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Ms. Barbara Coria November 9, 2015 Page 6 This data indicates that no subsidence has been observed to date. The mine plan going forward is controlled by the BLM with a stipulation in the mining permit that the recovery of nahcolite is limited to 221 tons per foot of cavern length. Natural Soda plans to maintain the spacing between caverns similar to the historical spacing of 200 feet. This results in an extraction ratio of less than 40%. The concern is that the "Applicant provide information sufficient to demonstrate that the stability of any structures located within two hundred feet of the operation or affected land will not be adversely affected." Given the historical data from the first 25 years of operation during which no measurable surface subsidence has been observed, the expectation is that if the basic mine plan is followed in the future, no subsidence will occur and no surface structures will be adversely impacted. The structures of concern are the gas pipelines and electric power transmission lines not owned by Natural Soda. Figure 1 shows the power lines and gas pipelines not owned by Natural Soda. Natural Soda has extended a natural gas pipeline from the south up to the plant site; this is shown in yellow with blue dots. There is another gas pipeline traversing the southeast corner of the lease area that travels from the American Soda plant site to the existing well pads owned by WPX Energy Rocky Mountain, LLC (WPX). This line traverses within 300 feet of the surface location of the wellheads for wells 10H and 11H and approximately 1,000 feet from the solution mining caverns. As no subsidence is expected above caverns 10H or 11H, no impact is expected at the WPX pipeline at this location. The overhead electric lines above the plant wellfield areas were installed by White River Electric Association (WREA), were paid for by Natural Soda, and are owned by WREA. WREA maintains the power lines and installs additional lines as needed as the wellfield expands. WREA is compensated for this service by their sale of electric power to Natural Soda. Since no subsidence is expected, no impact on the power lines is expected. Should tilt occur in the power lines, WREA and NS would replace the pole(s) as needed. The gas -well pads owned and operated by WPX Energy Rocky Mountain, LLC (WPX) have been developed subsequent to the development of the solution mining by Natural Soda under a cooperative agreement. WPX has federal oil and gas leaseholds that largely overlap Natural Soda's sodium lease boundaries. The attached letter from WPX illustrates the cooperative working relationship between the two parties. The historical record at Natural Soda where no subsidence has been recorded after 25 years of production suggests that any subsidence will be slow to develop. Full extraction of a seam, as is characteristic for longwall coal mining operations, can result in fully developed subsidence within a year or two of mining. With extraction of less than 50% of the mining horizon, most often no subsidence is detected. In shallow deposits, subsidence can develop over individual caverns, but when the depth of cover is over 500 feet, localized subsidence above a single cavern Agapito Associates, Inc.