By Richard Van Winkle, News of Mill Creek.
At their regular May 1, 2018, meeting the Mill Creek City Council unanimously approved a $480,000 increase to Sweetwater Ranch’s stormwater system repair project. Two additional sinkholes opened up in a homeowner’s yard on 144th Street SE during April.
The city council approved a $250,000 emergency time and materials contract in March to repair a failed 36-inch diameter corrugated metal stormwater pipe meant to convey stormwater from the Douglas Fir Neighborhood south through the Sweetwater Ranch Neighborhood to one of the city’s stormwater retention ponds.
A sinkhole that opened up in December 2017 was the city’s first indication of the failure. A second sinkhole opened up in January.
Director of Public Works & Development Services Gina Hortillosa said a closed-circuit television (cctv) inspection the week of April 9th showed the failed pipe was in such poor condition that slip lining, a relatively inexpensive repair method where a new pipe is inserted into the old pipe, was not feasible
She went on to say that the pipe had apparently not been conveying stormwater for a long time, resulting in very wet and unstable soil conditions at the site. These conditions make it very risky to dig a trench down to the pipe as the soil collapses on itself too easily.
According to Hortillosa the failed stormwater pipe is also not located in the center of the 30-foot utility easement between the affected Sweetwater Ranch homes. She said the new pipe would be installed in the center of the easement using new underground boring technology.
She said using this repair method is more expensive than slip lining or opening up a trench in which to lay the new pipe, but carries the least risk to the adjacent homes’ foundations.
The city council approved an increase of $480,000 to the contract to utilize the more expensive trenchless repair method. She said that the new repair estimate of $770,000 includes a 15% contingency but is not a fixed-cost contract.
Councilmember Mike Todd asked if there were sufficient funds in the city’s stormwater capital funds account to pay for the project.
Finance Director Peggy Lauerman answered that there is currently $830,000 in the account. She went on to say that the state requires the city maintains a $100,000 reserve, so she is investigating other ways the project can be funded.
Todd commented “the rainy day fund just got wiped out.”