Tasman Mine. Site Water Management Plan. Peter Dundon & Associates. Updated Final. April Dakar Place, Pymble 2073

Transcription

1 Site Water Management Plan Updated Final April Dakar Place, Pymble 2073

2 Table of Contents 1 INTRODUCTION SITE CHARACTERISTICS AND FACILITIES CLIMATE SURFACE WATER AND DRAINAGE Regional Catchments Local Catchments Surface Water Quality SURFACE GEOLOGY AND SOILS MINE FACILITIES Water Requirements Roadworks and Drainage Diversion of Clean Runoff Hardstand Area and Portal Service Road Administration Centre and Amenities Pollution Control Dams SURFACE WATER MANAGEMENT OPERATION OF SURFACE WATER MANAGEMENT FACILITIES IMPACT ASSESSMENT CRITERIA SITE WATER BALANCE SURFACE WATER MONITORING Water Quality Monitoring Flow Monitoring DECOMMISSIONING OF SURFACE WATER FACILITIES GROUNDWATER REGIME AND MONITORING GROUNDWATER REGIME GROUNDWATER LEVELS GROUNDWATER QUALITY IMPACT ASSESSMENT CRITERIA MINE WATER INFLOW VOLUME AND QUALITY MONITORING GROUNDWATER LEVELS AND QUALITY MONITORING EROSION AND SEDIMENT CONTROL PLAN BACKGROUND EROSION AND SEDIMENT CONTROL GENERAL REQUIREMENTS General Erosion Control Sediment Control swmp report - updated final.doc ( i )

3 5.2.4 Site Clearing Stabilisation and Revegetation Monitoring and Maintenance WORK SCHEDULE Stage 1: Site Security and Entry Stage 2: Sedimentation Basin Stage 3: Access Road and Portal Service Road Stage 3a: Culvert Under the Access Road Stage 4: Hardstand Area and Facilities Stage 5: Loading Loop and Coal Stockpile Stage 6: Pollution Control Dams SURFACE AND GROUND WATER RESPONSE PLAN WATER FLOW MITIGATION MEASURES WATER QUALITY MITIGATION MEASURES RESPONSE TO UNFORESEEN IMPACTS swmp report - updated final.doc ( ii )

4 List of Appendices Appendix A Appendix B Appendix C Drawings Hydrologic and Hydraulic Design Surface Water Balance Analysis List of Tables Table 2.1: Long Term Rainfall Data for East Maitland Bowling Club... 2 Table 2.2: Long Term Evaporation Data for Cessnock and Paterson... 2 Table 2.3: Rainfall Intensity:Duration Data for the Tasman Mine Site... 2 Table 2.4: Cumulative Rainfall Depths (mm) over Consecutive Days... 3 Table 2.5: Estimated Annual Catchment Runoff (ML/year)... 4 Table 2.6: Surface Water Quality Blue Gum Creek Tributaries... 5 Table 2.7: Summary of Surface Soil Characteristics at the Site... 5 Table 2.8: Estimated Project Water Requirements... 7 Table 2.9: Design Features of Pollution Control Dams... 9 Table 3.1: Predicted Mine Water Inflows and Process Water Requirements Table 3.2: Summary of Surface Water Balance Analysis Table 4.1: Representative Water Quality Data for Fassifern Seam, Roof and Floor Aquifers Table 4.2: Groundwater Inflow Monitoring Program Table 4.3: Piezometer Monitoring Program Table 5.1: Soil and Site Physical Characteristics swmp report - updated final.doc ( iii )

5 1 INTRODUCTION This has been prepared to meet the specific requirements of Conditions 16 and of the Approval for the Tasman Mine project given by the Minister for Infrastructure and Planning on 16 March The concept plans presented in the EIS have been updated as a result of detailed design of the mine operations and site facilities undertaken since the EIS was prepared. In particular, the area occupied by the surface facilities and access road has reduced from 8 ha to less than 6 ha. In addition, as required in the Conditions, all water storage facilities have been relocated outside the creek lines. These changes have led to consequential modifications in the water management arrangements originally proposed in the EIS. In the course of preparation of this plan, Cessnock City Council and Lake Macquarie City Council were consulted, as required in the Minister s Conditions of Approval, and the concerns expressed by officers of both councils have been taken into account in preparing this document. In particular, it was apparent that both councils required a comprehensive document that described the design and operation of the water management facilities as well as covering the water monitoring and management issues identified in the Conditions of Approval. In order to provide the context in which various aspects of water management occur and to demonstrate compliance with Condition 16, this report provides an overview of the site layout and the final design of the water management facilities (Chapter 2) while Chapter 3 sets out details of the operation of the surface water management system and the surface water monitoring program to be implemented for the site in accordance with the requirements of Condition 20. This chapter also provides details of the actions required for decommissioning of the surface water management facilities. Chapter 4 provides details of the groundwater monitoring program in accordance with the requirements of Condition 21 while Chapter 5 presents the erosion and sediment control plan to be implemented during construction of site facilities. Finally, Chapter 6 provides details of a surface and groundwater response plan to mitigate any adverse impacts on flows or water quality in Blue Gum Creek or unforseen surface or groundwater impacts. In addition to providing a specific response to Conditions 16 and 19-23, this report also demonstrates the way in which the project has been designed and will be operated in compliance with other Conditions of Approval relating to surface and ground water management: It describes the facilities and operational measures designed to prevent and/or minimise the potential surface and ground water impacts of the development (Condition 12). It demonstrates that the only element of the project that could possibly obstruct floodwaters (namely the culvert under the access road) has adequate capacity to ensure that flood flows are not obstructed (Condition 14). It provides details of the surface water quality monitoring regime that meets the requirements of Condition 17. It provides details of the groundwater level and quality monitoring regime that meets the requirements of Condition swmp report - updated final.doc Page 1

