Boron and lithium isotopes as groundwater tracers: a study at the Fresh Kills Landfill, Staten Island, New York, USA

摘要

A study was conducted at the Fresh Kills landfill, Staten Island, New York to investigate the use of B and Li isotopes as tracers of mixing and flow in the groundwater environment. Four end-member waters are present at the Fresh Kills: freshwater, seawater, a geochemically distinct transitional groundwater (that occurs in the zone of mixing between seawater and freshwater) and landfill leachate. The delta(11)B and delta(6)Li values of end-member waters are distinct and have isotopic compositions that reflect the solute sources: freshwater delta(11)B similar to + 30parts per thousand, delta(6)Li similar to -22parts per thousand; transition zone groundwaters delta(11)B similar to + 20parts per thousand, delta(6)Li similar to -27parts per thousand; seawater delta(11)B + 40 to + 75parts per thousand, delta(6)Li-37 to-44parts per thousand; leachate delta(11)B similar to + 10parts per thousand (delta(6)Li not determined). Those wells influenced by seawater exhibited a clear chemical mixing trend, with seawater contributions ranging from 3 to 85%. Well waters with a high percentage of seawater (> 30%) had delta(11) B values that were within 1parts per thousand of the seawater value ( + 40parts per thousand), whereas a trend of increasing delta(11)B values ( + 55 to + 75parts per thousand) was observed for wells with a lower percentage of seawater (<30%). delta(6)Li values for well waters impacted by mixing with seawater ranged from-37 to-44parts per thousand, significantly more negative than pure seawater (-31parts per thousand). This deviation from the isotopic composition of seawater, for both delta(11)B and delta(6)Li values, represents non-conservative behavior and is likely the result of isotopic fractionation during ion exchange reactions. The wide range of delta(11)B and delta(6)Li values and the distinct isotopic compositions of end-member waters makes B and Li isotopes useful for recognizing solute sources, however isotopic fractionation may limit their use as simple tracers of groundwater flow and mixing. (C) 2002 Elsevier Science Ltd. All rights reserved. [References: 36]