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Targeted Drainage Report — Twentieth Ave Substation <br />WO# 100026553 <br />1.2 EXISTING CONDITIONS <br />In addition to existing Twentieth Avenue substation, the site is in use as the District's Operations Center. <br />Twentieth Avenue substation consists of (2) metalclad switchgear units, a control house, 12kV switches, (2) <br />115kv-12kV power transformers, 115kV circuit switchers, 115kV switches, transmission termination structures <br />(dead ends), cables, conduits, grounding system and various ancillary electrical equipment. <br />The site is bordered; westerly by the Boeing plant, northerly by Community Transits Seaway Transit Center, <br />easterly by commercial businesses and southerly by State Route 526. <br />The site is subject to a number of different easements. In the area of the project site include AFN 201703025002 <br />which includes an 8' easement for CT upon District property, a 20' and 30' easement for the District upon CT <br />property and a.signal loop easement. Review the site plan S-76-K2 for greater detail. <br />The Operations Center storm drainage is serviced by a numerous catch basins and drainage pipes which collect <br />and convey the runoff to either the northerly detention pond or the southerly detention pond. Twentieth <br />Avenue substation is not connected to this drainage system. <br />The nature of substation construction results in little to no surface water runoff being generated on -site. The <br />substation is layered with 4-inches of substation rock (1-1/2" clear open graded rock) and typically underlain by <br />a permeable gravel base course material. The voids within these layers hold the surface water and allow it to <br />slowly infiltrate into the native soils below. <br />Page 3 <br />