IN SITU BIOREMEDIATION - APPLICABLE CONTAMINANTS AND GEOCHEMICAL CONSIDERATIONS

Enhanced in-situ bioremediation (EISB) has application to many different contaminants, hydrogeologic settings, contaminant plumes, and contaminant source zones, and can be applied through a number of strategies tailored to site-specific conditions. EISB is increasingly selected because it results in contaminant destruction or immobilization (not ex-situ transfer to a different media), with lower cost, less disruption/exposure, and often less time than more traditional engineered remedies. EISB is an evolving field with ongoing new discoveries and refinements.

EISB can be applied to a large number of contaminants, including:

• Petroleum hydrocarbons
• Chlorinated solvents (chloroethenes, chloromethanes, chloroethanes)
• Other VOCs (e.g., acetone, MEK, chlorobenzene)
• Metals (As, Co, Cd, Cr, Cu, Hg, Ni, Zn) (Ur and Tc-99-partial immobilization)
• Energetics- TNT, RDX, HMX, perchlorate
• Nitrate, sulfate
• PAHs, PCBs, pesticides (limited success).

The success of EISB is intrinsically tied to aquifer oxidation/reduction (redox) conditions before, during, and after active treatment. The bacteria responsible for contaminant degradation/immobilization function under specific redox conditions, both aerobic and anaerobic. Different target contaminants require specific aquifer redox conditions and corresponding bacteria for successful treatment.

EISB is stimulated through addition of various electron donor/acceptor substrates. Substrates are delivered to the aquifer through injection/infiltration of liquids or slurries, or construction of solid substrate reactive barriers. The preferred treatment approach depends on aquifer characteristics including, depth, saturated thickness, permeability, heterogeneity, natural redox, and groundwater velocity.