Enhanced Reductive Dechlorination (ERD) using anaerobic in situ reactive zone (IRZ) technology
-- At Hanscom AFB, the pilot test was conducted using one injection well and an array of monitoring wells. A total of 47 substrate injections were conducted during the period of operation. A total of 1,250 gallons of raw blackstrap molasses, 11,250 gallons of dilution water, 7,575 gallons of push water and 4,732 grams of potassium bromide were injected into the injection well. The substrate solution was batch-fed and the monitoring wells were sampled for various parameters such as dissolved oxygen, pH, oxidation reduction potential (ORP), specific conductance, temperature, and water level.
-- At Vandenberg AFB, the pilot test was conducted using three injection wells and an array of monitoring wells. A total of 31 substrate injections were conducted during the period of operation. A total of 683 gallons of raw blackstrap molasses, 6,830 gallons of dilution water, 1,500 gallons of push water, and 7,718 grams of potassium bromide were injected into three injection wells. Molasses solution was batch-fed and the monitoring wells were sampled for various parameters such as dissolved oxygen, pH, oxidation reduction potential (ORP), specific conductance, temperature, and water level.
The IRZ technology is covered by U.S. Patent Numbers 5,554,290; 6,143,177; 6,322,700; and 6,562,235.
Environmental Security Technology Certification Program (ESTCP); Air Force Center for Environmental Excellence (AFCEE)
Dr. Andrea Leeson
901 North Stuart Street, Suite 303
Arlington, VA 22203
AFCEE, Technology Transfer Division
3207 Sydney Brooks
Brooks AFB, TX 78235
Federal Facilities Superfund Section
EPA Region 1
1 Congress Street, Suite 1100 (HBT)
Boston, MA 02114
Christopher C. Lutes
ARCADIS G&M, Inc.
4915 Prospectus Drive, Suite F
Durham, NC 27713
Trichloroethene (TCE), Dichlorothene (DCE), Vinyl chloride (VC)
Type/Quantity of Media Treated:
Groundwater (quantity not specified)
Purpose/Significance of Application:
The purpose of both pilot tests was to demonstrate the ability of ERD using IRZ technology to remediate chlorinated aliphatic hydrocarbons (CAH) in the subsurface in a relatively short time period and to gather information for estimating long-term treatment effectiveness, life span, and costs.
Regulatory Requirements/Cleanup Goals:
At the Hanscom AFB, a Superfund site, the long-term cleanup goal is to achieve drinking water standards or federal maximum contaminant levels (MCL). The Vandenberg AFB site is overseen by state agencies in California under a Federal Facilities Site Remediation Agreement. In the absence of a negotiated cleanup goal at this site, the default primary goal is MCLs.
At the Hanscom AFB, the two year pilot test demonstrated a reduction of TCE and dichloroethene (DCE) in the source area by 97 to > 99 percent. This pilot test also demonstrated long term effectiveness of the treatment technology in a source zone since no rebound of CAH concentrations occurred even as late as 17 months after the last injection. The demonstration was successful in achieving MCLs for TCE and cis-DCE. Although the concentration of VC has dramatically decreased, the MCL for VC was not attained due to variable groundwater flow directions and thus inconsistent dispersal of reagent. However, generation of ethene indicated that TCE was being completely degraded without dead-ending at intermediate compounds.
At the Vandenberg AFB, the low buffering capacity of the aquifer affected system performance and caused pH to be depressed to levels below the desired operating range. However, after a buffer was added to the injecting substrate and more reagent was delivered, reductions in TCE concentrations of ≥ 80 percent were observed at specific monitoring wells after 26 months of active injections.
At the Hanscom AFB, actual demonstration costs totaled $432,921 while at the Vandenberg AFB, actual demonstration costs totaled $323,976.
The pilot test site at Hanscom AFB was known as Fire Training Area II and was reportedly used from the late 1960s through 1973 by the Hanscom AFB Fire Department for training exercises and for research on pyrokinetic materials. At this site, CAHs were detected in groundwater in a narrow plume that extended from the source area. The area in the immediate vicinity of the pilot test area was underlain by 18 to 25 feet of glacial till overburden on granitic bedrock. The till comprised the lower aquifer and consisted of very dense, coarse to fine sand with variable amounts of silt, fine-to-coarse gravel, cobbles and boulders. Hydraulic conductivity for the lower aquifer ranged between 3 feet per day to 48 feet per day, and averaged 26 feet per day; the hydraulic gradient of the lower aquifer was estimated at 0.006, and the effective porosity of the lower aquifer materials was estimated at 20%. The depth to groundwater ranged from 2 to 9 ft below ground surface (bgs) in the pilot test area. The natural regional groundwater flow direction was to the east/northeast.
The pilot test site at Vandenberg AFB was at Site 35 in the northern part of the base, where dry pad technology was used for missile launches and typically generated waste such as TCE, mixed solvents, lubrication oils, and hydraulic fluids. The stratigraphy of the site included Orcutt Formation sediments at the surface, deposited unconformably on Sisquoc Formation shale and mudstone. The Orcutt Formation consists of loosely consolidated lenticular beds of sand, gravel, and clay of predominantly continental origin, with the upper zone representing eolian and beach sand. At the pilot test site, the depth to groundwater was approximately 10 to 15 feet bgs, and the depth to bedrock is approximately 40 feet bgs. The predominant direction of groundwater flow was to the southwest, with a local hydraulic gradient of approximately 0.041 feet per feet and a hydraulic conductivity estimate of 0.92 to 3.83 feet per day.
The anaerobic IRZ technology used for both the pilot tests involved addition of food grade, soluble carbohydrate substrates such as molasses that served as supplemental energy source for microbiological processes in the subsurface and created suitable conditions for biodegradation of the CAHs.