2022-09-26_PERMIT FILE - M2022042 (6)

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Windsor East Mine, Exhibit G – Water Information September 2022 Page 5 | 11 corner of the lease boundary, and approximately 1,500 ft from the nearest planned mining cell. A loop of the Cache la Poudre River extends between the lease area and the likely location for the well. The parcel that this well sits on is owned by GWIP LLC, the property owner for this reclamation permit application Wells on the Adjacent Parsons Mine Property Monitoring wells installed as part of the Parsons Mine operations were considered as part of this permit application. Twelve of the fourteen wells were installed in 2010 and the other two were installed more recently. Table 2 includes construction details and depth-to-water information. Measuring point elevations are believed to have been estimated based on a topographic map for the area. Appendix G-2 provides water levels measured over time for the Parsons Mine monitoring wells. 1.3.3 Site Monitoring Wells Martin Marietta installed five monitoring wells (Figure G-3) in August 2022 to support the monitoring plan associated with the project, documenting the groundwater conditions before initiation of mining, during mining, and after mining is complete. Through the well monitoring program, the wells will serve as points at which water levels will be measured and water quality samples collected. The boreholes for each of the wells were advanced until bedrock was encountered. Lithologic logs documenting the valley-fill sediments observed and the bedrock during drilling were recorded. The monitoring wells were constructed of two-inch Schedule 40 PVC casing and screen. Silica sand was placed from approximately two feet above the top of the screen to the bottom of the borehole (bedrock). Above the silica sand, a bentonite seal was placed in the borehole annulus to restrict infiltration of surface water. Each of the monitoring wells was finished at the surface with a locking, aboveground, steel protective casing set in concrete. Table 3 provides additional details of the monitoring well installations. Appendix G-1 presents borehole logs and well completion details for the monitoring wells. 1.4 HISTORIC AND FUTURE GROUNDWATER LEVELS Monitoring wells established at the Windsor East site in August 2022 were used to collect groundwater elevation data. This set of water level data was supplemented by water level data collected from monitoring wells on the adjacent Parsons Mine site located east of the Windsor East property. Water level data measured for the wells are included in Tables 2 and 3. Depth to water at the Windsor East site varies from 7.9 to 10.4 ft below the top of the well casing, corresponding to a range of water level elevation from 4732.14 at MW-06 to 4717.44 at MW-11. Figure G-5 presents the general direction of groundwater flow (southeast). Since 2010, regular groundwater measurements have been collected from the 14 monitoring wells around Martin Marietta’s Parsons Mine site. These wells shall hereafter be referred to as the Parsons Well Network, are numbered MW-1 through MW-14. Appendix G-2 shows the variation in water level measurements from monitoring wells MW-1 to MW-12. Water levels measured in the Parsons well network vary from 4730 feet at MW-5 to 4690 feet above mean sea level (amsl) at MW-1 where the effects of dewatering are visible in late 2021 through 2022. Water levels are seasonally at their highest elevations in August or September following the irrigation season, and typically at their lowest elevations in February to March when irrigation has been suspended for the longest period of time. The water level at MW-12 before initiation of local dewatering in 2019 ranged from 5.8 to 7.8 ft bgs (4720.5 to 4722 ft amsl), then dropped to an average of 11.3 ft bgs (4716.7 ft amsl), a drawdown of approximately 4.6 ft. This monitoring well is located approximately 100 feet from the dewatering trench of the nearest active mining cell at the Parsons Mine, and the 4.6-foot change in water levels experienced at the Parsons Mine is expected to be representative of the drawdown that will be associated with dewatering of the mining cells at the Windsor East site. Based on observed water levels at the Windsor East and Parsons sites, dewatering will lower water levels to within 2 feet of the top of bedrock in the immediate vicinity of each mining cell. The lowered groundwater effects will be transmitted horizontally by the gravel aquifer, reducing water levels in the surrounding area as a “cone of depression” forms around the mining cell. During mining, water in the area will flow radially toward the dewatered cells, where it will be removed using the dewatering trench drainage system and discharged into the river.