POTENTIAL IMPACTS ON GROUNDWATER OF PURE-PHASE METHANOL RELEASES

A model study is presented which examines the transport and persistence of methanol in a shallow aquifer. Two scenarios are considered; one involving a release of pure phase methanol into a pristine aquifer, and the other a release of pure-phase methanol into an aquifer containing a gasoline residual and a 5 year old BTEX plume. Processes considered include multi-component dissolution of gasoline, enhanced solubility of BTEX due to co-solvency, inhibition of methanol and BTEX degradation at high methanol concentrations, 3D advective dispersive transport, and electron acceptor limited competitive biodegradation with microbial growth. In the situation where a methanol spill on the ground surface leads to concentrations of methanol at the water table that are at or below the inhibition threshold, the simulations suggest a methanol plume may persist in groundwater for a period of 1 to 2 years. If site conditions and the spill volume result in high concentrations of methanol at the water table, methanol will persist in groundwater until dispersive processes lead to concentrations in the core of the plume that fall below the inhibition threshold. For the site conditions considered here, this initial phase is 5 to 10 years in duration. If methanol escapes containment at a site where an existing gasoline pool or residual is present, the simulations suggest that relatively high concentrations in the core of the benzene plume will extend significantly greater distances beyond the source zone, and the total length of the benzene plume may increase by 30 – 35%.