South Walker Creek Mine Kemmis II –Impacts on water ... · Kemmis Creek in the vicinity of the Farm Dam and Kemmis 1 tributaries is a 4th order stream with an upstream catchment

South Walker Creek Mine

Texel Solutions

August 2013

1308/2

KemmisII–Impactsonwaterqualityandhydrology

South Walker Creek Mine – Kemmis II Impacts on Water Quality and Hydrology

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CONTENTS

EXECUTIVE SUMMARY ....................................................................................................................................III

1. BACKGROUND AND SCOPE ...................................................................................................................... 1

1.1 KEMMIS II PROJECT AND HYDROLOGICAL SETTING ............................................................................................. 1

1.2 SCOPE ...................................................................................................................................................... 2

2. IMPACTS ON HYDROLOGY OF FARM DAM TRIBUTARY ............................................................................ 5

2.1 IDENTIFICATION OF ASPECTS ......................................................................................................................... 5

2.2 CHANGES TO FARM DAM WATER LEVELS AND AVAILABILITY ............................................................................... 5

2.3 CHANGES TO THE FREQUENCY AND DURATION OF OVERFLOWS FROM FARM DAM .................................................. 5

2.4 CHANGES TO HYDROLOGY OF FARM DAM TRIBUTARY ....................................................................................... 6

3. IMPACTS ON THE HYDROLOGY AND WATER QUALITY OF KEMMIS 1 TRIBUTARY .................................... 7

3.1 IDENTIFICATION OF ASPECTS ......................................................................................................................... 7

3.2 CHANGES TO HYDROLOGY OF KEMMIS 1 TRIBUTARY ....................................................................................... 10

3.3 CHANGES TO WATER QUALITY IN KEMMIS 1 TRIBUTARY .................................................................................. 12

3.3.1 Data Review and Water Quality Objectives .................................................................................... 12

3.3.2 Desktop Assessment of HEV Receiving Water Values ..................................................................... 13

3.3.3 Assessment of Impacts .................................................................................................................... 14

4. IMPACTS ON WATER RESOURCES .......................................................................................................... 16


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FIGURES

FIGURE 1.1 SOUTH WALKER CREEK MINE LOCATION WITHIN FITZROY BASIN.................................................................. 3

FIGURE 1.2 SOUTH WALKER CREEK MINE WITHIN THE BEE CREEK CATCHMENT .............................................................. 3

FIGURE 1.3 SOUTH WALKER CREEK MINE WITHIN THE BEE CREEK CATCHMENT .............................................................. 4

FIGURE 2.1 FARM DAM TRIBUTARY AND PROPOSED KEMMIS II EXTENSION .................................................................... 8

FIGURE 3.1. KEMMIS 1 TRIBUTARY AND PROPOSED KEMMIS II EXTENSION ..................................................................... 9

FIGURE 3.2 PREDICTED CHANGE IN PEAK FLOW AT KEMMIS 1 OUTFLOW FOR DESIGN STORM EVENTS ................................ 10

FIGURE 3.3 PREDICTED CHANGE IN PEAK FLOW AT KEMMIS TRIBUTARY OUTFLOW FOR DESIGN STORM EVENTS .................... 11

FIGURE 3.4 COMPARISON OF DISSOLVED ALUMINIUM CONCENTRATIONS BETWEEN EXISTING KEMMIS DAMS AND BACKGROUND

MONITORING LOCATION. .................................................................................................................................... 14

FIGURE 3.5 PREDICTED CHANGES IN FLOW FREQUENCY AND SALINITY IN KEMMIS 1 TRIBUTARY ........................................ 15

FIGURE 4.1 PREDICTED CHANGES IN MEAN ANNUAL FLOW ........................................................................................ 18


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EXECUTIVE SUMMARY

BHP Mitsui Coal (BMC) is proposing to further develop the Kemmis mining area at South Walker

Creek Mine (SWC) by extending the strike of the existing Kemmis 1 workings approximately 3km in a

north westerly direction. The proposed extension is referred to as Kemmis II. Texel Solutions has

been engaged by BMC to evaluate the nature and magnitude of impacts from Kemmis II on

hydrology and water quality.

The Kemmis II project involves the direct disturbance of four 1st order streams with a combined

catchment area of approximately 250 ha at the downstream most extent of the Kemmis II

disturbance. These streams are associated with two 2nd order un-named tributaries of Kemmis

Creek that will not undergo any direct disturbance. These tributaries are identified as Farm Dam

tributary and Kemmis 1 tributary for the purposes of the assessment. A large constructed dam is

located on the Farm Dam tributary downstream from the Kemmis II mining area. This dam has

already altered the flow regime of this tributary.

Kemmis Creek in the vicinity of the Farm Dam and Kemmis 1 tributaries is a 4th order stream with an

upstream catchment of approximately 10,700 ha and is located in the upper Isaac River sub-basin.

The Isaac River, a regional waterway, is located approximately 160 km downstream from where the

tributaries impacted by Kemmis II flow to Kemmis Creek. All of the above mentioned creeks and

rivers, including the Isaac River, are ephemeral watercourses, flowing only intermittently, after

significant rainfall, which typically occurs during the wetter months between November and

February.

The evaluation of hydrological and water quality impacts involved the undertaking of both event

based hydrological modelling and a long term daily AWBM runoff and water balance. Predictions

from this evaluation were compared with predictions for the existing condition, EPP Water - Water

Quality Objectives (WQO) and other relevant guidelines and are summarised on the next page.


