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I~ JUN ~ 95 1515 No .005 P.08 <br />, ~ <br />~~ 1 <br />SIEFFEN HOBEI~TSQN AN!) Klfi '(f N <br />C:onsul,~nG Engineers and Sr..~ent~sts <br />MEMORANDUM <br />TO: Ahu,t Scott, BMRI <br />i~ <br />l~lt[)M;\ )~~ )ave )lallrnan, Steffen Robertson & Kirstcu (U.S.), Ittc. <br />1)A'1'1s: ,lanttury 20, 1994 <br />1tL•': SAN LUIS i'ROJEC7' -TAILINGS IMPOUNDMENT PIF~%OMETERS <br />As per your rcyuest, we. have prepared this memorandum to provide our recommendations wiU, <br />regard «, the installation of piezometers in the San Luis Project tailings. As a result of their <br />review of the design and i:in,stntction of the first Yhase II dam raise, the Division of Minerals <br />and Geology (Division) t~ueguested the installation of standpipe piczometcrs on the existing <br />tailings surface in the amt of the proposed second Phase II raise. The intent is to provide <br />itifcirtnniion on t c- s~at~'u~ion conditions in the tailings which will form the foundation for the <br />second r:usc. <br />We have serious nttcrvations shout the data which can be obtained through the: installation of <br />standpipe piczonieters in the tailings. As demonstrated by the CP"1' program conducted for the <br />first dam raise, saturated conditions within the "beach" tailings is presently restricted to <br />iclativcly thin isolated layers of tailings. If such layers arc also present within the tailings <br />deposited prior to construction of the second raise, the standpipe piezometers intercepting Ihi•sc <br />layr.rs will provide no indication of the extent of the saturated zones. Furthermore, the suutdpipe <br />piezometers would provide for hydraulic communication between tailings layers. Water cvminl; <br />into the piezomrtcr from a saturated layer or freshly deposited r<~ilins would flow from the <br />piezontclcr out into tailings which had desiccated and were not saturated. 'thus, the presence <br />of the pieronu•.tcr would acu,a)ly alley the characteris[ics of the tailings immediately surrounding <br />the piczomc.ter. In addition, the ability to physically access the standpipe piezometers for taking <br />rradinfs would he limitctl to periods when the tailings in the vicinity had desiccated sufficiently <br />to allow foot traffic on the tailings. 'ITus, the ability to read the pieramr.lers during periods of <br />active. tailings delwsiliun in the area is doubtful. <br />ns an altcnu,tivc u, the standpipe piezi,merers, we rccummend the installation of a series u( <br />vibrating wire piczometcrs to provide piezomeu•ie data within the failings without altering the <br />cltaractrr islics of thr tailings. 'these piezometers could be utilized to provide piezomm~•ic Ie.vcl <br />dour both before and aflrr construction of the dam raise as direct access is not required for <br />t.,king, rcarlings, 1"hr. rncaose;d figure depicts a piezometer "tree" which could bc. utili~etl lv <br />piovide. piczvmetric data within the tailings without altering the characteristics of the tailings. <br />I'I,c interval hctwcxn piezrnncu:rs or the total number of piezometers could br. adjusted to suit <br />the- 17ivision's re:duiu•u,cnrs. <br />StC+Ilr.i fgobei ison and Kirslcn (U.S.), InC. <br />s2 ;ioWh Vancr. Street, Lakewood, Coiorano Fl0227. U:i.l1 <br />Tci Cs(C4, r~t3, t333 Fncsimde (;iG31 at35~99a/ <br />;)!~icr nllire5 m U S.A.. Canada. Uialed KingGUrn and Alncn <br />