New report by Olin Corp. claims chemical unlikely to spread into
Gilroy
San Martin – South County’s perchlorate plume is dissipating and unlikely to expand into Gilroy, according to a new report on the plume issued by the Olin Corp.
Olin is responsible for the 9.5-mile plume that stretches from the company’s former road-flare factory in Morgan Hill through San Martin and east of Gilroy.
In its most recent round of well tests, only 31 of more than 800 wells tested above 6 parts per billion, California’s public health goal for the contaminant known to interfere with thyroid activity. Almost all of those wells were within a mile or two of the factory site.
The report, which is part of the cleanup order issued to Olin last year by the Central Coast Regional Water Quality Control Board, analyzes perchlorate levels in hundreds of wells in 2004 and 2005.
It concludes that the contaminant is falling rapidly enough in most areas to make efforts to contain the plume unnecessary, outside of a small area immediately surrounding the site.
Hector Hernandez, a regional board engineer overseeing cleanup efforts, said his agency agrees with Olin’s characterization of falling perchlorate levels, but will not make a decision on any clean-up or control measures until the company submits a final clean-up proposal later this year.
“We generally agree with this at this point, but we have to wait and see the clean-up plan and what they actually propose,” Hernandez said. “Now that we’re seeing the plume adequately delineated, we’re seeing what the trend is.”
Perchlorate levels have been falling steadily since the contamination was revealed in 2003. More than 1,000 wells were polluted, but the number with concentrations above the public health goal has fallen sharply. The number of wells with levels at or above 6 ppb has dropped from 198 to 31 in the last year or so.
The cause of the drop is unclear. Hernandez said it could be due to rainfall and natural dilution, pumping and clean-up of the earth at the factory site. He said monitoring will be necessary for many years to ensure that levels don’t go back up if there’s a draught or some other change in the groundwater basin.
Why You Should Care
Perchlorate is a salt known to interfere with thyroid activity. It’s the water supply in Morgan Hill and San Martin, but not in Gilroy. A new report from the polluter says a downward trend in perchlorate levels indicates Gilroy is safe from a potentially harmful contamination.
