Extraction Plan - Peabody Energy

Extraction Plan – North Wambo Underground Mine Longwalls 7 and 81.6.1 Wambo Homestead Exclusion ZoneLongwall 8 has been designed with a WHEZ to avoid/mitigate potential impacts on the WHC(Figure 8). This layout was also approved through the application for mining within the curtilage of theWHC under section 60 of the NSW Heritage Act, 1977.The WHEZ was developed based on selecting an appropriate angle of draw to limit key subsidenceeffects (tilt, curvature and horizontal strain) to within tolerable limits. Due to the range of buildingsizes, structure type (i.e. masonry or timber frame), measured subsidence effects to date and existingcondition, the WHEZ is based on the minimum set back distances from Longwalls 7 and 8 presentedin Table 6 and the resulting predicted levels of impact risk.Table 6Wambo Homestead Exclusion Zone Dimensions and Impact Risk to BuildingsBuilding No.(See Figure 8)Minimum Angle of Draw(for 67 m of cover)Minimum SetbackDistance (m)Impact Risk toBuildings 1Longwall 7 Longwall 8 Longwall 7 Longwall 81, 2, 3, 4, 5, 7 35° 35° 47 47 Negligible6, 9 17° 35° 20 47 Slight8 4° 35° 5 47 SlightSource: After DgS (Technical Report 1).1 Impact risk is based on low strength grout placed to full roadway height around two pillars in the Whybrow Seam thatare directly below Building No. 6 (Stud Master’s Cottage) (Section 1.6.2).1.6.2 Grouting of the Previous Homestead Mine WorkingsSubsidence management measures will include grouting of sections of the previous Homestead Mineworkings located in the Whybrow Seam to increase the stability of these workings. The bulkfilling/grouting will be undertaken within historical workings of the Homestead Mine which underliealluvium above Longwalls 7 and 8 (Figure 6). The bulk filling/grouting will be completed prior tosecondary extraction of Longwalls 7 and 8 within these areas. WCPL has implemented an internalmonitoring process so that bulk filling/grouting will be completed on schedule.The grouting is being undertaken primarily as a mitigation measure to minimise the potential forflooding due to chimney failure and pot hole development resulting from failure of remnant pillarswithin the Homestead Mine workings. In addition, grouting of some of the previous Homestead Mineworkings is a requirement of WCPL’s approval to mine within the curtilage of the WHC. The methodbeing undertaken is outlined below:• Boreholes will be drilled from the surface into the Homestead Mine voids.• Boreholes will be cased and capped for the duration of the project to reduce potential water inflowto the Homestead Mine voids.• The seal and backfill material will be mixed and prepared at the surface.• To ensure containment of the backfill a sealer material will be pumped into the Homestead Minevoids through the boreholes.• After the mine is sealed, a low strength grout backfill mixture will be injected via the boreholesinto the Homestead Mine voids.• The backfill mixture will disperse within the Homestead Mine voids to a designated level.• On completion the boreholes will be surveyed and assessed to ensure the relevant HomesteadMine voids are adequately filled and stabilised.EP/SMP LW7-8 Rev B December 2012 Page 19