Third Well Closed In M.H.Mar 21, 2003 | Mercury News Morgan Hill has shut down a third municipal well after tests found a low level of the chemical perchlorate in its water, officials said Thursday, but contamination dropped below detectable levels in two other city wells that had been shut down in February.
The city is keeping all three wells temporarily closed as a precaution, with further tests for perchlorate a chemical linked to thyroid disorders scheduled next month.
Eight other municipal wells will continue to supply water to the city's 34,000 residents. Officials said there is no water shortage now, but they are concerned about summer when demand is greater.
``We're getting the biggest mixed bag of results you could imagine,'' public works director Jim Ashcraft said of the tests.
On Tuesday night, the Morgan Hill City Council authorized spending $640,000 to drill a new well at Cochrane and Peet roads near Anderson Reservoir to make up for some of the lost water supply.
``That's about as far north as I can get and stay in the city of Morgan Hill,'' Ashcraft said.
Morgan Hill residents are not drinking contaminated water, although all of their supply comes from wells.
Perchlorate contamination has been a hot-button issue in the South County since its presence was disclosed in January. The contamination originated at a former Olin Corp. highway-flare manufacturing plant operated from 1955 to 1995 at the south edge of Morgan Hill.
Over the years, the contamination has spread with the normal flow of groundwater through aquifers at least seven miles to the southeast, contaminating hundreds of private wells that provide drinking water to nearly 2,000 people in San Martin.
Meanwhile, the Santa Clara Valley Water District continues to test drinking water wells in the San Martin area. As of Thursday, the district had results from tests of 782 wells. Of those, 291 or about 37 percent of the wells turned up with detectable perchlorate in the water, officials said.
Of those, 273 had low levels ranging from 4 parts per billion to 9.9 parts per billion. Fourteen wells had levels ranging from 10 to 19.9 parts per billion. Four others had contamination ranging from 20 to 100 parts per billion.
Perchlorate is used in rocket fuel and other explosive products. It disrupts iodine intake in the thyroid gland, which regulates hormone functions. Some studies suggest it may cause thyroid cancer. Pregnant women and infants are at highest risk because perchlorate may impair neurological development in fetuses and small children.
The perchlorate detection in the Morgan Hill wells was the first sign that the contamination moved north or ``upstream'' from its source at Tennant and Railroad avenues. It was discovered in Feb. 24 tests of the city's drinking water wells. Two of them measured perchlorate levels of 5 parts per billion and 6 parts per billion, just above the state Department of Health Services' 4 parts per billion ``action level.'' The two wells were retested Feb. 28 and came up clean, with no measurable levels. And the test results this week also showed no detectable contamination.
The latest tests showed, however, that the third well at Dunne Avenue and Condit Road, previously clean, now had a 4 parts per billion level of perchlorate in its water. But no perchlorate was found in a companion well 30 feet away. ``It's pretty odd,'' Ashcraft said.
The 4 parts per billion level the equivalent of one person in the 280 million population of the United States is also the lowest level that can be reliably detected by most laboratories. However, state regulations allow water with perchlorate levels up to 40 parts per billion to be served.
The city's wells pump water, treated with chlorine at the well head, into a grid of 100 miles of pipelines.
Although the water from all the wells is blended in the system, diluting the contamination to below detectable levels, there's no way to guarantee that some customers won't get perchlorate in their water. So the three wells were taken out of production.
Private consultants and government regulators have said it will take decades and tens of millions of dollars to clean up the contaminated aquifers. Olin Corp., which is responsible for the perchlorate, must pay the cost to treat billions of gallons of water.
Meanwhile, an alternate drinking water source must be found for San Martin residents whose wells are tainted. Olin has provided them bottled water for drinking and cooking.
The Central Coast Regional Water Quality Control Board, the state agency in charge of the cleanup, has given Olin until March 31 to submit a plan to clean up the source site, and later this year Olin will have to devise a plan to clean up the groundwater basin.