Apparent 85Kr ages of groundwater within the Royal watershed, Maine, USA.
Specific 85Kr activity is mapped from 264 domestic and municipal wells sampled during 2002-2004 in the Royal watershed (361 km2), Maine. Gas samples are collected at 20 m, 40 m, and > 50 m interval depths within the unconfined aquifers. Gas extraction for 85Kr from wells is obtained directly via a wellhead methodology avoiding conventional collection of large sample volumes. Atmospheric 85Kr input to the recharge environment is estimated at 1.27 Bq m(-3) by time-series analyses of weighted monthly precipitation (2001-2004). Numerical simulation of Kr gas transport through the variable unsaturated zones to the water table suggests up to 12-year time lags locally, thus biasing the 85Kr groundwater ages. Apparent 85Kr ages suggest that approximately 70% of groundwater near 20 m depth was recharged less than 30 years BP (2004). Mass-age transport modeling suggests that post mid-1950s recharge penetrates to part of the basin's floor and that older groundwater seeps from the underlying fractured bedrock may occur.
Sidle
W C
WC
Isotope Hydrology Laboratory, Water Supply & Water Resources Division, Office of Research & Development, US Environmental Protection Agency, Cincinnati, OH 45268, USA. sidle.william@epa.gov
D003198:Computer Simulation; D019015:Geologic Sediments / Q000737:chemistry; D007726:Krypton / Q000032:analysis*; D007727:Krypton Radioisotopes; D008281:Maine; D008956:Models, Chemical; D013997:Time Factors; D014867:Water / Q000737:chemistry*
D007727:Krypton Radioisotopes; D014867:Water; D007726:Krypton