Metropolitan Coal Project Independent ... - Peabody Energy

METROPOLITAN COAL PROJECT INDEPENDENT ENVIRONMENTAL AUDIT
mm/m, however this maximum observed value was in the base of a valley. The observed tilts
along the D-Line away from the topographic highs and lows are generally similar to or below
the predicted tilts. No anomalous movements have been identified”.
The End of Panel Report for LW20 (dated 25 January 2012) included the results of the Subsidence
Monitoring Program that forms part of the Extraction Plan for LWs 20 to 22. The extraction of Longwall
20 commenced on 9 May 2010 and was completed 16 August 2011.
In summary, measured surface subsidence effects and impacts were generally within predicted
ranges. The occurrences where measured subsidence was in excess of predicted subsidence effects
were either associated with disturbed pegs or movements that were within the accuracy of the survey
and prediction methods (i.e. the subsidence magnitudes were very low). The observed subsidence
impacts were also consistent with, or less than those predicted.
Aboriginal Heritage sites within 35 o angle of draw are not scheduled to be surveyed / inspected until 3
to 6 months after LW20 is completed. The pre-mining condition of the sites was assessed during the
Environmental Assessment phase of the project.
A summary of the predicted subsidence effects after the completion of LW20 were:
Measured subsidence effects above LW20 were less than predicted values or within survey
tolerances where several minor exceedences had occurred.
Valley closure and uplift were minor and less than predicted values.
No impact (i.e. cracking) or instability (i.e. rock-falls) was observed along Cliff No’s OH1 and
OH2 and complies with prediction that less than 3% of length of cliff line would be impacted
by mining.
No impact (i.e. cracking) or instability (i.e. rock-falls) was observed on steep slopes and
complies with prediction that tension cracks are not expected to exceed 0.1 m width and 25 m
length due to mining.
Some minor cracking along existing joints with fresh widely spaced cracking across Waratah
Rivulet and exposed rock bars was consistent with the range of predicted impact have
occurred due to valley closure effects south of LW20.
No surface water flows appear to have been diverted or re-routed through rock bars or below
the creek bed, which was indicated to be a potential impact.
No surface ponds along the Waratah Rivulet have been impacted by the observed mine
subsidence to-date, which was indicated to be a potential impact.
No mining related impact to upland or valley swamp surface and groundwater levels have
been detected in Swamps that exist above or within a 35 o angle of draw from LW20 (S16-18,
20 and 25). Paired piezometers in the sub-strata and underlying sandstone units supporting
the swamps clearly show natural recharge/discharge cycles are continuing to occur. Several
new piezometers were installed along Waratah Rivulet and Eastern Tributary during the
review period as indicated in the management plans.
Ecological surveys have not detected any change to flora species populations, riparian
vegetation or creek bank instability.
Stream water quality sampling results were presented along the Waratah Rivulet, Tributary B
and D and Eastern Tributary (C) and appear to meet the Performance Measure requirement
of “negligible environmental consequence”.
raw water quality data demonstrates that the overall water quality of most Indicator
parameters has not been noticeably affected by mining.
Analyte concentrations were relatively consistent between the sites with all watercourses
experiencing spikes or pulses throughout the time series. The Waratah Rivulet appeared to
have higher manganese concentrations and the Woronora River higher aluminium
concentrations.
4.14.5 Gas Releases
The AEMR’s have reported a gas release from Pool H on the Waratah Rivulet identified on 5 January
2011. The gas release is not an exceedance of the Metropolitan Colliery performance measures that
34 trevor brown & associates
applied environmental management consultants
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