Predicting coliform presence in private wells as a function of well characteristics, parcel size and leachfield soil rating
Section snippets
Background
Water contaminated with pathogens can cause illness if ingested without appropriate treatment (Wallender et al., 2014; Beer et al., 2015; Benedict et al., 2017). Illnesses that result from consuming pathogenic contaminated water includes acute gastrointestinal illness, acute respiratory illness, and neurologic illnesses (Benedict et al., 2017). Waterborne diseases may even lead to early death (Cortese and Parashar, 2009; Morgan et al., 2015). For example, Chaudhry et al. (2015) found that the
Well sampling and testing
Gaston County Department of Health and Human Services (GC DHHS) in partnership with the University of North Carolina at Charlotte (UNCC) organized free well water sampling across Gaston County to evaluate groundwater quality and protect human health (Dye and Zarate-Bermudez, 2018; Lan et al., 2020; Owusu et al., 2020a; Owusu et al., 2020b). Student teams from UNC Charlotte visited every permitted private well in Gaston County, North Carolina (Fig. 1), from October 2017 to October 2019. The
Descriptive statistics
The maximum well age in the data was 30 years and this reflects the period when Gaston County enforced standards on well construction from 1989. Pre-1989 wells were not sampled for this study. Samples were obtained from 1091 drilled wells and 72 bored wells. As shown in Fig. 2A, we found well age for bored wells (median well age = 24 years) were significantly (p < 0.05) older than drilled wells (median age = 19 years).
The median well depth was 70.1 m. We found well depths for bored wells
Discussion
Coliform bacteria were reported in 290 of 1091 drilled wells and 39 of 72 bored wells. Coliform bacteria were more likely to occur in older wells. A high proportion of bored wells that were positive for coliform bacteria were found in the northwestern part of Gaston County. Compared to bored wells, drilled wells that were positive for coliform bacteria were closer to each other. In some instances, out of more than nine samples within a 1-km area in the northeastern parts of the county, 60% of
Conclusions
We found evidence of groundwater contamination with regards to the U.S. EPA standards for the presence of coliform bacteria in water. We used GIS techniques to map possible spatial patterns of positive coliform samples and learned of the increased likelihood of wells near one another to test positive for coliform bacteria, suggesting common contamination sources, particularly in the northeastern part of the county. We then used multivariate logistic regression to investigate possible causes of
CRediT authorship contribution statement
CO conceived the idea of modeling the presence of Coliform bacteria in private wells in Gaston County, North Carolina. CO designed the overall study, prepared the data with technical support from ED, GS, DV, KB and RP. The first draft of the manuscript was written by CO, and all authors provided extensive inputs on different versions of the manuscripts. All authors read and approved the final manuscript.
Funding
This work was supported by the National Center for Environmental Health [CDC-RFA-EH15-1507].
Declaration of competing interest
None.
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Cited by (1)
An assessment of total coliforms and associated thresholds as water quality indicators using a large Ontario private drinking water well dataset
2022, Science of the Total EnvironmentCitation Excerpt :E. coli are considered indicators of recent faecal contamination as they are found almost exclusively in the gastrointestinal tract of humans and animals, unlike the rest of the TC group, which can exist naturally in soil and water (Croxen et al., 2013; World Health Organization, 2017). Previous studies of TC contamination (i.e., detection rates and concentrations) in private wells have facilitated an improved understanding of groundwater contamination mechanisms and susceptibility factors (Gonzales, 2008; Invik et al., 2017; Owusu et al., 2021), but a limited number have examined the relationship between multiple concurrent susceptibility factors and TC contamination, and still fewer have focused on identifying links between TC and E. coli contamination of groundwater. According to the Ministry of the Environment, Conservation, and Parks (MECP), well water microbial test results of five or fewer colony-forming units (CFU) of TC per 100 mL are indicative of acceptable water quality in the absence of a chlorine residual, as long as zero CFU of E. coli are detected (Ministry of the Environment, Conservation, and Parks, 2021).