Viability of interceptor trenches for monitoring groundwater quality near landfills

Computer models were used to quantify the detection capability of four alternative groundwater monitoring systems in a shallow aquifer near a 50-m by 75-m landfill oriented oblique to groundwater flow. The monitoring systems included a network of five wells, and 1-m, 3-m, and 5-m wide gravel interceptor trenches. Each trench was 42-m long. Wells and trenches were positioned on a monitoring locus located 15-m, in the direction parallel to groundwater flow, from the landfill's downgradient boundary. There was an equal spacing, in the direction perpendicular to groundwater flow, between monitoring wells, and the trenches were positioned near the middle of the monitoring transect. The five-well network detected 81% of contaminant plumes originating within the landfill's footprint before they reached a buffer zone boundary located 50-m from the landfill's downgradient corner. By comparison, the 1-m, 3-m, and 5-m wide trenches detected 77, 84, and 88% of the contaminant plumes, respectively. Convergent flow induced by wider trenches yielded slightly higher detection efficiencies. Although the well and trench monitoring systems registered similar detection capability, estimated costs for installing the trench systems were more than 10 times those of constructing the wells. Overall, results of this study suggest that, even for shallow aquifers, gravel interceptor trenches are not a cost effective method for detecting leaks from landfills.