The RT3D software, one of the computer codes used in the Battelle Chlorinated Solvent Design Service, was used in the case study described here to evaluate the role of natural attenuation in remediation of contaminated plumes at Dover Air Force Base in Delaware. This case study was a Natural Attenuation Analysis, in which the bioremediation team analyzed the site to evaluate the performance of natural degradation processes.  Battelle provides natural attenuation analyses and other bioremediation services to clients around the country.

Past operations have resulted in chemical contamination of subsurface soil and associated groundwater at the Dover Air Force Base (DAFB) in Dover, Delaware.  Groundwater contaminants include fuel hydrocarbons and chlorinated solvents such as tetrachloroethene (PCE) and trichloroethene (TCE).  A TCE groundwater plume present at the Area-6 site is the largest detected plume on the base, covering an area that is approximately 9500 feet long (in the north-south direction) and 6000 feet wide (in the east-west direction).  The groundwater flow at this site is predominately from the north to the southwest at an average rate of 140 ft/yr.  The aquifer beneath the base consists of a mixture of sand and gravel materials designated as the Columbia formation.

Use the RT3D computer code to predict the natural fate of PCE, TCE, and their degradation products in the groundwater.  Two specific tasks were required in this analysis: 

• Model calibration:  Calibrate a flow and transport model against regional flow data to properly predict the present conditions.
• Model simulations:  Perform forward simulations to estimate the fate and transport of the contaminants under natural conditions and quantify the effects of various natural attenuation processes.

The model calibration results show that the flow and reactive transport models successfully recreated the flow and contaminant patterns observed in the site.  Both anaerobic and aerobic processes are found to play important roles in degrading the contaminant mass present at this site.  Results of forward-forcasting simulations show that when the sources are removed, the dissolved contaminant plumes will naturally atttenuate to an extent that does not pose a significant risk to the environment.  These results support the hypothesis that the natural attenuation strategy is an effective strategy for managing the dissolved contaminant plumes currently present at Dover AFB.

 

For more information, contact:
Michael Truex Program Manager Field Hydrology and Chemistry Group	Battelle 902 Battelle Blvd., K6-96 Richland, WA 99352 USA	509-376-5461 509-372-1704 FAX mj.truex@pnl.gov