Evaluating the influence of septic systems and watershed characteristics on stream faecal pollution in suburban watersheds in Georgia, USA.

AIMS: To determine the impact of septic systems on water quality and in so doing identify watershed level characteristics that influence septic system impact. METHODS AND RESULTS: Water samples were collected from streams in 24 well-characterized watersheds during baseflow to analyse for the levels of faecal indicators Escherichia coli and enterococci. The watersheds represent a gradient of land-use conditions from low to high density of septic systems, as well as developed to undeveloped uses. Our findings indicate statistically significant interaction between septic density and season for enterococci count (P = 0·005) and stream yield (P = 0·04). Seasonal variations in bacterial count and stream yield were also observed, with significant differences between spring-winter and summer-winter. Results from multiple linear regression models suggest that watershed characteristics (septic system density, median distance of septic systems to stream, per cent developed area and forest cover) and water temperature could explain approximately half (R(2) = 0·50) of the variability in bacterial count and yield in spring and summer. CONCLUSIONS: There is a significant positive relationship between septic system density and faecal pollution levels. However, this relationship is season dependent and is influenced by watershed level characteristics such as median distance of septic systems from streams, per cent developed area and forest cover. SIGNIFICANCE AND IMPACT OF THE STUDY: This study confirms the significant impact of septic systems on faecal pollution during baseflow and provides the tools that will enable effective pollution monitoring at the watershed scale.

Examination of factors for use as potential predictors of human enteric pathogen survival in soil.

AIMS: Three soils that varied in their physicochemical characteristics and microbial diversity were inoculated with Escherichia coli O157:H7 and Salmonella to determine the relative impact of abiotic and biotic factors on the pathogens' survival when the soil was held at 25°C. METHODS AND RESULTS: Three soils that were classified as having low, medium and high microbial diversity were divided into two batches for adjustment to 20% of water-holding capacity and to 40% of water-holding capacity. Soils were inoculated with both green fluorescent-labelled E. coli O157:H7 and red fluorescent-labelled Salmonella (5 log CFU g(-1) dry weight) and held at 25°C. Pathogens inoculated into an acidic soil died off within 9 weeks, whereas they were still detected in the other two soils by enrichment culture after 18 weeks. Moisture did not affect inactivation of E. coli O157:H7, but did affect Salmonella inactivation in soil having the greatest organic load and microbial diversity. Using multiple linear regression analysis, 98.7% of the variability in the inactivation rate for E. coli O157:H7 was explained by a model that included the variables of initial pH and electrical conductivity. Salmonella's inactivation rate was predicted by a model that included pH and initial cell numbers of copiotrophic and oligotrophic bacteria. CONCLUSION: This study provided evidence of specific properties that impact inactivation of E. coli O157:H7 and Salmonella in soils at 25°C. SIGNIFICANCE AND IMPACT OF THE STUDY: Identification of factors influential in the die-off of enteric pathogens will assist in developing guidelines for safe intervals between field contamination events and planting or harvesting of fresh-cut produce crops.

Microbial water quality before and after the repair of a failing onsite wastewater treatment system adjacent to coastal waters.

AIMS: The objective was to assess the impacts of repairing a failing onsite wastewater treatment system (OWTS, i.e., septic system) as related to coastal microbial water quality. METHODS AND RESULTS: Wastewater, groundwater and surface water were monitored for environmental parameters, faecal indicator bacteria (total coliforms, Escherichia coli, enterococci) and the viral tracer MS2 before and after repairing a failing OWTS. MS2 results using plaque enumeration and quantitative reverse transcriptase polymerase chain reaction (qRT-PCR) often agreed, but inhibition limited the qRT-PCR assay sensitivity. Prerepair, MS2 persisted in groundwater and was detected in the nearby creek; postrepair, it was not detected. In groundwater, total coliform concentrations were lower and E. coli was not detected, while enterococci concentrations were similar to prerepair levels. E. coli and enterococci surface water concentrations were elevated both before and after the repair. CONCLUSIONS: Repairing the failing OWTS improved groundwater microbial water quality, although persistence of bacteria in surface water suggests that the OWTS was not the singular faecal contributor to adjacent coastal waters. A suite of tracers is needed to fully assess OWTS performance in treating microbial contaminants and related impacts on receiving waters. Molecular methods like qRT-PCR have potential but require optimization. SIGNIFICANCE AND IMPACT OF STUDY: This is the first before and after study of a failing OWTS and provides guidance on selection of microbial tracers and methods.

Tracking microbial transport through four onsite wastewater treatment systems to receiving waters in eastern North Carolina.

AIMS: To examine microbial transport through properly functioning and failing onsite wastewater treatment systems (OWTS) and its implication in surrounding water quality. METHODS AND RESULTS: Water samples were collected from monitoring wells near leach lines of OWTS and nearby ditches and receiving surface waters to analyse for Escherichia coli and enterococci. Tracer studies with Rhodamine WT (RWT) and coliphage MS2 were also carried out to understand the fate and transport of contaminants through each OWTS. Escherichia coli and enterococci concentrations were higher around failing than properly functioning OWTS by as much as 85-fold. A storm event resulting in 9·5 cm of rainfall increased E. coli and enterococci concentrations by averages of 4·1 × 10³ and 7·9 × 10³ MPN per 100 ml, respectively, in wells close to the OWTS. MS2 persisted in the wastewater distribution boxes of the OWTS for several months and was detected in some outer perimeter wells. CONCLUSIONS: Properly functioning OWTS in eastern North Carolina were effective in treating wastewater, whereas the failing OWTS affected the groundwater quality more adversely, especially after a rain storm, but had minor impact on the nearby coastal surface water. SIGNIFICANCE AND IMPACT OF THE STUDY: The study is the first description of the microbial contaminant signature stemming from properly functioning and failing systems under regular use in a high-priority coastal area.