6 2 SITE CHARACTERISTICS AND FACILITIES This chapter provides an overview of the site and the main characteristics that of relevance to this water management plan. Material for this section has been drawn from the EIS as well as subsequent detailed design work for the mine surface facilities and access road connecting the mine to George Booth Drive. 2.1 CLIMATE Table 2.1 summarises the long term rainfall record for the East Maitland Bowling Club which is the station closest to the site (13.3 km north-north-east) while Table 2.2 provides average monthly pan evaporation data for Cessnock and Patterson which are the nearest evaporation recording stations. Table 2.1: Long Term Rainfall Data for East Maitland Bowling Club Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Year Mean (mm) Decile Median Decile Highest Monthly Lowest Monthly Highest Recorded Daily Mean No of Rain days Table 2.2: Long Term Evaporation Data for Cessnock and Paterson Jan Feb Mar Apr May June July Aug Sep Oct Nov Dec Year Cessnock ,351 Paterson ,570 These data show that evaporation significantly exceeds the mean monthly rainfall during the summer months, and is similar to but marginally in excess of rainfall during the winter months. These data indicate that water will be required for dust suppression on about 250 days per year and that runoff into the site stormwater management system is likely to be ephemeral. Table 2.3 summaries the rainfall intensity:duration data for the site (as used in the design of the water conveyance and capture systems). Table 2.3: Rainfall Intensity:Duration Data for the Tasman Mine Site ARI Rainfall Duration (minutes) (years) A further climatic characteristic of relevance to this report is the rainfall erosivity which is used to assess the erosion hazard of the site. The RAINER program developed by the NSW Soil swmp report - updated final.doc Page 2

7 Conservation Service provides the following estimates derived from the same rainfall intensity data used to derive the values in Table 2.3. The erosivity estimates are: Average annual :10 year storm 1400 Table 2.4 (data derived from Managing Urban Stormwater: Soils and Construction ) provides details for the nearest quoted station (Newcastle) of cumulative depth of rainfall over consecutive days for a range of percentile probabilities (as required for sediment basin design). Table 2.4: Cumulative Rainfall Depths (mm) over Consecutive Days Percentile Duration (days) Probability % % % % % SURFACE WATER AND DRAINAGE Regional Catchments The Tasman Mining Lease is located in the vicinity of Mt Sugarloaf at the northern end of the Sugarloaf Range, 15 km west of Newcastle, and is situated near a regional divide between three catchments (Figure 1): Blue Gum Creek, which flows northeast and east to Hexham Swamp, via Lenaghans Flat; Slatey Creek and Burkes Creek catchments to the south and southeast, that in turn flow into Cockle Creek and thence into Lake Macquarie; and Surveyors Creek to the west, that flows to Wallis Creek and into the Hunter River east of Maitland. The Tasman Project lease area is covered with dry open eucalypt forest on the hilly slopes, with dense corridors of riparian vegetation along Blue Gum Creek and its tributaries in the gullies. The project site is traversed by a number of power transmission line easements that run from southwest to northeast. All surface facilities for the Tasman Mine will be located in the upper reaches of the Blue Gum Creek catchment. The total catchment area of Blue Gum Creek above Lenaghans Flat, is 1,775 ha, approximately 306 ha of which lies within the Mining Lease area. The surface facilities and access road will disturb a total area of 5.8 ha, of which about 3 ha has already been cleared of trees within power transmission easements. Of the area disturbed by the mine facilities, only 2.7 ha will be controlled to ensure that any surface water pollutants are retained within the site by achieving zero or negligible discharge. The area of controlled catchment (2.7 ha) represents less than 1% of the Blue Gum Creek catchment at George Booth Drive and less than 0.2% of the catchment above Lenaghans Flat swmp report - updated final.doc Page 3

