Benzene, toluene, ethylbenzene, and xylenes (BTEX) degradation in vadose zone soils during vapor transport: First-order rate constants
- Shell Development Co., Houston, TX (United States)
Many currently available screening-level models for predicting long-term vapor-phase diffusive transport from soils and groundwater to ambient and indoor air neglect degradation mechanisms. In this paper, we summarize ranges of conditions which support aerobic biodegradation of benzene, toluene, ethylbenzene, and xylenes in unsaturated soils, and examine existing experimental information on the range of possible biodegradation rate under these conditions. Mathematical solutions for incorporating degradation mechanisms into vadose-zone vapor transport models an presented for the purpose of consistent definition of degradation rate parameters. Results of previous experiment measurements, and published data on vadose zone BTEX degradation are tabulated as first-order rate parameters and half-life values, with supporting information, including chemical concentration levels, soil characteristic, oxygen levels, and details on the particular experimental scenario. The tabulated first-order rate parameters are presented in a format consistent with the previously mentioned mathematical definitions. Results of this investigation, review, and compilation show that defining a degradation rate based on soil pore water concentration, and presuming that degradation is limited to the pore water phase of the soil matrix, may help explain some observed phenomena, such as reduced degradation for chemicals sorbed to soil, or which are partitioned into a residual hydrocarbon phase. In aerobic soil conditions over broad ranges in soil pore water concentrations, it appears that microbial degradation of BTEX is reasonably described by Monod-type kinetics. At soil pore waters concentrations below approximately 0.2 mg/L, first-order kinetics apply. At and below concentration level, based on available data, a conservative estimate (underpredicting degradation) of a first-order rate constant is 0.4 hr{sup -1}, based on soil pore water concentration.
- OSTI ID:
- 569942
- Report Number(s):
- CONF-971116-; TRN: 98:000778-0027
- Resource Relation:
- Conference: 1997 petroleum hydrocarbons and organic chemicals in ground water: prevention, detection, and remediation conference, Houston, TX (United States), 12-14 Nov 1997; Other Information: PBD: 1997; Related Information: Is Part Of Proceedings of the 1997 petroleum hydrocarbons & organic chemicals in ground water: Prevention, detection, and remediation; PB: 811 p.
- Country of Publication:
- United States
- Language:
- English
Similar Records
Use of aerobic and anaerobic microcosms to assess BTEX biodegradation in aquifers
Natural attenuation of BTEX compounds: Model development and field-scale application