REP19624

• 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

Third Party Oversight i Water, Waste & Lend, Inc.
' San Luis Mine Juna 9, 1994
' EXECUTIVE SUMMARY
' This document contains results of the third-party review for the design and
construction of the Phase II, Raise I Expansion at the San Luis Mine in Costilla County,
Colorado. This document was prepared on behalf of the Colorado Division of Minerals and
Geology (DMGI and Battle Mountain Resources, Inc. (BMRII, to provide technical review of
issues related to the expansion. This document was organized to address the specific issues
which concerned the DMG regarding construction of the expansion. This report was initially
submitted to the DMG in January and has been revised to include information from the
technical review of the Final Construction Report prepared by BMRI.
The third-party review consisted of an initial site visit, review of the original design and
' geotechnical issues, review of technical submittals, construction oversight, evaluation of
quality assurance testing, and technical review of the Final Construction Report. Discussions
on the design issues, the intent of the design, and the initial and final phases of construction
' are provided in this document. Daily field lags and weekly construction activity updates are
included as appendices to this document.
' The tailings disposal facility is valley impoundment operated as a managed discharge
or thin-lift system. The tailings embankment has been designed for for three stages of
construction. The elevation of the Phase I Embankment was 8590 feet. The second stage
expansion consisted of increasing the height of the tailings embankment by constructing the
Phase II, Raise I Embankment to a height of 8605 feet, and increasing the lined irpoundment
area to the ultimate tailings elevation. The embankment was constructed in an upstream
' manner over previously deposited tailings. The liner system consisted of a low permeability
compacted soil layer overlain by a synthetic liner. A drain pipe network was placed on top
of the synthetic liner, which was then covered by a drainage layer/liner cover.
' Although materials utilized for the construction of the Raise I Embankm@nt were not
within the specifications stated in the original design report, it is WWL's opinion that the
' embankment will generally function as intended. This conclusion is based on acceptable
quality assurance testing during construction and the assumption of appropriate monitoring
after construction. Although no information was found concerning their installation,
' performance of the embankment and tailings disposal facility should be verified by the
installation and monitoring of piezometers. From a review of the settlement data provided for
the Raise I Embankment, the embankment appears to be experiencing insignificant settlement.
'' Approximately 0.75 acres within the expansion area contained out of specification
drainage layer/liner cover materials based on particle size distribution. This area is small in
comparison to the overall expansion and should not significantly affect the overall
performance of the drainage layer/liner cover. The permeability of the drainage layer/liner
cover material is one to two orders of magnitude greater than the mean tailings permeability
(based on results of confirmatory laboratory tests). Based on this permeability and the
performance of the drainage layer and drain system after Phase I construction, the drainage
layer should perform as intended in the original design.
' From the results of field quality assurance and laboratory confirmation tests, it appears
that the low-permeability layer should perform as intended in the original design. Quality
assurance test results for the installation of the synthetic liner were acceptable. Installation
' of the drain pipes on top of the liner system and drain pipe spacing were also adequate.