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Modeling natural attenuation of petroleum hydrocarbons (btex) in heterogeneous aquifers

Uçankuş, Tuğba
Natural Attenuation can be an effective cleanup option for remediation of Groundwater contamination by BTEX. One of the important aspects of the methodology that has been recognized recently is that mass removal rates, the most important parameters used to determine effectiveness of the methodology, is controlled by groundwater flow regime, which to a large extent controlled by aquifer heterogeneity. Considering this recognition, the primary objective of this research is to quantitatively describe the relationship between natural attenuation rates of BTEX and aquifer heterogeneity using numerical solution techniques. To represent different levels of aquifer heterogeneity, hydraulic conductivity distributions are simulated using Turning Bands Algorithm, changing statistical parameters Coefficient of Variation (CV) and correlation length (h). Visual MODFLOW is used to model the transport of BTEX contamination, at different hydraulic conductivity fields. Degradation rates are calculated by Buscheck&Alcantar and Conservative Tracer Methods. The results show that, for a given h, as CV increases, the plume slows down and stays longer at the domain, so areal extent of plume decreases. For anisotropic field, plumes are more dispersed along x and y-direction, and areal extents of the plumes are greater. During MNA feasibility studies, for the aquifer heterogeneity level of CV and h smaller than 100 % and 10 m, respectively, a minimum recommended biodegradation rate constant of 0.02 d-1 can be used, whereas for the aquifer heterogeneity level of CV and h greater than 100 % and 10 m, respectively, using a minimum biodegradation rate constant of 0.06 d-1 can be recommended.