The natural fluctuations of groundwater levels are most pronounced in shallow wells and wells that are failing, both tend to go dry in the fall of a drought year. Groundwater levels are usually 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 streams draws water from the groundwater aquifer to keep flowing. Natural groundwater levels usually reach their lowest point in late September or October when fall rains begin to recharge the groundwater again.Geology also impacts groundwater, fractured siltstone is very porous and filled with water while diabase stone has very low yielding wells.
Groundwater supply can change because groundwater systems are dynamic. The Piedmont where I live is bordered by the “fall zone” on the east and the Blue Ridge Mountains on the west. The Piedmont is the largest geological region in Virginia and has a diverse geology largely dominated by igneous and metamorphic rocks, with some areas of sedimentary rocks. The fractures and fault lines formed in the rocks store and transmit groundwater. The size and number of water bearing fractures decrease with depth so significant supplies of water are generally located in the first few hundred feet. There is a wide variation in groundwater quality and yield ranging from under 1 gallon per minute to over 50 gallons a minute depending on location and specific site geology. The largest yields are obtained where fracture and fault system are extensive. In other areas of the Piedmont there are carbonate rocks within the areas of Karst terrain with the most robust and easily contaminated wells and finally there are also area where disintegration of the granite bedrock forms a zone of granular material with slow recharge and relatively high and annoying amounts of iron and sulfur. To be productive a well must be located within a fracture or pass through them.
In the Valley and Ridge of Virginia the geology is characterized by unconsolidated overlay underlain also by fractured rock. Fractured rock systems tend to be water rich areas of Virginia, but not uniformly so. Fractures can run dry. In unconsolidated sediments of the coastal plain ground water is pulled from the saturated zone which is being overtaxed and may be significantly impacted by drought. In the Appalachian Plateau which is a flat layered rock system with horizontal fractures, the coal seams are typically the aquifer and groundwater is typically shallow. Coal country is the location of many shallower dug wells which tend to follow the weather and be noticeably drier every fall.
If your well has gone dry or is down to a dribble you have four basic options: do nothing and hope the well replenishes after the winter, drill a new well, hydrofracture the existing well, or re-drill the existing well down to a lower aquifer. What is the best solution is dependent on geology, the condition of the aquifers, whether there is another likely location for a well on your property, and your financial resources. In many parts of the Piedmont, with enough money you can fix a well. Many wells draw water from more than one aquifer- there is more than one water zone. If you look at the water well completion report that you can obtain from the County Department of Environmental Health, VA DEH, you will see more than one water zone. Recently, I have seen wells where the shallow water zone appears to be dry and the lower aquifer still has some water, but is not providing enough flow to support a household.
It is impossible to look at a well and know if the aquifer has failed or just the well. The best proxy is the U.S. Geological Survey, USGS, monitoring wells and other wells in the neighborhood. Checking with VA DEH, the USGS and neighbors and the HOA will give a better picture of the aquifer. Several wells in a particular neighborhood in Prince William County have failed, though it did not seem apparent to individual homeowners, the problem was with the shallow aquifer. According to the nearest U.S. Geological Survey monitoring wells the lower aquifer appeared to be fine, and there is a possibility that there is some flow left in the shallow aquifer (around 60 feet) foot aquifer even in the drought water levels have fallen only about 10-12 feet in the USGS monitoring well. The aquifer itself cannot be seen so intelligent speculation is the best that can be done.
In Prince William County, the aquifers are not over pumped, but wells can still fail. Over time debris and deposits can build up in a well and the small earthquake that occurred last fall could have increased the deposits then this year’s drought reduced the water quantity and suddenly the well has failed. Fall and winter rains might recharge the shallow aquifer and the problem could be a seasonal or drought related problem, but drought can go on for years and living with limited water for months or having the well bore dry out even more is not an good solution. Using hydrofracking to flush out the hole by might get enough flow back into the well now to function adequately to keep the well itself full of water. Every two feet of well can hold just under 12 gallons of water, so a well producing half a gallon a minute with 100 feet of well below the static water level can support a household.
Hydrofracturing, commonly referred to as hydrofracking, is a well development process that injects water under high pressure through the well into the bedrock formation. This process is intended to flush and remove fine particles and rock fragments from existing bedrock fractures and/or increase the size and extent of existing fractures, resulting in an increased flow of water, and a larger network of water bearing fractures supplying water to the well. The procedure is often used to increase well yields of new deep drilled wells with inadequate water production rates. It may also be used for older wells that have diminished water recovery rates over time, which is usually caused by the build up of minerals and fine particles in the rock fracture over time. It can be very successful in parts of the Piedmont and other bedrock rock formations, but the improvement may not last beyond a few weeks or months. In diabase hydrofracking may do nothing and in siltstone it is unpredictable what may happen to the fractured system. I could not find statistics on long term failure rates for hydrofracking (only the impressions and experience of the VA DEH and USGS), but hydrofracking could work at least for a period of time- whether that time is weeks, months or years can not be predicted. Hydrofracking a water well should cost $3,000-$4,000. It is a good first step in trying to restore a well with a viable aquifer, and that is structurally sound.
