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Appendu D, CormnentsJrom Rocky Mountain Consultants, Inc., Hydrokinetics, Inc. & Hydrodynamics,lnc. (Cont.) Page 1/
<br />The alleged flow of water at the seeps reported by Mr. McGox~an has not been substantiated with respect to occurring from the
<br />West Pit. The historic seep area has been visited by the DMG, CDPHE, and the EPA (NPDES and Emergency Response
<br />groups) recently (May 2000), and al! ojthe inspectors have aJftrnted that the seeps that have been historically influenced by the
<br />backftlled West Pit no longer flow. No historic seep discharges from the West Pit have occurred since February 8, 2000. In
<br />addition, water levels recorded jor groundwater in the backfl[led West Pit demonstrate that the hydraulic gradient between the
<br />backfilled West Pit and the Rito Seco alluvial aquifer tuts been reversed as described in the TR-026 rater management plan.
<br />Thus, the groundwater flow from the West Pit to the Rito Seco alluvial aquifer cannot occur oral the surface water and
<br />groundwater flow associated xRth 002 Jrorn the West Pit has been eliminated.
<br />An estimate of the current groundwater flox• rare from the backfilled West Pit is not necessary at this tune because the hydraulic
<br />gradient has been reversed and groundwater is now flowing imo the backfilled West Pit. The response of the groundwater
<br />system in rlre vicinity of the West Pis, as recorded by the performance monitoring program that is included in the rater
<br />management plan, has occurred in a rwnner that is consistent wilt [he representation of the system developed in TR-026.
<br />Comment:
<br />3. Section /LG. Hare 2
<br />The standards listed for arsenic, mercury, and selenium in the CDPHE Regulation 36 jor Rio Grande Stream Segment 28 are jor
<br />the total recoverable form of the metals, not total.
<br />Elevated concentrations of aluminum have been reported in Borne backfill wells (i.e., the BE-series wells) and seeps. Aluminum
<br />sJtould be included in the list of parameters.
<br />Response:
<br />The discussion of the stream standards for these metals has been clarified. The CDPHE laboratory has indicated that these
<br />three metals are measured as total, not as !oral recoverable.
<br />The Division has determined that limitations and monitoring will be included in the permit jor potentially dissolved aluminum jor
<br />outfalls OOIa, OOlb, and 00le. Since concentrations of dissolved aluminum have been greater in the pit backfilf monitoring well
<br />data (0.208 mg/l per Appendix A) than the applicable 30-day average limitation (0.087 mg/I), there is a reasorwble potential to
<br />support adding permit limits for this parmneter. Also, since drere has been no monitoring data jor aluminum from the treatment
<br />facility, aluminum xdl! need to be evaluated as pan oJthis permit.
<br />Comment:
<br />4. Section H.G. Dare 2
<br />Staton RS-2, specifically the period ojrecord 1-//-90 through 7-20-1999, is not representative of background hardness
<br />conditions in the Rito Seco. Station RS-2 is located about 3,OOOJeet dox~nstreorn of the West Pit and, as such, has been
<br />influenced by BMR! mining actions jor the entire period of record used. !n addition, review of the hardness data for Station RS-
<br />2 indicates a defrnite impact due to leaAnge from the West Pit during the period ! 998 and 1999. The Biz hardness values
<br />reported between December 2/, 1998 and April 14, /999 range Fran 14/.4 to / 76.3 mg/L CaCO~. Inclusion of these obviously
<br />impacted data in the hardness calculation is inappropriate.
<br />Station RS-1 should be used to provide representative data jor the lwrdness evaluation. Station RS-1 is located upstream of oll
<br />BMR! disturbances and has mr extensive monitoring record. We also recommend drat the RS-/ hardness database be tested jor
<br />seasonality to deterntine if the use ojseason hardness values is appropriate, rather the using the median value jor all seasons.
<br />Response:
<br />The Division has determined that the RS-1 location is not representative jor either the antidegradarion baseline evaluation or the
<br />total hardness evaluation (see previous discussions, page 24 of the rationale and page 7 oJAppendix O). Hardness is used to
<br />calculate Table Value Starsdard (TVS) concentrations of constituents that shox~ variable levels of toxicity to aquatic x~ldlife as
<br />buffered by the hardness of the receiving water. The value of hardness reported in the August 30, 1999 Technical Support
<br />Document (57.3 mg/L as CaCO~ was calcula[ed using the period of record for RS-2 beginning 1987 and ending 1989, which is
<br />prior to any potential BMRI mining-related effect on water quality in the Rito Seco. Hardness values are used to calculate the
<br />TVS jor selected metal constituents using t/re general form of a power function wherein the value aJ the exponent depends, in
<br />part, on the natural logarithm ojlhe hardness value. Titus, the difference in the natural (ogarithm ojthe hardness value
<br />referenced by dre reviewers (i. e., natural logarithm of 64) versus t/re natural logarithm aJthe hardness value reported in the
<br />Technical Support Document (i.e., natural logarithm oj57.3), as well as considering the mean value for hardness at Station
<br />RS-1 (i. e., natural logarithm oJ54.5 mg/l), all result in a rninirwl difference in the final calculated TVS value. Also, seasonal
<br />hardness values are not appropriate as these values must be correla[ed to [ow flow periods, as is specified in the Colorado Total
<br />Maximum Daily Load and Wasteload Allocation Guidance (WQCD. November 1991). Thus, the Division is sell using the value
<br />of 64 mg/l as CaCO~ jor /tardness, since this was determined according to established criteria used.
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