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'•� COLORADO LEGACY LAND
<br /> OREM
<br /> The post-2017 data presented in this table only covers a period of 31 months,not quite a full three year Table E-2 has been updated to included data collected since September 2020.
<br /> 18a period.Has the operator considered including data collected over the past year(since September 2020)in
<br /> this analysis?Would adding this data change the results?
<br /> Without further demonstration,the Division does not accept that the 2017 data(considered to be CLL is providing the last three plus consecutive years of data for this amendment for the period of mine ownership by CLL,
<br /> 18b 'suspect")is unrepresentative of the actual mine pool chemistry.Therefore,it may be appropriate to consistent with the February 20,2018,letter'Revised Approval of SO-01 ivith Conditions, Transfer of Permit for Colorado Legacy
<br /> include this data in the analyses presented in Table E-2 as well as Figure E-5. Land,LLC as Successor Operator,Schwartzwalder Mine,Permit No.M-1977-300" The 2017 data falls outside of the last three
<br /> consecutive years.
<br /> Given the fairly wide range in post-2017 concentrations for some of the constituents of concern(e.g.,total Table 37 was presented in a Whetstone report to show the summary statistics.Table E-2 was presented as a comparison of the
<br /> 18c uranium minimum=2.87 mg/L and maximum=23 mg/L),is comparing the mean values of this data set to statistics.Therefore,a comparison of the means is a valid method to show differences between the two data sets.Oddly enough,
<br /> the mean values of the pre-2017dataset(which may also have a large range) the best method for the pre-2017 dissolved uranium ranged from 3.9-61 mg/1(Cotter laboratory) or 4-32.4 mg/I(Sintrex laboratory)and the total
<br /> comparing these two datasets? uranium ranged from 30.06-37.59 mg/1 Cotter laboratory)in contrast to thepost-2017 results.
<br /> There appears to be several errors in the post-2017 data presented,in which,the mean value is lower than Table E-2 has been updated to correct the errors and the text has been updated to reflect any changes.
<br /> or equal to the minimum value,including for:bicarbonate as CaCO3,calcium,conductivity,pH,potassium,
<br /> 18d sodium,temperature,dissolved aluminum,dissolved magnesium,dissolved zinc,total antimony,total
<br /> copper,total zinc,and dissolved radium 226.Please correct these errors and update the analysis
<br /> accordingly.
<br /> 18e Please provide further discussion on the increases observed in post-2017 data for chloride,iron,and The increase in these constituents may be a result of the treatment system. For example,the increase in chloride concentrations
<br /> arsenic.Does the operator have any idea what might be causing these increases?Could the in-situ may be attributed to the addition of barium chloride into the treatment stream before injecting back into the mine.However,
<br /> treatments and/or the injection of RO reject brine into the mine pool have any effect on these constituents? natural variations in the mine may have an effect on the increase in iron concentrations.The increase in arsenic concentrations is
<br /> very minimal,e.g.,0.0005-0.05 mg/1 from 2000-2007 compared to 0.0026-0.0344 and may also be attributed to natural
<br /> variations in the mine.Please note that the pre-2017 data represents seven years of data whereas the post-2107 represents only
<br /> three plus years of data.
<br /> Note also that the location of return of the RO concentrate to the mine pre-2017 (Figure E-3a)included a return injection port
<br /> that included RO concentrate being added to the"open hole"adjacent to the Minnesota Adit. In discussion with Cotter geologists
<br /> at the time,they suggested that this area of the mine may have more leachable arsenic and iron,and that led to the changes in
<br /> injection location illustrated in Figure E-3b .
<br /> Please provide a graph which plots all available data collected since 2012/2013 for uranium,molybdenum, Figure E-7 has been added as requested and text has been added to describe the figure.
<br /> 19 chloride,iron,and arsenic concentrations in the mine pool.Please include available mine pool elevation
<br /> data,dates for in-situ treatments,and the date the operation began injecting RO reject brine into the mine
<br /> ool.Please provide a discussion of the relationship and any trends observed between these plots.
<br /> On page 24,the operator provides a section titled"Physical and Chemical Stabilization Conclusion".The Please see responses to specific comments on this subject. CLL has updated this section with additional and modified discussion.
<br /> Division has several comments in this letter requesting additional information and/or evaluation regarding
<br /> 20 the mine pool water quality data presented,in-situ treatments,sampling procedures,water treatment
<br /> plant/dewatering operations,and potential groundwater migration pathways at the site.Based on the
<br /> information provided,this section may need to be updated.
<br /> On page 25,the operator provides a brief summary of the conclusions made based on the tracer test Please see responses to specific comments on this subject.CLL has updated this section with additional and modified discussion.
<br /> 21 results.The Division has several comments in this letter requesting additional information regarding the
<br /> tracer study.Based on the information provided,this section may need to be updated.
<br /> On pages 25-26,the operator discusses the proposed water treatment plant operating strategy. Current Please see responses to specific comments below.
<br /> plans include operating the plant seasonally for approximately 6 months to manage the mine pool,and
<br /> possibly less than 6 months if supported by additional data.During operations,the 60-hp pump will be
<br /> 22 used to dewater the mine to approximately 400 feet below Steve Level.During the period the plant is shut
<br /> down,in-situ treatment of the mine pool will be conducted as needed to maintain chemical stabilization.
<br /> The criteria for in-situ treatment of the mine pool will be when the annual concentration of dissolved
<br /> uranium indicates an increasing trend as compared to the prior year.The Division has the following
<br /> comments regarding this section:
<br /> What is the target mine pool level (in feet below Steve Level)at which,the water treatment plant and The target mine pool elevation to begin dewatering is 170 feet below the Steve level.As the refill is projected into the spring,the
<br /> pump are brought back online? water treatment plant is brought online 2 weeks prior to the start of dewatering.The plant is run in circulation to test all systems
<br /> 22a and address any problems before the target elevation is reached. At the target elevation,there is a 20-foot buffer until the permit
<br /> level is breached.This would give the operator approximately 30 days to address any problem that may arise before the permit
<br /> level is breached.
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