HYDRO25125

• Permit No: C1981022
• IBM Index Class Name: Hydrology
• Doc Date: 5/28/1999
• Doc Name: STABILITY EVALUATION TEMPORARY MINE DISCHARGE POND E
• From: MONTGOMERY WATSON MINING GROUP
• To: OXBOW MINING INC
• Permit Index Doc Type: PROF POND CERTIFICATIONS
• Media Type: D
• Archive: No

© MOfUTGOM€93Y rJUQ.TSOiV
Mining Group
'~ECEI!/ED
May 24, 1999
Thomas Anderson, P.E.
Oxbow Mining, Inc.
P.O. Box 535
Somerset, Colorado 81434
MAY 2 8 1999
_ ..n of Minerals 8 Geology
999
r_
Re: Stability Evaluation -Temporary Mine Discharge Pond E
Dear Tom:
The following summarizes the stability assessment for the recently constructed Temporary Mine Discharge
Pond E and is provided to document compliance with applicable provisions of Rule 3.05.6(1 I)(k) of the
Regulations of the Colorado Mined Land Reclamation Board.
1.0 BACKGROUND INFORMATION
Pond E is a temporary pond constructed m retain water pumped from the portion of the mine which was
Flooded to extinguish the recent mine fire, allowine settlement of suspended solids and other treatment, if
necessary, prior to discharge. Given thm a limited yuantity of water was pumped into thu mine and an
effective system exists for handling normal mine water inflows, it is expected that Pond E will be used for a
relatively short period of time. Once the water accumulations in those areas that were Flooded to extinguish
the mine fire are removed by pumping to Pond E, discharge to Pond E will cease, and any subsequcm mine
inflows will be pumped to the existing underground mine water sump, with any excess Flows being pumped
to the surface and discharged through the existing Mine Water Settling Pund. Once it is no longer needed
for mine water discharge, Pond E will be removed and the associated disturbance area reclaimed.
2.0 POND CONFIGURATION
The Pond E As-Built Drawing previously submitted shows the location and configuration of the pond by
Oxbow. The upstream and downstream embankment slopes are not steeper than 2.SH:1 V and the
embankment crest width is 12 (vet. The embankment heieht (measured from the invert of the emergency
spillway to the original upstream ground elevation) is approximately 5 feet. The emergency spillway im•ert
is I.5 feet below the embankment crest and the pond basin is incised an additional 3 feet below the original
ground elevation into native material. Total heiehl from bottom of pond to top of embankment is 9.5 feet.
3.0 POND CONSTRUCTION
Pond E was constructed by a contractor under the supervision of qualified Oxbow personnel. Soil
descriptions and the following construction information were supplied by the Oxbow personal responsible
for monitoring pond construction:
I. Prior to placement of embankment materiah all topsoil was removed and stockpiled.
2. Following soil removah the foundation area was inspected and found to be well compacted with
no soft areas.
3. Pond construction involved cut/fill operations, with the use of material excavated from the pond
basin for embankment construction (no fill material was imported).
4. Foundation and embankment materials were described as silty sand with gravel and cobble (SM).
5. The Pond E embankment was constructed in procressive lifts using a D9 Dozer, with each lift
compacted by multiple dozer passes prior to placement of the next lift.
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