Union City sinkhole repairs expected to take until Tuesday

UNION CITY, Calif. (KTVU) - What began Wednesday afternoon as a small depression and sinkhole in the road that slowly filled in with water by Thursday had grown to a 25 foot by 25 foot, ten foot deep gaping maw cutting off the northwest lanes of Alvarado Boulevard  lanes between Fair Ranch and New Haven streets.

The Union City water main failure that caused the sinkhole is turning into a major repair effort even though the reason for the break remains elusive. With this event, we can see what it's critical to keep water mains from failing.

"Our crews were on site; they worked over night.  We were able to restore service using a temporary fix," said the Alameda County Water Agency's Sharene Gonzales.

So far, no one can say for sure exactly what happened 

"The water main break occurred as a result of the sinkhole. The sinkhole, we do not know what the cause is. The only way for us to determine the cause of the sinkhole is to dig deeper, at this point, into the ground." said Union City spokeswoman Lauren Sugayan.

That means the owner of the lower sewer pipeline, the Union Sanitary District, will dig down at least another five feet.

"They will dig down a little bit deeper where their sewage pipes are and that will help us move closer to determining the cause of this sinkhole," added Sugayan.

When you have really large 16-inch water pipes like this one break, all the high pressure water immediately starts turning the dirt into mud and that creates a void. That will cause the roadway to collapse down on it creating a sinkhole.

In short, it is a perfect excavating machine.

"Our main priority right now is securing water service, permanent water service, for our customers. And we expect that later this evening," said Gonzales.

Logic dictates that only one of three things could explain the sinkhole. The 44-year-old water main sprang a leak and caused the sinkhole, the sewer line five-feet below the water main sprang a leak and caused the sinkhole, or the sewer agency improperly compacting of the earth when it installed the sewer line, causing the ground under the pipe to subside causing the pipe to bend downward and break.

Alvarado Boulevard is closed between Fair Ranch Road and New Haven Street but firefighters can still access Alameda County Fire Station 32 at that intersection, though they can only make right turns on to Alvarado.

The traffic disruptions have also complicated matters for parents picking up and dropping off students at nearby Alvarado Middle School. The school's parking lot is closed and parents are being asked to use Fredi Street for drop-offs and pickups, school officials said.

City officials hope to have repairs fully completed and the streets reopened by Tuesday afternoon.