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Appendix D, Comments from Rocky Mountain Consultants, /nc., Hydrokr'nerics. /nc., & Hydrodynamics,/rrc. (Cont.) Page 9 <br />The reviewers suggest that separate discharge points be assigned to all of the seeps referred to in the NOV/CDO issued August <br />20, /999. Each seep identified in the NOV/CDO is a surface ezpressian of groundwaterJlow in the vicinity of the West Pit and <br />the flow and quality associated with each seep is influenced by a variety of factors including: (I) stage ojrhe Rito Seco, (2) <br />presence and location of beaver ponds, and (3) upgradienr groundwater flow. Tlrus, the potential exists t/rat there [night be flow <br />at one or more of the historical seep locations that would not be related to groundwater flow from the West Pit. The <br />performance monitoring program implernerrted as pan of the rater management plan, includes the original seepage area as a <br />sampling pour[ if there is sufjtcient flaw to collect a representative sample, whit/r, in combination with the other x•ater quality <br />and quantity information provided by the monitoring program, should address the potential natural variability of flows <br />associated with the historical seepage area. The monitoring program xill be subrnitred under separate cover, and monitoring <br />submittal requirements have been added [o the permit. !n addition, a compliance schedule has been added ro this CDPS permit <br />that addresses actions and monitoring required for 002 in case seeps slrould reoccur in the future from the original defined <br />location in the West Pit drat would go to the Rito Seco alluvium. The reviewer should also note that there has not been flaw in <br />any ojtlre original seep locations since Febneary 8, 2000. <br />Comment: <br />2. Long-Tenn Water Groundwater Disclrar a Ig slues <br />!t is our opinion that the 7R-26 monitoring system (including the adjustments ro drat system made by DMG subsequent to <br />issuance ojTR-26) shoulAbe nrainlained throughout the long term. Specifically, wells Nd[hin the flow "xnndow"should be <br />identified as points of compliance, and discharge through the xdndow and from the seeps must be quantified. Mining has <br />permanently altered the groundwater flow regime in the vicinity aj the x~es[ pit (see TR-26 at pages (r/0). Consequently, we <br />believe "long teen" here should mean until the applicant can demonstrate that the West Pit is incapable of generating poor <br />quality for an emended period of lime once the active remediation programs are curtailed and the lydrologic connection from <br />the West Pit and the Rito Seco has been re-established. <br />We do not believe the "long term monitoring"as described in TR-28 is sufjtcieru given the applicant's characterization of the <br />hydrologic rystem in 7R-26 and in the August 30 Technical Support Document. Reducing the long renn monitoring requirement <br />to the wells identified in Section 4.1 ojTR-28 is insufjtcien[ to allow recognition or quantification ojre[eases to groundwater <br />before they signiflcantty impact surface water. Of the 4 alluvial wells identified, wells M-10 and M-34 are remote from the <br />window. Only well M-19 is in the vicinity of the window as mapped in TR-26. As the applicant points out, the alluvial aquifer <br />is heterogeneous. A single monitor well in the vicinity ojrhe window is insufficient to allow characterization oJ[he groundwater <br />discharges. Similar arguments can be made for the maintenance of the current TR-26 monitoring system in the bedrock x•e[ls, <br />and the Santa Fe Formation wells. <br />We also recommend that a slurry wall around the Wes[ Pit where it is in contact with the Rito Seco alluvium be considered as a <br />BMP. The slurry wall would inhibit alluvial groundwater inflow into the eastern corner of the West Pit, thus keeping clean <br />water clean, In conjunction with, or as a separate BMP, BMR/ should also evaluate rlre installation of a reactive subsurface <br />barrier/wall in or just downgradient of the window. The reactve wall would inhibit potential contaminated West Pit <br />groundwater from migrating into the Rito Seco. <br />Response: <br />Issues regarding long-renn water quality monitoring ojgroundwater in the vicinity ojrhe West Pit xi[l be addressed by the <br />DMG. BMRI lws developed and implemented a performance monitoring program that dre Division believes will provide the <br />information necessary to evaluate, assess, and protect the groundwater quality in the vicinity of the West Pit. This monthly <br />monitoring data will be required to be submitted to t/te Division as part ojrhe COPS reporting requirements of the permit. <br />/n response to the comments relating to TR-26 and TR-28, reference to these Mao documents is no longer included xdrhin the <br />permit. /t should also be noted that 7R-28, which addressed long-renn water quality in the West Pi[, xas xdthdrawn from <br />consideration by DMG ar the request of BMRl. <br />With regard to the installation of a slurn~ x•all, BMR/, WQCD, and COMG have reviewed the potential merits ojrhe slurry x~all <br />and all parties have concluded that the long-renn consequences of the slurry wall outweigh the short-renn benefits as perceived <br />by the reviewers. The flushing action provided by the inflow of groundwater from the Rito Seco alluvia( aquifer is a fundarnen[a[ <br />component ojrhe water rnanagemen[ plan because the inflow ojgroundwater xdth lower concentrations of constituents more <br />e(jectively flushes the secondary sulfate salts associated with the backfill material. Wren the water management program is <br />completed, the water qua(iry in the West Pit is expected to no longer contain elevated concentrations ojconstituents. Thus, the <br />issue of "keeping clears water clean "will have been addressed. Additionally, t/re installation of a slurry wall would further <br />disturb the hydrologic rystem beyond the changes induced as a result of t/re historical mining activity with no corresponding <br />benefits. <br />