1999-09-17_REVISION - M1999002 (3)

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ATTACHMENT 2 Technical Revision Responding to Mining and Reclamation Permit No. M-99-002 Stipulation No. 4 Surface Subsidence Monitoring Stipulation No. 4 of Mining and Reclamation Permit (112 Permit) No. M-99-002 requires American Soda to provide a Technical Revision to the 112 Permit incorporating subsidence monitoring monuments affixed to production well casings. Stipulation No. 4 states: "Americmi Soda mill providea teclrnicnl revision to iruorporatesubsidencemonitoringmonuments affixed to production well casings under this yermit. The technical revision nn~st be approved prior to injection of solution mining fluids. The Die~ision will provide copies oC the proposed technical revision to fhe objecting pnrtp to the application hearing and co~isider its connnents on the technical revision. "' In response to Stipulation No. 4 of the 112 Permit, American Soda will install surface subsidence monuments on 23 wells to be located within the 0-5 year mining panel, as shown in Figure 1 of this Technical Revision. These are all wells to be developed on the 600-foot spacing planned for the first pass of solution mining in the initial mining panel. The monuments will be attached to the well casings, which will be cemented in place. These monuments will be in addition to the 28 subsidence monitoring monuments identified in the Subsidence Monitoring Plan included in the Final Environmental Impact Statement (BLM 1999) and submitted to CDMG as part of the 112 Permit Application. The addition of these surface subsidence montunents will bring the total number of monuments associated with the 0-5 year mining panel to 51. The Subsidence Monitoring Plan submitted for the Yankee Gulch Project includes 20 surface subsidence monitoring monuments installed across the 0-5 year mining panel, plus S monuments located at nearby section and quarter-section corners. The subsidence monuments were sited away from the production well pads for two reasons: (1) so that, once wells are plugged and abandoned, the well casing can be cut flush with the pad prior to reclamation and (2) to eliminate the potential influence of thermal expansion of the casing on the subsidence data (Agapito 1999b). Reclamation of pads supporting production wells with surface subsidence monuments could be problematic. Pads that were constructed using cut and fill will either not be able to be restored to original contours or else the surface subsidence monument elevations will need to be adjusted to the reclaimed topography. Monumentelevationadjustmentwould require welding on an additional length of steel and reestablishing the subsidence monitoring elevation (Agapito 1999b).