January 11, 2010
6:00 - 7:30 pm
State Technical Community College
10915 Hardin Valley Road, Knoxville
J.L. Goins Administration Building, Cafeteria Annex
Use of Water Pillows for the Production of Anaerobic Water
During an In-Situ Groundwater Injection
Robert E. Mayer, Jr.
Shaw Environmental & Infrastructure, Inc.
Trichloroethene (TCE) has become a common contaminant in groundwater due to its abundant use as a cleaning solvent, degreaser, and in the dry cleaning chemical. At Spill Site #32 (SS-32), on Columbus Air Force Base (CAFB) in Columbus, Mississippi, TCE is the primary groundwater chemical of concern. The SS-32 site encloses a groundwater plume that is approximately ½ mile wide by 1 mile long. Much of the site lies along an active training runway.
Natural attenuation of TCE at SS-32 was determined to be nutrient limited; therefore, in-situ enhanced bioremediation using emulsified vegetable oil, sodium lactate and Shaw&rsquos dechlorinating consortium SDC-9 was performed. However, working along the runway posed special challenges. The first challenge was to create and store enough anaerobic injection mixture for a 442 point DPT injection, and the second was to reduce the height of equipment staged near the edge of a runway. To address these challenges, large water pillows were determined to be the most viable solution. Previous in-situ projects utilized large, rigid holding tanks for preparing and storing an anaerobic mixture for sub-surface injections. The rigid tanks had an air to water interface and required an inert gas to help purge the oxygen from the aqueous mixture. The use of water pillows eliminated the air to water interface and enabled microbial populations to create an anaerobic system more efficiently without an influx of ambient air; much like microcosms used in a lab. A system of four 6,000-gallon water pillows was used. Approximately 12,000 gallons of anaerobic water were produced every twenty-four hours without the use of an oxygen scrubber.
At CAFB, equipment that needed to be staged near the runway had to be less than fifteen feet high. Many rigid holding tanks of sufficient size would have been near the maximum height limit and would have required flashing lights for visibility during night flying. The water pillows were three feet tall when completely filled. Their low height was favored by CAFB flight operations staff and also removed the need for lighting. Also, due to faster production of anaerobic water, the time required to be in the field was reduced from 40 to 28 days. The shorter field duration reduced project costs and potential impacts to flight operations.
To assess the progress of the in-situ injection, chlorinated ethenes, anions, metabolic acids, Dehalococcides sp., and field parameters were analyzed. Degradation rates and estimated clean-up times for TCE to reach the federal maximum contamination level were calculated. The results indicate that use of water pillows for production and storage of anaerobic solution for in-situ injection is an effective approach. The innovative use of water pillows enabled anaerobic water to be produced more efficiently, surpassed the equipment requirements for working near active runways, and reduced overall project costs.
Page updated January 11, 2010