Intrinsic bioremediation for hydrocarbon groundwater contamination

Abstract

Intrinsic bioremediation is now being considered as an alternative technology for groundwater remediation because of the high cost and boor berformance associated with the pump and treat systems that have been used over the past several years. In this report, the degradation rate in the groundwater and the cost of intrinsic bioremediation were compared with the remediation rate and the cost of active remediation at a site located near Harvey, NB. Four years were needed to remediate the site when using active remediation. A pump and treat system including an air stripper was used to remediate the groundwater at the site. As part of the intrinsic bioremediation assessment, the flow model Bioscreen (USEPA model) has been used to determine the distance travelled of the plume and the transport time before reaching the sum of BTEX (166 ppb) concentration, specified in the New Brunswick Department Of Environment (NBDOE) Level 1 guidelines. Bioscreen includes two different simulation models dealing with BTEX contaminants. The two reaction models are the first order decay and the instantaneous reaction model. Because many parameters were estimated when performing the analysis, a sensitivity analysis was required. From the sensitivity analysis it was found that the half life is the parameter having the most effect on the first order decay reaction model, and that the dispersivity value and the retardation factor are the parameters that have the most effect on the instantaneous reaction model. When assuming a continuous source of BTEX the distance travelled by the plume was determined to be between 30 m to 60 m and the transport time to be between 20 years and 30 years. The cost of active remediation was obtained from documents supplied by the NBDOE. For intrinsic bioremediation, the cost was determined using the advective travel time of the Level 1 concentration from the source calculated by Bioscreen. For the cost analysis, the source of BTEX was assumed to be removed because a continuous source would give an infinite cost for intrinsic bioremediation. If intrinsic bioremediation had of been used at the site instead of active remediation, it was calculated that savings would have been between 40% and 60% with a maximum range between 16% and 70%.