LBG Receives Minnesote Chapter of ACEC Grand Award03/02/2007
ST. PAUL, MN — Leggette, Brashears & Graham, Inc. (LBG), a professional groundwater and environmental engineering services firm has been recognized by the Minnesota Chapter of the American Council of Engineering Companies (ACEC) with its Grand Award in the 2007 Engineering Excellence competition.
LBG was cited for the development of an innovative and cost effective bioremediation system responsible for successfully eliminating a large dissolved-phase petroleum plume at a gasoline spill site in the Midwest.
The aquifer in question contained a dissolved plume of toxic petroleum compounds. Due to anaerobic conditions that had developed within the aquifer, the dissolved petroleum plume had not only persisted, but expanded over a large area in the unusually thin aquifer underlying the site.
Combining principles from numerous fields including chemical engineering, water-treatment engineering, groundwater modeling and drainage engineering, LBG developed a new method to significantly speed up oxygen delivery to the aquifer in order to facilitate the rapid aerobic bio-degradation of the plume. The team used an off-the-shelf pressure-swing adsorption oxygen generator routinely employed by chemical engineers to inexpensively produce nearly pure oxygen on site from atmospheric air. Next, instead of utilizing common oxygen/water contacting techniques, a confined plunging-jet gas/liquid contactor process was used to generate water with dissolved oxygen concentrations over 35 mg/L, which is nearly four times the normal saturation level. The super-saturated water was then re-injected into the aquifer where indigenous microbes utilized it to consume the dissolved petroleum compounds at an expedited rate.
The conditions in this type of system are perfect for the proliferation of microbiological activity – good for remediation of the aquifer, but can quickly wreck havoc within system components and well screens to the point of failure. To control biofouling ozone was produced on site and added as a disinfectant to the oxygenated water. However, ozone’s high reactivity meant that it could not be dissolved into the oxygenated water in a single centralized gas/liquid contactor. The ozone simply would have been depleted before traveling all the way through the underground piping system and reaching the well screens.
To overcome this problem, LBG developed a novel method that actually moved the plunging-jet gas/liquid contactor technology from a central location out to the re-injection well, allowing the ozone to retain its disinfection efficacy out to the point of use. Made from “off-the-shelf” plumbing components and “hot tub” spray nozzles, these adapted gas/liquid contactors were so cost-effective that it was financially feasible for them to be installed at each individual injection well.
The innovative remediation system completely eliminated the petroleum plume from the aquifer in less than 27 months–nine months ahead of schedule. The project was completed for a price $30,000 under budget, saving in excess of $200,000 when compared to the next best remedial alternative This technology provides environmental engineers with an effective new remediation tool to bring contaminated sites back into productive use in an effective and cost efficient manner.