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also supports that the R-6 zone is an effective aquitard. Previous pressurization of the dissolution aquifer <br />(increase of over 150 feet of head) did not result in pressurization at the B-groove. <br />There are essentially two components relating to isolation of mining fluid from the overlying <br />aquifer systems. The first component is the mechanical integrity of the well bore and injection system. <br />The' second component is geological integrity of the receiving formation. While American Soda tests for <br />mechanical integrity and can generally confirm the mechanical integrity of the injection system through <br />operational data, it cannot control the geologic integrity of the mining zone. Natural fractures in the host <br />rock have the potential to provide a pathway for mining fluid to reach the dissolution surface. Fractures <br />may self-heal as a function of the mining process but there is a potential for mining fluid to reach the <br />dissolution surface, even though well mechanical integrity is intact. Such an occurrence would place <br />American Soda in a technical violation of its UIC permit even though it was operating within the <br />prescribed limits of its permit. <br />American Soda has requested the establishment of an injection interval and an injection zone. <br />The injection interval would equate to the mining zone (effectively the current injection zone from 150 <br />feet below the dissolution surface to about 800 feet below the Dissolution Surface). The Injection Zone <br />would be increased to include the Dissolution Surface and any overlying aquifers up to the base of the R- <br />6zone. Thus, if mining fluid travels via a fracture into the dissolution aquifer it would not constitute a <br />Permit violation. Any migration of fluids into the Dissolution aquifer noted by the production <br />monitoring or by any monitoring wells, would require action by the operator to determine the cause of <br />the problem and initiate changes to eliminate further fluid movement. <br />Although the aquifer(s) overlying the Dissolution Surface does not generally meet USDW <br />standards and the R-6 zone has been shown to be an aquitard, it is still possible that some hydrologic <br />connectivity could exist between the Dissolution Surface and the B-groove. For this reason, American <br />Soda proposes that if mining fluid does migrate above the Dissolution Surface (within the Injection <br />Zone), corrective action would be taken to halt further incursion and pressurization of the dissolution <br />aquifer. <br />Pressure monitoring of the Dissolution Surface is known to be effective in identifying excursions <br />of fluid. Previous experience at both American Soda's site and at the neighboring Natural Soda site has <br />indicated that the lower aquifer (overlying the Dissolution Surface) shows a substantial pressure increase <br />when fluid travels into the zone. To enhance American Soda's ability to identify and respond to an <br />incursion into the dissolution aquifer, American Soda will expand its pressure monitoring of the <br />Dissolution Surface. American Soda would convert some exhausted production wells into pressure <br />monitoring wells completed in the aquifer immediately overlying the Dissolution Surface. The converted <br />wells would be in addition to the existing 25 monitoring wells, which already include 4 wells in the lower <br />aquifer. American Soda proposes to convert up to six (6) exhausted wells in each mining panel to <br />pressure monitoring wells. The general location and spacing for these converted monitoring wells will be <br />determined by any identified needs for additional monitoring. Selection of specif c wells to be converted <br />to monitoring wells will be based on the cavity history and the condition of the well at the time the well is <br />retired. For example, if a particular well at end of its operating life has good wellbore integrity and is <br />located near other operating wells that are distant from any other dissolution surface monitoring well, or <br />if it is located near an operating well that had shown one or more pressure losses during its operating life, <br />then the well might be a good candidate for conversion to a monitoring well. <br />FINAL Addendum to SOB For Modification No. 9, UIC Area Permit No. C030858-00000 Page 7 0}'29 <br />