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Determination of dispersivities and reactionkinetics of selected basalts of columbia river plateau using an inverse analytical solution technique
Abstract
The Columbia River Plateau consists of over 100 layers of tholemtic flood basaits, ranging in thickness from 1 m to greater than 100 m, with groundwater flow occurring predominantly along the fractured and weathered flow tops. This study focuses on the determination of transport parameters by modeling sodium transport in the Priest Rapids and Roza flow tops of the Wanapum formation, and Rocky Coulee and Umtanum flow tops of the Grande Ronde formation, within the Cold Creek Syncline of the Hanford Nuclear Waste Reservation. Regional scale lateral dispersivities and reaction rate coefficients were determined from sodium concentration distributions, using an inverse analytical solution technique developed by Domenico (1987) to model nonconservative mass transport. Deuterium, a conservative species, was also modeled using the same technique, to determine a "baseline" reaction rate coefficient. Source concentration values and source dimension sizes were also produced by the model. Model results were compared to those determined by LaVenue (1 985) for chloride, and Adamski (1 993) for boron and potassium. Results from the Wanapum formation yielded a source Y dimension ranging from 11581 m to 13583 m and a lateral dispersivity value ranging from 26 m to 96 m. Relative reaction rate coefficients for this formation were determined to be 10-'-10-' and 10-'-10-9, respectively for sodium and deuterium. Results from the Grande Ronde formation yield a source Y dimension ranging from 6500 m to 12360 m, and a lateral dispersivity value ranging from 70 m to 488 m. Relative reaction rate coefficients for sodium and deuterium in the Grande Ronde formation were determined to be approximately 10-' m-1 and 1 O-Il̲ 0-7 m-1, respectively. Larger variations in values of source Y dimension and lateral dispersivity (ay) for the Grande Ronde formation are probably due to a minimum amount of available data control points. Oxygen-18 and deuterium isotopic data for waters from the flowtops upgradient and downgradient of the Cold Creek Barrier (a hydrologic discontinuity), and from a deep formation well support the hypothesis that deeper formation waters are moving upward along the Cold Creek Barrier and then laterally along the flow tops in the downgradient direction. Fluids found in deeper flow tops have an isotopic signature closer to those of the deep formation well; and fluids of shallower flow tops have an isotopic signature suggesting mixing between local meteoric waters and deep formation waters.
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Citation
Fahlquist, Lisa Armstrong (1994). Determination of dispersivities and reactionkinetics of selected basalts of columbia river plateau using an inverse analytical solution technique. Master's thesis, Texas A&M University. Available electronically from https : / /hdl .handle .net /1969 .1 /ETD -TAMU -1994 -THESIS -F157.
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