- Soil & Groundwater Remediation
Textron Inc. retained Burns & McDonnell to implement dual-phase vacuum extraction (DPVE) technology to remediate an area of soil and shallow groundwater impacts beneath a manufacturing plant in Hutchinson, Kan. The facility is owned and actively operated as a manufacturing facility by Eaton Corp. The area targeted for DPVE is a known source of groundwater contamination contributing to a site-wide groundwater contamination plume that is part of the Obee Road Superfund Site. The source of the impacts was a former trichloroethylene (TCE) degreaser.
- Remedial technology selection
- Pilot testing
- Remedial design
- Remediation system fabrication
- Full-scale implementation
- System operations, maintenance and performance monitoring
The source area is approximately 100 feet long by 70 feet wide and exhibits TCE soil concentrations from 10 to 70 milligrams per kilogram (mg/kg) and groundwater concentrations from 1,000 to 130,000 micrograms per liter (µg/l). The geology consists of silty clay to approximately 10 feet below ground surface (bgs) overlying well-graded sand. Groundwater is typically encountered in the source area at approximately 10 to 15 feet bgs. The highest contaminant concentrations in groundwater are generally encountered above 20 feet bgs.
The site-wide groundwater contamination plume is addressed by a conventional pump-and-treat system that uses three extraction wells to recover groundwater at a combined flow rate of approximatey 1,500 gallons per minute (gpm). Water recovered by the system is treated by a packed tower air stripper treatment system before discharge. The system has been in operation since 1993 and operation and maintenance costs total approximately $100,000 per year, plus electricity.
The primary objectives of implementing DPVE in the source area are:
- To eliminate the continued loading of the groundwater contamination plume, thereby significantly reducing the timeframe required for future operation of the pump-and-treat system.
- To minimize the potential for exposure to contaminant vapors inside the manufacturing facility.
A pilot test was conducted in the location of the former TCE degreaser at the site in December 2006 to determine the feasibility of using DPVE for remediation. The results confirmed that DPVE is a viable technology, and data collected during the pilot test was used to prepare the full-scale DPVE system design.
Full-Scale DPVE System
The full-scale DPVE system was designed to use three extraction wells for the continuous recovery of impacted soil vapor and groundwater. Well and subgrade piping installation were conducted inside the manufacturing facility during normal plant operations. The remediation equipment was designed and fabricated by Burns & McDonnell. The equipment was installed in an enclosed trailer and was transported to the site in May 2008. Once on-site, the system was placed inside the facility, adjacent to the extraction wells, and connected to the DPVE well piping, water discharge piping and exhaust piping.
The system includes a rotary claw-type vacuum pump with a capacity of approximately 80 standard cubic feet per minute (scfm) at 15 inches of mercury column (in. Hg) vacuum. Water recovered by the DPVE system is discharged on a batch basis to the existing on-site air stripper treatment system. Discharge is accomplished via a high pressure, multi-stage centrifugal transfer pump and approximately 1,200 feet of discharge piping.
The system includes several innovative features including a remote telemetry auto-dialer system that notifies operation and maintenance personnel of alarm conditions, including vacuum pump shutdown, high water discharge pressure and high knockout tank water level. The auto-dialer also allows personnel to remotely monitor and shut down the system using any touchtone telephone or modem-equipped computer. The system also includes a groundwater treatment system shutdown interlock with a radio-based remote input/output device to automatically shut down the DPVE system when the treatment system experiences a shutdown. The radio equipment includes a receiver antenna mounted on the plant roof above the DPVE system trailer location and a transmitter antenna installed at the air stripper treatment system location.
Since startup, the DPVE system has recovered volatile organic compound (VOC) impacted soil vapor at a rate of approximately 100 scfm, and groundwater at a rate of approximately 3 gpm. The total VOC vapor-phase removal rate has declined from approximately 66 pounds per day during system startup (May 2008) to approximately 2.5 pounds per day in late September 2008. As of Sept. 25, 2008, approximately 600 pounds of VOCs had been removed in the vapor-phase since startup. During the same time, approximately 7 pounds of VOCs had been removed in the dissolved-phase, via the extraction of approximately 150,000 gallons of contaminated groundwater.
A pre-startup (baseline) groundwater sample collected from a monitoring well installed approximately 65 feet downgradient from the DPVE system indicated a TCE concentration of approximately 14,000 µg/l. After about 5 weeks of DPVE operation, the well was resampled. Results showed a TCE concentration of approximately 100 µg/l.
These results indicate that the DPVE system is rapidly accomplishing contaminant mass reduction in the source area. Completion of the source area removal action was expected to occur in late 2009 or early 2010. The schedule for discontinuing operation of the site-wide pump-and-treat system is expected to be accelerated, resulting in significant remediation cost savings for the client.
- Source remediation for accelerated groundwater plume attenuation
- DPVE implementation inside active plant facility
- Custom-designed remediation system
- High-pressure discharge into existing wastewater pipeline
- Automated operation
- Remote telemetry dialer monitoring
- Radio-based communications for automatic shutdown on water treatment plant shutdown