Remediation of BTEX contaminated groundwater: best technology assessment between pump&treat and bioremediation by oxygen injection

The presence of benzene, toluene, ethylbenzene and xylene (BTEX) dissolved in the groundwater and migrated from a light non-aqueous phase liquid (LNAPL) source in an alluvial aquifer required a remedial action to be taken by the responsible party as established by the Italian regulation (Legislative Decree 152/06 and subsequent amendments). For such purpose, field investigations were conducted on site in order to define the site conceptual model and to identify the appropriate remediation technology to be applied. The remediation design was developed by means of a flow and reactive transport mathematical model, applied to saturated media, using the numerical codes MODFLOW and RT3D. Groundwater field observations showed evidence of occurring BTEX biodegradation processes by bacteria naturally present in the aquifer. Since such specific bacterial activity would be significantly enhanced by the injection of free oxygen in the aquifer, the performance of traditional pump and treat systems (P&T) was assessed and compared with cost/efficiency of reactive oxygen bio-barrier technology (OD). The results showed a clear advantage in terms of cost/efficiency with the application of the OD. This presents an overall cost of about 30% of the P&T installation and maintenance, and it reaches remedial target in a shorter timeframe. Moreover, the system is also applicable as a bioremediation technology in case of Environmental Emergency Measures (MISE). The site examined is part of an industrial plant located in Central Italy.