7000 HARDESON RD 2020-06-05 - Laserfiche WebLink

replacement in localized damage areas, large area replacement of significant concrete panel failures, partially repaving the south employee parking lot, partially repaving and replacing trees which are heaving the paving of the north employee parking lot, striping, and pavement marking. PROJECT SCOPE AND SEQUENCING: This project will re-pave portions of MCOB, reconstruct portions of the storm water drainage system (by installing flow splitters and replacing outfalls), and install conduit for future fiber optic lines (within the boundary of the facility). No additional footprint will be added to the previously developed area. Erosion control BMPs will be placed along the eastern boundary of the project and at outfall replacement areas where there is potential risk of soil erosion during construction. Existing damaged areas of asphalt and PCC (rigid) pavement will be removed by jackhammering and bucket excavators. 230,000 sq. ft. (12,494 cubic yards) of PCC, 18,000 sq. ft(122 cubic yards) of asphalt grind and 3,300 sq. ft(90 cubic yards) of asphalt will be removed off-site and disposed of in an approved materials management center. The subbase will be compacted prior to placement of new paving. Replacement of material will be like for like. Existing outfall pipes will be excavated for replacement along their current alignment. Below is a summary of the outfall performance due to upgrades. Structure ID Tatal Area Pipe Size 10 YR 10 YR 100 YR 100 YR Proposed Proposed Outfall location Tributary (in): peak(cfs) velocity peak(cfs) velocity Invert diameter upgrade acres Otis) (Ws), Elevation component 600 5.18 16 2.71 1.53 4.35 2.46 same as increase 3 Outfall is stable in previous inches current condition 500 4.59 18 2A 1.35 3.86 2.16 lower 3.36 in increase 3 Outfall is stable in inches current condition 400 3.05 12 1_59 2.03 2_56 3.26 raise 1.12 ft same Fill plunge pool, place energy dissipating quarry spalls. 300- 3.03 12 1.58 2.01 2.54 3.24 raise 1.03 ft same Fill plunge pool, place energy dissipating quarry spells 200 2.02 12 1.05 1.35 1.7 2.17 raise 1.0 ft same Fill plunge pool:, place energy dissipating quarry spalls DRAINAGE REPAIR AND OPERATIONS: In the areas of repaving, the existing trench drain structures will be removed and replaced with a surface gutter to divert storm water into (new) catch basins. The existing trench drains tie into an onsite conveyance system that includes five flow splitters that allow the water quality treatment storm flowrate to continue downstream to the onsite water quality treatment system. Flows that exceed the water quality treatment flowrate discharge directly to Merrill Creek. The existing flow splitters are in need of repair and enhancement with added spill control measures. This project includes redesign and reconstruction of the five flow splitters to continue direction of surface water flows (up to the water quality flowrate)to the onsite water quality treatment system. Flows in excess of the water quality treatment flowrate will overtop a weir and discharge to Merrill Creek. The majority of onsite pollutants are collected in the more frequent smaller storm events and flow in the water quality treatment system. Runoff from storm events in excess of the water quality treatment SEPA Environmental checklist(WAC 19741-960) July 2016 age 3 of 15)