A long-awaited levee repair job in Marysville has been stalled by disagreement about the construction of a new seepage barrier.

The first phase of the project, led by the U.S. Army Corps of Engineers, was to be completed this month, but will now be delayed by a year.

"We're confident it was the right thing to stop this based on public safety," said Col. William Leady, Sacramento District commander of the Army Corps.

Marysville is unique in that, during big storms, the city of 13,000 people becomes an island. A 7.5-mile ring of levees encircles the city, protecting inhabitants from the Yuba and Feather rivers as well as Jack Slough.

But because Marysville was settled at the confluence of these streams, it sits atop deep, ancient layers of porous sediment.

That sediment is the cause of deep seepage beneath the levees; the problem emerged in 1997 during storms that flooded surrounding areas. It also is the source of the disagreement that halted repairs earlier this year.

The $95 million project includes installing new seepage barriers deep within some levee sections, as well as widening levees in areas that are now too narrow.

The first phase, projected to cost $12 million, began last spring. The Army Corps hired Raito Inc., a San Leandro contractor, to build a seepage barrier about three-quarters of a mile long in a levee section on Marysville's northwest edge.

The work was expected to be done this month. But in August, a disagreement emerged about the progress of the barrier, also called a slurry wall.

The job involves mixing cement and a type of clay, called bentonite, in a trench as deep as 118 feet beneath the levee. When complete, the material is intended to become impervious, blocking water from seeping through the levee when rivers flood.

The seepage wall is one of the deepest ever in California.

Army Corps officials became concerned that the materials were not mixing properly underground, and that a seepage risk might remain. They blame it on the very deep and "eclectic" mix of sediment under Marysville.

"We're just not confident the slurry wall is meeting contract specifications," Leady said. "Our contractor is doing a good job and using a proven technique. But this is a unique site."

The Corps stopped work on the project for three weeks in August to assess progress. New testing methods are being developed, Leady said, to analyze the slurry mix.

Due to the timing – nearing the end of the construction season, with winter approaching – the delay means the project will take another year to finish. November 2012 is the new estimated completion date for phase one.

The delay will likely add costs as well, but Leady could not estimate the amount.

David Miller, a senior vice president at Raito Inc., disagreed about the need for the delay. He said the work was going well and could have been finished this year.

"We've never had the specifications interpreted quite the way they're looking at it," Miller said. "The industry certainly wouldn't agree with their position. Our peers (contractors) certainly are perplexed."

The Marysville Levee Commission is the project's local partner. Commissioner Pat Ajuria, contacted by The Bee, declined to comment.

Leady emphasized that the Corps and Raito continue to have a good working relationship, and that the project has already boosted flood safety. About 2,000 linear feet of levee has been improved, with another 2,600 feet still to go.

Including additional phases, the project is expected to be done in 2015. The goal is to bring Marysville up to a 200-year level of flood protection, or the ability to withstand a flood with a half- percent chance of striking in any given year.

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Call The Bee's Matt Weiser, (916) 321-1264. Follow him on Twitter @matt_weiser.

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