DETERMINING THE SOURCES OF BACTERIAL CONTAMINATION IN A LIMESTONE AQUIFER, ONEIDA COUNTY, NEW YORK

In rural areas of central New York, residents use water from domestic wells and have individual septic systems for waste disposal. Land use in these areas is mainly agricultural with corn and alfalfa as the most common crops. In aquifers that are sensitive to contamination, manure and improperly constructed septic systems are the principal sources of groundwater contamination. We are studying contaminant sources and movement in a limestone aquifer in Oneida County, New York. The limestone has been affected by solution and there are several karst features in the study area. The project was prompted by an incident in November 2014 in which two domestic wells produced brown water contaminated with fecal bacteria. The wells remain contaminated one year later and a DNA analysis of the bacteria showed that the water is contaminated with both human and animal waste.

We are using flourescein dye tracer tests, analysis of fecal coliform bacteria, and ion chromatography to study the aquifer. We found that there are four houses in the area that have significantly higher concentrations of fecal coliforms, indicating manure and/or septic contamination. There is no correlation between nitrate and coliform bacteria, which may imply that the main source of contamination is septic rather than agricultural. To date, no dye has been detected in the domestic wells, but more dye tracer tests are in progress. Comparisons of the bacterial communities from field and well samples may reveal patterns that will help us determine a spatial and animal source.