Water quality

A. Groundwater Properties

Constituents dissolved in water can be considered from two aspects, (a) chemical composition, and (b) water quality.

The chemical composition is the character of the water, and largely determined by the major dissolved species. This usually depends on the geological materials that a water has been in contact with. For surface waters it is mostly soils and weathering processes; for groundwaters it is the aquifer materials.

Water quality is an assessment of the "goodness" of a water for a specified use. For example, drinking (potable) water must be of very high quality. Water of slightly lesser quality can be used for irrigation, and even lower quality for stock supplies.

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B. Chemical Character of Groundwaters

The amounts and ratios of the different major dissolved ions in groundwater can be used to help identify the source of the waters, and various processes it has undergone. These main ions can also identify different bodies of water, give information about their history and also show processes such as mixing.

Within the Lockyer Valley both the salinity, and the chemical type of groundwaters vary. This is for both the alluvium and the sandstones. Many deep alluvial bores have a component of bedrock water, which typically increases during dry period irrigation.

Also a significant influence is natural evaporation in streams of poor flow, or in pools; there is also evaporation from irrigation runoff. This evaporation can increase salinity.

Discharge of deep artesian basin groundwaters into the base of alluvial aquifers can result in high HCO3 waters from the CO2.

Waters that originate from the ranges, either as surface runoff, or as groundwater flows from the basalt aquifers, for example, can have relatively low salinity but tend to have higher amounts of Mg.

Piper diagram of major dissolved ions in Lockyer waters (Wilson 2005). This plot shows the chemical type of the waters by relative proportions of major cations and anions.

piper diagram of dissolved ionts in lockyer waters



Chemical types of different groundwaters in Lockyer Valley (Wilson, 2005)


aquifer type TDS [mg/l] chemical type of water
Alluvium (Lockyer plain) 800 - 3700 Mg, Na, Ca-Cl, HCO3, Na-HCO3
Alluvium (Ma Ma catchment) 5400 - 7700 Mg, Na, Ca-Cl
Alluvium (Tenthill catchment) 1000 - 2500 Mg, Ca, Na-Cl, HCO3
Basalt 800 Mg, Ca-HCO3
Sandstone (Koukandowie Fm) 3000 - 6800 Na, Mg-Cl
Sandstone (Gatton ss) 5700 - 7500 Na-Cl, Na, Mg-Cl
stream water (flood) 160 Ca, Mg, Na-HCO3
stream water (standing pool) 280 Mg, Ca, Na-HCO3

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C. Aspects of Water Quality

The quality assessment can be related to major components (e.g. salinity), or minor components (e.g. nutrients), or trace components (e.g. metals, bacteria), or other properties (e.g. acidity).

There is also a "quality" aspect to water chemical type, as excesses of some ions can be detrimental to soils or crops.

Chemical analyses of water routinely done are:

  • major dissolved species - e.g. Na, Ca, Mg, Cl, SO4, HCO3
  • minor dissolved species - e.g. Fe, K, Al, Mn, Si, nutrients (NO3, PO4)
  • trace elements - e.g. As, Hg, Zn, Cu, Pb, Cd, Ba (in solution or adsorbed)

Concerning water quality for agricultural purposes, we mostly measure:

  • salinity - TDI [mg/l] - total dissolved ions
  • hardness - content of CaCO3, MgCO3
  • sodium adsorption ratio (SAR) - Na vs. Ca+Mg
  • residual alkali - HCO3 vs. Ca+Mg
  • pH
  • electric conductivity (EC) - [uS/cm]
  • water temperature - [°C]

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Further information

jpg photo: water sampling pump   [646.56 kB]  - Small downhole pump used to collect samples from observation bores, good to about 10 m deep. Shows bore casing of 50 mm PVC.
jpg photo: salinity meter   [588.56 kB]  - Field meter for measurement of physico-chemical parameters (EC, pH, Eh and temp). Probes shown in plastic bucket.
jpg photo: collecting water   [653.67 kB]  - Another method of collecting water samples, a stainless steel downhole bailer.
jpg map: groundwater quality   [265.97 kB]  - Summary map of groundwater salinity (NR&M report)which shows conductivity (EC) as uS/cm. There is a lot of information on this map if you enlarge it. The map also shows the locations of the recharge weirs, and the outline of the Central Zone Declared Area.
jpg map: temperatures of groundwater within GAB   [276.78 kB]  - Deep groundwater temperatures in Great Artesian Basin, shown for interest. Lockyer Valley is in very southeast corner. (NR&M report).

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