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9 2.2.2 Local Catchments The local tributary catchments in the vicinity of the proposed mine are shown on Figure 2. These tributaries are ephemeral, steep, immature, and devoid of significant deposits of alluvium. All surface facilities associated with the Tasman Mine (Drawing ) will be located on the ridge between Tributaries 3 and 4. The majority of the surface facilities, including the coal stockpile and loading facilities and the machinery maintenance facilities will drain via two pollution control dams that will only discharge to Tributary 3 in exceptional circumstances. A staff car park and the majority of the mine access road to George Booth Drive will drain to Tributary 4. Tributaries 1 and 2 will be unaffected by the mining facilities. The EIS presented an analysis of the estimated annual flow (based on rainfall:runoff modelling) in Blue Gum Creek where it crosses George Booth Drive (364 ha catchment) and at Lenaghans Flat (1,775 ha catchment). These estimates are summarised in Table 2.5. Table 2.5: Estimated Annual Catchment Runoff (ML/year) Rainfall Statistic Rainfall (mm) Blue Gum Lenaghans Flat Blue Gum George Booth Drive 10 th Percentile Mean 895 2, th Percentile ,125 1,056 This table indicates that the annual yield of surface water within Blue Gum Creek may vary from 15% to 220% from the annual average yield. This large variation in yield is due to the high variability in annual rainfall and the ephemeral nature of runoff from the catchment. It has been observed (Newcastle Coal Company, pers comm) that the tributaries of Blue Gum Creek in the vicinity of the mine are ephemeral and only exhibit measurable flow following significant rainfall events, being generally less than 1 L/min along the tributary and main creek lines for the remainder of the time Surface Water Quality Upstream of George Booth Drive, the tributaries of Blue Gum Creek receive runoff from the Mt Sugarloaf Reserve and vegetated slopes above the Tasman Mine surface infrastructure area. This flow is also supplemented by small, ephemeral groundwater discharges. The only existing disturbed areas in the catchment are the transmission line corridors running north/south through the eastern part of the Mining Lease, communication towers near the summit of Mt Sugarloaf, the paved access road to the Mt Sugarloaf Reserve and a number of four wheel drive tracks. Blue Gum Creek has been inspected on a number of occasions since 2001 for collection of surface water samples. However, because of the highly ephemeral nature of flow in Blue Gum Creek and the drought conditions, the only samples collected for analyses were collected on 5 September On all other occasions the creeks have been dry at the time of intended sampling. The results of the surface water sampling are shown in Table 2.6. The water sample analyses set out in Table 2.6 indicate that the electrical conductivity (EC) during periods of low flow is significantly greater than the ANZECC (2000) guideline trigger value of 350 µs/cm for upland rivers. The cause of the high EC is probably the significant contribution of groundwater seepage to low flows. Because of the similarity of water quality between the surface and groundwater, it appears that the base flow in the creek is derived predominantly from groundwater seepage swmp report - updated final.doc Page 4

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11 Table 2.6: Surface Water Quality Blue Gum Creek Tributaries Analyte Blue Gum Creek Tributary 1 near Bore TAS011 Blue Gum Creek Downstream of Tributary 3 ph EC (µs/cm) 1,590 1,000 Total Dissolved Solids (mg/l) 1, Total Hardness (calculation) Sulphates (mg/l) Chlorides (mg/l) Total Alkalinity as CaCO3 (mg/l) Calcium (mg/l) Magnesium (mg/l) Sodium (mg/l) Potassium (mg/l) Iron (mg/l) SURFACE GEOLOGY AND SOILS The surface facilities are to be located on the crest of a ridge that is orientated approximately NNE. The eastern side of the ridge, which will only receive runoff from the staff car park and a section of the access road, drains to Tributary 4 of Blue Gum Creek. The majority of the site drains in a westerly direction to Tributary 3. The Soil Landscapes of the Gosford-Lake Macquarie 1: Sheet (Murphy 1993) indicates that the majority (approximately 80%) of the surface facilities are located on the Killingworth Soil Landscape Unit with the remainder on the Sugarloaf Soil Landscape Unit. Relevant characteristics of these soil landscape units, which have been taken into account in developing the Erosion and Sediment Control Plan for the construction phase (see Chapter 5), are summarised in Table 2.7. Table 2.7: Summary of Surface Soil Characteristics at the Site Characteristic Soil Landscape Unit Topsoil Sub-soil Killingworth Shallow (<250 mm) loamy sand to sandy clay loam on hill crests Up to 400 mm dispersible clay subsoil Sugarloaf Shallow (<200 mm)sandy clay Up to 750 mm clay sub-soil Permeability Moderate to slow permeability topsoil with low permeability subsoil Moderate permeability in both topsoil and sub-soil Erodibility K factor = (high) K factor (high) swmp report - updated final.doc Page 5

12 2.4 MINE FACILITIES The surface facilities that are relevant to this report are shown on Drawing (prepared by Geoff Craig & Associates) (see Appendix A) and include: A sealed access road to George Booth Drive suitable for both light vehicles and coal trucks; A hard-stand area for machinery including: Maintenance shed; An under cover bunded fuel storage and machinery wash-down bay; Bath-house, amenities and administration buildings; Potable water supply tank (80,000 L) and reticulation system; Rainwater tanks adjacent to all buildings; (2 x 5,000 L on administration and amenities buildings, 2 x 9,000 L on workshop building); Pump-out wastewater collection tanks (40,000 L); Bunding and contour drains to direct clean runoff around the works area and to direct dirty runoff into two pollution control dams; Conveyor gantry to link the mine portal with the coal stockpile area; Coal stockpile and truck loading area; Mine portal service road; Under-body spray wash system for coal trucks leaving the site; An unsealed section of access road between the under-body wash facility and the coal loading loop. Relevant hydrologic and hydraulic design details for these facilities are provided in Appendix B. All coal produced by the mine will be transported by truck to the Bloomfield coal washery for processing Water Requirements Water requirements for production related activities including dust suppression and truck underbody spray wash facility are estimated to be approximately 50 litres per tonne of coal extracted. The requirements for potable water for construction, administration employees and production employees are estimated to be approximately 100 litres, 75 litres and 200 litres per person per day respectively. The estimated water requirements for the 12 year life of the project are set out in Table 2.8. All potable water will be brought to site and stored in the on-site supply tank. Rainwater collected from roofs will be utilised for appropriate purposes such as toilet flushing. Maximum use will be made of all water derived on site from mine water inflows and from capture of runoff from the mine infrastructure area, in preference to importing water from outside sources. Based on the mine water balance discussed in Chapter 3, the mine may need to import some water to make up the shortfall from internal sources at certain stages in the project life. As necessary, makeup process water will be brought to site by road tanker from the Donaldson mine, which has an excess of water derived from mine water inflows and internal runoff swmp report - updated final.doc Page 6

