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reach the dissolution surface, even though well mechanical integrity is intact. Such an occurrence would place American Soda in a technical violation of its UIC permit even though it was operating within the prescribed limits of its permit. American Soda has requested the establishment of an injection interval and an injection zone. The injection interval would equate to the mining zone (effectively the current injection zone from 150 feet below the dissolution surface to about 800 feet below the Dissolution Surface). The Injection Zone would be increased to include the Dissolution Surface and any overlying aquifers up to the base of the R-6 zone. Thus, if mining fluid travels via a fracture into the dissolution aquifer it would not constitute a Permit violation. Any migration of fluids into the Dissolution aquifer noted by the production monitoring or by any monitoring wells, would require action by the operator to determine the cause of the problem and initiate changes to eliminate further fluid movement. Although the aquifer(s) overlying the Dissolution Surface does not generally meet USDW standards and the R-6 zone has been shown to be an aquitazd, it is still possible that some hydrologic connectivity could exist between the Dissolution Surface and the B-groove. For this reason, American Soda proposes that if mining fluid does migrate above the Dissolution Surface (within the Injection Zone), corrective action would be taken to halt further incursion and pressurization of the dissolution aquifer. Pressure monitoring of the Dissolution Surface is known to be effective in identifying excursions of fluid. Previous experience at both American Soda's site and at the neighboring Natural Soda site has indicated that the lower aquifer (overlying the Dissolution Surface) shows a substantial pressure increase when fluid travels into the zone. To enhance American Soda's ability to identify and respond to an incursion into the dissolution aquifer, American Soda will expand its pressure monitoring of the Dissolution Surface. American Soda would convert some exhausted production welts into pressure monitoring wells completed in the aquifer immediately overlying the Dissolution Surface. The converted wells would be in addition to the existing 25 monitoring wells, which already include 4 wells in the lower aquifer. American Soda proposes to convert up to six (6) exhausted wells in each mining panel to pressure monitoring wells. The general location and spacing for these converted monitoring wells will be determined by any identified needs for additional monitoring. Selection of specific wells to be converted to monitoring wells will be based on the cavity history and the condition of the well at the time the well is retired. For example, if a particulaz well at end of its operating life has good wellbore integrity and is located near other operating wells that aze distant from any other dissolution surface monitoring well, or if it is located neaz an operating well that had shown one or more pressure losses during its operating life, then the well might be a good candidate for conversion to a monitoring well. Establishing a thicker Injection Zone with these monitoring and protective measures will continue to ensure protection of USDWs and prevent American Soda from violating their permit due to geologic conditions. Proposed Modifications for Infection Interval: • Part II C (3) is proposed to be changed as follows: Current Laneua¢e: Draft Addendum to SOB For Modification No. 9, UIC Area Permit No. C030858-00000 Page 7 of 27