School of Earth Sciences - Theses

Permanent URI for this collection

Search Results

Now showing 1 - 4 of 4
  • Item
    Thumbnail Image
    The potential for natural attenuation of petroleum hydrocarbons in groundwater: Shell Newport Terminal, Victoria
    Lavis, Amelia Jayne ( 2000-10)
    Groundwater in the fractured and jointed Quaternary Newer Volcanics basaltic aquifer system beneath the Shell Newport Terminal has been contaminated by petroleum hydrocarbons. This petroleum hydrocarbon contamination has resulted from a number of different spill incidents over the terminal's long operation. Petroleum hydrocarbon contamination has led to the formation of a light nonaqueous phase liquid (LNAPL) floating on the water table. Associated dissolved and vapour phases have also developed within the basaltic aquifer. The effectiveness of natural attenuation processes to remediate the petroleum hydrocarbon contamination has been evaluated based on the gas chromatography / mass spectroscopy analysis of LNAPL samples and changes in groundwater geochemistry. Three distinct LNAPL plumes were identified within the Shell Newport Terminal jet facility plume (kerosene source); off-site plume along High 8t (mixed source of leaded petrol, kerosene, and diesel); and black oil fuel gantry plume, which is migrating off-site to Digman Reserve (mixed source of leaded petrol, shell sol A, and diesel). LNAPL ratio analysis revealed only that the samples were degraded compared to their estimated source composition. Further interpretation of ratios was difficult due to constraints involved in source compositions, sampling limitations, heterogeneity of the groundwater system, and high transport velocities of the groundwater compared to LNAPL migration. (For complete abstract open document)
  • Item
    Thumbnail Image
    The fate of cyanide in groundwater at gasworks sites in south-eastern Australia
    Meehan, Samantha ( 2000-09)
    The fate and transport of cyanide in groundwater was investigated at gasworks sites in southeastern Australia. Two gasworks sites were investigated during this research: one in Tasmania and the other in Adelaide. The research followed three principal methods of investigation: field work, laboratory work and numerical modelling. The field work was aimed at observing the behaviour of cyanide in highly contaminated groundwater environments. Measured field parameters and laboratory analytical results from groundwater sampling were used to describe the hydrodynamics and hydrochemistry of the groundwater environment, providing a framework for groundwater flow and solute transport modelling. Groundwater and soil samples were also collected for use in laboratory experiments. The results from both field sites indicate contrasting hydrogeological environments, however, inorganic (metallic and non-metallic) and organic contaminants were measured in solution at both sites. The maximum concentrations observed at both sites were up to 5,300 mg/L CN(Total) (Adelaide site) and 21 mg/L CN(Total) (Tasmanian site). Results from geochemical modelling of solutes in groundwater at the field sites indicate that cyanide was predominantly in its free form in solution, with metallo- and alkali-cyanides also present.
  • Item
    Thumbnail Image
    Occurrence of nitrate in soil and groundwater in the Corangamite area, Western Victoria
    Bayne, Phillip James M. ( 1996)
    Soil and groundwater samples taken from two areas of different land use in the Corangamite Region, 200 km west of Melbourne, were analysed for nitrate and ammonium, and in some cases chloride. Both sites are located on the Later Newer Volcanics 'stone rises', and groundwater was sampled from nested bores which intersect the shallow unconfined aquifer and deeper semi-confined aquifer at both sites. The Carpendeit site is an area of native Eucalypt forest, and the Purrumbete North site is a pasture for grazing dairy cows. Low concentrations of nitrate (< 1 mgN/L) in groundwater at Carpendeit correspond to low soil nitrate concentrations (< 3 µgN/cm3 ). Higher groundwater nitrate concentrations occurred in the shallow unconfined aquifer at Purrumbete North, (up to 3 mgN/L), but not in the lower semi-confined aquifer, and corresponds to higher nitrate concentrations in soil (1 to 60 µgN/cm3 ). Elevated nitrate concentrations also occurred in groundwater discharge at McVeans Springs, in the range 2.61 to 4.72 mgN/L, and at Ettrick Springs in the range 8.08 to 16.07 mgN/L, greater than the limit of 10 mgN/L for drinking water specified in ANZECC water quality guidelines. Nitrate in soil under the pasture is probably derived primarily from the activity of nitrogen fixing bacteria associated with subterranean clover introduced to the pasture. Soil nitrate distributions suggest intense return of nitrogen in dung and urea occurs at 'camps' locations on the pasture, where cows tend to gather for shelter. Transport of nitrogen to shallow groundwater is stimulated by cracks and channels in the basalt clay soils. Local groundwater flow includes interaction with the many lakes and temporary ponds 'which form in surface depressions at times of high rainfall. The ponds probably serve as an effective nitrate supply in recharge to the shallow aquifer.
  • Item
    Thumbnail Image
    Physical and chemical hydrogeology of the Otway Basin, southeast Australia
    Bush, Angela L. ( 2009)
