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Wattenberg Mine, Exhibit G—Water Information May 2023 <br /> 5.0 AVAILABLE SATURATED THICKNESS <br /> The available well information for the monitoring wells on site indicates bedrock was encountered at depths of up <br /> to 27 feet below ground surface. Water levels at the time of well installation in 2002 ranged from 2 to 9 feet below <br /> ground surface. Based on this data, the saturated thickness of aquifer beneath the site ranges from approximately <br /> 7.5 to 22.5 ft(Table 2). <br /> Water wells completed in sand and gravel aquifers typically provide approximately 25 to 30 gallons per minute per <br /> foot of drawdown of saturated thickness in the well. Domestic wells are typically permitted for maximum pumping <br /> rates of 15 gallons per minute(gpm). As a result, less than 2 feet of saturated thickness above the pump intake is <br /> likely to be required to provide the allowed pumping rates of 15 gpm. Mine dewatering in 2006 was not observed <br /> to have an adverse effect on off-site wells, and minimal, short-term dewatering activities are anticipated to <br /> occurring during the remaining mining, where dewatering water will be routed to the nearby Stillwater Ski Lake. <br /> Owing to this, the response to previous dewatering activities noted in Appendix G, and the high transmissivity of <br /> the shallow alluvium, adverse effects to off-site wells are not anticipated. <br /> 6.0 HYDRAULIC IMPACTS <br /> There will be 6.2 acres of additional mining at the Wattenberg Lakes site, limited only to the Struck Pond <br /> expansion area, which will require temporary, short-term dewatering. During dewatering a cone of depression will <br /> form around the Struck Pond excavation and spread to some extent over time. Currently, dewatering water is <br /> sent to Stillwater Ski Lake; this helps to offset downgradient impacts. Nevertheless, the dewatering has the <br /> potential to impact the wells listed above in addition to the ski lake and the Huett Seep/Ditch. Due to the proximity <br /> to the South Platte River, the spread of dewatering impacts is expected to be limited as was observed during the <br /> period of time shown in the hydrographs for the wells around Pond 3. The short-term nature of the dewatering will <br /> keep any long-term impacts to a minimum. Based on the high water table and the responses shown in the <br /> Appendix G hydrographs, additional dewatering is unlikely to have a long-term effect on nearby water wells. <br /> The slurry wall construction around the Struck Pond may have a localized effect on groundwater, the Huett <br /> Seep/Ditch, and the Stillwater Ski Lake, namely some mounding and shadowing. Based on the observed <br /> hydraulic response to construction of the slurry wall around Pond 3, these responses will likely be minimal and <br /> localized in nature and will likely not affect any nearby water wells. The hydrologic effects may be amplified locally <br /> but only slightly due to the location of the Struck Pond between two structures that currently have slurry walls, but <br /> it is anticipated that the perimeter drain on the Struck Pond will help to minimize these potential effects. <br /> 7.0 WATER USE <br /> Section 6.4.7 of the Colorado Mined Land Reclamation Board's Construction Material Rules and Regulations: <br /> (3) The Operator/Applicant shall provide an estimate of the project water requirements including flow rates and <br /> annual volumes for the development, mining and reclamation phases of the project. <br /> (4) The Operator/Applicant shall indicate the projected amount from each of the sources of water to supply the <br /> project water requirements for the mining operation and reclamation. <br /> (5) The Operator/Applicant shall affirmatively state that the Operator/Applicant has acquired(or has applied for) a <br /> National Pollutant Discharge Elimination System (NPDES)permit from the Water Quality Control Division at <br /> the Colorado Department of Health and Environment, if necessary. <br /> There will be minimal water use after mining when most of the site is in the reclamation phase. The minor amount <br /> of mining at the site will intercept some groundwater tributary to the South Platte River. Consumptive uses of <br /> groundwater at the site include evaporation from groundwater exposed to the atmosphere, water retained in <br /> material hauled off-site for processing, and water used for dust control. <br /> Evaporative losses at the site are attributable to exposed groundwater that is ponded or removed through <br /> dewatering for storage in the Stillwater Ski Lake. Evaporative losses were calculated as the difference between <br /> OTETRA TECH Page 5 1 8 <br />