The Gas Research Institute (GRI) is conducting a comprehensive research program in Natural Gas Industry Exploration and Production (E & P) Site Remediation and Residuals Management to assist the industry in achieving cost effective compliance with evolving environmental protection regulations. Biological processes are considered to be a key component of the remedial strategy since most of the chemicals of interest in soils and groundwater at E & P sites have been reported to be biodegradable. Bioventing/biosparging is an in situ biological process which may have significant potential for remediating subsurface contamination caused by compounds such as benzene and natural gas liquid alkanes. Bioventing/biosparging is defined as the engineered movement of air through the subsurface to effect the removal of volatile and semi-volatile organics by both physical transport and microbially mediated mineralization.
This paper describes a bioventing/biosparging field demonstration which has been conducted over a ten month period at a former glycol dehydrator site, located near Traverse City, Michigan. The goal of the demonstration was to determine the feasibility of using this technology to remediate dehydrator sites and to develop engineering guidelines for other such sites.
The project was conducted at a former stand-alone glycol dehydrator site. Dehydrator reboiler condensate handling practice common at the time resulted in contamination of the saturated zone of the subsurface. The constituents-of-interest at the site are aromatic hydrocarbons such as benzene, toluene, ethylbenzene, and xylene (BTEX); and alkanes (C1 thought C10), particularly the compounds C4 through C10 (Butane through Decane). Sampling has indicated that the unsaturated zone is relatively free of the constituents-of-interest, with the primary impacted locations being the capillary fringe and saturated zones. A pump and treat system has been used since 1991 to reduce the size of the groundwater plume. The bioventing/biosparging system was installed to treat the impacted soils and groundwater in the source area. Five air sparging wells were screened in the saturated zone for air and nutrient injection. An additional well was screened in the capillary fringe for soil gas sampling and for soil vapor extraction, if needed to control subsurface air flow. A shallow soil vapor extraction well was used to collect the injected air as a means of measuring offgas constituent discharge.
This paper describes the results of the remediation in terms of soil permeability; air flow patterns, and sparge and vapor extraction well radius of influences; constituent stripping rates; and, constituent biodegradation rates. The experimental results are discussed in the context of a mass balance engineering model of the subsurface which can be used to guide the design of future bioventing/biosparging dehydrator site remediation projects.
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