Pilot project on groundwater dating in confined aquifers of the North Carolina Coastal Plain

helium;tritium;north carolina coastal plain;confined aqufiers;black creek aquifer;upper cape fear aqufier;carbon-14;groundwater dating

Kennedy, Casey David ; John Fountain, Committee Member,David DeMaster, Committee Member,David Genereux, Committee Chair,Kennedy, Casey David ; John Fountain ; Committee Member ; David DeMaster ; Committee Member ; David Genereux ; Committee Chair

University:North Carolina State University

关键词: helium;    tritium;    north carolina coastal plain;    confined aqufiers;    black creek aquifer;    upper cape fear aqufier;    carbon-14;    groundwater dating;   

Others  :  https://repository.lib.ncsu.edu/bitstream/handle/1840.16/1541/etd.pdf?sequence=1&isAllowed=y

美国|英语

来源: null

【 摘 要 】

This pilot project presents 14C groundwater ages in the Black Creek and Upper Cape Fear aquifers of the Coastal Plain of North Carolina, an evaluation of the relationship between He concentration and groundwater age, and 3H concentrations in groundwater.Groundwater samples were collected with a Bennett pump from 7 wells that lie along a trend roughly parallel to groundwater flow (at least, predevelopment groundwater flow).14C, 13C, DIC, DOC, He, Ne, Ar, N2, O2, CO2, CH4, H2, 3H, S, Fe, Al, Mn, Si, Na+, K+, Ca2+, Mg2+, Cl-, SO4-, and NO3- were measured in all samples.Estimation of groundwater age involved inverse mass balance modeling with NETPATH to account for geochemical reactions (calcite dissolution, organic matter oxidation, and cation exchange) affecting 14C activity in groundwater, as well as a separate correction to account for loss of 14C by diffusion into contiguous aquitards.14C groundwater ages were 580, 10700, 19100, and greater than 35300 years old at four wells in the Black Creek aquifer, and 15100, 26900, and 31100 years old at three wells in the Upper Cape Fear aquifer.These groundwater ages, together with falling heads, suggest that groundwater withdrawals in these aquifers represent a sort of'mining.'He concentration in groundwater increased with 14C groundwater age with one exception (a sample very high in He concentration from the Upper Cape Fear where it directly overlies crystalline basement rocks).Groundwater from 6 of the wells had 3H concentrations that are consistent with the presence of young water, but it is uncertain whether the 3H in these wells is from relict drilling fluid, downward leakage along the well casings, or a more broadly distributed downward leakage.