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Iune 13,2023 <br />HWA Project No. 2022-188-21 <br />4.12.5 Temporary Excavations <br />For all excavations maintenance of safe working conditions, including temporary excavation <br />stability, is the responsibility of the contractor and must be performed in accordance with Part N <br />of Washington Administrative Code (WAC) 296-155, latest revisions. The fine-grained <br />alluvium and coarse-grained alluvium and fill at the site classifiy as Type C soils. <br />Time and the presence of seepage and/or precipitation can significantly reduce the stability of <br />temporary unsupported cut slopes. Therefore, all temporary slopes should be protected from <br />erosion by installing a surface water diversion ditch or berm at the top of the slope and by <br />covering the cut face with well-anchored plastic sheets. In addition, the contractor should <br />monitor the stability of all temporary cut slopes and adjust the construction schedule and slope <br />inclination accordingly. <br />4,12,6 Erosion and Sediment Control <br />The site soils have relatively high fines content and in the wet season this will result in <br />substantial entrained sediment load in runoff water and, in the dry season, large amounts of dust <br />and fines. <br />The work site should be protected from uncontrolled runoff during construction by constructing <br />berms and ditches to direct runoff around the work site, and the use of temporary sumps to <br />collect runoff and prevent water from ponding and damaging exposed subgrade areas. Crushed <br />gravel should be provided, where necessary, to protect against soil erosion. Erosion of the work <br />site can be minimized by careful grading practices, the appropriate use of silt fences and by <br />implementing the recommendations in the Wet Weather Earthwork section of this report. Surface <br />grading measures and drainage systems should be incorporated in the final grading design such <br />that surface runoff is permanently directed away from paved areas and into swales or other <br />controlled drainage devices. <br />Permanent fill slopes should be protected from erosion by seeding for growth of vegetation as soon <br />as possible after grading. <br />4,12.7 Wet Weather Earthworks <br />Although earthwork under wet weather conditions is not recommended for this site, if it is <br />necessary, the following recommendations apply to wet season earthworks: <br />Earthwork should be undertaken in small sections to minimize exposure to wet <br />weather. Excavation or the removal of unsuitable soil should be followed promptly <br />by the placement and compaction of a suitable thickness of clean crushed rock or <br />sand and gravel. The size and type of construction equipment used may have to be <br />limited to minimize soil disturbance. <br />a <br />2022-188-2I KCTS - Final Geotechnical Report 24 HWA GEOSCIENCES INC.