEQ's report outlines 11 specific recommendations submitted to the General Assembly. Rather than attempting to manage the problem with existing weak rules, the DEQ is explicitly asking lawmakers to rewrite the Ground Water Management Act of 1992 to grant them actual enforcement power.

The primary solutions suggested by the DEQ to fix the aquifer depletion include:

1. Striking Down Permits Based on Alternative Availability

The DEQ requested the statutory authority to deny or heavily limit any groundwater withdrawal permit if an alternative water source is physically available. This would allow regulators to legally force industrial giants (like the paper mills) or future data centers to connect to available surface water or recycled municipal water instead of drilling deeper wells into the Potomac aquifer.

2. A Hard Freeze on New Industrial Permits

The department recommended that lawmakers explicitly prohibit the DEQ from issuing any new permits for significant groundwater withdrawals within the designated management areas. This serves as an immediate "stop-loss" measure to prevent new water-intensive industries from accelerating the aquifer's collapse. 

3. Aquifer-Level Trigger to Deny Applications

The DEQ is asking for the explicit right to auto-deny any water withdrawal application if the requested pumping would lower local aquifer water levels to a predefined danger point. This replaces the current reactive permitting process with a legally binding environmental threshold.

4. Forcing Municipalities to Budget Growth around Water

The DEQ suggested a legislative mandate requiring local governments to limit their long-term comprehensive growth plans based strictly on groundwater availability. This would stop local counties from zoning and approving massive residential subdivisions or industrial parks when the local geology literally cannot provide the water to support them.

5. Funding for Real-Time Infrastructure Monitoring

The DEQ requested $1.7 million in immediate funding over the next two years from the General Assembly to upgrade its science. This money is earmarked to buy real-time monitoring equipment to evaluate active groundwater recharge methods and hire dedicated compliance officers to enforce strict permit limits.

The Governor should convene a special session of the legislature because Virginia cannot continue treating groundwater depletion as a technical issue for regulators alone. The DEQ report shows that the problem is statutory, economic, and political. Regulators cannot protect the aquifer if the law tells them to keep permitting withdrawals that the resource cannot sustain. Local governments cannot responsibly plan growth if the state does not require them to confront water limits. Businesses cannot make reliable investments if the Commonwealth pretends that every site has water capacity when the science says otherwise.

Virginia’s groundwater management areas have become a warning label rather than a safeguard. The DEQ report shows that the Commonwealth knows where the danger lies, knows why existing law is inadequate, and believes they know what tools are needed to prevent further decline. What remains is political will. Calling a special session would signal that the Governor understands the urgency of the crisis and is prepared to move Virginia from symbolic management to enforceable protection of its groundwater future.

**While private well users return the water they use to the ground through their septic systems. The effect of this return in the Coastal Plain is very different that the effect in the Culpeper Basin. Unlike the fractured rock system  system of the Culpeper Basin where this water use is neutral, water from septic reaches the aquifer.  In the Coastal Plain there is a highly stratified geology made of alternating layers of permeable sand (aquifers) and impermeable clay (confining units).  The vast majority of private residential wells are drilled deep into confined aquifers which sits hundreds of feet below the surface. This deep groundwater is under pressure and has been locked away for thousands of years. This septic effluent recharges the surficial (shallow, unconfined) aquifer. It does not sink back down into the deep Potomac Aquifer because thick, dense layers of clay block it from migrating downward. Instead of replenishing the drinking water supply, that septic water and garden water use in the Coastal Plain flows laterally through the sand lay into nearby shallow creeks, rivers, and the Chesapeake Bay. 

Running Dry: Northern Virginia’s Hidden Data Center Water Crisis

Understanding how further development will affect the Occoquan Reservoir is now one of Northern Virginia’s most urgent water questions. The reservoir is a major source of drinking water for nearly 1,000,000 people, and its health depends on the condition of the surrounding watershed—the forests, soils, streams, and groundwater systems that slow, filter, and carry water into the supply. As more land is cleared and paved for data centers, roads, substations, and related infrastructure, the region needs a clearer picture of how that transformation will change runoff, recharge, pollution, salinity, and long-term source-water reliability.

The limits of what we know are significant. Existing watershed assessments were built on assumptions that predate the current data center boom and do not fully capture the speed, density, or scale of today’s industrial development. Earlier models often relied on construction baselines from slower-growth years, making them poorly suited to predict what happens when thousands of acres are graded, compacted, and converted to impervious surface in a compressed period. That means current decisions are being made while important questions remain unresolved: how much additional runoff will reach reservoir tributaries, how much groundwater recharge will be lost, how quickly pollutants and road salt will move through the system, and how much treatment burden will increase over time.

