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<br /> <br />Portland Limestone Quarries (M-1977-344) Permit Amendment-02 <br />Holcim US Inc, 3500 Highway 120, Florence, CO 81226 Revised pursuant to preliminary adequacy review November 20, 2023 <br />Phone (719) 288-1443 www.holcim.us 95 <br />model. The site-specific Leapfrog geologic model includes the base Codell Sandstone, overlying Fort <br />Hayes Limestone, and additional overlying sediments. The contact between the Codell and Fort Hayes <br />dips toward the north across the site. Groundwater occurs primarily within the Codell Sandstone and <br />within the lower portion of the Fort Hayes limestone in localized areas. Sediments overlying the Fort <br />Hayes are generally unsaturated. <br />Based on conservatively high potential impacts to the Codell, it was determined that the rate of <br />groundwater entering the quarry may increase from Mine Plan Block 0-10 through Mine Plan Block 20-30. <br />Following Mine Plan Block 20-30 the pit floor elevations are above the interpolated water table and are <br />therefore dry. The evaluation of mining impacts to Red Creek suggested no significant influence on the <br />creek. <br />The model results discussed represent a simplistic assessment for mining influence on groundwater in <br />RCQ. To improve and extend model predictions beyond Mine Plan Block 20-30, additional groundwater <br />monitor wells will be installed throughout the site as mining progresses into Year 20-30 block. <br />2.7.4 Potential Mining Impacts to Water Quality and Quantity <br />Based on groundwater modeling, mining will not impact water quantity in Red Creek. To be protective of <br />water quality, Holcim will implement a surface and groundwater monitoring plan. <br />2.7.4.1 Monitoring Plan <br />Surface and groundwater monitoring will recommence on a semi-annual basis immediately prior to mine <br />development. Sampling and monitoring will occur during the second calendar quarter (April thru June) and <br />fourth calendar quarter (October thru December) each year. Reporting will occur no more than 30 days <br />after the end of the sampling quarter. The second calendar quarter report will be submitted by August 1 of <br />each year. The fourth calendar quarter report will be submitted by February 1st of the following year. <br />Groundwater locations will include Well 1 that lies north of Red Creek, and Wells 3 and 4 that lie south of <br />Red Creek. Two wells will be monitored south of Red Creek because the groundwater shows natural <br />variation in water quality as observed during the baseline water quality program. Surface water will be <br />sampled at the seep and at SW RC2. SW RC2 is the furthest east location thus it is the most <br />downgradient surface water location. Groundwater level data will be collected using the installed pressure <br />transducers during the interim monitoring program. Red Creek flow data will be collected at the flume <br />using the installed pressure transducer. Transducer data will be downloaded and reviewed quarterly. <br />The following analytical suite for surface and groundwater samples is proposed based on the results of the <br />Baseline Study (Tables 2.7.4.1-1 and 2.7.4.1-2). The analyte lists are the same for surface and <br />groundwaters to be able to evaluate the connection between the water quality for both types of water. <br />After three years of monitoring, Holcim will submit a Technical Revision requesting a reduction of the <br />analytical suite for those constituents with concentrations that are consistently below instrument detec tion <br />limits or below regulatory standards. <br />In the event of a water quality exceedance, Holcim will notify the appropriate regulatory agency and <br />implement an Adaptive Management Plan (AMP) strategy. An AMP strategy allows for the inclusion of <br />knowledge gained and adaptation of mitigation measures as mining operations evolve. The basic AMP <br />process includes the following steps: <br />1. Identify source of exceedance and operational uncertainties; <br />2. Quantify impacts; <br />3. Evaluate strategies and mitigation implementation; and <br />4. Monitor the performance.