Groundwater Hydrology


CMJA provides services in three areas of groundwater geochemistry. These are:

  • Natural attenuation assessment
  • Acid rock drainage
  • Acid sulphate soils

Natural attenuation is the reduction in contaminant concentrations that occurs as a result of the combination of dilution, abiotic and biotic reactions that take place along the pathway between pollutant source to receptor. Mechanisms include dispersion, adsorption, and aerobic and anaerobic biodegradation.

For many organic pollutants, the key attenuating process is biodegradation by naturally-occurring subsurface micro-organisms. Natural attenuation is a potential restoration strategy for many sites - if natural processes can be demonstrated to be reducing risks to acceptable levels, then active cleanup will be unnecessary. This requires a fundamental understanding of processes controlling the fate of pollutants in the subsurface, identification of environmental factors which limit biodegradation, the development of methodologies for accurate performance assessment and robust modelling approaches for the prediction of plume behaviour.

Many inorganic contaminants do not biodegrade, but their concentration may be reduced by the processes of dispersion and adsorption to aquifer minerals, and by precipitation reactions.

Acid rock drainage occurs when mining exposes rocks containing natural reactive sulphides to the atmosphere. Under these changed conditions minerals such as pyrite and arsenopyrite, which may have remained unchanged for millions of years, oxidise and generate sulphuric acid, which may in turn leach other heavy metals from the rock.

The oxidation process involves a complex cycle of inorganic and biologically-mediated reactions, which, once started, may be self-sustaining.

A range of techniques are available to assess the acid generating potential of sulphidic rocks. These include acid-base balance methods, based on whole-rock geochemistry, and methods based on laboratory oxidation of rock samples. A range of methods is generally employed to assess both long tern acid generating potential, and the likely rate of acid formation.

© C. M. Jewell & Associates Pty Ltd - 1/13 Kalinda Road, Bullaburra, NSW, 2784. PO Box 10, Wentworth Falls, NSW, 2782.
Ph (02) 4759 3251. Fax (02) 4759 3257.