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<br />be removed and placed in the pit impoundment. This condition is subject to confirmation <br />of these criteria by the Department based on information supplied by LAC Minerals. <br />Material left in the South Waste Dump shall be thoroughly investigated by surface <br />trenching to define the extent of the remaining rock capable of generating acid. LAC <br />Minerals shall submit a sampling plan that will characterize the waste rock left behind. <br />Based on best professional judgement, small discontinuous (isolated) zones of waste with <br />NAG pH of less than 3, and paste pH less than 4.5, may remain in the South Waste <br />Dump. <br />3. LAC Minerals shall submit for approval a sampling/investigation plan that will <br />characterize the waste to remain in the South Waste Dump. <br />4. In areas where waste rock is removed, drainage channels shall be constructed. These <br />drainage cl>amrels shall as nearly as possible match the location and grsdient of pre-waste <br />dump natural drainages. The channels shall be stabilized as necessary with non-acid <br />generating materials. <br />5. By July 1, 1994 LAC Minerals shall submit to the Department for approval a plan to <br />dispose of sludge resulting from treatment of acid mine drainage. If the sludge disposal <br />site is located within the mine property, it shall be of an alkaline environment. <br />1. Surface water runoff from the waste impoundment shall not cause South Dakota Surface <br />Water Quality Standards, South Dakota Groundwater Quality Standards, or NPDES <br />permit requirements, as applicable, to be exceeded. <br />2. To further prevent the possibility of acid mine drainage, and to allow for a factor of safety <br />in terms of additional buffering, spent ore to be used in the thermal protection/drainage <br />layer in the pit impoundment shall have a NAG pH greater than 3 indicative of an ABA <br />of less than -5 T/KT CaC03, and also having a paste pH of greater than 4.5. This <br />condition is subject to confirmation of these criteria by the Department based on <br />information supplied by LAC Minerals. <br />3. To determine adequacy of the ceP system for frost protection, LAC Minerals shall submit <br />a plan for approval that addresses the installation of temperature probes (thermistors) in <br />the clay layer to determine temperature. If it is determined that the integrity of the clay <br />layer is compromised to an unacceptable level due to freezing, the cap shall be reinstalled <br />with an appropriate frost protection layer. <br />The plan shall also include provisions for the installation of thermistors, oxygen probes, <br />and/or other monitoring devices in the backfilled waste rock to monitor oxidation and heat <br />of sulfide reaction, or Lick thereof. If it is determined that elevated temperatures have <br />2 <br />