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HomeMy WebLinkAboutCM_Construction_Mitigation_Description_220712_v1 1133 LAKE WASHINGTON BLVD. N  SUITE 90  RENTON  WASHINGTON  98056 TEL: 425/282-5833  FAX: 425/282-5838 Southport West Construction Mitigation Description Proposed construction timelines – 1. Phase 1 - Tower 1 & 2 with garage: July 2023 – July 2027 2. Phase 2 - Tower 3 & 4 with garage: July 2027 – July 2031 3. Phase 3 – Tower 5: Post July 2031 The days and hours of operation will be Monday through Friday, 7 AM to 8 PM. The Stormwater Pollution Prevention Plan (SWPPP) will be prepared as part of the Stormwater General Permit requirements for the office towers per ecology guidelines (SWMM-WW 2005). The purpose of the SWPPP is to describe the proposed construction activities and all temporary and permanent erosion and sediment control (TESC) measures, pollution prevention measures, inspection/monitoring activities and record keeping that will be implemented during the project. Implement Best Management Practices (BMPs) to prevent erosion and sedimentation, and to identify, reduce, eliminate, or prevent stormwater contamination and water pollution from construction activities are few of the key objectives of the SWPPP. Existing and new impervious surfaces constructed on the site are and would continue to be the source of water runoff from the proposed project. Piped stormwater conveyance systems will be extended to collect and convey stormwater to natural discharge locations which ultimately drain to Lake Washington. As well, a portion of the development will connect to an existing stormwater outfall to John’s Creek. Approximately 7.7 acres will be disturbed for the construction of the 5 office towers at grade with associated parking garages under, like the 3 office towers currently built on site. Construction activities will include demolition, excavation, grading, shoring and foundations, utilities, new building construction, and miscellaneous site improvements. Approximately 25,000 cubic yards of excavation and 39,200 cubic yards of fill would be required for the project. The depth of excavation is anticipated to not exceed approximately two feet below ground level, except for building cores where excavation will be deeper: locations are currently being designed. The proposed project could result in localized increases in air emissions due to construction vehicles, equipment, and activities. Dust could also result during construction activities. Emissions would not be expected to result in exceedance of ambient air quality standards. The proposed project will be designed to conform to the applicable regulations and standards of agencies regulating air quality in Renton. These include the Environmental Protection Agency (EPA), Washington State Department of Ecology (DOE), and the Puget Sound Clean Air Agency (PSCAA). Proposed measures to reduce or control erosion – Temporary Erosion and Sediment Control (TESC) Plan approvals (including Construction Best Management Practices) would be submitted as components of the building permit. Best Management Practices will be instituted to reduce soil being tracked onto the roadway and water quality will be maintained during excavation per City of Renton and King County standards. Ground Water/Excavation – Groundwater would not be withdrawn for drinking water purposes. The depth of excavation for most of the proposed development is anticipated to not exceed approximately two feet below ground level, which would not extend into groundwater located approximately seven to 10 feet below ground level. Proposed building cores excavation could extend to a depth of 20 feet below ground level. Excavation below approximately 7 to 10 feet below ground level would likely require dewatering system using drilled wells or well points. Dewatering would be conducted consistent with applicable City of Renton requirements and would include filtration, de-sedimentation and return of water to the system for drainage to Lake Washington (as under current groundwater flow conditions). Federal Aviation Administration (FAA) – SECO is familiar with the required notification of cranes use, as well as the determination process of no hazard to air navigation. The original Southport included this process for the Hotel and the office buildings. Hazardous Materials Management Statement – Not applicable: The property was part of the former Shuffleton Steam Plant that was built in 1929 on ground leveled by dredge-and-fill activities. The plant, which was located directly north of the property, was an oil-fired, steam- powered electricity-generating plant from 1929 to 1989. In addition, there was a gasoline underground storage tank (UST) that was located on the property. The Shuffleton Steam Plant was demolished in the mid-1990s, and a comprehensive environmental cleanup was completed. There is no known impacted soil or groundwater at the property that will be encountered during redevelopment activities. However, if any signs of unknown impacts in soil are encountered, an environmental consultant will be on-call to address. A preliminary draft of a site logistics plan by Exxel Pacific is provided below.