A case study highlighting SMART® characterization to address residual petroleum hydrocarbon impacts associated with historical UST removal is presented. The site is an active transportation facility with minimal access and is thus incompatible with traditional site characterization techniques. Therefore, numerous depth-discrete soil and groundwater samples were collected in a single mobilization using a hydraulic profiling tool and an onsite laboratory to identify contaminant mass transport zones. The primary contaminant mass transport zone was defined northerly of the former UST area, extending beneath the 29,000 square foot building. The selected remedial strategy is physical removal using air sparge/soil vapor extraction (AS/SVE). Given the access constraints of the facility, horizontal drilling replaced traditional trenching to install conveyance piping which was then tied into the remediation wells. This installation method generated less waste (~80% reduction) and expedited system construction (reducing the construction timeframe by 30 days) with minimal disruptions to the operations. Strategic placement of remediation wells to target the primary contaminant mass transport zone resulted in influent vapor concentrations of 9,700 mg/m3, suggesting that historical “over excavation” of the former USTs left significant contamination in situ. Since initial system operation began in October 2016 (as SVE only) an approximate 16,000 pounds of hydrocarbons have been recovered.

Primary Author / Conference Presenter:
Nicholas Miller
Project Engineer
Novi, Michigan, USA