HVO 2009 Annual Environmental Management Report - Final

Coal & Allied – Hunter Valley Operations
Comparison of 2009 Water Quality Data with EIS Predictions
South Pit EIS Predictions
The South Pit EIS estimated an ‘instantaneous’ water quality for EC of 3,700mg/L (EC 5,700μS/cm) as an
upper limit. Instantaneous water quality is a simple estimate obtained by dividing the total salt available by the
maximum amount of possible void water. Actual water quality can vary widely as it is affected by prevailing
climate, mine spoil configuration, dewatering efficiency, surface drainage and river usage among other things.
Water held in Lake James had an average EC of 3,106μS/cm in 2009. This is low compared to the EIS
predictions, though this EC is not uncommon after periods of wet weather. Lake James is a mine water
discharge dam, and the relatively low EC is probably due to a relatively short contact time with mine spoil and
coal before it was pumped out of pit.
The South Pit EIS estimated average runoff water quality from undisturbed catchments to be 400mg/L for
TSS and 615μS/cm for EC. Comleroi Creek, South of Cheshunt Pit had an average EC of 490μS/cm in 2009.
West Pit EIS Predictions
The West Pit EIS included the data in Table 32 as representative of water quality.
Table 32: Representative Water Quality for West Pit
Water Stream pH EC (S/cm)
Davis Creek 7.7 to 8.4 767 to >8,000
Emu Creek 7.5 to 8.8 365 to >1,000
Farrells Creek 7.0 to 9.2 195 to >12,000
Mine Water (Parnells Dam) - 2,400 to 6,300
Davis Creek was reported as dry in 2009 with the exception of a single sample collected following sufficient
rain for runoff in April 2009. The pH at the time of sampling was 7.2 with an EC of 2,630μS/cm.
The average EC in Emu Creek was 5,107μS/cm showing a significant increase on the average value in
previous years. Due to the ephemeral nature of Emu creek the samples were only collected following
significant rainfall and samples collected in following months reported EC values around 10,000μS/cm due to
a function of the creek “drying out” to a position of no flow. The pH ranged from 7.4 to 8.7.
The average EC in Farrell’s Creek (W11) was 525μS/cm increasing slightly from the 2008 and 2007 average
of 495μS/cm and 402μS/cm respectively. The pH ranged from 8.1 to 8.4 in 2009. The ephemeral nature of
Farrell’s Creek means that samples were only successfully collected for 33 per cent of occasions.
The EC in Parnells Dam in 2009 was consistent through 2009 reporting an average of 4,204μS/cm, which is
within the ranges predicted in the EIS. This EC average value is similar to the 2008 average of 4,143μS/cm,
however it should be noted that high EC values have previously been recorded at this site, 7,640μS/cm in
2007, due to extended periods of drought conditions with no dilution from rain into an otherwise closed circuit.
The pH ranged from 8.9 to 9.4 during routine monitoring.
Carrington Pit EIS Predictions
The long term mine water quality for Carrington is discussed in the Carrington Mine Environmental Impact
Statement (ERM 1999). The EIS estimated an “instantaneous” water quality for TSS of about 4,750mg/L and
7,050μS/cm for EC.
Dewatering from Carrington is a mixture of surface runoff from overburden emplacements, coal mining areas
and seepage from the coal seams and alluvium, which all pass through Dam 9N and into Dam 11N. The
average EC in Dam 11N during 2008 was 4,877μS/cm and is considered representative of mine water quality
for Carrington.
AEMR 2009 88