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JUI,- 5-:95 WED 2:27 PM TESSF~CT PRODUCTIONS FAX N0. 379713 <br />Item 9. While it may be true that wash-down water flows down to the <br />lower levels as stated, it is also true (from actual observation) that <br />an event like apump-seal failure in a slurry line can result in rapid <br />deposition of solids leading m damming and diversion of flow out <br />the man-0oor near the N W corner of ffie building, We believe that <br />en adequate sill at this door is required to assure containment. <br />We share COM, Inc. engineering opinion that catastrophic failure <br />of the thickener rank is highly unlikely (absent some presently <br />unlmown corrosion process, end assuming that the necessary solids <br />removal from that tank is accomplished without compromising tank <br />integrity). However, (again based upon actual operating history) <br />it is known that the interior heating of the Mill building is poor, <br />especially at the lower level, leading to frxae-up and rupture of <br />fittings such, perhaps, as those on the thickener tank underfloor <br />line, Such as event led Lo the loss of the contents of the <br />concentrates tack, much of which ended up itr the tailings pond, <br />but some of which escaped the Mill building. This occurred on a <br />weekend and was not discovered until the following Monday, by <br />which time everything that could drain had drained. Fortunately, <br />the floor drain system functioned as intended, thus m;n;m;~ing the <br />loss of containment. <br />On the basis of actual operating history, ther+efors, we believe that <br />calculations of Mill b"'tom containment requirements should <br />assume the possibility of such an underfloor line (or equivalent) <br />failure. <br />Item 12. We believe that remote monitoring of Hazel A water level (i.e. at <br />the Mill) should be implemented in light of recent experience. <br />Such monitoring will be far easier W accomplish and thus far more <br />likely to occur in actual operation. (We have much more to say <br />about the Hazel A below.) <br />Item 13. All water (and other} lines should be checked prior to use after auy <br />extended period of inactivity. This should be part of a standard <br />pre-startup punchlist. <br />TSiJingc Em nkm nt nnctn cr'on <br />Introduction <br />Extension of the embankment toe by as much as 110 feet below the <br />existing dam toe, coupled with the lack of riptap, raises erosion- <br />comtnl concerns for us. We question whether significant gullying <br />can be avoided over limo without some preventive design features. <br />P, 3 <br />