Tuesday, October 30th – 11:30 am – 11:55 am*
Background/Objectives. The site is located in Kansas City, Kansas and currently operates as an active grain elevator facility. The site entered into the Voluntary Cleanup and Property Redevelopment Program (VCPRP) in 2000 following groundwater and soil detections of grain fumigant constituents of concern (COCs), including carbon tetrachloride, in the vicinity of a former fumigant aboveground storage tank (AST). Following source area investigation and groundwater plume delineation activities, dual-phase vacuum extraction (DPVE) was implemented in 2007 for the removal of COCs in source area soils and groundwater. Groundwater is encountered at the site approximately 7 to 8 feet below ground surface (bgs). Lithology within the targeted source zone generally consists of well sorted, loose, silty-sand to depths ranging from approximately 13 to 17 feet bgs, underlain by silty clay.
After approximately 6 years of DPVE operation, resulting in the removal of over 9,000 pounds of total VOCs, a subset of source area extraction wells continued to exhibit elevated COC groundwater concentrations. Additional investigation was conducted to assess the nature and extent of residual COC mass in the source area and provide data required for the evaluation of alternatives that could expedite source area remediation. The investigation results indicated significant sorbed-phase COC mass, generally limited to the shallow, sandy interval of an area bound by the DPVE wells exhibiting elevated COC concentrations. Light non-aqueous phase liquid (LNAPL) heavily impacted with the site COCs was also identified. Surfactant enhanced extraction (SEE) was subsequently identified as the optimal source zone remedial alternative because of the technology’s ability to quickly and efficiently remove a concentrated, but relatively isolated and shallow zone of contaminant mass with relatively low surfactant application concentrations. In addition, the existing DPVE infrastructure could be utilized to implement SEE at the site, thereby minimizing intrusive activities.
Approach/Activities. Surfactants are biodegradable, environmentally friendly compounds that can enhance organic contaminant extraction by promoting desorption and lowering the surface tension of groundwater. These effects increase contaminant mobility and enhance recovery. Burns & McDonnell conducted a SEE pilot study at the site in April and May 2015 to evaluate the efficacy of the technology under site-specific conditions. The pilot study included single-well “push-pull” tests and multi-well “point-to-point” tests using a solution consisting of 1 to 2 percent (by volume) Ivey-sol® 106 biodegradable surfactant. In general, the solution was gravity fed into each well to achieve a targeted injection radius, then allowed to remain in the formation for a prescribed residence time period. In 2016 the application was expanded to full-scale The surfactant solution, groundwater, and liberated COCs were subsequently extracted using the DPVE system.
Results/Lessons Learned. Based on a comparison of baseline (April-May 2015) and full scale (September 2016), pre to post-SEE groundwater monitoring results, SEE resulted in carbon tetrachloride groundwater concentration reductions of up to 99 percent. The full-scale SEE targeted remaining COC mass in source zone, and required of additional injection/extraction well installation, and surfactant delivery/extraction methods similar to those employed during the SEE pilot study. The objective of the full-scale SEE application is/was to achieve source zone COC mass reductions that allow for permanent shutdown of the DPVE system. Post full-scale SEE observations and data will be available for presentation and will be discussed.
Burnes & McDonald
Chesterfield, MO, USA
Conference Presenter / Co-Author:
George Ivey, Ivey International, BC, Canada
*date & time subject to change