2025-08-28_HYDROLOGY - M1983194 ‎(7)‎

• Permit No: M1983194
• IBM Index Class Name: Hydrology
• Doc Date: 8/28/2025
• From: NSI
• To: EPA
• Archive: No

Natural Soda LLC 2024 Project Status Report & Annual Plan of Development
24 January 2025

5.0 Environmental Monitoring and Protection
5.1. Hydrology Monitoring
5.1.1. Introduction
NS’s hydrology monitoring program concentrates on groundwater, as there are no
perennial streams or springs located on the NS sodium leases. The USGS stream
gauging station-monitoring program is conducted, with NS support, to provide regional
surface stream flow data on Yellow Creek and Piceance Creek.
The hydrology-monitoring plan is designed to identify impacts of NS’s solution mining
operations on underground sources of drinking water, as designated by the US EPA.
Refer to Figure 3 and Figure 4 for the locations of existing monitor wells. Groundwater
analytical results are presented in Appendix A.
5.1.1. Monitoring Wells
Per regulatory requirements, dedicated groundwater monitoring wells have been
constructed to monitor four water-bearing intervals identified as the Perched, A-Groove,
B-Groove, and the Dissolution Surface (DS) Aquifers. The DS Aquifer has been
exempted as an underground source of drinking water in the NS lease and permit areas.
The DS Aquifer monitored by NS contains total dissolved solids (TDS) values in excess
of 10,000 parts per million (PPM). These four aquifers are monitored at several locations
across the solution mining area: up and down-gradient, remote down-gradient, and near
the southeast portion of Section 26. Baseline and current groundwater monitoring data
have been obtained from 1991 through present. Refer to Figure 3 and Figure 4 or well
locations.
The Perched Aquifer is characteristically lower in TDS, conductivity, fluoride, SAR
(sodium absorption ratio) and moderate to higher in sulfate and pH. The A-Groove and
B-Groove Aquifers are similar in water quality with moderate TDS, conductivity, SAR, but
higher fluoride. However, the B-Groove Aquifer generally has slightly higher levels of
TDS, conductivity, SAR, and fluoride. The DS Aquifer is characterized by very high TDS
and conductivity (30,000 to >100,000 ppm), higher SAR, magnesium, potassium,
moderate pH, and a generally higher fluoride and boron.
In 2024, the results of groundwater monitoring were analyzed for potential anomalies in
order to prevent or mitigate potential negative impacts to the USDW’s.
Appendix A contains detailed sampling results for groundwater monitoring wells.