Preparing Gilroy for the Plume

It’s just a matter of time before perchlorate invades city water
Gilroy – The Olin Corp. isn’t telling Gilroyans to take it on faith, but the company’s plans to monitor for perchlorate in the city’s water supply fall short of the certainty city leaders want.

“We have said from the very beginning that some system of monitoring that ensures that the water is not moving toward us is very important,” City Administrator Jay Baksa said. “The rub is that Olin doesn’t agree with us [about the best way to do that].”

The city wants Olin to install new so-called sentry wells that would help determine if perchlorate-contaminated water is flowing into town. But Olin counters that the wells are unnecessary because other tests performed on the groundwater basin indicate that Gilroy is safe.

Rick McClure, who heads up the South County perchlorate cleanup for Olin, said initial tests show water from heavily-contaminated Morgan Hill and San Martin is not heading for Gilroy. He said the city is also protected by clean water flowing west down from the Santa Cruz Mountains.

“We are continually evaluating the situation to figure out exactly what direction groundwater is flowing in,” McClure said. “I think there’s probably additional steps that need to be taken, but we’re not there yet. Our motive is the same as Gilroy’s. We want to be assured that the water supply of the city is not impacted by perchlorate.”

Almost no one who has spent the last three years studying South County’s perchlorate contamination believes Gilroy’s water supply is at imminent risk, but there is widespread apprehension that without better information it will be difficult to know if perchlorate does infiltrate the groundwater feeding the city’s eight municipal wells.

And perchlorate has been detected at low concentrations in several wells about a mile east of Highway 101. Tom Mohr, a geologist with the Santa Clara Valley Water District, said existing evidence is not enough to prove that those wells will be the extent of the city’s perchlorate problem.

“One of the problems is that there’s a gap in the area south of Leavesley Road where there are fewer wells and less is known about perchlorate and water levels,” Mohr said. “The perchlorate appears to go around Gilroy and not right into it, but there’s not enough of a basis to draw hard conclusions about flow direction. So many people use Gilroy water it’s important to be very sure about this.”

The city has taken several steps to clean its water supply should perchlorate ultimately be detected in town. It has purchased two patches of land east of 101 where cleaning equipment can be installed should perchlorate be found in the city. Also, the city tests each of its eight supply wells monthly.

“Gilroy is being very vigilant in making sure the public water supply is protected,” Mohr said. “The goal is to prevent [contamination]. It’s now a matter of Olin finding the best way to verify that Gilroy’s wells really are out of harm’s way.”

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