1800 41ST ST 2023-06-23 - Laserfiche WebLink

If the primary BMP options are deemed ineffective or inappropriate during construction to satisfy the requirements set forth in the General NPDES Permit(Appendix 2D), or if no BMPs are listed above but deemed necessary during construction,the Certified Erosion and Sediment Control Lead shall implement one or more of the alternative BMP inlet protection options. Element#8-Stabilize Channels and Outlets Where site runoff is to be conveyed in channels, or discharged to a stream or some other natural drainage point, efforts will be taken to prevent downstream erosion. The specific BMPs for channel and outlet stabilization that shall be used on this project are identified in Appendix 2B. Alternate channel and outlet stabilization BMPs are included in Appendix 2C as a quick reference tool for the onsite inspector in the event the primary BMP(s)are deemed ineffective or inappropriate during construction to satisfy the requirements set forth in the General NPDES Permit(Appendix 2D). To avoid potential erosion and sediment control issues that may cause a violation(s)of the NPDES Construction Stormwater permit,the Certified Erosion and Sediment Control Lead will promptly initiate the implementation of one or more of the alternative BMPs after the first sign that existing BMPs are ineffective or failing. The project site is located west of the Cascade Mountain Crest. As such, all temporary on- site conveyance channels shall be designed, constructed,and stabilized to prevent erosion from the expected peak 10 minute velocity of flow from a Type 1A, 10-year, 24-hour recurrence interval storm for the developed condition. Alternatively, the 10-year, 1-hour peak flow rate indicated by an approved continuous runoff simulation model, increased by a factor of 1.6, shall be used. Stabilization, including armoring material, adequate to prevent erosion of outlets, adjacent stream banks, slopes, and downstream reaches shall be provided at the outlets of all conveyance systems. Element#9- Control Pollutants All pollutants, including waste materials and demolition debris,that occur onsite shall be handled and disposed of in a manner that does not cause contamination of stormwater. Good housekeeping and preventative measures will be taken to ensure that the site will be kept clean,well-organized, and free of debris. Any required BMPs to be implemented to control specific sources of pollutants are identified in Appendix 2B. The contractor shall implement the following measures as much as is practicable, in order to mitigate pollutant impacts from vehicles, construction equipment, and/or petroleum product storage/dispensing: • All vehicles, equipment, and petroleum product storage/dispensing areas will be inspected regularly to detect any leaks or spills, and to identify maintenance needs to prevent leaks or spills. • On-site fueling tanks and petroleum product storage containers shall include secondary containment. • Spill prevention measures, such as drip pans,will be used when conducting maintenance and repair of vehicles or equipment. • In order to perform emergency repairs on site,temporary plastic will be placed beneath and, if raining, over the vehicle. 1800 41st Street—Parking Expansion Drainage Report