Impacts of Site Demolition and Tank Removal: A Case Study

摘要

Site demolition and tank removal are common aspects of many site closures. These practices may result in the alteration of the surface cover and emplacement of fill material that is more permeable than the natural soils. As a result, recharge to the aquifer is increased locally, which may change the character of the underlying aquifer and significantly alter flow and transport of contaminants. The impacts of site demolition and tank removal were evaluated at a former petroleum retail site that had been impacted by separate phase gasoline. The site, which is located in an area characterized by seasonal precipitation, was monitored prior to and post site demolition. The demolition involved the removal of facility features and the asphalt surface cover as well as excavation of underground storage tanks and product lines with subsequent backfilling. The alteration in conditions promoted the development of a groundwater mound in the former tank field with radial groundwater flow in the vicinity of the site and increased fluctuations of the groundwater table. These conditions resulted in the trapping of free product and the development of a large hydrocarbon smear zone. Reductions in free product thicknesses in wells were observed during subsequent monitoring events. Hence, the site demolition activities changed the form of the contamination from a condition of mobile separate phase gasoline to residual product undergoing dissolution. As a result, remedial activities needed to address residual phase contamination instead of free product removal.