An offsite plume at a Superfund site was controlled by ground water extraction for 11 years. TCE was the original contaminant but only cis-DCE and vinyl chloride remained. I developed the technical approach to evaluate NA (1999) and presented the results to the agencies (EPA, Washington Department of Ecology). Ethene/ethane measurements had never been done; the analysis showed the plume was in the final stages of degradation. The ethene + ethane to vinyl chloride ratio ranged from 2 to 88, indicating that at least 66 - 98% of the vinyl chloride had already been transformed to harmless end products. The approach used modeling to predict down gradient concentrations, cleanup time frame and to estimate half-lives for DCE and vinyl chloride.
MNA was accepted as the remedy; extraction ceased in May 2000 (Lehmicke et al. 2000). In 2005, concentrations dropped below MCLs as predicted (Lehmicke and Johansen 2005). Concentrations were below detection limits in 2012. Cost savings: $125,000/year.
