Vulnerability of headwater catchment resources to incidences of 210Pb excess and 137Cs radionuclide fallout

Recent identification of elevated excess ²¹⁰Pb (≤302.6 mBq L⁻¹) and ¹³⁷Cs (≤111.3 mBq L⁻¹) activity in drinking water wells up to 20 m depth indicates some transport of airborne radionuclide fallout beyond soils in the Shaker Village catchment, Maine. Estimated airborne mass loading ²¹⁰Pb_ex fluxes of about 0.9 mBq m⁻³, canvass this headwater catchment and may be sufficient to pose risks to unprotected shallow wells. Inventories of ²¹⁰Pb_ex and ¹³⁷Cs in pond sediments indicate maximum median activities of 943 mBq g⁻¹ and 40.0 mBq g⁻¹, respectively. Calculated ²¹⁰Pb_ex fluxes in the catchment soils range from 0.62–0.78 Bq cm⁻² year⁻¹ and yield a mean residence time of near 140 years. Measured ¹³⁷Cs activity up to 51.1 mBq g⁻¹ occurs in sediments at least to 5 m depth. Assumed particle transport in groundwater with apparent ⁸⁵Kr ages less than 5 years BP (2005) may explain the correlation between these particle-reactive radionuclides and elevated activity in some drinking water wells.