2015-11-09_HYDROLOGY - M1983194 - Laserfiche WebLink

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2.4 Monitoring Reports The end of the "water year" is September 30th. The monitoring reports are submitted annually and generally nine months after the end of the water year. This report is submitted to the BLM in the NS annual report. Pursuant to BLM stipulations, NS will notify the Authorized Officer within 10 days of the occurrence of any significant changes to the hydrologic system. 3 Subsidence Monitoring Plan The Natural Soda LLC subsidence monitoring plan includes both surface and subsurface monitoring of the potential vertical ground movement on the NS Lease. Subsidence monitoring will be performed throughout the commercial operating life of the solution mining operations and for a period of three years following cessation of mining activities. Results of the subsidence monitoring (both surface and subsurface) will be checked periodically as needed, to verify and calibrate numerical models used in the design of the well -field layout. Surface subsidence monitoring will be conducted by establishing permanent surveying monument locations. Subsurface monitoring will be conducted by periodic borehole geophysical logging of the well bores and strata overlying the cavities produced by the solution mining activities. Pursuant to BLM and EPA stipulations, NS will perform the following activities. • Survey for surface subsidence on a biennial basis. • Pursue appropriate methods to determine cavity configuration. • Determine extent of caving when noted. • Attempt to determine impacts on USDW aquifers from caving or pillar failure. Prior to implementation, the revisions and updates to the plan will be submitted to the appropriate agencies for review and approval. 3.1 Subsurface Monitoring The purpose of the subsurface subsidence monitoring is to ascertain movement of strata overlying the solution -mined cavities. Borehole geophysical techniques will be employed for determination of potential subsurface movement of the overlying strata. In pre-existing solution mining areas south of the plant (Figure 6) (historical Panel 1) and south and east of the plant (historical Panel 2), Time Domain Reflectometry (TDR) was employed. Currently, NS monitors these TDR locations on a monthly basis. In addition, an independent third party monitors the locations on a quarterly basis. This method of subsidence monitoring has proved to be problematic and unreliable. This method is not as robust as was originally Daub & Associates, Inc. Page 12 Natural Soda LLC 2015 EMP