REP19488

• Permit No: C1982056
• IBM Index Class Name: Report
• Doc Date: 10/8/1987
• Doc Name: FOIDEL CREEK RENEWAL ISSUES
• From: MLRD
• To: KAREN HELLNER
• Permit Index Doc Type: HYDROLOGY REPORT
• Media Type: D
• Archive: No

~r~°.~~, 9~ lr~~ E OF COLORADO
Roy Romer, Govei
DEPARTMENT OF NATURAL RESOURCES
MINED LAND RECLAMATION DIVISION
DAVID C. SNELTON, Director
HATE: October 8, 1987
T0: Karen Hellner

FROM: ,~ D
Cathy 8egej ! %.F~~ b~
RE: FOIDEL CREEK RENEWAL ISSUES
There are several issues associated with the Foidel and Fish Creek Tipple
permits which should be considered during the Foidel Creek renewal process.
As I am preparing the Fish Creek Tipple Mid-Term at this time, and have
recently reviewed that Dermit. it is timely to oreoare this memo.
There are two hydrology issues associated with the Foidel Creek permit which
should he addressed: the validity of the assumptions used in the PHC to
calculate spoils impact and the inadvertent elimination of a subsidence
monitoring well (001-5-6) during the last hydrologic monitoring plan revision
(TR). The latter issue is self-explanatory. Some historical background on
the former follows.
Discussions during the life-of-Mine permitting process focused on the presence
of saline spoils springs and their influence on the streams in the area.
Conductivity values in the stream approached 1,000 umhos/cm and discharges
from the underground workings and from sedimentation ponds at the adjacent.
surface mine exceeded 1,000 umhos/cm. As the material damage standard for
plants sensitive to salinity was 1,000 umhos/cm, additional permitting in
Twentymile Park hinged on a re-assessment of this standard. Twentymile Coal
Company provided vegetation surveys which indicated that very few grass
families in alluvial valley floors downstream from the mines were in the
category of plants least tolerant of salinity. This raised the standard to
2,000 umhos/cm. The Division devised an artificial framework with which to
evaluate hydrologic impact to the alluvial valley floor. It is this framework
which I would like evaluated during the renewal process with 1987 hydrologic
data.
This framework evaluates alluvial conditions during peak runoff and low flow
periods in flood irrigated and sub-irrigated conditions. Predictions of worst
case alluvial conditions were based nn average discharge and streamflow values
and salinities during a low flow year. Low flow year discharge values were
derived by data obtained in 1981 and data which was projected back to 1981
from developing a ratio between the more complete 1984 data set and 1981's
data set. The value of the ratio was 3.5. I would like Twentymile Coal
Company to verify the predictive methodology using data collected in 1987,
another low flow year. I am concerned that the averaging concept will not
work and I am curious to see whether 1987 data fa low flow year) showed better
or worse conditions than those predicted.
423 Centennial Building, 1313 Sherman Street Denver, Colorado 80203-2273 Tel. [phone]