Friday, August 9, 2019

Proper handling of contaminated soil means State Route 530 fish passage project will take longer

By Tom Pearce

If you dig up your yard, it's always a good idea to call 811 first so you don't get any nasty surprises, like hitting fiber optic, electrical, sewer or gas lines. We always work closely with utilities when our projects require excavation. But even 811 can't always help us if we find something other than utilities. Fortunately, we have plans in place for when that happens.

Right now, we are replacing a culvert for Schoolyard Creek that goes under SR 530 east of Arlington. When the original culvert was installed many decades ago, it was common practice for construction crews to fill holes with whatever was available. Under SR 530, this included construction debris.
Excavation to replace a culvert under SR 530 revealed soil contaminated by construction debris

Anytime contractors excavate for us, we check the material removed to be sure it is clean. It turns out, some of the construction material that was used long ago as fill under SR 530 contained creosote, a wood preservative that contaminated some of the soil. That means it's going to take until after Labor Day, Sept. 2, to finish the work and put SR 530 back on its regular route.

Our contractor, Kiewit, discovered the contaminated soil July 28, when it was hauled to a storage area. We have specific protocols for dealing with this sort of thing. The material is stored in a lined, covered area to keep the contamination from further leaching into the ground. We develop an environmentally sound plan to dispose of it that must be approved by the Department of Ecology – in this case our contractor will haul it to a business in South Seattle that handles this type of material.
The contaminated material that was excavated is temporarily stored in protective
plastic until proper disposal can be arranged.

With an approved plan in place, our contractor crews can get back to work. They've already removed about 80 percent of what needs to go; they'll start work on the last 20 percent by the week of Aug. 12.

When the excavation is complete, several steps remain:
  • Setting the box frames for the new culvert
  • Putting in base material for and building the creek bed
  • Adding the caps to the culvert
  • Filling around the sides of the box frames, then the rest of the hole
  • Repaving the section of highway
Being a good steward of the environment is one of our top priorities. If it takes a little longer to do a job the right way, that's what we'll do.