2019-11-14_PERMIT FILE - M2019025 (20)

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Compatibility calculations between the filter material and adjacent soils were made based on methods given in Seepage Drainage and Flow Nets, Cedergren 1977, pp 179-181 as follows: TH-11 TH-8 TH-1 1. D15 of Coarser Material >= 5 0.75 = 2.78 0.75 = 5.36 0.75 = 4.69 D15 of Finer Material 0.27 0.14 0.16 2. D15 of Coarser Material <= 5 2.20 = 0.11 2.20 = 0.20 2.20 = 0.35 Des of Finer Material 20.00 11.00 6.30 3. D50 of Coarser Material <= 25 3.20 = 0.54 3.20 = 2.56 3.20 = 5.71 D5o of Finer Material 5.90 1.25 0.56 4. D50 of Drain Material >= 1 2.80 = 1.00 Pipe Slot Size 2.80 Equation number 1. of the grain size compatibility calculations does come in slightly below the desired value of 5 for TH-11, however the average of the 3 samples is close to 4.3, so the filter should be expected to still perform well. The layout and construction specifications for the underdrain are given in Exhibit G Sheets 1-3. The underdrain has been placed horizontally up-gradient of the proposed clay liner. Vertically, the underdrain has been placed at the approximate elevations of groundwater at the time the boring s were made (April 2018). Groundwater elevations generally occur near the boundary of the overburden and gravel seam, which is as high the underdrain should be placed in order for it to have a good hydraulic connection to the gravel aquifer. The plan section of pipe with a minimum slope of .19% will flow 0.7 c.f.s. by gravity which is adequate to flow the Qaguifer value of 0.68 c.f.s. calculated above. Additional underdrains adjacent to the remaining mining cells may be also required depending on if groundwater mounding occurs. For the purpose of determining if significant mounding will occur adjacent to those cells, the applicant proposes the installation of groundwater observation wells along the upgradient property boundary as shown in Exhibit F - Reclamation Plan - Sheet 1. Wells OW-1 through OW-7 will be installed following completion of the project permitting process. Existing wells EW-1, EW-2 and EW-3 will also be utilized to observe groundwater elevations. The applicant proposes monthly observations of groundwater elevations (observations) for all wells for a minimum of 5 quarters prior to mining, during mining and for 2 years following reclamation of each mining cell. If the reclamation condition water levels are shown to occur at less than 2 feet above Amen Aggregate Resource Specific Exhibits Page 49 of 84