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Summary of predicted impacts from Kemmis II on water quality and hydrology.

Kemmis II Potential Impacts

Minor tributaries - 1st

order streams Kemmis 1 tributary – 2nd

order tributary, stream length 6.0 km

Farm Dam tributary – 2nd

order tributary, stream length 3.3 km

Kemmis Creek – 4th

order tributary

Direct disturbance Direct disturbance of tributaries with a combined catchment of 250 ha at the downstream limit of Kemmis II disturbance

None. None. None.

Hydrological impacts Full diversion of catchment and flow path.

Changes in peak flow rates of between -45% and +30% at the mining area outlet.

15-45% reduction in critical peak flow rates (maximum predicted flow rate for a given ARI) at the mining area outlet.

Changes in peak flow rates of between -5-0% at the tributary outlet.

Occurrence of tributary flows immediately downstream from Farm Dam already reduced by >80% from natural condition as a result of the dam.

Kemmis II results in a further 5% reduction in these occurrences.

25-35% reduction in peak outflow rates from Farm Dam.

Changes in peak flow rates of between -0.7% and +1.5%

Water quality impacts

NA No change in the achievement of the locally derived Environmental Authority low flow release limit for EC.

7% increase in the occurrence of salinity WQO being exceeded.

Salinity conforms to the stock and irrigation WQOs 100% of the time and the drinking water (aesthetic) limit for good quality water 99.7% of the time.

No changes anticipated. No change in achievement of WQO.

Water resources NA 12% increase in mean annual flow at the tributary outlet.

27% reduction in mean annual flow at the tributary outlet.

0.3% reduction in Kemmis Creek mean annual flow immediately downstream of Kemmis II tributaries.


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1. BACKGROUND AND SCOPE

1.1 Kemmis II project and hydrological setting BHP Mitsui Coal (BMC) is proposing to further develop the Kemmis mining area at South Walker

Creek Mine (SWC) by extending the strike of the existing Kemmis 1 workings approximately 3km in a

north westerly direction. The proposed extension is referred to as Kemmis II. Texel Solutions has

been engaged by BMC to evaluate the nature and magnitude of impacts from Kemmis II on

hydrology and water quality.

SWC is in located in the upper catchment of the Isaac River sub-basin of the Fitzroy Basin. Significant

(4th order) streams traversing and adjoining SWC are Kemmis Creek and Walker Creek, both of which

flow to Bee Creek, a tributary of Connors River system. The Connors River flows into the Isaac River

approximately 75 km downstream from its confluence with Bee Creek.

SWC is located approximately mid-catchment within the Bee Creek catchment. The Bee Creek outlet

to Connors River is located approximately 70 km downstream from the confluence with Kemmis

Creek and Walker Creek tributaries while the headwaters of Bee Creek are approximately 70 km

upstream from these tributaries. The location of SWC in relation to these hydrological features is

shown in Figure 1.1 and Figure 1.2. All of the above mentioned creeks and rivers, including the Isaac

River, are ephemeral watercourses, flowing only intermittently after significant rainfall, which

typically occurs during the wetter months between November and February.

The Kemmis II mining area, shown in Figure 1.3, is located in the northern portion of SWC mining

leases. The Kemmis II mining area is located on the catchment divide between Walker Creek and

Kemmis Creek. While the 10 year planned mining extents are generally located within the Kemmis

Creek catchment, approximately 100 ha in the south western portion of Kemmis II is located within

the Walker Creek catchment and drains to the west. Runoff from this area will be contained by the

pit and managed within the site mine water management network, or directed to Kemmis II dams,

effectively removing this area from the Walker Creek catchment. Given that the resultant reduction

in catchment area represents less than 0.3% of Walker Creek’s 38,300 ha total catchment area (at

the confluence with Bee Creek), a detailed assessment of impacts on Walker Creek hydrology and

water resources has not been undertaken.

Drainage from the majority of the Kemmis II mining area is towards Kemmis Creek. Direct

disturbance of streams by Kemmis II activities is limited to four minor, 1st order streams three of

which have catchments < 40 ha in area. The northern portion of Kemmis II is within the catchment

of a substantial dam (Farm Dam). Farm Dam is a man-made dam and was constructed within a

neighbouring property on a tributary of Kemmis Creek (Farm Dam tributary) in order to supply

construction water for the adjacent railway. The Kemmis II development directly disturbs the Farm

Dam tributary up to a point at which it presently has a 150 ha catchment. Impacts of the Kemmis II

development on Farm Dam itself have previously been assessed and are referenced in Section 2.2.

Mine infrastructure and overburden emplacements are planned for within the Farm Dam

catchment, which until now has been undisturbed by mining activity. It is proposed by BMC that in

order to avoid any risk of mining activity impacting on water quality in Farm Dam, runoff from


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Kemmis II overburden emplacements is directed south and away from the dam via drainage

channels on the overburden emplacements and a dam and transfer network. Two new sediment

dams are planned to be constructed for this purpose with a combined capacity of approximately 75

ML. The southernmost of the new dams, Kemmis II South Sediment Dam, will overflow via an

excavated channel to a tributary of Kemmis Creek at the eastern boundary of the existing Kemmis 1

mining area. This tributary of Kemmis Creek is referred to as the Kemmis 1 tributary. In order to

enhance sediment capture for subsequent rainfall events and to facilitate maintenance of the dams,

the water level in these sediment dams will be drawn down following rain through use of captured

water in road watering.

