LP150100395: Groundwater flow age distributions: Understanding open pit mine hydrology
Collaborating Organisations: Rio Tinto, Flinders University/NCGRT, The University of Western Australia, University of Utah, University of Bern.
Chief Investigators/Partner Investigators: Craig Simmons, Peter Cook and Shawan Dogramaci
NCGRT and Rio Tinto combined their expertise in a major ARC project to understand groundwater flow and groundwater mixing processes within the Pilbara region of northwestern Australia.
Because many of the open pit mines extend below the natural position of the water table, groundwater surrounding the mines is extracted to lower the water table and provide dry mining conditions. Significant volumes of surplus groundwater are being pumped every year, and this is discharged into rivers and creeks. The NCGRT research focusses on understanding of the source of water pumped and the ultimate fate of the dewatering discharge. The understanding gained from this study will ultimately support sustainable mine operations, and protection of water resources and dependent ecosystems following mine closure.
The project (completed in 2020) provided an opportunity to address several research issues. These include understanding the nature of groundwater mixing in the subsurface and the development of methods for collecting discrete water samples from long-screened wells. Dewatering bores in the Pilbara typically have intake zone more than 100 m long, and this poses a problem with interpreting groundwater chemical data because it is difficult to determine which depths are contributing to the pumped samples.
Problems of unravelling groundwater chemistry from long screened wells are not unique to the mining industry but often arises for groundwater sampled from irrigation and town water supply wells. The project also examined the uncertainty of groundwater models in areas of heterogeneous and uncertain subsurface geology, and how this can affect predictions of water table response to pumping.
Key project outcomes, and sources of further information are:
- Development of new methods for disentangling the effect of mixing on the groundwater age data obtained from environmental tracers. Application of this approach to the Pilbara allowed historical periods of high groundwater recharge to be determined.
Underwood SC, McCallum JL, Cook PG, Simmons CT, Dogramaci S, Purtschert R, Siade AJ and Prommer H (2018) Physical and chemical controls on the simultaneous occurrence of young and old groundwater inferred from multiple age tracers. Water Resources Research, 54 (11):9514-9532.
McCallum JL, Dogramaci S, Cook PG, Banks E, Purtschert R, Irvine M, Simmons CT, Burk L (2018) Stochastic correction of carbon-14 activities: A Bayesian approach with argon-39 validation. Journal of Hydrology, 566, 396-405. doi: 10.1016/j.jhydrol.2018.08.047.
McCallum JL, Cook PG, Dogramaci S, Purtschert R, Simmons CT and Burk L (2017) Identifying modern and historic recharge events from tracer-derived groundwater age distributions. Water Resources Research, 53: 1039–1056, doi:10.1002/2016WR019839.
- During long-term pumping, analysis of changes in groundwater age with time can provide information on changes in sources of pumped water. For one of the open pit mines in the eastern Pilbara, groundwater pumped to dewater the mine represents a mixture of old and young water. The young water is recharge from an ephemeral creek, which was downgradient of the mine site until pumping caused a change in the groundwater flow direction.
Cook PG, Dogramaci S, McCallum J and Hedley J (2016) Groundwater age, mixing and flow rates in the vicinity of large open pit mines, Pilbara region, northwestern Australia. Hydrogeology Journal, 25(1): 39-53. doi: 10.1007/s10040-016-1467-y.
- Developed a method for identifying infiltration of groundwater that has been pumped from the aquifer and subsequently discharged to the land surface. This water is typically difficult to distinguish from ambient groundwater using traditional chemical analysis, but can be readily identified from analysis of dissolved gases in groundwater. The method is applied to identify recharge of mine water that has been discharged to ephemeral creeks.
Cook PG and Dogramaci S (2019) Estimating recharge from recirculated groundwater with dissolved gases: An end-member mixing analysis. Water Resources Research, 55(7):5468-5486.
- Quantification of the effect of inter-borehole flow in long-screen wells on groundwater chemistry, and well purging times necessary to remove inter-borehole flow water. Our work determined that purging this water is not possible if wells have been left unpumped for long periods of time, and so understanding the effect this flow has on sampled groundwater is critical.
