California water officials are working to determine the source of an industrial solvent that has contaminated five wells in southern San Luis Obispo.
Recent tests of five of 11 domestic wells in the area of Buckley Road, east of Davenport Creek and Evans roads, showed levels of trichloroethene, or TCE, that exceed the state’s allowable limit of 5 micrograms per liter of water.
Levels of the contaminant in the five wells ranged from 45 micrograms at a residence on Thread Lane to 5.5 micrograms at a residence on Angie Lou Lane, according to records at the San Luis Obispo County Department of Environmental Health Services.
“Some of those are not huge exceedances, but they are above the maximum contaminant level and we need to find the source,” said Thea Tryon, enforcement coordinator with the Central Coast Regional Water Quality Control Board.
The five wells that exceeded state limits are located at four residences and one business, Dolphin Shirt Co., at 757 Buckley Road. County staff sent letters to the affected residents Dec. 17 and issued a public health alert on Christmas Eve.
County health officials are recommending that residents with contaminated wells use bottled water for drinking and cooking. They are also recommending that they install carbon filtration systems on their wells, which effectively remove the contaminant.
Searching for a possible source, the agency investigated three industrial properties in the immediate area surrounding the contaminated wells, but the agency did not find evidence indicating any of the sites as the source, Tryon said. The agency has now shifted its attention to the nearby San Luis Obispo County Regional Airport.
Water officials are investigating the airport as a possible source because the southern portions of the airport are up-gradient from the contaminated wells, meaning that pollutants could flow down from the airport to the impacted wells.
“TCE is known to have been used for airplane parts washing up to the 1970s when it was phased out of use because of its toxicity,” the control board wrote in a letter to airport officials. “In addition, a common practice, especially with the military, was to spray wash airplanes with TCE, often allowing the waste to discharge to the ground.”
State water officials have requested information about past use of TCE at the airport, as well as other information, and they have given Kevin Bumen, the airport’s manager, until Jan. 20 to respond.
TCE is a colorless, volatile, nonflammable liquid that has a sweet solvent or chloroformlike odor, county health officials said. However, odor is not a reliable method for detecting TCE in drinking water, because people cannot smell the contaminant at levels near the state limit.
Long-term exposure to TCE can cause liver or kidney damage and may pose an increased risk of cancer.
TCE was historically used as an industrial solvent and metal degreaser. It was also used in the production of textiles, dry cleaning, food processing, and as a general anesthetic through the ’70s. Its use as a metal degreaser began to decline in the ’70s in favor of less toxic alternatives.
TCE poses a groundwater threat throughout the nation, county health officials said. Drought conditions, groundwater level declines and reduced aquifer recharge from creeks may be exacerbating the problem.
In October, a resident near Buckley Road reported an odor from his well water, Tryon said. County staff tested the well and found elevated levels of TCE. More wells were tested and four were found to also have TCE levels that exceed state limits.
“We are currently working on sampling more domestic wells to determine if TCE is present in their wells in the surrounding area,” Tryon said. “We are also continuing to work toward finding the source of the TCE.”
State water officials are planning to hold a public meeting in early January to provide additional information.