The southern portion of the Kemmis II extension interfaces with the existing Kemmis 1 mining area,

which includes an existing sediment dam (Kemmis 1 Sediment Dam). While the catchment area of

the Kemmis 1 Sediment Dam will remain largely unchanged through the development of Kemmis II,

there will be an increase in the disturbed portion of the catchment as Kemmis II overburden

emplacements are situated within its catchment. Overflows from this dam currently report to the

Kemmis 1 tributary, with no changes to this arrangement proposed as part of the mining extension.

1.2 Scope The Kemmis II proposal described in Section 1.1 has the potential to alter the local hydrology and

water quality in Kemmis Creek and its associated tributaries. The Kemmis II development plan was

reviewed in the context of the current topography, drainage and surface water infrastructure, with a

view to identifying significant hydrological and water quality aspects. The following aspects and

potential impacts were identified:

In establishing the pit and controlling or treating runoff from the northern portion of Kemmis II,

runoff from proposed disturbance areas that currently drain to the Farm Dam will be intercepted

and re-directed to the south, thereby altering the magnitude and occurrence of outflows from

the dam.

Directing mine area runoff away from Farm Dam and to the south will increase the catchment of

the Kemmis 1 tributary, thereby altering the downstream hydrology.

The runoff from disturbed ground and overburden emplacement areas has the potential to

contain higher than background levels of contaminants such as sediment and dissolved salts.

While sediments will be captured in purpose built sediment basins, dissolved contaminants have

the potential to adversely impact nearby receptors such as the local watercourses. Given that

mine affected runoff will be directed away from the Farm Dam tributary, the potential for

adverse water quality impacts is limited to the Kemmis 1 tributary

The new sediment dams may detain flows in the Kemmis 1 tributary, thereby reducing

downstream peak flow rates.

Drawing down the water level in the sediment dams through road water, evaporation and

infiltration may reduce the availability of water downstream from the dams.

Mine affected water generated at the Kemmis II area will be managed through the mine’s water

management system and discharged into Walker creek via the current EA conditions


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Figure 1.1 South Walker Creek Mine location within Fitzroy Basin

Figure 1.2 South Walker Creek Mine within the Bee Creek Catchment

Kemmis Creek

Walker Creek

Kemmis II mining area


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Figure 1.3 South Walker Creek Mine within the Bee Creek Catchment

The following tasks have been undertaken in order to evaluate the nature and magnitude of the potential impacts

identified above:

Undertake a water and solute balance using long term historical rainfall data to compare the occurrence of flows

and associated water quality between the existing case and the developed case at significant locations.

Undertake hydrological modelling of design rainfall events with various durations and recurrence intervals,

including the critical duration, and identify hydrological changes between the existing case and the developed

case at significant locations.

The assessments described above are based on the 10 year Kemmis II extents. The justification for this is twofold:

There is insufficient detail beyond the 10 years planning horizon to undertake an assessment of this nature

After 10 years, the net area of disturbance and its composition is expected to remain relatively static as

progressive rehabilitation will have commenced and will be approximately equivalent to new disturbance.

Drainage from established rehabilitation will be directed away from the dams so that they do not become

hydraulically overloaded.

Details of the water and solute balance and hydrological modelling methods are included in Appendix A. Findings

are presented in this report.

10,693 hectares

742.82 hectares

662.91 hectares

771.90 hectares

Kemmis II

Existing operation

Kemmis 1


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2. Impacts on Hydrology of Farm Dam Tributary

2.1 Identification of Aspects The catchment area of the Farm Dam tributary to the confluence with Kemmis Creek is

approximately 770 ha. As is shown in Figure 3.1, approximately three quarters of this catchment

area (590 ha) currently reports to Farm Dam, which has an estimated capacity of 450 ML. As a

result, the catchment area of the reach between Farm Dam and the Kemmis Creek confluence is

effectively reduced from 770 ha to 180 ha unless the dam is overflowing. This remains unchanged

with the development of Kemmis II as the proposed extension does not impact the 180 ha of

catchment area that contributes directly to flow downstream of Farm Dam and therefore the

proposed Kemmis II extension is not expected impact hydrology at an event level in the Farm Dam

tributary downstream from Farm Dam unless the dam is overflowing.

The Kemmis II extension will reduce the catchment area to Farm Dam from 590 ha to approximately

405 ha as runoff from the mining area is to be directed away from the dam. Direct impacts on the

volume of water in Farm Dam, has been previously assessed and results from this assessment are

res-stated in Section 2.2. The reduction in catchment also has the potential to reduce the frequency

of overflows from Farm Dam as well and reduce the runoff volume and peak flows of events when

Farm Dam is overflowing. These aspects have been assessed, with results presented under the

following headings.

As runoff from the proposed mining area is to be directed away from the Farm Dam tributary,

impacts on water quality are not anticipated.

