Zidell Remediation: Use of Multitier Adaptive Management to Meet the Requirements of a Compressed Regulatory Work Window

摘要

Background/Objectives. A 12-acre engineered sediment cap was required to isolate sediment contamination at a former World War II ship dismantling facility on the Willamette River in Portland, Oregon, USA. The regulatory in-water work window for the lower Willamette River is July 1 to October 31. Construction of a new transit bridge directly over the new sediment cap was timed to begin work in the same work window with the west tower rising less than 100 feet from the edge of the cap. Furthermore, the realignment of the only street access route to the site complicated delivery of upland import materials for the river bank construction and off-haul disposal of contaminated bank and hot spot soils. The regulatory restriction, coordination of three major projects in the same space, and complexities of constructing a cap design with varied materials and slopes required an accelerated schedule to complete the work in one season and avoid cost impacts to the owner. Approach/Activities. A multitiered adaptive management strategy was implemented so that the remedial design intent was achieved through construction, and certifiable to the regulatory agencies. The strategy required direct oversight of all units of construction, daily digital analysis of in-water construction progress, and daily coordination conferences with contractor, engineer, owner and (periodically) regulators. Direct oversight was completed by the engineering design team to help interpret design intent during construction, observe and report all field conditions, identify potential implementation deficiencies, assist contractor in developing daily work plans, keep real time measurements, and provide material placement approval and tracking. Digital analysis was completed using 3D design software to process bathymetric surveys of each placement area for verification of daily and cumulative material placement grades, volumes, and limits. Analysis included comparing the digital terrain models generated during design and calculated volumes to as built data (e.g., survey, verification diver cores), and was completed onsite in direct coordination with the contractor and surveyor to approve placement, verify compliance with the specifications, track pay items for contract administration, and maintain continuous workflow. Daily coordination conferences served to facilitate contractor and subcontractor schedule coordination, track incoming material deliveries, closely track the compressed critical path items and their impacts on the overall schedule, and identify any issues of material procurement or manpower shortages early. Results/Lessons Learned. The engineering team worked directly with contractors, management, and regulators during the course of construction to ensure all components of the project were implemented per the design intent within a complex and dynamic river environment under strict schedule requirements. Utilizing engineering design staff intimately