303 S RIVER ST
March 24, 2016:
Remedial Action: The site occupies a portion of Slip 3 of the Lower Duwamish Waterway Superfund Site (LDW) & is required to meet the conditions of the associated ROD. The EPA requires dredging & capping of a 1,700 sf area (approx. 40 cy) associated with contaminated material. An approx. 2,800 sf area east of the proposed dredge & cap area will be capped with a 6 in. enhanced natural remediation (ENR) layer of clean sand. A 6 in. ENR layer of clean sand will also be placed in a 2 ft buffer extending along the south side of the dredge area & in an approx. 5 ft buffer area along the existing sheet pile wall where dredging could not be completed in order to prevent wall destabilization.
Shoreline Protection: The proposed project consists of placing approx. 3,000 cy of riprap (12 to 15 in. in size) & "fish rock" (approx. 3/8 to 1 in. in size) as shoreline protection along approx.180 ft of the shoreline to replace the deteriorating steel & timber sheet pile wall. Existing mudline elevations along the face sheetpile wall currently range from approx. -8 ft to +8 ft MLLW . The placement of the riprap will convert this shallow subtidal zone to intertidal area. The riprap will include a topping of "fish rock" (coarse sand & fine/medium gravel to 1 in.in size) to enhance the habitat characteristics of the rip rap buttress. The existing shoreline protection consists of a deteriorating timber pile & steel sheetpile tied-back wall with steel & timber wales located on the seaward side of the wall. The riprap/fish rock habitat bench will create intertidal habitat where a vertical wall with limited habitat value currently exists from +16 ft MLLW to the mudline (ranging from approx. 0 to -6 ft MLLW). The area beneath the east side of the building, above MHHW, will be armored with shotcrete placed in the dry. Riprap will also be placed in a small area under the west side of the building, above +12 ft MLLW.
Canceled.
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