MORGAN HILL
– Olin Corp. sent its plans for removing perchlorate from soil
on its former Tennant Avenue site to the California Regional Water
Quality Control Board on Friday.
MORGAN HILL – Olin Corp. sent its plans for removing perchlorate from soil on its former Tennant Avenue site to the California Regional Water Quality Control Board on Friday. According to a Tuesday afternoon press release from Olin, the company studied several soil treatment methods, checking them against U.S. Environmental Protection Agency criteria, and decided that bioremediation will defuse perchlorate more quickly than other methods.
The regional board must review and approve the plans before Olin can begin the soil remediation process.
The soil treatment plan is part two of the Regional Board’s order to repair the damage caused by perchlorate leaching from Olin’s former road flare plant into the groundwater. The board approved Olin’s plans for containing the chemical and treating contaminated water on the site on Oct. 28.
Bioremediation introduces naturally occurring bacteria to water that then filters down through the contaminated soil. The bacteria essentially “eats” or degrades the perchlorate into harmless chloride and oxygen.
“Perchlorate biodegradation is a proven perchlorate treatment technology that is being implemented at other sites in California and our background testing shows that it can be successfully applied to this site,” said Rick McClure, Olin’s project manager for the Tennant Avenue site. “After about two years of continuous operation of this treatment technology, the desired soil remediation objective will be achieved. This method scored with the highest of all soil remediation options.”
The plans include an ion exchange method groundwater containment and treatment system being installed at the Tennant Avenue site is scheduled to begin working by year’s end. It will capture and treat all on-site groundwater and will operate before, during and after the implementation of the soil remediation.
The Central Coast Regional board, based in San Luis Obispo, also received Olin’s quarterly groundwater monitoring report last week. That analyzed the amounts of perchlorate in the shallow, intermediate and deep flow groundwater areas on and off the company’s property.
Tuesday’s press release said the report showed that the highest concentrations of perchlorate in groundwater are beneath the company’s property, with concentrations decreasing significantly downgradient from the site. Samples for the monitoring program were collected from 273 offsite wells; tests showed that perchlorate concentrations in most wells were lower during the third quarter than during the second quarter of 2003.
Part of Olin’s charge from the Regional Board is to discover where perchlorate occurs within the complex aquifer system.
Another recent development provided some hope for the City of Morgan Hill, which has shut down several wells northeast of the Olin site because detectable (4 parts per billion and above) levels of perchlorate were found. Olin had previously disclaimed responsibility for the perchlorate’s appearance since water in the area is considered to flow south/southeast.
Late testing showed that some of Olin’s perchlorate may have indeed ended up in Morgan Hill city wells.
“These data represented a departure from previous information on local groundwater flow,” McClure said. “We will need to further evaluate these localized anomalies to determine possible causes which could include the geologic variability of the aquifer zones, unique monitoring well construction methods, seasonal variation, and/or potential impacts of pumping by other wells very near the site.”
Hundreds of private and municipal wells from Morgan Hill, through San Martin to north Gilroy have been affected by perchlorate.
