Enhanced In-Situ Anaerobic Bioremediation
Phase I (Pilot-scale):
-- Approximately 110 gallons of food-grade soybean oil was injected into one injection well at an average flow rate of 0.36 gallons per minute (gpm) and with 20 to 32 pounds per square inch (psi) of back pressure.
-- Following injection, a pneumatic diaphragm pump was used to remove groundwater and mobile vegetable oil in order to leave the oil in a non-mobile phase.
-- Over the three weeks following injection, a peristaltic pump was used to continue to remove oil free oil until additional oil could not be extracted. Approximately 62 gallons of oil was recovered and 48 gallons of oil remained in the aquifer.
Phase II (Full-scale):
-- Over 33 injection points, a total of 1,815 gallons of pure soybean oil was injected. Each injection was followed by an injection of 200 gallons of native groundwater to help distribute the oil.
-- The maximum oil injection flow rate was 9.2 gpm and maximum injection pressure was 28 psi.
-- Injection wells and groundwater monitoring wells were installed using cone-penetrometer technology (CPT) rig. Additional/replacement groundwater monitoring points were installed using a Geoprobe® rig.
AFCEE Project Manager:
3300 Sidney Brooks
Brooks City-Base, TX 78235
Bruce M. Henry
1700 Broadway, Suite 900
Denver, CO 80290
Dichloroethene (DCE); Tetrachloroethene (PCE); Trichloroethene (TCE); Vinyl chloride; Volatiles-Halogenated
Accidental release of chlorinated solvents that were stored and used at the missile assembly facility.
Type/Quantity of Media Treated:
Groundwater (160 acres of contaminated groundwater plume)
Purpose/Significance of Application:
To determine if vegetable oil would act as a suitable substrate to enhance reductive dechlorination rates. Also, to determine the effect on the contaminant mass through partitioning of the chlorinated solvents within the oil.
Regulatory Requirements/Cleanup Goals:
Phase I (Pilot-scale):
-- The concentration of TCE and it dechlorination products decreased by up to three orders of magnitude within the first month (from 100,000 micrograms per liter [ug/L] to 110 µg/L).
-- Groundwater sampling results indicated strongly anaerobic conditions and limited reductive dechlorination.
Phase II (Full-scale):
-- Measurements of the oxidation-reduction potential indicated an optimal environment for reductive dechlorination.
-- Concentrations of TCE in the treatment zone decreased approximately four orders of magnitude.
-- Increases as well as decreases in daughter dechlorination products show a reduction of TCE as well as a reduction of the daughter compounds. Increases in ethene concentration point toward the dechlorination of vinyl chloride, which is the last step in the dechlorination process.
The total capital cost for the Phase I pilot test was approximately $72,000. Cost for the Phase II full scale application totaled approximately $97,000. Cost for installation of the Phase II injection and monitoring system, and conducting substrate injection was approximately $67,000. The cost for performance monitoring averaged approximately $24,000 per sampling event, including project management, procurement, and reporting. To date, six Phase II performance monitoring events have been conducted over the 69-month period from July 2000 through April 2006. Total costs to date for the Phase II demonstration are approximately $241,000.
The Hangar K Site is located in Cape Canaveral Air Force Station, Florida. It was previously used as a missile assembly facility where launch support activities occurred and chlorinated solvents were stored at the site. Accidental release of the solvents into the shallow unconfined aquifer beneath and downgradient from site resulted in a 160-acre groundwater contaminant plume consisting of TCE and its daughter dechlorination products. The maximum TCE concentration in the groundwater was 300,000 micrograms per liter (µg/L), at a depth of 4 to 6 feet below the ground surface.
The injection of vegetable oil enhanced reductive dechlorination of chlorinated ethenes (PCE, TCE, DCE, and VC) in groundwater at the Hangar K site. Both pilot- and full-scale studies demonstrated that reductive dechlorination could be enhanced by supplementing the natural concentrations of organic carbon via injection of food-grade soybean oil. Concentrations of TCE were less than 5.0 µg/L at all locations sampled within the treatment zone. This represents a reduction in TCE concentrations in groundwater by approximately four orders of magnitude.