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<br />a value for SOq of 500 mg/1. If the 250 mg/1 value is used instead, the record must reflect that <br />higher values described by the data base cited above would be ambient concentrations. <br />As noted above, it may be more appropriate to assign more definitive triggers for cyanide than <br />for manganese and sulfate. CC&V has not proposed to change the trigger levels presented by <br />the OMLR. The designated species for the trigger level, CNWAp, is, however, not the cyanide <br />species established as a water quality standard. It is a more conservative species in that it <br />measures cyanide in compound form which is not harmful unless the cyanide dissociates from <br />the cation. Dissociation begins to occur at a pH of 4.5 and lower (Smith & Mudder, The <br />Chemistry and Treatment of Cyanidation Wastes, 1991, p57). This pH is not normally measured <br />around the area. Therefore, a rise in CNWAp must be accompanied by detectable CNF~re to be <br />a potential exceedence of water quality standards and the dissociation is not anticipated to occur <br />at the ambient pH levels experienced. If CNWAp is detected and CNr~~ is not, there is not a <br />potential exceedence of applicable water quality standards. Rather, a CNWAp rise is a threshold <br />to carefully monitoring the CNr~~ levels. <br />With respect to pH, the general interest in the Cripple Creek Mining District is in decreases, <br />rather than increases, in pH. The pH should be considered in terms of a trend over time to <br />determine if there is a potential for CC&V's operations to be a cause of changes. Using <br />WCMW-6-234 as an example again, the 10 wells located upgradient of this well show minimum <br />pHs of 7.71, 7.08, 6.84, 6.87, 6.07, 6.78, 6.08, 7.02, 6.29, and 5.49. A trigger level must <br />take into account that granodiorite terrains may lead to lower pHs than acknowledged by the 6.5 <br />level proposed and that lower levels already occur in upgradient areas. Based on CC&V's <br />biological investigations, pHs lower than 5.5 should not be of concern. CC&V has proposed <br />that the lower pH limit for all wells be 6.0. If the OMLR decides that a pH of 6.5 is their <br />choice for wells WCMW-6-234 and GVMW-8A-250, the record shows that if lower values <br />described by the data base identified above are measured, they will remain descriptive of <br />ambient conditions. <br />The minimum pHs in wells up-gradient of GVMW-8A-250 over the period of record are 5.75, <br />5.92, 6.34, 6.24, and 6.83. While the minimum pH at well GVMW-8A-250 has been 7.63, it <br />is apparent that lower pH waters exist upstream and, therefore, that decreases in the pH at <br />GVMW-8A-250 could occur as water moves downstream. Therefore, it is best to establish a <br />trigger level that respects this up gradient variability. <br />With the trigger levels proposed by CC&V in place, if any one of the proposed trigger levels <br />is exceeded in any of the three ground water monitoring wells, CC&V will notify [he OMLR. <br />A "verification sample" will be taken within two weeks of CC&V's learning of the <br />"exceedence," or, if the well is dry, when water is again available in that well. If the <br />concentration of the verification sample is in compliance with the criteria, regular monitoring <br />will resume. If the concentration level in the verification sample also exceeds the criterion, a <br />second "verification sample" shall be collected within four weeks of learning of the results of <br />the second sample. <br />8 <br />