USE OF LARGE-SCALE AQUIFER DYE TRACER TEST FOR DESIGN OF IN-SITU BIOREMEDIATION THROUGH VEGETABLE OIL INJECTION

Jacob, C.L., B. Jonsson, C.B. Kimmel, K.G. Chaput, J.A. Parsons, and M.D. Kent.
Program and Abstracts: The 7th Annual Washington Hydrogeology Symposium, 28-30 April 2009, Tacoma, Washington. Washington Department of Ecology and the U.S. Geological Survey, p 46, 2009

A large-scale aquifer tracer test was implemented to support design of electron donor substrate injection for stimulation of bioremediation at an aerospace manufacturing facility in Portland, Oregon. Trichloroethene (TCE) is present in an upper unconfined aquifer and lower confined aquifer where a groundwater pump-and-treat system has operated since 1997 to provide hydraulic containment and contaminant removal. Dye tracer testing was performed to obtain design parameters for donor injection and to determine the influence of extraction wells that will continue to operate for hydraulic containment. The target treatment zone is 30 to 70 ft of saturated clean-to-silty sandy gravel in the unconfined aquifer, over an area of ~150,000 ft² (i.e., 280,000 yd³ aquifer). Tracer injection was performed in March 2008 using 95,000 gallons of rhodamine WT dye solution and 26,000 gallons of fluorescein dye solution into two wells planned for donor injection. Results discussed include estimates of maximum dye extent, groundwater seepage velocity, radius of injection, and effective porosity for flow. The bioremediation design utilizes six existing wells (to be decommissioned due to facility expansion) and two new temporary wells for a one-time electron donor injection. The total design injection volume is 240,000 gal, consisting of a 20% oil-in-water emulsion utilizing 10 tanker truck loads (400,000 lb/53,290 gal) of vegetable oil/surfactant mixture. Extraction wells will be operated selectively during injection to distribute emulsion in the target treatment zone and to minimize transport toward extraction wells that will operate following injection. Contingency measures will address groundwater treatment system fouling and unacceptable concentrations of biological oxygen demand and dissolved metals in the system discharge.