Gerard E. Spinnler

Bioaugmentation for MTBE Remediation

Bioaugmentation to treat methyl tert-butyl ether (MTBE) in groundwater was considered a promising technique for several years, with several researchers involved in developing and testing MTBE-degrading bacteria. Although the effort yielded important insights into the biodegradation of MTBE and its daughter product tert-butyl alcohol (TBA), bioaugmentation for these contaminants is not used currently, and it is likely to remain a minor field of endeavor. The costs and time required to generate enough biomass to seed a barrier system has proven to be prohibitive for most applications, and generally not necessary for effective aerobic treatment. Although MTBE and TBA were originally considered to be highly recalcitrant, indigenous microorganisms have proven capable of effective aerobic treatment, given sufficient oxygen, and it also has proven possible to create stable and robust zones of oxygenation even in relatively complex lithologic systems. Lessons learned in the course of the research on MTBE/TBA bioremediation include: (1) sufficient delineation is critical, (2) sufficient oxygen delivery is a common limitation, (3) biostimulation is typically sufficient, though a time lag may be experienced, (4) bioaugmentation activity can persist for years in situ, (5) typical cocontaminants must be considered, (6) effective treatment typically requires a minimum of 6–12 months, and (7) large numbers of bacteria may be needed for effective treatment.

Application of an In Situ Bioremedy Biobarrier at a Retail Gas Station

Located in western Connecticut, this site has been in use as a gas station since 1950. It is situated in a mixed commercial and residential area and is now operating as a retail gas station and convenience store. The site rests on fairly flat ground with a slight northwest topographic grade toward the Pomperaug River. Bedrock underlies the site approximately 12 meters (40 feet) bgs and drops to more than 60 meters (200 feet) bgs to the northwest. The un-consolidated material above the bedrock is stratified drift consisting of fine to coarse sand with silts, gravels, and cobbles. A dense cobble-rich layer was encountered at approximately 4 meters (14 feet) bgs beneath the site.