Effects of rainfall and septic systems on the occurrence of human sewage markers and traditional indicator organisms in private wells in southeastern Pennsylvania

Authors: MURPHY, HEATHER - Temple University; MCGINNIS, SHANNON - Temple University; BLUNT, RYAN - Temple University; WU, JINGWEI - Temple University; CAGLE, ALEXANDER - Temple University; DENNO, DONNA - University Of Washington; Spencer, Susan; STOKDYK, JOEL - Us Geological Survey (USGS); FIRNSTAHL, AARON - Us Geological Survey (USGS); Borchardt, Mark

Submitted to: Environmental Science and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/19/2020
Publication Date: 2/19/2020
Citation: Murphy, H., Mcginnis, S., Blunt, R., Wu, J., Cagle, A., Denno, D., Spencer, S.K., Stokdyk, J., Firnstahl, A., Borchardt, M.A. 2020. Effects of rainfall and septic systems on the occurrence of human sewage markers and traditional indicator organisms in private wells in southeastern Pennsylvania. Environmental Science and Technology. 54(6):3159-3168. https://doi.org/10.1021/acs.est.9b05405.
DOI: https://doi.org/10.1021/acs.est.9b05405

Interpretive Summary: Rural homeowners without access to public water systems rely on private wells for their household water needs. 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 intensively sampled five private wells in rural Pennsylvania 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. All five wells were positive for the type of microorganisms only found in human fecal wastes. When we added dye to the three of the well owners’ septic systems the dye appeared in their wells, clearly demonstrating that septic system effluent was reaching the wells. In addition, we found the greater the amount of rain, the more likely a well would be contaminated with human fecal wastes. These findings further our understanding of private well water quality and highlight the importance of septic systems as a contamination source.

Technical 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 2016-2017, weekly or biweekly samples were collected from 5 private wells in rural Pennsylvania (N=105). Samples were tested for general water quality parameters, conventional and sewage-associated microbial indicators, and human pathogens. Total coliforms, human Bacteroides, and pepper mild mottle virus were detected at least once in all wells. Regression revealed significant relationships between human Bacteroides 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 3 wells confirmed the impact of household septic systems on well contamination. Microbiological measurements, chemical water quality data, and dye tracer tests show that human fecal contamination is present in private wells and that household septic systems are the source of this contamination.