Selection of a remediation scenario for a diesel-contaminated site using LCA

Goal and Scope. A comparison of in situ and ex situ treatment scenarios for a diesel-contaminated site was performed using an evolutive LCA. Treatment time along with primary (residual contamination left in soil or groundwater after treatment) and secondary (impacts due to remediation) environmental impacts were considered. The site under study had a Light Non Aqueous Phase Liquid (LNAPL) thickness of up to 1 m, a diesel soil concentration of 10,500 mg/kg and a residual contamination in groundwater. Methods. Four treatment scenarios to remove LNAPL and to treat soil and groundwater were compared: 1) pump and treat 2) bioslurping, bioventing and biosparging 3) bioslurping, bioventing and chemical oxidation and 4) ex situ treatment using biopiles. The technologies(1) design was performed using simulation tools and analytical equations. The LCA was evaluated for each year of treatment. Environmental impacts were assessed using the U.S. EPA Tool for the Reduction and Assessment of Chemical and Other Environmental Impacts (TRACI) method. Results and Discussion. The biological in situ scenario (2) showed the least primary and secondary impacts but its treatment time was more than 4 times longer than that obtained for the ex situ scenario (4). The ex situ scenario showed the best treatment time but its secondary impacts were significantly higher than those found for the biological in situ scenario due to the pavement of the treatment area. The combined biological and chemical in situ scenario (3) was the worst in terms of secondary impacts while the pump and treat scenario (1) was the worst in terms of primary impacts. Two scenarios were selected: one based upon low environmental impacts and the other on the fastest treatment time. Conclusions. Even without excavation, an in situ treatment can generate more secondary impacts than an ex situ treatment. Low environmental impact scenarios require time while rapid treatment scenarios generate high environmental impacts. The selection of the best remediation scenario will depend on the site owner's priority. Recommendations. Better characterization factors for aggregated substances are required.