Bench-scale analysis of diesel-PCE mixture behavior for the Park-Euclid WQARF Site

Abstract

The Park-Euclid WQARF (Water Quality Assurance Revolving Fund) Site is contaminated with a complex light non-aqueous phase liquid (LNAPL) mixture of tetrachloroethene (PCE), its degradation products and diesel (PCE-diesel). Because complex mixtures like PCE-diesel are composed of many compounds, accurately predicting their physiochemical behavior is often very difficult. This project was initiated to examine the mass-transfer behavior of the Park-Euclid complex mixture. Two 2-dimensional bench-scale soil vapor extraction (SVE) systems were designed and constructed. One was packed with Accusand and residual amounts of PCE-diesel and water (FC-1). The other flow cell contained only PCE-diesel and water with no media (FC-2). A 1-month long study was conducted to gain information about the evaporation behavior of the PCE-diesel mixture and the potential for a more mobile phase to form during simulated SVE. Samples of gas, water and PCE-diesel were taken before the experiments began and, in FC-2, at one week intervals during the experiment. For both flow cells, gas samples of the effluent air were taken at regular intervals during the experiments. Over the course of the experiments an estimated 20.8 percent of the original PCE was removed from FC-1 and an estimated 41.6 percent of the original PCE was removed from FC-2. For FC-2, more than half of the mass of the organics removed were determined to be hydrocarbons in the C9-C16 range which, in the field, would greatly reduce the efficiency of an activated carbon treatment system. No noticeable change in density or other physiochemical behaviors were observed for the immiscible liquid. These bench-scale experiments serve to demonstrate a scenario where all rate limitations are minimized. Real field conditions are much more complicated and removal rates would undoubtedly be much slower but the relative behavior observed in these bench-scale experiments should still apply.