2.2 Changes to Farm Dam Water Levels and Availability The potential for Kemmis II to impact water levels in Farm Dam is described in the report “Kemmis II

– Options for the Management of Drainage from Overburden” (Texel Solutions, June 2013). The

modelling undertaken in the above assessment predicted that while diverting all mine generated

water away from Farm Dam resulted in the least impact on water quality in the dam, this approach

had the greatest impact on the water level in Farm Dam. The modelling predicted that under the

proposed Kemmis II drainage arrangements, the volume of water in Farm Dam would on a daily

basis typically be between 22 and 51% lower than it would be under the existing catchment

arrangements. The occurrence rate of the dam supply failings is predicted to approximately double,

as is the average annual rate of supply shortfall in the event the dam is utilised for supply.

2.3 Changes to the Frequency and Duration of Overflows from Farm Dam The frequency and volume of overflows from Farm Dam in the existing case and for the Kemmis II

case were assessed using the AWBM/GoldSim water balance model. Given the influence Farm Dam

already has catchment hydrology, a pre-Farm Dam case was also developed in order to provide

context to any changes identified. For the cases including the Farm Dam, the model was used to

simulate daily Farm Dam levels over a long term synthetic rainfall series that was sourced from the

Bureau of Meteorology (BOM). Further details of the modelling are provided in Appendix A. Model

predictions are tabulated below.


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Changes in frequency and duration of Farm Dam outflow

Flow conditions Pre-Farm Dam

Existing Kemmis II

Mean Period Between Overflows

(Years)

0.21 1.2 1.8

Mean Duration of Overflows (Days) 5.4 3.6 3.3

Longest Duration Overflow

(Continuous Days)

27 14 13

Longest period Between Overflows

(Continuous Years)

1.9 22.2 22.5

The predictions tabulated above indicate that the establishment of Farm Dam has resulted in

notable changes in the flow regime of the Farm Dam tributary. From the original Pre-Farm Dam flow

condition to the existing Farm Dam catchment harvesting 75% of the Farm Dam tributary, there has

been an 83% reduction in the occurrence of catchment runoff contributing to flow at the Farm Dam

tributary outlet. The development of Kemmis II is predicted to result in a further 5% reduction in the

occurrence of catchment runoff from upstream of Farm Dam contributing to flow at the Farm Dam

tributary outlet. The mean and maximum duration of overflows and the longest period between

overflows is similar between the existing case and the Kemmis II case.

2.4 Changes to Hydrology of Farm Dam Tributary Changes to peak flow rates and critical duration for the Farm Dam tributary were assessed at the

Farm Dam outflow location and immediately downstream of its confluence with Kemmis Creek

(Kemmis Creek 1). These locations are shown in Figure 3.1. The assessment was made using the

WBNM model and assumes that Farm Dam is full at the time of the event and a full catchment

response in the Kemmis Creek upstream catchment. Further details of the modelling are provided in

Appendix A. Results are tabulated below.

Predicted Change From Existing

Farm Dam Overflow Kemmis Creek 1

Peak flow (all ARI and durations including critical

duration)

25 to 35% reduction 0.6 to 1.3% reduction

Critical duration no change no change

The modelling predicts that for rainfall events occurring when the dam is full, Kemmis II will effect a

reduction in peak flows of between 25 and 35% at the dam outlet. It is noted from the hydrological

modelling that prior to the establishment of Farm Dam, peak flows in the vicinity of the Farm Dam

outlet were between 25% and 150% higher than the existing peak flows for events of the same

recurrence interval and duration.


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Under the condition of full catchment response, the change in peak flows between the existing case

and the Kemmis II case is predicted to reduce to -1.3 to -0.6% immediately downstream from the

confluence with Kemmis Creek, indicating that hydrological impacts are limited to the Farm Dam

tributary.

3. Impacts on the Hydrology and Water Quality of Kemmis 1 Tributary

3.1 Identification of Aspects The catchment area of the Kemmis 1 tributary to the confluence with Kemmis Creek is

approximately 665 ha. As is shown in Figure 3.2, approximately 15% of this catchment area (97 ha)

reports to Kemmis 1 Sediment Dam, which has an estimated capacity of 15 ML. Under the existing

condition, approximately 25% of the Kemmis 1 Sediment Dam catchment comprises overburden

emplacements with infrastructure and undisturbed areas making up the remainder.

The Kemmis II extension will not materially alter the catchment area to Kemmis 1 Sediment Dam,

however, the portion of the catchment comprising overburden emplacements will increase from

25% to 45%. Further, runoff from an additional 130 ha of mining disturbed land, of which

approximately 60% is overburden emplacements, will be directed to the Kemmis 1 tributary

immediately downstream from the Kemmis 1 Sediment Dam via a series of drains, a pump and pipe

transfer network and the new sediment dams (Kemmis II North Dam and Kemmis II South Dam). The

drainage layout is shown in Figure 3.2.

Run off from overburden emplacements can have a higher than background salinity, however, this

reduces over time as a leached surface profile is established, or rehabilitation works provide cover.

During the period for which runoff from overburden has a higher than background salinity, there is

potential for the achievement of downstream water quality objectives (WQO) to be impacted.

Catchment areas formerly within the Farm Dam catchment are to be directed to the Kemmis 1

tributary via the Kemmis II dams, potentially altering the downstream hydrology. Further impacts on

hydrology may arise as a result of the overburden emplacements generally having a lower rainfall

excess than natural catchment areas and peak flows being attenuated through the new sediment

dams.

These aspects have been assessed, with results presented under the following headings. While this

section evaluates the potential hydrologic and water quality impacts associated with these aspects,

the associated water resources impacts are evaluated in Section 4.


