Residential Water Wells

The majority of residential wells in Virginia are located in a random fashion. That is, that once standoff distance from streams, ponds, buildings and drainfields have been met, wells are drilled in the most convenient location. More often than not, this method works fine for a residential groundwater supply because water use is very modest. For instance, the Fauquier County, Virginia Water and Sewer Authority estimate that the average household consumes approximately 235 gallons of water per day. This translates to a well producing approximately 0.16 gallons per minute (gpm)!! Most well drillers will tell you that a well possessing a "blown yield" of 3 gpm can satisfy most long-term residential needs. Still, some residential sites can experience difficulty in obtaining even this modest yield.

When Does a Hydrogeologist Become Involved?
Hydrogeologists usually become engaged in residential water prospecting after the health department, the well driller and the dowser have given it their best shot. This is due to the homeowner's reluctance to pay money and the fact that adequate water can usually be found without professional advice. However, people do call me and by the time I get involved a number of mistakes have been made. More often than not I get called to a job and the first thing I notice is several wells clustered in a hilltop position. This is absolutely the wrong way to prospect for groundwater.

Case Study-Residential Well:
The graphics represent an example of job where the owner's two wells "flat" gave out during the drought of 2003. The site was on top of a mountain in the foothills of the Blue Ridge in the northwestern piedmont province of Virginia. Two dowsers recommended that our client drill a replacement well on the highest part of her property (within 35 feet of a dying well). My client thought better and decided to obtain some technical-based advice

Once contacted,  we consulted the geologic map of Virginia and observed the area was mapped as a granite, or granite equivalent. Now here's where someone familiar with local conditions can make a difference. Since I have been working in the foothills of Virginia for 18 years, I knew that "feeder" dikes of Catoctin Greenstone often occupy the hilltops of these small mountains. In other words: not a good place to drill if you have other choices.

The next step was to conduct a fracture trace analysis of the site and site vicinity. Figure 2 on the left is one of a pair of air photos I obtained from the Virginia Department of Transportation (for $11.23). The dark lines are suspected fractures I observed after studying these photos. Some scientists use the words "Remote Sensing" to describe this exercise. I can tell you that "Remote Sensing" has absolutely no value if the geologist does not become intimately familiar with the landscapes of the site. The only way to achieve this is by performing a thorough reconnaissance of the property (with air photos in-hand) and verify the landforms observed from the photos and then make a decision regarding drilling locations.

After visiting the property I recommended several well drilling "targets". Figure 3 to the right is placed on a USGS Topographic Map and shows the fractures along with three test well locations (TW-1, TW-2 and TW-3). My client and I decided to drill TW-1 first, since it was more conveniently located (even though it represented the least potential of the three targets). Drilling the well here resulted in a 450-foot well that yielded approximately 25 gallons per minute (gpm). Needless to say, this satisfied all her water needs and no other wells were drilled.

Quick and Dirty Advice
For parcels of land less than 5 acres in size, my advice to most homeowners is that after the first well is drilled without success, they should move as far as possible from the dry-hole into a different landscape position altogether. For example: if you drill the first well on a hilltop, then move to a side-slope. If that well is unsuccessful, move down the hill to as close to a stream as possible. Generally, a change in landscape will produce the water required for residential purposes. While this can be a painful financial experience, it should, nonetheless, be conducted in a systematic fashion.

For parcels greater than 5 acres, fracture trace analysis coupled with a thorough site reconnaissance usually produces excellent results in sighting a long-term groundwater well supply. Every situation is different and requires interpretation of subtle features related to the soil and geology. True North Environmental can conduct these studies for homeowners at a very reasonable price. Please call to discuss.

Before You Purchase
If you are considering purchasing rural real estate dependent upon groundwater, I highly recommend that you contact a local well driller or a hydrogeologist to obtain a general idea of well yields. This kind of information is free and will give the purchaser some kind of "feel-good" information regarding the chances for success on the first try.

Well drillers and (good) hydrogeologists have more experience than anyone regarding well yields on a local scale. The Virginia Water Well Association is good source for contacting local Virginia drillers.

And feel free to contact us.