designed. This points to a need to consider uncertainty in, and verification of, source zone extent when designing thermal remediation systems. It also suggests that decision makers and designers should weigh the incremental costs of additional source zone characterization data versus the costs of a larger system footprint and costs of failure of achieving remedial goals. Triplett Kingston et al. (2010a,b) found that sampling dissolved groundwater concentration transects perpendicular to groundwater flow and immediately downgradient of a source zone was a valuable approach for verifying source zone width.
In summary, the data in Table 4-3 are indicative of state-of-the-practice performance, but are likely not indicative of the technologies’ true capabilities. Site No. 9 is probably most indicative of what thermal technologies can achieve in simple geologic settings because of the way it was designed and operated. At that site, dissolved chlorinated solvent concentrations were reduced from >10,000 µg/L to <100 µg/L levels, with final concentrations being <1 µg/L in many parts of the plume transect immediately downgradient of the source zone.
Chemical transformation processes used for the treatment of both organic and inorganic contaminants have advanced significantly since 2005. There are three basic approaches to the use of abiotic chemical amendments to treating groundwater: (1) ISCO, (2) chemical reduction (discussed in the permeable reactive barriers section) using zero-valent iron (ZVI), bi-metallic reductants (BMRs), and other reductants (e.g., iron minerals such as magnetite), and (3) newer methods like the application of ISCO in permeable reactive barriers and the use of in situ generation of ozone using electrodes, which are discussed in Chapter 6. In most cases chemical transformation processes result in the formation of by-products that are either less toxic or amenable to subsequent degradation or natural attenuation. In a few cases, however, there is the potential to form undesirable and toxic by-products. Thus, multiple approaches may be required to ensure that complete detoxification can occur at the targeted site. In many cases, chemical transformation requires the injection and delivery of a reactant-containing fluid to the treatment zone, and is subject to the same limitations experienced by all flushing technologies—most notably the bypassing contaminants stored in low-permeability media.