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Figure 3.1 Farm Dam tributary and proposed Kemmis II extension

Farm Dam, 447 ML Existing catchment, 590 ha Developed catchment, 404 ha

180 ha downstream

from Farm Dam

10,693 hectares

Farm Dam Outflow

Kemmis Creek 1


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Figure 3.2. Kemmis 1 tributary and proposed Kemmis II extension

Kemmis 1 Sediment Dam, 15 ML Existing catchment, 97 ha Developed catchment, 90 ha

12,208 hectares

Kemmis 1 Outflow

Kemmis Creek 2

Kemmis 1 Trib Outflow

Kemmis II North Dam, transfer pump to Kemmis II South Dam

Kemmis II South Dam

`

Boundary of additional area reporting to Kemmis 1 tributary


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3.2 Changes to Hydrology of Kemmis 1 Tributary Changes to peak flow rates and critical duration for the Kemmis 1 tributary were assessed at the

Kemmis 1 Outflow location, the Kemmis 1 tributary outflow and immediately downstream of the

Kemmis 1 tributary confluence with Kemmis Creek (Kemmis Creek 2). These locations are shown in

Figure 3.2. The assessment was made using the WBNM model and assumes that all dams are full at

the time of the event and a full catchment response in the Kemmis Creek upstream catchment.

Further details of the modelling are provided in Appendix A. Results are tabulated below. .

Predicted Change From Existing

Kemmis Outflow Kemmis 1 trib. Outflow

Kemmis Creek 2

Peak flow (all ARI and durations including critical duration)

-45% to +30%

Variation with ARI and duration shown in

Figure 3.3.

-5% to 0% Variation with ARI and

duration shown in

Figure 3.4.

- 0.7 to +1.5%

Critical duration No change. No change. No change.

Figure 3.3 Predicted change in peak flow at Kemmis 1 Outflow for design storm events


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Figure 3.4 Predicted change in peak flow at Kemmis tributary outflow for design storm events

The above table and figures indicate that despite there being an increase in catchment to the

Kemmis 1 Outflow from the Kemmis II development case, peak flows are generally predicted to be

lower than the existing case in most circumstances, with the exception of the Kemmis 1 outflow

location for events with high runoff volumes1. The general reduction in peak flows is attributed to

the detention provided by the Kemmis II South Dam, which is necessary to ensure effective removal

of sediment from the flows.

Changes in peak flows at Kemmis Creek 2, downstream from the confluence of Kemmis 1 tributary

and Kemmis Creek are predicted to be between -0.7 and +1.5% for all modelled ARI and durations,

indicating that hydrological impacts are limited to the Kemmis 1 tributary.

1 The model predicts increased peak flows for only 100 year ARI events with duration > 24h duration, and 72

hour events with recurrence interval > 10 year ARI.


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3.3 Changes to Water Quality in Kemmis 1 Tributary

3.3.1 Data Review and Water Quality Objectives

SWC water quality monitoring data from water courses and the existing Kemmis 1 Dams was

reviewed in order to identify potential contaminants and characterise runoff for the modelling. The

existing Kemmis 1 dams have overburden emplacements within their catchments, with materials

sourced from the pit immediately adjacent to the Kemmis II. The water quality in these dams is

considered to be reflective of the quality expected from the Kemmis II area. Potential contaminants

were identified as those present in levels exceeding the water quality objectives (WQO) set out in

the Environmental Protection (Water) Policy 2009 – Isaac River Sub-basin Environmental Values and

Water Quality Objectives (EPP Water). Salinity and aluminium were identified as potential

contaminants and relevant WQO for these contaminants are presented below.

Contaminant Guideline Criteria

Electric Conductivity

(EC)

EPP Water Aquatic Ecosystems – moderately disturbed

low flow – 430 uS/cm

high flow – 250 uS/cm

Stock Water

3,000 uS/cm based on 2,000 mg/L for poultry, most sensitive

South Walker Creek Mine

Environmental Authority

Locally derived limit for low flow releases up to 28 days

after flows in the receiving water

700 uS/cm

Australian Drinking Water

Quality Guidelines

No health guideline value provided

Palatability

900 uS/cm – based on 600 mg/L threshold for good quality

Aluminium EPP Water Aquatic Ecosystems - Australian and New Zealand

Guidelines for Fresh and Marine Water Quality

(NWQMS 2000) 95% level of protection trigger value for

freshwater

55 ug/L

Stock (low risk) and Irrigation (Long Term Value – LTV)

5,000 ug/L

Australian Drinking Water

Quality Guidelines

No health guideline value provided for aluminium.

Salinity monitoring of water in the Kemmis 1 dams indicates a higher than background EC with a

median EC of 340 uS/cm compared with an ambient median EC of 230 uS/cm recorded in Walker

Creek at locations upstream of South Walker Creek Mine activity. While the median EC value for the

Kemmis 1 dams is higher than the EPP Water high flow WQO for salinity of 250 uS/cm it is below the


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low flow WQO for salinity of 430 uS/cm. Although the observed higher than background EC in dams

may in part be a result of concentration in the dams through evaporation, it was assumed for the

purposes of characterising runoff from overburden that this variance is attributable solely to the

proportion of overburden area within the catchment. The resultant EC in runoff from overburden

was calculated to be 660 uS/cm and this value was applied to runoff from overburden in the model.

