Landfill operations
Solid waste-management facilities such as landfills can affect the quality of underlying groundwater resources. It is therefore vital to get the best possible advice.
Our hydrogeologists have considerable depth of expertise and project experience. We can assess the suitability of a site for a proposed new landfill development, and predict potential impacts. We can also manage installation, monitoring and investigation for contaminants at existing landfill operations. Described below is a hydrogeological investigation - conducted by CMJA - for the Whylandra Landfill in Dubbo, Central West NSW.

The Whylandra Landfill has been in operation since 1977. We evaluated existing information on the hydrogeology of the surrounding area; this indicated that Mesozoic-age sandstone lithologies underlie the entire landfill area, and constitute the only zone available for groundwater movement. A number of deep piezometers were drilled through deeply weathered sedimentary rocks, and the zone of saturation (water table) located at over 40 metres depth.

Our overall assessment of climate, hydrogeology and waste containment practices indicated that there was little risk of significant groundwater contamination resulting from leachate movement. We completed our investigations with landfill gas testing, which again showed little cause for concern.

Effluent irrigation of land
Increasingly, water authorities are recognising the benefits of properly managed effluent irrigation systems, and so hydrogeologists are often called upon to help mitigate the effects of effluent discharge on groundwater resources.

CMJA's hydrogeologists have a strong background and field experience in hydrogeological investigations of this type. Our work has covered a wide variety of industries including feedlots, sewage discharges, milk processing facilities, dewatering re-injection and landfill leachate discharge.

The innovative free-stall dairy operated by Moxey Farms at Gooloogong, NSW, is one example of a project assisted by an effluent irrigation investigation carried out by CMJA. An outline is provided below.

Proposals to expand dairy effluent irrigation at Moxey Farms were assessed in relation to their potential impact on groundwater. The farm is underlain by an alluvial sequence that hosts a multi-layer aquifer system. The groundwater quality of this aquifer system was potentially vulnerable, following the use of dairy effluent to irrigate areas used for pasture and fodder production.

Investigative work comprised extensive electromagnetic surveys to locate higher permeability sand lenses, DC resistivity soundings to enhance depth resolution, backhoe test pit examination, soil permeability testing, drilling of boreholes into the unconfined aquifers and delineation of pre-irrigation groundwater quality.

CMJA's investigations identified those pasture areas with greater sensitivity to contamination from effluent irrigation. We also designed and implemented a programme to monitor shallow groundwater quality.

Mining
CMJA has conducted a wide range of investigations for the mining industry. These include locating suitable groundwater resources to support mining operations, conducting impact assessments of mining/quarrying operations on neighbouring groundwater resources, and designing and installing groundwater monitoring programs.

When it is proposed to mine below the water table, assessments must take into account all impacts resulting from dewatering and aquifer depressurisation. Similarly, the potential impacts of open-cut or underground mines on natural surface water and groundwater flow systems must be assessed.
Risk-based assessments regarding the potential for aquifer contamination, or the identification of contaminant migration pathways, may also be requested. Regulatory authorities will often require such work before considering an application to develop and/or expand a mining operation.
CMJA has conducted numerous mining impact assessments. Our clients have included Peak Hill Gold (Peak Hill Gold Mine), Tailings Treatment (Tomingley), Enhance Place Pty Ltd (Enhance Place Colliery near Lithgow, NSW), David Mitchell Pty Ltd (Sulcor Limestone Mine and Attunga Limestone Quarry, both near Tamworth), Concrite Quarries Pty Ltd (Exeter Basalt Extraction Area, Southern Tablelands, NSW), ACI Industrial Minerals (silica sand mining at Tanilba Northern Dune, Port Stephens, NSW), Rocla Quarry Products (Calga, Central Coast) and Kelian Equatorial Mining (East Kalimantan, Indonesia).

Groundwater modelling of flow and solute transport
Groundwater professionals are frequently challenged to make predictive quantifications of groundwater behaviour. They may need to assess how much groundwater is present, by using flow modelling; or they may be required to predict the concentration of solutes contained within flowing groundwater, by using contaminant transport modelling.

Depending upon the objectives, models can vary from a simple analytical equation embedded in a spreadsheet program through to a highly complex time-variant numerical model designed to simulate subtle changes in groundwater movement within a complicated geological environment over a period of several decades.

We use several of the industry standard modelling codes and integrated modelling software programs, including Visual MODFLOW, INTERSAT/INTERTRANS, SEEP/W and SEEP 3D. Also available to us are supporting software packages such as Visual Groundwater, Mapinfo and Surfer.

More important than the modelling packages are the users, however. CMJA's hydrogeologists have the experience and insight to make the critical choices in designing the model approach most appropriate to the application.

One CMJA groundwater modelling project was that undertaken for the Eastern Distributor Motorway, Sydney, NSW. The motorway link from Woolloomooloo to Sydney Airport involves a tunnel through sandstone and a 'parkway' excavated below the water table in the Botany Sands aquifer. On behalf of the main contractor, Leighton, CMJA carried out a suite of modelling studies, using analytical and numerical finite element and finite difference techniques. These were used to assess the regional and local impacts of both the construction dewatering and the permanent structure, and to optimise a dewatering system design and the implementation of a re-injection system.

Other groundwater modelling assignments include the Parkes borefield (water supply), Thredbo Landslide Inquiry (expert witness), and Beemery cotton farm (irrigation).