2002]. Biological enhancement of PCE solubility occurs by biological transformation of

dissolved PCE to its more soluble daughter products, TCE and DCE. At the NAPL water

boundary, this allows additional PCE mass transfer to the aqueous phase [Carr et al., 2000].

This has the advantage of decreasing source zone longevity [Yang andMcCarty, 2000].

Increased dissolution creates greater aqueous phase DNAPL, thus greater accessibility for

microbial use [Carr et al., 2000].

1.10 Solvent Extraction Residual Biotreatment

 During standard bioremediation methods, the biostimulation or bioaumentation agents are

delivered to the source or plume to provide the necessary requirements for biodegradation.

Mixing and contact with DNAPL are the limiting processes. Source zone depletion only occurs

at the DNAPL-water interface, so the agents must be delivered to this region if this is the goal.

One of the distinct advantages of the solvent extraction residual biotreatment (SERB) technology

is that the mixing and contact of biotreatment agents with contaminants is achieved directly

during the flushing event [Mravik et al., 2003]. The limitation of all flushing technologies is that

the remedial fluids primarily flow through zones of higher hydraulic conductivity. Thus, even in

the SERB method, there will be lack of contact in lower permeable zones where DNAPL tends

to accumulate [Sewell et al., 2006]. The mixed areas will stimulate bioremediation as the

flushing agent can act as the electron donor and the DNAPL can act as the electron acceptor. If

electron donors, electron acceptors and dechlorinating microbes are present, the environment

may be suitable for reductive dechlorination to occur [Sewell et al., 2006].

 As a result of this pilot alcohol flushing test, some ethanol was not able to be recovered at

the RWs. This residual ethanol serves as an electron donor and PCE will be the electron

acceptor. Of the 34 kL of ethanol injected into the source zone, 92% was recovered leaving a