Capital Drive <br />The applicant has proposed to use a number of underground storage facilities with orifices in <br />order to meet the flow control requirements of EC 9.6793. These underground detention tanks <br />will direct stormwater runoff to a location that mimics where runoff drains to under existing <br />conditions. According to Tables 1 and Stormwater Management Plan and <br />Drainage Study, runoff from Capital Drive will discharge in three locations Discharge Sites 1, 3, <br />and 4. The applicant has demonstrated that the proposed stormwater system receiving runoff <br />from Capital Drive will result in peak discharge rates that are less than (Discharge Sites 1 and 4) <br />or equal to (Discharge Site 3) pre-development conditions. Staff concurs that this is consistent <br />with the requirements set forth in EC 9.6793(3)(a). Staff also notes that the facilities appear to <br />be consistent with EC 9.6793(3)(c), which requires that facilities be sited and designed <br />according to the flow control provisions and the facility design requirements set forth in the <br />Stormwater Management Manual. <br /> <br />Private Roadway <br />Similar to the system proposed for Capital Drive, the applicant has proposed to collect <br />stormwater runoff from the private street into a series of underground storage facilities with <br />orifices in order to meet the flow control requirements of EC 9.6793. As shown in Tables 1 and <br />Stormwater Management Plan and Drainage Study, runoff contributed by <br />the construction of the private street will be discharged at Discharge Sites 1, 2, and 3. For the <br />northern and southern portions of the proposed private street, runoff will be collected into <br />underground detention vaults with orifices that will reduce the peak discharge rate that are less <br />than or equal to pre-development conditions. Water will then connect into the proposed public <br />system where it will discharge at the locations identified in the Stormwater Management Plan <br />and Drainage Study. Tables 1 and 2 show that the peak discharge rate at Discharge Site 1 will be <br />less than that under existing conditions, and the peak discharge rate at Discharge Site 3 will be <br />equal to that under existing conditions, consistent with EC 9.6793(3)(a). <br /> <br />For the remaining portion of the private street, runoff will be directed into a series of <br />underground storage tanks with orifices that will reduce the peak discharge rate. Runoff will <br />then be released through level spreaders into a designated preservation area on the east side <br />of the development site. Based on existing topography, the proposed system closely mimics <br />existing runoff locations. The discharge location is identified as Discharge Site 2 in Tables 1 and <br />Stormwater Management Plan and Drainage Study. As shown in Table 2, <br />the peak discharge rate being released out of each level spreader mimics that of the existing <br />conditions. It is noted in the report that a 38-foot wide section was used to establish the <br />existing basin and its peak discharge rate of 0.16 cubic feet per second (cfs). The proposed <br />system includes two 38-foot wide level spreaders, each being 38 feet long and each having a <br />peak discharge rate of 0.16 cfs, which matches the existing condition. Staff concurs that this is <br />consistent with the flow control standards outlined in EC 9.6793(3). <br /> <br />Individual Lots <br />The applicant has stated that individual lots will address flow control and water quality <br />standards when applying for building permits on a case by case basis. Staff concurs that the <br />flow control standards for the individual lots will be addressed on a case by case basis at the <br />time that each lot applies for a building permit. <br /> <br /> <br />Capital Hill PUD (PDT 17-1) February 2018 51 <br />Page 51 <br /> <br />