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.
|Inorganic Contaminant||MCLG (mg/L)||MCL or TT (mg/L)||Potential Health Effects from Long-Term Exposure Above the MCL (unless specified as short-term)||Sources of Contaminant in Drinking Water|
|Antimony||0.006||0.006||Increase in blood cholesterol; decrease in blood sugar||Discharge from petroleum refineries; fire retardants; ceramics; electronics; solder|
|Arsenic||7||0.010 as of 01/23/06||Skin damage or problems with circulatory systems, and may have increased risk of getting cancer||Erosion of natural deposits; runoff from orchards, runoff from glass & electronics production wastes|
|Asbestos (fiber >10 micrometers)||7 million fibers per liter||7 MFL||Increased risk of developing benign intestinal polyps||Decay of asbestos cement in water mains; erosion of natural deposits|
|Barium||2||2||Increase in blood pressure||Discharge of drilling wastes; discharge from metal refineries; erosion of natural deposits|
|Beryllium||0.004||0.004||Intestinal lesions||Discharge from metal refineries and coal-burning factories; discharge from electrical, aerospace, and defense industries|
|Cadmium||0.005||0.005||Kidney damage||Corrosion of galvanized pipes; erosion of natural deposits; discharge from metal refineries; runoff from waste batteries and paints|
|Chromium (total)||0.1||0.1||Allergic dermatitis||Discharge from steel and pulp mills; erosion of natural deposits|
|Copper||1.3||TT7; Action Level=1.3||Short term exposure: Gastrointestinal distress||Corrosion of household plumbing systems; erosion of natural deposits|
|Cyanide (as free cyanide)||0.2||0.2||Nerve damage or thyroid problems||Discharge from steel/metal factories; discharge from plastic and fertilizer factories|
|Fluoride||4||4||Bone disease (pain and tenderness of the bones); Children may get mottled teeth||Water additive which promotes strong teeth; erosion of natural deposits; discharge from fertilizer and aluminum factories|
|Lead||zero||TT7; Action Level=0.015||Infants and children: Delays in physical or mental development; children could show slight deficits in attention span and learning abilities Adults: Kidney problems; high blood pressure||Corrosion of household plumbing systems; erosion of natural deposits|
|Mercury (inorganic)||0.002||0.002||Kidney damage||Erosion of natural deposits; discharge from refineries and factories; runoff from landfills and croplands|
|Nitrate (measured as Nitrogen)||10||10||Infants below the age of six months who drink water containing nitrate in excess of the MCL could become seriously ill and, if untreated, may die. Symptoms include shortness of breath and blue-baby syndrome.||Runoff from fertilizer use; leaking from septic tanks, sewage; erosion of natural deposits|
|Nitrite (measured as Nitrogen)||1||1||Infants below the age of six months who drink water containing nitrite in excess of the MCL could become seriously ill and, if untreated, may die. Symptoms include shortness of breath and blue-baby syndrome.||Runoff from fertilizer use; leaking from septic tanks, sewage; erosion of natural deposits|
|Selenium||0.05||0.05||Hair or fingernail loss; numbness in fingers or toes; circulatory problems||Discharge from petroleum refineries; erosion of natural deposits; discharge from mines|
|Thallium||0.0005||0.002||Hair loss; changes in blood; kidney, intestine, or liver problems||Leaching from ore-processing sites; discharge from electronics, glass, and drug factories|
|Radionuclide Contaminant||MCLG (mg/L)||MCL or TT1 (mg/L)||Potential Health Effects from Long-Term Exposure Above the MCL (unless specified as short-term)||Sources of Contaminant in Drinking Water|
|Alpha particles||zero||15 picocuries per Liter (pCi/L)||Increased risk of cancer||Erosion of natural deposits of certain minerals that are radioactive and may emit a form of radiation known as alpha radiation|
|Beta particles and photon emitters||zero||4 millirems per year||Increased risk of cancer||Decay of natural and man-made deposits of certain minerals that are radioactive and may emit forms of radiation known as photons and beta radiation|
|Radium 226 and Radium 228 (combined)||zero||5 pCi/L||Increased risk of cancer||Erosion of natural deposits|
|Uranium||zero||30 ug/L as of 12/08/03||Increased risk of cancer, kidney toxicity||Erosion of natural deposits|
Maximum Contaminant Levels (after EPA, 2012)
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.
|Recommended Test||Recommended Frequency||If the lab report shows:||Then you may want to consider:|
|Coliform Bacteria||Test for total coliform annually; fecal if total coliforms are detected.||Present||First re-test another sample to verify the results. Eliminate cause, disinfect, and retest. Increase testing frequency; if recurrent problems persist, consult a water treatment professional for more advice. Some bacteria may cause serious illness or death.|
|Nitrate ( N03)||Annually||≤ 45 mg/L as N03 or ≤ 10 mg/L as N||First re-test another sample to verify the results. Install a treatment system or find an alternate water supply. Consult a water treatment professional for more advice.|
|pH||Annually||> 8.0 SU||Testing for metals, especially selenium, chromium, and arsenic|
|Electrical Conductivity (EC)||Annually||> 1600 μmhos/cm or significantly different from previous result.||Test for minerals, nitrate, and/or VOCs to determine the possible cause of the high EC.|
|Chloride||Annually||> 250 mgl||Retest; also sample for Na, B|
|Sulfate||Annually||> 250 mgl||Retest; Consult water treatment professional|
|MINERALS Aluminum (Al) Arsenic (As) Barium (Ba) Cadmium (Cd) Chromium (Cr) Fluoride (F) Iron (Fe) Lead (Pb) Manganese (Mn) Mercury (Hg) Selenium (Se) Silver (Ag)||Every 5-10 years or if the following significant changes occur: • EC changes • Taste, color, or odor changes • Surrounding land use changes||Al >0.2 mg/l As > 0.01 mg/l Ba >1.0 mg/l Cd >0.005 mg/l Cr >0.05 mg/l F >2.0 mg/l Fe >0.3 mg/l Pb >0.015 mg/l Mn >0.05 mg/l Hg >0.002 mg/l Se >0.05 mg/l Ag >0.1 mg/l||Compare to previous results. Consider retesting for any high results. Install a treatment system or find an alternate water supply. The appropriate treatment system depends on your overall water chemistry and the constituents that need to be removed. Consult a water treatment professional for more advice.|
|Volatile Organic Compounds||See MINERALS, above||Any detection||Ask lab to re-test. If confirmed, consult a water treatment professional for more advice.|
|Some labs report minerals in μg/ L. 1 mg/ L is equal to 1, 000 μg/ L. “>”means “greater or equal to.”|
Water Quality Test for Domestic Well Owners (modified after CSWRCB, 2011)
John Harrington, P.G., CFM
Director, Water Resources Division
Lake Overholser Water Treatment Plant, Bethany, Oklahoma