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Section 20 Rationale <br /> February 9,2023 <br /> Page 4 of 7 <br /> The Applicant submitted a groundwater model titled, "Gilcrest Area Alluvial Groundwater Model— <br /> Potential Impacts of Proposed Gravel Mine" with the application. The model took into <br /> consideration the operations proposed at the Section 20 site and the Monarch DENM site. The <br /> Monarch DENM site is an approved permit application located immediately west of the proposed <br /> Section 20 property. The model predicts an increase in the groundwater elevation at the Shimon's <br /> property of 4.9 feet with the final construction of the proposed Section 20 slurry walls and an <br /> increase of 6.7 feet with the completion of the proposed slurry walls for the Section 20 and the <br /> Monarch DENM sites without the proposed mitigations measures. The installation of the proposed <br /> mitigation measures decrease the projected rise of groundwater to 0.10 feet at the Shimon's <br /> property. <br /> The primary proposed mitigation plan involves the installation of underdrains or a series of wells to <br /> remove groundwater from the aquifer along the southern boundary of the site. The removed <br /> groundwater will be conveyed to a manhole located at the mid-point of the southern permit <br /> boundary and piped to an infiltration pond located on the north end of the permit boundary. All <br /> mitigation structures are located within the proposed permit boundary. The secondary proposed <br /> mitigation plan would collect groundwater along the southern permit boundary,the same manner <br /> as stated above, but the removed groundwater would be conveyed in a pipe and discharged South <br /> Platte River. If the Applicant were to utilize the secondary mitigation measures,they are required <br /> to submit and obtain approval of an amendment application due to the increase in affected lands to <br /> the permit. Both mitigation plans are designed to maintain the groundwater elevation at or slightly <br /> above the historic groundwater elevations on the Shimon's property. Finally, any impacts to the <br /> groundwater elevation will dissipate with distance away from the permit boundary. The Division <br /> reviewed and accepted the groundwater model for the Section 20 permit application. <br /> The Applicant submitted a groundwater quantity monitoring plan with the groundwater report.The <br /> monitoring wells will be measured monthly to identify potential changes in the groundwater flow or <br /> elevation associated with mining and reclamation activities. Baseline data will be collected prior to <br /> dewatering or construction of the slurry walls. The baseline data will provide a range of relative <br /> groundwater elevation associated with pre-mining groundwater conditions. Groundwater <br /> elevations tend to fluctuate seasonally with the highest elevations during the summer irrigation <br /> season and the lowest elevations in the winter and early spring. <br /> If the Applicant receives a complaint or if a defined groundwater elevation trigger point is reached, <br /> the following mitigation plan will be implemented by the Applicant. If during mining or <br /> reclamation,the groundwater elevation at monitoring wells#5 (MW-5)or#6(MW-6) indicate <br /> mounding of more than two(2)feet and the condition was not observed during baseline <br /> monitoring, or if the Applicant and/or the Division receives a complaint from any water user within <br /> the vicinity of the site,the Applicant will notify the Division, evaluate the cause and take action <br /> within 7 days of the complaint. <br /> After the Division is notified,the Applicant will review the data and available information and <br /> submit a report to the Division within 30 days. The report will include discussions with the water <br />