GILROY
– City officials say there are still no signs that potassium
perchlorate contamination spreading southward from Morgan Hill has
entered Gilroy’s water system – although continued testing is
showing positive hits of the chemical popping up ever-closer to the
city and at least one of its municipal
wells.
Officials at the city’s water department said testing performed
Feb. 4 on all eight of Gilroy’s municipal wells did not show
detectable levels of the chemical, which has appeared so far in one
municipal well in Morgan Hill and roughly 111 private wells in the
area between that city and Gilroy.
GILROY – City officials say there are still no signs that potassium perchlorate contamination spreading southward from Morgan Hill has entered Gilroy’s water system – although continued testing is showing positive hits of the chemical popping up ever-closer to the city and at least one of its municipal wells.
Officials at the city’s water department said testing performed Feb. 4 on all eight of Gilroy’s municipal wells did not show detectable levels of the chemical, which has appeared so far in one municipal well in Morgan Hill and roughly 111 private wells in the area between that city and Gilroy.
“All eight (city) wells showed up non-detect, so that’s good news,” said Dan Aldridge, operations services supervisor for the city’s water system on Tuesday.
Tests for perchlorate run last November on city wells also showed “non-detect,” Aldridge said.
However, as tests on non-municipal wells continue and the results trickle in, signs of perchlorate are appearing closer and closer to the city water.
Aldridge said tests at a monitoring well at Leavesley Road east of U.S. 101 showed the presence of perchlorate at 4.1 ppb, just above the “action level” of four ppb where officials must report the findings to the state.
The well – which is not used for drinking or agricultural production – was installed several years ago and is used to test for the gasoline additive MTBE and for nitrates, chemicals that are generally linked to fertilizer use and intensive agriculture.
Aldridge estimated the monitoring well is roughly a quarter mile from the city’s Well No. 5, which sits in the area of Leavesley Road and Murray Avenue and is the one city officials have said they would be most concerned about if the plume proceeds southward.
In late January, officials had estimated the closest signs of the chemical had been 2 3/4 miles away from Well No. 5.
The monitoring well draws water from 350 to 395 feet, according to officials with the Santa Clara Valley Water District. Well No. 5, which is one of the city’s newer and larger wells, ranges between 390 and 840 in depth.
Perchlorates have leached into the underground aquifer – and into many private wells – from a former Olin Corp. plant on Tennant Avenue in Morgan Hill, extending at least seven miles south. Water district and Olin contractors are in the process of testing hundreds of private wells southeast of the old site that they said could be in danger of contamination.
Water district hydrogeologist Tom Mohr said so far data is fairly sketchy on the depth of the private wells that have been tested, since many private well owners don’t have records and many of their wells are relatively old. The district has records for less than a third of the wells it’s testing, he said.
Of those, the majority draw water at 174 to 250 feet below the surface and do not go beyond 400 feet, he said.
Aldridge said the city hopes the chemical plume will miss the city well. Data produced so far seems to suggest it’s moving east, he said.
“The good thing is that the chemical seems to be heading east, and that’s our hope that it continues east,” he said. “The data seems to point to that.”
All of the city’s wells are tied into a centralized distribution and tank system and are rotated weekly. Individual wells may not run at all for certain periods of time but may be pumping heavily at other times, Aldridge said. If perchlorate does appear at Well No. 5, the city will act accordingly, he said.
“That’s where the state comes in and tells us what we need to do, as far as shutting down the well or providing treatment as far as removing the perchlorate,” he said.
In the meanwhile, the city is stepping up its monitoring plans for the chemical, Aldridge said, and plans to test quarterly at a minimum. That frequency could change once better overall data on the plume comes in from the state and Santa Clara Valley Water District investigation.
“Once the data comes in and they get more of a handle on where the plume is, the state could come up with something different,” Aldridge said.
“We’re going to monitor and watch closely so we can keep a close eye on it,” he said of the perchlorate plume. “We want to be on top of it. If the plume reaches any of our wells, we’ll address it accordingly.”
Potassium perchlorate is a byproduct of fusee production, which Olin and Standard Fusee conducted on the site from 1955 to 1996, officials said. It is a naturally occurring salt and is used in flares, matches, solid rocket propellants and fireworks.
The chemical is known to cause thyroid problems. County health officials have said the developing fetus and infants are most susceptible. Drinking bottled water is recommended for all pregnant women and small children.
