2016-05-04_PERMIT FILE - C1982056 ‎(7)‎

• Permit No: C1982056
• IBM Index Class Name: Permit File
• Doc Date: 5/4/2016
• Section_Exhibit Name: 2.06 Special Categories of Mining
• Media Type: D
• Archive: No

An arca in the Foidel Creek drainage in sections 21, 22 and 28 has been designated an alluvial vallev Floor
on the basis of the potential for subirrigation. The U.S. Department of Interior, Office of Surface Mining,
• Division of Reclamation and Enforcement released in June 1985, Reconnaissance Maps to Assist in
Identifying Alluvial Valley Floors in Northwestern Colorado. The reconnaissance map of potential alluvial
valley floors for the Yampa and Danforth Hills Coal Field of Northwest Colorado (Eastern half) delineates
the subject area as having the potential for Flood irrigation but not for subirrigation. TCC has previously
submitted the results of a water availability investigation which demonstrates that there is insufficient
water available in the Foidel Creek drainage to support flood irrigation.
The evaluation of no subirrigation in the area is consistent with information submitted in the permit for the
Lckman Park Mine including an analysis of infra -red photography taken in September, 1978 which
showed no evidence of subirrigation in this area (Permit 979-177, pages 785-15 to 785-16). In addition,
TCC has recently acquired water quality information from the alluvial deposits in this area (P&M-1
through P&M4, see Map 13, Twentymile Park Hydrology and Table 67, Alluvial Well Data for Sections
21, 22 and 28). This data indicates that salinity levels are several times higher than threshold levels at
which plant growth iS affected.
Several shallow boreholes (Auger I -Auger 5, See Map 13, Twentymile Park Hydrology) were drilled in the
vicinity of this alluvial valley on July 3, 1986 during construction of a powerline. These holes were used
to examine the nature of the alluvial deposits and the characteristics of the alluvial groundwater by TCC.
The alluvial deposits were observed to be almost entirely clays and silty clays presumably derived from
reworking of the underlying Lewis Shale unit (Table 68, Alluvial Drill Hole Logs). The alluvial deposits
were observed to yield very little water to the borehole, indicative of very low permeabilities typical of
clay materials. Inflows to the borehole were observed to be significant only after the boreholes penetrated
the underlying bedrock. Much of this flow was observed to occur at the alluvial/bedrock contact.
• Llectrical conductivity values of alluvial groundwater measured by TCC personnel on July 7, 1986 in
existing piezometers completed in the alluvium in one of the shallow boreholes and an existing large -
diameter dug well ranged from 598 to 5400 mmhos/cm (Table 67, Alluvial Well Data for Sections 21, 22
and 28). These values are far in excess of threshold values for initiation of detrimental effects on plant
g,rowth according to CMLRD guidelines. The high solutes concentrations indicated by the electrical
conductivity values are believed to be a result of dissolution of minerals within the Lewis Shale material
which makes up the bulk of the alluvial deposits.
It is TCC's contention that the high salinities of alluvial groundwaters preclude the designation of this area
as an alluvial valley,floor as subirrigation will not benefit agricultural activities. Given that the current
solute concentrations in the alluvium of sections 21, 22, and 28 is higher than typical values of Foidel
Creek during the potential recharge period. TCC further contends that no detrimental effects to water
quality in the alluvium can occur as a result of operations of the Foidel Creek Mine.
Despite the evidence that subirrigation is probably not occurring in this area, the reach was examined to
investigate whether recharge of Foidel Creek waters during the spring runoff period might affect the
potential subirrigation function. A survey of the creek channel through this area was conducted by TCC
staff on time 30, 1986. The survey demonstrates that the alluvial deposits directly underlying the creek
channel consist of clays and silty clays which have very limited potential to allow significant recharge to
the adjacent alluvial deposits.
[lei ncability values for clay are in the range of 10-6 to 10-2 gals/day/ sq. ft. (Freeze and Cherry, 1979).
I'hc average width of the Foidel Creek channel through this reach is less than 5 feet. Measurements of
. Nk:ater levels in three existing piezometers, Table 67, Alluvial Well Data for Sections 21, 22 and 28,
indicate that hydraulic gradients in the alluvium are in the order of 0.01. A simple calculation using, the
MR 97-154 2.06-21 12/09/97