Metropolitan Coal Project Independent ... - Peabody Energy

METROPOLITAN COAL PROJECT INDEPENDENT ENVIRONMENTAL AUDIT
Suggested Action:
The installation of deep borehole extensometers above the centre of future long-wall panels at
Metropolitan to provide strata dilation profiles would complement the piezometric data and increase
our understanding of the mechanism’s impacting upon the groundwater regime.
4.14.8 Remediation and Mitigation Activities
Remediation measures associated with subsidence have been carried out using polyurethane (PUR)
injection at rock bars (WRS3 and WRS4) in the Waratah Rivulet following consultation with the SCA
and rigorous laboratory testing and assessment in relation to the suitability of the use of PUR within
the catchment.
Key outcomes of an initial trial included:
PUR was successfully injected into the rock bar with no environmental harm;
Fracture spaces can be successfully filled from 100mm voids);
The permeability of the overall rock mass was decreased to the extent that the rock bar once
again acts as a natural weir to retain water; and
The method is transportable to any other rock bar along the Waratah Rivulet.
4.14.9 Audit Site Inspection Observations
An inspection of some of the significant surface features within the zone of subsidence effect from
LW20 was conducted by a Principal Engineer on the 30/1/12. The following sites were visited:
• Southern Freeway Overpass bridge (to the east of LW20) and Princess Highway monitoring
sites: No impacts observed.
• Fire Roads 9H and 9C: No impacts observed.
• PUR injection site (WRS4) on the Waratah Rivulet upstream of Flat Rock Crossing: Low-stream
flows and pools have apparently been restored at the site.
• The stream and pool gauging and subsidence monitoring stations along Waratah Rivulet and
downstream of Flat Rock Crossing: Strong stream flows had dislodged a pool gauging station
after recent rains.
• Several open and persistent subsidence cracks (10 - 20 mm wide on east-west strike) were
observed upstream and downstream of Flat Rock Crossing along Waratah Rivulet. (Note: The
cracks did not appear to be causing any effect on the surface flow route).
• Shearing and minor spalling along a persistent joint (east-west strike) and had apparently been
activated by the passing of LW20: No effect on stream flow function.
• A fresh surface crack < 10 mm wide on an east-west strike has developed across Waratah
Rivulet and had apparently been activated (and predicted) by the passing of LW20 due to value
closure effects: No effect on stream flow function observed.
• Several sections of rock bar that had been cracked by LWs 1-18 have subsequently been
dislodged and transported tens of metres downstream after recent rains.
• Two gas emission sites in pools between Flat Rock Crossing and LW20’s southern extraction
limit. Note: One of the sites was known to exist prior to LW20 with the second site appearing
after the passing of LW20.
• Cliff No’s OH1 and OH2: no impact observed.
• Swamp No. 16 and 17 and the swamp Ground water Level piezometer: no impact observed.
There were no perceptible differences between conditions observed at the sites visited and the level
of impact reported in the Extraction Plan documentation prepared by Metropolitan Mine.
Conclusion:
Based on the review of the of the Extraction Plan, and Annual Review documents for 2010 and 2011
and End of Panel Report for LW20, it is concluded that the Metropolitan Coal has complied with the
Project Approval conditions for mine subsidence impact management for the 2010 to 2011 period.
37 trevor brown & associates
applied environmental management consultants
aemc