title: Using a Gas-Phase Tracer Test to Characterize the Impact of Landfill Gas Generation on Advective-Dispersive Transport of VOCs in the Vadose Zone.
abstract: A gas-phase tracer test (GTT) was conducted at a landfill in Tucson, AZ, to help elucidate the impact of landfill gas generation on the transport and fate of chlorinated aliphatic volatile organic contaminants (VOCs). Sulfur hexafluoride (SF6) was used as the non-reactive gas tracer. Gas samples were collected from a multiport monitoring well located 15.2 m from the injection well, and analyzed for SF6, CH4, CO2, and VOCs. The travel times determined for SF6from the tracer test are approximately two to ten times smaller than estimated travel times that incorporate transport by only gas-phase diffusion. In addition, significant concentrations of CH4and CO2were measured, indicating production of landfill gas. Based on these results, it is hypothesized that the enhanced rates of transport observed for SF6are caused by advective transport associated with landfill gas generation. The rates of transport varied vertically, which is attributed to multiple factors including spatial variability of water content, refuse mass, refuse permeability, and gas generation.
authors.affiliation: Soil, Water and Environmental Science Department, School of Earth and Environmental Sciences, University of Arizona, 429 Shantz Bldg., Tucson, AZ 85721.
authors.forename: Gregg R
authors.initials: GR
authors.lastname: Monger
authors.affiliation: Soil, Water and Environmental Science Department, School of Earth and Environmental Sciences, University of Arizona, 429 Shantz Bldg., Tucson, AZ 85721.
authors.forename: Candice Morrison
authors.initials: CM
authors.lastname: Duncan
authors.affiliation: Soil, Water and Environmental Science Department, School of Earth and Environmental Sciences, University of Arizona, 429 Shantz Bldg., Tucson, AZ 85721 ; Hydrology and Water Resources Department, School of Earth and Environmental Sciences, University of Arizona, 429 Shantz Bldg., Tucson, AZ 85721.
authors.forename: Mark L
authors.initials: ML
authors.lastname: Brusseau
keywords: VOCs; gas tracer test; gas-phase transport; landfill gas generation