Olin Corp. received an official response Friday to its Initial
Design Proposal on cleaning perchlorate from the Olin site on
Tennant Avenue, source of groundwater contamination from Morgan
Hill to north Gilroy, and from groundwater underneath.
Olin Corp. received an official response Friday to its Initial Design Proposal on cleaning perchlorate from the Olin site on Tennant Avenue, source of groundwater contamination from Morgan Hill to north Gilroy, and from groundwater underneath.
Olin had presented the proposal to the Central Coast Regional Water Quality Control Board – the agency regulating the situation – in August, proposing a two-pronged effort that would treat the water with an ion exchange system and flush the highly soluble perchlorate out of contaminated on-site soil with the treated water.
Rick McClure, Olin’s project manager for the South Valley cleanup, received the letter Monday at his office in Tennessee.
“It is what we expected,” McClure said. “It’s mostly technical issues that will be addressed; there’s nothing that can’t be overcome.”
At its quarterly meeting on Sept. 12, the Regional Board staff suggested and the board agreed, that digging up the badly tainted soil and trucking it away would be a quicker and more efficient way of eliminating the problem than trying to flush it out. The Sept. 19 letter to Olin asks the company to consider this strongly.
By Oct. 31, Olin is instructed to present the Regional Board with a study of alternative fixes for the soil, added to that already proposed in initial design report.
By Oct. 24, the letter said the board wants “a report documenting the installation and hydraulic testing of wells for an interim on-site groundwater extraction and treatment system.” The system originally proposed is acceptable to the board as long as a shallow well screen is lengthened or a third well added to capture groundwater below the surface.
By Dec. 31, Olin will produce a report on starting up the interim on-site groundwater extraction and treatment system.
The process developed in the initial proposal – extract groundwater from two wells, treat it on-site and apply the rest to the surface to clean the soil by filtering down – is welcomed by the board and “should proceed without delay,” the letter said, independent from board approval of the soil remediation process.
The board would prefer, the letter said, for some treated water to be disposed of elsewhere and only some reapplied to the soil. The board also would prefer more monitoring wells to be installed along the southern edge of the site – Tennant Avenue – screened in several zones down to bedrock, which is about 400 feet below the surface in that area. Groundwater at the site, the board’s letter said, begins about seven feet below the surface.
Additional monitoring wells should also be installed to the east and west that would notice any sideways movement of perchlorate from the site.
As to soil remediation, since Olin proposed only one method – the filtering – the board said it cannot decide whether this is the best method without hearing of others.
“Soil flushing at a site with identified clay layers in the vadose zone (the Tennant situation) presents a very real risk of spreading contamination into previously non-impacted soil,” the letter said, “and there is a risk that perchlorate flushed into groundwater may not be captured by the proposed groundwater extraction wells.”
The board said it would prefer to see a ranking of technical and cost elements in the remedial alternatives. It would like Olin “to seriously consider” excavating soil with the highest concentration of perchlorate, above 500 mg/kg, and remove it from the site to avoid further threatening the groundwater.
The soil could be stored safely on site, the letter said, waiting to be treated by some future bioremediation method. Or it could be trucked off-site to a landfill. Once the worst soil leaves the area, the board would consider Olin’s proposed leaching/filtering method to be appropriate.
Some other possible methods of treating perchlorate-contaminated soil:
• Contaminated soil can be treated in bioreactors, with aerobic microorganisms (bacteria that must have an oxygen source). The soil is scooped up, mixed with clean soil and bacteria and replaced, allowing the bacteria to eat the perchlorate.
• Phytoremediation uses a natural plant process and aerobic microorganisms to remove and/or degrade the contaminants in soil and in water.
Jim Ashcraft, director of public works, read the report late Monday and said he was satisfied with the Regional Board’s action.
“I am obviously pleased that the board is doing what the cities of Morgan Hill and Gilroy and the Santa Clara Valley Water District recommended,” Ashcraft said, “since they followed our comments and put in some of their own.”
Ashcraft said the soil-flushing idea, while technically sound, is fraught with potential problems.
“Olin will probably have more a formal response,” McClure said.
The Perchlorate Community Advisory Group meets Thursday, Sept. 25, 7-9 p.m. at the San Martin Lions Club, 12415 Murphy Ave., behind the airport. Details: 683-2667. Perchlorate information: www.smneighbor.org; SCVWD, www.valleywater.org or 888-HEY-NOAH• RWQCB: www.swrcb.ca.gov/rwqcb3/
