Abstract: Enhanced In-situ Aerobic Biodegradation of Soluble Hydrocarbons in a Sandy Aquifer or CoBioReM

Steve Rouse, Tracy Boyd, Chen Chiang, Joe Salanitro

An aerobic bioremediation field-scale project was developed as part of Cooperative Bioremediation Research for Michigan (CoBioReM). The research objective was to develop a socially and politically acceptable method to achieve remediation of groundwater contaminated by hydrocarbon leaks and spills. The objective was achieved: total benzene, toluene, ethylbenzene, and xylene (BTEX) mass were reduced by more than 90% in less than a year, from 0.96 lb (7/31/91) to 0.08 lb (6/23/92). A slight modification in treatment technique further reduced contaminant levels to 0.03 lb (6/17/93). The purpose of this paper is to concisely describe the major findings of the research. More detailed analysis and description of each specific element may be referenced in the CoBioReM Conference Proceedings ( 993) and in future publications.

The most critical design parameter of an aerobic system is efficient delivery of dissolved oxygen (DO) to the contaminant. In this case, gaseous oxygen was dissolved into the pressurized groundwater purge system to a concentration of 20 ppm. Elevated DO concentrations, equal to that injected, were measured 400 ft downgradient within 10 months. The effectiveness of an aerobic bioremediation system depends primarily upon the amount of mixing between soluble organics and dissolved oxygen. To quantify these parameters, a nonreactive tracer, bromide, was injected into the aquifer and monitored as it passed through the study area. Its transport behavior, which was consistent with DO plume behavior, demonstrated that groundwater seepage velocity appears to decrease slightly as the capillary ringe is approached (i.e., 1.8 ft/day ten ft into the aquifer, and 1.5 ft/day at the capillary fringe). Thus, DO delivery to the saturated/unsaturated interface was impeded slightly in the very region of greatest demand. A first-order decay rate was exhibited by the mass degradation curve and is estimated to be 0.6%/day.

AAPG Search and Discovery Article #90984©1994 AAPG Annual Convention, East Lansing, Michigan, September 18-20, 1994