Just four years after opening the 15 million gallon peaking storage tank off 96th Street, the city of Bonney Lake is preparing to send divers in to inspect the tank, which appears to be losing water at a faster-than-expected rate.

“It’s leaking more than a standard concrete tank should,” Public Works Director Dan Grigsby said Wednesday.

The $6 million tank was opened in Oct. 2007 and is designed to hold water for times when the draw on the city’s water system is more than the wells can produce, which Grigsby said happens approximately three weekends per year in the summer.

Unlike the city’s four other storage tanks, the peaking storage tank is constructed of concrete, so some leakage was expected.

“In any concrete tank, unlike a steel tank, water percolates through the concrete,” Grigsby said.

But Grigsby said the amount of water seeping through the tank appears to be more than expected and divers will go into the tank and inspect the structure’s 60,000-square-foot footprint and the seals between the concrete sections.

Grigsby said after cleaning the tank, the divers would squirt a dye into the water and follow it to see where there are leaks.

“It’s more than normal, but is it more than is acceptable?” he said of the water loss. “That’s the question we have to figure out.”

If leaks are found, the next step will be to decide what – if anything – can be done.

“The question is how much can we fix this problem?” he said. “But first we have to figure out what the problem is.

Grigsby said the usual warranty on a public works project is one year, meaning any repairs are on the city’s dime. But if flaws are found in either the design or the construction, the companies responsible may still be liable.

The issue surfaced during Tuesday’s city council meeting as the councilmembers discussed a contract to inspect the city’s water storage facilities.

Grigsby said a finding from state health inspectors regarding the time since the tanks had been inspected prompted the city to put out a request for bids to inspect and clean the tanks.

The state recommends water tanks be cleaned every five years. According to Grigsby, only two of the city’s tanks presently meet that standard.

The contract approved Tuesday will cost the city $18,455. The money will come from the $35,000 water fund budget.

The contract passed 4-2 with Councilmembers Laurie Carter and Dan Swatman opposed and Councilmember Dan Decker abstaining.