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December 15, 1992 5 923-1184 <br />permcable zones within Ihc relalivcly impervious lill soil. The groundwatcr Icvcl obscrved in <br />fhc pervious, nalive oidwash sand and grevcl probably represenls Ihc conlimwus <br />groundwafcr lablc (or lhc local arca. 'I'hc deplh and quantily o( groundwalcr should be <br />expecicd lo vary tvith the season, local rainfall, and Icvcl of Silver Lakc. Th� annual high <br />groundwaler Icvels should be rxpecled during lhe lalc tvinler and spring months. <br />Surface tvater tvas ol,,erved to be generelly confined lo Ihe larger welland areas wilhin Ihe <br />soulhcrn and ivestcrn porlions of lbr sile and Ihe casl-wcsl trending drainage .iilch <br />lravcrsing lhe central portion of fli � site. Sntall pudJles were naled Ihrou�hout the site. <br />The surface water and �;roundwaler condilions noled were lhose experienced during our (ield <br />tvork conducled on November 25, ]992 and Oclober 1987. T'hese condilions may vary over <br />timc duc to seasonal a((ecls, variations in rainfall, or alleration of thc hydrology of thc <br />surroundin� tvatershed. <br />5. CONCI.USIONS AND ItIiCOMM1iNDA7'IONS ' <br />51 Gcucral <br />I]ased on lhe resulls of our supplemenlal sile invesligalion, we conclude Ihal Ihe geofechnical <br />engineering conclusions and recommendalions presenled in Section 5 of our F,revious reporl, <br />dated Oclober 28, 1987, are applicable lo lhe proposed projeci. We presenl additional <br />geolechnical engineering conclusions and recommrndalions in the (ollo�ving seclions lo <br />supplemenl lhe infortnalion cunlaincd in the 1987 reporl. <br />Thc majority of Ihc silc is undcrlain by poor quality fill and compressible peat ovcrlying <br />dense glacial deposits. In Ihe soulhwest corner of lhe sile, lhe lest �its did not encounlercd • <br />airy (ills or peats. �igurc 2 shows lhe infcrred thickness of existing fill and peat. <br />'fhe building loads can be supporled on sprcaJ (oolings on lill or compacled fill afler <br />excavalion of Ihe exisling loose fills, pcal, and oihcr loosc/sofl soils. Thc deplh of excavalion <br />and b:ick(iil required rangc•s from esscntially zero to about 10 fecL Allcrnatively, Ihe <br />fowidalions can be supporled on tivood piles driven inlo the lill. In amas tvhere lhc exisling <br />(ill and peat is left in place, �ve provide recommendalions lo conlrol selUement and provide <br />an adequate pavemenl subgrade. Specific Peolechnical condusions and recenunendations are <br />presenled belotv. <br />5.2 liuildi��g I�ounJ�lions and Slabs <br />5.2.7 Gencral <br />Shallow conventional sprcad foolings may bc usal in Ihosc porlions of lhc sile where Ihcy <br />can be founded on compelent native lill soil or compacted slruclurel fill a(ler excavalion of <br />unsuifable soils. Wc recommend thal foolin�s nol be founded on Ihe loose fill or peal soils, <br />which are not considered suitablc bcaring malcrial for convenlional sprcad footings due lo <br />Golcler i.ssoclules <br />