2022-07-25-minutes-public-works-study-session

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From: Bryan Condon Sent: Tuesday, June 21, 2022 3:16 PM To: Mark Cook Cc: Kurt Addicott Subject: Hangar Taxilane Project Summary Hi Mark - Per your request made during our call last week, I am providing the following summary of the Hangar Taxilane Project... For reference, I've attached an exhibit showing a visual overview of the project. Century West has a task order (#11) in place with the County to provide design and bidding services for the hangar taxilane project. We submitted our 60% design deliverable on Friday 6/3/22 and have since stopped progress on the design until we hear from you that you'd like us to continue. We are currently $50k in to the $106K budget. Century West's planning level construction cost estimate for the project, provided during the scoping phase, was $281,618 (this cost does not include consultant inspection services during construction). Once we started design, and collected topo and geotech, we determined that construction of the project would involve a greater quantity of embankment fill material than we anticipated while assembling the planning level construction cost estimate of $281,618. There are two factors contributing to this need for additional embankment fill material than originally anticipated: 1. Topographic survey taken in the project area revealed that the existing ground drops off steeply just south of the existing PCC apron, where the new taxilane would be located. The lower than originally expected ground elevations result in a need for a larger quantity of embankment fill material, which of course results in a higher construction cost. 2. Geotechnical investigations revealed that the infield area in which the taxilane is to be constructed contains a level of organic material that would necessitate 'over excavation' and removal of existing subgrade material, as opposed to constructing the new taxilane directly on the existing organic laced subgrade material. Organic material, such as what was found in this area, does not provide for quality structural subgrade and, in time, would result in a faster failure of new taxilane pavement. To address this issue, it is recommended that the existing subgrade, which contains organics, is over excavated approximately 2 feet deep and replaced with suitable (imported) subgrade material. The two factors described above resulted in a need for a significantly higher quantity of embankment material, and thus a higher construction cost than originally estimated. Compared to Century West's planning level construction cost of $281,618, the project construction cost estimate at 60% design is $407,683 (neither cost includes consultant inspection services during construction). Additionally, for your consideration, in December of 2021, WSDOT awarded the County a CARIB loan in the amount of $100k to partially fund this project. Additional information is forthcoming from David Chenaur (WSDOT), but generally the terms of the CARB loan are as follows: • Loans can be up to 20 years in duration, repaid annually. • fixed interest rate of 2.0%.