Generation of Enriched, Anaerobic "Chase Water" to Repair Aquifer Biogeochemistry

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Understanding of the Problem

“DCE Stall” is a problem frequently encountered when simple, “carbon-only” substrates such as hydrogen releasing compounds, emulsified oils, lactates or sugars are used to stimulate in situ reductive dehalogenation of chlorinated solvents. In response to the excessive accumulation of these problematic intermediates (e.g., 1,2-DCE and Vinyl Chloride), inoculation of groundwater with Dehalococcoides sp., or other dehalogenators, is sometimes required.

With increasing frequency, however, various microbial inoculants do not survive well in aquifers that have been previously treated with substrates other than EHC®.  Hence a viable population of dehalogenators is not established and the accumulated metabolites persist and potentially migrate off site.  The” failure” of the inoculum is usually caused by unsuitable environmental conditions such as:

  • unacceptably low pH; unacceptably high Eh
  • low availability of required nutrients;
  • microbial toxicity due to surfactants/emulsifying agents present in the remedial amendments; and /or
  • microbial inhibition due to induced mobilization of toxic heavy metals, such as arsenic. 

These conditions are the direct result of using non-buffered, simple carbon-only remedial amendments. Thus, re-establishment of environmental conditions more conducive to the growth and proliferation of the inoculant is often needed to yield effective remediation of the impacted aquifers.

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