Update on the Dayton Street sinkhole: repairs continuing this week

The sinkhole at the center of the Dayton/Railroad intersection, just west of the railroad tracks.

Here’s an update on that sinkhole that appeared just west of the railroad tracks on Dayton Street Feb. 24. According to City of Edmonds Public Works Director Phil Williams, the initial thought was that the sinkhole was caused by missing grout in a new manhole installed by contractor ICI on behalf of the city last year — and ICI was asked to respond and fix the problem at their expense.

However, inspection of the manhole revealed that the sinkhole was caused by a broken 24-inch unreinforced concrete storm line with an approximate one-square-foot hole in the top of the pipe, rather than the manhole itself. “This line surcharges during normal operations, so water leaving the pipe through this hole had, over time, eroded away surrounding soils,”  Williams said, at first causing a depression in the road, which was noticed earlier in the week, followed by “complete breakthrough” at street level.

As a result, the contractor started work Monday to replace approximately 65 feet of storm pipeline with new 24-inch PVC pipe and will also repair the street at a cost not to exceed $67,500, Willliams said. Repairs were delayed until this week to take advantage of better weather and more favorable tides, and it’s estimated the work will take two days.

However, the issue highlighted a bigger — and more expensive — problem, and that is the overall condition of the existing 24-inch unreinforced pipeline, particularly the section that passed under the railroad tracks. “Video inspection of the line shows extensive cracking in the pipe and staff believes its condition warrants repair or replacement as soon as possible,” Williams wrote in an email sent to the Edmonds City Council and Mayor Mike Cooper Monday. “The best option is likely to be a Cured In Place Pipe technology (CIPP) lining system of which there is more than one choice. We are researching those options and costs now. Just as a starting point for this discussion I would “guesstimate” a cost for this at $400k – $550k. To make room for this project in the 2011 work plan and budget we will recommend the construction portion of the anticipated project on Talbot Rd. be postponed until 2012 and the rest of the stormwater CIP be rebalanced as necessary to accommodate this project on Dayton.”

Expect to see that issue on the Edmonds City Council agenda in the near future.

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