GENERAL48692

• Permit No: C1981019
• IBM Index Class Name: General Documents
• Doc Name: Proposed Decision & Findings of Compliance
• Permit Index Doc Type: General Correspondence
• Media Type: D
• Archive: No

-14-
Stipulation No, Z
WITHIN SIX MONTHS OF PERMIT ISSUANCE, THE PERMITTEE WILL SUBMIT A
REVISED SURFACE WATER MONITORING ALAN SUFFICIENT TO VERIFY THE
PREDICTED EFFECTS OF MINING ACTIVITIES. SPECIFICALLY, THE
PLAN WILL ADDRESS MONTHLY MEASUREMENTS OF FLOW AND FIELD PARAMETERS
ON GOOD SPRING CREEK AND TAYLOR CREEK, IN ADDITION TO THE POND
DISCHARGE SAMPLING AND QUARTERLY STREAM SAMPLING AS SPECIFIED IN THE
APPLICATION. THE LOCATION OF ALL MONITORING STATIONS SHOULD BE INDICATED
ON A MAP. THE MONITORING PLAN WILL BE SUBJECT TO APPROVAL BY THE
REGULATORY AUTHORITY.
Upon completion of one year's monitoring, the number of parameters and
frequency of sampling will be reviewed by the Division if the permittee
requests, It may be o iss ble at that time to further refine the
monitoring requirement based on site-specific conditions.
The Division's concerns pertaining to sediment and drainage control at
Colowyo have been satisfactorily resolved. Concerns identified in the
Preliminary RPdequacy Letter of April 9, 1982, included the applicability of
peak flow estimates used in culvert design and sediment yield estimates
used by Colowyo. Colowyo revised its estimates of peak flow using regression
equations developed by the U.S.G.S. for Colorado watersheds, as requested by
the Division. Colowyo agreed to install rock riprap at the inlets to culvert
installations to the headwater height.
In the review letter of July 9, 1981 to Colowyo, the Division noted that the
sediment yield estimate of .00081 acre-feet per acre over three years accrual
appeared extremely Zow. Colowyo responded that the calculations reflected
the degree of revegetation success and resultant erosion control achieved
at the Colowyo mine. In field studies performed at the site, and subsequently
described in the report, Establishment of Native Shrubs on Disturbed Land in
the Mountain Shrub Vegetation~Type.; R.W. Draves and W.A. Berg, CSU, 1978,
sediment production under three vegetation treatments is presented. A
shrubs only treatment yeelded. 00668 acre-feet per acre over three years, while
a shrubs, grass and forbs-mulched and fertilized treatment yielded .00032
acre-feet per acre. The latter treatment most closely resembles reclamation
procedures used at the mine and the Division accepts Colowyo's contention
that the .00081 acre-feet per acre figure for lands undergoing mining and
reclamation is conservative. This conservative estimate is supported by
observations of sediment yield from the face of the Streeter Fi11.
In order to clarify specific regulatory obligations regarding sediment pond
certification and maintenance, as well as to provide documentation on runoff
and sediment generation, the permittee has committed to;
A. Inspect the condition of alI sediment pond embankments, spillways and
dewatering devices quarterly and,
B. Survey the sediment ponds to determine the actual volume of sediment
in each pond once a year after spring runoff.
The information will be submitted to the Division in an annual report.