13 Table 2.8: Estimated Project Water Requirements Year Potable Water Process Water Mon - Fri Sat Annual Mon - Fri Sat Annual (litres per day) (ML/y) (litres per day) (ML/y) Year 1 6, , Year 2 9,750 7, ,500 60, Year 3 15,125 11, , , Year 4 16,125 12, , , Year 5 16,125 12, , , Year 6 16,125 12, , , Year 7 16,125 12, , , Year 8 16,125 12, , , Year 9 16,125 12, , , Year 10 16,125 12, , , Year 11 16,125 12, , , Year 12 10,750 8, , Roadworks and Drainage As noted previously, the project roadworks comprise two components from which runoff is directed to different locations: 1. The sealed entry road that runs from George Booth Drive to the under-body spray facility for trucks located approximately at chainage 825 m. This section of road will drain towards Tributary 4 via roadside drains and mitred outlets (approximately 50 m spacing) that direct runoff away from the road. Trucks transporting coal from the site will have covered loads and will pass through an under-body spray wash facility before driving onto this section of road. Accordingly, the pollution potential from trucks on this section of road is considered to be similar to that on public roads and no stormwater pollution facilities are proposed for this section of road. In order to minimise scouring, the roadside drains will be provided with suitable scour protection where slopes exceed 5%. As shown on Drawing , the last 20 m of each mitre drain will be constructed as a level spreader to ensure that water is discharged over the slope as uniform sheet flow in order to minimise the risk of downstream gully formation. 2. An unsealed section of road to the west of the under-body spray facility, including the road loop around the coal stockpile and the coal loading area. This section of road, which will have a steelstone (modified slag) surface, will drain to the two pollution control dams (see Section 2.4.6). Runoff from Tributary 4 will be conveyed under the sealed access road from George Booth Drive by means of twin 1,500 mm diameter culverts which have been designed to convey flows in excess of the 100 year ARI flow from the catchment. Details of the hydrologic and hydraulic design of the culvert are provided in Appendix B Diversion of Clean Runoff Runoff from up-slope areas that are not disturbed by the mine facilities will be diverted away from the surface facilities and directed to Tributary 3 as shown on Drawing : A diversion drain along the upper edge of the batter leading down to the coal stockpile area and unsealed section of the access road. A culvert under the access road, as shown on Drawing , will convey drainage to a level spreader on the northern side of the road, swmp report - updated final.doc Page 7

14 Diversion drains along the southern side of both pollution control dams to divert runoff from the small up-slope catchments that are not part of the site facilities Hardstand Area and Portal Service Road The hardstand area of about 0.6 ha is located immediately north of the mine office as shown on Drawing The drainage divide between areas draining northward towards Tributary 3 and those draining to Tributary 4 lies along the southern edge of the portal service road (i.e. the portal service road and the hardstand areas all drain northward towards Tributary 3). Stormwater drainage and pollution control features of the hardstand area are: Roofed fuel storage and machinery wash-down shed (180 m 2 ) containing a 5,000 L fuel storage tank located in a separately bunded area. As required, the retention volume within the bund is 110% of the volume of the tank; An oil separator located on the northern side of the fuel storage and machinery wash-down area to treat all effluent from these facilities; A roofed workshop (450 m 2 ) with two 9,000 L rainwater tanks. The remaining surface of the hardstand area and portal service road will comprise compacted steelstone. The piped stormwater drainage system shown on Drawing will collect surface runoff and drain it to Pollution Control Dam A. Coal stockpile and loading facility The coal stockpile and loading facility comprises a loop road with a central island for a coal stockpile of up to 5,000 t. The stockpile is fed by an overhead conveyor from the mine. Truck loading will be by means of a front end loader. Before moving onto the sealed section of the main access road leading to George Booth Drive all loaded coal trucks pass through an under-body spray facility. All surface runoff from the unsealed section of the access road (to the west of the under-body spray facility), the coal stockpile area and the conveyor will be directed to Dirty Water Dams A and B via the stormwater drainage system shown on Drawing Administration Centre and Amenities All roof runoff from the administrative and amenities buildings will be directed into rainwater tanks (2 x 5,000 L). Water from the rainwater tanks will be used for toilet flushing and irrigation of the amenity planting. All runoff from the car park area will be directed to a first flush collection pond (16 m 3 capacity = 10 mm runoff from 1,600 m 2 car park) located in the south-east corner of the car park area. A perforated riser (as per Drawing SD 6-3 in Managing Urban Stormwater: Soils & Construction) will permit slow discharge from the pond to a level spreader for distribution across the hill slope that drains to Tributary 4. Water supply for showers, hand-basins, drinking and catering will be provided from an 80,000 L tank that will be replenished by road tanker. As noted in Section 2.4.1, the average daily water requirement at peak production levels is estimated to be about 16 kl/day. All grey wastewater from the administration and amenities buildings will be directed to Pollution Control Dam A while all effluent from toilet flushing and kitchens will be directed to the two septic storage tanks located adjacent to the administration building. These tanks will be emptied by a road tanker as required. No sewage treatment or effluent disposal will be undertaken on site swmp report - updated final.doc Page 8

