Safe drinking water is one of the most fundamental requirements for human health and survival. Indicator bacteria (i.e., total coliforms and fecal coliforms) are typical indicators of microbial water quality. In the state of North Carolina (NC), new private drinking water wells are required for total coliform and E. coli testing. New private drinking water wells are typically only tested once before use in NC, so consistent and accurate testing is critical. Herein, we analyzed a large data set of 32,839 water samples collected from private drinking water wells, representing 80 of North Carolina’s 100 counties, using stepwise logistic regression to determine if bacterial detection is influenced by: spatiotemporal characteristics of the wells, sample collection and analysis protocols, and transport methods, and using this information recommend best practices to improve bacteriological sample collection and handling. Specifically, we examined the dataset for significant differences between sample positive rates for E. coli and/or total coliform depending on the county and region of collection, transport method, sampling collection point, day of the week, month, year, season, treatment method, the time elapsed between collection and incubation, the test used, and the person reporting the sample results. Our results showed that 34.11% of samples were tested positive for total coliform, while 1.38% tested positive for E. coli. The total coliform positive rate ranged from 16.4% to 60% among the 80 counties. While nine counties reported no positive E. coli samples, positive E. coli rates for the remaining counties ranged from 0.17% to 12.7%. The likelihood of total and E. coli positives differed significantly between counties and regions. Samples from the Inner and Outer Coastal Plains were more likely to be positive for total coliforms, while samples from the Outer Coastal Plains were more likely to be positive for E. coli. Delivery method, sampling site, month of collection, year of collection, season, treatment type, elapsed time between collection and analysis, and person reporting sample results were also correlated with positive total coliform results. Similarly, sampling point, month, treatment type, test type, and the person reporting the results were correlated with positive E. coli samples. Providing clear and complete information for the samples collected, future research could be improved to better inform well water sampling outcomes.

Factors influencing indicator bacteria sampling results in new water wells in North Carolina, USA

ACS Spring Meeting 2021

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.