Understanding Water Management in the Quarrying Environment

ALEXIS VALENZA MHydroEng– Director at Valenza Engineering and Paul Larkin BSc MEnvLaw–Consultant.

WHO WE ARE

Alexis Valenza and Paul Larkin have been involved in groundwater, surface water and environmental consulting services for the mining and quarrying industry for the last 25 years, both in Australia and internationally.

Their combined experience, in excess of 50 years, covers quarry and mine water supplies, water master planning, environmental impact assessment, mine de-watering, numerical modelling, environmental monitoring and environmental law and policy consulting.

REGULATORY FRAMEWORK

The increase in demand for cement and construction materials over the last few decades has led to the extension and deepening of numerous quarries in Victoria. The permitting process is often associated with stringent requirements aiming to protect our fragile environment.

The main acts that govern water related issues in quarries are the Water Act and the Environment Protection Act. However, significant conditions can be imposed through Take and Use Licences, Works Approvals, Planning Approvals and Work Authorities. It is therefore essential to consider all of these when determining what water management (and related risk management) measures are required at each quarry.

Dry -above water table- quarries

Dry quarries have experienced rain water inflow with the recent return to wet conditions which has led to the return of water management issues. Operators can apply for emergency approval to discharge under certain circumstances but this is only a short-term and “one off ” solution.

In other cases, it will be necessary to apply for long term approval to discharge to the surface water drainage system. If an environmental impact is expected on and particularly off-site, then a Works Approval is needed from the EPA. The operator will need to prove that the chemical and physical properties of the discharged water are similar to that of the receiving water. They will also need to estimate the quantity of water to be discharged. The monitoring of rainfall and evaporation using automated weather stations will help provide a realistic water balance for the site.

Wet quarries

A quarry cannot operate below the water table without a Take and Use Licence issued under the Water Act based on a reasonable estimate of the amount of groundwater to be pumped from the quarry.

The licence application generally has to be accompanied by an independent hydrogeologist’s evaluation report. The licence may (and usually does) stipulate that the water pumped from the quarry is metered.

The licensing authorities generally interpret the provisions of the Water Act to mean that any groundwater taken from a quarry needs a take and use licence even if the groundwater is not used. The metered amount of water that is pumped from the quarry would include any rainwater on the surface of the quarry and any run-off from its surrounds.

Theoretically, this should be excluded from the Take and Use Licence volume (provided that this rain and surface water is not used by the quarry or others) and so water balance studies are important. This requires modelling of groundwater inflows as well as monitoring of rainfall and evaporation.

The modelling of groundwater inflows requires monitoring of groundwater levels, estimation of aquifer hydraulic properties (preferably through pumping tests) and recharge estimation.

IMPORTANCE OF WATER MANAGEMENT IN THE INDUSTRY

Groundwater pollution

The impact of quarrying on aquifers in terms of potential contamination and change in groundwater flow patterns is often ignored, regardless of the amount of material quarried below the water table.

Storage of fuels, lubricants, chemicals etc. must be done such that there is no leakage to underlying aquifers. Recent higher rainfall periods have caused higher recharge and higher risk of leakage of pollutants to groundwater. Groundwater (and surface water) pollution is an offense, and relevant potential pollutant storage conditions are normally included in the Planning Permit and/or Work Authority.

Monitoring of water quality, groundwater levels and meteorological data is important before the commencement of quarrying, during a quarry’s lifetime and after closure to establish a defensible database.

Impact on surrounding users

The impact assessment will analyse the potential impact of the de-watering – or quarry water supply – on environmental receptors and surrounding groundwater and surface water users.

A typical assessment will involve, amongst other things, a desktop study which collates and analyses existing data from neighbouring bores, field investigations, including collection of data from neighbouring bores, computer modelling of the impacts on neighbouring properties and establishment of appropriate monitoring networks. The overall assessment will determine if water is present and at what depth, if it is easily available, if its quality is suitable and if surrounding bores are extracting from the same resource and hence their owners could potentially object to the development.

Using computer modelling techniques allows forecasting of the impacts of groundwater extraction during the life of the quarry under different quarrying scenarios (deepening of the pit after 5 years, extension after 10, etc.).

This assessment will help quarry operators to predict groundwater inflows, to estimate the depth and lateral extent of the associated drawdown and to cost-effectively managing their on-site water use.

Appropriate assessment of the availability and vulnerability of the resource allows for good site-management of water and ameliorates impacts upon the surrounding community, thereby minimising costly community objections.

Safety, cost savings and community

Effective water management is critical to the viability of modern operations as it is often a key factor in profitable quarrying.

Effective water management helps stabilise highwalls, lowwalls and stockpiles during and after extraction. Effective de-watering prevents temporary flooding of the operation and its assets, optimising production and reducing operational costs (by reducing cost of haulage for drained material, for example).

Applying correct treatment to any water discharges to meet permit requirements will help avoid costs and delays caused by interventions by regulatory authorities.

By engaging with the community, operators can improve the way they operate at no extra cost. Examples of community engagement include temporary or permanent transfers of groundwater allocations, supplying fresh water to nearby users and ensuring dust emissions are minimised by using runoff water collected on site for dust suppression.

For more information, contact CMPA member Alexis Valenza on 0423 305 420 or Paul Larkin on 0418 310 324.

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