Evaluation of indicators of fecal contamination in Groundwater

Abstract

Detecting fecal waste contamination of groundwater is usually accomplished by testing for fecal “index” or “indicator” bacteria. The authors examined 128 samples from 26 public groundwater sources in New Jersey and compared the ability of nine potential indicators to detect fecal contamination. Each sample was tested for heterotrophic plate count; total coliform (TC); fecal coliform (FC); Escherichia coli, enterococci, and Clostridium perfringens bacteria (100 mL); somatic and F+ coliphage (100 mL); and coprostanol (1 and 4 L). Data from a source with known contamination showed that the TC test was the most reliable indicator, followed by the FC test. Fecal pollution contains high concentrations of TC bacteria, but because some TC bacteria in the environment may not be of fecal origin, a positive TC test result should be followed by an FC, E. coli, or enterococci test to confirm contamination. The sanitary significance of the occasional presence of TC bacteria or coliphage without other fecal indicators was uncertain. Methods capable of analyzing 1‐L volumes should be investigated. A groundwater should be analyzed multiple times (i.e., 10 or more) to confidently determine its sanitary status.