The Rural Crescent May Not Always Have Water

Virginia State law requires that Counties plan to have good quality water for all its residents present and future. This became part of the law in 2018 when the Virginia Legislature amended the enabling legislation for the comprehensive planning process (§§ 15.2-2223 and 15.2-2224 of the Code of Virginia ) to require planning for the continued availability, quality and sustainability of groundwater and surface water resources. However, the current proposals from the Prince William County Planning Office, and from various community groups and landowners for the future of the Rural Area do not address this extremely important issue. Our water supply is NOT unlimited and without planning and management it is not sustainable. Without a sustainable supply of water there is no future for the existing and future residents of the Rural Crescent.

Changing the character of the Rural Crescent (or Rural Area as it's also called) to include cluster development houses clustered in “transition areas” or even increasing the current population could further impact water availability to the existing residents and impact base flow to our rivers.  There are already indications that groundwater resources have been decreasing in the past 15 years despite having normal or higher rainfall for most of that period. Without proper planning and management of impervious surfaces, density of development and water demand, groundwater resources may prove to be inadequate to supply reliable and sustainable well water to all current and future residents. There are indications from the Prince William Service Authority, the U.S. Geological Survey (USGS) and NASA research that a problem with groundwater supplies is beginning to appear in Prince William County.

Currently, public water in the Evergreen area in the northwest edge of the Rural Crescent is supplied by a series of groundwater wells. Based on the recent PW Service Authority study of the Evergreen water system,  that system does not have adequate capacity to withstand a leak nor to recover from a problem, let alone provide supply to a larger area. While groundwater is a renewable resource it is NOT unlimited. The sad truth is that we do not know how much water we have in the groundwater basin underlying the Rural Crescent, the Culpeper basin. We do not know what the sustainable rate of ground water use is for the area, but we seem to have exceeded that rate.

The USGS and NASA tells us that our groundwater basin is under stress. In a study published in 2013 in Science, "Water in the Balance," researchers looked at the ten year trend in groundwater in the United States. The lead author was Jay Famiglietti, a professor of Earth System Science at the University of California, Irvine, and Director of the UC Center for Hydrologic Modeling (UCCHM). and co-author Matt Rodell, Chief of the Hydrological Sciences Laboratory at NASA’s Goddard Space Flight Center. Using data from the NASA Gravity Recovery and Climate Experiment (GRACE)  satellites collected over a 10 year period they were able to track changing groundwater availability all over the United States and the world. The GRACE satellites were launched in 2002 and were replaced in 2018 with the second mission satellites. The data set was for 2003 throught 2013.

from Famiglietti et al  "Water in the Balance" 1

The GRACE mission is able to monitor monthly water storage changes within river basins and aquifers that are 200,000 km2 or larger in area using small changes in gravity. Though their resolution is improving, more data needs to be gathered to study groundwater at a smaller scale. In the image above from their study, the yellow and orange area seen in the Virginia Piedmont region is indicating that the groundwater mass decreased over the ten years of the study.  Using GRACE data, the researchers were able to identify several water ‘hotspots’ in the United States, including our own Mid-Atlantic region as can be seen on the image below and the graph.

from Famiglietti et al  "Water in the Balance"1

In addition, the U.S. Geological Survey, USGS, maintains a group of groundwater monitoring wells in Virginia that measure groundwater conditions daily and can be viewed online. Only one of the Virginia wells is within the Rural Crescent. That well is in the northwest portion of the Rural Area just west or Route 15 in the Culpeper groundwater basin. Daily monitoring data available from that well go back to 2004 (other records exist further back and appear in the table below covering 39 years 1975-2014). What can be seen in the graph below is the slow decline in the water level despite not experiencing any significant droughts since 2008 and having the wettest year on record in 2018. The decline is modest over this period, but will continue and get worse over time especially if demand for groundwater is increased and impervious surfaces continue to grow, reducing recharge.

USGS monitoring well 49V Prince William County VA

The water level in a groundwater well usually fluctuates naturally during the year which is seen in the above data. Groundwater levels tend to be highest in the early spring in response to winter snow melt and spring rainfall when the groundwater is recharged. Groundwater levels begin to fall in May and typically continue to decline during summer as plants and trees use the available shallow groundwater to grow and streamflow draws water. Natural groundwater levels usually reach their lowest point in late September or October when fall rains begin to recharge the groundwater again. In the monitoring well the fall lows have been getting lower and the recharge even in 2018, the wettest year on record, did not reach the level of recharge during a drought in 2007-8. We appear to have a problem in this area. There is no information available in any other area of the Rural Crescent.

drought in Virginia from 2000-2019 from US Drought Monitor

Land use changes that significantly (more than 10%) increase impervious cover from roads, pavement and buildings does two things. It reduces the open area for rain and snow to seep into the ground and percolate into the groundwater and  the impervious surfaces cause stormwater velocity to increase preventing water from having enough time to to percolate into the earth, increasing storm flooding and preventing recharge of groundwater from occurring. Slowly, this can reduce water supply over time. Increasing population density as we have been doing increases water use. Significant increases in groundwater use and reduction in aquifer recharge can result in the slowly falling water levels over time showing that the water is being used up. Unless there is an earthquake or other geological event groundwater changes are not abrupt and problems with water supply tend to happen slowly as demand increases with construction and recharge is impacted by adding paved roads, driveways, houses and other impervious surfaces. That appears to be what is happening in this area of Prince William County.

Sustainability of groundwater is hyper-local. Little is known about the sustainability of our groundwater basins, but potential problems are still at a manageable stage. Groundwater models and data from more monitoring wells can help develop a picture of the volume of the water within the groundwater basin and at what rate it is being used and at what rate it is being recharged. We need to know if the current and planned use of our groundwater is sustainable even in drought years. We need to understand how ground cover by roads, parking lots and buildings will impact groundwater recharge and what level of groundwater withdrawals are sustainable on site to determine if a proposed change in land use or additional use of groundwater is sustainable before it is granted.

As Drs. Famiglietti and Rodell point out in their paper without coordinated and proactive management, the aquifers supplying our region will be depleted.

All the lows have been exceeded in the past 5 years.

The above data was "clipped" from the old USGS site for well 49 v before they changed over. It's useful because its got decades of data tracking and the lowest groundwater levels in the past few years have fallen below the lowest levels recorded in the 35-40 years before that.

1. Water in the Balance;By James S. Famiglietti, Matthew Rodell

Science14 Jun 2013 : 1300-1301 .