NHDES Technical Bulletin WD-WS-1-2
Three sections of the Department of Environmental Services (DES) provide assistance to those citizens having private wells. They are the DES Laboratory Services Unit, and the Water Supply Engineering Bureau and the New Hampshire Water Well Board. Their addresses and telephone numbers appear at the end of this document.
For the most part, this document assumes the typical reader will be installing a new well. See comments near the end for suggestions concerning inspection of existing bedrock wells. For well abandment see the DES fact sheet WD-WSEB-1-10.
GOVERNMENT REGULATIONS
State: A person or firm in the well construction business must be licensed by the NH Water Well Board of DES. The Board requires the submission of a "well completion report" describing the well design, soil and rock conditions encountered and the well yield.
There are statewide design criteria rules for bedrock (artesian) well construction and placement. These rules were originally adopted by the Board in 1983 and revised in 1990. The rule number is Env-We 100-900. There is no state requirement concerning minimum well quality or quantity.
Finally RSA 477:4-c requires, when selling a home with an on-site water system, disclosure of the water system's location, malfunctions, date of installation, date of the most recent water test, and whether or not the seller has experienced a problem such as an unsatisfactory water test.
Local: At the local level, some towns may have local permit requirements relative to the placement, construction, water quantity or quality for private. Please contact your local Health Officer or code enforcement office for particulars.
EVALUATING A NEW WATER SOURCE
Determining How Much Water You Use
To determine needed well yield, you must first estimate your water demand. A typical household requires approximately 5 gallons per minute (gpm) to meet modest domestic water needs, however, as little as two or three gpm could be tolerated. Factors to be considered when determining your family's minimum demand on your water system include: the number of water uses that you have, their flow rates, how many of these uses could occur simultaneously and for what duration.
Determining How Much Well Yield You Need
What minimum well yield will satisfy your family's water needs is more difficult to identify. A low yield well (1-3 gpm) may be acceptable if one makes use of water stored in the well bore or in storage tanks. This well bore storage may not be available if the water table drops during the summer and fall. The typical 6-inch well casing has a storage volume of approximately 1.5 gallons per foot of water depth.
"Well Yield, How Much Water is Enough" is available from the NHDES Water Well Board for $2.00. The United States Department of Agriculture, Farmers Home Administration guidelines require a minimum well yield of 1200 gallons for a four-hour period.
Storage in the well may allow installation of a higher capacity pump if the duration of pumping will be short. In such cases, a low water cut-off device should be installed to prevent overheating damage to the pump's electrical motor. Large storage tank(s) installed in your basement can serve this same function of accumulating water during periods of low demand. However, an additional pump will be necessary to pressurize this water.
Drilled (artesian) wells are somewhat less affected by drought conditions than dug wells. Drought effects can be minimized by planning to drill a deep well. If you have a well yield of only a few gpm at a well depth of 100-200 feet, we recommend that you try to increase the well's yield by drilling deeper. On the other hand, if you have only a few gpm at depth of 700-800 feet, you would probably want to end drilling on that particular well.
It should also be noted that a well's yield may change with time. A one gpm loss on a two gpm well is critical while a similar change in a 10 gpm well is not too significant. Thus, one should try to develop the maximum well yield possible, within economic reason, when the well is first drilled.
The distribution of groundwater in the bedrock is very irregular and depends on the distribution of rock fractures, their size, orientation, the number of interconnections with other fractures, and with the overlying water-bearing soil to name but a few factors.
Typical New Hampshire Well Statistics
Most wells for household use are in the 100-500 foot deep range; a few are over 1,000 feet. The median depth of bedrock wells in New Hampshire is approximately 295 feet deep. The median yield was 6.5 gallons per minute. More specific information for your locale can be obtained from the New Hampshire Water Well Board.
Hydro-Fracking to Increase Well Yield
Well yields can be increased by fracturing the bedrock immediately around the drill hole. One technique to accomplish this fracturing is to pump high volumes of water into the drill hole at high pressure, up to 3,000 psi. This process is called hydrofracking. In the past dynamite, dry ice, and compressed air were used to accomplish this same fracturing. If hydrofracking is being considered, ask your licensed water well contractor or the New Hampshire Water Well Board about the various methods available. See the DES fact sheet WD-WSEB-1-3 for detailed information on hydro-fracking.
Water Quality Considerations
Bedrock wells have generally been believed to have superior quality to dug wells. This depends on the water quality factor being discussed. Some water quality characteristics in bedrock wells such as bacterial quality are improved due to the longer time required for the water to percolate through the soil and into the bedrock and the tighter construction of a bedrock well casing due to superior materials.
The occurrence of iron, manganese, taste and odor in bedrock wells is approximately the same as in dug wells.
Bedrock wells can experience approximately 3-5 percent of one or more of the following water quality problems: arsenic, fluoride and radioactivity (including radon, radium and uranium). Radon gas occurs in all wells. In bedrock wells radon concentrations are, on average, much higher. Dug wells rarely experience the chemical problems mentioned above but are much more affected by bacterial occurrences, "backyard" pollutants and low volume during droughts.
