By Ann McCreary
A faulty valve on a Twisp water storage tank resulted in a large volume of municipal water lost last month.
The leak was discovered in a reservoir on the Lloyd industrial property, one of three tanks that store Twisp’s municipal water. By the time it was located, “a staggering 19 acre-feet” of water had flowed out of the tank and subsequently recharged back into the aquifer, said Howard Moss, public works superintendent.
An acre-foot equals 325,851 gallons, so the total amount of water that escaped the tank is about 6,191,177 gallons.
The reservoir was improperly designed and was built about four feet lower in elevation than the other two reservoirs, which are located on the bench above town known as School Hall Hill, Moss said. Water pumped to the reservoirs would fill the tank on the east side of the Methow River more quickly than the others.
To deal with the initial design flaw, an underground altitude valve was installed to control the tank from overflowing. There was no telemetry designed to warn if the valve failed, Moss said.
Without the valve to prevent the tank from overfilling, water spilled from it into a large underground drywell located nearby.
Public Works officials noticed higher-than-normal municipal water use in March, and began looking for potential leaks.
“I suspect the valve began to fail in March and completely failed around the first of May,” Moss said in a report to the Town Council.
“I have implemented an inspection program in order to prevent it from occurring in the future,” Moss said.
Since Moss became the public works superintendent in 2010, the department has made numerous repairs to the town’s aging water system, including locating and fixing two large underground leaks in 2011 that amounted to a loss of about 60 acre-feet a year.
The water system improvements have allowed Twisp to dramatically reduce its municipal water use in the past two years and stay within its state allocation of water.