| Popis: |
Computer simulations tested the capability of an extraction and injection well pumping at low volumetric rates to detect contaminated groundwater in an unconfined aquifer beneath a hypothetical landfill. The wells occupied a line oriented perpendicular to groundwater flow and located downgradient of the landfill. They pumped at equal rates, but in opposite directions (extraction or injection). Through an iterative process, a mass transport model identified the lowest pumping rates and corresponding well locations necessary to detect plumes of contaminated groundwater originating from leaks within the footprint of the landfill. A plume was considered detected if it passed through the extraction well prior to reaching a downgradient buffer zone boundary. The most efficient well pair discharged +/- 1.7 m3/d and occupied a line located 12 m downgradient of the landfill, or 24 percent of the distance from the landfill's downgradient corner to the buffer zone boundary. The extraction well was near the most downgradient edge of the landfill, and the injection well was outside the cross gradient corner of the landfill farthest from the extraction well. In contrast, six collinear conventional (non-pumping) wells were necessary to detect contaminant plumes emerging from the landfill. Results of this study suggest that low-discharge extraction and injection wells may be an effective contaminant detection strategy at some waste storage facilities. |
