Leo Lehmicke - Co2 and Water
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Transition from Pump & Treat to Natural Attenuation (Washington)

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 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 66 - 98% of the vinyl chloride had already been transformed. The approach used modeling to predict down gradient concentrations and 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). Concentrations dropped below MCLs in 2005 as predicted (Lehmicke and Johansen 2005). Monitoring showed concentrations below detection limits as of 2012. Cost savings to the client were $125,000/year.