Experimental investigations of unconfined aquifer pollution from recharge basins

Abstract

Experiments in a sand-filled flume simulate contaminant movement in an unconfined aquifer from a long strip recharge basin. Sodium chloride is used as a tracer with its distribution being monitored via electrical conductivity measurements controlled and stored through a minicomputer. The effects of initial saturated depth and magnitude of the recharge rate on the pattern of contaminant movement are discussed. Comparisons with results from numerical models are provided for the speed of movement of the contaminant front and the thickness of the mixing zone as well as for the rise in the free surface level. INTRODUCTIONGroundwater pollution is usually less apparent than surface water pollution and is also more difficult and more costly to reverse. Unconfined aquifers are particularly susceptible to pollution from surface sources when little or no cleansing is afforded by overlying strata as the polluted water infiltrates down to the aquifer. The pollutant moves through the aquifer by convection and dispersion, and a knowledge of hydrodynamic dispersion in groundwater flow is required for accurate prediction of the extent of pollution at any specified time.Some early experimental investigations were concerned with fundamental characteristics of dispersion coefficients as exemplified by the papers of Ruiner [1962], Harleman and Rumer [1963], Banks and Ali [1964], and Hoopes and Harleman [1967]. Experimental studies were also extended to other conditions such as unsteady flow [Banks and Jerasate, 1962; Rumer, 1962] and two-dimensional dispersion [Bruch and Street, 1966]. Well flow situations have been dealt with by Hoopes and Harleman [1967], Kumar and Kimbler [1970], and Gelhar et al. [1972].The present investigation covers laboratory work on dispersion in groundwater domains with a moving free surface, a case which, in spite of its common occurrence, has received little attention.The study is confined to recharge of an idealized unconfined aquifer through an infinitely long spreading basin. The hydraulic conductivity, porosity, and average grain diameter are constant throughout the flow domain. The recharge water or the invading fluid is assumed to be nonreactive and of identical temperature, viscosity, and density to the host fluid. The two-dimensional flow in the aquifer is represented experimentally with a narrow sand-filled box.The experimental results are compared with theoretical predictions from numerical models developed for this problem. The experimental procedure and results are presented

Analytical solutions of one-dimensional advection-diffusion equation with variable coefficients in a finite domain

“…It was done either by introducing moving co-ordinates (Ogata and Banks 1961;Harleman and Rumer 1963;Bear 1972;Guvanasen and Volker 1983;Aral and Liao 1996;Marshal et al 1996) or by introducing another dependent variable (Banks and Ali 1964;Ogata 1970;Lai and Jurinak 1971;Marino 1974 andAl-Niami andRushton 1977). Then Laplace transformation technique has been used to get desired solutions.…”

A pore size distribution-based chloride transport model in concrete

“…The analytical solution of Equation 6 for a 1D, one-side exposure migration problem can be obtained by introducing moving coordinates (Guvanasen and Volker, 1983;Harleman and Rumer, 1963;Marshal et al, 1996) …”

Analytical Solution to the One-Dimensional Advection-Diffusion Equation with Temporally Dependent Coefficients

“…For example the analytical solution of the advectiondiffusion equation with constant coefficients in an initially solute free semi-infinite domain for a continuous uniform input point source 0 at the origin has been reported by Ogata and Banks [1], Harleman and Rumer [2], Guvanasen and Volker [3], Marshall et al [4], by using the transformations in Equation (2), as…”