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Examples of Anthropogenic ContaminantsAnthropogenic contaminants are those chemicals that have been introduced to the environment by the activity of man. These contaminants include industrial chemicals inadvertently released into the environment, as well as those derived from land use actitivies such as oils and grease flushed off roadways and agricultural chemicals applied to crops. In early June of 2003, the cause of the death of aquarium fish in Tucson was traced to mercury in the water supply. The source of mercury was discovered to be a broken water-level indicator, a mercury switch, within one of the wells of the water provider for the neighborhood. This incident points to the fact that water contaminants can be found very close to home. A neighborhood of recently installed private domestic wells in a new subdivision in New York was tested for contaminants after concern was expressed about the proximity of a nearby landfill. All wells failed water quality testing because a dissolved industrial solvent was found. Since the solvent is also a common contaminate associated with landfills, an extensive investigation was conducted to tie the pollution to the landfill, but no link could be found. The source of water contamination was discovered to be the solvent used to glue the PVC pipe used to construct the wells and plumbing. Chemical plants, manufacturing facilities, gas stations, repair shops, landfills and mining activities all have the potential to release contaminants into the environment. Many Superfund Sites (EPA mandated environmental clean-up sites) were first discovered because domestic wells owners noticed an unusual odor as they showered or an odd taste to their well water. In some cases, plumes of ground water contamination have extended miles beyond their original source. The contaminant concentration decreases with distance as the contaminant plume dissipates and mixes with uncontaminated water, and as it moves down gradient. Superfund Sites can be found at www.epa.gov/superfund/sites/index.htm. If there is one in your neighborhood, you may want to follow up with ADEQ to obtain information to determine if your water supply is at risk of contamination. The gasoline additive MTBE (Methyl tertiary-butyl ether) was added to gasoline in the late 1970’s to boost octane, to replace the toxic metal lead, and to reduce air pollution. Unfortunately, the fate of this chemical in the water environment was not fully tested before it was approved as a gasoline additive, and has since been tied to respiratory problems. Since then, this chemical has been found to be very soluble and stable (degrades slowly) and has resulted in the contamination of numerous ground water supplies from leaky underground gasoline tanks. Today, the fate of MTBE is the subject of numerous research studies. It is now banned in California, and EPA is taking actions to reduce and eventually eliminate MTBE use (www.epa.gov/mtbe/faq.htm#actions). 
Figure 12: Typical sources of pollution near domestic wells Often, the most likely source of ground water pollution in a domestic well is found near the well-head (Figure 12). Stored pesticides, lawn amendments, oil and grease, and failing septic systems are the most likely sources of domestic water supply pollution. Septic tank de-greasers are banned in many states because the chemicals, industrial solvents, rapidly percolate through the soils and contaminate the aquifer. It is worthwhile to note that the odor threshold (the concentration at which the human nose can detect an odor) of some natural and industrial chemicals is lower than the detection capacity of a testing laboratory. What this means is that sometimes we can be alerted to the presence of contaminants in water by their smell. However, one should not rely on the sense of smell only to determine the possible presence of contaminants in well water. See the following section for more details on well water testing. PathogensDrinking water supplies that depend on ground water are subject to contamination by enteric waterborne pathogens. The detection of these pathogens (and other indicator organisms) may indicate fecal contamination of the ground water. These pathogens can originate from leaking sewer lines, septic systems, or improperly protected well heads that allow contaminated surface water to drain into the aquifer along the outer well casing. Contaminated ground water represents approximately half of the waterborne disease outbreaks documented in the United States every year. Organisms of particular concern with respect to ground water contamination include waterborne pathogenic human enteric viruses such as Adenovirus, Rotavirus, Hepatitis A, and Norovirus; enteric bacteria such as the pathogenic strain of Escherichia coli 0157:H7, Salmonella, Campylobacter, Pseudomonas, Helicobacter, Aeromonas, Vibrio cholerae and Shigella spp.; protozoan pathogens such as Cryptosporidium and Giardia; and, the recently reported amoeba Naegleria fowleri. These organisms present a human health risk to those who ingest the water. Typical symptoms associated with an infection include acute gastroenteritis, severe cramping, abdominal pain, dehydration and diarrhea. Although all of the above mentioned organisms pose a risk to human health, viral contaminants are typically considered more of a threat to ground water than bacterial or protozoan contaminants for two reasons. First of all, because of the small size of viruses, they typically can be transported further into the aquifer than bacteria and can eventually reach the ground water. Secondly, viruses are thought to be more persistent in the environment than their bacterial counterparts and require greater disinfection procedures to render them inactive. Approximately one-third of the ground water drinking wells used by utilities across the United States (448 wells in 35 states) contained human pathogenic enteric viruses (Abbaszadegan et. al, 2003). However, in another study focused specifically on ground water supplies in Arizona, none of the 49 ground water samples tested in 7 counties across Arizona reported detection of human pathogenic enteric viruses (Karpisack et al. 2006). Although viruses were not detected, 74% of the Arizona samples exceeded at least one of the primary Drinking Water Standards, 80% exceeded at least one secondary Drinking Water Standard, and 95% exceeded one primary and/or one secondary Drinking Water Standard (Marrero-Ortiz, 2007). Certain bacteria are liable to form biofilms within wells if enough nutrients are available for their survival. Occurrence could be due to the use of biodegradable oils used to lubricate pumps in addition to the high temperatures of ground water in Arizona. The oils may act as a food source for bacteria, and other organisms, such as the amoeba N. fowleri, may feed upon bacteria growing on the oils within these wells. Iron bacteria thrive in ground water with high concentrations of naturally occurring dissolved iron and are non-injurious to health. Iron bacteria are nuisance organisms that cause plugging of the pores in the aquifer and the openings of the well screen. The bacteria produce accumulations of slim within the well, and precipitate iron and manganese. The combined effect of the growth of the organisms and precipitated mineral has been reported to reduce well yield by 75% within a year in some locations (Johnson, 1972). New ContaminantsThe EPA is always evaluating so-called “emerging” contaminants that need to be regulated in our community water systems. Emerging contaminants include those chemical constituents, for which new analytical methods allow us to measure very small concentrations, revealing the presence of common household chemicals that were not expected to end up in our water supply. Very small concentrations of chemical fire retardants, antibiotics used in household soaps, and chemicals originating in well-known products such as Teflon, Scotchgard, and Gore-Tex are being found. Chlorinated water generates new chemical compounds as the chlorine reacts (bonds) with other chemicals dissolved in water, and these water disinfection by-products are being researched as to their impact on the environment and human health. Of increasing concern are pharmaceuticals and personal care products (PPCPs), and many may affect the endocrine system of living organisms (also called endocrine disruptors). Pharmaceuticals in general may be flushed through our bodies and end up in the sewer systems. A recent national survey showed that several of these chemicals are not completely removed during the treatment of wastewaters. Thus, reclaimed waters, when discharged into the environment, may affect the quality of water sources. According to EPA PPCPs include: therapeutic and veterinary drugs, fragrances, cosmetics, sun-screens, diagnostic agents, and vitamins. See: www.epa.gov/ppcp/basic2.html. In addition, the EPA is evaluating other environmental contaminants for potential for regulation. These include the perchlorate ion, found in rocket fuel and explosives but also naturally occurring, which has been detected in both the ground water and surface water of several states (including Colorado River water). Although the EPA has not yet set or passed any national standards on these newly recognized contaminants, individual states may choose to have additional or stricter drinking water quality guidelines, as is the recent case of perchlorate in the state of California. |