National Drinking Water Clearinghouse
West Virginia University
PO Box 6893
How well is your well?
By Larry Rader • NDWC Environmental Consultant
When it comes to well water, most folks think their water comes from the ground pure and pristine. But those of us who have operated groundwater treatment plants with any or all of the following contaminants—iron, manganese, carbon dioxide, arsenic, radon, iron and sulphur bacteria—tell a different story.
Do I have carbon dioxide?
Carbon dioxide (CO2) may seem to be an odd place to start an article on groundwater treatment, but, in my area at least, it contributes to more treatment problems than any other contaminant. CO2 reduces pH, which, in turn, contributes to a wide range of treatment difficulties.
Throughout the Lead and Copper Rule, we learned that decreased pH contributes to
corrosion problems and the leaching of lead and copper into customers’ water. Also, the lower the pH, the more time it takes to oxidize metals, like iron, in the treatment process.
Carbon dioxide tends to be most prevalent in areas with large underground deposits of carbon, such as coal, petroleum, or brine. Companies, including Hach and LaMotte, sell CO2 test kits that are quick and accurate for onsite testing, or an operator may choose to use an approved lab. Using a pH meter, you can detect carbon dioxide’s presence, if not the concentration. To check for CO2, grab a sample of raw water and quickly check the pH. Then pour the sample back and forth between two beakers several times and check the pH again. If the pH has gone up, the chances are that your water is the proud owner of CO2.
The treatment for CO2?
Think a bit about pouring the raw water sample back and forth between the two beakers: what were you doing? Aerating.
CO2 vaporizes easily when aerated. This is a lesson that those working in West Virginia learned early on. A pH level in the fours is not uncommon here. Consequently, almost all groundwater treatment plants in this state come equipped with an aerator. It may be as simple as coke trays or as state of the art as vortex aerators, but they are there releasing the CO2, hydrogen sulfide (H2S), radon, and other contaminants, making the water safer and easier to treat.
There are states that have decided aerating water turns it into surface water, therefore, requiring full treatment. In my opinion this is foolish and wrong-headed. These same states allow chemical treatment using soda ash up to 300 milligrams per liter (mg/L). Using that much soda ash is expensive, and it’s not even very effective.
Another design requirement often used as an argument against aeration is “double pumping.” Aeration usually requires a basin or tank following the aerator to allow oxygen to release prior to filtration or pumping into the distribution system. A double-pumping design requires a second pump to move the aerated water through the filter and into the distribution system.
There are degassing units, which allow CO2 removal without the need for double pumping. However, the head loss through the unit makes single stage pumping practical in limited situations only.
A perfect example of the effectiveness of aeration is the water treatment facility in Mt. Hope, West Virginia. The Mt. Hope plant was built just as the Lead and Copper Rule was getting into full swing. The raw water source was an artesian spring emanating from an abandoned coalmine. The Mt. Hope’s water system operator decided the raw pH (6.3) needed to be raised to 7.5 to make the water non-corrosive.
Because the plant was new and there was no money left in the budget for an aerator, the system’s management decided to use soda ash to chemically adjust the pH. For more than ten years the operators fed 400 pounds of soda ash each day to adjust the pH of 350,000 gallons of treated water.
Finally, using the ingenuity all operators gain from years of making poor designs work, the operators at Mt. Hope constructed their own aerator. The pH increased to 7.5, and they were able to stop feeding soda ash altogether. The savings for the small town amounted to approximately $1,000 per month.
How to Shock Chlorinate a Well
Chlorine is highly toxic to bacteria at concentrations of 200 mg/L and greater. This procedure uses hypochlorite containing about 65 percent calcium hypochlorite or non-scented household bleach containing about 5.25 percent sodium hypochlorite.
Mix a solution using five gallons of water in a clean, non-metallic container with the appropriate amount of either hypochlorite or bleach required for 10 feet of water depth.
Iron Is Common
Iron is the most common mineral in the Earth’s crust and, therefore, the most common contaminant found in well water. Although iron is a secondary contaminant, its secondary maximum contaminant level is 0.3 mg/L. Together with manganese, they make up the terrible twins of groundwater treatment. Customers can drink water containing any number of harmful contaminants without notice, but one washer load of white clothes covered with brown iron stains will cause most operators to lock the doors and take the phone off the hook.
