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The thresholds for flow control within each threshold discharge basin are as follows: <br /> • Projects in which the total of effective impervious surfaces is 10,000 square feet or <br /> more in a threshold discharge area, or <br /> • Projects that convert 3/ acres or more of vegetation to lawn or landscape, or <br /> convert"2:5 acres or more of native vegetation to pasture in a threshold discharge <br /> area, and from which there is a surface discharge in a natural or man-made <br /> conveyance system from the site, or <br /> • Projects that through a combination of effective hard surfaces and converted <br /> vegetation areas cause a 0.10 cubic feet per second increase in the 100-year flow <br /> frequency from a threshold discharge area as estimated using the Western <br /> Washington Hydrology Model or other approved model and one-hour time steps <br /> (or a 0.15 cfs increase using 15-minute time steps). <br /> This project proposes to construct less than 10,000 sf of new effective impervious <br /> surfaces (EIS) including roof and driveway areas and less than 20,000 sf of pervious <br /> surfaces will be affected by all the proposed improvements. Finally, the site has been <br /> analyzed for the existing conditions and developed conditions to determine the increase <br /> for the 100-year peak runoff rate is below the 0.15 cfs threshold in each threshold <br /> discharge area. Therefore, no further flow control measures are required. Refer to <br /> Appendix A to see hydrology model calculations. <br /> Seahurst'SP 18-0727 <br /> September 2019 Page 15 <br />