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6.4.4 Exhibit D -Mining Plan Mining Description The Mining Plan is described in this section and correlated with Exhibit C-2, Mine Plan Map. Mining is sequenced with designated mining Phase I -Cells 1 through 4 (West Pit) and Phase II -Cells 1 through 3 (East Pit) as shown in Exhibit C-2. Stripping and mining will incorporate conventional aggregate mining methods, including use of scrapers and dozers to strip overburden, hydraulic excavators and scrapers to mine sand and gravel, and haul trucks to move material onsite. To facilitate "dry" mining below the groundwater table and the creation of developed water resources (reservoirs) at reclamation, a slurry wall will be constructed surrounding Phase I -Cells 1, 2, and 3. First, a perimeter drain will be constructed around the area to mitigate predicted groundwater mounding due to slurry wall placement. The perimeter drain design is given in Attachment G-1, Groundwater Modeling Report and Perimeter Drain Design. A perimeter slurry wall will then be constructed surrounding Phase I -Cells 1,2 and 3. The slurry wall will be three feet wide and keyed into the bedrock to prevent groundwater migration into or out of the mining excavation and proposed reservoirs. To protect the slurry wall, all areas adjacent to the slurry wall will be mined at 2H:1 V slopes with a 10 ft offset. Upgradient of the slurry wall and perimeter drain, seven water table observation wells will be installed, as shown on Exhibit C-2, Sheet 2. The wells will be monitored monthly for one year and quarterly for two more years following completion of the slurry wall and perimeter drain installations to verify that the predicted groundwater impacts have been sufficiently mitigated. For Phase I -Cell 4, dewatering trenches will be dug around the bottom perimeter of the mining cell and any accumulated water will be pumped to a sediment pond shown on Exhibit C-2. Phase II will undergo the same pattern as Phase I -construction of a perimeter drain, then slurry wall, installation of two water table observation wells (to be monitored monthly for the first year and quarterly for two more years), followed by mining. Additionally, Phase II mining will be dependent on the seasonal mining of Cell 3. Because Cell 3 lies within the floodway, it will be mined only during the non-flood season -September 15 through April 15 -and backfilled prior to the end of each season. Cells 1 and 2 will be mined year-round. Stockpiling will occur outside the floodway as shown on Exhibit C-2. February 20, 2006 Bokelman/Walters Pit Page 2 of 36 Regular 112 Permit Application