At a large industrial site, traditional horizontal and vertical extent investigations failed to reveal what eventually turned out to be highly localized seams of Trichloroethylene (TCE) DNAPL at areas of the property where unusual lithology came into play. In addition to the “hide & seek” nature of finding the contamination in these areas, it became clear that Trap & Treat® BOS 100® injections would need to be more precise than usual in order to achieve the project cleanup objectives.
A high resolution sampling strategy was implemented to evaluate why BOS 100® treatment was less effective in the trouble spots. As with most Trap & Treat® projects, the laboratory analyses (method 8260B GC/MS) were provided by Remediation Products, Inc. (RPI) at no cost to the project. The sampling strategy enabled detection and definition of numerous disjointed and highly localized pockets of DNAPL distributed over an area of approximately 230 square meters. Previously undiscovered percent level TCE impacts as high as 5.4% (wt) were observed within extremely narrow zones ranging from a fraction of a centimeter to several centimeters in thickness.
To achieve the pinpoint injections of BOS 100® slurry required, the Well Improvement Company of Fort Collins, Colorado provided unique equipment and expertise. On average, the pulse volume for each slurry injection was 30 to 50 gallons injected at rates ranging 150 to 250 gpm. Exit velocity of the injectate ranged from 12,000 to over 20,000 ft/min. Injections were completed in 10 to 15 seconds.
Groundwater TCE concentrations in this difficult area of the site ranged from 140 ppm to 1,280 ppm. TCE concentrations were reduced by more than 99%. As a part of the overall closure plan, a pair of monitoring wells were installed in the vicinity of the highest concentrations. After treatment was completed, TCE concentration fell to less than 5 ppb in both monitoring wells and has remained below the standard for more than a year. The dissolved phase plume was also mitigated and site closure monitoring began in 2011.
Want to Know More?
Click to read the paper entitled “Innovative Injection Technique to Treat DNAPL in Granular and Fine Grained Matrices” which was presented by Scott Noland, President of Remediation Products, Inc., at The Eighth International Conference for Remediation of Chlorinated and Recalcitrant Compounds (May 21 -24, 2012 – Monterey, California).