Field Evidence of Dissolution and Degradation Rates Enhancement During ISCR and ENA Treatments of Chlorinated Solvents

Abstract

This article presents field tests comparing two methods of treatment of chlorinated solvents undertaken at the same site. The site is an automobile factory where two chlorinated solvents (CS) plumes were identified. At the first source, in situ chemical reduction (ISCR) was applied, while at the second one, enhanced natural attenuation (ENA) was used. A set of specific multilevel sampling wells were installed approximately 20 m downgradient of the sources to estimate the efficiency of the treatments. The presence of a low-permeability layer (source 1) or a thick oil lens (source 2) in the top part of the aquifer prevented the CS from reaching the bottom of the aquifer. These layers led to difficulties treating the contamination. At the ISCR and ENA treatment zones, the concentrations of tetrachloroethene (PCE) and trichloroethene (TCE) did not change significantly, while the concentration of metabolites (cis-1,2-DCE, vinyl chloride, and ethene) significantly increased 50 to 150 days after treatment. Due to high concentration of CS in the source zone, a mass balance calculation, including chlorine, was possible. It showed that around 1 to 2 percent of the injected products were used to reduce the CS. A detailed analysis and 1D analytical modeling of CS concentrations showed that the treatment led to a large (two to three times) increase in dissolution of the organic phase. This explains why, despite an efficient treatment, the PCE and TCE concentrations remained virtually unchanged. Degradation rates also increased due to the treatment. Due to some differences in the source-zone chemistry, it was not possible to differentiate between the ISCR and ENA efficiencies. O

Comparison of residual NAPL source removal techniques in 3D metric scale experiments

“…• Liquid (aqueous) phase sampled in all tanks during conditioning part and Tank 1, 2 and 4 during specific treatment technique, was collected in headspace vials (Barnier et al, 2013). The headspace vials were heated at 40°C during 20 min.…”

“…Similarly, Brooks et al (2008) compared remedial efficiency at two sites, showing a 90% reduction flux of TCE at both sites, but a significant increase of DCE flux in presence of biodegradation downgradient the source zone. Barnier et al (2013) compared two pilot treatments (In Situ Chemical Reduction (ISCR) and Enhanced bioremediation (ENA)) on two sources at the same site, showing similar increase in degradation rate (increase by a factor of 1.5 to 2) and dissolution rate (increase by a factor of 2.5 to 3). However, none of these two papers could strictly compare the techniques, as it was not conducted on the same source zones.…”