Company says groundwater contamination is now cut-off at the
source
Morgan Hill – Olin Corporation has completed a multi-million dollar soil remediation project at its Tennant Avenue plant one year ahead of schedule.
The news suggests the industrial byproduct perchlorate is no longer leaching into South County aquifers.
Despite the promising information, which came by way of an Olin press release, officials from the California Water Quality Control Board were guarded in their response on Monday.
“In general, it’s good news,” said water board engineer Hector Hernandez. “Cutting-off the source of contamination is a major accomplishment in any groundwater cleanup effort. However, since we have not completed our review of the report and a formal response has not been prepared, we may not provide any further comment at this time.”
Water board officials anticipate a formal response to Olin’s on-site cleanup report will be completed within the next couple of weeks. Officials are also in the midst of reviewing a massive cleanup feasibility report submitted by Olin in June that proposes a passive monitoring approach to South County wells for the next two decades.
Geologist Tom Mohr of the Santa Clara Valley Water District said figuring out where the existing perchlorate plume has gone remains a difficult challenge in the years ahead.
Olin Project Manager Rick McClure said the on-site cleanup went faster than anyone expected. Warm weather created favorable conditions for a process known as bioremediation to take effect, allowing hungry microorganisms in the soil multiply quickly and break down perchlorate on their own accord.
The process works by stimulating naturally occurring microorganisms by feeding them common foods such as citric acid and acetate. The invisible bacteria army then grows and effectively wipes out the unwanted perchlorate, a type of salt that can cause health problems in humans if consumed at high enough levels. The helpful microorganisms themselves pose no threat the water supply.
Hernandez said the goal of cleaning up the ground around the defunct factory was to reach a level of perchlorate in the soil that is protective of underlying groundwater. This is, to ensure rain drops sinking into the ground at the factory won’t pull more perchlorate into the water table.
The state’s public health goal for safe perchlorate levels in drinking water is 6 parts per billion or less. To ensure that goal is met, water board officials told Olin in 2004 to lower soil concentrations at the old plant to 0.05 milligrams per kilogram. If a perchlorate concentration in soil at 0.05 mg/kg were to leach to underlying groundwater, the 6 ppb state health goal would not be exceeded, Hernandez said.
Florida-based engineering firm GeoSyntec implemented the on-site plan for Olin. Phase one involved excavating 1,000 cubic yards of soil. Phase two involved treatment of the remaining 40,000 cubic yards of soil at the site containing perchlorate.
Engineers pumped groundwater to the surface, treated it with citric acid and allowed it to percolate back into the dirt.
“It’s a closed-loop process,” McClure said, adding that GeoSyntec recently won an award in Georgia for its efficiency.
Tony Burchyns covers Morgan Hill for The Times. Reach him at (408) 779-4106 ext. 201 or tb*******@mo*************.com.
