More Wells Tainted With PerchlorateAug 15, 2003 | The Dispatch Five Gilroy wells between Leavesley and Gilman roads east of U.S. 101 have tested positive for the toxic chemical perchlorate.
Now, of the nearly 450 contaminated wells between Tennant Avenue in Morgan Hill and north Gilroy, six are located south of Leavesley Road, bringing the garlic town more deeply into the perchlorate mix. In June, a perchlorate test on a private well at Holsclaw Road south of Gilman Road showed a 4.7 parts per billion (ppb) contamination level.
The level at which the state requires water users to be warned about the contaminant is 4 ppb. The five most recent detections ranged from 4 ppb to 6.4 ppb.
Officials downplayed the significance of the news, saying the new set of tainted water sources does not imply the perchlorate plume is heading farther south, as it was feared in June when the Holsclaw Road well tested positive. All of the wells testing positive in this latest round of monitoring were north of the Holsclaw Road well.
“This merely indicates the plume is there, but not that it is moving,” said Santa Clara Valley Water District spokesperson Mike DiMarco. “The plume has been there all along, now we’ve just discovered it. This is not a cause for alarm.”
So far, the perchlorate plume stretches 9.2 miles with detections ranging from around 4 ppb to 100 ppb. Olin’s most recent monitoring tested up to 161 wells. Roughly 14 wells tested were south of Leavesley Road.
Roughly 1,200 wells between Morgan Hill and north Gilroy now have been tested for perchlorate.
County and regional water officials confirmed the latest contamination data Wednesday in Palo Alto at a perchlorate seminar for lawyers. Olin Corp., the company responsible for the Morgan Hill contamination, and the Santa Clara Valley Water District have not formally released the latest test data, so some details are sketchy.
Sources for this story did not release contamination levels for each well, nor did they release which streets had contaminated wells.
What is known is that none of the contaminated wells are Gilroy city water sources. City water operations supervisor Dan Aldridge this week said tests done on the eight city wells in July came back negative earlier this month. Results from August’s testings have not been returned from the lab.
In April, a Gilroy city monitoring well on Leavesley tested positive for perchlorate in the 4 to 10 ppb range. The monitoring well is not used for drinking water.
“All of the new detections are from wells that are located farther (away) from Gilroy’s municipal wells (than the monitoring well),” a press release issued by the City of Gilroy stated.
Olin Corp. will still have to test wells another one to two miles south of the southernmost contaminated well.
“Olin understands our directive well, which is to find the extent of the plume and for the tests to extend as far south as they need to,” said Harvey Packard, a senior groundwater resources engineer with the Regional Water Quality Control Board.
Packard’s agency is overseeing Olin’s perchlorate investigation.
Perchlorate is used in the manufacture of rocket fuel, flares and fertilizer. Its health risk is still unclear, and jockeying for regulation standards at the state and federal levels is under way. At some exposure levels, perchlorate is known to cause thyroid problems and tumors in humans.
It is not known for certain the levels at which exposure becomes a danger. At the Wednesday seminar, state water toxicologist Robert Howd said a 2002 study revealed that thyroids in humans have trouble uptaking iodide when a mere dosage of .0068 milligrams per kilogram of body weight enters one’s diet. That means a 150-pound person would have trouble uptaking iodide with a total dosage of 2.25 milligrams.
The warning level for perchlorate was lowered in 2002 by the state from 18 ppb to 4 ppb.
On Aug. 7, Santa Clara County’s perchlorate problem focused north. An explosion demolished a building last week at a United Technologies Corp. facility in San Jose causing a 10-acre grass fire.
United Technologies is an aerospace and manufacturing conglomerate that uses perchlorate in its rocket fuel, so there was concern the chemical may have seeped into the groundwater basin around Anderson Reservoir as firefighting efforts doused the flames.
“The conventional wisdom is that it all burned up, but we say ‘prove it,’ ” said Thomas Mohr, an engineering geologist for the water district.
Anderson Reservoir is the district’s largest drinking water supply. So far, tests for perchlorate have come up clean, but further monitoring is ongoing, Mohr said.