If restoring an existing well does not work or does not appear to be an option because of geology or the condition of the aquifer, then it will be necessary to drill a new well or re-drill the existing well to a lower aquifer. There are times on a small property with only an acre or two of land that there are no other likely locations for a new well or that the cost to pipe the water from a distant corner of the property makes using the existing well bore the best choice. With the right equipment, an existing well can be re-drilled to a lower aquifer. Not every well driller has the expertise and equipment to hydrofrack or re-drill wells, and locally based well drillers are familiar with the geology of a region. Well drilling equipment is expensive to move great distances- if your hire an out-of-town well driller, chances are they will subcontract the actual drilling anyway. Stay local when hiring well drillers. Get references, check insurance, and licenses. Since 1992 private drinking water well construction has been regulated in Virginia and well drillers have to be licensed. In many other places well drilling and water wells are still not regulated. Generally speaking, a new well or re-drilled well costs $12,000-$20,000 plus other costs for piping to the house, pumps and pressure tanks.
If a property has a low producing well in the neighborhood of 0.5 gallons, there are ways to deal with it. First is water conservation and the second is to increase water storage within the system. Water conservation involves changing water–use behavior such as taking shorter showers, but usually involves installing water saving devices like a front-loading washer (saves over 20 gallons of water for each load- about half), low flush toilets, flow restricting faucets and shower heads. Installing water saving appliances can reduce household water use by up to 30%. Water conservation may solve the problem of a 4 gallon a minute well, but increasing water storage can make a reliable 0.5 gallon a minute well viable for a modern household. An intermediate storage system can either be the well itself if deep enough or a storage tank, reservoir or cistern that can be installed between the well and pressurized distribution system. The reservoir or storage serves as the primary source of supply for the pressure pump supplying peak demand. Ideally, the storage tank or cistern should be able to hold at least a day’s water supply and be regulated by a float switch or water level sensor. A 0.5 gallon a minute well can pump 720 gallons per day more than adequate for a household. The rule of thumb is to size a storage tank or cistern at 100 gallons per person in the household. Every two feet of well below the static water level holds almost 3 gallons so that 120 feet of well below the static water level will hold about 175 gallons this may be adequate only if water use is spread out throughout the day.
I am a Fairfax County, VA homeowner and my house has county water. I am wondering whether it would be cost effective to have a well dug solely for irrigation purposes - for a sprinkler system. I'd continue to use county water for the house (drinking, washing, etc.).ReplyDelete
Would adding a well be worth it in the long run versus using county water to water the lawn and flower beds? Any idea what it might cost and what the buy-back period would be? Or how could I assess that? I have no idea how much water I might use for the yard, although I suppose a sprinkler company could probably give me an estimate. Any thoughts you might have would be helpful. Thanks.
Novagirl, Look me up on VAMWON network for my email and phone and I will tell you how to get the information you need to do the calculation. Fairfax water rates are usage dependent so looking at your water bill in summer is a good start.ReplyDelete
I do not know what diameter of well you have, but for a standard 6 inch diameter well, you will only have approximately 1.3 gallons of water per foot of well.ReplyDelete
Check your math. Volume equals pie time the radius squared times height which is 0.1963 cubic feet per foot times 7.48 gallons per cubic foot equal 1.47 gallons per foot.
Elizabeth, you said almost 12 gallons in 2 feet in the article, but said 1.47 gallons per foot in your reply above. I think you need to claify, unless I'm missing something one of these must be wrong.ReplyDelete
This is rather interesting. But I’m curious though — if one re-drills the existing well that had already ran dry, is there a possibility that it would bring the water production back to normal? Well, I guess it will depend on how the water in the lower aquifer behaves. If the pressure below is relatively high, I think one can expect positive results.ReplyDelete
Jermaine Ryan @ Loadcraft Industries, Ltd.
π is spelled "pi" not "pie".ReplyDelete
Thanks, of course it is!.So...Volume equals pi time the radius squared times height which is 0.1963 cubic feet per foot times 7.48 gallons per cubic foot equal 1.47 gallons per foot. LizReplyDelete
Since some weeks there is hard water problem in my home, bore well is getting dried. Please suggest me dua to have sufficient water in bore well?ReplyDelete