Considering the problems iron can cause, it is actually very easy to control—just oxidize, then filter. Iron is fairly easy to oxidize, changing ferrous (soluble) iron into the ferric state, which are particles of rust. If you have an aerator, it will introduce oxygen and possibly raise the pH that begins the process. Chlorine or potassium permanganate can then be applied to finish turning soluble iron into particles, which filtration easily removes.
When removing oxidized iron the filter must have several inches of anthracite capping the filter sand or greensand. Ferrous iron may be sequestered in concentrations of less than 1.0 mg/L. Ferric or oxidized iron may not be sequestered in any concentration. Removal is always the best practice when possible.
Iron’s Terrible Twin
Manganese is the terrible twin of groundwater treatment and usually is found keeping company with its sibling, iron. The secondary maximum contaminant level for manganese is 0.05 mg/L, six times less than iron. Several years ago a popular hair tonic for men advertised “A little dab will do ya,” and so it is with manganese. Even in concentrations less than 0.05, you can have a cumulative effect on the insides of pipes and fittings that will show up in customers’ homes following line breaks, use of fire hydrants, or any other time the line flow has been drastically altered. It reaches the customers’ homes either as black particles or black staining.
Although more difficult than iron to oxidize, in my opinion, the best treatment is to bring the soluble manganese into a properly operated and maintained greensand filter or one of the many look-alike manganese oxide coated media. If iron is present, and it usually is, the filter should be capped with anthracite, chlorine applied to oxidize the iron that will be trapped in the anthracite, and then allow the greensand to remove the manganese. Soluble manganese may be sequestered in small concentrations; insoluble manganese cannot be sequestered. (For more in-depth answers concerning iron and manganese removal, see “How to Operate and Maintain Manganese Greensand Treatment Units,” in the On Tap Winter 2003.)
Radon Can Be Aerated
Radon is a naturally occurring radioactive gas formed when uranium breaks down in the soil. Breathing air that contains radon can cause radioactive particles to become trapped in your lungs and lead to lung cancer. Radon is the second leading cause of lung cancer in the U.S. each year, second only to cigarette smoking. Most radon enters the home, and therefore your lungs, by seeping from the soil under and around your house. However, groundwater can also contain radon and contribute to the problem.
Although there are health issues from drinking water containing radon, most concerns center on radon in the air. Radon is released into the air in the customer’s home from the shower and other sources of running water. What action is taking place when you turn on the shower and radon is released into the air? That’s right, aeration! According to the Federal Register Vol. 64, No. 211, the best available technology for the removal of radon in groundwater is “high-performance” aeration. For individual home wells, granular activated carbon (GAC) filters are effective providing all water used in the home passes through the GAC.
What do iron andsulphur bacteria do to a well?
Although neither iron bacteria nor sulphur bacteria pose a particular health hazard, they can, in fact, render a well field useless. Iron bacteria are generally the more common of the two simply because of the abundance of iron in groundwater. They are usually discovered when a well begins to lose efficiency. The well pump ispulled only to find the screen is covered with a foul smelling brown slime. By the time they are discovered, you are quite likely in big trouble.
Iron bacteria can grow extremely fast by combining iron in groundwater with oxygen. Iron bacteria cannot only reduce a good-producing well to a trickle, but the biofilm can also mask the presence of other more harmful bacteria, such as fecal coliforms. They are usually found in more shallow aquifers and the best protection is to make certain the well is properly cased and employs approved wellhead protection.
Sulphur bacteria are divided into two basic categories: 1) Sulfur-oxidizing bacteria converts sulfide into sulfate and produces a dark brown slime that plugs well screens, plumbing, and pumps, similar to iron bacteria; 2) Sulfur-reducing bacteria (SRBs) on the other hand, live in oxygen-deficient environments. SRBs produce hydrogen sulfide gas during the process of breaking down sulfur compounds. SRBs are the morecommon
of the two sulfur bacteria, and the hydrogen sulfide gas they produce is extremely
Do I have iron or sulphur bacteria?