Those uncertainties matter because the volume of construction in the pipeline is enormous, and the associated water demand is not theoretical. Data centers require large amounts of water directly or indirectly—through cooling, construction, power generation, and the broader infrastructure needed to support them. Even where individual projects appear manageable on paper, their cumulative effect across the watershed may be very different. The central concern is not one building or one campus, but the combined impact of many large projects arriving at once in a watershed that already serves as a critical drinking-water source.

That is why ongoing scientific work is so important. Researchers, water utilities, and regional planners are moving beyond older watershed tools toward more advanced modeling and monitoring systems that can better account for rapid land-use change. Newer frameworks are being designed to combine streamflow records, soil-water data, groundwater recharge estimates, land-cover changes, and water-quality monitoring so planners can test scenarios before damage becomes irreversible. These tools cannot eliminate uncertainty, but they can help identify where development is most likely to increase runoff, reduce infiltration, elevate salinity, or stress reservoir operations.

In short, Northern Virginia is being asked to approve massive growth before it fully understands the consequences for one of its most important water supplies. The purpose of improved modeling and monitoring is not simply academic; it is a public-safety tool. Without reliable forecasts and ongoing watershed data, officials cannot know whether today’s land-use decisions will leave the Occoquan Reservoir harder to protect, more expensive to treat, or less resilient during drought and extreme weather.

Here is why the region’s water limits are becoming an unprecedented threat to our taps.

• The Potomac River Is Reaching Its Limits (ICPRB Warning)
• The Potomac River is the lifeline for 5 million people across D.C., Maryland, and Virginia, supplying nearly 80% of the region’s drinking water.
• The “Perfect Storm”: The ICPRB has warned that, during a severe drought, the Potomac may be unable to meet regional demand as early as 2030.
• Explosive Growth: ICPRB forecasts show data centers’ share of water consumption in the D.C. metro area rising from 8% in 2025 to 25% by 2035.
• The Summer Squeeze: River levels are typically lowest in July and August, exactly when data centers need the most water to cool overheated servers. Peak demand arrives when the river can least afford it.

The Danger Zone vs. the Suburbs (The Backup Water Problem)

The risk of running out of water depends largely on where you live. Some suburbs have built larger safety buffers like the Occoquan, but the core of the capital region has no true backup plan.  Washington, D.C., and Arlington County are among the country’s most vulnerable urban areas. Both rely entirely on the Potomac River and have only about one day of backup water storage. If a chemical spill or infrastructure failure closed their intakes, the capital region could run dry within 24 hours.

Virginia and Maryland suburbs are somewhat better protected, drawing on regional reservoirs and local quarry storage that can last several days or longer. The Occoquan Reservoir cannot serve this role if we destroy it’s source water by development. Because the region’s water security is so uneven, water leaders launched the $25 million “Secure the Source” study. Its goal is to create a shared secondary supply that could provide emergency water for several weeks and reduce the capital’s one-day vulnerability.

Paving Over Our Natural Filter (The Occoquan Reservoir Threat)

While the Potomac supplies D.C., the Occoquan Reservoir is a major drinking water source for 1,000,000 people in Northern Virginia. It now faces growing pressure from large data center projects underway and proposed in Prince William County.  Areas such as the “Rural Crescent” were intended to remain undeveloped so forests could naturally filter rainwater before it reached the Occoquan. Much of that protection is now being weakened as rural land is rezoned for industrial uses and higher-density housing.

Replacing forests with concrete, driveways, and data centers increases runoff, carrying road salt, sediment, and pollution directly into the drinking water supply. The reservoir is already facing rising salt levels. Industrializing the watershed makes the water harder to treat and may pose risks for people on low-sodium diets.

The “Consumptive Use” Problem

This is where the industry’s preferred accounting becomes misleading. Data center groups often compare their water use to that of ordinary office buildings, but the key distinction is between water withdrawn and water consumed.

• Residents: When people shower or wash dishes in Fairfax, Prince William or Loudoun, that water is treated and returned to the Potomac or Occoquan. The watershed keeps nearly all of it.
• Data Centers: When data centers use water for cooling, much of it evaporates. As much as 85% can disappear into the air instead of returning downstream to help D.C. during a drought. For the local environment, that water is effectively gone.

The Bottom Line

We cannot rely on national averages to explain a local crisis. Northern Virginia has a booming tech industry competing for limited water, a capital region with only a one-day backup supply, and a vital reservoir under growing development pressure. The real question is not whether data centers look efficient on paper, but whether our local water systems can withstand their demand.

Significance of the Occoquan Watershed

Prince William County encompasses approximately 44% of the Occoquan Watershed. More importantly, the watershed covers over two-thirds of the county’s land. Therefore, decisions made within Prince William County have wide-reaching consequences for all Fairfax Water customers and nearby groundwater users. Protecting the Occoquan Watershed and the regional water supply requires a thorough understanding of the impacts of ongoing and planned development.