Poulsen D, Cook P, Simmons C, McCallum J and Dogramaci S (2019) Effects of intraborehole flow on purging and sampling long-screened or open wells. Ground Water, 57(2): 269-278.
Poulsen DL, Cook PG, McCallum JL, Simmons CT and Dogramaci S (2017) Effects of intraborehole flow on purging and sampling long-screened or open wells. Oral presentation at the Australasian Groundwater Conference, 11-13 July 2017, Sydney, Australia. (Abstract)
Poulsen DL, Cook PG, McCallum JL, Noorduijn S, Simmons CT and Dogramaci S (2018) The importance of measuring flows in long-screened or open wells. Oral presentation at the Australian Geological Council Convention. 14-18 October 2018, Adelaide, Australia. (Abstract)
- Development of an injected tracer method for quantifying rates of inter-borehole flow. The method compares favourably with borehole flowmeter approaches if density issues can be overcome.
Poulsen D, Cook PG, Simmons CT, McCallum JM, Noorduijn SL and Dogramaci S (2019) A constant-rate tracer dilution method to quantify pumped flows in long-screened or open wells. J. Hydrol., 574: 408-420.
Development of approaches for obtaining depth-specific samples in long-screened wells.
Poulsen DL, Cook PG, Simmons CT, Solomon DK and Dogramaci S (in press) Depth-resolved groundwater chemistry by longitudinal sampling of ambient and pumped flows within long-screened and open borehole wells. Water Resources Research.
Poulsen D, Cook P, Simmons C, Solomon DK and Dogramaci S (2019) Depth-resolved groundwater chemistry by longitudinal sampling of ambient and pumped flows within long-screened and open borehole wells. Oral presentation at the Australasian Groundwater Conference, 24-27 November 2019, Brisbane, Australia. (Abstract)
Poulsen DL, Cook PG, Simmons CT, McCallum JL, Noorduijn S and Dogramaci S (2018) Making the most of long-screened wells in groundwater investigations. Oral presentation at the NZ Hydrological Society & Meteorological Society of NZ Joint Conference, 4-7 December 2018, Christchurch, New Zealand. (Abstract)
- Development of criteria for assessing conditions under which hydraulic barriers can influence recovery of groundwater levels following cessation of groundwater pumping. If hydraulic barriers occur close to pumped wells, then their presence is likely to be detected during pumping. If they are very remote, then they will not influence pumping or recovery. However, at intermediate distances, hydraulic barriers will not affect drawdown during pumping but may exert a major control on recovery rates.
Marshall S, Cook PG, Miller A, Simmons CT and Dogramaci S (2019) The effect of undetected barriers on groundwater drawdown and recovery. Ground Water, 57(5): 718-726.
Marshall SK, Cook PG, Miller AD, Simmons CT and Dogramaci S (2019) Modelling the effect of undetected barriers on groundwater drawdown and recovery. Oral presentation at the Geological Society of America Annual Meeting, 4-7 November 2018, Indianapolis, USA. (Abstract)
- Assessment of the utility of hydraulic head and groundwater age data to detect the presence of hydraulic barriers, when sampling takes place under steady state flow conditions. Decreases in hydraulic head and increases in groundwater age often occur downgradient of hydraulic barriers, although the extent to which these parameters are perturbed by the presence of the barrier will depend upon aquifer and barrier characteristics.
Marshall SK, Cook PG, Konikow LF, Simmons CT and Dogramaci S (2019) Conjoint use of hydraulic head and groundwater age data to detect hydrogeologic barriers. Oral presentation at the Australasian Groundwater Conference, 24-27 November 2019, Brisbane, Australia. (Abstract)
Marshall S, Cook PG, Konikow L, Simmons C and Dogramaci S (2020, in press) Conjoint use of hydraulic head and groundwater age data to detect hydrogeologic barriers. Hydrogeology Journal.