Apart from EC, aluminium was the only contaminant identified from the monitoring to be present in

concentrations exceeding the EPP Water WQO2. Samples from the existing Kemmis North and

Kemmis South Dam returned dissolved aluminium concentrations of 200 ug/L and 310 ug/L

respectively compared with the EPP Water WQO for aquatic ecosystems of 55 ug/L . The aluminium

concentration in both samples was well below the EPP Water WQO for stock and irrigation of 5,000

uS/cm. The relevant guidelines do not provide a health based threshold for aluminium in drinking

water.

A review of the existing receiving water environment monitoring data was undertaken to assess

background aluminium concentrations in the vicinity of the Kemmis mining area. While no

monitoring data is available for Kemmis Creek, thirteen samples taken upstream of the SWC mining

operations from Bee Creek, the receiving water for Kemmis Creek, have undergone laboratory

analysis for dissolved aluminium. The data is presented in Figure 3.5 and indicates that the

aluminium concentration in samples from the Kemmis Dams is consistent with background levels.

Operational phase monitoring is recommended to evaluate and review the potential for

contaminants originating from the mining area to exceed the water quality objectives and

background concentrations.

3.3.2 Desktop Assessment of HEV Receiving Water Values

A desktop assessment was undertaken with the objective of identifying any high environmental

value features associated with the streams and receiving waters potentially impacted by Kemmis II.

A review of Queensland Government mapping for High Environmental Value (HEV) waters and

Environmentally Sensitive Areas (ESA) was undertaken with relevant maps attached in Appendix B.

The review identified the nearest downstream HEV as Dipperu National Park, located adjacent to

Bee Creek. This HEV is located approximately 50 km downstream from the Kemmis II impacted

Kemmis Creek tributaries. The nearest ESA is an area mapped as Endangered Regional Ecosystem

(ERE) approximately 1.1 km from the Kemmis 1 tributary. This ERE is located adjacent to the Kemmis

Creek riparian zone and is entirely outside the Kemmis 1 tributary catchment.

Receiving water impacts resulting from the Kemmis II development are predicted to be limited to

the Kemmis Creek tributaries and indiscernible within Kemmis Creek. Therefore no specific

consideration has been given to these high environmental value features in this assessment.

2 The EPP water references the NWQMS guidelines for the 95th

percentile level of protection trigger value for freshwater


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Figure 3.5 Comparison of dissolved aluminium concentrations between existing Kemmis dams and background monitoring location.

3.3.3 Assessment of Impacts

The frequency and quality of outflows from the Kemmis 1 mining area in the existing case and in the

Kemmis II development case were assessed using the AWBM/GoldSim water balance model. The

modelling involved a long term simulation of the mining area water network and contributing

catchments both on the mine site and downstream from the mine site. The model used a daily

synthetic rainfall series that was sourced from the BOM. Further details of the modelling are

provided in Appendix A.

Flow frequency and salinity were predicted using the water balance model at Kemmis 1 Outflow

location, the Kemmis 1 Tributary Outflow and immediately downstream of the Kemmis 1 tributary

confluence with Kemmis Creek (Kemmis Creek 2). These locations are shown in Figure 3.2. The

predictions were compared against the WQO and results are summarised in Figure 3.6.

Mean: 476310200

0

500

1,000

1,500

2,000

2,500

3,000

3,500

4,000

4,500

5,000

0

500

1,000

1,500

2,000

2,500

3,000

3,500

4,000

4,500

5,000

Background - BeeCreek Upstream (n=13)

Existing Kemmis Dams

Dis

solv

ed

Alu

min

ium

(u

g/L)

Monitoring Location

Comparison of Dissolved Alumimium Concentration in Existing Kemmis Dams With

Background (Bee Creek Upstream)

Kemmis S Dam

Kemmis N Dam

EPP Water Stock (low risk) &Irrigation LTV - 5,000 ug/L

EPP Water - Aquatic Ecosystems(NWQMS) - 55 ug/L

LOD - 10

Chart legend

Candle chart key

Maximum 80

th percentile

Mean

20th

percentile Minimum


P a g e | 15

While the modelling predicts no discernible changes with regard to the achievement of the

Environmental Authority low flow release limits within the Kemmis 1 tributary, the occurrence of

WQO exceedances is predicted to increase by 7% within the tributary. Predicted occurrences of

drinking water quality guideline being exceeded are less than 0.3% in both the existing and Kemmis

II case and there are no predicted occurrences of the stock water guideline being exceeded. These

changes in salinity are limited to the Kemmis 1 tributary and no discernible increases in EC relative to

the WQO are predicted within Kemmis Creek at the Kemmis Creek 2 location.

Figure 3.6 Predicted changes in flow frequency and salinity in Kemmis 1 tributary

The modelling outputs were further interrogated to investigate whether the concentration of any

contaminants potentially present in runoff from overburden would be likely to be magnified

following extended containment without flushing and evaporation. The event averaged

concentration of a contaminant with a relative concentration of 1 in the runoff from overburden was

predicted for each flow event (flow on consecutive days is a single event) at Kemmis 1 Outflow

location, the Kemmis 1 Tributary Outflow and immediately downstream of the Kemmis 1 tributary

confluence with Kemmis Creek (Kemmis Creek 2). These locations are shown in Figure 3.2. Model

predictions are tabulated below and indicate that the predicted occurrence of contaminant

magnification is rare (occur on average every 40 – 100 years) and moderate in scale (maximum 23%

increase in concentration compared with concentration in runoff from overburden).


