In Situ Bioremediation of a Former Natural Gas Dehydrator Site Using Bioventing/Biosparging

Abstract

Abstract The Gas Research Institute (GRI) is conducting a research program on site remediation and residuals management for natural gas exploration and production (E&P) activities. Biological processes are considered to be a key component of the GRI remedial strategy since most of the chemicals- of-interest in soils and groundwater at E&P sites have been reported to be biodegradable. A bioventing/biosparging field demonstration was conducted over a ten month period at a former glycol dehydrator site, located near Traverse City, Michigan. The chemicals-of-interest at this site were benzene, toluene, ethylbenzene, and xylenes; and alkanes (primarily C4 through C10). The goal of the project was to determine the feasibility of using this technology for dehydrator site remediation and to develop engineering basis of design concepts for applying bioventing/biosparging at other similar sites. Operation, sampling and analysis, and field monitoring plans were developed. Three different air sparging operational modes (pulsed, continuous, and offgas recycle) were tested to determine the optimum process configuration for site remediation. Introduction of gaseous phase nutrients, nitrous oxide and triethyl phosphate, to stimulate the rates of biodegradation was also evaluated. Operational mode performance was evaluated by conducting in situ respirometry studies. Depletion of oxygen and hydrocarbons and production of carbon dioxide were used to calculated biodegradation rates in the vadose and saturated zones. The mass of hydrocarbons biologically degraded was estimated based on these biokinetic rates. In addition, biodegradation was also estimated based on contaminant removal shown by analytical sampling of soil and groundwater and based on other losses attributed to pump and treat and soil vapor extraction systems. Results of the analytical- and respirometry-based mass balances are compared. In addition, an engineering evaluation of the operating modes is presented. The results of this study suggest that bioventing/ biosparging is a feasible technology for in situ remediation of soil and groundwater at gas industry glycol dehydrator sites and that the pulsed operating mode may have an advantage over the other modes.