Evaluation of on-site wastewater system Escherichia coli contributions to shallow groundwater in coastal North Carolina.


Journal Article

The study goal was to determine if on-site wastewater systems (OSWWS) installed in coastal areas were effective at reducing indicator bacteria densities before discharge to groundwater. Groundwater Escherichia coli (E. coli) densities and groundwater levels adjacent to 16 OSWWS in three different soil groups (sand, sandy loam, and sandy clay loam) were monitored and compared to background groundwater conditions on four occasions between March 2007 and February 2008 in coastal North Carolina. Groundwater beneath OSWWS had significantly (p≤0.05) lower densities of E. coli than septic tank effluent, but significantly higher densities of E. coli than background conditions for each soil type. Twenty three percent of all groundwater samples near OSWWS had E. coli densities that exceeded the EPA freshwater contact standards (single sample 235 cfu/100 mL) for surface waters. Groundwater E. coli densities near OSWWS were highest during shallow water table periods. The results indicate that increasing the required vertical separation distance from drainfield trenches to seasonal high water table could improve shallow groundwater quality.

Full Text

Duke Authors

Cited Authors

  • Humphrey, CP; O'Driscoll, MA; Zarate, MA

Published Date

  • January 2011

Published In

Volume / Issue

  • 63 / 4

Start / End Page

  • 789 - 795

PubMed ID

  • 21330729

Pubmed Central ID

  • 21330729

Electronic International Standard Serial Number (EISSN)

  • 1996-9732

International Standard Serial Number (ISSN)

  • 0273-1223

Digital Object Identifier (DOI)

  • 10.2166/wst.2011.310


  • eng