Geochemical and Hydrochemical Analysis of the Bedrock Aquifer in Monkton, Vermont, Poster 4

Previous studies have identified groundwater contamination from naturally occurring inorganic constituents in fractured bedrock aquifers in parts of Vermont. This study assesses a fractured bedrock aquifer comprised mainly of... [ view full abstract ]

Previous studies have identified groundwater contamination from naturally occurring inorganic constituents in fractured bedrock aquifers in parts of Vermont. This study assesses a fractured bedrock aquifer comprised mainly of Cambrian Monkton Quartzite and Dunham Dolostone. No systematic information on groundwater quality, aquifer potential or bedrock composition has been collected from this part of the Champlain Valley. Groundwater from 28 wells and representative rock outcrops has been analyzed for major and trace element composition. Alpha radiation > 5 pCi/L (VDH action level) was found in 11% of wells. 68% of wells contain > 2 µg/L uranium, but none exceed 20 µg/L (MCL). Alpha radiation and U are positively correlated in groundwater, suggesting that U is the likely alpha radiation source. Mn concentrations are >100 µg/L in 14% of wells, with 7% > 300 ppm MCL. Fe exceeds 100 µg/L in 36% of wells. Arsenic in all wells was < 10 µg/L (MCL). Results imply that the Monkton Quartzite contributes less radionuclides to groundwater than older Cheshire and Pinnacle quartzites – this may be explained by compositional differences of sediments deposited in early rift and drift stages of the Iapetus Ocean (Cheshire and Pinnacle) compared to later passive margin deposition (Monkton Quartzite).