In Situ Soil & Groundwater Remediation via Electrical-Resistance Heating

Location: Former fuel terminal in Greensboro, NC
Project Value: $3.7 Million

 

The project site is a former bulk fuel terminal which had an estimated release volume of gasoline and diesel fuel of over 350,000 gallons to soil and groundwater over its history.

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LWR has been the remedial construction, system installation, operation and maintenance contractor at the Greensboro, NC Electrical-Resistance Heating (ERH) project since pilot testing work began in 2005. The project site is a former bulk fuel terminal in Greensboro, North Carolina, which had an estimated release volume of gasoline and diesel fuel of over 350,000 gallons to soil and groundwater over its 25-year operating history. LWR worked with a team of consultants and technology vendors to develop a comprehensive and complex remedial strategy for the site. The technology selected for the project is electrical-resistance heating (ERH). Arcadis was the primary design and oversight consultant for the project team which also included GES Consultants (Richmond, VA), McMillan-McGee Corporation (Alberta, CA), and MK Environmental (Chicago, IL).

This project is the largest ERH remediation project ever constructed world wide, and includes a diverse set of design/construction elements. LWR provided turn-key construction, operation and maintenance services at the site. These services included site grading, installation of storm water controls, construction of concrete foundations, erection of a Sprung structure to house treatment equipment and installation of associated piping. LWR also coordinated their system installation work with electrical power and SCADA controls systems subcontractors and technology vendors.

ERH thermal treatment using ELECTRO-thermal dynamic stripping process involves the installation of electrodes, recovery wells, and sensor wells throughout treatment zones. Voltage is applied to the subsurface electrodes in a 3-phase configuration, heating the soil and groundwater to 100-degrees C (212-degrees F) over a 5- to 6-month period. Heated groundwater and liquid-phase petroleum hydrocarbons are recovered and treated on site using conventional water treatment equipment (e.g., oil/water separators, sand filters, and carbon filters) and recycled back through the electrodes to keep them cool. Heated soil gas, steam, and gaseous-phase petroleum hydrocarbons are extracted from the recovery wells, cooled using fin-fan heat exchangers, and treated using two separate air treatment devices (Thermal Oxidizer and Catalytic Oxidizer). Special engineering controls were required because the oxygen and hydrocarbon levels within the recovered gases cause the mixture to pass through the LEL and UEL zones.

The final design included a building comprised of a large Sprung structure (i.e., large tent constructed using flame-retardant materials). The tent was designed to be open at both ends and sides to allow adequate ventilation. Two Class I/Div II classified areas separate processes that might contain flammable liquids and gases from non-classified areas. Also, sophisticated control panel and control logic were designed and constructed to detect upset conditions, and immediately notify plant personnel in the event of potential hazards. Two LEL meters were incorporated into the control logic to shut down the plant in the event of hazardous vapor levels (>10% LEL) detected in ambient air within the plant. The recovered waste gasoline was re-condensed using heat exchangers and oil-water separators, and then sold to local fuel recyclers.

Explosion mitigation equipment (i.e., Fike System) was also built incorporated into the system. The Fike system utilizes approximately 13 infra-red (IR) detectors and pressure sensors throughout the process plant that will detect flames (IR) and/or a pressure front within the plant’s piping and/or tanks. The program logic for the Fike system closes a series of fast-close valves and releases sodium bicarbonate into the processes tanks and piping systems to extinguish a flame front (deflagration) should it occur.

The site was subdivided into 4 treatment areas each covering approximately 1.2 acres of surface area. Treatment in Zone 1 was 100% complete as of October 12, 2007 where a total of 214,000 pounds of hydrocarbons were recovered and recycled or destroyed in the treatment process. Energy consumption including electric power and natural gas for Zone 1 was 15% less than original estimates.

All system components including electrodes and piping arrays have been reused as the zoned equipment was dismantled and re-installed in Treatment Area 2 and is currently operating in Treatment Area 3.

The entire project Team vigorously promoted H&S during all phases of work, including the integration of LPS into its work processes. This project was also recognized as the 2007 National Groundwater Association’s Outstanding Groundwater Remediation Project.