For more information see fact sheet WD-WSEB-1-4 "Dug Wells" and WD-WSEB-2-3 "Recommended Water Quality Testing for Private Well."
Well Protection and Placement
Artesian wells take water from fractures in the bedrock. The fractures receive their recharge from the water table in the overlying soils above. Care should be taken in what activities are allowed to occur near your well. Bedrock wells can be more immune to local pollution because the recharge occurs along the bedrock "fault line" over a long distance.
Examples of chemical hazards to your well include the application or inadvertent spillage or fertilizer, pesticides, and inappropriate disposal of old crankcase oil, anti-freeze or solvents, or salt brine from water softeners to name a few. Thus, the use of chemicals in your backyard or in that of your uphill neighbors may negatively affect the quality of the aquifer from which your well draws. Tests for modern pollutants involve complex and costly laboratory procedures. Thus, the best and least costly approach to achieving good water quality is prevention of pollution rather than treatment after the fact.
The following protective distances are required or recommended when locating a well for a private single family home:
Although costly, there are modern techniques for determining the most advantageous location for a bedrock well. These techniques use satellite photography to identify bedrock fractures hidden below the ground surface. Knowing these areas, the well can be located where the rock conditions are most favorable for high yields. This process is called "fracture trace analysis." The cost of such analysis would typically exceed the cost of drilling the well. This procedure is not normally used for private wells. The DES and US Geological Survey have recently embarked on a substantial effort to identify zones of highly fractured bedrock on a state wide basis.
Choosing The Well Type You Will Purchase
Based on the considerations above, such as soil depth, water needs, and existing pollution, etc., you should now be ready to choose the type of well (either bedrock or dug) that you believe is best for your lot and home. As previously stated, this fact sheet pertains to bedrock wells.
Contracting With a Well Driller
Prior to actual drilling you will need to provide the driller with guidance as to what concept will govern the amount of work to be done. Typical options include: a) drill to a specific depth, b) drill to a specific well yield and c) drill to a specific budget amount. The nature of the contract is between well owner and well driller.
Drilling Techniques
Two techniques are used to drill "artesian" wells. In the Rotary process, a drill bit on a long shaft is rotated so as to grind and crush the rock at the bottom of the well hole. A water/mud slurry is pumped down through the rotating drill bit to flush rock cuttings up and out of the well. These cuttings overflow the casing and typically fill the annular space between the outside of the steel well casing and the existing soil. This action normally produces a tight seal between the steel casing and the bedrock and the steel casing and the soil. See additional comments on grouting below. This sealing action generally minimizes the need for cement grouting of the steel casing into the bedrock. Most bedrock wells are drilled using the rotary process.
In the Percussion process, otherwise known as cable tool drilling or "pounder" drilling, a falling weight is used to pulverize the bedrock at the bottom of the drill hole. Periodically a separate, long, thin bailing device is used to remove these cuttings from the drill hole.
Some experts contend that the percussion process better fractures the rock in the immediate vicinity of the hole and the bailing of water and pulverized particles keeps the fractures from becoming clogged with the drilling mud and rock cuttings. These two actions are believed to result in higher yield of those wells drilled by the percussion process.
In recent years, drill bits for the rotary drilling machines have been designed to include a percussion action. Rotary drilling is normally less expensive and much less time consuming than percussion. DES does not recommend any one method of construction over another.
DRILLED WELL CONFIGURATION
Steel Casing
A steel pipe is normally seated into a socket in the bedrock by 10-20+ feet. Cement grouting the casing to the bedrock is suggested by some experts to insure a good seal. Grouting is expensive and is not the normal practice in New Hampshire. A hardened steel "drive shoe" is required on the leading edge of the steel casing. The drive shoe improves the alignment and sealing of the steel casing to the bedrock socket.
Pipe and Cable Spacer (Cable Guard)
Spacers prevent the abrupt swinging of discharge pipe and power cable within the well hole as the pump starts and stops. Uncontrolled, this action can result in abrasive damage to pipe and wire and possible short circuit of the power cable. Spacers are placed on the discharge line every 20 feet or so.
Anti-Torque Device
A torque arrestor prevents the twisting of the pump in the well, at each start and stop of the pump motor. This will also extend the life expectancy of the discharge line and power cable. The anti-torque device recognizes that for every action there is an equal and opposite reaction, i.e., when the pump impellers begin to turn in one direction, the pump body turns in reverse.
Water Supply Line and Pump
A submersible type pump is most often used in bedrock wells. The pump is set to provide at least a 20-50 foot clearence between the bottom of the well and the submersible pump. Jet type pumps can be used but are not energy efficient.
Drilled wells often act as electrical grounds. Lightening protection of the motor and electrical controls is recommended. The National Electric Code requires a ground from the electric service and pump to the well casing.
