Radial Groundwater Flow at Landfills in Karst

摘要

Broad investigations into the extent of landfill groundwater impacts are often discouraged by adjacent property owner concerns. As a result, inferred groundwater potentiometric surfaces, flow directions, and monitoring well networks are often confined to the landfill property. In many circumstances, particularly in karst settings, this confined, myopic view can result in gross misinterpretations of groundwater flow directions and contaminant transport. Monitoring techniques utilizing existing offsite spring and well networks enable a better understanding of the distribution and migration of landfill groundwater impacts. Characterizing the extent of offsite impact in karst often reveals that the flow paths surrounding landfill sites situated in karst settings are radial rather than linear. Several case studies at closed landfill sites situated in karst areas of the Valley and Ridge geologic province of Tennessee are presented to illustrate the potential for complex conduit radial flow and offsite impacts. At each case study site, initial interpretations of groundwater flow were linear, and monitoring well networks were installed, sampled, and analyzed accordingly. Just one problem, the upgradient well(s) were impacted! Why? Radial Flow. By stepping back, and understanding groundwater flow from a more regional perspective, it was apparent that the supposed upgradient wells were actually downgradient due to radial flow patterns at these sites. Although newer Subtitle D landfills are considered dry tombs, many older landfills are inadequately lined and capped, leading to significant groundwater and surface water intrusion. This often creates mounding of groundwater within the disposal area. Radial flow patterns can evolve when groundwater elevations overcome former groundwater divides and create new flow patterns.