Protect Your Private Drinking Well Water
A source of clean drinking water is critical for human health. Many rural residents obtain their drinking water from a well and thus they need to take special care to protect their water source from contamination. Locating and controlling sources of pollution to groundwater can be challenging, but it is more cost effective and easier than treating contaminated groundwater. Ironically, wells are often the most direct route for pollutants to get into our groundwater. Even wells which are not used as a drinking source need to be protected, because contamination that enters may pollute a neighboring well.
Whether a well taps water just below the ground or hundreds of feet deep, its location on top of the ground is a crucial safety factor. A well downhill from a livestock farm, a leaking fuel tank, or a septic system, runs a greater risk of contamination than a well on the uphill side of these pollution sources. Surface slope does not always indicate the direction a pollutant might flow once it gets into the ground. Shallow groundwater often flows in the same direction as surface water. Water deep below the surface, however, may flow in a different direction than surface water.
Minimum separation distances apply to new well installation. Existing wells are required by law only to meet separation requirements in effect at the time of well construction. Make every effort, however, to ensure that existing wells exceed “old requirements,” and strive to meet current regulations whenever possible. Simply separating your well from a contamination source may reduce the chance of pollution, but it does not guarantee that the well will be safe. Stormwater and groundwater can carry bacteria, oil products, and pesticides from one place to another.
Location is Key
Wells located in the path of polluted water run the risk of contamination from overland flow washing into the well. This risk is increased for wells that were not constructed and grouted properly, especially in low lying areas. Some wells pump groundwater that lies beneath a fairly waterproof or impermeable layer, such as clay.
The water from these artesian wells is under pressure, and usually flows freely at the surface. These wells are often protected from contamination sources nearby because the confining layer tends to prevent mixing of the deeper groundwater with surface water or groundwater above the layer. Pollutants may enter these wells, however, from sources at the recharge area, which may be a considerable distance away. Artesian wells are more likely, therefore, to be affected by activities outside the homestead.
Wells located in low lying areas or without proper grouting or a cap can allow contaminated surface water to drain directly into the drinking water supply. Proper well design reduces the risk of pollution by sealing the well from contaminants that might enter it from the surface. The way in which a well is constructed, even if the design is sound, affects its ability to keep out contaminants.
The well driller installs a steel or plastic pipe called a casing during construction to prevent collapse of the borehole. The space between the casing and the sides of the hole provides a direct channel for polluted surface water or undesirable water from an overlying aquifer to seep down to the well intake. To seal off this channel, the casing is surrounded with grout (cement or a type of clay called bentonite, depending on the geologic materials encountered). A layer of grout at least 1 1/2 inches thick must surround the casing.
The Question of Casings
Well casings below the water level in the well can provide greater protection from contamination. A well casing extending at least 25 feet below the water level can ensure that surface water is filtered through soil and geologic materials before entering the screen. Typically, the casing extends above surrounding land, which prevents surface water from running down inside the well. At least 18 inches of casing pipe should extend above the final grade of the land. Additionally, the well casing should extend 3 feet above the greatest flood level of record. Surface water should drain away from the casing.
To prevent contaminants from flowing down the inside of the well casing, the driller installs a tight-fitting, vermin-proof well cap. The cap should be firmly installed in a manner to prevent easy removal by children and entry by insects or surface water. Some wells have vents, allowing air to enter. If the well has a vent, be sure that it faces the ground, is tightly connected to the well cap or seal, and is properly screened to keep insects out. Check the well cap to see that it is in place and tightly secured. Wiring should be in the conduit.
Well age is an important factor in predicting the likelihood of drinking water being contaminated. Wells constructed more than 70 years ago are still at the center of many homesteads. These may be shallow wells and are probably surrounded by many potential contamination sources. Older well pumps are more likely to leak lubricating oils, which can get into the well. Older wells are also more likely to have thinned and corroded casing. Even wells with modern casings that are 30 to 40 years old are subject to corrosion and pitting.
Keep an eye on water quality in existing wells by testing them annually. Of course, you cannot have your water tested for every conceivable pollutant, but some basic tests can indicate whether or not other problems exist. At a minimum, test your water annually for bacteria and nitrate. This should be done after a period of heavy runoff.
A good initial set of tests also includes corrosivity, hardness based on calcium and magnesium, pH or alkalinity, chloride, sodium fluoride, sulfates, electrical conductivity, and salts or total dissolved solids. Well owners considering investing in water treatment devices may also wish to determine the level of iron and manganese. In addition, you may choose to test your water for a number of specific contaminants that have been found in local groundwater.
Keep in mind that activities off your property can affect your groundwater. Chemical spills, changes in land use, and the presence of landfills can increase the risk of pollutants getting into your water. If your water has a high nitrate or bacteria level, you may want to talk with your local health department about additional testing.