MONITORING GROUNDWATER AQUIFERS IN ANTICIPATIONOF THE GROUND WATER RULE

摘要

An objective of the pending Ground Water Rule (GWR) is to determine which potable groundrnwater sources are vulnerable to fecal contamination so appropriate remediation actions can berntaken. One reason for the delay in finalizing the GWR is disagreement on the fecal indicators tornbe used to determine when that ground water source is free of fecal contamination. Inrnanticipation of the GWR, large volumes (200–1,000 ml) of ground water samples from the islandrnof Kauai were analyzed for all of the microbial fecal indicators (total coliform, Escherichia coli,rnenterococci, Clostridium perfringens, FRNA coliphages, somatic coliphages) being consideredrnunder the GWR. Kauai, one of the smaller island in the state of Hawaii was selected as the studyrnsite because cesspools and septic tanks are extensively used to discharge untreated and poorlyrntreated sewage into shallow sub-surface soil, often over potable water aquifers. Over a 14-monthrnperiod, 48 groundwater samples from 37 wells operated by the County of Kauai and 61rngroundwater samples from 10 wells operated by private water utilities were analyzed. The resultsrnshow that 15% (7/48) of the well water samples operated by the County of Kauai was positivernfor total coliform but none of these samples was positive for E. coli (0/48), enterococci (0/41),rnFRNA coliphages (0/48), somatic coliphages (0/48) and C. perfringens (0/47). In comparison,rn16% (10/61) of the well water samples from private sources was positive for total coliform, 2%rn(1/61) was positive for E. coli, and 11% (6/53) was positive for enterococci. However, none ofrnthese samples was positive for FRNA coliphages (0/61), somatic coliphages (0/61) and C.rnPerfringens (0/56). These results provide evidence that based on monitoring groundwater sourcesrnfor the fecal microorganisms being considered for monitoring under the GWR, the potablerngroundwater sources on the island of Kauai are not vulnerable to contamination with fecalrnmatter. Moreover, the monitoring data show that extensive use of cesspools and septic tanks onrnKauai is not measurably contaminating the potable groundwater sources.