Suspect water contaminant not a concern at Lake Tahoe
Pregnant women in the Tahoe Basin can drink as much locally produced water as they want with no concern for possible medical complications, despite a California study last week that linked a common contaminant with an increased chance of miscarriages.
That’s the overriding conclusion from a survey of Tahoe Basin water suppliers, which showed that the organic compound is practically absent from the basin’s treated water supply.
In its study, the California Department of Health Services found a connection between high exposures to total trihalomethanes, or TTHM, with spontaneous abortions. Health specialists cautioned pregnant women not to drink more than five glasses of tap water a day if the water contained high levels of the compound, which is formed through the interaction of chlorine and organic matter.
But a survey of Lake Tahoe water providers Thursday showed that no district has found TTHM levels that even come close to the existing standard or tougher, proposed standards.
The reason, say local water suppliers, is the remarkable purity of Lake Tahoe water and groundwater, and the relative absence of organic matter.
“This contaminant is caused by organic material exposed to chlorine, which could be leaves or pine needles,” said John Hassenplug, general manager of the North Tahoe Public Utility District. “If you were taking water out of the Sacramento River, it would have a very high level of organics, but Lake Tahoe doesn’t have a lot of organic material.”
Water providers are required to add small amounts of chlorine to water taken from surface water, which would include water drawn from Lake Tahoe, in order to kill any dangerous microorganisms. While chlorine is not required to treat some groundwater, many districts add small amounts as part of their treatment process.
In the health department study, women exposed to TTHM in excess of 75 parts per billion had a 50-percent-greater chance of spontaneous abortions. The current standard of the U.S. Environmental Protection Agency is 100 ppb, but the standard is scheduled to be lowered to 80 ppb, which may be followed by a further reduction to 40 ppb.
By comparison, the highest actual measurement of TTHM at Lake Tahoe recently was 6.63 ppb, in a water sample from the Kingsbury General Improvement District taken in November.
“The levels are far below the federal limits, and the amount doesn’t vary much,” said Candi Rohr, the district’s general manager.
Four water providers contacted Thursday reported they have found no detectable amounts of the contaminant in their treated water supplies. Those districts are the Tahoe City and North Tahoe public utility districts, the Incline Village General Improvement District and the privately owned Tahoe Keys Water Co.
Of the four, Tahoe Keys does not use chlorine.
Because it relies exclusively on groundwater, the South Tahoe Public Utility District is not required to monitor actual levels of trihalomethanes. Instead, the district has a lab estimate the highest potential levels of TTHM in its water in a process that keeps the chlorine and organic matter in contact for a longer period than is typical in the district’s water treatment plant.
The measure, which describes the potential formation of TTHM, has averaged about 20 ppb, according to district spokesperson Dawn Forsythe. Even that worst-case scenario is safely below existing and proposed health standards.
This week, the South Tahoe district notified South Shore obstetric physicians of the state health study and assured them that South Shore drinking water does not pose a risk to pregnant women.
Dan St. John, director of engineering for Incline Village, said the Incline district studied the potential for the formation of TTHM before building an ozone disinfection plant in 1994.
“We determined that there is an extremely low potential in Lake Tahoe water,” St. John said. “The water here is so pure, the formation potential is low.”
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