Solidification of Petroleum-Based Tar Material with Cap Closure

Solidification of petroleum-based tar material with capping was selected as the closure methodology for a former nonhazardous industrial waste landfill in the Eastern United States. While more expensive in the short term, this closure approach met the major long-term goals of the customer (site owner): rapid exit strategy, salability, and reduced long term monitoring. Value engineering changes to the mix design and cap closure, constructability verification through bench-scale studies, and selection of more efficient, less expensive solidification equipment significantly reduced the overall project cost and enhanced the project’s success. Waste at this site consisted of non-hazardous glass and debris, overlying a thick, compressible, petroleum-based refinery tar from a previous owner. This former landfill was subject to solid waste regulations, requiring only a traditional multi-layer clay cap to effect closure. Since migration of the tar was of concern to regulators, an in-situ barrier wall may have been required along the cap perimeter. Capping alone, however, was not the optimal solution to meet the long-term goals of this progressive industrial site owner. Construction of a traditional landfill cap likely would have resulted in an unattractive parcel, suitable for little else than a pasture given the requisite deed