Capabilities

The core business of Eureka Hydrologic is the assessment of groundwater systems. Capabilities include:

• Groundwater flow modelling: analytical and numerical models simulating groundwater flow, including density-dependent flow, unsaturated flow and pit drainage.
• Hydrochemical modelling: Groundwater chemistry evolution, pond water and process water chemistry.

The following associated Brisbane companies specialise in other complementary aspects of environmental and water management:

• Waste Solutions Australia Pty Ltd (email: office@wastesolutions.biz) has capabilities in: Groundwater investigations and modelling; Contaminated Land and Third Party Review; Waste Management; Environmental Management studies and licensing; Assessment/Application of New Technologies; Environmental Auditing
• Baseline Pty Ltd: Environmental microbiological services
• Phytolink Australia Pty Ltd: Phytoremediation

MODEL METHODOLOGY - WHAT IS A MODEL?

A "model" is any simplified representation of a real physical system. However, the term is rather ambiguous. The term is increasingly taken as being synonymous with “computer-based mathematical model” because of the increasing use of computer-based models for simulation of physical systems.

It is important to make a clear distinction between these terms, partly because complex computer-based mathematical models may be either unnecessary or impractical for particular applications. Assessment of the suitability of models and model computer codes is an important component of model methodology.

A model is composed of two parts: a conceptual model and a mathematical model. A "conceptual model" is a necessary, largely quantitative, preliminary description of a system. A "mathematical model" may be analytical if a simple or non-distributed system is being considered or may be computer-based if a geometrically complex system is being considered. As a rule-of-thumb, preparation of a conceptual model may comprise half of a typical modelling project.

THE INHERENT UNCERTAINTY IN ASSESSMENT OF GEOLOGIC AND HYDROLOGIC SYSTEMS

There are inherent uncertainties and limitations in conceptual and mathematical modelling of geologic and hydrologic conditions. It is beholden upon all professional scientists to outline such uncertainties to clients at project proposal and in subsequent stages. Knowledge and information regarding model uncertainty is an essential component of scientific reports and in other communication. Much model uncertainty is related to measurement of systems’ properties and inputs, associated scale issues and spatial or temporal variability in properties and inputs.

In hydrologic systems, rainfall variability provides an example of uncertainty. Point measurement estimation of rainfall over large areas invariably relies upon to measurement of rainfall at a limited number of points , i.e., rain gauges. The extrapolation factor between several rain gauges and a whole catchment extending over many square kilometeres may be a billion-fold.

In hydrogeologic systems, the possible range of hydraulic conductivity (K) values of unconsolidated sediments can vary by up to nine orders of magnitude (one billion-fold). While characterisation of K values of materials at a particular site greatly reduces this uncertainty, scale factors and local variability of materials produces uncertainty of at least an order of magnitude.

DEALING WITH UNCERTAINTY

It is often possible to reduce the degree of uncertainty in model results to a level acceptable to clients and regulators. Steps within model methodology that address uncertainty include calibration and validation of model results. Where appropriate, statistical assessment of uncertainty can be carried out (e.g. sensitivity analysis, Monte Carlo analysis). The effect of future uncertainies (e.g. climate change) are often dealt with by examining various scenarios.

The above statements are not intended as a disclaimer of liability, but to ensure that expectations of models and associated uncertainties are recognised and understood. If regulators or clients have queries regarding the matters raised, they should seek further information from Eureka Hydrologic.

ASTM, Standard Guide for Application of a Ground-Water Flow Model to a Site-Specific Problem. ASTM Standard D 5447-93, 6p.

Charles W. Fetter (2001): Applied Hydrogeology, 4th Edition, , Upper Saddle River, New Jersey, Prentice Hall, 598p.

Charles W. Fetter (1999): Contaminant Hydrogeology, 2nd Edition, Upper Saddle River, New Jersey, Prentice Hall, 500p.

Clifford Voss (1998): Editor’s Message - Groundwater Modelling: Simply Powerful. Hydrogeology Journal, Volume 6, No. 4, pp A4-A6