Atkinson Construction proposed a Washington State Department of Transportation (WSDOT) Cost Reducing Incentive Process (CRIP) change order which resulted in a full redesign of three miles of highway widening, rock cuts, and replacing the snowshed covering the westbound lanes with a bridge. This bridge design exposed approximately three acres of additional pollution-generating impervious surface draining to a water body with listed species, making innovative stormwater conveyance and mitigation critical.
PACE staff worked with the contractor, roadway design team, WSDOT, Ecology, Washington Department of Fish & Wildlife, and other agencies to develop a unique best management practices application with an engineered soil layer to produce an infiltration system like a rain garden. The siting of these facilities between the roadway and an excavated rock face required close coordination of roadway, hillside, and facility grading. The drainage scheme provides treatment for the additional pollution-generating impervious surface and provides a net increase in treatment of other project areas. Water quality and flow control elements included water quality treatment (media filter drains and bioinfiltration ponds), open and enclosed conveyance design, pavement drainage design, MOT temporary drainage for multiple stages of construction, bridge drainage, wall drainage, and subsurface drainage design.
In addition, staff managed, oversaw, and designed 10 construction stages over a 6-year period. Each stage required roadway design plans, including horizontal control, profiles, sections, and channelization plans to maintain the continuous operation of two travel lanes in each direction during construction.