Thursday, October 24, 2013

Using Chlorine to Fix Problematic Well Water

I have been rethinking water treatment after working with some local well owners to solve their problems. Water softeners are the most often sold to treat well water. Water softeners work by replacing hard water ions (calcium and magnesium, which are positively charged ions) with sodium ions. This ion exchange occurs as water flows through the ion-exchange resin in the softener tank. Water softener systems require the regular addition of sodium pellets and are expensive to install. To a limited extent these systems can address low levels of iron and manganese, but really only soften water. However, water softeners can create a slew of problems by offering a hospitable environment for nuisance bacteria to thrive.

Though there are frequently more issues to consider than if the water is hard or soft, water containing approximately 125 milligrams of calcium, magnesium and iron per liter of water (or 8 grains per gallon) is considered hard. Concentration of magnesium and calcium above 180 milligrams per liter is considered very hard. As the mineral level climbs, bath soap combines with the minerals and forms a pasty scum that accumulates on bathtubs and sinks. You either must use more soap and detergent in washing or use specially formulated hard water soap solutions which are available in most locations. These hard water minerals also combine with soap in the laundry, and the residue doesn’t rinse well from fabric, leaving clothes dull. Hard water spots appear on everything that is washed in and around the home from dishes and silverware to the floor tiles and car, but adding a half cup of white vinegar to laundry and dishwasher, occasionally boiling your kettle with vinegar solves many of these problems. Hard water is likely to reduce the life of your hot water heater due to the buildup of sediment in the tank. Nonetheless, I, like many people, have a personal preference for the taste and feel of slightly hard water, so I have never considered softening.

In many parts of the country (including mine) the water contains high levels of dissolved minerals beyond just calcium. Groundwater very slowly wears away at the rocks and minerals picking up small amounts of calcium, iron and magnesium ions as well as other elements in the rock and soil. Water analysis should be performed before any treatment is considered to make sure the selected treatment is necessary and appropriate for your water. Remember a treatment system not only has to be maintained, but curing one problem may cause another. No treatment is without consequences and an inappropriate treatment could create other problems.

That said, I have been thinking about chlorination, the oldest method of disinfection to solve the most vexing problems in private wells- especially here in Prince William County. Iron, manganese and hydrogen sulfide are together responsible for more people labeling their water “bad” than hard water, or for that matter water that contains coliform bacteria. Chlorine will oxidize iron and manganese so they can be filtered out and also oxidize hydrogen sulfide to reduce or eliminate the rotten egg order that can render well water here undrinkable. Chlorination followed by a media filter or a rechargeable carbon filter to capture particles and precipitate and the free chlorine can produce pleasant, sanitary water.

Typically, I recommend shock chlorination to address storm related flooding or a significant infestation of iron bacteria, and have used it for that myself. Continuous chlorination can be used to ensure a bacterial free well when coliform bacteria are a recurring seasonal problem. However, if fecal coliform or E-coli bacteria have entered your well water supply, it is recommended that the source of contamination be eliminated- find the leaking septic system and repair it or drill a new well. Chlorine will not remove nitrates from water and the elevated levels of nitrates associated with septic contamination can kill infants. Adding chlorine may prevent nitrates from being reduced to the toxic nitrite form; however, nitrates are not removed from water by chlorination.

In addition, chlorine does not kill Giardia or Cryptosporidium, two microscopic parasites that can be found in surface water and groundwater that has been impacted by surface water in karst terrain. Both parasites produce cysts that cause illness and sometimes death. After feeding, the parasites form new cysts, which are then passed in the feces of the host. Giardia are often found in human, beaver, muskrat, and dog feces. Cattle feces appear to be the primary source of Cryptosporidium, although these parasites have also been found in humans and other animals. Drinking water can become contaminated when feces containing the parasites are deposited or flushed into water. Membrane filtration is the usual treatment for these parasites- a one micron membrane is required.

Chlorine in water at the concentrations used for treatment is not poisonous to humans or animals. However, chlorine can impact the smell and/or taste of water even in very low concentrations. Household chlorination systems often use higher chlorine concentration than the typical 0.3 - 0.5 ppm (parts per million) concentration used for chlorination of public water supplies because the contact time is much shorter in home systems. The typical home system uses 1-2 ppm. This elevated level of chlorine can result in the swimming pool smell and can impact the taste of food and my beloved cup of coffee. This smell can be removed using an activated carbon or charcoal filter. Trihalomethanes (THMs) are organic chemicals that may form when chlorine is used to treat water supplies that contain humic compounds. This is often the concern in large water systems that use surface water for their supply. Humic compounds form as a part of the decomposition of organic materials such as leaves, grass, wood or animal wastes. Because THMs are very seldom associated with groundwater, they are primarily a concern where surface water supplies are used. THMs can be removed from drinking water through use of an activated carbon filter.

Chlorine treatment will control nuisance organisms such as iron, iron bacteria and sulfate-reducing bacteria. Iron bacteria feed on the iron in the water. They may appear as a slimy, reddish mass in the toilet tank but microscopic examination is needed to confirm their presence. Iron bacteria that have penetrated the water-bearing formation are extremely difficult to eliminate using shock chlorination of the well and will likely re-infest the system over time. In this situation you will need to repeat chlorination treatment periodically. Sulfate-reducing bacteria produce hydrogen sulfide gas (H2S) which has that horrible “rotten egg” smell and awful taste. Your nose alone can verify the presence of hydrogen sulfide, but not its cause. Nuisance bacteria do not cause disease. Low levels of chlorine are able to oxidize large concentrations of iron, manganese and sulfate or hydrogen sulfide into an insoluble form that can then be filtered out.

When installing a continuous chlorination system a chemical feed pump chlorinator is installed before the pressure tank in the basement and wired to water pump pressure switch. A fixed amount of chlorine solution is delivered with each pump discharge stroke. The chlorination system should be tested for free chlorine with test strips to adjust the dose. When the filter is in line the residual free chlorine should be under 1 ppm. You adjust the amount of chlorine by changing the length of the discharge stroke, the speed of the pump, or the running time of the pump to optimize performance of the system. Keeping a supply of good chlorine test strips and monitoring your water will allow you to optimize your system.
from Excel Water Web Site
A contact tank for additional contact time, and a carbon media filter, for de-chlorination and removal of precipitated contaminants should be installed after the pressure tank. It might be necessary to install a larger pressure tank since to operate optimally a garnet media filter typically requires 50 pounds of pressure and small pressure tanks typically operate in 40-60 pound range. A larger pressure tank might eliminate the need for a contact tank, but be aware that the rubberized bladder can be oxidized by the chlorine over time. If you are removing large quantities of particulates from oxidized iron, manganese and sulfate a media filter that uses a graded from coarse to fine media to trap the suspended particles is necessary followed by activated carbon will deliver the best tasting water. Monitoring chlorine levels in the finished water (at the tap) assures you a supply of disinfected, water free from iron and manganese staining and hydrogen sulfide.

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