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OLORADO DEPARTMENT OF HEATH. Water Ounliry Division <br />Nionnte - Pnge 3. Permit No. CO-0043648 <br />At Outfatl OOIA, the potential sources of pollutants are the four-inch spring collection system beneath the Arequa u c r <br />Area, the active Arequa Gulch Overburden Storage Area (which includes the lower layer ofrelocated <br />ill tailing material in Arequa Gulch, rand subgrade <br />Overburden Storage residual Carlton M <br />material underlying the VLF which includes detoxified Ironclad tailing material. The following descriptimt oft e mme <br />Carlton Mill tailing material), the active VLF, Menbiiity of ELGs to discharge Outfa11001A. <br />features is provided to support the discussion of the app <br />Summa -M»rragQ nhdesrofA~ gala Gulch ivOverburdenmaterialsthave been sttorred in what referred tocas tlae~ Arequa <br />dient om the mining operations. Slightly downgradient <br />in the far uppe ' a short distance downgra .~' <br />Gu1eM overburden storage area (OSA)' nnodiorite in the area <br />of this point the VLF has been constructed. Flaws in Arequa Gulch historically were associated with n spring system t ra <br />Quad water that is now collected by <br />was the surface expression of shallow ground water in the colluvium, The tens penneab e ~ edundertheVLF <br />functioned as a physical barrier responsibleforthe surfnceexpression ofthe slrallowgr <br />the spring collection system. Water captured by the spring collection system is separatedfrom rand convey <br />to a lower portion of ~~toconveyshallowgroundwat~ thatrwouldnlsohavehiostor~callyflowedtothelowertenchesof <br />ewistructed ur:der the <br />Arequa Gulch. <br />Carina Collection System -The spring collection system consists of a series of perforated pipes that were laid in rtnturnl y <br />wet nretts identified during constniction in the upper Arequa Gulch urea. As noted above, the springs are a surface <br />g adientsideof <br />expression ofshaliowgroundwnterinthecolluviumneartltegeo(ogiccontactwiththegrarrodiorite. Theperfornte pipes <br />connect to a solid walled four-inert dimneter~pe thntfl ere ermit derneaih the VLFand erner es on the downgr <br />the VLF Phase II toe bean, as shown an Fi re 5 of P ua Gulch <br />Underdrnins -The Phase I primary underdrain extends from the Phase II toe bettn into the upper reaches ofAreq eel to <br />where the old State Highway 67 fill slope crosses upper Arequa Gerice'surroundedbyro~frlltha~angesfrom ~Of low- <br />mtderdrnin is n 2d-inch diameter corrugated perforated polyethylene p p <br />the Phase IVa double liner system in <br />100feet in width and two tof ve fe~rpericover th e rimary six mclres of select structural fill, geotextile, and 8 -rm ve <br />underdrain fill. Extension of underdrain into <br />VLDPE) P <br />densitypolyethylene (" underdrain. Secondary Underdrnins extend forum feet wride a d two jeer deep. <br />2002 Mns entirely covered the Phase I primary <br />what were identified as "wet areas" during construction activities and are a minimum off <br />The Phase I secondary) nderdrnin excavations nrefilledwith granular ntnterinl less than 12 inches in sizeand covere wrt t <br />ect sh'uciurnl fell, geotextile, and 80-rail VLDPE liner. The secondary wrderdrains join the rock fall <br />underdrains. All of the Phase <br />rand secondary <br />at least six inches ofse <br />of the primary underdrain. A similar design was used for the Phase II primary <br />1 and 77 underdrains are beneath the VLF multi-layer Liner system. The watershed area potentially contributing o <br />tirruall decreases as die VLF advances upgradient in the Phase III and Phase N areas. As a result, the <br />base III and Phrase IV underdrnira consist of excavated <br />underdrains con Y <br />canfigurntion of the Underdrnins changes accordingly. The P <br />trenches f lied with granular material wrapped in geotextile. These trenches range from three feet to five feet in wilt an <br />eet to three feet in thickness. Locations of the existing Prn nethelleQ~lp g solution contained wul initherVLFust'ng a <br />two f <br />Figure 5. The underdrains below the VLFhave been isolated f 'French drain"), which surrounds the <br />multi-layer liner system. At thePhnse II toe bean, wtltedtwtith broken rock ~~e uaderlying theVLFexits the system, t ere a <br />a constructed 5 feet deep, 100 feet wide channel, f stream towards the face of the toe bean: <br />following pipes, which are listed in order, goingfrom left to right when looking up ortion of the VLF ("north <br />a) One perforated 24-inch pipe, which collects ground water flowing underneath the western p <br />underdrain'). lmrned <br />er the leaching operation was completed. It has been <br />b) One 24-inch snotliW [ a0~odws fromlithe ArequatGutch OSAI aft algid at the upper end, but which was original yp <br />removed rat the upper end due to site activities rand is no longer needed due tofuture routing ofstorm water in diversion <br />to carry stor <br />channels. <br />c) One 4-inch solid-walled Pipe' which carries the flow from the historic Arequa Gulch spring. <br />south <br />er orated 29-inch pipe, which collects ground water flowing underneath the eastern portion of the VLF (" <br />d) Onep f <br />underdrain ). <br />The constructed rock chamrel surrounding these pipes also curries local ground water flowing underneath the V <br />