4027 4TH ST SE 2018-01-01 MF Import

January 14, 2003 HWA Proiect No.2002-146-21 4.7 TEMPORARY EXCAVATIONS AND SHORING Excavations may be needed to facilitate construction of the new pile caps and to install utilities. Based on the soil conditions observed in our explorations, we anticipate that the on-site soils can be excavated using conventional excavating equipment. Maintenance of safe working conditions, including temporary excavation stability, is the responsibility of the contractor. All temporary cuts in excess of 4 fcet in height should be sloped in accordance with Part N of Washington AdminisVative Code (WAC) 296-I55 or shored. The existing fill and alluvial soils classify as Type C soil and may be inclined no steeper than 1%H:I V according to WAC 296-155. This allowable cut slope inclination is applicable to excavations above the water table only. Flatter slopes may be required where ground water is present. With time and the presence of seepage and/or precipitation, the stability of temporary unsuppoRed cut slopes can be significandy reduced. Therefore, temporary cut slopes should be protected from eros�on by installing a surface water diversion ditch or berm at the top of the slope and covering the wt face with well-anchored plastic sheets. Heavy construction equipment, building materiais, and surchazge loads such as excavated soil should not be allowed within l/3 the slope height from the top of any excavation. 4.8 DEWATERING Based on the site topography and proximity to the Snohomish River, ground water may be encountered at relatively shallow levels. It should be noted that ground water conditions can vary substantially over time, with the tides, and over relatively short distances. Although not planned at this time, if the pile caps extend significantly below existing grade, the conhactor should be prepared to deal with ground water during conswction. We understand that the City and Plant may require. all groundwater to be released into the Water Pollution Control Facility and not re-infiltrated into the environment. Design and implementation of any dewatering system is the responsibility of the contmctor. 4.9 SITE DRAINAGE AIVD EROSION CONSIDERATIONS Surface runoff can be controlled during constcvction by cazeful grading practices. Typically, these include the construction of shallow, upgrade perimeter ditches or low earthen berms and the use of temporary sumps to col(ect runoff and prevent water from damaging exposed subgrades. [n addition, measures should be taken to avoid ponding of surfacc water during construction. Pcrmanent control of surface water should be incorporated in the final grading design. Adcquate surface gradients and drainage systems should be incorporated into the design '_00:146 ¢port - final 1i HWA GEOSCIENCES INC. ��