Assessing the vulnerability of groundwater sources to fecal contamination
Fujioka, Roger S. and Bunnie S. Yoneyama
The Honolulu Board of Water Supply (HBWS) selectively chlorinates half of its groundwater supply to provide drinking water that meets the Total Coliform Rule. The objective of this study was to determine whether the groundwater sources used by HBWS are vulnerable to contamination with fecal matter and would require routine disinfection. Larger volumes (1,000 ml) of samples from groundwater and from the distribution system were more sensitive than standard volumes (100 ml) in the detection for total coliform, fecal coliform, Escherichia coli, and fecal streptococcus. Confirmed fecal indicator bacteria were detected in 2 of 79 groundwater samples and from none of the 152 distribution system water samples, indicating that the groundwater has a low incidence of contamination and the selective chlorination program effectively reduces this level of contamination. Analysis of 1,000-ml samples of groundwater is recommended but is not included in the recent guidelines of the proposed Ground Water Rule.