Assessing multicomponent DNAPL biostabilization. I: Coal tar

Subsurface spills of high-molecular weight, multicomponent, dense nonaqueou s-phase liquids (DNAPLs) are intractable for remediation by conventional te chniques. This paper introduces the concept of biostabilization of the DNAP L source region as a means of achieving risk reduction at DNAPL-contaminate d sites. Successful biostabilization depends upon the interplay among disso lution, degradability, and toxicity of various DNAPL constituents, difficul t to predict a priori for the mixture. Bench-scale screening tests are prop osed for identifying those DNAPLs that are amenable to biostabilization. Th e screening protocols compare four criteria: (1) microbial activity, (2) co mposition of the DNAPL residue; (3) aqueous phase contaminant concentration s; and (4) aggregate aqueous phase toxicity-across unbiotreated controls an d in mixed versus unmixed biometers. The unmixed system represents slow dis solution from DNAPL pools in the quiescent subsurface. The protocols are de veloped and evaluated with DNAPL coal tar in the first paper of this set (P art 1). Unmixed coal tar biometers, characterized by slow mass transfer and low-level microbial activity, exhibited reduced, aqueous-phase contaminant concentrations and aggregate toxicity, as well as stable DNAPL composition , consistently indicating favorable potential for in situ biostabilization.