MORGAN HILL
– The regional board regulating the cleanup of perchlorate from
the Olin site on Tennant Avenue is strongly urging Olin Corp. to
dig up the badly tainted soil and truck it away.
MORGAN HILL – The regional board regulating the cleanup of perchlorate from the Olin site on Tennant Avenue is strongly urging Olin Corp. to dig up the badly tainted soil and truck it away.
However, the Central Coast Regional Water Quality Control Board said in a letter to Olin it is willing to consider a plan the company presented in August to treat the water with an ion exchange system and flush the highly soluble perchlorate out of the contaminated on-site soil with the treated water.
Olin received the letter with the regional board’s comments Friday. 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.”
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 is added to capture groundwater below the surface.
By Oct. 31, Olin is instructed to present the regional board with a study of alternative fixes for the soil, added to the flush method already proposed in the initial design report.
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. The Tennant Avenue site is the source of the groundwater contamination that has spread from Morgan Hill to Gilroy.
Additional monitoring wells should also be installed to the east and west that would notice any sideways movement of perchlorate from the site, the letter said.
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.
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, until it could 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.
Jim Ashcraft, director of Morgan Hill’s 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 a more formal response,” McClure said.
The Perchlorate Community Advisory Group meets tonight from 7 to 9 p.m. at the San Martin Lions Club, 12415 Murphy Ave.
