Effect of uncertain hydraulic conductivity on the fate and transport of BTEX compounds at a field site

Journal Article · Sat Jan 05 04:00:00 EST 2002 · Journal of Environmental Engineering-ASCE

OSTI ID:861284

Lu, Guoping; Zheng, Chunmiao; Wolfsberg, Andrew

A Monte Carlo analysis was conducted to investigate the effect of uncertain hydraulic conductivity on the fate and transport of BTEX compounds (benzene, toluene, ethyl benzene, and xylene) at a field site on Hill Air Force Base, Utah. Microbially mediated BTEX degradation has occurred at the site through multiple terminal electron-accepting processes, including aerobic respiration, denitrification, Fe(III) reduction, sulfate reduction, and methanogenesis degradation. Multiple realizations of the hydraulic conductivity field were generated and substituted into a multispecies reactive transport model developed and calibrated for the Hill AFB site in a previous study. Simulation results show that the calculated total BTEX masses (released from a constant-concentration source) that remain in the aquifer at the end of the simulation period statistically follow a lognormal distribution. In the first analysis (base case), the calculated total BTEX mass varies from a minimum of 12% less and a maximum of 60% more than that of the previously calibrated model. This suggests that the uncertainty in hydraulic conductivity can lead to significant uncertainties in modeling the fate and transport of BTEX. Geometric analyses of calculated plume configurations show that a higher BTEX mass is associated with wider lateral spreading, while a lower mass is associated with longer longitudinal extension. More BTEX mass in the aquifer causes either a large depletion of dissolved oxygen (DO) and NO{sub 3}{sup -}, or a large depletion of DO and a large production of Fe{sup 2+}, with moderately depleted NO{sub 3}{sup -}. In an additional analysis, the effect of varying degrees of aquifer heterogeneity and associated uncertainty is examined by considering hydraulic conductivity with different variances and correlation lengths. An increase in variance leads to a higher average BTEX mass in the aquifer, while an increase in correlation length results in a lower average. This observation is explained by relevant partitioning of BTEX into the aquifer from the LNAPL source. Although these findings may only be applicable to the field conditions considered in this study, the methodology used and insights gained are of general interest and relevance to other fuel-hydrocarbon natural-attenuation sites.

• Research Organization: Ernest Orlando Lawrence Berkeley National Laboratory, Berkeley, CA (US)
• Sponsoring Organization: USDOE Director, Office of Science
• DOE Contract Number: AC02-05CH11231
• OSTI ID: 861284
• Report Number(s): LBNL--50464; BnR: 820101000
• Journal Information: Journal of Environmental Engineering-ASCE, Journal Name: Journal of Environmental Engineering-ASCE Journal Issue: 5 Vol. 131
• Country of Publication: United States
• Language: English

Related Subjects

54 ENVIRONMENTAL SCIENCES
58 GEOSCIENCES
AQUIFERS
BENZENE
DENITRIFICATION
DISSOLVED GASES
DISTRIBUTION
HYDRAULIC CONDUCTIVITY
OXYGEN
PLUMES
PRODUCTION
RESPIRATION
SIMULATION
SULFATES
TOLUENE
TRANSPORT