After weeks of investigating and a multitude of calculations, city officials now know how much water was lost due to a Dec. 22 water tank malfunction.

Public Works Director Mark Watkins said the 5-million-gallon water tank that overflowed in Thousand Oaks lost 700,000 gallons of water.

He said an overflow of a cityowned water tank is very rare, but that’s what happened when electronic, mechanical and hydraulic shutoff, alerts and drainage protections all broke down at once.

It couldn’t have come at a worse time for the Laveau family. Their home was flooded just days before Christmas. The water pushed mud that then covered their yard and the inside of their home in the 2300 block of Rutland Place.

The city is expected to pay for the damage the flooding caused to the Laveaus’ property and to the yards of their neighbors.

The tank, built in 1979, seemed determined to overflow.

Pumps kept working even though they’re set to turn off when the water reaches a certain level. Also, when the water reaches capacity level, an alarm is supposed to electronically alert a member of the public works department with a phone call. The tank’s safeguard system didn’t dial the phone. Another safeguard—an altitude valve that uses a spring trigger to shut down everything when rising water levels are detected—didn’t work.

When all else fails, a drainage system is in place to steer water away from homes.

It clogged.

According to a timeline provided by Watkins, the Laveaus’ heard the water at 11 p.m., called 911 at 11:15 p.m. and had the fire department on the scene and calling public works by 11:30 p.m.

“At first they thought it was a water main that had broken,” Watkins said.

The public works crew member on call took 45 minutes to arrive on the scene. When he determined it wasn’t a water main, he tried to shut off the pumps on the water tank remotely, but the pumps wouldn’t respond.

“(The pumps) should’ve turned off remotely using a laptop,” Watkins said.

The worker had to drive to the pump station and deactivate the pumps manually. He was able to stop the water flow at about 1:30 a.m. He also went to the Sunset Hills water tank and found that although that tank also had a pump malfunction, when the water level went too high, the automatic shut-off system worked, Watkins said.

“The SCADA (supervisory control and data acquisition) was giving false readings,” Watkins said. That’s why the pumps wouldn’t turn off remotely at the Lang Ranch tank.

The maintenance worker did everything he should have done and was in contact that night with his supervisors, Watkins said.

The 700,000 gallons of water lost, much of which went down the drains before they were clogged, is about the same amount as the flow from one or two fire hydrants for two hours, Watkins said.