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<br /> <br />`= ~~ED <br />ocr 1 s ~ss2 <br />,,~~;~ OF <br />'~'•t^~~~ d '~ECLOGY <br />Technical Revision No. 8 (TR-08) evaluated if the ground water gradient in the Santa Fe aquifer <br />is towards the west, as was previously established regionally through Ilse water level data <br />obtained in existing Santa Fe aquifer wells and through published literature, and as was inferred <br />locally by the installation of monitoring wells M-2, M-6, M-7, M-8 and M-9. Furthermore, TR- <br />08 evaluated if the installation of two additional monitoring wells (M-12 and M-13) would <br />adequately monitor downgradient water quality conditions in the Santa Fe aquifer (in conjunction <br />with the existing wells). This evaluation was to be in the context of the site-specific geology <br />and hydrogeology. <br />Site-specific drilling that has been conducted to date by BMR in the Santa Fe Formation, both <br />related to the ground water monitoring system and the geoteclmical assessments telated to siting <br />of the tailings facility, has indicated that the Santa Fe Formation is unsaturated to a depth of <br />over 100 feet in this area, and tests have shown that the moisture content in this matrix is well <br />below specific retention. Therefore, significant volumes of water would need to be added to <br />overcome specific retention and provide a driving head for the downward movoment of water. <br />The seepage analysis performed by BMR as a part of the CMLRB permit process, and a similar <br />analysis conducted by Division staff and presented at the June 24, 1992 Board meeting, indicated <br />that there would not be sufficient seepage from the tailings facility under normal operating <br />conditions to increase soil moisture above soil retention to allow such downward flow of water <br />into the Santa Fe aquifer. The BMR analysis was based on EPA criteria for hole density in the <br />liner and, therefore, followed accepted practice for evaluating Flow through the liner (see <br />Adequacy Responses for Permit No. M-88-112). <br />The second phase submittal for TR-08 demonstrates that the installation of monitoring wells M- <br />12 and M-13 has not only confirmed that the local ground water gradient is to the west (down <br />valley), but has also confirmed that the Santa Fe at these locations is characterized by extremely <br />low permeability, heterogeneous material. In addition, TR-08 shows that if water does reach <br />the aquifer it then migrates very slowly (approximately 15 ft/yr). Based on these data, tl~e <br />second phase submittal for TR-08 demonstrates that the existing monitoring well system is <br />adequate; i.e. these wells monitor the local ground water quality downgradient from the mine <br />facilities. <br />However, the CDMG and Mr. Mefford have raised questions about the values Of porosity and <br />dispersivity used in the TR-O8 second phase submittal report in evaluating the adequacy of the <br />existing monitoring well system to monitor downgradient water quality below the tailings facility <br />and collection pond. The value of porosity, and longitudinal and transverse dispersivity, used <br />in the TR-08 submittal were based on JCHA's knowledge of the Santa Fe Formation from <br />drilling that has been conducted on site, the field geologist's experience with similar materials <br />~ iii iiiiiiiuiiu iii • <br />999 <br />ADEQUACY RESPONSES TO ADEQUACY COMDIENTS <br />TO TECHNICAL REVISION NO. 8 - (PHASE II SUBMITTAL) <br />EXISTING GROUND WATER MONITORING SYSTEIII <br />