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1 IJ ~~ 1 LI 1 Third Party Oversight 11 Water, Waete $ Land, Inc. San Luis Mine January 10, 1993 As seen from the tables above, the major change to the specifications was a significant increase in the percent passing the #40 and #200 (fines) screens. With increasing fines content, permeability of the Raise I Embankment could potentially be lower than. that which was intended in the original design and lower than that of the original (Phase q embankment. A lower permeability within the embankment could result in a decrease in the rare of tailings fluid drainage into the embankment, and a corresponding increase in the phreatic surface within the tailings. In addition to the gradation change, a larger maximum particle size was defined in the revised specifications. Piping of tailings into and through the embankment is E1 potential if significant quantities of oversized materials were placed in the embankment concurrently with low compactive effort. 3.2 INITIAL CONSTRUCTION During the initial site visit, significant quantities of material larger than the revised maximum size specification I6 inches) were observed on the top surface and upstream face of the embankment. Materials up to 30 inches in diameter were located along the upstream face of the embankment. No embankment fill was being hauled and placed on that day. 3.3 TECHNICAL ISSUES The key technical issues for acceptable Raise I Embankment materials are shear strength (for acceptable static and seismic stability), permeability (far drainage of tailings fluids), and filter compatibility (for protection against piping of tailings into the ernbankmentl. The proposed Raise I Embankment material was swell-graded, and if compacted would form a material with acceptable shear strength and protection against piping. The remaining issue is permeability and drainage of the Raise I Embankment material. Although materials used for the Raise I Embankment were not within the specifications stated in the original design report ISRK, i 993a), acceptable drainage of the Raise I Embankment can be verified by the installation and monitoring of piezometers. Five piezometers installed at the crest of the embankment and screened at or near the base of the fill, and five piezometers installed at the toe of the upstream face of the embankment, would allow monitoring of the phreatic surface (if present) within the embankment or in tailings (if present) near the embankment. Water levels within the piezometers should be monitored on a quarterly basis.