9001 AIRPORT RD Geotech Report 2018-01-02 MF Import

�y��e�ploration. Geofogic Hazard, and PreGmina,Y Geauchnlcal Engu'eering Repon Sho-/sle Sfdlls CeNer Addition Geo(agic Hazards a�M�g�O"'f Eve�en. Washin%�on Therefore, the flow lengch within a temporary sediment control trap or pond � ��'�Y °0 effect on the water quality of the dischazge siuce it is not going to settle out of suspension in the tise it takes to flow from one end of tl�e pond to the other. Reduction of turbidity Crom a cunstruction site is almost entirely a fun`o co�o�e m�S8=atenof the runoff and to prov d ' sediment traps and ponds aze necessary a catchment for sand-s�zed and lazger soil pazucles, but aze very ineffective at reducing �e turbidity of the runoff. Silt fencing should be utilized as buffer protection and not as a flow-control measure. Silt fencing is meant to be placed pazallel with topographic con'ours to prevent sediment-laden runoff from leaving a work area or entering a sensitivc azea. Silt fences should not be placed to cross contour ]ines without having sepazate flow control in front of the silt fence. A swale/berm combination should be constructed to provide flow control raSher than let the runoff build up behind the silt fence and utilize the silt fence as the flow-control measure. Runoff tlowing in front of a silt fence will cause addition��o�e n anna��ol��e a much failure of the silt fence. Improperly installed silt fencing P ]azger erosion hazazd than if the silt fence was not installed at all. The use of silt fencing shouid be lunited to protect sensitive areas, and swales should be used to provide flow control. 7 1 Erosion Hazar_„a Ml��ga�l°n To mitigate the erosion hazards and potential for off-site sediment ttansport, we would recommend the following: 1. The winter performance of a site is dependent on a well-conceived plan for control of site erosion and storm water runoff. It is easier to keep the soil on the ground than to remove it from storm water. The owuer and the d�ersegn ��e�I�� bidto gi e che ground-cover measures, access roads, and staging selected contractoT a workable situiredhmeasures ro r�u� �e �ount of e posed implement and maintain the req ground. A site maintenance plan should be in place in the event storm water lurbidity measurements aze greater than the F.cology standazds. 2. All TFSC measures for a given azea to be graded or otherwise worked should be installed prior to any activity within an azea other than insta11in8 the TESC f ivenearea tunber harvesting. The recommended sequence of construction witlrin a g after timber harvesting would be to insta:� seda ent traps and/or ponds and establish perimeter flow conri'ol pror to starting mass gr g� 3. During the wetter mont6s ef the year, or when large storm events are pcedicted during the summer months, each work azea should be stabilized so that if showers occur, the work azea can receive �`�e rainfal! without excessive erosion or sediment transport• The ASSOCUTED F.ARTH S��E7�`�'ES, lNC. �une Jl. 2008 Page 8 ff,lld-EE%SOL3A5-Pmledt1200B02I31EE1WP