Well Tests Expand Near San Martin
WATER MAY HAVE TRACES OF CHEMICAL PERCHLORATEFeb 23, 2003 | Mercury News
Water officials are significantly expanding a program to test San Martin drinking water wells for a chemical used in rocket fuel after concluding that a plume of contamination has spread much farther than suspected through the semi-rural area's groundwater.
The Santa Clara Valley Water District and Olin Corp. have tested more than 900 drinking water wells in a four-mile-long area of San Martin and found traces of perchlorate in 40 percent of those for which it has verified results. That test area has now been extended two miles farther south.
Olin, the huge ammunition and chemical manufacturer responsible for the contamination, and state officials plan to test 340 additional wells in the area between San Martin and Gilroy.
Perchlorate has spread in an underground plume stretching as far as seven miles from its source a former highway flare manufacturing plant on the southern outskirts of Morgan Hill. The chemical, known to cause thyroid illnesses, could be tainting the drinking-water supplies for more than 2,000 people. Residents are being urged not to drink the water until tests show it is not contaminated.
Perchlorate is a salt primarily used as an oxidizer for rocket fuel, highway safety flares, matches, fireworks and other products.
The chemical 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 the highest risk because perchlorate could impair neurological development in fetuses and small children.
Olin and its technical consultants analyzed the groundwater flow, geology and hydrology of the aquifers beneath San Martin and developed a plan to test 340 more wells, said Harvey Packard, senior resources engineer with the Central Coast Regional Water Quality Control Board, the state agency in charge of the investigation.
The water district initially tested wells in an area bounded by Tennant Avenue on the north, Center Avenue on the east, Monterey Highway on the west and Masten Avenue on the south. However, some well tests done by others outside those boundaries also showed perchlorate contamination. So Olin and the regional board expanded the testing program.
Most of the additional wells to be tested are between Masten and Leavesley avenues, south of the original area, Packard said. Some wells east of Center Avenue and some west of Monterey Highway near San Martin Avenue also will be tested.
Packard said Olin notified the registered owners of those wells, asking them to contact the company to arrange for free tests of their wells and to receive bottled water until their wells show no perchlorate detections.
``The program will start as soon as someone calls,'' Packard said. Olin estimates it will finish sampling in the expanded area by the end of March, with all of the test results known by late April.
Once officials determine the size of the contamination, they can develop a plan to clean it up, an extremely costly process that will probably take decades.
So far, 959 wells have been sampled in the water district's study area and just beyond its boundaries. The district has received verified results on 317 wells. Of those, 188 had no perchlorate or concentrations of less than 4 parts per billion (ppb), district spokesman Mike Di Marco said. There were 118 wells with concentrations ranging from 4 ppb to 10 ppb, and 11 wells with perchlorate from 10 ppb to 100 ppb.
There are no enforceable federal or state safe drinking-water standards or maximum allowable contaminant levels for perchlorate, although both the U.S. Environmental Protection Agency and the state are working toward establishing standards.
The state Department of Health Services considers 4 ppb as the level at which action must be taken to resolve a problem. That's also the lowest limit of detection for most laboratories.
State Sen. Byron Sher, D-San Jose, has written a bill requiring the state to adopt a standard by Jan. 1. The U.S. EPA has set a provisional level of 1 ppb as the level the agency considers safe to consume each day.
Scientists have been able to detect perchlorate levels below 400 ppb only since 1997.
Di Marco said 4 ppb is the lowest detectable level at which scientists are confident they have accurate results.
``When you get below that, there's a lack of confidence in whatever numbers you have,'' he said. ``The technology we employ has trouble reading below 4 ppb.''
Most laboratories can't reliably identify perchlorate concentrations below 4 ppb, agreed Packard, of the regional board.
``They may be able to say there's something out there, but it's less than four,'' he said. ``Or they might say we're certain it isn't greater than four.''