15 2.4.6 Pollution Control Dams In line with the Minister s Consent, no dams will be constructed on any of the watercourses. Two pollution control dams are to be located within the Tributary 3 catchment on the hillside to the north of the mine facilities (see Drawing ). Both these dams have dual functions: A lower storage zone for the supply of water for the truck under-body spray facility and dust suppression on the unsealed sections of the haul road, portal service road and hardstand area. During years when there is anticipated to be a shortfall of mine inflow for operational purposes (see ), water may be taken from the pollution control dams for operational purposes; An upper sediment settlement zone (see capacity in Table 2.9) that has been sized, and will be operated, in accordance with the requirements of Condition 16 and the principles for the design and operation of Type F basins as set out in Chapter 6 of Managing Urban Stormwater: Soils & Construction (2004). In order to provide capacity for the capture and retention of runoff containing coal dust or fine sediment, the settlement zone has been designed to function as a Type F sedimentation basin based on a 90 th percentile 20 day storm. Details of the hydrologic design of the sedimentation zone are provided in Appendix B and are summarised in Table 2.9. Appendix B also provides details of the estimated rate of accumulation of coal dust in the dams on which the sediment storage zone has been determined to allow for annual cleanout of sediment. The table shows that both pollution control dams have a total storage capacity which significantly exceeds settlement zone requirements. Table 2.9: Design Features of Pollution Control Dams Dam A Dam B Catchment area (ha) Required settlement zone capacity (m 3 ) 1,800 1,200 Settlement zone depth (m) Sediment storage zone capacity (m 3 ) Water storage zone capacity (m 3 ) 3,900 2,600 Total dam storage capacity (m 3 ) 6,000 4,000 As required for the operation of Type F sediment basins, whenever the water level encroaches into the upper settlement zone, steps will be taken to ensure that the water level is drawn down below this zone within 20 days of the end the rainfall event. Further details of the operating procedures for drawdown of water within the pollution control dams are set out in Section 3.1 below swmp report - updated final.doc Page 9

16 3 SURFACE WATER MANAGEMENT 3.1 OPERATION OF SURFACE WATER MANAGEMENT FACILITIES The surface water management facilities on the site provide for the separate conveyance and management of three different classes of runoff: All clean runoff from untouched catchment areas and the sealed section of the access road will be discharged via stabilised outlets without receiving any treatment. Runoff from the staff car park will be directed into a first flush pond that will be cleaned out as necessary. Dirty runoff from areas likely to contain pollutants such as coal dust, oil and grease. Runoff from this controlled catchment (2.7 ha) will be directed to two pollution control dams. The two pollution control dams provide the primary means for minimising the volume and frequency of discharge from the controlled area of the site and provide an appropriate level of treatment for any necessary discharge. As noted in Section 2.4.6, the pollution control dams have an upper sediment settlement zone and a lower water storage zone. The dams will be operated in the following manner: While ever the water level in the dams is below the upper sediment settlement zone (as designated by a permanent marker), the dams will be operated as water storage dams that provide a source of water for various on-site purposes. Whenever the water level encroaches into the sediment settlement zone, the water level will be drawn down to the bottom of the settlement zone within 20 days after the end of rainfall in accordance with the operational requirements set out in Managing Urban Stormwater: Soils and Construction. The following priority order will be given to various options for achieving this drawdown: Utilise water for dust suppression on the unsealed sections of road, the coal stockpile and the hardstand area (average usage 40 m 3 /day). Once sufficient underground storage capacity has been generated following completion of sections of underground workings (expected to be from Year 2 onward), any excess water that cannot be utilised for dust suppression will be pumped underground. In the event of conditions in which insufficient water can be used for dust suppression and there is no underground storage capacity available, water in the dams will be flocculated using floc-blocks or gypsum in order to achieve a suspended solids concentration of less than 50 mg/l prior to controlled discharge to Tributary 3. Water extracted for discharge to the environment will be drawn from below the surface in order to ensure that any floating oil or grease is retained within the dams. Water balance analysis for the surface facilities (see Section 3.3) indicates that all surface runoff from the works area will be required for dust suppression and other on-site purposes. There is, therefore, very low probability that the pollution control dams would reach a level that would require treatment prior to discharge from the site. It is expected that the controlled catchment area will substantially operate as a zero discharge area swmp report - updated final.doc Page 10

