Extraction Plan - Peabody Energy

Extraction Plan – North Wambo Underground Mine Longwalls 7 and 82 DEVELOPMENT OF THE EXTRACTION PLAN2.1 REVIEW OF PREDICTIONSThe predicted subsidence effects, subsidence impacts and environmental consequences of the NorthWambo Underground Mine have been assessed in the EIS (WCPL, 2003) and the North Wambo SEE(WCPL, 2005) (Section 1.1). This section describes the process of reviewing and updating thesepredictions.2.1.1 Predicted Subsidence Effects and Subsidence ImpactsReview of Subsidence Prediction MethodologyThe predictions of subsidence effects for Longwalls 7 and 8 were developed by DgS usingcontemporary prediction techniques (Technical Report 1). DgS (2012b) conducted a review of thesuitability of this subsidence prediction methodology for use at the North Wambo Underground Mineby comparing subsidence predictions with measured subsidence from Longwalls 1 to 4 (TechnicalReport 5).The review of the subsidence prediction methodology indicates that the Upper 95% Confidence Limitspresented for the maximum subsidence predictions are likely to be reliable for Longwalls 7 and 8(including for sections of panels with or without multi-seam mining interaction effects) (TechnicalReport 5). The predicted final subsidence profiles generally exceeded the measured subsidenceprofile to date and are therefore considered appropriate for the impact assessment of Longwalls 7and 8 (Technical Report 5).Comparison with Previous Predictions of Subsidence EffectsThe predictions of subsidence effects presented in the North Wambo SEE under predicted verticalsubsidence above the areas affected by multi-seam mining interaction effects, as the predictionmethod used did not include additional subsidence due to reactivated goaf in the overlying WhybrowSeam workings (Technical Report 1). It is therefore considered appropriate to adopt the predictionmethodology used by DgS that correlates with measured subsidence data at Longwalls 1 to 4.The predictions of maximum vertical subsidence by DgS for Longwalls 7 and 8 are approximately1.0 m to 1.6 m greater above the areas affected by multi-seam mining interaction effects (TechnicalReport 1). The tilt and strains predicted by DgS are similar in magnitude, if not slightly lower, than theNorth Wambo SEE predictions (Technical Report 1).Predicted Subsidence ImpactsGiven that the revised tilt and strains predicted by DgS are similar in magnitude, if not slightly lower,than the North Wambo SEE predictions, the cumulative subsidence impacts previously predicted aretherefore unlikely to change significantly over the Longwalls 7 and 8 Application Area (TechnicalReport 1).EP/SMP LW7-8 Rev B December 2012 Page 21