There is No Resilience for Private Wells

There are over 50,000 residents of Prince William County who depend entirely on groundwater for their water supply. In all it's planning and spending the Prince William County government has entirely ignored their needs and right and interest. Sustainability of groundwater supply is not understood or considered in any decision of the Planning Department or the Board of County Supervisors. They are stealing our water and our future and ignoring our rights and needs. 

The "public" groundwater systems managed by Prince William Water is the Evergreen & Bull Run Mountain System . This system serves approximately 2,000 residents and lacks redundancy. As the local water table slowly drops due to the "delayed debt" of 1990s development, the entire neighborhood faces simultaneous shortage.  

Prince William Water has spent millions on the Bull Run Mountain Well Upgrades to drill deeper and interconnect these systems. This is an engineering attempt to buy "robustness" because the natural "adaptability" of the aquifer has been stripped away by increasing deforestation, development and use.

There is other groundwater use that is essential to the county. There are  an estimated 16,000 Private Wells (serving about 50,000 residents) in the county.  These are individual wells owned by homeowners, primarily in the former Rural Crescent and mid county areas.

• Scale of Problem: These represent 16,000 individual points of failure.
• The Resilience Crisis: These residents have zero federal or county safety net. As the loss of tree cover and increasing impervious cover prevents recharge groundwater, the water level in private wells will slowly drop and depending on geology may go dry. Once a private well fails, the "rapidity" of recovery is non-existent. The homeowner bears the full cost (often $15,000–$30,000) to drill deeper. With a even higher cost to connect of public water supply if feasible. There are large areas of the county where there is no easy access to water mains.
• The Data Gap: There are only two groundwater monitoring wells in the county and only one of them is a relevant monitoring well (49V) for this entire region, these 16,000 homeowners are "flying blind." They are the first to feel the "savings account" hitting zero, but they are the last to be reflected in county infrastructure planning.
• The county has failed to track the incidence of well failure, or permits to drill deeper. They remain willfully ignorant of the condition of the water supply for 50,000 residents. 

Groundwater is not only the source of drinking water for all private and public wells, it is  also the savings account for all rivers and streams. The county's rivers and streams feed the Occoquan Reservoir.  Maintaining natural open areas provides groundwater recharge. Increasing impervious cover levels increases stormwater runoff and reduces groundwater recharge. The groundwater is essential as the base flow to the streams and rivers that feed the Occoquan Reservoir during the dry months and serves as free water storage. As the private wells begin to respond to development the rivers and streams will become seasonal an then ephemeral. 

Groundwater is the moisture and water that exists in the spaces between rocks, the pores in the soil and fractures in the geology-the invisible portion of the water cycle. Groundwater is renewed through precipitation infiltrating into the ground. Though there is a seasonal aspect to rainfall, it can be extracted year-round provided that there is adequate replenishment. Groundwater can be extracted indefinitely and can be robust in the face of drought. However, groundwater is not unlimited.

Increase the amount of groundwater extracted beyond what is replenished, then slowly over time the aquifer is used up, the water level falls and wells go dry. Reduce groundwater recharge by eliminating forested areas and replacing them with compacted soils (lawns that need to be watered), pavement, buildings and over time the aquifer will become exhausted.

We do know that groundwater availability varies by location even within Prince William County (Nelms and Richardson, 1990) . Precipitation and soil type determines how much the shallower groundwater is recharged annually. The water level in a groundwater well usually fluctuates naturally during the year, but as seen in the chart above, it has been very slowly decreasing. 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.

However, groundwater levels can be affected by development. Land use changes that increases 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 percolate into the earth, increasing storm flooding and preventing recharge of groundwater from occurring. Slowly, over time, this can reduce groundwater supply and the water table falls.

Changes begin to take place in a watershed in response to development almost immediately, but the true impact is seen in the long-term as groundwater is drawn down and not recharged fully. Very slowly, the groundwater level begins to decrease. This These ecological and physical changes emerge over 20 to 50 years. Replacing 35–50% of a forested area with impervious surfaces permanently alters how water moves through the landscape causing profound hydrological and ecological shifts that take years to be seen.

It has been over twenty years since the last big building boom in the county. What changes we are seeing (formerly perennial streams drying out in the summer, water levels falling in the Evergreen Bull Run system) are the cumulative changes from building during the 1990’s -2007. That impact will be followed by the impact from the current building boom.