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SC�lCillUrf 23, 2��% <br />Mr. Jeff \Vhiniey/Brookstune Development <br />�x�� �o� no. �nosa <br />�.�E� 3 <br />silt, s�nd, gravel, and scaucrcd cobbles and bouldcrs, oRcn rcferrcd to as "hard pan". Thc fresh <br />till is practically impen�ious. It has the strength of low-gradc cor.cretc and can stand in a stcep <br />natural or cut slopc and remain stable for a long period. If remains imdisturbed and wcll-drained, <br />the fresh tiil can provide e�ccllcnt fotmdation support �vith littic setdement expectcd. <br />Thc �Vhidbey fonnation is composcd of non-glacial rivcr (lood-plain dcposits. lt consists of <br />light-brown to gray, finc-sandy silt to claycy silt wilh occasional gravcl. Thc \Vhidbey fonnation <br />deposits arc generally very-stiff to hard as they had been over-consolidalcd by Veshon Glacier. It <br />is of extrcmely low permeabiliq� and tends to perch stonmvater infiltraiing into thc more. <br />penneable surlicial soils. Seepagc would emcrge out of slopes where thc �Vhidbcy fortnation is <br />cxposcd. �'Vhen the seepage pressure is high, the emerging ���ater can erode lhe soils in thc <br />seepage zone and cause thc o��crlying soils to slough and slidc. <br />'Chc V4'ludbcy lormation is normallY ovcrlain by an advance out���ash soii unit. l�hc advancc <br />outwash soil unit is composed of stratified sand .md gravel �vith minor amounts of silt and clay, <br />dcpositc� by ihc melhvatcr of advancing glacial icc. Duc to thcir gcncrally gramdar composition, <br />tlic advance ouhvash deposits arc of moderatcly high pernicability. 'l�he advancc ouhvash <br />deposits are glacially overridden and are gci�ernlly dcnse to vcry dense in its nalural, undisturbed <br />state, cxcept the top 2 to 4 fce( �vhere cxposed on slopes which may be wcathcred te� a loose to <br />mcdiunrdcnsc stalc. T'hc advancc ouhvash deposits can stand in stccp cuts or naliu�il slopcs �or <br />c�tcndcd period whcn undisturbed. �'��hcrc cxposcd on slopcs wilh poor vcgctation covcr and <br />subjcct to storm runoff rn groimdwntcr sccpagc, tlic advancr. ouhvash dcposils can bc gradually <br />croded and may slough and redcposit to a flaucr inclination. <br />Ground�r:�tcr Conditiuns <br />"I he band of slopc covcrcci by horsetail bushes dcscribcd abovc indicates thal the prescnce of <br />advancc ouhvash soils ovcrlying thc \Vhidhcy fonnation on thc slopc. Stormwatcr can sccp inlo <br />LIU & ASSOCIATCS, INC. <br />