A select group of residents in Oak Harbor and Island County received a surprise in their mailboxes this week.

But they didn’t receive an unexpected tax refund.

Instead, they opened letters notifying them that 1,4-dioxane, a chemical solvent that the EPA “reasonably anticipates” will cause cancer, may be in their water. The letters request private well owners’ permission to test the wells for 1,4-dioxane levels.

Island County health department staff and environmental staff at Whidbey Island Naval Air Station, the source of the chemical, won’t know if the 1,4 dioxane is in private wells until after a couple of months of testing.

“We’re trying to determine where the dioxane’s gone and how far it’s gone,” John Mosher, Naval Air Station Whidbey Island environmental protection specialist, said Wednesday.

In November 2004, 1,4-dioxane levels were found in wells at the southern edge of Navy property and in wells at the adjacent, now closed, city landfill. The site, known as Area 6, holds the now-capped landfill, and is a Superfund site. Full extent of contamination has not been determined.

People who are connected to city water have nothing to worry about, Mosher said. And wells in the area may not contain dioxane at all. No safe levels have been established for dioxane in drinking water, but several states have set levels between 50 to 85 parts per billion.

The highest detection of 1,4-dioxane in monitoring wells found on Navy property is 14 ppb. At the edge of the property, the level is closer to 7 ppb.

Mosher said no one knows how much dioxane may be in Whidbey Island’s shallow aquifer. Only recently have tests been developed to measure 1,4-dioxane levels.

Marie Piper, Island County environmental health specialist, said state records show six wells in the test area, which includes land across Highway 20 in a rough triangle between NE 16th Avenue and Torpedo Road. Piper said 70 people may be using the wells.

And “may” is a key word. Most people in the test zone use city water. And at least two wells are for non-residential use.

If early tests show any possible health risks, people using private wells will immediately be connected to city water lines at Navy expense, Mosher said.

“We’re paying for past practices,” Mosher said.

Those past practices included pouring chemicals into the ground. From the late-1960s to the mid-1980s, dumping chemicals into below ground pits was an accepted method of waste disposal. From these pits, chemicals have seeped into the shallow water aquifer, Mosher said. That aquifer level ranges from 65 to 80 feet below the surface, he said.

Water from the site is cleaned using a pump-and-treat system. Groundwater is pumped from wells along the landfill’s boundaries and chemicals are removed in an evaporation process. Treated water is discharged to seep back into the ground.

The dioxane was a component of other chemicals that were dumped in oil and acid pits at a site in Area 6, the old Navy landfill.

Dioxane doesn’t stick to soil particles, so it travels faster than other chemicals.

Mosher said tests at wells at the southern edge of the Navy’s property show the dioxane has moved off the site. But no one knows how far the chemical may have traveled.

Piper said they would like to test as many wells as possible, including ones that have been unused for years.

“More data is better data,” she said.

Mosher and Piper said they will call residents who received letters get the testing process started.

Anyone who lives in the area of east of Highway 20, between NE 16th Avenue Torpedo Road and has questions about their water’s safety are asked to call Piper at 679-7350 or e-mail MarieP@co.island.wa.us.

The Navy no longer dumps chemicals or other hazardous materials on Whidbey Island. Everything classified as hazardous waste is sent to a certified facility for proper disposal.