Field study of dispersion in a heterogeneous aquifer: 1. Overview and site description

Abstract

Results are presented for a large-scale natural gradient tracer experiment conducted in a heterogeneous alluvial aquifer at a site near Columbus, Mississippi. The study was initiated with a 48-hour pulse injection of 10 m 3 of groundwater containing bromide and three organic tracers (pentaftourobenzoic acid, o-trifiuoromethylbenzoic acid, and 2,6-diflourobenzoic acid). Over a 20-month period, seven comprehensive samplings of the tracer plume were performed at approximately 1-to 4-month intervals using an extensive three-dimensional sampling well network. The dominant feature of the tracer plume that evolved during the study was the highly asymmetric concentration distribution in the longitudinal direction. This asymmetry was produced by accelerating groundwater flow along the plume travel path that, in turn, resulted from an approximate 2-order-of-magnitude increase in the mean hydraulic conductivity between the near-field and far-field regions of the site. The Columbus study is distinct from previous natural gradient experiments because of the extreme heterogeneity of the aquifer, the large-scale spatial variations in groundwater velocity, and the extensive set of hydraulic conductivity measurements for the aquifer.

Space‐fractional advection‐dispersion equations with variable parameters: Diverse formulas, numerical solutions, and application to the Macrodispersion Experiment site data

“…[35] The natural-gradient tracer tests conducted from 1986 to 1997 at the Columbus Air Force Base in northeastern Mississippi, commonly known as the MADE site, have addressed continuous interest, probably because of the strong influence of ''high'' subsurface heterogeneity on solute transport Adams and Gelhar, 1992;Boggs and Adams, 1992]. The MADE site has a variance of log conductivity [ln(K)] as high as 4.5 [Rehfeldt et al, 1992], which is much larger than previous natural gradient experiment sites, including the Borden site (0.29 [see MacKay et al, 1986]), the Cape Cod site (0.26 [see Garabedian, 1987;LeBlanc et al, 1991]), and the Twin Lake site (0.031 [see Killey and Moltyaner, 1988]).…”

An adsorption isotherm for bromide

“…They were collected in preparation for numerical experiments on how mildly nonlinear adsorption of a tracer originally assumed to be conservative may affect the results of natural gradient dispersivity tests in aquifers. Detection of anionic tracers over such a wide range is required for many field dispersivity tests [e.g., LeBlanc et al, 1991;Boggs et al, 1992].…”

A Practical Estimation Technique for Spatial Distribution of Groundwater Contaminant

“…Moreover, it is easy to see that, for any positive constant c > 0, 4) and, hence, the estimator Rp preserves any scaling factor. Therefore, if the original data set has a large range of values, then the range can be scaled by multiplying by a fixed positive constant without destroying any correlation structure found within the original data.…”