2012-11-06_REVISION - C1982057 (6)

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Project: Pond 16 -Area Remediation Location: Seneca IIW Mine Client: Peabody Energy Work Performed: NORTHWEST COLORADO CONSULTANTS, INC. FIELD REPORT Project No.: 08 -8099 Report No.: 11 Date: 10/03/11 Time: 3.5 Mileage: 74 Engr. /Tech: BDL As requested, we visited the project site on this date and conducted compaction test No.'s 54 through 56 on the material being placed for Pond 16A fill. The excavation contractors, Seneca Mine, were placing and compacting on site borrow material in the south third of Pond 16A for pond backfill. In addition, crews were in the process of cutting in the PM -2 drainage channel southwest of the shrub plot. Several test pits were excavated within the proposed PM -2 drainage channel below the shrub plot to try and evaluate the depth to groundwater seepage. The soils exposed at the base of the excavated channel consisted of organic fill materials that were saturated. Groundwater seepage was encountered surfacing in these materials however not observed in the sidewall of the excavation. A test pit was excavated in the base of the channel and to a depth approximately 12 feet below the existing channel excavation. A considerable amount of groundwater seepage was observed at a depth of approximately 4 feet beneath excavated channel subgrade. Natural clays were encountered below the organic fill materials at this depth. The moist natural clays extended to a depth of 11 feet and were underlain by weathered shale which was moist to slightly moist. Two additional test pits were excavated upstream (northeast) of the excavated PM -2 channel. Groundwater seepage was not encountered in either test pit. The test pits were excavated to a depth of 15 feet and mine spoils were encountered to the maximum depth investigated. The portion of the PM -2 channel above Pond 16A was near completion and it appeared that the base and sidewalls of the channel excavation had been constructed into competent bedrock materials. We did not observe any groundwater seepage in the exposed overburden soils or bedrock materials along the uphill side of the trench or in the base of the trench. Remarks: The material tested generally met the project specifications for compaction. Please refer to the attached sheet for the results of today's testing. Verbal Discussions: Jim Rolando of Seneca Mine was aware of today's compaction test results. We also advised Mr. Rolando and Roy Karo of our observations made in the test pits excavated along the PM -2 channel. We advised them that the channel excavation below the shrub plot would have to be extended to a depth at least 5 feet lower than the present channel excavation so that the groundwater is effectively cut off. We also suggested that they shift/move the channel excavation to the northwest so that a 3 (horizontal) to 1 (vertical) cut slope can be maintained between the shrub plot and the base of the excavation. Based on the saturated condition of the fill materials overlying the natural clays, we stated that additional stabilization of the exposed fill materials may be required along the uphill side of the trench excavation.