Identification of an assemblage of indicator organisms to assess timing and source of bacterial contamination in groundwater

Bacterial contamination of drinking water wells is a common problem in many rural areas. Some of this contamination may be related to manure spreading or housing of livestock; another source is on-site septic systems. Current indicator organisms are able to detect the presence of fecal contamination, but where there may be more than one potential source of fecal material, the current indicators are unable to ascertain the origin. This laboratory investigation was undertaken to determine the longevity and reliability of a selected suite of indicator organisms. Total coliform, fecal coliform, fecal streptococci and Clostridium perfringens were monitored in a simulated contaminated groundwater environment for 6 months. All four indicator organisms were present at the end of 6 months. The number of fecal streptococi bacteria decreased most noticeably, allowing assessment of relative age of contamination. C. perfringens was found to be a reliable indicator of contamination from animal manure. Fecal material from 28 different animals and three septic systems were assessed for the presence of the indicator organisms. Total coliform, fecal coliform and fecal streptococci were present in the fecal material of all animals tested including reptiles. C. perfringens was detected in feces from all but two of the animals assessed. Using an assemblage of indicator organisms provides more information regarding source and timing of contamination than just testing for total coliform and fecal coliform bacteria.