An investigation of monitorability issues for groundwater in the Zachs Knob syncline area, Northeast Tennessee, USA

Abstract

A dye trace was conducted in 2007 to verify a site conceptual model for groundwater monitorability near an orphan landfill in Sullivan County, Tennessee. The old landfill is in the Valley and Ridge physiographic province. Multiple tracing efforts in this area dating back to 1980 were either unsuccessful or yielded ambiguous results, causing the site to be deemed un-monitorable. Available geologic information, water chemistry data, and subsurface investigation results were compiled to produce a site conceptual model for about 120 ha of land, including the old landfill area. Eosine dye was used as a mimic for potential contamination effects in order to document the monitorability of the local aquifer as part of a hydrogeologic report for a new disposal facility permit. The site exhibits characteristics of a youthful karst setting at the surface. Overflow conduits left behind from a geologically older hydrologic system were found after detailed investigation. These remnant karst features were adjusted to a higher baseflow regime and act as a constraint to the maximum water table elevations in the present hydrologic system. Eosine dye was chosen as the best surrogate leachate after background water and bench scale leachate/dye interaction tests were done. The eosine injection was conducted in a variety of ways across the site to mimic potential leachate release scenarios from the proposed liner system for a new solid waste disposal facility. Eosine was visually detected in local springs and positively detected in some domestic supply and monitoring wells. Subsurface drainage patterns indicated two main groundwater basins in the area of study. Follow-up dye traces with simultaneous injections of pyranine and sulforhodamine B were conducted in 2009 to comply with the request of State regulators. The inferred drainage patterns were confirmed with dye detections at proposed monitoring points for each of the two main groundwater basins.