Data says sources of water fairly stable here

The Rappahannock County Planning Commission heard a presentation from hydrogeologist Brad White at its monthly meeting Wednesday night (Dec. 19). White, who works for the Ground Water Characterization Program – part of Virginia’s Department of Environmental Quality (DEQ) – outlined how groundwater systems work, how they can be sustained and what the town of Washington should look for when it eventually adds a second well to its water system.

The bottom line was simple: Because of the location and geological makeup of Rappahannock County, the county’s water supply is in no danger of running dry.

plannersWellhead-27W

White began by explaining how groundwater systems work. The top layer of earth, which geologists call the regolith, essentially acts as a giant sponge, soaking up water from rain or snow. This spongy outer layer, also referred to as the “water table,” is also what replenishes supplies of groundwater – and thus well-water.

Beneath that lie layers of bedrock with a range of cracks, or “fractures,” as geologists say, where most of the water is stored and from which wells draw their water. These fractures are essentially pipes; drilling a well is akin to adding a new pipe in the system and helps redirect the water where necessary.

White compiled all the available data on the county’s wells, then plotted it on a geologic map of the county. “Rappahannock is a banged up, ratty sliver of rocks,” White said jokingly, drawing laughs from the crowd of 20 gathered in the courthouse.

There are several wells in the county that produce 150 gallons of water per minute, including the wells serving Rappahannock County Elementary School and the town of Washington. There are also many wells producing 40-100 gallons per minute. White added that he believes the reason for this is because the fractures in Rappahannock County are “discrete and local . . . like an ice cube tray.”

This relative isolation of fractures means that, despite what some residents at the meeting feared, it’s extremely unlikely that any neighboring counties – such as the heavily developed Culpeper County – could use any of Rappahannock’s water supply.

That’s good news for the county as a whole, but particularly beneficial to the town of Washington – which, as Mayor John Sullivan said during the meeting, has to add a second well to the town’s water supply at some point, per health department instructions.

When asked by Sullivan about his recommendations for drilling a new well, White said the trickiest thing about groundwater studies is that the fractures themselves can never really be seen. By studying water flow over time, an approximation can be formed, but can never be truly confirmed.

However, White did provide some tips for the town when drilling wells. “Don’t be afraid to go deep,” White said, as sometimes excellent water sources are deep underground. White said the deepest well he’d heard of was 1,300 feet deep.

“After 300 feet I might be a little worried,” White said, “but that doesn’t mean water isn’t there.” White did add that if a water source has “grime” in it, it’s time to stop digging; having significant debris in the water means you’ve stumbled onto a stagnant water source, and that won’t function as a well.

White also stressed the importance of doing pump tests on any new wells. A pump tests is when a mechanical pump is hooked up to a new well; the pump is then pressurized and kept active for 48 hours while the water flow is constantly monitored. The downside is the cost; the bright side is that pump tests can help predict how a well will react when put under pressure.

For example, White said that some fractures may initially seem like they hold a lot of water. A pump test can help definitively prove if it’s a viable well or simply a water reserve incapable of servicing the desired number of people.

Furthermore, surrounding wells can be (and, as White said, should be) monitored during a pump test. If the output from any surrounding well dips during the test, that means the two wells share a fracture. Any water taken from one well would directly affect the other; the water supply wouldn’t last nearly as long and would take longer to replenish.

White said that fractures can be extremely long, so simply digging far away from existing wells isn’t a guaranteed fix. White said he once had wells 1,200 feet apart that, testing revealed, were drawing from the same water source.

“You don’t want two straws in the same cup,” White remarked.

White’s complete report is available under the “Library” and “Events” tabs on the county’s documentation website at: boarddocs.com/va/corva/Board.nsf/Public

Print Friendly, PDF & Email