MONTHLY MONITORING OF ELEMENTAL ABUNDANCES IN DRINKING WATER FROM PRIVATE WELLS OF THE MOUNT DESERT ISLAND, ME REGION

Chronic low-dose exposure to toxins through drinking water can have long-term adverse health effects. Contaminants such as arsenic and uranium are naturally sourced from the Paleozoic metasedimentary and igneous bedrock throughout Maine; fractures and faults provide conduits for groundwater flow and host mineralized zones concentrating the mobilized elements. As governmental monitoring does not extend to private wells, the >40% of Maine residents relying on private wells for their drinking water are responsible for making sure it is safe to drink. The state recommends testing for arsenic every 3-5 years and has set a maximum contaminant level (MCL) of 10ppb. Some states have recently lowered the As MCL to 5ppb. Studies have shown that many factors may influence well yield over time (e.g. seasonality, pumping rates, proximity to other wells, extreme weather events) raising the concern that contaminant concentrations may also fluctuate periodically, potentially to levels above the MCL. A study of >150 private wells near Mount Desert Island, ME identified spatial relationships between geology and elemental abundances. This study also identified complications for private well owners: seasonal variations in water yield and quality as well as issues with filtration options. Building on this work, we resampled >50 wells during the dry season to complement the existing wet season data. We selected 25 bedrock wells to sample every month on the same day for a year. These bedrock wells are >80’ deep, have As values ranging from <0.1 ppb to >50 ppb, and have a variety of filtration methods in place. Where possible we sampled both pre and post filters measuring 14 different elements in each sample. This sampling strategy enables us to evaluate the efficacy of common filtration options and to compare the water chemistry of multiple proximal wells. Preliminary data reveal elemental fluctuations throughout the year and during rain events. Arsenic concentrations typically varied on the order of a few ppb in a given well. Some wells show increased concentrations during the wet season, while others increased during the dry season. Taken together, these new data suggest well owners should sample their wells at least twice a year when first establishing a mitigation and maintenance plan for their water.