MANGANESE SOURCING AND TRANSPORT IN MASSACHUSETTS GROUNDWATER: UNDERSTANDING DISSOLUTION MECHANISMS AND CREATING A TEMPORALLY VARIANT DATABASE

Manganese (Mn) in groundwater is ubiquitous in the U.S., with an estimated 2.6 million people consuming groundwater with elevated Mn concentrations. Many New England states have groundwater with Mn concentrations over the USEPA secondary maximum contaminant limit of 0.05 mg/L for Mn. Temporal variability of Mn in groundwater is suggested to be a larger issue than it appears, primarily relating to redox variability throughout the year. While redox conditions are important to Mn dissolution, it is one of multiple factors for conditions favoring Mn dissolution. Sampling is often point-sampling and does not capture the finer-scale fluctuations and processes that may offer more specific insight into conditions driving dissolution. We have begun developing a temporally variant database to investigate the mechanisms and conditions behind elevated Mn in groundwater, and use preliminary data to explore temporal variations and the impact of flow path lengths on Mn concentrations. Wells in Western Massachusetts were utilized to build a time-series of Mn concentrations in groundwater from a variety of aquifer types and various well depths. Samples are analyzed for trace metals and micronutrients using inductively coupled plasma - mass spectrometry and inductively coupled plasma - optical emission spectroscopy, respectively. These wells have corresponding depth to water, well screen geologic information, and stable water isotopic compositions. It has previously been found that Mn concentrations tend to be higher in shallower wells; our preliminary data thus far does not correspond with these findings and we hypothesize that in geologic settings found in Massachusetts, Mn dissolution and transport is more of a bottom-up process rather than a top-down process. We also expect to see a difference in Mn concentration between the different aquifer types sampled, with those more affected by recharge showing a greater seasonal flux in Mn concentration. Private wells are often not extensively treated for Mn contamination, as many public groundwater supplies are, but offer an opportunity to better investigate the mechanisms behind manganese sourcing and transport across a wide range of geologic and soil conditions.