905 80TH ST SW MTORRES AMERICA 2018-09-18

11400 SE 8th Street P 425-453-9501 Suite 345 F 425-453-8208 L p w' D Bellevue.WA 98004 WWW.PACLAND.COM Memorand u m MTORRES AMERICA IMPROVEMENTS The proposed improvements shown below are for one main building and one smaller secondary building along the 80th Street frontage. The total impervious areas proposed for the MTorres America plans have summarized in the table below. MTorres America 2016 Imp. Area Acres Building 43934 1.01 Lego Building 3138 0.07 Lower Parking+access 127856 2.94 Upper Parking 73944 1.70 Sidewalks 8092 0.19 Total 5.90 In addition the MTorres America is proposing to install a vortex separator as supplemental treatment and sediment removal for all stormwater entering the proposed pond that was sized for the Hardeson Road Business Park— Phase 1 improvements. The 6' diameter Downstream Defender model by Hydro International has a treatment flow rate of 4.1 cfs (106pm)with an overflow rate of 32 cfs. The site flowrates for water quality are 1.00 cfs and for the 100-year are 8.42 cfs based on WWHM3 modeling. Per comments received from the City of Everett, dated May 11, 2016, a secondary overflow "jailhouse" inlet was added to the pond outfall. Design calculations for the secondary overflow are attached to this memo. SUMMARY The Berg Engineering stormwater facility has been designed and vested for 7.56 acres of proposed impervious surface. The MTorres America proposed impervious is area is 5.90 acres. Therefore the Hardeson Road Business Park— Phase 1 vested storm pond design accounted for all of the proposed improvements for the MTorres America project. Attachments: • Hardeson Rd Business Pk— Phase 1 Drainage Report by Berg Engineering • Hardeson Road Business Park (Phase 1) Construction Plans by Berg Engineering • MTorres America Developed Conditions Exhibit by PACLAND • MTorres America Overflow Structure Calculations