SLO airport didn’t contaminate wells, county study finds

An investigation by San Luis Obispo County into the source of a toxic solvent that has contaminated 13 wells south of San Luis Obispo has concluded that the San Luis Obispo Regional Airport is not the source.

In a report released Wednesday, the Central Coast Regional Water Quality Control Board said that groundwater sampling at five locations on the southwest side of the airport along Buckley Road and more than 100 passive soil-gas samples did not detect the solvent called trichloroethylene, or TCE, on the airport property. Water board staff oversaw the county’s field investigation activities.

The results of the two-month soil-gas investigation were presented in a 118-page report by the Long Beach-based consulting firm Roux Associates, Inc., Soil-gas readings detect TCE by the vapors it gives off. The groundwater investigation results are tentative, with the final report due Oct. 10.

“Based on preliminary results, no TCE was found in groundwater on the airport property which supports the conclusion that the airport is not a source of the TCE contamination in the groundwater wells south and west of Buckley Road,” the report concluded.

About 50 residents of the Buckley Road area have filed claims against the county on the basis that mismanagement of the airport caused their wells to become contaminated. The attorney representing the claimants, John Fiske, was not available Friday to explain what, if any, effects the newly released report will have on the claims.

Testing of wells near the airport began in October 2015, when a well near the Thread Lane industrial area was found to contain concentrations of TCE that exceed the state limit. In all, 67 wells in the area were tested and 13 were found to exceed the state TCE limit of 5 micrograms per liter.

“The current maximum detected concentration of TCE in a private domestic well is 45 micrograms per liter from a well located on Thread Lane,” the water board report stated.

State water officials suspected the airport as the source of the contamination because TCE was used as an aircraft solvent until it was phased out in the 1970s due to its toxicity. County officials disagreed, saying that records searches found no evidence that TCE had ever been used at the airport.

The TCE investigation is ongoing. The next step is to conduct further investigations within the industrial area overlying the TCE groundwater plume along Thread Lane to further delineate the highest concentration area and identify potential sources.

“It is unfortunate that we have not found the source, yet,” said Dean Thomas, an engineering geologist with the water board.

This story was originally published September 30, 2016 at 6:27 PM with the headline "SLO airport didn’t contaminate wells, county study finds."