Numerical Simulation of a Natural Attenuation Experiment with a Petroleum Hydrocarbon NAPL Source

Abstract

A three-dimensional solute transport model with biological reactions is presented for simulating the natural attenuation study (NATS) at the Columbus Air Force Base in eastern Mississippi. NATS consisted of the release of a petroleum-based nonaqueous phase liquid (NAPL) and subsequent monitoring of BTEX (benzene, toluene, ethylbenzene, p-xylene), naphthalene, decane, and bromide in a shallow, unconfined aquifer. Conceptual and mathematical models were developed for NAPL source release, sequential aerobic/anaerobic biodegradation, and sorption during NATS. A multiple species, solute transport code (SEAM3D) was used to simulate fully three-dimensional transport and aerobic, nitrate-reducing, ferrogenic, and methanogenic hydrocarbon biodegradation. Simulation results matched individual BTEX concentration distributions collected five- and nine-months following NAPL release. SEAM3D mass-balance calculations at t = nine months indicated that 49% of the hydrocarbon mass that dissolved into the aqueous phase was consumed by biodegradation, 13% of this mass was sorbed, and the remaining 38% was present in the aqueous phase. Mass calculations at t = nine months further indicated that aerobic biodegradation accounted for the majority of hydrocarbon biodegradation (46% of the biodegraded mass), followed by ferrogenesis (28%), nitrate-reduction (21%), and methanogenesis (5%). Model results were particularly sensitive to the NAPL release rate, the initial ferric iron (Fe[III]) concentration, hydrocarbon utilization rates, initial condition for the anaerobic microbial populations, and dispersivity.

Influence of Petroleum Deposit Geometry on Local Gradient of Electron Acceptors and Microbial Catabolic Potential

“…Such sequential depletion of TEA has been well documented in case of NAPL contaminant plumes in groundwater [29,72,73]. In fact, redox gradient has been shown to develop even on a pore scale, when Jakobsen 2007, indicated that separation of redox processes within a single average pore space is possible [65].…”

Statistical estimation of the relative efficiency of natural attenuation mechanisms in contaminated aquifers

“…Examples can be found in Leij et al, (2000) and Domenico and Robbins (1985). Such modelling could be used as part of a model for bio-degradation as has been implemented in software like BIOSCREEN (United States Environmental Protection Agency, 1996), BIOPLUME (United States Environmental Protection Agency, 1998) and SEAM3D (Brauner and Widdowson, 2001) . There are three problems related to this approach.…”

“…Conventional methods of evaluating biodegradation in ground water comprise either static microcosm or flow-through column studies in the laboratory (Althoff et al, 2001), field-based estimates with reactive well tests (Istok et al, 1997;Istok et al, 2001;Haggerty et al, 1998), or field data analysis especially via numerical modelling (Brauner and Widdowson, 2001;Thornton et al, 2001;Huling et al, 2002;Prommer et al, 2002., Bockelmann et al, 2003.…”

Scenario-based modelling of mass transfer mechanisms at a petroleum contaminated field site-numerical implications

“…Considering the overall effect of mass transfer processes within the domain, the transient transport equation for the dissolving component under uniform flow conditions is given by (Schaerlaekens et al, 2000;Brauner and Widdowson 2001…”