1615 112TH ST SW 2016-01-01 MF Import

I'OST DCVELOPED SITE CONdIT10NS As shown on the construction plans, the site ��•ill be developed with 12 new single-family dwelling units. The existing duplexes will remain. Runo}i from the driveway und new units will bc conveyed in n stortn drain pipe system to wet tank detention pipe system located in the common access drivew;ty. The systcm has been designed to release flo�vs at one-half the pre developed rnte for the 2 year stortn as well as release flows at thc pre developed rates for the 10, and 100 year storms. T'he total storage volume in the detention pipe has bcen increased in accordance with the requirements of Section 1-3.1 of the Everett Stormw�ter Management Manual. Water quality for the development will be provided by 3 feet of dead storage in the bottom of the detention pipc, as well us dead storage in a vegetated trentment cell at the outfall from the detention pipe. Approximately 85 percent of the rcquired runo}'f treatment stomge volume will be provided in the detention pipe, vrith the remnining IS percent of the required runoff treatment storage volume provided in d�e vegetnted treatment cell ut the outfall of the detention pipe. The boundaries of the proposed drainage area tributary to the detention system are delincated on the detention system dminnge uren mup at the end of this report. The "Watenvorks" program with the Santa Barbnra Unit Hydrograph (SBUFIj method nnd Type IA rainfaU distribution was uscd in the design of the proposed facility. Control in the detention system will be provided by the follow•ing set insidc of a Type 11 Catch Basin. • A 1.00-inch diameter orificc with un outlet clevation of 50530. • A 3.2?-inch diameter orifice «�ith an outlet elevation of 508.G0. • A 1.00-inch diameter orifice with nn o�det ele��alion of'S09.10. A 12-inch diamter riscr has bcen designed to pro� ide cmcrgenc�� ovcrflo�v. 7 �\ U