17 3.2 IMPACT ASSESSMENT CRITERIA The principal surface water impact assessment criteria for the Tasman project are: Frequency and volume of discharge of treated runoff or uncontrolled overflow are key indicators of the performance of the surface water management system. Greater than expected accumulation of surface runoff in the pollution control ponds could occur as a result of wetter climate than represented in the historic record, greater percentage of runoff than anticipated from the controlled catchment area and/or reduced requirement for water for dust suppression or other purposes. If a greater than expected accumulation of surface runoff occurred in combination with greater than expected groundwater inflow to the workings, there would be reduced opportunity to store any excess surface runoff underground. Such a situation could result in more frequent controlled discharge of treated water and more frequent overflow of untreated water. While greater than expected accumulation of surface runoff could (if opportunities for underground storage of excess runoff were restricted at the same time) require greater expenditure on chemicals for treatment of accumulated surface runoff, the system would still be capable of operating within the design and operational guidelines in Managing Urban Stormwater: Soils & Construction in terms of the frequency and quality of any discharge. It should also be noted that the controlled catchment area constitutes less than 1% of the catchment of Blue Gum Creek above George Booth Drive. Accordingly, any changes in runoff from the site are unlikely to be measurable in the annual flow in Blue Gum Creek. Controlled discharge of treated runoff from the pollution control dams into Tributary 3 has the potential to lead to an extended period of flow above the natural base flow in the tributary. The rate of discharge (a maximum of 3 ML over, say, 10 days or 4 L/s) might impact on the riparian ecosystem in the immediate area of the discharge point by extending the period of saturation, but is unlikely to have any effect on downstream riparian ecosystems or users. The primary function of the pollution control dams is to retain water laden with coal dust or sediments for reuse within the site. If excess runoff needs to be discharged it will be treated so as to achieve an acceptable level of NFR (<50 mg/l). By extracting water for discharge from below the surface, the dams will provide a backup system for retention of any oil or grease that is not captured by the oil separator system within the refuelling and washbay area. However, the pollution control dams will have no effect on any elevated salinity or lowered ph derived from coal. 3.3 SITE WATER BALANCE Groundwater inflows to the mine workings have been estimated by the modelling on a year by year basis, and are summarised in which also includes the estimated process water requirements (50 L/t - which includes the underground mining process, dust suppression and the under-body spray wash facility). In order to provide an overview of the year by year water balance for the mine, Table 3.1 includes the average annual surface runoff into the surface water pollution control dams (7.1 ML/year) derived from the surface water balance analysis that is summarised in Table swmp report - updated final.doc Page 11

18 Stage of Project Table 3.1: Predicted Mine Water Inflows and Process Water Requirements Coal Productio n Groundwater Inflows to Workings Surface Runoff to Pollution Control Dams Mine Process Water Requirement s Water Supply Surplus / (Shortfall) Cumulative Surplus / (Shortfall) (t/year) ML/year ML/year ML/year ML/year ML/year Pre- Nil Mining Year 1 330, Year 2 507, Year 3 975, Year 4 975, Year 5 975,000 Negligible Year 6 975, Year 7 975, Year 8 975, Year 9 975, Year , Year , Year ,000 Negligible Post- Mining Nil The table shows that there is an estimated shortfall in process water from groundwater inflow during Years 3, 5, 6, 11 and 12. However it can be seen that the cumulative predicted water balance is positive for all years. For Year 1, water required for the mining process (including dust suppression) will be derived from a combination of groundwater inflow and surface runoff. If necessary, additional water will be brought to site by road tanker. Priority will be given to use of surface runoff for dust suppression and under-body spray wash facility in order to minimise the chance of overflow from the pollution control dams. By Year 2, it is expected that an area at a lower elevation than the rest of the mine will be worked out and will be available for use as a sump for underground storage of surplus water. There will be sufficient storage capacity in that area to accommodate any surplus groundwater inflows that occur from Year 2 onwards as well as any surplus surface runoff collected in the surface water pollution control dams. As noted earlier, the main risk of surface water discharge will occur during Years 1 and 2 prior to sufficient void space becoming available underground to permit the storage of any excess surface runoff collected in the pollution control dams. Water balance modelling for the surface water management system has been undertaken using 16 years of daily climatic data to ascertain the likely volumes of surface runoff and the ability of the mine to use the water for dust suppression. Table 3.2 summarises the results of the daily water balance analysis, details of which are set out in Appendix C swmp report - updated final.doc Page 12

