Samples from 146 household-supply wells were analyzed for organisms indicative of fecal contamination, including total and fecal coliform bacteria (Bickford and others, 1996). Total coliform bacteria were detected in water from nearly 70 percent of the household wells sampled, indicating that the water should not be used for drinking without treatment. Fecal coliforms were present in water from about 25 percent of those same wells. In an 88-well subset, approximately 30 percent had waters containing Escherichia coli bacteria (E. coli). Fecal streptococcus bacteria were present in water from about 65 percent of the wells sampled. Bacteriological contamination was more likely to occur in water from wells in agricultural areas than in water from wells in forested areas. Water from wells in areas underlain by limestone had higher concentrations of bacteria than areas with other types of bedrock.
Few household wells from which water was sampled were grouted, and few had sealed, sanitary caps at the top of the casing. Lack of these protective features can enable the entry of bacteria into well water and may have contributed to the number of detections of bacteria. It is uncertain whether the bacteria detected were the result of widespread aquifer contamination or local factors. In most counties in Pennsylvania, testing and treatment of private wells is not required. It is uncertain whether bacteriological contamination of well water is caused by inadequate protection of wells from surface runoff, septic-system failure, application of animal manure to fields, or other causes.
Fecal contamination of water supplies is a leading cause of waterborne-disease outbreaks. Most outbreaks shown here are from public supplies; outbreaks of diseases involving water from private household wells are usually neither identified nor reported. The cases from public supplies illustrate the potential effects of drinking contaminated water. All of the cases listed above except acute gastrointestinal illness of unknown cause (AGI) are transmitted by fecal contamination.
Although samples were not tested for protozoan pathogens, such as Giardia lamblia and Cryptosporidium, the presence of fecal bacteria indicates the potential for these protozoans and other pathogens of fecal origin to be present in the drinking water. Gastrointestinal diseases related to wells used for household-water supply have symptoms such as diarrhea and stomach cramps and commonly go unreported. With waters from nearly 70 percent of the wells sampled showing one or more bacteriological indicators, the presence of bacteria in water from rural wells is one of the most important water-quality issues related to human health in the Study Unit.
The presence of bacteria in water from rural household wells is an important drinking-water issue. Total coliform and fecal coliform bacteria were detected in water from many of the wells.