ANTIOCH -- Work is under way to widen a major thoroughfare on Antioch's western edge.

After resolving a dispute with Discovery Builders over the expansion of Somersville Road last year, Antioch took over design work and construction of a wider pipeline and road crossing for Markley Creek.

"We took it upon ourselves to handle it before all the environmental permits expired," said Ron Bernal, the city's public works director.

The long-awaited culvert project went out to bid earlier this year, with work starting last month, Bernal said. Dublin-based Platinum Pipeline Inc. was awarded the just over $996,000 contract in April.

The culvert should be completed by the end of September, Bernal said.

The work includes replacing the existing 72-inch diameter corrugated steel pipe culvert under the road with a 96-inch concrete pipe trench, and installing new walls around the drain. It also adds a second 60-inch culvert to move water from the Estates at Black Diamond subdivision to the creek.

The larger diameter pipe will keep stormwater moving in the event of larger-than-normal rainfall, prevent the new homes from flooding, Bernal said.

Once the culvert is complete, Discovery Builders, an affiliate of Concord-based A.D. Seeno Construction, must widen Somersville from two to four lanes from James Donlon Boulevard to Buchanan Road -- a condition set in its 2003 development agreement with Antioch for the Black Diamond subdivision.

Discovery

Widening Somersville Road is expected to improve traffic flow in the area and accommodate planned growth. The city has made several short-term fixes to Somersville over the past several years.

The widening must be completed by December 2014, but that deadline could be extended if Antioch doesn't finish the culvert by the end of 2013.

Discovery will be billed by the city, though it can dispute the costs if the culvert project costs more than $821,900.

Contact Paul Burgarino at 925-779-7164. Follow him at Twitter.com/paulburgarino.