19 Table 3.2: Summary of Surface Water Balance Analysis Average Rainfall Climatic Conditions 1 in 10 (Dry) Median Rainfall 1 in 10 (Wet) Rainfall (mm) ,133 Evapotranspiration (mm) 1,184 1,317 1,148 1,082 Runoff (ML) Water Demand (ML) Controlled Discharge (ML) Overflow (ML) Dams Empty (days) In the table, Water Demand is based on the assessed requirement for dust suppression on the unsealed roads and the hardstand area and takes account of those days on which sufficient rainfall occurs for there to be no requirement for dust suppression. Controlled Discharge accounts for those occasions on which water within the settlement zone cannot be fully utilised for dust suppression within 20 days of the rainfall event and therefore requires transfer to the underground workings or treatment prior to discharge to Tributary 3. Overflow relates to those occasions in which the storm runoff exceeds the capacity of the dams, resulting in uncontrolled overflow from the dams. The analysis shows that: Water demand for dust suppression is likely to exceed the available volume generated by surface runoff even in wet years. The additional water for dust suppression will be drawn from underground workings (see ) or supplied by road tanker if there is a short-term shortage; Under conditions where the pollution control dams are operated in compliance with the operating procedures for Type F dams, even in a 1 in 10 wet year, only about 0.9 ML of water would need to be discharged to the underground workings or treated (by flocculation) prior to discharge; Even in a 1 in 10 wet year there is negligible chance of uncontrolled overflow occurring. It can be seen that even during the years prior to underground water storage capacity becoming available, there is only a small risk that some water might need to be treated prior to discharge into Tributary 3. Once underground storage capacity becomes available, the controlled catchment will be able to operate as a zero discharge area. 3.4 SURFACE WATER MONITORING The primary objective of the surface water management system is to retain and use as much runoff as possible within the controlled catchment area and thereby minimise any adverse impact on water quality in the creeks. The surface water balance modelling (see above) indicates that onsite uses will utilise all surface runoff in all years except very wet years. As noted previously, once sufficient underground storage capacity becomes available, any excess surface runoff will be directed underground for storage. The surface water balance modelling indicates that until underground storage becomes available, approximately 0.9 ML would need to be treated for discharge in a 1 in 10 wet year. Such discharge would be necessary on about 10 days. Under this operating regime, there is a small chance (about 1 in 5) that pumped discharge of treated water swmp report - updated final.doc Page 13

20 would be necessary on one occasion during Years 1 and 2. The chance of an uncontrolled overflow is negligible. It can be seen, therefore, that the water management system is expected to provide a significantly higher standard of environmental protection than would be achieved by the design and operating standards set out in the Conditions of Approval (ie strict compliance with the requirements of Managing Urban Stormwater: Soils and Construction which could be expected to give rise to uncontrolled overflow several times per year) Water Quality Monitoring Given that treated discharge or overflow from the pollution control dams is likely to be a rare event, the following monitoring regime will be implemented: Monthly baseline sampling and analysis of any flow in Blue Gum Creek at George Booth Drive (downstream of the site) and near Bore TAS011 (upstream of the site on Tributary 1). These samples will be sent for analysis of the following analytes: NFR Turbidity ph Conductivity On any occasions when there is treated discharge or overflow from either of the pollution control dams, daily water samples will be collected from the discharge point and from Blue Gum Creek at George Booth Drive and sent for analysis of the same suite of analytes listed above. Monthly sampling and analysis of any flow in Tributary 4 downstream of the access road. These samples will be sent for analysis of the following analytes: NFR Turbidity Oil & Grease ph Conductivity The water quality analyses from Tributary 4 will be reviewed annually. If, after two years of monitoring, the monitoring indicates no contribution to NFR or oil & grease as a result of the development, then the monitoring may be discontinued Flow Monitoring Condition 20(c) requires that flow monitoring in Blue Gum Creek be undertaken. At George Booth Drive, Blue Gum Creek has a catchment of 364 ha of which only 2.7 ha (<1%) would be subject to controlled runoff by the pollution control dams. The relatively small area of controlled catchment is unlikely to make any measurable difference to high flows. Investigations undertaken for the EIS indicated that there are a number of seeps and springs which are considered to provide an important base flow groundwater contribution to the flow in Blue Gum Creek. However, the flow from these groundwater sources is only likely to be apparent in the creek under very low flow conditions and will not be apparent during episodic surface runoff events. (Note that during the recent drought there was frequently no flow in Blue Gum Creek at George Booth Drive either as a result of reduced flow from groundwater or increased evaporation and seepage loss in the creek system.) swmp report - updated final.doc Page 14

21 Because of the perceived importance of groundwater seeps and springs to the base flow in Blue Gum Creek and any dependent ecosystems, the flow monitoring regime will be focussed on monitoring the climatic and seasonal variability in base flow and any changes that might occur as a result of the underground mining operations. The following arrangements are proposed: Construct a small 90 o V notch weir within the constructed low flow channel immediately upstream of the culvert that conveys Blue Gum Creek under George Booth Drive. A 150 mm high V notch weir will be capable of measuring flows up to 10 L/s. This height of V notch weir will not have any significant effect on the hydraulic capacity of the culvert. For flows greater than 10 L/s, flow assessment will be dependent on a depth:discharge rating relationship for the culvert that takes account of the dimensions and hydraulic characteristics of the culvert. This analysis will provide reasonable estimates of peak discharge but, because of the width of the culvert, will not be capable of providing good estimates of the mid-low flow range (10 L/s to about 500 L/s). An ultrasonic water level sensor connected to a datalogger will provide a continuous record water level. Data from the datalogger will be down loaded every three months and interpreted to determine the flow pattern and the total flow volume. 3.5 DECOMMISSIONING OF SURFACE WATER FACILITIES The following works will be undertaken to decommission the pollution control dams, which are the main significant structures within the surface water management facilities: Pump any water remaining in the pollution control dams into the underground workings. Alternatively, if underground storage is not available, treat the water prior to discharge to Tributary 3; Backfill the dams using material from the embankments; Revegetate the area using seed from vegetation endemic to the area (see Section 5.2.5). In the event that the access road is decommissioned, erosion and sediment control techniques similar to those outlined in Chapter 5 will be employed where the road embankment is excavated and the culvert removed swmp report - updated final.doc Page 15