A series of tests called BART (Biological Activity Reaction Tests) are available. BART kits are easy to use and simple to understand. They consist of a plastic vial containing a ball coated with appropriate chemicals. A sample of raw water is poured into the vial, which is then tightly capped.
Color changes will begin to appear that correspond to a color chart provided with each test. Extremely or very aggressive levels of the appropriate bacteria will provide color changes within 12 to 24 hours. Moderately aggressive to background levels may take from two to 32 days to reach the correct color change. The charts provided with each test also show various other color changes along with the explanation. I have used BARTS almost from the time they became available. They can be found in most any water treatment supply catalog and cover a wide range of different bacteria.
The method I used before BARTS was also simple. The test was only for iron-related bacteria and consisted of the following equipment: One small jar that can be tightly sealed (my preference was a baby food jar) and a bright new nail that would easily fit into the jar. The jar and cap I sterilized with boiling water, were placed upside down on a clean paper towel, and allowed to cool. The shiny nail is cleaned with alcohol to remove any traces of oil. The nail was placed in the baby food jar, which was then filled with raw water and tightly capped.
I put the jar was on a shelf and checked for brown hair every few days, which indicates the presence of iron bacteria. If the raw water did contain iron bacteria, it immediately began looking for a food source and discovered the nail. In a few weeks, if the sample contained iron bacteria, strings of brown hair (slimy by-product) could be detected rising from the nail. You won’t find this in the American Water Works Association’s “Standard Methods,” but it was all I had available.
If I have iron or sulphur bacteria, what can I do?
Because these bacteria are extremely difficult to completely destroy, the best defense is a proactive offense. Wells should be monitored frequently, in my opinion every six months, using something like the BART tests.
The other part of that offense is also extremely important. Anything—and I do mean anything—that goes into the well must be disinfected with a 250 mg/L solution of chlorine. This includes pumps, electric cables, pipe or hose, portable water level indicators, or anything else that enters the well. If you discover bacteria early, shock chlorination may work. (See the water well disinfection table.)
If the bacteria are advanced, ask your well driller about other options. But remember, it is best to catch the problem early, or better yet, prevent it from happening at all.
Hydrogen Sulfide Is an SRB Byproduct Hydrogen sulfide (H2S) is not only a byproduct of SRB; it can also exist naturally in the ground. A rotten egg odor that becomes stronger as the levels increase announces its presence. Although H2S can be toxic, the odor at those levels should prevent anyone from drinking the water. The major concern with H2S is its corrosiveness to metals such as copper, iron, brass, and steel. There are kits available to check H2S concentrations; however, testing must be preformed onsite because it vaporizes very quickly. If samples are sent to a laboratory, ask for directions to stabilize the sample.
What’s the treatment for H2S?
Because it readily vaporizes, aeration can remove high levels of H2S. Other methods of oxidation such as chlorination, ozonation, and potassium permanganate treatment also are effective if there is at least twenty minutes of contact time. Manganese greensand filters can remove H2S up to 6 mg/L, and activated carbon filters work well through the process of adsorption. If your system contains H2S, it may be necessary to retrofit hot water heaters by replacing the magnesium corrosion control rods with rods made of aluminum.
Although I am a believer in aeration for most, if not all, groundwater systems, there are cautions. H2S, for instance, can be flammable when vaporized.
It can also be toxic when high levels of the vaporized gas are breathed. Other volatiles such as radon would be hazardous if contained inside a building, for instance, following aeration. Make certain the vaporized gasses are vented to the outside air, and you have checked with the agency that regulates air quality in your state.
About the Author: Larry Rader has more than 25 years in the water industry. If you have a question for Rader, he can be reached by e-mail at firstname.lastname@example.org.
Nebraska Health and Human Services System. 2003. “Iron and Sulfur Bacteria in Water Supplies.” Water Well Disinfection. www.hhs.state.ne.us.
U.S. Geological Survey. 2003. “Bacteria and Their Effects on Groundwater Quality.” www.usgs.gov.
American Groundwater Trust. 2003. “Bacteria and Water Wells.” www.agwt.org/gwinfo.htm.
Well Owner.Org. 2003. “Iron Biofouling/Iron Bacteria.” Hydrogen Sulfide, What You Need to Know. WellOwner.org.