HYDRO21407

• Permit No: C1982056
• IBM Index Class Name: Hydrology
• Doc Date: 4/17/1986
• Doc Name: WATER QUALITY ISSUES AT THE FOIDEL CREEK MINE FILE C-056-82
• From: MLRD
• To: TWENTYMILE COAL CO
• Permit Index Doc Type: CORRESPONDENCE
• Media Type: D
• Archive: No

Mr. Larry Damrau
- 2 -
April 17, 1986
Since the standard applies to irrigated crops, we looked at average 1985
July-September EC values. On Foidel Creek the upstream (undisturbed) EC
averaged below the 1,000 umhos/cm suspect level at only 650 umhos/cm.
However, the EC values adjacent to the Foidel Creek Mine increased to almost
2,000 umhos/cm downstream of the mine. Since the mine discharge water has an
electrical conductance ranging between 1,800-2,500 umhos/cm, it is probable
that the mine discharge is having an effect on the stream. This effect is
being felt a considerable distance downstream.
Data from another mine (Mine No. 3) shows average summer EC ranges 7,670
umhos/cm upstream on Foidel Creek to 1,160 umhos/cm downstream from Mine No. 3
on Middle Creek.
In summary, the Division is concerned that salt loading from Twentymile Coal
Company's (TCC) Mine may have the potential to affect irrigated crops grown on
Foidel Creek, and Lower Middle Creek. The low flow effects on these streams
and even Trout Creek are also not known.
The Division finds that it is necessary for TCC to investigate several issues
to evaluate whether there is in fact a problem. Since evidence indicates that
the potential for an impact is real, the Division requires that TCC conduct a
reevaluation of the probable hydrologic consequences (PHC) of mining. The
original PHC completed by TCC did not predict the high TDS mine discharges to
the surface water system in the basin. Therefore the PHC must be reevaluated
for our findings of compliance to be valid. The Division cites the authority
in Rule 2.08.3, periodic review of permits; the hydrologic performance
standards of Rule 4.05.1; the alluvial valley floor performance standards of
Rule 4.24, and the PHC requirements of Rule 2.05.6(3)(b)(iv) in making such a
request.
Our recommended approach in addressing the issue is as follows. First, TCC
should determine whether the elevated TDS could be attributed in whole or in
part to natural conditions, other land uses, or other mines.
If TCC is causing some or all of the salt load to the streams, an
investigation should be made as to whether any AVF's or other crop production
land uses exist on the stream segments in question. If such crop production
exists, formal AVF determinations may need to be completed.
If AVF's exist on the affected drainages, an inventory of the types of crops
grown will have to be made. This inventory will provide a basis fora precise
EC standard to ensure the protection of the specific crops grown in the
basin. The Division will use the material damage criteria specified in the
AVF Rules (Section 2.06.8(5)(c)(i)) in determining a crop salt tolerance
standard.
If it appears that water quality is approaching or exceeding this standard,
TCC may need to measure actual soil extract electrical conductivity for
various soil types throughout one growing season on the potentially affected
AVF's. This will establish a site specific relationship between irrigation
water salinity and soil solution salinity.
TCC will also need to make predictions on what the water quality levels will
be for 10 year 7 day low flows, during the remainder of the 5 year permit
term, for the life of mine term, and for post-mining conditions.