4805 BELVEDERE AVE 2016-01-01 MF Import

Beh cdcre La1t Eru7 Evsrc�L µ'ashingta Subsurface Exploration, Geclogic Nazard, and P�eliminary Geotechnica! Engineering Rrpon detailed s�bsurface information organized from the shallowest (youngest) to the deepest (oldest) sediment rypes. 4.1 Strau�ra h Transilionn! Beds Sediments encountered direcdy telow the ground surface in our explorations generally consisted of loose to medium der.se sand with variable silt and gravel content. These sediments generally becamc dense lo very dense below a depth of approximately ]0 feet. Exceptions include the locations o: exploration pits EP-1 and LP-3, located in and just beyond the soudiern portinn of the site, where the near-surface sediments consisted predominantly of stiff �o hard silt. Similar silt sediments were also encountcred in exploration pit EP-10, located across Belvedere Avenue to the west. At the location o[ explora�ion pit EP-3, the silt was limited to the depth interval from approximately 2.5 to 5.5 feet below grouud surface. At the location of exp!oration pit L-P-1, the silt extended beyond tne maximum depth explored of approximately 7 feet. Exploration boring EB-2, located in the northern po�tion of the site, encountercd a layer of hard, brownish gray, micaceous silt within thr sand over the depth interval from approximately 80.5 to 88.5 feet. We interpret these sediments to have been deposited in an environment in transition between the Vashon Stade of [he Fraser Glaciation and the previous, nonglacial time period. "l�he high relative density/consislenc}' characteristic of the transitional beds is due to their consolidation by the massive «�eight of the glacial ice which overrode these sediments during Vashon time (approxima�ely 12,500 to 15,000 years ago). Revie�~ of the regional geologic map 77ie DistriHuiia� n�id Desrnp�inn q(ll�e Geo(ogic Units Di die Mukilren Quadrm�gle, R'nshingrrn� by Jame� Tlinard (1982) indicates that the subject site is underlain by sediments nf the transition�l heds with �'ashon lodgement till along the crest of the adjacent ridec. Clur findin�s arc in �eneral agreement �cith the regional geologic map. 4.2 1lvdroloe�' Gruund �+'ater seepage ��as encountered at the location of exploration boring EB-2 within the s�nd of thc transitional beds below• a depth of approximately 70.5 feet. The elevation where ground water Nas encountered in this buring approximately coincides with the elevation of a spring u�e obsen�ed on the adjacent steep slope to the cast. The ground water was perched atop thc pre� iouslp discussed hard silt layer encountered in this exploration over the depth interval frum approximately 30.5 w SA.S fert. The silt and underlying sand sediments were unsaturated :o the maxirtwm depth explored of approximately 96 feet. It should be noted that thc nccurrence and level of ground �aater seepage heneath the site may ��ary in response to such faciors a� chanecs in season, precipitation, and site uce. — -- ASSOCIATED F�1R7N SC/ENCCJ. Inti. h1�+rr/t S, 'INIJ Fa�e 4 ,.. �.: Ir � .!�� I'•��c�i�...i'�Af k^ u�:l.