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<br />zI <br />The behavior of the Cresson materials relative to acid generation and acid neutralization <br />appears related to the particle size of samples tested. Finer sample grinds accentuate acid <br />neutralization capacity at the net expertse of acid generation capacity, probably due to <br />exposure of more basic reactive minetakSwith minimal exposure of additional reactive <br />sulfides. <br />Segregation of the most pyritic material, in relatively coarse sizes, from the more <br />neutralizing materials (as is proposed through separation on the basis of sulfur content) <br />may accentuate the likelihood that low pH drainage will develop from these segregated <br />materials as they are contacted by oxygen and air. Original plans to place overburden in <br />Arequa Gulch with the more acid neutralizing material surrounding the higher sulfide <br />material were purportedly aimed at reducing acid release potential from the mixed pile and <br />segregation of the materials as now proposed seems to run counter to this concept. <br />Projected ability of the local micro environment at the Cresson site to neutralize acid and <br />fix mobilized metals are based on the observations of naturally occumng waters in Arequa <br />Gulch and other areas and on the proposed model for the weathering of the in-place post- <br />depositional Cresson materials. Whether the receiving environment can deal with possible <br />"shock loads" of acid and metals in waters effluent from the waste piles of Cresson <br />overburden is not assured by these arguments since contact times and accessibility of <br />neutralizing minerals in the disturbed material may be much different than in the bulk <br />undisturbed deposit. <br />The uncertainty in projecting acid generation, particularly in the higher sulfide overburden <br />(Type B) disposal area, suggests that monitoring ability to detect, sample, and permit <br />analysis of waters accumulating in or draining from this area be incorporated into the <br />system. <br />If waters which have contacted this overburden are found to be unacceptably high in <br />acidity or metals, then consideration must be given to minimizing the amount of this water <br />generated, possibly to treating it if this is deemed necessary, and controlling its discharge <br />so that negative impacts on the receiving micro environment are minimized or eliminated. <br />One possible option to control the amount of waters which may be contaminated by <br />contact with the overburden materials is to provide an impermeable cap on the overburden <br />disposal pits but this may prove to be an unacceptably expensive approach with significant <br />likelihood of failure due to cracking, subsidence, or intrusion of subsurface waters into the <br />filled pit. In this case, monitoring for water accumulation, analysis of the water for acid <br />and metals, and possibly the need to still pump and treat the water to avoid unacceptable <br />discharge would still be a possible need. Here, the cap on the deposit could significantly <br />impact the cost and feasibility of the monitoring and treatment option. <br />OMt.R951DEH <br />