Northrop Grumman has been supplying the data to the Nebraska Department of Environmental Quality on an annual basis. Pumping to mitigate the contamination was performed in conjunction with ongoing groundwater monitoring. "The goal was not only to reduce it [TCE levels] but to halt the movement and spread of it," said Jeff Gwinn, lead consultant for the project with Orion Environmental Inc., an environmental consulting company hired by Northrop Grumman.
Illustrations provided by Northrop Grumman show that in 1997 the plume was approximately 4,800 feet in length and varied from 300 to 850 feet in width. It began at the former TRW facility location and spread southeast reaching past Kelley Creek. By 2001 the data showed that it had been broken into two separate plumes and began retracting from its previous southernly spread.
The smaller plume was approximately 1,500 feet long and no more than 375 feet wide and the larger was approximately 2,300 feet long with a fairly steady width of 750 feet.
The 2002 data represented the first year that TCE levels in excess of 1000 ug/L were not detected in the northern plume near the TRW facility site.
In 2004 Northrop Grumman added a bio-remediation pumping station to the southern plume, just north of the railroad tracks. It was situated in the last remaining "hot spot," which was the only area left that contained TCE levels in excess of 1000 ug/L. The bio-remediation pumping station pumps ground water to the surface, then adds microorganisms that are specifically cultivated, before injecting the amended water back into the ground.
This continual flushing of the water resulted in a successful reduction of the hot spot, so that by 2007 all TCE levels within the two plumes had been reduced to less than 1000 ug/L and the southern plume no longer reached past Kelley Creek.
2010 data for the site shows that the southern plume has continued to decrease and has been reduced to a length of approximately 2,000 feet, with an average width of 500 feet. The northern plume is now approximately 900 feet long with an average width around 350 feet.
In December Northrop Grumman expanded the bio-remediation system just north of the railroad tracks that is operated by Milco Environmental Services Inc., who also performed the December 2010 soil analysis and risk assessment report.
"This is a long term project that Northrop Grumman is committed to for as long as it takes to ensure the aquifer stays stable. We will continue to give the site the same level of attention that it has been given, until the project is complete," said Kurt Batsel, Northrop Grumman project manager for the site.