Development and application of an analytical model to aid design and implementation of in situ remediation technologies

Innovative in situ remediation technologies using injection/extraction well pairs which recirculate partially treated groundwater as a method of incre asing overall treatment efficiency have recently been demonstrated, An impo rtant parameter in determining overall treatment efficiency is the fraction of flow that recycles between injection and extraction points. Numerical a nd semi-analytical methods are currently available to determine this parame ter and an analytical solution has been presented for a single injection/ex traction well pair. In this work, the analytical solution for fraction of r ecycled flow for a single injection/extraction well pair is extended to mul tiple co-linear well pairs. In addition, a semi-analytical method is presen ted which permits direct calculation of fraction recycle for a system of ar bitrarily placed injection/extraction wells pumping at different rates. The solution is used to investigate the behavior of multiple well pairs, looki ng at how well placement and pumping rates impact capture zone width and fr action recirculation (and, therefore, overall treatment efficiency). Result s of the two-well solution are compared with data obtained at a recent fiel d-scale demonstration of in situ aerobic cometabolic bioremediation, where a pair of dual-screened injection/extraction wells was evaluated. A numeric al model is then used to evaluate the impact of hydraulic conductivity anis otropy on the overall treatment efficiency of the dual-screened injection/e xtraction well pair. The method presented here provides a fast and accurate technique for determining the efficacy of injection/extraction systems, an d represents a tool that can be useful when designing such in situ treatmen t systems. (C) 1999 Published by Elsevier Science B.V. All rights reserved.