1530 51ST PL SW 2016-01-01 MF Import

Geotechnical Gnginccring [valuauon Lcucr Mosman Bascment Evcrctt, Wazhiogton Erosion Control Measures NGA File No. 886013 December 17, 2013 Pagc G The erosion hazard for the on-site soils is considcrcd to be sligh[, but the actual hazard will be dependent on how the site is graded and how water is allowed to concentrate. Best Management Yrac:ices (BMPs) should be used to ,:ontrol erosion. Arcas disturbed during conswction should be protected from erosion. Erosioi: control m�asures may include diverting surface water away from the stripped or disturbed areas. Silt fences and/or straw bales should be crected to prevent muddy water from leaving the site. Stockpiles should be covered with plastic sheeting during wet weather. Disturbed areas should bc plantcd as soon as practical and the vegetation should bc maintained until it is established. The erosion potential for areas not stripped of vegetation should be low. Temporary and Permanent Slopes We anticipare that temporary excavations will be utilized around the basement for the purpose of installing the drainage and waterproofing systems. Temporary cui slope stability is a function of many factors, including the :ype and consistency of soils, depth of the cut, sureharge loads adjacent to the excavation, Ieng?h of time a cut remains open, and the presence of surface or goundwater. It is exceedingly difficult under these variable conditions to estimate a stable, temporary, cut slope angle. Therefore, it should be the responsibility of the contracror to maintain safe slope configurations since he is continuously at the job si�e, able to observe the subsurface materials and groundwater conditions encountered and abic to monitor thc nature and coodition of the cut slopes. 7he followiug informntion is providcd solcly for the benefit of the owner and other design consultants and should not be consUucd to imply that Nelson Geotcchnicai Associates, Inc. assumes responsibility fer�ob site saCcty. Jot sitc s�ifcty is tl�e solc responsibiliry of thc project contractor. For planning purposes, wc recommcnd that temporarv cuts in lhe on-site soils bc no stecper than 2 Horizontal to I Vertical (2H:IV). if significant groundwater seepage or surface water Flow werc cncountered, we would cxpect that flauer inclinations would be necessary. Wc recommcnd that cut sbpes be protected from crosion. The slope protection mcasures may include covering cut slopes with plastic shceting and diverting surface runoff away from the top of cut slopes. We do not recommend vertical slopes for culs deeper than four feet, if worker access is necessary. We recommend that cut slope hcights and inclinations confortn to appropriatc OS}iA/WTSHA rcgulations. NELSON GEOTECHNICAL ASSOCIATES, /NC.