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REP19624
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REP19624
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Entry Properties
Last modified
8/24/2016 11:48:17 PM
Creation date
11/27/2007 2:41:43 AM
Metadata
Fields
Template:
DRMS Permit Index
Permit No
M1988112
IBM Index Class Name
Report
Doc Date
5/15/1995
Doc Name
SAN LUIS PROJECT
From
WESTEC
To
DMG
Media Type
D
Archive
No
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i <br />Third Perty Oversight 5 Weter, Waste & Land. Inc. <br />' San Luis Mine June 9, 1994 <br />The tailings disposal facility is a valley impoundment with an embankment constructed <br />across the valley and tailings contained in the lined portion of the valley above the <br />embankment. The design intent of the tailings disposal facility was a managed discharge or <br />' thin-lift tailings disposal facility. A thin lift disposal operation discharges tailings from different <br />locations around the perimeter of the disposal facility. The discharge locations are rotated on <br />a schedule that allows the tailings to be deposited in relatively thin lifts (approximately 1-foot <br />thick). After discharge lines are moved, newly deposited tailings are allowed to desiccate and <br />' density by evaporation and by drainage into underlying tailings. This type of managed <br />discharge system functions adequately when a sufficiently large tailings surface area in <br />combination with a relatively dry climate allow drying of the thin lifts prior to subsequent <br />' tailings discharge. <br />The facility was designed for phased construction. After the initial phase of <br />' embankment construction, subsequent lifts were to be constructed in an upstream manner, <br />with each embankment raise constructed over previously deposited tailings. The embankment <br />was designed as afree-draining or "leaky" embankment, constructed with sands and gravels <br />' to expedite drainage of tailings near the embankment. The design cross section is shown on <br />Figure 1. <br />' In addition to the free-draining embankment, a drainage layer was designed above the <br />liner system to promote drainage of tailings fluids and convey this drainage through the toe <br />of the embankment (Figure 11. This drainage layer was also designed to minimize the zone <br />of saturation (and driving head far flow) above the liner system, as well as provide a <br />protective layer for the liner system. <br />' The composite liner system (which extends beneath the free-draining embankment) <br />consists of a 40-mil thick very low density polyethylene (VLDPEI synthetic liner underlain by <br />alow-permeability compacted silt soil zone. <br />' 2.3 GEOTECHNICAL ISSUES ASSOCIATED WITH THE RAISE I EXPANSION <br /> <br />1 <br /> <br />1 <br /> <br /> <br /> <br />The tailings disposal facility was approved for Phase I construction, with the Phase II <br />design approved in concept. The detailed design of the Phase II, Raise I Expansion was <br />submitted for DMG review in July 1993 (SRK, 1993a). <br />DMG's original concern with the Raise I Expansion was with potential instability of the <br />Raise I Embankment as it was to be constructed over recently deposited tailings near the <br />original embankment. The Raise I Embankment could become unstable or experience <br />excessive settlement if constructed over saturated tailings. As a saturated zone of tailings <br />was discovered beneath the embankment during field investigations (SRK, U993a1, the <br />potential for unacceptable deformation of the Raise I Embankment did exist (DMG, 1993a). <br />These concerns were alleviated after BMR( installed DMG-mandated piezometers through the <br />existing embankment (BMR(, 1993f1, and it was verified that the phreatic surface was no <br />higher than 10 feet above the Phase I Embankment foundation/liner interface (BMR(, 1993f). <br />DMG also required that BMR( initiate a monitoring program to observe the quantity and rate <br />of tailings consolidation which was occurring as construction of the Raise I Embankment <br />continued (DMG, 1993c). <br /> <br />
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