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Downstream Analysis: <br /> Task 1—Define and map the study area <br /> A site map has been created that displays the project boundary,the existing stormwater system <br /> within Dorn Ave, and the proposed stormwater system for this project. The topography is shown, <br /> and the map is at a scale of 1"=20'. <br /> Task 2—Review all available information on the study area <br /> This project is not within the immediate vicinity of a critical area or floodplain. It appears that <br /> the existing stormwater system within Dom Ave eventually discharges to North Creek. The <br /> surrounding area consists primarily of residential development. <br /> Task 3—Field inspect the study area <br /> The study area has been inspected by the design team. The area is consistent with information <br /> provided in the survey. The site is primarily grass,with flat topography, and no existing <br /> structures. There do not appear to be any existing drainage problems. The field inspection was <br /> conducted mid-day,on August 22,2018. The weather was sunny. <br /> Task 4—Describe the drainage system, and its existing and predicted problems <br /> The drainage system appears to be functioning properly. There are no known drainage issues, <br /> and it is not anticipated that the current system will experience any future problems. <br /> This project intends to meet the low impact development performance standard. It does not <br /> appear that there is and ground water onsite according to Nelson Geotechnical Associates,Inc. It <br /> is not anticipated that downstream properties or conveyance systems will be negatively impacted <br /> by development of this site. The conveyance system downstream of this site,located in Dorn <br /> Ave, appears to discharge into North Creek.North Creek flows south, eventually discharging <br /> into the Sammamish River and ultimately Lake Washington. <br /> 3.1.4 Determination of Applicable Minimum Requirements: Vol 1,Section 3.1.4 <br /> This project proposes greater than 5,000 square feet of new hard surface and triggers the <br /> evaluation of minimum requirements 1-9. <br /> 3.1.5 Preparation of Permanent Stormwater Control Plan: Vol 1, Section 3.1.5 <br /> • Existing Site Hydrology <br /> The site is currently vacant of structures and is primarily occupied by grass. Some concrete from <br /> the foundations of previous structures and a driveway remain on site. Runoff from the site likely <br /> disperses within the existing vegetated cover, and is collected by the conveyance system in Dorn <br /> Ave. <br /> • Developed Site Hydrology <br /> The developed site will have a total area of 0.28 acres with a total of 7,825 sf of new and <br /> replaced impervious surface. The runoff on site will be collected and conveyed into a <br /> bioretention facility that is designed to achieve the low impact development performance <br /> standard,and flow control standard. <br /> 11 <br />