Apparent ⁸⁵Kr ages of groundwater within the Royal watershed, Maine, USA

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• 作者：W.C. Sidle
• 关键词：Krypton-85 ; Groundwater age ; Recharge ; Maine
• 刊名：Journal of Environmental Radioactivity
• 出版年：2006
• 出版时间：2006
• 年：2006
• 卷：91
• 期：3
• 页码：113-127
• 全文大小：1711 K

文摘

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 ≈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.