With Every Decision PW moves closer to Destroying our Watershed

The Bay Journal reports: “A recently completed analysis of high-resolution aerial surveys of the six-state watershed finds that the amount of land covered by roads, rooftops, parking lots and other impervious surfaces expanded annually by 13,226 acres, or 20 square miles, from 2013 through 2021… The data comes from a federally funded effort to map and track changes in land use and land cover across the Bay watershed every four years. Collaborators on the project include the nonprofit Chesapeake Conservancy, the U.S. Geological Survey, University of Vermont and the federal-state Chesapeake Bay Program.” 

Stream health and groundwater recharge begins to decline when pavement, buildings and compacted soils of suburban lawns and sports fields cover more than 5% of a watershed. The problem with impervious surfaces is that they prevent the natural soaking of rainwater into the ground and recharging the groundwater.

Groundwater flow and storage is often viewed as static reservoirs that serve as the savings account for surface water flow. Through the hyporheic zone groundwater feeds streams between rain storms, but groundwater is dynamic and continually changing in response to human and climate stress [Alley et al., 2002; Gleeson et al., 2010]. Changes in precipitation patterns, the amount of precipitation, and the changes in land use impacts available groundwater and surface water.

Land use changes that increase impervious cover, add more suburban lawns, roadways, buildings, pavement and eliminating woodlands does two things. It reduces the open area for rain and snow to seep into the ground and percolate into the water table and groundwater and the impervious surfaces cause stormwater velocity to increase preventing water from having enough time to percolate into the earth, increasing storm flooding and preventing recharge of groundwater from occurring. Land use changes also potentially increase the use of groundwater by adding more homes and businesses that utilize groundwater.

Very slowly, changes in land use change the ecology of thewatershed and can reduce the water supply over time. As groundwater continues to be used levels fall, perennial steams that feed the rivers become intermittent during dry periods as we have seen recently in Prince William County, Loudoun County and Fauquier County.

Changing land use and the changing climate that are bringing new patterns of rain and drought and are impacting the Occoquan Reservoir.  From The Bay Journal: “The aerial surveys conducted in 2017-18 spotted 3,000 square miles of impervious cover. That’s just 4.75% of the Bay watershed’s land area, seemingly below that 5% threshold for impacting water quality. But pavement and buildings aren’t evenly distributed…(there are areas) in the spreading suburbs of Maryland and Virginia where more than 20% of their watersheds are covered with pavements and buildings.”

“Peter Claggett, a research geographer with the U.S. Geological Survey who’s helped analyze the data garnered from the high-resolution aerial surveys, said he was surprised by the pace at which impervious cover continued to expand… and noticed a change in the type of development... It’s warehouses, data centers, chicken houses … he said. “Those are the kind of buildings we’ve seen that are new. And you also have the solar panel arrays…The 2021-22 surveys spotted only about 4,400 acres of arrays across the six-state watershed, nearly two-thirds of that in Virginia.”

Data Centers also impact the stream flow. As Prince William Water points out: “Once used by data centers in western Prince William County, the wastewater is treated at the Upper Occoquan Service Authority Water Reclamation Plant and released as reclaimed water to the Occoquan Reservoir. In this water cycle, water used from the Potomac is reclaimed and released into the Occoquan Reservoir, adding volume.” Higher wastewater effluent while the changing climate and land use reduce river flow can introduce higher relative concentrations of minerals and salts, pharmaceutical, personal care and cleaning chemicals into the drinking water supply, potentially requiring additional treatment lines at great expense for all customers of the Griffith plant.

We need more information before we damage or destroy our fragile Bull Run and Occoquan Watersheds. We are paving over the watershed with roads, data centers, parking lots houses and electrical infrastructure reducing the groundwater recharge, reducing our stream flow, increasing the contaminants in the Occoquan and increasing the water demand. Although hidden in the subsurface, groundwater is the most important freshwater component in the hydrological cycle. Groundwater exists below all land with varying distance to the surface, but only in 20-30% of the land area is groundwater close to the land surface to feed surface streams and provide ecological services.

Groundwater releases water to streams sustaining the base flow of streams and rivers (Hare et al., 2021). Groundwater is the primary source of springs and many wetlands (Bertrand et al., 2011; Havril et al., 2018; Gleeson et al., 2020a). Finally, the groundwater saturated subsurface, the hyporheic, makes up the largest continental biome contributing to the health and purity of our water resource. The small changes that the Bull Run Conservancy has reported in the springs, seeps and streams is telling us that our watershed is changing, and not in a good way.

It appears that even with just the current level of development, the depth to groundwater is increasing enough to disconnect some streams from the groundwater during summer months. These are the first small signs that the watershed is beginning to die- streams become intermittent and eventually become ephemeral- flowing only during rainstorms. These streams flow into the Bull Run and the Occoquan River that provide the portion of our eastern service area drinking water supply that is not from recycled wastewater. Of course, increasing numbers of data centers will increase the amount of wastewater available, but that may not be all good. During rainless periods the fraction of treated wastewater could exceed the amount of natural water very soon. 

Prince William County is beginning to see changes in the watersheds within the county.  The groundwater is becoming disconnected from Little Bull Run and Catlett’s Creek in the area of the headwaters of those streams. Once the hydrology and ecological biome is destroyed by development, it cannot be easily restored, if at all. Protecting the Occoquan Reservoir requires protecting all the water resources in a region because all water in the watershed is connected. Impact on our water resources need to be considered when planning for the future of Prince William County and our county has not done that. We are sacrificing the future of our region and our water supply to dollars from building data centers and more and more development.