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SE7VT BY ~ ~17-97 ~ 15 ~ 29 : I NDEPFJVDINCE M I N I N•G ~ 303 832 8106: # 3
<br />needed with high pregnant solution heads. The ptttttping systtms of the LVSCSs for both Phase [and Phase Ii
<br />maintain solution levels in the LVSCSs that tniaitnize the risk of traosmiaing the pressure appliod to the upper liner
<br />by Pregnant Solution to the lower liner system. Considering that (1) the fluid depth, based oa which CC&V
<br />trmnagcs the runoval of solution from the LVSCS, is measured az the lowea[ point in the entire triple-lined syctetn,
<br />and (2) the rapidity of the response by LVSCS flow to a rise In pregnant solution head, this irtditates (and wnfitms)
<br />the high permeability of the LVSCS gravel as well as the effectiveness of the ptrforated pipe drain system az tha
<br />base of the LVSCS. 'Chas, the potential for the LVSCS fluid solution m ssturare the full thickness of the LVSCS
<br />gravel is quite low.
<br />The LVSCSs for both Phases I and ll were ddigaod with submusible pumps sad coostructal to avoid long-term
<br />transmission of the full wtttplitttt:nt of pregnant !wlurion "head" (which refers to the hydrostatic pressure head
<br />generated by the column of Iuid above the liner system) to the double litter system (this is commonly referred to
<br />as a 'composite liner' and cansista of cotrtpac[od soil liner and synthetic litter) that underlies the entire Valley Leach
<br />Facility. These systems are being operated in compliance with the design speeifiwtiotts and the permit
<br />cotamitmeats, and the systems are achieving their objective of fluid removal, The Cresson Projcet i,VSCSs are
<br />unusual in that they axe pumped, while tmst other drainage layers for lined con*~;nrtv+.u, considering all types of
<br />liner systems, are gravity drains. This system has positive wntrol over a wide tattge of entrained fluid flow through
<br />the pumping.
<br />CC&V has htxn operating the Phase I LVSCS since January 1995, for approximately 26 months, and began
<br />operations of the LYSCS far Phase lI is early February of 1997, above 2 months ago. Obsmatioaa to date of both
<br />systems indicate that, in comparison to the rate of flow ptuhpetl from the Phase I LVSCS since 1995, the flow rate
<br />from Phase II LVSCS observed is higher than that observed in LVSCS I. Of worse, the PIS area of the Phase
<br />II Brea has less-steeply dipping topography and, therefore, more atce of the upper liner is tAVered by solution for
<br />a given pregnant solution head than at Phase I. More flow a[ an equivalwt head mould, then, be expected.
<br />Nonetheless, the installed LVSCSs of ~ Phases have the capaaty m remove fluid from their tespouive LVSCS
<br />gravel fills az rates that will. and do, wntrol the head experienced by the underlying wmposire liner system. This
<br />removal pruuxlure ~+tn,.n;,r° rite potential to develop, over time, a "driving force" toward or into the wtoposite
<br />liner through ttte use of the paonping system. Tltc prescttre levels on the wttrposite liner systetrts within the area
<br />of the LVSCSs have been maintained at suitable levels that do not allow ttansmissiou of HVSCS fluid ec,uams (i.e.,
<br />"pressure') to the lowermost wutposite liner. Further, and as is evidenced by ezamiaatioa of the as-built wmours
<br />on the Soil Liner Fill, [he heads ttteasured by the LVSCS art: limirtd to a small arts of the Pteg»aat Liner Syarem
<br />('PLS'), which is the area of the sump (ta. 30' x 100') and possibly smaller (in view of the sloping of the base
<br />of the sump inward these pumps). Theac hpdc in Phase 11 have beta maintained 8< low levels just u is normally
<br />achieved For Phase I. As hu been the case since initiation of opue[ions, there is m indication of eay escape of.
<br />leach solution from the Valley Leach Pacility, either through the underdrain system or the leak Detection Sttatpa,
<br />which wafitttu the proper functioning of the Valley Leach Facility.
<br />Ia CC&V's 1993 Application for Amendment Number 6 to the teCrrenced permit, a theoretical estimating technique
<br />was used to project the order of tnagaitude of flow that otu might amicipate through a single synthetic liner
<br />cantainirtg a "normal' number of imperfections. See Volume 1, §6.76., pp fr31 rhmugh 6-33 (for the PLS). This
<br />dexription drew its information from other material in the Appliwtioa, specifit~lly from li4.8 of the document titled
<br />"Pertrdtting Level Evaluation of the Expansion of the Mining and Ore Processing Facilities -Casson Project,"
<br />whidt is in Voltttne i[ (ace pp 22-28 of that document). The estimation technique used me approximations reported
<br />by Bonaparte ct al (1987), in "Bsektgottnd Docutncnt on Proposed Liner and Leah Detection Rule" (EP,-,/530-SW-
<br />87~)IS),13onapatte et al (1989), in "Rates of Lealcage'I]trough Landfill Liners," and Yan 2yl (1960) in "ctUiabiliry-
<br />IJased Design of Heap Leach Pads and Ponde.' On lone 13, 1995, CC&V provided a more wtttplete axplanarion
<br />of the estimating technique. Ia particular, CC&V dcsc:ribed that the estimating tecbaigtte was hot designed by the
<br />Envirottrtteatal Pro[a;tion Agency ("EPA ") to sern as a litruratioa oa pum ed drainage systems: rather the estimates
<br />were developed fur purposes of sizing, principally, vi drainage systems in a mamter to mint..,+~. the delay is
<br />draining fluid through the drainage layer and to thereby limit the potential for the fluid to fill the drainage layer in
<br />a manna? that transntiucd much larger fluid pressures to dtC underlaying liner system.
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