FULL-SCALE REMEDIATION OF A MTBE/BTEX PLUME IN A FINE-GRAINED AQUIFER IN NORTHWESTERN MONTANA USING ELECTRICAL RESISTANCE HEATING TECHNOLOGY

Fine-grained aquifers contaminated with petroleum constituents present a unique and potentially costly challenge to state environmental remediation programs. Conventional remediation technologies may not be appropriate in these settings. Contaminated sites in fine-grained settings typically require more intensive investigation, more thorough preparation of a site conceptual model, and careful consideration of the use of innovative remediation alternatives.

In one example, leaking underground storage tank systems located in Ronan, Montana contaminated soil and groundwater with methyl tertiary butyl ether (MTBE), benzene, toluene, ethylbenzene, xylenes (BTEX), and other petroleum compounds. Complete remediation of the site has been difficult due to the presence of fine-grained glacial lacustrine sediments (sand, silt and clay) present beneath the site, and because of the presence of a widespread residual light non-aqueous phase liquid (LNAPL) plume that extends beneath US Highway 93, a primary north-south traffic corridor in NW Montana.

The site conceptual model for the Ronan site was recently modified to include data obtained from a recent comprehensive investigation using direct push technology. Results of this investigation found that the residual petroleum source mass was much more widespread than originally thought.

Previous results of an innovative pilot remediation approach using electrical resistance heating (ERH) at the Ronan site supported the conclusion that remediation of fine-grained petroleum-contaminated sediments could be greatly accelerated and achieve regulatory cleanup requirements in a shorter timeframe. In 2007 and 2008, a full-scale remediation system using ERH technology, coupled with air sparging and soil vapor extraction (SVE), was implemented at the Ronan site. The remediation system, which consisted of 48 electrodes, 41 air sparge wells, and 32 SVE wells, targeted a treatment volume of approximately 16,000 cubic yards of petroleum-contaminated soil and resulted in the removal of over 3,500 gallons of gasoline over a 12 month operational period. The soil treatment cost averaged approximately $57 per cubic yard. Results indicate that ERH technology can meet regulatory objectives and successfully compete with conventional petroleum cleanup technologies on a unit cost basis.