Optimization of Contaminant Mass Removal and Remedial Timeframe with Hydraulic Containment

Remediation of multi-species contaminant plumes within a complex heterogeneous aquifer system poses significant challenges. In cases, where site-specific conditions require a pump-and-treat remedial strategy, the primary focus lies with hydraulic containment of contaminant plumes to prevent downgradient migration. In addition, the remedial strategy also involves proper placement of recovery wells for removal of contaminant mass within the plume footprint. However, there exists some balance between effective removal of contaminant mass and reduction in remedial timeframe. In our present study, we investigated the optimization of a pump-and-treat remedial system to achieve that balance, and thus to reduce the remedial cost through increased operational efficiency.       

Our approach evolved from placement of minimum number of recovery wells at strategic locations given various site-specific constraints to ensure complete hydraulic containment of contaminant plumes within various hydrogeologic units. A few recovery wells were then added within the plume footprint until hydraulic interference between wells was observed to determine the maximum possible extraction rate. This process yielded the optimum number of recovery wells for efficient recovery of contaminated groundwater. Afterwards, the recovery well system was optimized through time-varying extraction rate adjustments to minimize the remedial timeframe. During this process, recovery wells, where contaminants achieved regulatory levels, were progressively inactivated with time, and the remaining recovery wells continued to operate with an incremental rate increase as allowed by the site-specific hydrogeologic conditions to maximize mass removal.

Results from the optimized system were then compared to a conventional case, where all recovery wells continued operating until effective removal of contaminant mass was achieved. Analysis of the results indicated more rapid pace of contaminant mass removal associated with the optimized system. Furthermore, the optimization strategy resulted in a significant reduction of initial total extraction rate after only a few decades of operation while also minimizing the overall remediation timeframe.