Tasmania is fortunate in that many of its groundwater aquifers are capable of yielding useful supplies, which are also of relatively good quality. This water quality varies according to the aquifer type, hydrogeological setting and location. There is also a very general relationship with rainfall. The eastern part of Tasmania, which receives less rainfall, generally has poorer quality groundwater than areas of higher rainfall in the west, north and northeast.
Most bore water is either potable (salinity less than 1500 mg/L) or has relatively low salinity (less than 3500 mg/L). There are few areas of highly saline poor quality water like those that occur over large areas of mainland Australia.
Because of its generally good quality, groundwater in Tasmania is suitable for a wide range of uses. A significant proportion of bores are used for irrigation and rural domestic purposes, and there are very few palces where the water is not of suitable quality to support stock.
In general, aquifers formed in Tertiary sedimentary rocks, Jurassic dolerite and Upper Triassic sedimentary rocks in low rainfall areas produce groundwater of a significantly poorer quality than other aquifer types. This difference is likely to be related to the mechanism of aquifer recharge, water storage and transport, as well as the mineralogy of the materials forming these aquifers.
Generally the salinity of bore water decreases as the age of the rocks forming the aquifer increases. The main exception is Tertiary basalt, which usually occurs as dissected plateaux in elevated positions where groundwater movement is rapid. Lower lying basalt in the northern Midlands can have significantly higher salinity.
In Tasmania, groundwater is known to have been polluted in several localities, and it is almost certain that there are other examples of undetected groundwater contamination. Fortunately most known sources of groundwater contamination are small and localised, with shallow groundwater aquifers being the most prone to contamination. Tertiary basalt aquifers in the Devonport/Port Sorell areas have elevated levels of nitrate, probably caused by fertiliser use.
Acidic groundwater
In certain areas of Tasmania, the mineralogy of the aquifer material, or that of other geological materials surrounding the aquifer (including recent overburden), has had a marked effect on the pH of the groundwater in the aquifer. Groundwater derived from the Mathinna Beds and Devonian granites in northeast Tasmania (including Flinders Island) has a very low pH at certain locations. Similarly, in northwest Tasmania, acid sulphate soils in Quaternary swamp deposits in the Mella area, which are in direct hydraulic connection with the underlying carbonate aquifer, have caused significantly acidic groundwater. In some cases the pH value may be as low as 1.
Industrial Pollution
The most common potential point sources of contamination include municipal landfill sites, leaking fuel storage tanks, agricultural chemicals, wastes from mining sites, manufacturing plants, dairies and abattoirs. Pollution from waste water re-use schemes has the potential to become a significant threat. Diffuse sources of pollution are pesticides, fertilisers and septic systems.
Salinity
The proximity of aquifers to recharge areas and the rate of flow within aquifers are major influences on water quality. Groundwater that has a longer residence time will tend to interact chemically with the aquifer material. This interaction has a detrimental effect on water quality. The nature of the aquifer material and hydrogeological regime present will also influence the degree of this interaction.
Groundwater Quality
