- Chlorinated VOC Groundwater & Soil Remediation
Burns & McDonnell was retained to perform soil and groundwater remediation of chlorinated volatile organic compounds (VOCs) such as perchloroethylene and trichloroethylene (PCE and TCE) at a warehouse facility in Dallas. A historical spill of the chlorinated VOCs behind the warehouse building resulted in the contamination of soil in the immediate area and shallow groundwater leading from the spill area. Subsurface soil and groundwater sampling have defined the extent of contamination. Soil contamination was limited to a small area on-site, while groundwater contamination extends off-site onto property owned by the City of Dallas. The site is in the Texas Voluntary Clean-Up Program under the authority of the Texas Commission on Environmental Quality (TCEQ).
- Fixed price remediation
- Remedial design
- Bench-scale treatability study
- Soil remediation (excavation and disposal)
- Groundwater remediation (chemical oxidation and reactive barrier)
- Construction-phase services
- Enhancement of permeability through fracturing
Burns & McDonnell has entered into a three-way agreement with the buyer and seller of the property to facilitate the sale of the property. Burns & McDonnell has agreed to indemnify the buyer and seller of all environmental remediation liability at the site through the use of pollution legal liability coverages and cost-cap insurance policies. Burns & McDonnell is solely responsible for completing the soil and groundwater remediation at the site until a Certificate of Completion (No Further Action) is obtained from TCEQ.
Burns & McDonnell has submitted a response action plan (RAP) to TCEQ to address the remediation of impacted soil and groundwater. The RAP was approved by TCEQ in spring 2004. Remediation activities began in June 2004, and soil remediation was completed by July 2004. Soil remediation consisted of the excavation and disposal of impacted soil from the source area.
Groundwater remediation activities also began in June 2004. Chemical oxidation with permanganate is being used for groundwater remediation. The permanganate was first delivered using large-diameter injection borings within the backfilled excavation and via fractures. Permanganate was placed in the large borings first, and then the fractures. The volume of permanganate was determined by a laboratory bench-scale study completed by Burns & McDonnell.
The large-diameter borings are 36 inches in diameter and were drilled from the base of the excavation to the water table, approximately 20 feet below ground surace (bgs). The borings were then filled with a 2-to-1 ratio of permanganate and sand up to approximately 5 feet, bgs. The fractures were emplaced via hydraulic fracture techniques using a permanganate slurry. Approximately 40 fractures, with approximately 1,000 pounds per fracture, were emplaced in the groundwater plume downgradient of the excavation.
A water injection system was designed, fabricated and installed by Burns & McDonnell to place the permanganate in the large-diameter borings and fractures into solution, and to increase the advective downgradient movement of the permanganate solution. The system began operation in August 2004, and over 2 million gallons of water were injected through May 2005. The injection system was monitored remotely by Burns & McDonnell via a SCADA system, and monthly site visits were conducted to collect on-site data and perform operations and maintenance activities. Since all permanganate had gone into solution, water injection was stopped in 2005.
Additional fracturing activities were completed in June 2005, and additional injection activities were completed in October 2007. These activities focused on residual elevated levels at the margins of the groundwater plume and at the discharge point of the plume into a surface water channel. Permanganate was injected via direct push borings to treat the margins of the plume and a reactive barrier consisting of granular zero-valent iron and EHC from Adventus was created via direct-push injection just upgradient of the channel.
Quarterly monitoring was initiated in October 2004 and continued until October 2006, when it became semi-annual. After the 2007 injection, four confirmation samplings were conducted in April and October 2008 and January and April 2009. These confirmation sampling events have confirmed that the main source area has been removed/remediated via oxidation. Also, groundwater concentrations have been significantly reduced throughout the plume (more than 90 percent), the plume is stable with no statistically increasing trends, and only a few minor exceedances above maximum contaminant levels (MCLs) remain in a few off-site monitoring wells. Semi-annual monitoring will continue until the MCLs are met in the off-site wells. This is anticipated in 2010.