Old irrigation pipe under freeway cause of Interstate 5 sinkhole

A deteriorating abandoned irrigation pipe below the pavement of Interstate 5 is being blamed for a sinkhole that has detoured motorists near Tracy this week.

While the cause of the sinkhole has been discovered, fixing the problem means the detour will remain in place on northbound lanes until 5 p.m. Friday and until 8 p.m. Saturday for southbound lanes.

The sinkhole was discovered about 7 a.m. Tuesday when a crew doing routine maintenance noticed a small sinkhole that was about a foot wide and 10 feet deep on the shoulder of the roadway.

A maintenance supervisor closed the northbound lanes for safety. A 6-mile detour was set up, taking northbound motorists to eastbound Highway 132, then to Highway 33 and then back onto northbound I-5.

“The traffic handled it pretty well once people got used to it,” said Greg Lawson, Caltrans public information officer.

Crews began to dig on the northbound side of the freeway and shortly discovered that the 40-year-old underground pipe was the problem. On Wednesday afternoon, they found the 36-inch pipe about 35 feet below ground.

“We were able to determine that there was a hole in the top of the irrigation pipe and soil started to seep through over the years, causing the roadway to give way a little bit,” said Lawson.

Crews dug out the pipe on the north side and then decided to close the southbound lanes about 7 p.m. Wednesday to determine if that side should also be excavated.

The investigation did not reveal much of a problem on the southbound side, but, as a precaution, the decision was made to dig the pipe out from under the southbound lanes.

The southbound detour sends motorists off I-5 at Highway 33, then to Highway 132 before re-entering the freeway. There was a backup Thursday morning during the commute, but travel was fairly smooth, said Lawson.

Lawson said that I-5 is still a good bet for travelers because the detour is not especially long. Highway 99 is also an option.

This story was originally published June 2, 2016 at 12:20 PM with the headline "Old irrigation pipe under freeway cause of Interstate 5 sinkhole."