NATURAL ATTENUATION OF MTBE IN A DUAL POROSITY AQUIFER

摘要

The natural attenuation of MTBE, TAME and other petroleum hydrocarbons in the UK Chalk aquifer, a fractured dual-porosity formation, is described. Approximately 55,000 L of MTBE and TAME-amended petroleum fuel was accidentally released from underground storage tanks at a retail filling station in early 1999. LNAPL has migrated from the site transverse to the hydraulic gradient and to a depth of 18 m below the water table along the dominant fracture sets. The migration of dissolved contaminants is also controlled by bedding plane fracture dip. Vertical profiles through the aquifer show that contaminant distribution and flux are strongly controlled by fracture transmissivity and recharge events. Groundwater quality data show that MTBE and TAME have migrated further from the site than BTEX. The BTEX compounds are degraded using O_2, NO_3, MnO_2, Fe(OH)_3 and SO_4 in the aquifer, whereas the presence of TBA in the groundwater suggests that MTBE is degrading aerobically, downgradient of the BTEX compounds. Mass balances indicate that natural attenuation is effective in reducing the flux of contaminants from this site, by a combination of dilution, sorption, degradation and matrix diffusion.