Assessing multicomponent DNAPL biostabilization potential. II: Aroclor 1242

Aroclors are dense nonaqueous-phase liquids (DNAPLs) composed of polychlori nated biphenyls, which are common subsurface contaminants. Because complete remediation of Aroclor is very difficult, biostabilization may offer an al ternative where risk reduction can be achieved without destruction of the D NAPL mass. The potential for aerobic in situ biostabilization of Aroclor 12 42 was evaluated using laboratory protocols similar to those described in t he companion paper. Total microbial concentrations increased and stabilized in both mixed and unmixed systems, while the respiring cells did not stabi lize in either system. After 100 days, the DNAPL in mixed biometers was dep leted in dichlorobiphenyls; the DNAPL composition in unmixed biometers did not change significantly. The total aqueous polychlorinated biphenyl concen tration was lower in the unmixed than mixed biometers, both were below the predicted equilibrium concentration. After 100 days, the chronic toxicity o f the aqueous phase to Cerodaphnia was greater in the biotreated systems th an in the unbiotreated systems. The results indicate that aerobic microbiol ogical activity may be insufficient to fully stabilize Aroclor in the subsu rface, in contrast to the clear biostabilization potential of coal tar.