2011-12-01_REVISION - C1981019

• Permit No: C1981019
• IBM Index Class Name: REVISION
• Doc Date: 12/1/2011
• Doc Name: Updates to Yampa River CHIA as a Result of PR3 ‎(Memo)‎
• From: Rob Zuber
• To: File
• Type & Sequence: PR3
• Email Name: RDZ
• Media Type: D
• Archive: No

DIVISION OF RECLAMATION, MINING AND SAFETY
Department of Natural Resources
1313 Sherman St., Room 215
Denver, Colorado 80203
Phone: [phone]
FAX: [phone]
MEMO
STATE OF COLORADO
Date: December 1, 2011
From: Rob Zuber R
To: Yampa River CHIA file
Re: Updates to Yampa River CHIA as a result of PR -3 (Collom area) for Colowyo Mine
(C- 1981 -019)
DRMS assessed the cumulative hydrologic impact of the proposed Collom area (PR -03), which
adds approximately 17,000 acres to the Colowyo permit area (over 2,000 acres of disturbed area).
This memorandum is based on work completed by Tom Kaldenbach, DRMS hydrologist/geologist,
in 2011 and previous years. It was determined in the PR -03 findings that the only likely cause of
material damage from the Collom area is the increase in TDS in the Yampa River due to spoil
springs.
DRMS assessed the cumulative hydrologic impact of the Collom area by conducting a sensitivity
analysis to determine if the proposed mine expansion could cause material damage in the Yampa
River watershed. The TDS input from the Collom area into the Yampa River occurs via Morgan
Gulch and its tributaries.
This sensitivity analysis is conducted only for the month of August because this is the month when
mine impacts to streams are likely to be greatest due to low stream flows and large irrigation use.
This sensitivity analysis consisted of using a mass - balance analysis and inputting an extreme value
for flow from new spoil springs that could result from Colowyo's proposed expansion (2 cfs is
likely an order of magnitude greater than the actual value). If this extreme value does not indicate
material damage, then it can be safely assumed that a more reasonable value would not cause
material damage.
The table below shows a mass balance analysis within Morgan Gulch and for the Yampa River. It
also shows that during the month of August in a historically dry year (192 cfs in the Yampa River
below Milk Creek), a 2 -cfs flow of 4,000 mg/1 spoil leachate would raise the TDS in the main stem
of the Yampa River from 352 mg/1 (upstream of Morgan Gulch) to 430 mg/1 (downstream of
Morgan Gulch). The source of the concentration of 352 mg/1 is the existing Yampa CHIA for the
August scenario that includes mine pumping in a historically dry year. The predicted 430 mg/1 is
well below the approximate 700 mg/1 material damage suspect level. Therefore, the proposed
mining would not cause material damage.
COLORADO
D I V I S I O N O F
RECLAMATION
MINING
SAFETY
Office of Office of
Mined Land Reclamation Denver • Grand Junction • Durango Active and Inactive Mines