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

摘要

The study goal was to determine if on-site wastewater systems (OSWWS) installed in coastal areasnwere effective at reducing indicator bacteria densities before discharge to groundwater.nGroundwater Escherichia coli (E. coli) densities and groundwater levels adjacent to 16 OSWWS innthree different soil groups (sand, sandy loam, and sandy clay loam) were monitored and comparednto background groundwater conditions on four occasions between March 2007 and February 2008nin coastal North Carolina. Groundwater beneath OSWWS had significantly (pr0.05) lower densitiesnof E. coli than septic tank effluent, but significantly higher densities of E. coli than backgroundnconditions for each soil type. Twenty three percent of all groundwater samples near OSWWS hadnE. coli densities that exceeded the EPA freshwater contact standards (single sample 235 cfu100 mL) for surface waters. Groundwater E. coli densities near OSWWS were highest during shallownwater table periods. The results indicate that increasing the required vertical separation distancenfrom drainfield trenches to seasonal high water table could improve shallow groundwater quality.