Date of Award
Doctor of Philosophy
Daniel D Larsen
Farhad F Jazaei
Scott S Schoefernacker
Brian B Caldwell
A confined to semi-confined water-supply aquifer beneath Memphis, the Memphis aquifer is protected in most areas by an upper natural hydraulic barrier referred to as the upper Claiborne confining unit (UCCU), which acts as an aquitard and is mainly comprised of clay and silt. Studies of the UCCU have revealed breaches, which allow cross-contamination or inter-aquifer exchange of water between the unconfined (shallow) and the underlying Memphis aquifers. This study examines the possibility of filling the voids within a preferential pathway in the UCCU via sand-bentonite mixture to reduce the inter-aquifer exchange between the shallow and Memphis aquifers. The research examined the development of a sand-bentonite mixture whereby the voids of the coarse particles of the sand are filled out by adding certain percentages of small-sized particles of bentonite to arrive at a maximum or optimal mixing ratio. Two types of parent media were used in the laboratory experiments: fine, medium, and coarse glass beads; and sand extracted from a core through a known breach in the UCCU. Hydraulic conductivity was measured in 76 samples prepared with a range of bentonite from 0%, 10%, 20%, 25%, and 30%, and the flow conditions were modeled in an idealized conceptual model using MODFLOW to assess the reduction of the flux resulting from the experimentally determined ideal sand-bentonite mixtures. The experimental results show that the hydraulic conductivity is reduced by two orders of magnitude in the coarse glass beads, four orders of magnitude in the medium glass beads, and achieves the same order of magnitude of a UCCU-type clay conductivity at 6% bentonite for the fine glass beads and the sand, reaching a 2-order of magnitude further decrease at 10% bentonite (4.22 x 10-6 m/day). Modeling showed that the vertical flux (q) reached at 6% bentonite approximated the flux through the UCCU clay. As bentonite percentages increased toward 10%, the flux reduced to 0.06 m/day, plateauing thereafter over differing injection thicknesses (0.5-5 m).
Dissertation or thesis originally submitted to ProQuest
Jimenez, Angel, "Reduction of Inter-aquifer Water Exchange by Sand-Bentonite mixture" (2023). Electronic Theses and Dissertations. 3054.