22 4 GROUNDWATER REGIME AND MONITORING 4.1 GROUNDWATER REGIME Aquifers in the immediate vicinity of the Tasman Project lease are limited to very minor alluvial deposits associated with existing drainage channels (eg. headwaters of Blue Gum Creek and Wallis Creek), and the deep hardrock coal measures aquifers. The alluvial aquifers in proximity to the mine lease are not exploited due to their limited storage potential. They are recharged entirely from rainfall and local runoff and tend to deplete rapidly during dry spells. Groundwater in the coal measures sediments occurs mostly within the Fassifern coal seam (and other deeper seams) as brackish to saline water stored in and flowing through limited permeability developed in cleats and joints. Groundwater also occurs in the overburden and underburden sediments, which comprise conglomerates, sandstones and siltstones offering very low intergranular porosity and permeability and limited secondary storage in joints. The identifiable aquifers within the potential zone of project impact are therefore: the Fassifern coal seam; overburden sediments in the immediate roof of the Fassifern seam; floor sediments, below the Fassifern seam; and surficial alluvium (very limited, and believed to be an ephemeral aquifer). Piezometers were installed to monitor the coal measures aquifers, viz: ODO003, TAS009a, TAS011 and TAS014a Fassifern Seam; TAS009b, TAS010, TAS012 and TAS014b Roof aquifers; and TAS013 Floor aquifer. The piezometers were monitored from July 2000 until October They were all constructed as standpipe piezometers within former coal exploration drillholes, some in very deep holes, and have proven to have a limited life. Recent inspection revealed that all the previous piezometers have become inoperative, and they are currently being replaced by a new piezometer network. 4.2 GROUNDWATER LEVELS Water level hydrographs for the above piezometers are shown in Figures 3 and 4. Piezometer locations are shown on Figure 5. The hydrographs show limited correlation with rainfall recharge, although clearly rainfall on the ground surface immediately above the project site is the recharge source for the groundwater contained within both the coal and the roof and floor aquifers. Piezometer observations indicate that groundwater levels are generally located within the Fassifern seam, or in some places slightly above the top of the seam. The Fassifern seam is therefore only partly saturated, and would behave as an unconfined aquifer. Piezometer levels measured in the overburden piezometers (TAS09a, TAS010 and TAS012) are interpreted to represent a perched aquifer (or aquifers) above the Fassifern seam swmp report - updated final.doc Page 16

23 GROUNDWATER LEVEL HYDROGRAPHS - FASSIFERN SEAM 180 ODO003 TAS009a TAS011 TAS014a 160 GROUNDWATER LEVEL (m AHD) Jan Jan Jan Jan Jan Jan Jan-06 Date

24 GROUNDWATER LEVEL HYDROGRAPHS - ROOF and FLOOR AQUIFERS TAS009b TAS010 TAS012 TAS014b TAS GROUNDWATER LEVEL (mahd) Jan Jan Jan Jan Jan Jan Jan-06 Date

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26 4.3 GROUNDWATER QUALITY Water samples were collected approximately monthly from most bores between September 2001 and October Sampling was very difficult from the deep piezometers TAS009a and b and TAS010, and only limited sampling was carried out on those bores. Representative water quality data for the Fassifern Seam, roof and floor aquifers are summarised in Table 4.1. Table 4.1: Representative Water Quality Data for Fassifern Seam, Roof and Floor Aquifers 1 Aquifer Type Fassifern Seam Roof Aquifers Floor Aquifers Bores ODO003, TAS011 TAS014a TAS009b, TAS010, TAS012 TAS013 ph EC (µs/cm) Total Dissolved Solids (mg/l) Total Hardness as CaCO 3 (mg/l) Sulphates (mg/l) Chlorides (mg/l) Total Alkalinity as CaCO 3 (mg/l) < Calcium (mg/l) Magnesium (mg/l) Sodium (mg/l) Potassium (mg/l) Iron (mg/l) Sodium Absorption Ratio (calc) CaCO 3 Saturation Index -1.8 to to to to -0.6 Generally, the groundwater quality is potable to sub-potable in the Fassifern seam, and brackish in the roof and floor aquifers. ph is slightly acidic, however repeat sampling from TAS014a revealed a persistent low ph in the range 4-5, indicating the presence of some moderately acidic pockets within the aquifer. Ephemeral streamflow in the upper tributaries of Blue Gum Creek may be supported by groundwater baseflow. Water quality sampling on the rare occasions when these streams flowed revealed salinity in the range mg/l TDS, and ph in the range 6.1 to Data shown in table are ranges of measured values. Insufficient data have been collected for meaningful statistical analysis swmp report - updated final.doc Page 17