Sulfate transport in a Coastal Plain confining unit, New Jersey, USA |
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Authors: | Amleto A Pucci Jr |
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Institution: | (1) Ground-Water Management and Conservation, Inc., PO Box 78 Erwinna, PA 18920, USA Fax: +1-610-294-9475 e-mail: puccia@epix.net, US |
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Abstract: | A transient 1-D, two-pathway non-equilibrium deterministic advective dispersion model was used to examine the distribution
of chloride (43–100 mg/L) and sulfate (57–894 mg/L) concentrations in the 35-m-thick section of the Lower confining unit,
Atlantic Coastal Plain, New Jersey, USA. The model was used to constrain hypotheses about how pore-water chemistry changed
over time. Explanations of the solute concentrations were explored by inverse and direct methods given a few known constraints,
including concentrations of pore-water constituents from 12 core samples, reported simulated flow rates, and estimated hydrogeologic
properties. The hypothesis that is best supported by the model results is that the distribution of chloride and sulfate concentrations
in the confining unit reflect the history of the aquifer system since it was filled with seawater at the last eustatic high,
about 84×103yr BP. The model simulates fresh-water flushing of the seawater-permeated silts at a steady upward pore-water flow velocity
of 8.8×10–6 m/d, with a dispersion coefficient of 9.2×10–7 m2/d, a dimensionless partition expression for chloride, βCl=0.981, and a dimensionless exchange coefficient, ωCl=0.31×10–2. Sulfate concentrations were simulated over the flow path using flow and dispersion values calculated for chloride transport
plus a retardation term. Parameters for sulfate transport include retardation coefficient=4.51, βSO4=0.994, and ωSO4=0.31×10–2. Sensitivity analysis indicates that the model is most sensitive to flow velocity, and that fresh-water flushing of the confining
unit is best simulated by having seawater concentration levels at the inflow boundary of the confining unit exponentially
decrease with a concentration half-life rate of 825 yr.
Received, January 1997 / Revised, April 1998, October 1998, January 1999 / Accepted, January 1999 |
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Keywords: | USA hydrochemistry confining units numerical modeling salt-water/fresh-water relations |
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