An investigation of coliform contamination in private well water on the Crow Reservation

Abstract

The Crow reservation has a rural population that depends on home well water for domestic use. Many of the home wells do not have a suitable well cap, allowing a potential pathway of bacterial contamination of groundwater. Fecal coliform is associated with acute health problems, such as gastrointestinal illness, diarrhea, and cramps. Therefore, total coliform contamination of well water is an important health concern among Crow home well users. This research examines patterns in total coliform contamination among home well samples with respect to a suite of well and local aquifer characteristics thought to influence vulnerability to contamination, including well protection factors. Well and aquifer characteristics considered in this research include: the geologic production formation, local land cover, and distance to the nearest river. Well protection factors include: cap type, cap condition, depth of completion and time since completion (or age). One hundred water quality samples were collected from home wells along the Little Big Horn River in 2017, and available data on the character of those wells and aquifers were collected for comparison with the patterns in fecal coliform contamination among the samples. Presence/absence of coliform contamination was assessed using the Colilert IDEXX Quanti-Tray 2000 method. Spatial variations in the characteristics of wells and aquifers were characterized through a combination of well logs, the National Land Cover Dataset, and the National Hydrography Dataset. Logistic regression was used to identify potential relationships between probability of coliform contamination and characteristics of associated wells and aquifers. Logistic regression models suggested two notable and statistically significant (? = 0.05 level) relationships: (1) wells completed in alluvium and farther from the river had a higher probability of total coliform contamination, and (2) wells with old style caps had a higher probability of total coliform contamination. The government of the Crow tribe can decide how to use the results for mitigation efforts and awareness for homeowners with contaminated wells. Also, the Crow Water Quality Project should archive and consider these results for future research, planning, development, and management.