A 4,300-foot sewer-pipe project will cost about $7 million more than initially planned after a consultant’s report failed to identify underground boulders that would get in the way of construction.

The City Council voted Tuesday 5-0 to allocate the additional funds to redo parts of the Chevy Chase Sewer Diversion Project, which will treat wastewater locally instead of letting it flow to a treatment plant in Los Angeles.

Last year, the city rewarded a $14.1-million contract to Upland-based Mladen Buntich Construction Co. Inc., which in November informed city officials there were boulders and cobblers in the way.

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Part of the project had to be redesigned, and the need for bigger machinery and bigger pipes arose, said Roubik Golanian, the city’s public works director.

“There is going to be extra work, extra effort and extra cost involved to move forward with the work,” he said.

There is going to be extra work, extra effort and extra cost involved to move forward with the work. Roubik Golanian, Glendale public works director

The project’s completion will also be delayed by a year, with a target date now set for 2018.

The borders of the construction are San Fernando Road, Elk Avenue, Chevy Chase Drive and Pacific Avenue.

Fugro Consultants Inc., a geotechnical agency, didn’t identify the subsurface rocks in its soil survey, Golanian said.

Golanian said the experience, so far, has been disappointing and frustrating, and that the city is looking into whether Fugro could be held liable.

Officials at Fugro’s Los Angeles office referred the News-Press to its Houston office, which did not return calls for a comment.

The goal of the project is to divert wastewater initially heading for the Hyperion Plant for treatment in Los Angeles and instead send it to the Los Angeles Glendale Water Reclamation Plant.

Another component of the project would have some of the wastewater be converted into recycled water for city vehicles, such as street sweepers, and save about 2.5 million gallons per year.

Golanian said because of the savings, it was estimated the project would recoup its cost in 14 years, but with the delay and additional costs, it will likely take about 17 to 21 years for that to happen.

However, City Manager Scott Ochoa told council members that moving forward with the project would still be worthwhile because once costs have been recouped, the diversion project will save the city about $1 million a year.

Council members elected to stay with Mladen Buntich Construction Co., although the option to terminate the contract and find another contractor to do the work was also on the table.

“Just based on the critical points, the shorter completion date, the least impact to the community and the least expensive … those things ring well with me,” said Councilman Ara Najarian.

The additional money will come from the public works department’s sewer fund, which had enough to cover the extra work.

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Arin Mikailian, arin.mikailian@latimes.com

Twitter: @ArinMikailian