Perchlorate In the Water Wells In the Area Near Morgan HillMar 7, 2003 | Mercury News Perchlorate, a chemical linked to thyroid disorders that has contaminated the groundwater beneath San Martin, has been detected in two of Morgan Hill's 11 municipal drinking water wells a mile to the north.
Although the contaminant levels were low, city officials shut down the wells as a precaution and will re-test them in a month, Morgan Hill Public Works Director Jim Ashcraft said Wednesday. The city, which gets all of its water from wells, will still have sufficient supplies for its 34,000 residents, he said.
This is the first time perchlorate used in rocket fuel and the manufacture of highway flares has been detected in drinking water north of a broad study area through San Martin where a plume of perchlorate has spread as far as seven miles southeast through the underground aquifer.
Officials of the Santa Clara Valley Water District and other agencies have been testing hundreds of wells in that area for chemical contamination, and residents are getting bottled water for drinking and cooking.
Morgan Hill closed the two wells Feb. 24 after getting initial test results, Ashcraft said. The Nordstrom well at East Dunne and Murphy avenues measured a perchlorate level of 6 parts per billion (ppb), and a nearby well on Condit Road tested at 5 ppb.
Both were slightly above the state Department of Health Services' "action level" of 4 ppb at which the results have to be reported. Most labs cannot reliably detect levels below 4 ppb, water officials say.
Morgan Hill officials took a second sampling of the two wells that turned up no detectable perchlorate, Ashcraft said. "However, the wells remain off line and will be reviewed in one month," he said.
No perchlorate was detected in the city's nine other wells. An additional two wells are out of operation for maintenance.
"At the moment, we have enough well water supply that I do not intend to serve water over 4 ppb as long as I can help it," Ashcraft said. The state health department allows water with perchlorate levels below 40 ppb to be served if the customers are notified.
Ashcraft said public works officials will ask the City Council in two weeks for authority to drill an emergency well should one of the two contaminated wells have to be abandoned.
Perchlorate has been a hot issue in south Santa Clara County since January when it was discovered that contamination had spread four to seven miles southeast in the underground aquifer from its source, a highway safety flare manufacturing plant operated by Olin Corp. from 1955 to 1996 near the intersection of Tennant and Railroad avenues in southern Morgan Hill.
The contamination could affect the drinking water for more than 2,000 people in the San Martin area, where residents are being urged not to drink the water until it's been tested by the water district.
Perchlorate disrupts iodine intake in the thyroid gland, which regulates hormone functions. Some studies suggest it may be a cause of thyroid cancer.
Pregnant women and infants are at highest risk because perchlorate may impair neurological development in fetuses and small children.
The initial area of concern was bounded by Tennant Avenue on the north, Center Avenue on the east, Monterey Highway on the west and Masten Avenue on the south. But tests since then have shown it has spread as far south as Leavesley Road in Gilroy.
As of late February, 959 wells had been sampled in the water district's study area and just beyond its boundaries. Of those, 118 wells had perchlorate concentrations ranging from 4 ppb to 10 ppb, and 11 wells with perchlorate from 10 ppb to 100 ppb.
Olin, the huge ammunition and chemical manufacturer responsible for the contamination, and state officials are testing 340 additional wells in the area between San Martin and Gilroy.