Objective:

Traditionally, bioremediation has been viewed as too passive for source area remediation due to limitations regarding the rate at which nonaqueous phase contaminants dissolve or diffuse to where bacteria can degrade them. Recent advances have shown, however, that mass transfer rates of chlorinated solvents from the nonaqueous phase to the aqueous phase can be substantially increased during bioremediation. The primary technical objective of this project is to demonstrate that facilitating this enhanced mass transfer allows bioremediation to be applied to chlorinated solvent source areas in a manner that realizes many of the benefits of more expensive and hazardous technologies, while retaining its benefits as a low cost, in situ technology.

Technology Description:

The approach for the field demonstration is designed to demonstrate and validate the enhanced mass transfer effects that can be achieved using bioremediation in a dense nonaqueous phase liquid (DNAPL) source area. Two different scenarios will be evaluated. Under Scenario 1, an electron donor will be added in a "conventional" concentration range (approximately 1,000 milligrams per liter or less). The resulting reductive dechlorination is expected to enhance mass transfer both by maintaining a steep concentration gradient along the entire water/DNAPL interface and by generating products of increasing solubility. In Scenario 2, the electron donor is added at concentrations or in specific mixtures to increase the effective solubility of the contaminants in addition to the benefits of the first scenario.

The conceptual design for the demonstration utilizes two treatment cells, one for each of the scenarios considered, located in a chlorinated solvent source area at the Fort Lewis Logistics Center near Tacoma, Washington. After an initial period of equilibration, the treatment cells will be monitored under the conditions of a forced hydraulic gradient but with no biostimulation. This phase will be used to determine the mass flux of contaminants moving through the treatment cells due only to dissolution of DNAPL in flowing groundwater. Subsequently, the biostimulation and enhanced mass transfer demonstration phase will commence. One cell will operate according to Scenario 1 above, while the other will demonstrate Scenario 2. This approach allows mass transfer for each biostimulation scenario to be compared to abiotic conditions as well as to the other scenario.

Expected Benefits:

Bioremediation is an attractive remediation technology because it involves low capital costs, does not generate secondary waste streams, is non-hazardous to workers and the environment, destroys contaminants in situ, is low maintenance, and minimizes site disturbance. The capital cost of implementing the technology at a site is limited to the monitoring and injection wells and the electron donor. When compared to capital costs for pump and treat, which can range from a few hundred thousand to several million, or to thermal technologies, which are typically even higher, savings of millions of dollars are readily achievable. Finally, if source lifetimes are reduced by factors of 10 to 20, operations and maintenance timeframes will be substantially less (potentially an order of magnitude less) than for pump-and-treat or barrier technologies. (Anticipated Project Completion - 2007)

Principal Investigator:
Dr. Kent Sorenson
Camp Dresser & McKee Inc.
1331 Seventeenth Street, Suite 1200
Denver, CO 80202
Telephone: (303) 383-2430
Fax: (303) 293-8236
E-mail: SorensonKS@cdm.com

DoD Liaison:
Ms. Kira Lynch
U.S. Army Corps of Engineers
Seattle District
4735 East Marginal Way, South
Seattle, WA 98134
Telephone: (206) 764-6918
Fax: (206) 764-3706
E-mail: kira.p.lynch@usace.army.mil