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2011-01-25_REVISION - M1977300
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2011-01-25_REVISION - M1977300
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Last modified
6/15/2021 3:11:55 PM
Creation date
8/9/2011 1:34:13 PM
Metadata
Fields
Template:
DRMS Permit Index
Permit No
M1977300
IBM Index Class Name
REVISION
Doc Date
1/25/2011
Doc Name
Review of EPP
From
ARCADIS
To
Denver Water
Type & Sequence
AM2
Email Name
DB2
Media Type
D
Archive
No
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Daniel Arnold, Esq. January 25, 2011 <br />Denver Water Page 17 of 21 <br />Alternatives (or strategies) are proposed in the EPP to address the alluvial groundwater <br />and valley fill, and each is preliminarily screened. ARCADIS /Malcolm Pirnie reviewed <br />of each alternative on the basis of its effectiveness to reduce contaminant concentrations <br />and ability to protect groundwater and surface water quality. The following sections <br />briefly summarize each alternative and comment on the alternative's ability to meet <br />mitigation objectives. <br />Pump and Treat <br />Pumping and treating alluvial groundwater is currently performed and is a planned <br />strategy to reduce contaminant concentrations in groundwater and the creek. An alluvial <br />groundwater pumping system is in place that collects water from Sump 1 and 4 and from <br />well MW -9, which has been converted to an extraction well. The collected water is <br />pumped to the water treatment plant building where it is treated by ion exchange. The <br />treatment rate is reported to be 100 gpm and has been increased to approximately 200 <br />gpm recently according to Cotter representatives at the November 5, 2010 site tour. The <br />treated water is discharged to the creek near the downstream end of the mine. <br />Ion exchange is a proven method for treatment of uranium and has been successfully used <br />at the mine. A limiting factor of the current water collection and treatment strategy is the <br />treatment capacity of only 200 gpm. Historic collection rates from the sumps have ranged <br />from 35 to 404 gpm and the treatment capacity could be exceeded at certain times of the <br />year. Additional sumps are being installed to collect groundwater that would increase <br />treatment capacity. If the sump pumping rate is scaled back to meet the current treatment <br />capacity, collection of impacted alluvial groundwater would be reduced, allowing <br />groundwater to enter and degrade the water quality of the creek. Additional treatment <br />capacity is necessary if the water collection system is to effectively operate and reduce <br />groundwater from entering the creek. <br />Source Removal <br />The mitigation option that is recommended in the EPP is source removal and disposal of <br />fill material. This is reported to be the most permanent and maintenance -free solution. <br />Existing gamma radiation surveys of the fill and planned soil sampling in 2010 will be <br />used to define the extent of impacted fill. The soil would be excavated and disposed, and <br />this option is contingent on identification and approval of a viable disposal location. <br />Possible locations for disposal of the fill include the Canyon City Milling facility, or at <br />the mine's existing waste rock piles, or placed back in to the mine workings. <br />Removal and disposal of the fill should be performed to reduce the contaminant loading <br />to the groundwater and creek. Sufficient data in the EPP indicate the fill is a contributing <br />source of water quality impairment. However, removal of the fill, alone, may not <br />significantly improve groundwater quality. The waste rock piles are leaching uranium - <br />rich water that impacts alluvial groundwater downgradient of the piles, as evidenced in <br />MW -0 that has recent uranium concentrations between 0.2 and 0.5 mg /L. Even if the <br />impacted fill material is removed, leachate from the rock piles and mine pool water will <br />still occur and can impact the creek. <br />
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