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_ COLORADO LEGACY LAND
<br /> M-1977-300 APPLICATION AMENDMENT#6,COMMENT AND RESPONSE SUMMARY TABLE
<br /> COMMENT NO. COMMENT dkbL RESPONSE TO COMMENT
<br /> While the alluvial valley excavation project is estimated to be approximately 95%completed,the current
<br /> approved underground disposal locations for contaminated soils encountered during this project have
<br /> reached capacity.In its July 21,2022 adequacy response,the operator proposes to place additional
<br /> contaminated soils excavated from the valley at the southeastern edge of the existing South Waste Rock
<br /> Pile(SWRP).This material would be tied into the Black Forest Mine backfill area(approved in Amendment
<br /> No.5),capped with three feet of cover material (sourced from within the permit area),and seeded with the
<br /> grass/wildflower mix provided in Table E-1.The Division has the following comments on this proposal:
<br /> a. Cap material will be locally sourced from within the permit boundary from either the north side of Ralston Creek near
<br /> a. Please describe the type of cover material to be used as a"cap"on the contaminated soils. the former laydown area,or from within the alluvial valley excavation area on the south side of Ralston Creek. Cap
<br /> material will consist of unimpacted loamy soils(concentration of radium-225 less than or equal to 7pCi/g) so that these
<br /> soils do not possess the potential to leach uranium above the EPA MCL to Ralston Creek. Section 17.1 Plant Growth
<br /> Medium (Soils)of Technical Revision 23,Attachment B Schwartzwalder Mine Environmental Protection Plan
<br /> (Whetstone Associates Inc.,2016)provides the following description of these cap soils:"Soils in the study area range
<br /> from fine-loamy to loamy-skeletal in texture.Soil pH ranges from 5.1 to 9.0,Electrical conductivity and sodium
<br /> adsorption ratios for soils in the study area range from 0 to 4 mmhos/cm and 0 to 2 respectively."
<br /> b. The materials that CLL is currently removing from the alluvial valley are residuals associated with previous mining
<br /> b. Early documents in the permit file indicate material placed into the two waste rock piles consisted activities. Trench profiles in Appendix A of TR-14 show that the majority of soils are less than 100 pCi/g of natural
<br /> of approximately 50%mine development rock mixed with approximately 50%ore sorter reject. uranium,which converts to 145 mg/kg of natural uranium or 0.0145%U308. Therefor these residuals are expected to
<br /> While the ore sorter reject had higher levels of uranium(up to 0.06%U30e),mixing this material have approximately half of the concentration than the previous SWRP materials.
<br /> with the development rock(average Of 0.01%U308)was expected to produce a final weighted
<br /> average of approximately 0.03%U308 in the waste rock piles.Please describe how the uranium No,the expansion material does not have an increased potential to contaminate alluvial groundwater. The primary
<br /> content of the proposed expansion material compares to that of the existing material in the SWRP. objective of the alluvial valley excavation project is to mitigate the potential for alluvial soils to leach uranium(above the
<br /> Could the expansion material have an increased potential to contaminate the alluvial groundwater EPA MCL)to shall groundwater or Ralston Creek. The uranium-impacted materials that will comprise the SWRP
<br /> system and/or creek,compared with the existing material in the SWRP? expansion are currently located in the alluvial valley adjacent to Ralston Creek. Therefore,these are not"additional
<br /> materials"because they are currently onsite. Removing these materials from the subgrade and consolidating them
<br /> under a cap,further away from Ralston Creek,will enhance the protection of surface water and groundwater resources.
<br /> c. Figure F-2 has been revised to include additional details on the natural drainages for clarity. During the construction of
<br /> c. It appears the proposed SWRP expansion will be situated below two natural drainages.Please the SWRP expansion an earthen berm(approximately 1 to 2 feet in height) shall be constructed to mitigate erosion at the
<br /> describe how water in these drainages will be managed in order to prevent erosion damage to the toe of the pile. The berm shall direct the water into the drainages and away from the SWRP materials. Additionally,CLL
<br /> pile (especially before a sufficient vegetative cover has been established)and also to minimize will armor the drainage channel near the toe of the SWRP with appropriately sized rip rap to mitigate any erosion
<br /> infiltration into the pile(thus minimizing the potential for water contaminated by this material damage at the slope transition from the hillside to the valley.The slope of the SWRP expansion ranges from 2:1 and 3:1
<br /> impacting the creek system). to match the surrounding natural topography,which will minimize infiltration into the pile.
<br /> d. As detailed in AM-06,CLL already conducts monthly surface water monitoring of SW-AWD(upstream of waste rock
<br /> d. Because creek flows are currently routed around the mine site via the bypass pipeline,surface piles)and SW-BPL(downstream of water rock piles) for compliance with their CDPHE Discharge Permit#CO-0001244.
<br /> water monitoring locations along the section of the creek within the mine area are typically dry, This compliance sampling includes a wide array of parameters including antimony,arsenic,boron,chromium III,
<br /> including location SW-A001,which was intended to monitor for impacts to the creek from the chromium VI,copper,cyanide,fluoride,gross alpha,gross beta,molybdenum,nitrate+nitrite,pH,phosphorus,
<br /> SWRP.Based on the water quality data observed in existing alluvial monitoring wells near the phosphate,radium 226+radium 228,silver,sulfate,total dissolved solids,total suspended solids,thallium,uranium,and
<br /> SWRP(MW-0 and MW-19),the Division has some concerns about the existing SWRP being a zinc.
<br /> potential contamination source to the creek.An extension of the footprint of this pile,especially if
<br /> the additional material has higher levels of contaminants per volume,creates additional concerns. In addition to these samples,CLL shall commit to collecting monthly surface water monitoring for dissolved uranium for
<br /> Therefore,the Division believes an increased monitoring frequency of the surface monitoring two years from all surface water stations within the MLRP boundary.The on site sampling locations and frequency shall
<br /> locations will be necessary after creek flows are re-established across the mine area,at least on a be documented in a Technical Revision along with the new monitoring well referenced above in Comment U. This
<br /> temporary basis,to better monitor for potential impacts to the creek.Please commit to sampling sampling effort shall begin once Ralston Creek flows are re-established across the site(i.e.not in the bypass pipeline).
<br /> all approved surface water monitoring locations on a monthly basis after creek flows have been re-
<br /> established across the mine area.The required sampling frequency will be reassessed after the
<br /> Division has reviewed the monthly monitoring data submitted.
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