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 SF6 from 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 CH4 and CO2 were measured, indicating production of landfill gas. Based on these results, it is hypothesized that the enhanced rates of transport observed for SF6 are 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.

Unsaturated Zone CO2, CH4, and δ13C‐CO2 at an Arid Region Low‐Level Radioactive Waste Disposal Site

“…Characterizing this transport through the unsaturated zone can be complicated by anisotropic flow and preferential flow paths—limited information and few studies exist for unconsolidated sediments in deep unsaturated zones (Green et al, 2015). Therefore, recent unsaturated zone studies in arid environments have focused on investigating and refining transport models (Green et al, 2015; Monger et al, 2014; Walvoord et al, 2014). Information from gas isotopes and environmental tracers offer important guidance for these refinements.…”