20% of private water wells contaminated, research shows
Alex Breitler
The Stockton Record
04/27/2009
STOCKTON - One out of five private drinking-water wells in the United States contains at least one contaminant that exceeds public health standards, and wells in the San Joaquin Valley are no exception, according to new research from the U.S. Geological Survey.
Private wells that typically provide water for homes in rural areas are not regulated as strictly as public water systems, leaving the responsibility for clean water to the property owner.
The far-reaching study, which included sampling of 2,100 wells over a period of 13 years, shows that "a large number of people may be unknowingly affected" by contamination, said Matt Larsen, USGS associate director for water.
"Certainly, if you have a private well, ... you should be concerned about the quality of the water from your well, and you should have it tested," added Leslie DeSimone, who headed the study. "Contaminants can occur even if your well is in an area that doesn't seem vulnerable" to pollution.
Most of the contaminants in wells come from natural geologic sources, with the exception of nitrate, a nutrient prevalent in agricultural areas.
Of the 57 Central Valley wells tested, 10.5 percent registered nitrate levels higher than health standards. Exposure to nitrate can cause the blood to transport less oxygen, a dangerous or deadly condition for infants.
Fertilizer, livestock and septic systems all can increase the amount of nitrate found in groundwater.
Laurie Kotulla, assistant director of the county's Environmental Health Department, said local officials are "fairly confident" that water quality in private wells is good. The county issues permits for new wells and well replacements; about 3,500 such permits have been issued since 1993, she said.
In areas where nitrate is known to be a problem, the county requires wells be drilled deeper, Kotulla said. However, there may be decades-old wells that are shallow and as a result have higher levels of contamination.
"Our current ordinance doesn't require private well owners to sample," she said. "We certainly do recommend it."
Mel Lytle, water resources coordinator for the county, said officials hope to fund additional studies to remedy the nitrate problem.
Other common contaminants in the area include trace elements arsenic, boron and uranium, which can pose a range of health issues such as increased risk of cancer, problems with the circulatory system or reproductive and developmental effects.
The study also showed that the Central Valley wells were more likely than other areas to see a mixture of multiple contaminants; these mixtures are sometimes more toxic, according to the USGS research...
At a glance
According to the U.S. Geological Survey on private well water:
• The most common contaminants found at levels above public health thresholds in the Central Valley were nitrate (10.5 percent of wells), arsenic (14 percent), boron (8.8 percent) and uranium (16.7 percent).
• Most contaminants come from natural geologic sources, against which wellhead treatment systems may be ineffective.
• Nationwide, 60 percent of wells had low levels of man-made compounds, such as herbicides, insecticides and solvents, but rarely did these exceed health standards.
• 43 million people rely on about 15 million private wells as their sole source of drinking water; these wells receive less monitoring from government health experts than do public water systems.
For information on how to get your well tested for contaminants, call the San Joaquin County Environmental Health Department at (209) 468-3420. In Calaveras County, call (209) 754-6399.
