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Mareb 2005 Hayden Gulcb Znadaut - 2004 AuuualHydrology Re~iort ~ Page 5 <br />While these values were greater than the WDEQ guidelines, historic values for these constituents at <br />both locations typically exceeded the respective benchmark values. <br />Time-[rend plots of manganese, sulfate and TDS concentrations are presented in Appendix C. <br />3.3 GROUNDWATER DATA <br />Groundwater data Eor 2004, as well as historic data collected since 1993 is presented in Appendix D, <br />GroundmaterQuality Data. Presently, HGTI is only monitoring alluvial groundwater in monitor well, <br />HGDAL3. In 1993, HGTI installed HGDAL3 as a new downgradient alluvial monitor well in <br />response to CDMG concerns that the two existing alluvial wells, HGDALl and HGDAL2, may have <br />been partially completed in the Lewis Shale, which could comprise the data. Groundwater quality data <br />was collected from monitoring wells HGDALl and HGDAL2 between 1987 and 1995. Groundwater <br />monitoring of these two monitor wells ceased in 1995. The locations of the groundwater monitoring <br />wells are shown on Figure 1, Monitoring Site Locations. <br />HGTI reported in the existing, valid Mining and Reclamation Permit (revision date of May 2002) that <br />chemistry infoxmation obtained in HGDAL3 is similar to the historic chemistry depicted by <br />monitoring wells HGDAL] and HGDAL2. CDMG, in their Adequacy Comments to Technical <br />' Revision TR-06, dated January 15, 2004, expressed concern that elevated concentrations of select <br />constituents reported from HGDAL3 may not be not characteristic of natural Dry Creek alluvial <br />chemistry, but may be indicative of impaired alluvial groundwater. HGTI has prepared an evaluation <br />' of upgradient and downgradient water chemistry, which is included in the TR-06 comment response <br />package. The upgradient chemistry data was obtained from Dry Creek alluvial mortitor wells <br />completed by Peabody Holding Company, Inc., HGTI's parent company, in the mid- to late-1990's <br />chat are located upgradient of the Hayden Gulch Loadout. In summary, the data indicate both <br />upgradient and downgradien[ alluvial groundwater contains elevated concentrations of both sulfate <br />and total dissolved solids ('I'DS) -the TDS concentrations were greater than the 10,000 mg/1 <br />groundwater standard in both upgradient and downgradient alluvial waters. This indicates that the <br />natural Dry Creek alluvial chemistry contains high concentrations of both constituents. <br />MWH attempted to sample monitor well HGDAL3 as part of the January 2004 monitoring event. <br />Water in the well casing was frozen, and consequently, the well was not sampled. The spring runoff <br />monitoring event (also conducted by MWH) occurred on June 2, 2004. The fall monitoring event, <br />conducted by Hydro-Environmental, occurred on November 2, 2004. <br />In general, the alluvial groundwater concentrations Erom HGDAL3 in the 2004 samples were similar <br />to previously observed values. Most constituent concentrations were within historic ranges. The June <br />sample contained a copper concentration that was slightly higher than the previously observed <br />' maximum concentration. Arsenic and boron concentrations in the November sample were also <br />slightly higher then their respective previously observed maximum concentrations. New minimum <br />values were measured for magnesium and sulfate in the November sample. Time trend plots for <br />~ common constiments are presented in Appendix D. <br />Hydro-Environmental Solutions, Inc. <br />f7 10~ Street, Suite B * P.O. Bax 772996 <br />Steamboat Spring,, CO 80477 <br />(970J 846-5112 <br />