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i • alter the values of AGP and ANP from that odginally permitted by the Mined Land Reclamation Board (MLRB). Humidity cell tests were conducted during the Initial permitting phases of the taillrtgs impoundment facility, as well as on a quarterly basis over the operating Iffe of the facility. Humidity cell test results Indicate that the existing tailings material does not exhibit the potential to generate acid under meteoric conditions. Static test data available for the INCO SO,/Air tailings indicate that the material is similar with respect to AGP and ANP to the material tested in 1989 (Tale 1). It mlgM be assumed that the INCO SO,/Air tailings also will behave in a similar manner under meteoric conditions (I.e., humidity cell test) to the 1989 tailings material. To confirm this behavior, a representative sample of INCO SOZ/Air treated tailings is currently undergoing humidity cell testing. As of the date of this submittal, humidity cell test results were not yet available. These data will be forwarded to MLRD upon receipt from the laboratory. At the time that the tailings impoundment was permitted, BMR agreed to monitor the acid generating characteristics ofthe material deposited In the tailings impoundment (Steffen Robertson and Kirsten, 1990c). In addition, BMR agreed to develop and implement an appropriate mitigation plan for acid generation, if necessary (Steffen Robertson and Karsten, 1990c). The purpose of the EPA Method 1312 leach test is to evaluate what constituents could leach from the tailings under meteoric condRions. Test results for the INCO/SO, Air treated tailings sample are included in Table 3. As shown, all concentrations were below method detection limits wRh the exception of iron which had a concentration of 0.1 mg/I. Overall, the data presented in Table 3 indicate that the leachate from the INCO SOZ/Air tailings will be benign. MONITORING AND NOTIFICATION Monitoring The INCO SOZ/Air system designed by INCO for the San Luis site is quite sophisticated and includes computer-aided process contrd. Processing parameters will be transmitted to the data cdlectlon system in the existing mill contrd room to allow constant monitoring. In addition, the system will be equipped with audible alarms to alert operators in the event of a system upset. A free cyanide electrode will be installed in the reactor to measure free cyanide concentrations on a 25301/RN0610.RPT INCO SO2/Air Technical Revision Page 10 June 16, 1992 San Wie Mine