Western Areas NL – Spotted Quoll
Western Areas is planning to mine its Spotted Quoll nickel deposit at its operations at Forrestania, located about 450 km east of Perth. The deposit is planned to be mined by the open-pit method and then by decline. An investigation was undertaken to assess the groundwater conditions with respect to dewatering operations. The programme included the design, construction, and test-pumping of seven production bores and four monitoring bores to 200 m depth into fractured-rock aquifers in the vicinity of the proposed pit. A MODFLOW numerical groundwater flow model was developed using results from pumping tests and natural groundwater levels to estimate required pumping rates to allow mining to 120 m below the water table.

Portman Iron Ore Ltd – Mt. Jackson J1 Deposit
Portman Iron plans to commence open-cut mining of iron ore at the J1 deposit, east of Mt Jackson, in early 2010. Dewatering of the pit will be required since the base of the pit is planned to extend 75m below the existing groundwater table. Rockwater planned and supervised the drilling of three observation bores and one production bore within the planned J1 pit area. Drilling of the bores and test-pumping of the production bore revealed that the fractured strata containing the deposit have high permeability and porosity.

Kimberley Diamond Company – Ellendale 4 and 9 Mines
On behalf of KDC dewatering investigations have been undertaken by Rockwater at the Ellendale 4 and 9 mines in the Canning Basin in the Kimberley Region of Western Australia. Hydrostratigraphic holes were drilled at prospective sites to identify aquifers associated with geological contacts and structures. Since 2003, water levels have been lowered 80 metres in each of the Ellendale 4 and 9 mines by pumping from shallow and deep aquifers. Mine closure plans have been adopted following final void studies to determine water quality and acid rock drainage within the resultant lake.

Portman Iron Ore Ltd – Windarling W2 Deposit
Mining of Portman’s W2 Pit at Windarling has been in progress since 2004, with mining scheduled to occur below the water table. Rockwater was engaged to design and supervise the construction and test-pumping of 3 production bores to dewater the pit ahead of mining operations. Pit dewatering and final void assessments have been made using results from the drilling and test pumping programmes and additional monitoring data. A groundwater flow model was calibrated to calculate water-level reduction induced by pumping at current rates to 2012. Furthermore, the model was used to estimate water-level recovery after pumping ceases, and a water-balance calculation was used to estimate the final void water level.

Western Areas NL – Digger Rocks and Digger South
Western Areas is investigating the feasibility of re-opening the Digger Rocks mine at Forrestania to extract nickel ore from underground workings beneath the old Digger Rocks pit, and from a 600 m long deposit situated to the south, known as Diggers South. Three production bores and a monitoring bore were constructed in the Digger Rocks area under the supervision of Rockwater. One of the production bores was drilled to a depth of 170 m into the underground workings at the Digger Rocks pit. The bore will be used to assist in dewatering of the pit and upper part of the underground workings. The other two production bores were drilled into fractures associated with the mineralised zone in the northern and central parts of the un-mined Diggers South ore-body. In order to estimate the amount of water that will be produced by dewatering at Digger Rocks and Diggers South, Rockwater constructed a numerical groundwater model using drilling data and results of test-pumping. The model was also used to predict what the water levels in the bores will be once Digger Rocks pit and the underground workings are dewatered, and then what the extraction rates from the bores will be.

Portman Iron Ore Ltd – Koolyanobbing
Portman Iron has re-commenced mining of iron ore in the A-Pit at Koolyanobbing, which was originally mined by Western Mining Corp in the 1970s. Rockwater was engaged by Portman to assess what the dewatering requirements of the pit will be once the floor of the pit has been excavated below the water table. A desk-top study of the available geological mapping and exploration drill data was performed, followed by test holes, construction of production bores, and test pumping.

KCGM - Deep Bore
Rockwater was commissioned by KCGM to design, tender and supervise construction of a deep (760 m) dewatering bore at the Superpit in Kalgoorlie. The bore intersected underground mine workings at about 720 m depth, before being continued to total depth; introducing a significant technical challenge in maintaining drilling circulation. The bore was successfully completed within budget and on time.

WMC - Phosphate Hill, QLD
Mining at WMC's Phosphate Hill project extends below the water table in the highly-permeable Beetle Creek Formation. Dewatering assessments by Rockwater have shown that up to 4.4 GL of groundwater will need to be extracted for every metre of water-level drawdown. As the mine will require up to 5.3 GL/annum for ore processing and potable use for the next 30 years, a fine balance is required to ensure groundwater discharged from dewatering operations is not wasted, but that groundwater levels are lowered at a sufficient rate to allow mining to proceed at a rate capable of meeting WMC's ore quantity and grade objectives. A detailed six-layer groundwater model was developed, using the results from monitoring of previous dewatering activities to determine the balance between preserving the water supply and dewatering the ore ahead of mining. The capacity of the existing borefield was also evaluated and recommendations made for the installation of new dewatering bores.

Drillers inspect the drill bit as it passes through mine workings in the KCGM Superpit

Golden Grove - Gossan Hill
A comprehensive hydrogeological investigation was undertaken by Rockwater to enable implementation of a dewatering system for the underground decline and mining operations at Gossan Hill. The investigation included logging of open fractures in diamond core; collection and assessment of water inflow data from previous drilling; definition of the aquifer boundaries; measurement and assessment of hydraulic parameters through inflow testing and numerical modelling of the aquifer system and; prediction of the mine water inflows. A detailed groundwater monitoring programme was developed and recommendations were made for ongoing assessment of the dewatering operations to enable the groundwater model to be recalibrated as required.

Tectonic Resources - Ravensthorpe
Dewatering investigations are often required as part of initial feasibility studies for the start up of new mining ventures. Rockwater has conducted several such investigations for Tectonic Resources in the Ravensthorpe area. These investigations included hydrogeological evaluation using existing data and information, diamond-core fracture logging, exploration drilling, design and construction of test production bores, aquifer testing and assessment, and numerical groundwater modelling. The results, including estimations for dewatering requirements and addressing potential environmental concerns, were reported for inclusion in the company's Notice of Intent.

Groundwater inflow testing for dewatering project at Gossan Hill