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Lot 2: <br /> This lot proposes to construct approximately 6,235 sf of New impervious surfaces. The <br /> following table summarizes the PGIS and NPGIS proposed. <br /> PGIS (sf) NPGIS (sf) Total (sf) <br /> Existing 0 2,337 2,337 <br /> Removed 0 784 784 <br /> Replaced 0 1,533 1,533 <br /> New 2,724 1,978 4,702 <br /> New + Replaced 2,724 3,511 6,235 <br /> Total On-Site Impervious 2,724 3,511 6,235 <br /> at Project Completion <br /> The new impervious roof surfaces on each lot for this project will be mitigated using on-site <br /> stormwater management BMPs including an engineered conveyance system with a <br /> discharge at the base on the bluff adjacent to the BNSF railroad embankment. Soil <br /> management will also be used to mitigate the portions of the site that have been graded, <br /> compacted or require soil amendments meeting BMP T5.13. <br /> A. UPSTREAM ANALYSIS <br /> During the site visit it was observed that due to the site grades and surrounding <br /> development/improvements that the primary area contributing runoff to the project site was <br /> limited to the roadway to the south. It was clear that all off-site flows will be allowed to <br /> pass through or around this site and will remain that way after construction. <br /> B. DOWNSTREAM ANALYSIS <br /> Runoff from the proposed disturbance areas of the three lots sheet flows north over flat <br /> landscaped slopes. The topography on the proposed 2 new lots is such that the runoff is <br /> directed west onto the existing middle lot, prior to the steep slopes. Once on the middle lot <br /> the runoff continues north down the steep forested slopes. Near the toe of the slope is the <br /> Great Northern Railway. A non-fish bearing stream is located approximately 200 feet to <br /> the west and it is believed that the runoff would enter this stream system. This stream <br /> flows north and passes under the Great Northern Railway and then drains immediately <br /> into the Puget Sound. Based on the on/off site observations the Puget Sound would be <br /> considered the receiving water body for this project and the downstream analysis can be <br /> stopped at that point. <br /> Robinett Short Plat 15-0403 <br /> Revised:April,2016 Page 7 <br />