2018-10-12_REVISION - C1982056 ‎(2)‎

• Permit No: C1982056
• IBM Index Class Name: Revision
• Doc Date: 10/12/2018
• Doc Name: Correspondence
• From: Twentymile Coal, LLC
• To: DRMS
• Type & Sequence: TR84
• Email Name: TNL
• Media Type: D
• Archive: No

performance modeling requirement was used to confirm the results for the final design system. The total
area for the final design system, including the 61VIN Pond, is 8.9 acres. With this final design area, the model
estimated an average 57% reduction in iron from 1.80 mg/L to 0.78 mg/L and a 20% sulfate reduction from
2520 mg/L to 2012 mg/L, thereby meeting the expected discharge targets outlined in Table 3. Although
pumping rates will fluctuate over the life of the mine dewatering activities, iron and sulfate targets are
expected to be achievable at minimum and maximum design flows.
Table 2-2: Basin Concentration Reduction Performance for the 357 gpm Design Dewatering Rate
Wetland Fe Rate Fe In Fe Out Sulfate Rate Sulfate Sulfate TDS Rate TDS In TDS Out
Basin Co �n t (mg/L) (mg/L) C(nsta t oin (mg/L) (mgt Consta t (mg/L) (mg/L)
Basin 1 45 1.80 1.37 5 2510 2436 2 5310 5241
Basin 2 16 1.37 1.24 5 2436 2366 2 5241 5174
Basin 3 16 1.24 1.13 5 2366 2304 2 5174 5114
Basin 4 16 1.13 1.02 5 2304 2237 2 5114 5048
Basin 5 12 1.02 0.78 5 2237 2012 2 5048 4811
Total Fe Reduction: 57% Total Sulfate Reduction: 20% Total TDS Reduction: 9%
It is understood that the pumping rates will fluctuate over the life of the mine dewatering activities.
Despite this variation, iron and sulfate targets are still expected to be achievable at minimum design
flows. Lower flows provide additional retention time for solids settling and water processing, and
therefore, lower final concentrations. Table 4 provides a comparison of iron, sulfate and TDS reduction
at the maximum and minimum flowrate of 357 gpm and 75 gpm respectively. Although this design
provides suitable performance for iron and sulfate, the target TDS removal is not achievable with a
constructed wetland system. Options for TDS treatment have been discussed with Peabody and TDS
treatment will need achieved outside the scope of this project.
Table 2-3: Wetland Performance Comparison for Min/Max Design Dewatering Rates
Size Flow Rate Fe k Fe In Fe Out SO42- k SO42- In SO42- Out TDS k TDS in TDS out
(Acre) (gpm) (m/yr) (mg/L) (mg/L) (m/yr) (mg/L) (mg/L) (m/yr) (mg/L) (mg/L)
8.9 357 18 1.80 0.78 5 2510 2012 2 5310 4811
8.9 75 18 1.80 0.07 5 2510 919 2 5310 3521
PEABODY FINAL DESIGN TM 20181010 2.2
COPYRIGHT 2012 BY CHZM H LL. INC. • COMPANY CONFIDENTIAL