When people think of groundwater, a common reaction is that it is clean, refreshing, sweet water.  Many bottled water companies display language that refer to their product as artesian well water, mineral water, spring water, or well water.  The implication is that groundwater is superior to tap or surface water and tastes better.

In reality, groundwater quality can be highly variable.  The water quality is almost always determined by the rock type the water is flowing through.  And although the water may taste sweet, it is often what one cannot taste that is the problem.

Contaminants may be natural or artificial in nature.   Artificial contaminants are commonly called pollution, which is the introduction of contaminants into a natural environment that causes instability, disorder, harm or discomfort to the ecosystem i.e. physical systems or living organisms.  Groundwater in central Oklahoma contains many natural contaminants, most notably metals such as arsenic, chromium, selenium, and uranium.

Public water supply wells are highly regulated and must follow guidelines established by the United States Environmental Protection Agency.  These guidelines, known as the maximum contaminant levels (MCL), are the legal threshold limit on the amount of a substance that is allowed in public water systems under the Safe Drinking Water Act. The tables below list the MCL limits for inorganic and radionuclides in drinking water.

 Maximum Contaminant Levels (after EPA, 2012)

Domestic Wells

Domestic well owners are not trained as well operators and are often unfamiliar with water quality standards and testing, and rarely know much about their systems or the local aquifer.  A recent nationwide survey of domestic well water quality conducted by the U.S. Geological Survey indicates that about 79% of the wells (12,318 of 15,495 tested) contained one or more contaminants that may be harmful to human health. Of those wells sampled, about 9-11% had arsenic and nitrate levels exceeding the U.S. EPA maximum contaminant levels (MCLs) established for drinking water standards (Focazio, et al., 2006). 

Domestic water wells in Oklahoma are not regulated.  Unlike public drinking water systems serving many people, they do not have experts regularly checking the water’s source and its quality before it is sent to the tap. The only mandated sampling for domestic wells is for coliform, which is typically done when a title change to a home occurs that depends on a domestic well for a water source.  Thus, water quality data for domestic wells is almost nonexistent, considering the number of domestic wells that exist in the state.

Making Sense of a Water Quality Report

There are several websites available to help domestic well owners make sense of their water quality reports.

• Utah State University Extension
• OSU Extension and the Ohio Environmental Protection Agency
• Penn State Extension

Disinfecting Your Water Well

The Oklahoma Water Resources Board (OWRB) recommends that you should have your well tested for coliform bacteria and nitrates at least once a year by the Oklahoma Department of Environmental Quality (ODEQ) or another qualified testing firm. Also, keep a record of all water quality tests. Significant rain events may raise groundwater levels to a height where they may come in contact with surface contamination sources, including nearby septic systems. If your well water gets cloudy or tastes different after a rain event, or if there is a sudden change of quality, test your well as soon as possible. If your water weII is found to be contaminated, it should be disinfected immediately. In addition, all new wells should be disinfected after completion or following repairs to the well or pumping equipment. Contact ODEQ for specific instructions on how to disinfect your well (OWRB, 1999).

The ODEQ and OWRB recommend following these general guidelines for well disinfection:

– Use ordinary liquid laundry bleach, containing 5.25 percent chlorine. Do not use scented or non-chlorine bleach.

– For a six-inch diameter well, use 5 pints of bleach for every 100 feet of standing water. This concentration will effectively destroy water -borne disease organisms.

– For larger diameter wells, use additional chlorine at a similar concentration. Avoid extremely strong chlorine solutions because they can reduce the life of rubber and neoprene components in water systems, such as air bladders in pressure tanks and a-rings. As a general rule, it is wiser and safer to use too much, rather than too little, chlorine.

– To determine the effectiveness of the disinfection procedure, sample and have the well analyzed again one to two weeks after it has been treated.

Well Location and Development

Construction of a domestic well requires compliance with state and local codes that serve to protect both the potential ground-water user and the ground-water resource itself. Well-site selection considerations include aquifer type, depth to water-bearing zone, topography, land use, and convenience.

The well should be located at the highest elevation that is practical in order to reduce the potential of surface water entering the well and to allow contaminants to migrate away from the well bore. To facilitate well maintenance, the top of the well should not be buried or located beneath a building.

The top of the well should extend above the surface of the ground and be surrounded by mounded dirt or, preferably, a poured concrete apron to prevent surface water from flowing into the well. The casing should be new and strong enough to withstand installation. Most well casing is steel pipe, although thermo-plastic and fiber-glass casings have also proven to be satisfactory for some applications. In order to reduce the risk of seepage from undesirable zones and possible contamination from other aquifers, casing joints should be watertight–either welded, cemented, or threaded.

When completed the well should be covered with a sanitary well seal, cap, or pump mounting. It is also desirable that the well be vented with the vent pipe pointing downward and covered with a fine mesh screen.

In most wells the upper 20 to 30 feet of the borehole is drilled over-sized to allow space for the permanent well casing to be grouted in place. The annular space between the hole and casing should be grouted with watertight cement or clay filled to whatever depth necessary to insure that surface runoff does not infiltrate into the aquifer along the outside of the casing. A grout should also be used to seal off contaminated or highly mineralized water in aquifers above the water-supply aquifer.

Well construction should not be considered complete until the well has been properly “developed”. Well development is important for three reasons; (1) well yield and efficiency are increased, (2) pump life is extended, and (3) the water is free of turbidity. Development consists of surging the well by one means or another. This may be accomplished by use of a surge-block, hydraulic or air jet, a pump, a special set of pipes, or by the drill stem itself. The simplest method is to turn the pump on and off at closely spaced intervals. This forces water to flow into and out of the screen. Surging causes a natural gravel-pack to form around the well screen. Finer material adjacent to the screen enters the welt leaving the coarser material behind. The fine material can then be removed from the well by bailing or pumping. Consequently, the gravel-pack has a higher permeability than the surrounding aquifer materials and more water can flow into the well with less friction loss. This ultimately results in increased well yield and decreased drawdown. When the natural gravel-pack stabilizes, that is, no additional fine materials enter the well, the pump may be installed.

Because the fine material is removed before installation of the pump, the pump does not produce sandy or dirty water and there is less wear on its moving parts.

The final step in well completion is disinfection to kill any organisms introduced into the well during construction. Chlorination is a common method of disinfection. A concentrated chlorine solution is poured into the well and mixed with well water. After being allowed to stand overnight, the well is pumped to waste to flush out excess chlorine. The water should then be tested for the presence of bacteria before drinking (Pettyjohn and White, 1986).

Taste and Odor Problems

The best way to test for your water is to contact the Oklahoma Department of Environmental Quality Laboratory or other equivalent laboratory conduct the analysis.  The laboratory will generally supply a sampling bottle (or a coliform test kit if you are testing for bacteria), and give instructions if you are testing for specific substances such as metals.  The following table  shows some guidelines to use to help determine issues to consider when you receive your laboratory analysis.

Water Quality Test for Domestic Well Owners (modified after CSWRCB, 2011)