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Chavers Mining Resource Groundwater Monitoring and Mitigation Plan January 2024 Page 1 1.0 BACKGROUND INFORMATION Asphalt Specialties Co., Inc. (ASCI) has prepared this Groundwater Monitoring and Mitigation Plan for the Chavers Mining Resource(Site) located at 12367 County Road 8, Fort Lupton, Weld County, Colorado (Figure 1). This plan details the results of the baseline groundwater characterization conducted and future monitoring activities to protect the existing and reasonably potential future uses of groundwater. This plan has been developed in accordance with the requirements set forth in the Construction Materials Rule No. 3, Section 3.1.7, and based on correspondence with Division of Reclamation, Mining, and Safety (DRMS) to ensure the appropriate data required for protection of groundwater quality and quantity is obtained. 1.1 SITE DESCRIPTION Mining activities at the Site occur within the unconfined alluvial aquifer of the South Platte River. The average thickness of the overburden is approximately 3.5 to 4 feet below ground surface (ft bgs). Beneath the overburden, are low terrace alluvial deposits of the South Platte River. The deposits vary from sandy lean clay in the upper zones,to coarse clayey sand and sand with gravel nearer the bedrock. The sand and gravel deposits vary in thickness but averages approximately 28 feet across the Site.Beneath the sand and gravel deposit is the underlying Denver Formation which is a consolidated bedrock stratum composed primarily of generally impermeable shale and claystone approximately 550—600 feet thick. Surrounding land uses in the area include multiple other sand and gravel mines,oil and gas industry sites,and rangeland/agricultural lands. Sand and gravel mining operations have been conducted at the Site since 2016 and the affected area is approx. 87 acres. Groundwater in the alluvial aquifer at the Site flows to the north-northwest towards the South Platte River. Per the Division of Water Resources (DWR) Colorado's Decision Support System (CDSS)website,the alluvial aquifer has rapid permeability with a transmissivity of approximately 85,000 gallons per day per foot (gpd/ft) and specific yield of 0.2. The estimated coefficient of storage is 1.5x10-5 to 3.lx10-5. The Site is located within the City of Fort Lupton Wellfield as classified by the Water Quality Control Commission (WQCC) Regulation 42. 2.0 BASELINE GROUNDWATER CHARACTERIZATION To characterize baseline groundwater conditions, ASCI collected data for eight (8) consecutive quarters beginning in the 1st Quarter of 2022. Data collected included monthly groundwater elevations(for groundwater quantity)and quarterly groundwater sampling events(for groundwater quality). For the first five(5)quarters, data was collected from the two (2)up-gradient monitoring wells (MW-2 and MW-3) as they were the only monitoring wells installed at the Site during this portion of the baseline data collection period. For the last three (3) quarters, data was collected from all five(5)monitoring wells(MW-2 through MW-6). The total data sets used to characterize baseline groundwater conditions included 24 months of groundwater elevations and eight (8) consecutive quarters of groundwater sample laboratory results during the data collection period (i.e., l st Quarter 2022 through 4th Quarter 2023).