Mass transport in groundwater near hanging-wall interceptors.

This study investigated mass transport near trenches designed to capture contaminated groundwater. Numerical models simulated migration of contaminant plumes toward trenches oriented perpendicular to regional groundwater flow, partially penetrating a hypothetical unconfined aquifer. Plumes originated at the top of the simulated groundwater flow system. The smallest trench necessary to capture a contaminant plume was identified for various sets of mass transport parameters. Results suggest that, in predominantly horizontal flow systems such as those simulated here: (i) vertical hydraulic conductivity has relatively little effect on downward propagation of contaminant plumes and required trench size, (ii) transverse vertical dispersivity exerts significant control on plume and trench depth, and (iii) recharge dilutes and thus reduces plume and trench width, but may induce downward vertical hydraulic gradients that deepen plumes and trenches. For all cases considered, trenches oriented perpendicular to regional groundwater flow, placed close to the leading edge of a contaminant plume, and sized slightly larger than the plume (in transverse cross-section) facilitate plume capture.