2021-01-04_GENERAL DOCUMENTS - C1981019

• Permit No: C1981019
• IBM Index Class Name: General Documents
• Doc Date: 1/4/2021
• Doc Name Note: CO0045161
• Doc Name: Correspondence
• From: Colowyo Coal Company
• To: DRMS
• Email Name: ZTT
• Email Name: JDM
• Media Type: D
• Archive: No

DocuSign Envelope ID: EBE28081-13782-41342-BAD13-D8C9313687131B
December 22, 2020
Angela Aalbers
Page 11 of 12
Reference: East Taylor Seep Investigation
Table 3 Taylor Creek Peak Flows
Flood
Flow
(cfs)
Culvert
Diameter (in)
2-yr
15.7
24
5-yr
25.7
30
10-yr
34.1
36
25-yr
46.1
42
50-yr
57.3
42
100-yr
69.4
48
As an alternative to piping the water, the Taylor Creek channel could be lined to prevent or limit infiltration,
and several manufactured solutions exist for channel linings. One product, SmartDitch, is advertised as a
leak -free channel liner that is constructed from HDPE. It can be used for temporary or permanent
applications in agricultural, landfill, and mining projects. The 24-inch, trapezoidal channel could convey the
100-year peak flow. Literature from the manufacturer suggests a cost of $55 per linear foot; installation,
permitting, and intercepting the alluvial flow would be additional costs. SmartDitch is considered a
"permanent" product and has a service -life of over 20 years. Stantec did not evaluate the practicality of
installing SmartDitch in the existing channel; this design work would occur if Colowyo wishes to proceed with
this option.
Summary
The seep study and water balance demonstrate that there are multiple water sources contributing to the East
Taylor Seep flows, and these sources include both infiltrated precipitation and intercepted stream water. The
study suggests the following:
• Precipitation infiltrates and collects at the north end of the pit, similar to the conditions during mining,
before daylighting at the seep location.
o Flows from infiltration are currently elevated by remaining disturbed areas, but seep flows are
expected to remain at 50 gpm to 100 gpm under fully reclaimed conditions.
o Flows follow sitewide climate trends, and the extents of this will be confirmed by ongoing
seep flow rate monitoring.
• Seepage flows respond immediately to precipitation events suggesting a direct connection to surface
water.
o Highwall miners likely intercept the Taylor Creek alluvium and divert stream water towards
the seep.
o Under low -flow conditions, approximately 30 gpm may be diverted from the creek to the seep.
High flow conditions have not been evaluated, and it is not known if larger amounts of water
are diverted in higher flows.
Design with community in mind
pk c:\users\pkos\documents\_projects\colowyo\easttaylorseepwaterbalance_22dec2020_final.docx