Provide a mimimum of five feet of cover over the water line to the home for frost protection. Before backfill, take field measurements and draw an accurate sketch of the precise route of the water line. Duplicate this sketch, laminate and attach one copy to your pressure tank and one to the water system fuse box. If the pump is installed in the well, seal the electrical conduit to reduce radon migration into the home.
Jaswel Seal (Not Shown)
In some cases, poor water quality from certain fractures or a poor seal of the casing to the bedrock can be eliminated by sealing off particular fracture zone(s). This can be achieved by the use of special mechanical seals (e.g. a Jaswel Seal) or concrete grouting. These seals consist of a 4" diameter pipe which is placed within
the well, at the proper elevation, and sealed at one or both ends.
It should be recognized, however, that it is very difficult to locate those fractures that contribute poor quality water versus those that contribute good quality water. Also sealing a water bearing fractures reduced the well's capacity.
NEW WELL FOLLOW-UP
Determining the Well's Safe Yield
You should know the well's safe yield. The safe yield of a newly completed well can be determined (and the well can be flushed) by pumping water to waste continuously over a sustained period of 24 or more hours.
The pumping rate should be measured by noting the number of minutes required to fill a known volume container (such as a 20/32 gal. trash can). The water level in the well should be measured as the pumping continues.
The intent of the test is to develop an equilibrium between the amount of water being pumped out of the well and the amount which is replenished naturally from the ground. The discharge should be piped at least 200 feet from the well, and downhill, if possible, to prevent recycling or "double counting." Do not run this dirty water through your home plumbing.
If the drawdown in the well, caused by the pumping, is at a relative maximum depth and has stabilized, this can be considered as the maximum safe yield of the well. This test should be run in the early fall when the groundwater table is at its lowest. The water level (i.e. drawdown) in a bedrock well can be measured by an air line, echo device or electrical probes. Consult your well driller for detailed information.
Disinfection - Chlorination
For newly installed bedrock wells or where well pumps have been recently replaced, it is most important to clear the well of rock cutting, and surface dirt before chlorinating the well or testing for bacteria. The well may have to be continuously pumped for days (or weeks, in a few new well cases) before this cleaning process
is complete. Chlorination is NOT able to reach bacteria trapped inside accumulations of drilling mud or soil attached to the newly installed pump, pump electrical cable or discharge line.
The well can be disinfected by adding chlorine. One gallon of 5.25 percent sodium hypochlorite (i.e., common store bleach, such as Clorox) in 1,000 gallons of water will provide a good disinfecting solution. Remember the number of gallons of water in a bedrock well is approximately 1.5 gallons per foot of water in the bore hole. To add the chlorine, loosen the top cap of the well or unscrew the center nut and pour in the solution. Then use a garden hose from your house to wash the chlorine off the pitless adaptor, and to dilute and push down the chlorine to the lower depths of the well. Run water through your plumbing system until you smell the chlorine. Let sit for approximately 24 hours, then flush to waste. Do not flush large volumes of chlorinated water through your septic system or into streams.
Testing New Wells for Water Quality
Remember all chlorine must be flushed from the well prior to sample collection. Water quality samples with any chlorine residual can NOT be tested for bacteria. The presence of chlorine can be checked by using chlorine test kit. Persons with larger swimming pools normally have such test kits.
For persons desiring to use the DES laboratory, the Legislature has established an $10 fee for a bacterial test and a $75 fee for "standard analysis" group of 10 water quality factors. See fact sheet WD-WSEB-2-3 for recommendations concerning water quality testing on private wells. Only agency sampling containers can be used. The time to process the standard analysis sample is approximately three weeks in the summer and two weeks during the off season. Different containers are required for sampling radon gas and industrial solvents. Sampling containers can be obtained from the Laboratory Services Unit.
INSPECTING EXISTING WELLS
The most common problem with an older bedrock well is that the top of the well is cut off below grade. If this is the case, it is quite possible to have bacterial problems caused by the leakage of unfiltered surface water directly into the well. In such a case, the well acts as a multi-hundred foot disposal sump for bacterially laden
surface runoff.
Adding a Pitless Adaptor to an Existing Well
If an existing well casing is cut off below grade, we strongly recommend that the casing be extended above grade and a pitless adaptor closure be used. This new extension must be water-tight at the connection point with the old casing. We recommend a steel extension, fully welded. The pitless adaptor not only provides the greatest protection against leakage and subsequent bacterial contamination but also provides a visual indication of the well's location and all season repair capability.
FOR MORE INFORMATION
Department of Environmental Services
Licensing Well Drillers, Well Design Code
Water Well Board
Box 2008
64 N. Main St.
Concord, NH 03301
271-3406
Water Quality Testing & Sample Containers
DES Laboratory Services Unit
6 Hazen Dr., PO Box 95
Concord, NH 03302-0095
271-3445 and 271-3446
Water Quality Analysis, Discussion of Treatment Options
Water Supply Engineering Bureau
6 Hazen Dr., PO Box 95
Concord, NH 03302-0095
271-3139