The Occoquan Watershed Model was developed over several decades to assess how land use changes affect the water quality of the Occoquan Reservoir. It is currently being updated and new The Northern Virginia Regional Commission has operated this model and plans to release its findings later this year. Despite this, the Board of County Supervisors recently approved comprehensive plan changes that eliminated the Rural Crescent and made sweeping land use changes without considering the potential impacts on the water supply.

Rising Salinity and Its Implications

Salinity levels in the Occoquan Reservoir have been steadily increasing and may be approaching a critical threshold. This rise in salt is primarily attributed to watershed runoff—especially from road salting during wet weather—and reclaimed water from the Upper Occoquan Service Authority (UOSA) during dry weather. The sodium content in reclaimed water from UOSA exceeds that of outflows from the two watersheds. As paved areas expand, salt runoff into the watershed also increases.

The removal of salt from the drinking water supply would require a major investment in desalination technology at regional water treatment plants, which currently lack this capability. The estimated cost of adding treatment lines at Fairfax Water to keep the Occoquan potable is between $1 and $2 billion, a financial burden that would ultimately fall on water rate payers, including the 350,000 public water users in Prince William County.

Urbanization and Watershed Health

The Occoquan watershed is frequently described as the most urbanized watershed in the nation. Although more heavily urbanized areas exist in the United States, these do not have functioning watersheds. Historically, cities like New York, Philadelphia, Baltimore, and Washington have confined and subsumed countless streams, erasing them and destroying their watersheds.

Scientific studies indicate that when 5–10% of a watershed is developed, it begins to decline, though restoration is still possible for a time. However, if urban land use surpasses this tipping point, water quality ceases to respond to restoration efforts. Once a watershed is destroyed, restoration may be impossible.

To avoid irreversible harm to the local ecology and regional drinking water supply, it is essential to understand the impacts of planned changes. The cost of restoring the basin and treating the water could reach billions of dollars, a financial responsibility for residents. The Occoquan Reservoir is a vital and irreplaceable component of the region’s water supply.

Average Water Flows to the Reservoir

Source	Percentage (%)
Bull Run Watershed	25%
Occoquan River Watershed	48%
Groundwater and Other Watershed	20%
UOSA Reclamation Facility	6%

Initial development of previously open areas mainly causes erosion and sediment transport via stormwater into local streams. After development, the primary concern shifts to higher stormwater volume and velocity, resulting from loss of tree canopy and replacement of pervious surfaces with impervious ones such as roads, parking lots, rooftops, driveways, and patios. This leads to the disappearance of small streams and a reduction in groundwater recharge. Current stream monitoring by the Conservation District already shows troubling signs of declining tributary health.

Connection Between Surface Water and Groundwater

The US Geological Survey emphasizes that virtually all surface-water features—streams, lakes, reservoirs, wetlands, and estuaries—interact with groundwater. All water is interconnected, and groundwater flow and storage are dynamic, constantly changing due to human and climatic stress. Altering the land changes both the quality and quantity of groundwater and streamflow.

Land use changes that increase impervious cover beyond 5–10% from roads, pavement, and buildings have two significant effects: they reduce open areas where rain and snow can infiltrate the ground and recharge groundwater, and they increase stormwater velocity, preventing water from percolating into the earth. This leads to more frequent flooding and less groundwater recharge.

Over time, reduced groundwater levels transform perennial streams into ephemeral ones, disconnecting groundwater from the surface water network. Once watershed hydrology is destroyed by development, restoration is extremely difficult, if not impossible. The Occoquan watershed is essential for the region’s drinking water supply.

Emerging Water Quality Issues

According to Dr. Stanley Grant, emerging water quality issues are mainly a result of the built environment. Ongoing development within the Occoquan Watershed threatens the sustainability of the water supply for up to one million people in northern Virginia. Population density increases lead to a rapid rise in impervious surfaces once the density reaches 100 people per square mile, accelerating the decline of the most urbanized watershed in the United States.

Water’s Journey Through the Region

Water originates in the Potomac River and is treated by Fairfax Water at the James J. Corbalis, Jr. Water Treatment Plant. It is then pumped to the western portion of the PW Water service area, including Haymarket, Gainesville, and Manassas, and supplemented by water from Lake Manassas treated at the City of Manassas Water Treatment Plant. After potable water is used in the western system, wastewater is sent to the Upper Occoquan Service Authority’s wastewater treatment plant in Centreville, where it is treated and discharged to Bull Run, a tributary of the Occoquan Reservoir. Water from the reservoir is then withdrawn by Fairfax Water and treated at the Frederick P. Griffith, Jr. Water Treatment Plant in Lorton before being pumped into the eastern PW Water service area. Wastewater from this area is sent to the H.L. Mooney Advanced Water Reclamation Facility, treated to Chesapeake Bay clean water standards, and discharged to Neabsco Creek, a tributary of the Potomac River.