In Simi Valley, California, workers venting a 10,000-gallon underground fuel tank caused a leak at the city’s Public Works Fueling Station that threatened the Arroyo Simi, the principal aquifer for the area. Eventually, the plume was controlled by a combination of oxygen and contaminant-devouring microbes and a four-way partnership that included the city, a private environmental consulting firm, researchers at Western Research Institute (WRI), and the U.S. Department of Energy.
In April 2009, the city recognized Western Research Institute with a commendation for the groundwater cleanup, specifically for remediating the gasoline additive MTBE. “Not many people know the details of remediation work,” says Ron Linton, Source Control Program Coordinator for the city of Simi Valley. “Those who can solve these problems by introducing new technologies are the unsung heroes.”
In California and elsewhere, MTBE has contributed significantly to cleaner air by reducing emissions from vehicle exhaust. Methyl tertiary butyl ether (MTBE) is an oxygenate that helps fuels burn more completely, but when it leaches into groundwater, as it did in Simi Valley in 1992, it poses a serious threat. And it is tough to clean up.
At WRI in Laramie, Wyoming, scientists Song Jin and Paul Fallgren optimized a chemical oxidation technique for mitigating petroleum contaminants such as MTBE in groundwater and soil. They needed a field site to confirm their bench-scale results. In Simi Valley, Linton realized that previous remediation efforts were not working. He needed a better cleanup technology. Jin and Linton met during an Association for Environmental Health and Sciences Conference in San Diego, California, in 2005 and made the match.
WRI recommended in-situ chemical oxidation (ISCO), in which chemical oxidants are introduced in place to reduce the mass, mobility, and toxicity of the contaminants. The increased oxygen promotes naturally occurring microbes that consume the MTBE. In 2005, the city of Simi Valley’s consultant, Tetra Tech of Pasadena, California, began implementing the two-part remediation approach designed by WRI. Further support came from the U.S. Department of Energy’s jointly sponsored research program with WRI.
At the source of the plume, Fenton’s reagent (hydrogen peroxide activated by iron) was added to break down MTBE, add oxygen, balance pH, and stimulate microbial growth. Down gradient from the plume core, a trailer was set up with an oxygen generation system that produces 70% to 90% pure oxygen, which is pumped into the groundwater through ten injection wells. This “curtain” of oxygen forms a barrier to contain and treat the groundwater contamination and prevent off-site migration.
“When we began,” says Linton, the MTBE was at 5,000 parts per billion at the source. Now we’re at or below 150 parts per billion.” The microbes are beating out (or eating up) the MTBE.
Says Linton, “WRI brought the research and technical know-how we needed. They were absolutely invaluable.” Linton reports that the chemical oxidation approach has already been applied elsewhere in Ventura County. “It has been one of those small steps toward a better way,” he concludes.
|Simi Valley At A Glance (from the city’s web site)|
The city of Simi Valley, with an estimated population of 126,291 (as of February 2009), is the third largest of Ventura County’s ten cities. Occupying an area of approximately 42 square miles, it is located in southeast Ventura County, adjacent to the northwestern perimeter of the San Fernando Valley, approximately 37 miles northwest of downtown Los Angeles.