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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. The four individual sodium leases (C-0118326, <br /> C-0118327, C-0119986, and C-37474) are unitized under the C-0118326 designation (the Lease). <br /> An EPA Area of Review includes the NS lease area and extends one quarter mile beyond the NS <br /> lease boundary. The EPA Area of Review encompasses 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 (Table 1). Perched and DS Aquifer GMWs will be sampled annually for <br /> groundwater constituents and parameters. Potentiometric water levels (WLs) for Perched and <br /> 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 daily, <br /> quarterly 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 (Table 1). Manual water level data will be collected from WL CDL equipped <br /> wells on a quarterly or monthly basis to maintain transducer calibration. All new NS GMWs will <br /> be 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 />