First of all let me say that according to the US EPA actual events of groundwater contamination have historically been rare and typically do not occur at levels likely to pose health concerns. This fact is the basis of the EPA and state health departments’ absolute acceptance of private and unmonitored use of groundwater for drinking water purposes for a significant portion of the United States. In Virginia 34% of the population is estimated to obtain their drinking water from private groundwater wells. However, as development in our modern society increases, there are a growing number of activities that can contaminate our drinking water and increased density brings more opportunities to impact groundwater. As an environmental engineer I tended to see a lot of contaminated sites, so I tend to focus on threats to the groundwater and worry about my groundwater quality more than most.
The most common sources of pollution to groundwater supplies come from two categories; naturally occurring ones and those cause by human activities. Naturally occurring contamination are those that are produced from the underlying soil and rock geology and wildlife. Microorganisms in the soil and from wildlife can travel into groundwater supplies through cracks, fissures, other pathways of opportunity or even through sedimentary and basaltic rocks that are highly fractured and overlain by a thin cover of overburden. Nitrates and nitrites from the nitrogen compounds in the soil can also enter the groundwater. From the underlying rocks radionuclides and heavy metals can enter the groundwater. There are areas with natural occurring arsenic, cadmium, chromium, lead, selenium and fluoride.
Human activities can also introduce contaminants into the groundwater. Bacteria and nitrates can be caused by human and animal waste. In our own neighborhoods septic systems, horses, backyard poultry can cause these problems. On a regional level small lots and dense population of septic systems or large animal or fertilized farm operations can cause problems. Heavy local use of pesticides for ornamental gardens (those small suburban lots again), heavy metals from mining operations, industrial products from manufacturing and industrial operations, leaks from underground storage tanks, solvents from automotive and airplane maintenance or dry cleaning operations. Landfills and household waste can introduce solvents, motor oil, and paint, paint thinner, water treatment chemicals and others.
It is cost prohibitive to test for every potential contaminant. To know what type of contaminants might be impacting your well a simple rule of thumb is to look out from your property. What you can see is likely to be the source of human contaminants to your drinking water well. Though some will see large farming operations, factories, military and industrial operations, gas stations, mining operations, most private well owners will see neighbors. Your and your neighbors septic systems, a few horses or dogs, maybe backyard poultry, lawns that have been fertilized (or over fertilized) and houses that may have been sprayed for termites.
You can not taste bacterial contamination from human and animal waste and you can not taste nitrate nitrite contamination. You can even grow accustomed to low levels of bacterial contamination, so that it is only house guests who develop intestinal disorders. Since bacterial contamination cannot be detected by taste, smell, or sight, all drinking water wells should be tested at least annually for Coliform bacteria and E Coli. Due to the extra cost (under $20) most health departments only recommend total coliform testing. Total coliform counts give a general indication of the sanitary condition of a water supply. Total coliform includes bacteria that are found in the soil, in water that has been influenced by surface water, and in human or animal waste. Fecal coliform is the group of the total coliform that is considered to be present specifically in the gut and feces of warm-blooded animals. E. coli is considered to be the species of coliform bacteria that is the best indicator of fecal pollution and the possible presence of pathogens.
Most state’s well construction code requires all new, repaired, or reconditioned wells to be disinfected with chlorine to kill bacteria that may have been introduced during construction. Testing is required initially to demonstrate that the water is free of Coliform bacteria before the well is put into service. Bacteria can be introduced into a new well during construction and can remain if the water system is not thoroughly disinfected and flushed. Well construction defects such as insufficient well casing depth, improper sealing of the space between the well casing and the borehole, corroded or cracked well casings, and poor well seals or caps can allow sewage, surface water, or insects to carry coliform bacteria into the well. Unplugged abandoned wells can also carry coliform bacteria into deeper aquifers. In an existing well system that formerly was bacteria free look for defects. All wells should be Coliform free when initially put into service. However, be aware that and unscrupulous well driller (or home seller) could test immediately after shocking the system with chlorine and in that way obtain a bacterial free sample of a well.
If the bacterial contamination is only Coliform bacteria and not E. coli, be sure to inspect the well for defects, check the grouting, casing, and clean the water delivery system and filter of slime and flush the system fully. Then retest. If the system passes let a few weeks go by and retest again. If repairing and cleaning the system does not solve the problem then one of the long-term solutions will have to be implemented. This includes continuous disinfection and replacing the well. Be aware that whole house filters, water softening systems for hard water do not remove bacteria or nitrate/nitrite from water. A reverse osmosis system can remove nitrate/nitrite from water.
If you do have a bacterial problem, fix it. There are four types of water treatment that can be easily and inexpensively used to remove bacteria. They are chlorination, ozonation, ultraviolet light, and heat. Chlorination is the most commonly used means of disinfection in private water systems. High chlorine concentrations can have objectionable tastes and odors, and even low chlorine concentrations react with some organic compounds to produce strong, unpleasant tastes and odors. To eliminate the excessive amounts of chlorine, the water is then dechlorinated. Activated carbon filters are the most common devices used to dechlorinate water, remove objectionable chlorine tastes, and reduce corrosion of plumbing systems. In addition to removing taste and odor problems, granular activated carbon absorption is a good method to remove other impurities including some pesticide residues, and radon. Boiling water will kill bacteria, but be aware if bacterial contamination is being caused by leaking septic or animal waste, you might also have a nitrate/nitrite problem (which can be lethal to infants) and boiling water concentrates the nitrate/nitrite. Also chlorine and UV light water treatment systems do not remove nitrate/nitrite.
Excessive levels of these nitrogen compounds in drinking water have caused serious illness and sometimes death in infants less than six months of age. This condition results when nitrate is converted to nitrite in the infant’s body. Nitrite then interferes with the oxygen carrying capacity of the blood. Symptoms include shortness of breath and blueness of the skin (methemoglobinemia). This is an acute disease in which symptoms can develop rapidly in infants from very minor exposure. So, if you well water contains bacteria, before you decide on a treatment option, test for nitrate/nitrite. If there is excessive nitrogen compounds it is important that you install a reverse osmosis system on the drinking water tap used to mix baby formula or make up bottles (and make coffee and food preparation for that matter). Under counter reverse osmosis systems generate 3-5 gallons of waste water for each gallon of treated water depending on the system.
Sometimes the installation of a new well may produce water with less nitrate and nitrite and bacteria, but is best to determine the source of contamination before a new well is installed. The new well would need to draw water from a different geologic horizon in order for it to have a reasonable chance of avoiding or lowering the contamination. To help determine whether a new well could produce better quality water the sampling of similar wells in the immediate neighborhood could assist in measuring the extent of the contamination present.