P a g e | 16

Kemmis 1 outflow

Kemmis 1 trib. Outflow

Kemmis Creek 2

Range of event concentrations 0.25 – 1.23 0 – 1.23 0 – 1.23

Median event concentration 0.56 0.11 <0.01

No of occurrences of event concentration >

1 (magnification)

3 1 1

Average interval between magnification

occurrences

40 years > 100 years > 100 years

4. Impacts on Water Resources

Changes to catchment boundaries, catchment type and potential losses through evaporation,

seepage and the drawing down of sediment dam water levels have the potential to alter the

quantity of water conveyed through each of the tributaries and ultimately flowing in Kemmis Creek

downstream from mine affected catchments.

To assess the potential changes, the water balance model was used to predict the annual (July to

June) volume of flow through each of the locations below, over the long term historical rainfall

simulation. The mean annual flow was calculated from this simulation and results are shown in

Figure 4.1.

Farm Dam Outflow

Farm Dam Tributary Outflow

Kemmis Creek 1

Kemmis 1 Outflow

Kemmis 1 Tributary Outflow

Kemmis Creek 2

The modelling predicts a reduction in mean annual flow of only 0.3% immediately downstream of

the Kemmis Creek confluence with the Kemmis 1 tributary, indicating that changes to water

availability resulting from the Kemmis II development are predicted to be limited to only two

Kemmis Creek tributaries, namely Farm Dam tributary and Kemmis 1 tributary.

While the Kemmis II development is predicted to result in an 82ML reduction in the mean annual

overflow volume from within the Farm Dam catchment, compared to the Pre-Farm Dam conditions,

the construction of the Farm Dam itself has already reduced the availability of water in the

downstream reach, and given the relatively infrequent occurrence of overflows at present, the

downstream reach is unlikely at present to provide a reliable or significant source of water.


P a g e | 17

Increases in the mean annual volume are predicted within the Kemmis 1 tributary, however,

hydrological modelling has shown that with the exception of events with a large rainfall excess (ie.

100 year ARI events > 24h duration, or 72 hour events > 10 year ARI), peak flows, including the

critical peak are not predicted to increase. This is a result of the routing of flows through the

Kemmis II sediment Dams.


P a g e | 18

Figure 4.1 Predicted changes in mean annual flow

Upstream

10,693 hectares

742.82 hectares

662.91 hectares

771.90 hectares

Kemmis II

Existing Kemmis 1

mining area

Kemmis 1 Outflow Existing: 79 ML Kemmis II: 137 ML Change: +73%

Kemmis 1 Trib. Outflow Existing: 463 ML Kemmis II: 521 ML Change: +12%

Kemmis Creek 2 Existing: 8,525 ML Kemmis II: 8,501 ML Change: -0.3%

Farm Dam Trib. Outflow Existing: 298 ML Kemmis II: 216 ML Change: -27%

Kemmis Creek 1 Existing: 7,557 ML Kemmis II: 7,476 ML Change: -1.1%

Farm Dam outflow Existing: 175 ML Kemmis II: 93 ML Change: -47%


AppendixA

Hydrological Model Methodology

The objective of this component of the study was to investigate the potential impact that the proposed

Kemmis mine expansion would have on the hydrology immediately downstream of the site and within

Kemmis Creek. As part of this investigation there were four locations within the catchment that were

assessed to gain a better understanding on any changes to:

1. Peak discharge; 2. Timing of the peak; 3. Discharge volume; and 4. Duration of discharge exiting the mine site.

Modelling has been carried out for the 1, 2, 5, 10, 20, 50 and 100 year Annual Exceedance Probability

(AEP) flood events. The following scenarios have been investigated:

1. Existing Scenario – Pre Kemmis expansion as currently exists on site

2. Developed Scenario – Post Kemmis expansion for the anticipated 10 year horizon

Hydrologic modelling of the catchment has been carried out using WBNM software developed jointly

by the University of Wollongong, Rienco Consulting and Balance R&D. The January 2007 version

has been used for this investigation. A peak flow rational method calibration has also been carried

out.

Catchment

Sub-catchments delineated for the WBNM model has been based on LiDAR survey of the site and

25m DEM obtained from the State Government. A breakdown of the sub-catchments for the existing

and developed scenarios is presented below in TABLE A1 and TABLE A2. Catchments SUB1 to

SUB9, and SUB12, represent the Kemmis Creek catchments which are external to the South Walker

Creek mining area. These catchments remained unchanged in the existing and developed scenario.

Under the existing scenario SUB11 contains part of the existing mine which drains to a sediment

basin. From here overflows discharge along a drainage line before entering Kemmis Creek.

In the developed scenario, the mine extends into SUB10. Areas that are disturbed from the mine

expansion are directed into a new sediment basin and the overflow is re-diverted into SUB11. This

results in a reduction in catchment to SUB10 and increase in catchment to SUB11. It is to be noted

that there is an area of 42.8ha which drains to a newly created dam on the northern extent of the

expansion. This catchment has not been represented as it does not have the ability to overflow. Any

waters collected here are pumped south to a suitable storage. The total areas of SUB10 and SUB11

have decreased by approximately 50ha when comparing the existing and developed. This is a result

of the active pit being expanded into SUB10 and SUB11 and not contributing to overland flow.


