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4. Groundwater Monitorin_q Plan <br />4.7 Introduction <br />The purpose of this section of the GMP is to provide the framework for monitoring groundwater quality to be <br />protective of the existing and reasonably potential future uses of the groundwater that may be affected by <br />leachate from disposal of CKD in previously mined areas. As was shown in Section 3.1 Groundwater Quality, <br />ambient groundwater quality exceeds WQCC groundwater table values for several parameters. These <br />exceedances occun•ed in groundwater collected from the upgradient monitoring well as well as from monitoring <br />wells completed downgradient of CKD disposal areas. Holcim wishes to incorporate existing groundwater data <br />into the determination of ambient groundwater conditions at the Site. Holcim also agrees with DMG's request <br />(DMG, 2002) to collect Four (4) additional quarters of groundwater quality data from MW-10 prior to a final <br />determination of ambient groundwater quality at the Site. <br />4.2 Installation of New Wells <br />To satisfy the requirements for approval of TR-06 set forth by the DMG in its second adequacy review letter <br />dated October 22, 2002, two new monitoring wells will be installed within the Permit boundary. The first well, <br />MW-11, will be installed adjacent to existing monitoring well MW-6 and will be completed to the base of the <br />Codell sandstone (Figure 2). The purpose of MW-11 is to chazacterize the quality of groundwater in the Codell <br />Sandstone upgradient of the mining and CKD disposal areas. The second well, MW-12, will be installed on the <br />bench near the quarry office (Figure 2). The purpose of MW-12 is to characterize the quality of groundwater <br />downgradient from all CKD disposal areas. Monitoring well MW-12 will be designated as the compliance well <br />for the permitted area. <br />Monitoring wells MW-11 and MW-12 will be installed by a qualified drilling company using air rotary drilling <br />techniques. Well casings will be constructed using two-inch diameter, Schedule 40 PVC, threaded blank pipe <br />and well screen (0.010-inch slot size). Colorado Silica 10-20 will be used as filter pack material and <br />cement/bentonite grout seals will be placed in each of the wells. <br />Due to the estimated low hydraulic conductivity of the aquifer (i.e., 10-8 fUsec) it is anticipated that well <br />development may be difficult due to insufficient flow of water into the wells. L` the inflow of formation water to <br />the new wells is insufficient for development, clean water may be introduced to the wells to facilitate well <br />development. Well development may consist of swabbing, bailing, and purging. After development of the new <br />wells, additional purging will take place prior to collecting groundwater samples from the welts. <br />A survey of the new wells will be performed by a qualified surveying company. The wells will be surveyed for <br />horizontal and vertical locations using NAVD88 and NAD83 Colorado Central State Plane Coordinate System. <br />The surveyed vertical location of the wells will be the top of each casing from which the depth to groundwater <br />will be measured. A referenced survey point will be demarcated with a black mark on the north side of each <br />well casing. Horizontal locations will be measured with an accuracy of 0.1 ft and vertical locations will be <br />measured with an accuracy of 0.01 ft. <br />BLASLAND, BOUCK & LEE, INC. <br />sznaioz engineers & scientists 4-1 <br />Groundwsser Monnaring Plan II dot <br />