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Review of CC&V Response to Commitment No. 36 Memo to B. Keffelew, June 27, 1994 Page 4 are not required by the NPDES discharge permits for surface water in Arequa Gulch. The Division advises CC&V to analyze for these parameters, and to establish background concentrations for these presently unregulated metals. Although it is not within the Division's authority to require measurement of elements which are not regulated, neither will the Division be able to defend the choice not to analyze for those parameters if and when the list of regulated parameters is changed by the WQCD. This comment is advisory only. CC&V have noted that the water in Arequa Gulch presently flows through "granite" identical to that which was evaluated using the MWMP.' CC&V should recognize that the water-rock relationships currently existing between Arequa Gulch water and the associated bedrock will change as a result of the excavation. Disturbance of the bedrock will expose unweathered surfaces which will be more reactive than those already exposed in the drainage which have been weathering for thousands of years. The Division notes that the rocks which were used for the MWMP tests consist of cuttings, whereas the rocks to be placed in the underdrain will consist of cobble or boulder-sized materials. Because the surface area of the cuttings, which were exposed to "weathering" under the MWMP test, is much greater than what will be exposed to weathering in the underdrain, the leachate metal concentrations reported in the Commitment Number " 36" repoR can be expected to be maximum metal concentrations. Thus, for those metals whose concentrations fall below the standards, it will be concluded that there will be no environmental degradation as a result of intrduction of those metals. For those metals whose concentrations are above the standards, the Division cannot draw conclusions based on the information presented other than that the values are above the standards. If these data are to be used to demonstrate compliance, they should be expressed in context of the circumstances under which they will be introduced into the environment, and evaluated appropriately. It is reasonable to assume that the data represent maximum concentrations that could be anticipated in the environment, and the metal concentrations in the leachate waters from the underdrain are likely to attenuate as a result of mixing with other water prior to reaching the 'On June 24, David Kidd presented to the Division two rock samples that are representative of those tested for the underdrain. Although these samples were thought to be from the Pikes Peak Granite, they appeared to be foliated granodiorite. To our knowledge, the Pikes Peak is not foliated. It is of no consequence to the Division whether the rock is granite, granodiorite, or any other rock. However, if CC&V chose certain outcrops on the basis of pre-existing rock strength or weathering characteristics, it may explain some of the unexpected results.