Effects of mass reduction, flow reduction and enhanced biodecay of DNAPL source zones

A mathematical model and an analytical solution are presented to describe field-scale dense non-aqueous phase liquid (DNAPL) source dissolution and source zone biodecay rates coupled with advective-dispersive dissolved plume transport. The model is employed to investigate various source remediation options on source zone mass depletion, net source mass flux, and dissolved plume attenuation for different source zone "architectures" (i.e., pools versus residual DNAPL) and compliance criteria. Remediation options considered include partial source mass removal, source flow reduction, and source zone enhanced biodecay. Partial mass reduction reduces the source zone mass flux and downgradient concentrations for residual DNAPL sources and pools, which can significantly reduce dissolved plume size and time to reach compliance criteria. Source zone flow reduction decreases the rate of source mass depletion, but can facilitate compliance, if concentrations at compliance locations are not too high initially. Increase in source biodecay rate, especially with concomitant increases in dissolution kinetics, can decrease the time to achieve compliance criteria over biodecay alone.