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APPARENT 85KRYPTON AGES OF GROUNDWATER WITHIN THE ROYAL WATERSHED, MAINE, USA
Citation:
SIDLE, W. C. APPARENT 85KRYPTON AGES OF GROUNDWATER WITHIN THE ROYAL WATERSHED, MAINE, USA. S.C. Sheppard (ed.), JOURNAL OF ENVIRONMENTAL RADIOACTIVITY. Elsevier BV, AMSTERDAM, Netherlands, 91(3):113-127, (2006).
Description:
85Kr activities were determined in 264 domestic and municipal wells from 2002-2004 in the Royal watershed (361 km2), Maine. Gas extraction for 85Kr from wells was effected directly via a well-head methodology permitting efficient widespread analyses at 20 m, 40 m, and >50 m zone depths within the glacially-derived, unconfined aquifers. The 85Kr input function was determined from local, monthly airshed measurements (2001-2004) to be near 1.26 Bq m-3, similar to global model projections in the region. Apparent 85Kr ages suggest that ≈70% of groundwater near 20 m depth recharged less than 30 yr BP (2004). Selected deep wells and mass-age transport modeling suggest that post mid-1950’s recharge has penetrated to much of the aquifer(s) floor and that some local recharge from the underlying fractured bedrock may occur. Numerical simulation of Kr gas transport through the variable unsaturated zones to the water table does suggest up to 12 yr time lags locally, thus biasing the 85Kr groundwater ages.