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-4- <br />will be of concern and should be monitored. As in the case of the North Pit <br />landslide mass, "flow attenuation areas" are also proposed to be constructed <br />upon the reclaimed overburden dumps. It will be important to determine <br />whether consolidation settlement will compromise the intended drainage and <br />erosion control designs of the various overburden dumps. <br />The operator should prepare and submit a monitoring program, including <br />location and description of monitoring facilities, frequency and methodology <br />of monitoring activities, and criteria for determining when final <br />consolidated, topographic configurations have been achieved (success <br />criteria). Prior to that determination of final success, appropriate surety <br />will be required of the operator. <br />Lowgrade Ore Disposal Structures <br />The operator proposes to construct two lowgrade ore storage/disposal piles, <br />upon the tie Camp overburden stockpile and the "10450" overburden stockpile in <br />the North Dump area. These stockpiles are proposed to be placed on one to two <br />foot thick clay pads and covered with one-half to one foot thick clay <br />membranes, followed by two feet of overburden material. Final facial slopes <br />of these lowgrade ore stockpiles are to be graded to 3:1 {horizontal to <br />vertical). <br />I have several concerns regarding these proposed lowgrade ore storage/disposal <br />structures. First, I am concerned that the one-half to one foot thick clay <br />cover membrane may not be adequate. While the cover will adequately prevent <br />radon diffusion while intact, its relatively thin structure will not allow <br />ad,)ustment to potential consolidation settlement. Located upon the <br />potentially consolidating overburden dumps, these lowgrade ore piles might be <br />sub3ected to differential movement which could compromise the integrity of the <br />clay underliners and cover membranes. I believe the cover membranes and <br />underliners should be thickened to perhaps two feet for practicality and <br />construction, and to allow additional protection against consolidation <br />settlement disruption. <br />Secondly, these lowgrade ore structures must be assumed to be permanent <br />disposal structures, absent a specific plan to utilize this ore. I am <br />concerned about the geomorphological stability of these two mounded piles, <br />superimposed upon the top of the two overburden dumps. I suspect that a <br />significantly more stable landform could be achieved by encapsulating the <br />lowgrade ore within the upper strata of the respective overburden dump <br />structures. This should result in lowered susceptibility to wind and water <br />erosion, in effect providing the lowgrade ore armorment protection. In <br />effect, the operator need only invert the proposed cross-section depicted in <br />figure 4 of the technical memoranda entitled "Geotechnical Aspects of <br />Reclamation of the Pitch Project Waste Dumps". Appropriate construction of <br />the clay membrane liner and the cover membrane should prevent ground water <br />infiltration and existing geotechnical investigation suggests that the waste <br />dumps are relatively dry. A simplistic geotechnical investigation could <br />ascertain the ground water conditions, in order to optimize sighting of the <br />encapsulated, lowgrade ore pods. <br />~~ <br />k~`r <br />~~~ <br />