Some of the most common misunderstandings about groundwater resources are addressed.
Myth: Ancient myths refer to magical underground lakes, while some ideas persist today of underground lakes or channels buried beneath our feet like pipework or veins.
Reality: In reality groundwater in most areas is found in the tiny pore spaces between sand and gravel, or in rocks with narrow fractures. Underground lakes or caverns with ponds are geological features that are only found in landscapes made of limestone. Limestone can be identified by sharp patterns eroded by rainfall and bubbling when dissolved by acidic liquids. Limestone landscapes in NSW are limited to Jenolan Caves, Wellington and other palaeo reefs in the Lachlan Fold Belt rocks.
"There appears to be much misunderstanding about groundwater, and some seem to believe it is a magic pudding of infinite good quality water."
Peter Cullen, 1943-2008.
Myth: There is a common belief that groundwater is freely available for all to tap, so many people have a casual attitude to how much groundwater they take. Every day new bores are drilled, and water is drawn without thought given to consequences, or without regard to the rules of civil society (AWA 2007).
Reality: If groundwater systems are pumped too hard, by too many bores there may be no recovery of useable water. Much better management systems are needed to bring groundwater systems into balance - allowing responsible and licensed users to rely on their bores permanently rather than not bothering about the future.
Myth: There's a favourite drilling story about aquifers found beneath the western plains that are strangely similar to those found by drilling in the New Guinea Highlands, or Inner China. Some people are convinced that groundwater in Australia is somehow connected to distant sources overseas.
Reality: Aquifers that support agricultural enterprises in the Murray-Darling Basin are part of regional groundwater flow systems that can extend thousands of kilometres, but have no connection with outside Australia. The fact is that the Murray-Darling Basin is like a bathtub that is partially filled with sand and mud, where the sides are sealed and cannot transmit water.
Myth: Concerns over drilling test bores and exploration bores commonly suggest that an aquifer can be cracked. The idea that an aquifer can be cracked like a piece of china has perhaps come from images of geological materials that have been fractured during movement of the earth.
Reality: Alluvial aquifers comprised of sand and gravel cannot crack. Moist clay sediments cannot crack. Fracturing or cracking can occur in swelling clay sediments due to moisture changes or in rock aquifers in response to changes in pressures or stresses. Over the past decades thousands of bores have been drilled through alluvial sediments into underlying rock in NSW. There is no evidence that drilling of any type (whether for water, testing or mineral resources) could damage aquifers, provided that sealing procedures in the Australian Standard and NSW DPI standards are adopted*. However, old corroded bores and water bores that have been gravel packed to the surface have caused leakage of shallow saline groundwater. The risk of impacts on groundwater levels or quality due to monitoring test holes or exploration drilling is negligible compared with other potential risks to the sustainability of groundwater resources.
A brief history of the divining rod or water witching
Ancients - The Scottish used the witch elm for divining rods, with immigrants to America becoming known as "water witches".
1518 - Martin Luther declared the use of the witching rod a violation of the First Commandment "Thou shalt have no other Gods before me".
1556 - First written account of witching used by metal miners in Bohemia.
1568 - St Teresa of Spain secured a plot of land for a monastery after a diviner guided diggers to a gushing source of underground water.
1645 - Athanasius Kircher tested the usefulness of a rod used by a diviner, by then suspending the same rod from a string. This time the rod failed to move when past over the drilling target identified by the diviner.
1850s - Scientific methods for finding groundwater become available.
Source: Chapelle (1997)
Myth: "Dig here", says the fellow with the forked willow rod,"and you'll find water 60 feet down". A well is drilled and strikes water. In the US today there are 20,000 to 30,000 water witches who practice the art finding water more often than not (Chapelle 1997).
Reality: There is as yet no scientific evidence supporting divining or witching to find water. The way in which the divining rod is typically held is like a spring which amplifies slight movement of the body. The claim that the rod dips involuntarily may well be telling the truth, but the fact is that if you pick any spot at random to drill, at least some groundwater will be found 90% of the time. An experienced local driller will often be able to pick suitable bore locations on the plains based on their knowledge rather than the rod. Drilling in rock however can be a hit or miss affair regardless of diving rods, and two holes drilled only a few metres apart yielding very differently.
Myth: For a fee, company X gives a 100% guarantee that a 20 L/second supply of fresh water can be tapped at a depth of 45 feet if the rig drills at the marked site.
Reality: The level of confidence that groundwater bore drilling will result in sufficient yields of fresh water depends on the extent of information that is available. At a specific site, there may be a low, moderate or high probability that a good fresh groundwater supply can be obtained. However, it is not possible to guarantee the depth, yield or salinity of a bore due to natural variability in the subsurface. Two bores drilled just metres apart can yield quite differently, particularly if drilled into fractured rock.
The best possible outcome for groundwater supplies is obtained by engaging the services of a hydrogeologist and a water bore driller. Feasibility assessments for large groundwater supply projects should include examination of geological maps and remote sensing (eg. satellite imagery) to identify promising geological structures. Drilling targets are best optimized on a local scale by geophysical surveys (eg. resistivity or electromagnetic surveys) that detect anomalies in the sub-surface due to changes in sediment type or groundwater salinity. There is currently no scientific method that can accurately predict depth and yield and salinity of groundwater.
*Sources and references:
ADIA (2003), Minimum construction requirements for water bores in Australia. Edition 2, Published by National Minimum Bore Specifications Committee including Australian Drilling Industry Association.
AWA (2007). Water in Australia - Facts and Figures, Myths and Ideas. Published by Australian Water Association, Sydney. Download.
Chapelle, F (1997). The Hidden Sea - Ground Water, Springs and Wells. Geoscience Press, Tuscan, Arizona.
WRL Solutions. Optimising groundwater supplies. UNSW Water Research Laboratory, WRL Solutions 3100.
NSW DPI (1997). Guidelines For Borehole Sealing Requirements On Land. Document 08060201.GUI - Department of Mineral Resources
Facts curated by Dr Landon Halloran, Dr Gabriel Rau and Dr Martin Andersen from UNSW Sydney. Graphics and design by Anna Blacka from UNSW Sydney. Funded by the NSW Research Acceleration and Attraction Program to support the Australian Government National Collaborative Research Infrastructure Scheme.
This resource introduces aquitards and aquicludes, and discusses some of the cutting-edge approaches used to understand the movement of water and contaminants through the ground.
Having a geologically realistic conceptual site model is important for characterising hydraulic connectivity throughout aquifer systems, and modelling water transit times.
The use of heat as a tracer promises to be an excellent alternative to traditional assessment methods for quantifying exchange between surface water and ground water.
There are two common mistakes often made when calculating how much groundwater storage levels have changed.
