Theme: 01. Remediation Technology Innovations

Topic Area: 1r2. Remediation of Legacy Contaminants using Thermal Conductive Heating

Formatted Title:

Thermal Conduction Heating (TCH) Removed over 400,000 Pounds of Jet Fuel Contamination from Former Bulk Fuel Source Area

Background/Objectives:

In situ thermal remediation using thermal conduction heating (TCH) was selected to remediate a large volume of soil and groundwater impacted with light non-aqueous phase liquid (LNAPL) jet fuel at the former Area D Jet Fuel Farm at the William J. Hughes FAA Technical Center in Atlantic City, New Jersey. Area D had previously been used for storage of jet fuel in aboveground and underground bulk fuel tanks. Historic reports indicated that an estimated 500,000 pounds (lbs) (227,000 kg) of Jet Propellant 4 (JP-4) LNAPL could be present in the TCH treatment zone. The total thermal treatment zone (TTZ) encompassed over 183,000 square feet (4.2 acres, 1.7 hectares), including treatment under an existing active groundwater treatment building. Treatment depths varied across the treatment areas, but generally extended from 5 to 24 feet below ground surface (bgs), totaling 77,496 cubic yards (59,250 m³), making this one of the largest TCH heating projects ever completed.

Approach/Activities:

The TCH treatment was split into two phases to accommodate available power capacity limits. Pre-design delineation activities resulted in expansion of the Phase 2 TTZ footprint to nearly double the originally expected area, including the additional need for TCH treatment around active utilities and beneath an existing building using angled TCH heaters and extraction wells. Thermal treatment in the Phase 1 area comprised 303 TCH heaters, 66 multi-phase extraction (MPE) wells with top-loading extraction pumps, and 28 Temperature Monitoring Points (TMPs), while Phase 2 treatment included 595 TCH heaters, 129 MPE wells and 44 TMPs. Treatment objectives were focused on removing LNAPL and maximizing contaminant mass reduction. Performance goals required of maintaining a treatment temperature of 100⁰C for at least 65 days with 90% of temperature sensors above 100⁰C (+/-3⁰C). The Area D site had an existing catalytic oxidizer (cat-ox) available from a prior remediation project. Preliminary calculations showed that contaminant loading could overwhelm the capacity of the existing cat-ox, so a thermal oxidizer (therm-ox) was secured for this project. The therm-ox provided primary vapor treatment during the majority of the project, with the cat-ox and vapor phase carbon available for use during non-peak operating periods and as emergency backups. With the large expansion of the Phase 2 footprint, it was necessary to stagger the start of TCH heaters into Phase 2A and 2B, to reduce peak power demand and contaminant loading to stay within the capacity of the therm-ox. Both Phase 1 and 2 operations integrated real-time lower explosive limit (LEL) monitoring of the influent vapor stream with the system controls to ensure safe operation. Peak contaminant removal exceeded 2,400 lb./day (1,093 kg/day) in Phase 2. TCH heater power input was reduced for 55 days during Phase 2 to maintain influent vapor concentrations within the safe operating limits of the therm-ox. Additionally, integrated real-time monitoring of the subsurface temperatures at in situ temperature sensors and TCH heaters allowed operators to determine progress toward performance goals and make system adjustments as needed.

Results/Lessons Learned:

Lessons learned in Phase 1 were incorporated into the design and operating strategy for Phase 2. In Phase 1, supplemental shallow heaters were added to boost shallow temperatures in several lagging areas. Based on those observations in Phase 1, areas that required treatment closer to ground surface in Phase 2 were designed with tighter heater spacing and an insulating cover. Cycling of MPE well pumps was found to enhance LNAPL removal in Phase 2. Both Phase 1 and Phase 2 met the temperature goals and were operated until diminishing returns in contaminant mass removal were reached. Phase 1 operated for 305 days and removed approximately 120,000 lbs (54,400 kg) of contaminants, including 3,814 gallons of LNAPL. Phase 2A and 2B operations ran for a total of 414 days (including the staggered start up), removing approximately 325,000 lbs (147,400 kg) of contaminants, including 12,177 gallons of LNAPL. In total, the TCH system removed over 445,000 lbs (202,000 kg) of contaminants, including nearly 16,000 gallons of NAPL from the subsurface, in a combined operating period of just under two years. The owner’s prime contractor stated that successful completion of this project resulted in an estimated cost avoidance of over $200 million and reduced the environmental remediation timeline by decades.

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Tim Mahoney