Storm water repairs could exceed original estimates by $480,000

By Dan Aznoff | May 03, 2018

Members of the Mill Creek City Council unanimously approved an amendment to a construction project to repair the storm water system that created four sinkholes in the Sweetwater Ranch neighborhood.

The council added almost a half million dollars to the emergency repair contract with Shoreline Construction approved in June after cameras discovered damage to the underground water system was far worse than had been anticipated.

The council vote on Tuesday, May 1, authorized expenditures not to exceed $480,000 to the $769,000 contract approved in early June.

A separate contract for $250,000 was approved by the council in March to deal with two sinkholes that appeared on 144th St. SE. Two additional sinkholes were created by the weight of the repair vehicles brought in to repair the original damage.

Gina Hortillosa, the director of public works and development services, outlined the scope of the repairs to the council. The original contract, she said, was intended to repair 250 feet of corrugated metal pipe with a slip lining process. When the repair work began in April, underground cameras discovered multiple holes and sections of collapsed pipeline.

The additional funding approved at the May 1 meeting will be used to bring in an auger boring system in place of the less expensive open trench repair methods that disrupt traffic and create a danger to homes near the worksite.

Due to the extent of the damage and the soil conditions, Shoreline Construction was brought in to control the damage by backfilling in the sinkholes with cement.

The damaged sections, according to Hortillosa, will be filled with inert material to form a U-shaped cement-filled tube that will stabilize the satirized soil. The boring, Hortillosa said, will provide space for 42-inch drainpipes that will run under two separate neighborhoods.

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