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Letter to J.J. Jones -3- August 27, 1996 monitoring program. In order to resolve the question of monitoring parameters for the ground water well at the Henderson Mine, the Division suggests that CMC collect a representative sample of untreated mine water, and subject that sample to analyses for a full suite of potential contaminants using analytical methods sufficiently sensitive to detect contaminants at the most restrictive applicable standard, including aquatic life standards. Required detection limits for certain critical parameters are provided here: Arsenic - 0.01 mg/L Cadmium - 0.0003 mg/L Copper - 0.005 mg/L Lead - 0.005 mg/L Selenium - 0.01 mg/L Silver - 0.0002 mg/L Any questions regarding required detection limits for the other parameters should be directed to the Division. Any potential contaminants, other than a core group of critical indicator parameters, that are found to be non-detectable in this screening analysis would be dropped from the analyte list. Contaminants that are detected would be included in the analyte list for monitoring of the point of compliance well until the Division is satisfied that representative samples have been collected for both a high water table and a low water table condition. At that time, any parameters that are found to be non-detectable, other than a core group of indicator parameters, would be dropped from the analyte list. The same procedure would be followed at the mill site, except that there will be two or three wells being monitored instead of one, and the initial screening for contaminants would be done using a representative sample of raw seep water from the tailing impoundment. 2. Numeric Protection Levels for Ground Water Since CMC and the Division have reached an impasse regarding the application of numeric protection levels for ground water at the Henderson Mine and Mill, the Division is taking CMC's position on this issue under advisement, and will contact CMC once a course of action to resolve the impasse has been developed. This will probably not occur until early in November, 1996. 3. Ground Water Monitoring of the Precambrian Basement Rock CMC has grouped ground water units at the Henderson Mill tailing site on the basis of geology, and has identified two basic units. The upper unit consists of the Troublesome Formation, glacial till, and alluvial material. The lower unit consists of precambrian basement rock. The Division and CMC have agreed that the upper ground water unit may be