2009-12-23_GENERAL DOCUMENTS - M1977285

• Permit No: M1977285
• IBM Index Class Name: GENERAL DOCUMENTS
• Doc Date: 12/23/2009
• Doc Name: Denison's response to the BLM remand
• From: Denison Mines
• To: BLM
• Email Name: RCO
• Media Type: D
• Archive: No

/nf0rmal %On to Su0,00# Denison BL MEnuironinenfalASSessmenf Remand
Denison Sunday Mines GIouo
and indicates that the potential for leachate production and potential
risks to groundwater are low.
As described in the data collection work plan (CDM 2008) provided to
BLM for review, Denison completed extensive trenching of development
rock at the Sunday Mines Complex, including many hundreds of feet of
excavated trenches at the various mine development rock piles. No
indications of seepage were observed in the trenches; trench photographs
and field notes were provided to BLM in the final report (CDM 2009). In
addition, rock samples were collected from the trenches and submitted to
analytical and geotechnical laboratories for analysis using standard
methods promulgated by the U.S. Environmental Protection Agency
(EPA) and American Society of Testing and Materials (ASTM) to evaluate
site - specific conditions. The volumetric water content of the rock samples
was a fraction of the field capacity indicating that at the time of sampling
downward percolation of moisture within the piles was unlikely to occur.
Additional site - specific geotechnical data (capillary moisture data) and
climate data were used to develop a detailed transport model to further
evaluate if downward percolation of water through the rock pile could be
a concern. The assessment activity also incorporated several conservative
assumptions such as using precipitation data from the wettest year on
record and incorporating sensitivity analyses to assess potential
uncertainties with site - specific parameters. These evaluations indicate
that leachate migration hazards are not present at the existing rock piles,
and therefore potential hazards would not be increased by expanding the
surface area of the piles in accordance with the proposed modifications to
the mine plans of operations.
Comment 2 4 report oflhe lechnicalgeochemical investigation ofrock ana'soil
malerial has I eenpreparedfor the mine area KMfflnc, flay, 2009
including characterization ofmine " developmenl" and waste d ump rock.
This report makes a strong case lere may he lowpotential mohilization of
the metalsfoundin the dumps (Zncluding.• anlimory, arsenic, cadmium,
fli�orile, molybdenz <m, selenium, uranium,• anel vanadium,) through
dissohilion in wale inlo the subsurface andsurroundingsoil and
environmen! However, even though the reporl is well done, it remains
theoretical, andsampling is necessary to gain empirical data to establish
creditahility. lVo dales erislsfol° thesuha'ump anddump- a,
conditions ofer �0 +years oflheir exislerrce. There is no data m ailahle
for knowing whal conditions exisl helow the mine dumps as they now erisl,
or what clean up measures Many,) may he needed with dump expansion in
lhefimi�re. There is some haselinesoilsamplingincl2 <dedin the repojl.
Wndandrunofftransporlalion offine graineddump malerialhas the
polenlialforsu facialdownwindanddowngradienlf om thesile
(IISEPf11OO7 /2008 Su face lranseclsampling over a dislance ofip lo .1
Final Sunday Mines BLM Remand Letter.doc