TABLE A1: Existing Scenario WBNM Sub-Catchment Breakdown

ID Area (ha)

Natural

(ha)

Spoil

(ha)

Road

(ha)

SUB1 1174.9 1174.9 - -

SUB2 1291.2 1291.2 - -

SUB3 1120.3 1120.3 - -

SUB4 1199.1 1199.1 - -

SUB5 1419.4 1419.4 - -

SUB6 1250.3 1250.3 - -

SUB7 1474.0 1474.0 - -

SUB8 932.4 932.4 - -

SUB9 841.4 841.4 - -

SUB10a (US Farm Dam) 590.0 590.0 - -

SUB10b (DS Farm Dam) 181.9 181.9 - -

SUB11a-Existing Sed Basin 97.2 55.6 25.4 16.2

SUB11b 553.7 553.7 - -

SUB12 742.8 742.8 - -

Total 12868.6 12827.1 25.4 16.2

TABLE A2: Developed Scenario WBNM Sub-Catchment Breakdown

ID

Area

(ha)

Natural

(ha)

Spoil

(ha)

Road

(ha)

SUB1 1174.9 1174.9 - -

SUB2 1291.2 1291.2 - -

SUB3 1120.3 1120.3 - -

SUB4 1199.1 1199.1 - -

SUB5 1419.4 1419.4 - -

SUB6 1250.3 1250.3 - -

SUB7 1474.0 1474.0 - -

SUB8 932.4 932.4 - -

SUB9 841.4 841.4 - -

SUB10a (US Farm Dam) 409.0 409.0 - -

SUB10b (DS Farm Dam) 181.9 181.9 - -

SUB11a-Existing Sed

Basin 90.0 41.2 43.9 4.9

SUB11c-New Sed Basin 89.5 6.9 76.6 6.0

SUB11b – DS Sed Basins 553.7 553.7 - -

SUB12 742.8 742.8 - -

Total 12769.9 12638.5 120.5 10.9


Model Parameters

Intensity Frequency Duration

The intensity frequency duration (IFD) data has been obtained from the Bureau of Meteorology

website using the ARR87 methodology for the co-ordinates: Latitude: 21.70S, Longitude: 147.375

(issued 19/08/2013).

Rainfall Losses

Suitable rainfall loss parameters were selected to represent the respective catchment breakdowns as

either natural, spoil or road. TABLE A3 highlights the respective loss parameters and

imperviousness applied to each catchment type.

TABLE A3: WBNM Model Loss Parameters

WBNM Sub-Catchment Natural Spoil Road

Initial Loss 15 40 1

Continuing Loss 2.5 5 0

% Impervious 0 10 80

Online Storages

There was one storage represented in the existing scenario and two in the developed scenario that

were used the investigation. The farm dam, located in SUB10 is a large water storage constructed by

the Rail Authority and has a water surface area of 27ha and a spillway 30m wide. This dam is present

in both the existing and developed scenarios. In the developed scenario the new sediment basin has

been represented in the model to which disturbed areas from the Kemmis expansion contributes too.

This basin is approximately 2.3ha and has a spillway 3m wide. Outlined below in TABLE A4 are the

storage curves used in the model setup. It is to be noted that each storage is assumed to be full at the

start of the model run and only the effects of routing runoff through the spillway has been accounted

for.

TABLE A4: WBNM Storage Curve

Farm Dam (SUB10) New Sediment Basin (SUB11)

Elevation (m RL) Volume (ML) Elevation (m RL) Volume (ML)

0.00 0.0 0.0 0.0

0.25 69.2 0.25 5.8

0.50 138.3 0.5 11.5

0.75 207.5 0.75 17.3

1.00 276.6 1.0 23.0

Rational Method Comparison


The WBNM model has been calibrated to Rational Method derived peak flows for three sub-

catchments; SUB6, SUB7 and SUB9. A summary of the Rational Method calculation is provided

below in TABLE A5. A WBNM catchment lag parameter of 1.8 was applied to each catchment as

part of the calibration method (recommended 1.3 to 1.8).

TABLE A5: 100 year AEP Rational Method Comparison Summary

WBNM Sub-

Catchment

Catchment Area (ha)

Rational Method tc

(min) C10

Rational Method Q100

(m3/s)

WBNM Q100 (m3/s)

SUB6 1250.3 198 0.53 80.9 72.3

SUB7 1474.0 223 0.53 89.8 81.0

SUB9 841.4 178 0.53 59.5 54.6

A flood study was prepared for South Walker Creek by Alluvium (2008), which investigated regional

flooding of the numerous creek systems in the area. The reported flows from the Kemmis Creek

catchment were 430m3/s (9 hour storm). The model used in this investigation was broadly extended

down to Bee Creek in order to represent the total Kemmis Creek catchment of over 21km2. Peak

flows in the 100 year AEP were estimated to be 508m3/s (12 hour storm). Whilst there is limited

calibration data specific to Kemmis Creek, we believe a reasonable fit is achieved using the available

rational method and flow comparison with other studies.


AppendixB

Environmentally Sensitive Areas – Queensland Government

High Environmental Value Waters – EPP Water

Documents

South Walker Creek Mine Kemmis II –Impacts on water ... · Kemmis Creek in the vicinity of the Farm Dam and Kemmis 1 tributaries is a 4th order stream with an upstream catchment