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During our site visits, we have observed exposed portions of the underdrain extending <br />up the two drainages beyond the limits of refuse till. We were provided photographs from <br />1991 and 1993 (Fig. 1) which show the drain extending above the fill present at the time <br />of each photo. These photos and our Bile observations ;ndiCaie ii,0 drain has been <br />installed in substantial conformance with the approved plan. <br />We have no knowledge whether the keyway cut planned at the base of the pile was <br />installed. If you have records regarding the keyway installation, we can review them. <br />Compaction and stability of the refuse was the focus of our investigation in 1991. We <br />have enclosed a copy of our 1991 report for MLRD reference. In general, our <br />investigations have indicated compaction of the refuse fill has generally achieved 80 to <br />100 percent of maximum ASTM 0698 dry density. We have reviewed compaction test <br />data by Lincoln-Devore, Inc. for testing which occurred September 30, 1987. In addition, <br />we performed additional tests in May 1993. The Lincoln-Devore tests showed 77 to i 00+ <br />percent compaction and our recent tests indicate 89 to 100+ percent compaction in the <br />top poRion of the fill (Appendix A). In general, we do not feel the planned 90% <br />compaction criteria has been met for the refuse fill. During our 1991 study, we found the <br />stability of the refuse slope to be comparatively insensitive to material density. Our <br />analyses showed the refuse till exceeds required factors of safety for slope stability. We <br />recommended measures to lower moisture content of the refuse materials to enhance <br />stability. Basin Resources has taken measures 20 achieve lower moisture as described <br />in our letter of May 3, 1993. These measures have apparently also enhanced the <br />workability of the materials (that is, the ease of compaction) as indicated by our recent <br />compaction tests. <br />MLRD requested we provide an opinion of the acceptability of the "dirt" and rock materials <br />which have been placed in isolated, wet areas of the fill surface to allow equipment <br />access. MLRD personnel indicated large rock fragments (up to six feet) have been <br />observed. In our opinion, the placement of these materials in the refuse pile is acceptable <br />and does not significantly influence slope stability of the facility. We have not found <br />documentation that placement of the materials in the fill was part of the approved plan. <br />It is not necessary to remove the materials from the fill iron a geotechnical perspective. <br />We reiterate that surface drainage should be maintained to reduce the need for use of <br />these materials. <br />Section 4.09.1 (11) requires inspection of the fill for stability by a registered engineer. Our <br />Mr. McOmber has observed the fill in 199t and in April 1993. During our site visits we <br />have found no appearance of instability, structural weakness, or other hazardous <br />condition. On the basis of our review of conditions at the facility in 1991 and 7993, our <br />analyses and review of the limited available data, we believe the Refuse Disposal Area <br />has been constructed in substantial accordance with the design approved by the Mined <br />Land Reclamation Division with the exception of compaction of the existing materials and <br />maintenance of the crown on the temporary fill surface. We believe the degree of <br />compaction achieved to date is adequate to ensure stability of the fill. Process changes <br />adopted since 1991 will further enhance stability. We recommend surface drainage on <br />the temporary fill surface be re-established as soon as practical when placement resumes. <br />3 <br />