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Introduction <br />Natural Soda LLC (NS) has sampled, monitored, and fully defined the groundwater aquifer <br />systems which are found within and proximal to the NS lease areas for more than 40 years. <br />Historic and current aquifer characterization has included sampling and independent laboratory <br />analysis (chemistry, metals, and parameters) of groundwater constituents in addition to <br />monitoring of aquifer potentiometric water levels. In the NS lease areas, four groundwater <br />aquifers are recognized: the Perched Aquifer (PA), the A -Groove (AG) Aquifer, the B-Groove <br />(BG) Aquifer, and the Dissolution Surface (DS) Aquifer. Over time, new groundwater monitor <br />wells (GMWs) are drilled and monitored and old wells are retired; additionally, current and <br />proposed mining areas migrate to different areas. For these reasons, and to take advantage of <br />the extensive body of existing, historical groundwater data, periodic updates to the NS water <br />quality Sampling Analysis Plan (SAP) become necessary. The updates, described herein, will <br />take effect during the fourth quarter of 2021 and the NS SAP and Environmental Monitoring <br />Plan (EMP) will be modified accordingly. <br />The NS sodium bicarbonate processing plant is located in Township 1 South, Range 98 West, <br />Section 26, in Rio Blanco County, Colorado. NS operations are near the depositional center of <br />the saline mineral rich Piceance Creek Basin, and are currently permitted on four sodium leases, <br />encompassing approximately 8,378.9 acres (Figure 1). The four individual sodium leases <br />(C-0118326, C-0118327, C-0119986, and C-37474) are unitized under the C-0118326 <br />designation (the Lease). An EPA Area of Review includes the NS lease area and extends one <br />quarter mile beyond the NS lease boundary. The EPA Area of Review encompasses <br />approximately 12,247 acres. <br />GMW Parameter and Constituent Sampling, and Water Level Monitoring <br />AG and BG Aquifer GMWs will be sampled for groundwater constituents and parameters on a <br />monthly, quarterly, and/or annual basis. The constituent sampling frequency of AG and BG <br />Aquifer GMWs will be dependent, in part, upon the well's proximity to the area of active <br />solution mining (Figure 2 and Table 1). Perched and DS Aquifer GMWs will be sampled annually <br />for groundwater constituents and parameters. Potentiometric water levels (WLs) for Perched <br />and AG Aquifer GMWs will be monitored on a quarterly basis. BG Aquifer WLs will be collected <br />monthly, quarterly, or annually. The monitoring frequency of BG Aquifer GMW WLs will be <br />dependent, in part, on proximity to current mining. DS Aquifer WLs will be collected quarterly <br />or annually, generally based on proximity to current mining. Field parameter data <br />(temperature, pH, and conductivity) will be collected during all groundwater quality sampling <br />events. Several DS and BG GMWs will contain WL continuous data logging (WL CDL) <br />instrumentation. Manual water level data will be collected from WL CDL equipped wells on a <br />quarterly or monthly basis to maintain transducer calibration. All new NS GMWs will be <br />sampled for five quarters, per DRMS protocols, after which the GMW will be <br />sampled/monitored in accordance with the above stated guidance and an updated NS GMW <br />Sampling/Monitoring Schedule. <br />Daub & Associates, Inc. Page 1 November2021 <br />