Pleasant Valley Wetland Mitigation

Client—Port of Chehalis, Washington

The Pleasant Valley site provides high-quality wetlands to mitigate for impacted wetlands located at the 250 acre Chehalis Industrial Park. Gibbs & Olson provided land surveying, design and construction management services for the 63 acre site.

To develop project drawings for bidding and construction, Gibbs & Olson converted the schematic layout (prepared by ELS) into grading plan sheets containing contours and cut/fill quantities and corresponding specifications. The entire 63 acre site was surveyed in just two days utilizing GPS survey equipment. A topographic map including contours was prepared from the collected survey data.

The site work was completed in two phases, Gibbs & Olson provided design engineering and construction management for both phases. Design engineering for the new mitigation site included grading and plan preparation. To meet the overall Regional General Permit (RGP) requirements, Gibbs & Olson prepared a comprehensive site analysis, opinions of cost and associated water quality technical memorandum to address potential pollutant loading on the wetlands located at the industrial park.

Phase I site work involved grading of 80,000 cubic yards of onsite material and removal and reinstallation of 1,200 feet of existing fencing, seeding and erosion control. Phase II involved additional site work that was needed based upon review of a post-construction storm event and consultations with ELS, the US Army Corps of Engineers, Fish and Wildlife, and Ecology. Work performed included locating existing under drain pipes within the site and eliminating the drain pipe discharge to Stearns Creek, regrading of 25,000 cubic yards of onsite material, the creation of two stream alcoves, and removal of an existing culvert on the southeast corner of the site.

The Army Corp of Engineers issued the first of its kind RGP to the Port of Chehalis. The RGP allows the Port to use the Pleasant Valley site for advanced mitigation. Having the RGP in place, the Port can reduce the time it would normally take to produce a wetland mitigation plan and obtain environmental permits—providing land that is more attractive for potential clients to develop.