Extraction Plan - Peabody Energy

Extraction Plan – North Wambo Underground Mine Longwalls 7 and 8Table 4Maximum Predicted Subsidence, Tilts and Strains for Longwalls 7 and 8Subsidence Parameter Longwall 7 Longwall 8Incremental Subsidence (Wambo Seam and Activation of Whybrow Seam Workings)Maximum Subsidence (m) 1.75 – 3.31 1.75 – 3.31Maximum Tilt (mm/m) 24 – 71 24 – 65Maximum Tensile Strain (mm/m) 1 5 – 26 5 – 29Maximum Compressive Strain (mm/m) 1 5 – 20 5 – 24Cumulative Subsidence (Wambo Seam, Whybrow Seam and Arrowfield Seam)Maximum Subsidence (m) 1.75 – 4.89 1.75 – 5.06Maximum Tilt (mm/m) 52 – 71 53 – 65Maximum Tensile Strain (mm/m) 1 10 – 26 5 – 29Maximum Compressive Strain (mm/m) 1 10 – 20 10 – 24mm/m = millimetre per metre.Source: After DgS (Technical Report 1).1 Predicted strains are ‘smooth profile’ strains. Discontinuous displacements can occasionally result in secondarycurvatures and strains that exceed predicted ‘smooth profile’ values by 2 to 4 times.Predicted Valley Related MovementsDgS (Technical Report 1) concluded that the likelihood of development of upsidence and valleyclosure movements, along North Wambo Creek and Stony Creek above Longwalls 7 and 8, is likely tobe negligible. This is because the valleys are very broad between crests, and there is a lack of thick,massive beds of conglomerate and/or sandstone units along the creeks and valleys.Predicted Far-Field Displacement MovementsBased on an empirical model for the Newcastle Coalfield, DgS (Technical Report 1) concluded thatmeasurable far-field displacement movements (i.e. greater than 20 millimetres [mm]) may occur fordistances up to 3 to 4 times the cover depth (i.e. 150 m to 720 m).DgS (Technical Report 1) also concluded that far-field displacement movements outside a distanceequal to one cover depth are unlikely to generate significant strains or movements to cause crackingor damage to the surface (i.e. are unlikely to have greater than negligible impact).1.5 SUBSIDENCE IMPACT PERFORMANCE MEASURESThe statutory requirements relevant to this Extraction Plan are summarised in Section 1.1.1. Inaccordance with of the Development Consent (DA 305-7-2003) (Condition 22 and 22A, Schedule 4),WCPL must ensure that there is no exceedance of the subsidence impact performance measuresoutlined in Table 5. This Extraction Plan has been developed to meet these performance measures.An application for mining within the curtilage of the WHC was submitted under section 60 of the NSWHeritage Act, 1977 and approved by the NSW Heritage Council, as required by Condition 57 ofSchedule 4 of the Development Consent (DA 305-7-2003). Based on the assessment of the potentialimpacts and mitigation measures in relation to the proposed underground mining, Godden MackayLogan (2012) concluded that there will be no adverse effects on the State heritage values ofthe WHC.EP/SMP LW7-8 Rev B December 2012 Page 17