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t <br />ii «UH <br />«*PI1fT*: <br />9.0. Box SSlOi <br />nplm., tm 5S43S <br />(«12> 941-5400 <br />m <br />ung opinioh <br />» of Fill to <br />ig Landfill <br />TH-12 at <br />I Lake <br />linneaotft <br />ition froifi three <br />orroed in April, <br />additional fill <br />>ere of the City <br />i existing laad- <br />ble failure into <br />t proposed land- <br />i the surface to <br />(rstand that the <br />Landfill area as <br />1 conditions in <br />assumed similar <br />although depths <br />first filled in <br />ted your desire <br />'ill area which <br />fill over the <br />1 area. <br />A <br />bi. <br />~VZ <br />13-157 <br />Fart Oottstreetlon -I-Nay 31. lill <br />foe Indicated that tlie bottom of the emieting landfill ■ateriai <br />If at about elevaiioo 9i0». The existing surface aleeatloa of <br />toe undisturbed wetland area Is at about eleeaiiwi 912* feet. <br />th«s 4-foot difference In elevation probably repfesents what <br />teould expect to be the tmo^nz of settleoent that baa resultadl <br />frtfi toe weight of tbo existing landfill natarial coapreasing the <br />organic subsoils balou. foe indicated that the existing landfill <br />natarial la about 14 foot thick. <br />Judging Iron the langth of tina that the aaiatlng 1. ndflll <br />natarial haa baan in plate, and your ladlcatlon that thura have <br />bean ao prawious atablllty problana. It ia oar opiaioa that the <br />proposed addition of 5 feat of ninaral aoll sboea the top of the <br />axiating landfill gradaa prasaota a wary alight risk of ahaar <br />failure. Our experlsnca with prolecta where edditlonal fill Is <br />placed above axiating landfill natariala above swaM ^poaita Ml <br />rttuitad in additional sattlaanat, but no ahaar falluraa. <br />con; dtition of the axiating landfill natarial la auch that it <br />probably poaaaaaas a rather high intarnal angla of frictic^ and h <br />rather high shear strength. toa aattlanant that haa occurred <br />over the peat 30 yaara has also iocraaaad the shear atrangth of <br />the upper sons of organic aoila which lasaaoa the risk of <br />or pttocHiny failure aa a result of plseing an additional <br />surchargo load. Thus, bassd on this infomatioo. it is our opi­ <br />nion that the addition of 5 fast of fill over the area prsaanta a <br />very slight risk of snbanknent fsllure. <br />It should be noted thst soil borings with power sguiptant have <br />not bean taken in the existing landfill sfsa to svsluats the con- <br />position and strength of the existing Isndfill natsrisl and <br />strengths end depths of the underlying organic soils. If the <br />sssusiptlons wa have sada ara inaccurata# our avaluation of the <br />potantlsl risk nay naad to te rs-avsiuatad. Additional borings <br />and tests st this tiu» do not sppssr wsrrsntad for tho 9r^»hg <br />planned. Howavsr, st a sinisua, wa reconn end that prior to <br />placing any fill, ssvarsl settlenent nonitoring pistes m <br />Ifistsllsd in various srsai, preferably around the <br />•sistirm landfill ll»4tSf ar.d that thm acklltlonal fill than ^ <br />placed in two stages of 2 1/2 fast par stag* • Bat%#ssn lifts, the <br />nonitoring plstss should be referenced to aid <br />rats of ssttlsnant caused by the addition of new fill. Possibly <br />a period of one to four weeks should be set ssida bstwaan staged <br />fill applications to allow nors time for nonitoring the platss. <br />If the additional ninaral fill sxtsnda over areas thst srs pre­ <br />sently virgin wetland, the risk of smbsnknent failure Is atgniCl- <br />cantly higher and a cnch more controlled filling technique win <br />be appropriate. <br />t: <br />I.BR/iun <br />e;'j<J5pr^ <br />f i« <br />i <br />♦ <br />I <br />f he f onteni <br />mm tnmiu*