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Pacific Ridge — DRH, LLC ES-8528.01 <br /> July 18, 2022 Page 6 <br /> Topsoil and Organic Material Removal and Replacement <br /> At four of seven test locations, relic topsoil horizons and/or buried organic deposits were observed <br /> underlying the fill — the buried organic soil horizons ranged in thickness between roughly one to <br /> two feet. The following is recommended for topsoil and organic material removal and <br /> replacement in structural areas: <br /> • Remove upper existing fill soil, segregate from organic and deleterious material, stockpile <br /> and protect from moisture. <br /> • Remove topsoil and organic material. <br /> • If moderate to heavy groundwater is present following removal, place a layer of quarry <br /> spalls and cover with filter fabric to establish a stable surface. <br /> • Begin mass grading with structural fill, utilizing the stockpiled existing fill if deemed <br /> suitable. <br /> Excavations and Slopes <br /> Based on the soil conditions observed at the subsurface exploration locations, excavation <br /> activities are likely to expose existing fill soils within the upper one to five feet of existing grades. <br /> Underlying the fill, native soil should be expected, becoming very dense and weakly cemented <br /> between roughly five and eight feet bgs. <br /> The following Federal Occupation Safety and Health Administration and Washington Industrial <br /> Safety and Health Act soil classifications and maximum allowable temporary slope inclinations <br /> may be used: <br /> • Areas exposing groundwater seepage 1.5H:1 V (Type C) <br /> • Loose soil 1.5H:1 V (Type C) <br /> • Medium dense soil 1 H:1 V (Type B) <br /> • Dense to very dense, cemented native soil 0.75H:1 V (Type A) <br /> Permanent slopes should be planted with vegetation to both enhance stability and minimize <br /> erosion and should maintain a gradient of 2H:1V or flatter. An ESNW representative should <br /> observe temporary and permanent slopes to confirm the slope inclinations are suitable for the <br /> exposed soil conditions and to provide additional excavation and slope recommendations as <br /> necessary. If the recommended temporary slope inclinations cannot be achieved, temporary <br /> shoring may be necessary to support excavations. <br /> Earth Solutions NW, LLC <br />