Septic Systems and Rainfall Influence Human Fecal Marker and Indicator Organism Occurrence in Private Wells in Southeastern Pennsylvania

Abstract

In the United States, approximately 48 million people are served by private wells. Unlike public water systems, private well water quality is not monitored, and there are few studies on the extent and sources of contamination of private wells. We extensively investigated five private wells to understand the variability in microbial contamination, the role of septic systems as sources of contamination, and the effect of rainfall on well water quality. From 2016 to 2017, weekly or biweekly samples (n = 105) were collected from five private wells in rural Pennsylvania. Samples were tested for general water quality parameters, conventional and sewage-associated microbial indicators, and human pathogens. Total coliforms, human Bacteroides (HF183), and pepper mild mottle virus were detected at least once in all wells. Regression revealed significant relationships between HF183 and rainfall 8–14 days prior to sampling and between total coliforms and rainfall 8–14 or 0–14 days prior to sampling. Dye tracer studies at three wells confirmed the impact of household septic systems on well contamination. Microbiological measurements, chemical water quality data, and dye tracer tests provide evidence of human fecal contamination in the private wells studied, suggesting that household septic systems are the source of this contamination.

Sources and Risk Factors for Nitrate and Microbial Contamination of Private Household Wells in the Fractured Dolomite Aquifer of Northeastern Wisconsin

“…There is ample evidence showing precipitation favors microbial contamination of private wells. Precipitation quantity in the period preceding sampling was positively associated with the occurrence in private wells of indicator bacteria (Hynds et al 2012;O'Dwyer et al 2014;Procopio et al 2017;Invik 2019) human enteric viruses (Allen et al 2017) and the human-specific Bacteroides marker HF183 (Murphy et al 2020). The antecedent precipitation periods associated with contamination varied between 30 (Invik et al 2019) and 5 d (Hynds et al 2012), and even shorter periods of rainfall (24 h) may be associated with contamination of vulnerable aquifers (Morrissey et al 2015).…”

“…Among 50 private wells in seven hydrogeological districts of Wisconsin, 8% were positive for human enteric viruses (Borchardt et al 2003b). Private wells completed in fractured Silurian dolomite in Ontario, Canada (11 wells), and fractured bedrock in Pennsylvania, USA (5 wells), had microbes of fecal origin in 45% and 100%, respectively (Allen et al 2017;Murphy et al 2020). Ninety-six percent of public wells tested in Minnesota, USA, for similar types and number of fecal organisms were positive (Stokdyk et al 2020), and, as in the present study, Cryptosporidium was the most frequently detected pathogen, suggesting it is more common in groundwater than previously thought (Stokdyk et al 2019).…”

“…In one study, vaccine poliovirus was introduced into the tank of a new conventional septic system, and the virus was cultured in multiple samples over time in a monitoring well 6 m down-gradient from the edge of the drainfield (Alhajjar et al 1988). More recently, detection in groundwater of the human-specific markers HF183 and HumM2 has been linked with septic system effluent (Schneeberger et al 2015;Murphy et al 2020). Groundwaterborne disease outbreaks (Yates 1985;Beller et al 1997;Borchardt et al 2011) and endemic diarrheal illness (Borchardt et al 2003a) have also been associated with septic systems.…”

“…In the region's four main agricultural counties, Brown, Calumet, Kewaunee, and Manitowoc, the number of milking dairy cows increased from 132,558 to 180,860 between 2002, a 36% increase (USDA NASS 2002. This number of milking cows produces approximately 5:9 × 10 9 kg of excrement (manure and urine) per year (Nennich 2005), which in northeastern Wisconsin is all applied to the landscape (Erb et al 2015). Population growth in the four-county region between 1950 and 2000 increased exurbanization by as much as 60% (Brown et al 2005).…”

Effect of Dilution on the Pollutant Monitoring in Decentralised Treatment Facilities Using Electrical Conductivity Sensors: Experimental and Modelling Insights

“…Domestic sewage in rural areas is an important part of nonpoint source pollution; its direct discharge into surface waters without efficient treatment has caused declining water quality in aquatic environments and threatened the safety of drinking water in rural areas (Dubber and Gill 2017;Gu et al 2016;Murphy et al 2020;Nsenga Kumwimba et al 2018;Sorensen et al 2016). Treating decentralised domestic sewage is an increasing and difficult challenge in numerous developing countries (Lam et al 2015;Li et al 2020).…”