Study Groundwater Resources Before Developing Rural Area

Prince William County’s Rural Crescent is nestled into the eastern edge of the Fauquier County. Groundwater does not abide by county lines, but sometimes rivers, streams and changes in geology are where the counties were divided. For example Bull Run Mountain separates Prince William County from Fauquier County north of Waterfall Road. The geology and water resources differ on either side of Bull Run Mountain. South of Route 66 the County line was simply drawn through what was once all farm land without regard to water sheds. Prince William County needs to learn from the experience of our neighbors before we blunder into unsustainable development and water use.

Fauquier County planned for most of their future development in what they call their "service districts." The County has eight Service Districts. The Service Districts include: Bealeton, Catlett, Marshall, Midland, New Baltimore, Opal, Remington and Warrenton. Portions of Warrenton, Bealeton, New Baltimore, Marshall, and Remington are currently served by public water and sewer, Catlett is served by public water and in Opal water service is under development.

Much of Fauquier’s water supply is from groundwater drawn from fractured bedrock aquifers for drinking and irrigation water. Currently, the county uses 3.9 million gallons of water a day for public supply. The water demand for agricultural and private use are not counted in that number, but those needs must continue to be met. The availability of groundwater is dependent upon subsurface geologic conditions which are not uniform throughout Fauquier County, the rainfall and the ground cover. In order to ensure the long-term sustainability, availability and quality of groundwater resources, Fauquier has discovered that they must manage their groundwater resources including paying attention to the natural watershed drainage areas and protect their well head areas from contamination.

Fauquier Water and Sanitation Authority (FCWSA) and Fauquier County have invested more than$100 million in wells and water infrastructure throughout the county. The County built out their public water supply system without identifying the groundwater recharge areas for its system of wells. Until recently there had been no money spent on protecting the wells and their recharge zones. Changes in land use have impacted the water quality and availability most notably in Marshall.

Suburban development has increased water-supply demands, added impervious surfaces that may have reduced groundwater recharge, and possibly caused transfers of water between water basins through water distribution and sewer systems. When the county designed and built the service areas for the various communities natural watershed and water availability was not considered. At the time little was know about the groundwater hydrology of the area.

With a groundwater wells a key factor isn’t just how much water you’re pumping out of the ground, but rather where in the watershed and in what geologic formations you are pumping. Different locations within the county have different water availability. The County can’t change the underlying geology or control the rate or pattern of groundwater recharge. Instead Fauquier must yield to nature.

Fauquier County is in the midst of a groundwater study estimated to cost half a million dollars. The study was designed by the U.S. Geological Survey (USGS) and spearheaded by the USGS and Virginia Department of Environmental Quality (DEQ). The goals of the study were:

• Develop a county-wide water-budget model to adequately characterize the range of past and current hydrologic conditions affecting aquifers;
• Couple groundwater and surface-water monitoring to permit assessment of the relationships between groundwater withdrawals and base flow in streams, and the effects of new or increased groundwater withdrawals;
• Develop tools and collect data to estimate the impacts of the overall trends in development and population growth on the water resources. This information would ultimately contribute to a future decision mechanism for allocation of water resources based on a physically-based, technical flow model.

Early results from the study found differences in the presumed soil-water balance. The USGS reported that with and actual annual precipitation of 40-56 inches a year the 20 year average recharge in the county varied between 2-10 inches a year NOT the presumed 10-14 inches a year that the FCWSA and their consultants had been using. In addition, during a drought years recharge in the county was less than 2-6 inches and the crystalline rock in the northern portion of the county dries out quickly in a drought-it has limited water storage. Differences were significant among the aquifers in the county.

The study is expected to be completed in mid-2021 and should address most of the issues and challenges to the development of the County’s water supply and the professional management of its water resources. Fauquier County waited to begin the study until Marshall had inadequate water to meet the demands for fire protection. To identify an uncontaminated additional water supply, FCWSA installed a well located outside the service area and added two water storage tanks to solve the immediate problem. Prince William County needs to learn from the experience of Fauquier County and study the groundwater and water resources before we plan for further development in the rural area.

In the USGS slide below you can see that the areas covered that are in Prince William County have an annual groundwater recharge of less than 2.5 inches a year. This is despite rainfall that ranged between 40-56 inches a year during the period covered. Impervious surfaces that added to a watershed by development will significantly reduce the groundwater recharge rate.