    The Otway Basin of southeast Australia is the subject of this thesis, which incorporates pre-existing geological, hydraulic and major element hydrogeological data with new isotope hydrogeochemical investigations. The region is an Upper Cretaceous–Tertiary basin, filled with siliciclastic and calcareous aquifers and aquitards and characterised by late volcanic activity, pervasive faulting and karstification. (For complete abstract open document.) As part of this study, an hydrogeological database is compiled for the Otway Basin region from existing distinct datasets from the states of Victoria and South Australia. Utilising this new resource, the data are reinterpreted into a 3D model of the hydrostratigraphy for the basin in GoCAD, and interpolated surfaces of hydraulic head and electrical conductivity are created for 5 aquifers/aquitards. The Victorian hydraulic head data is analysed for long term declining or inclining trends and hydrograph trend maps are created for different aquifer systems. The data are also compiled into representative cross sections of flow and chemical composition, with one section located in each of the three major sub-basins. The records of groundwater chemistry from the Victorian section of the Otway Basin are used to plot the relative concentration of major cations and anions for the main aquifers. More than 120 groundwater samples were taken for analysis of major and minor ion concentration and/or oxygen, hydrogen, carbon, strontium and chlorine isotope composition. These data are used to characterise the hydrogeochemical evolution of the groundwater and to identify the processes that the groundwater drives or experiences in the system. The potentiometric maps and cross sections reveal the interconnected nature of the flow in all aquifers and the relationship between local and regional flow systems. Regional flow paths originate inland near basement highs or the basin margins. In the shallower aquifers they terminate at the coastline where the groundwater mixes with ocean water at a diffuse interface and density differences induce groundwater discharge at the land surface or the ocean floor. In the deeper confined aquifers, discharge is submarine via several possible mechanisms, which include: diffuse intergranular leakage to overlying units; flow along faults or volcanic conduits; and/or seepage directly to the ocean from exposed sections of the aquifer, e.g. in submarine canyons. These mechanisms may be operating up to 50 km offshore but the interface is currently migrating landward, which will result in a shortening of that estimated distance. Local-scale flow lines are complex and may be oriented against the direction of regional coastward flow. Local hydraulic divides are often associated with volcanic eruption centres, which have elevated topography and relatively high hydraulic head, making them important recharge zones. These zones contain low salinity groundwater because infiltration is relatively rapid. Conversely, basalt flows that have developed clay horizons through weathering reduce drainage and allow significant evapotranspiration which concentrates the cyclic salts in solution. Many local flow systems discharge mainly via evapotranspiration, which acts again to concentrate the cyclic salts in solution. Other local discharge zones are rivers, creeks and lakes or lagoons that receive baseflow and seeps and springs associated with geological contacts or boundaries and faults. Evaporitic concentration of solutes in surface water bodies and shallow groundwater affects the quality of water recharging the underlying aquifers and aquitards. This quality has changed over the last 50,000 years or so due to fluctuations in climate and hence variation of the precipitation/evaporation ratio. Stresses on the aquifers are climate fluctuations, sea level change, land use change and groundwater extraction. These stresses have resulted in the system being out of hydraulic equilibrium in many cases. Lags in response to these changes in boundary conditions are identified and/or hypothesised. In particular, the confined aquifer’s response to sea level change could be subject to a lag in the order of millennia. The stress on an aquifer is often transferred to its adjacent units, in some cases inducing cross-formational leakage, which is possibly supported by radiocarbon dating evidence. The area of the Otway Ranges appears to have escaped the effects of stress to date because of its stable microclimate, its distance from the ocean and from groundwater extraction. Increase in demand on groundwater resources, development of geothermal, sequestration and hydrocarbon industries and future climate change may yet have a detrimental effect on the groundwater of the Otway Basin. Isotopic composition of the groundwater confirms its meteoric origin and chlorine isotopes from several samples of the deep groundwater indicate that accumulation of solutes along the flow path is not due to diffusion or dissolution of connate salt. Thus, the salinity of the water is sourced from cyclic salts and solutes from water-rock interaction, both of which may be concentrated by evapotranspiration. Water-rock interaction is dominated by dissolution of carbonates and weathering of silicates as a result of the surficial geology being dominated by calcarenite or limestone and young basalt. The volcanic activity has produced gas that has interacted with the groundwater, and continues to do so, fractionating oxygen, hydrogen and carbon isotopes and contributing fluorine, boron and sulphur to solution. The addition of volcanic CO2 creates an uncommon situation for water-rock interaction, where continued dissolution of carbonate and silicate minerals along the deeper flow paths is demonstrated by the silicon/chloride ratios and strontium isotopic composition of the groundwater. These water-rock interaction processes, with the addition of cation exchange, are responsible for the development of a relatively fresh Na+HCO− 3 type water that is characteristic in parts of the deep aquifer. The study confirms the existing hydrogeological understanding of the Otway Basin and forms new conclusions regarding the history of the groundwater and the processes of flow and chemical evolution by integrating numerous lines of evidence. Significant contributions of this work which improve current scientific knowledge include these findings: the maps and cross sections of hydraulic head and electrical conductivity reveal the connected nature of flow systems within all the aquifers and aquitards; geological features can induce discharge, e.g. at contacts or faults, and recharge, e.g. volcanic eruption centres; the changes to the surface drainage system as a result of the eruption of basalt flows have affected the water chemistry and flow systems in all the underlying units; there is a lag in aquifers’ responses to sea level change and therefore future migration of the interface is expected regardless of further boundary changes; climate change has influenced surface water quality by changing the regional water balance, and therefore has affected groundwater quality; the discharge from the confined aquifer is submarine via various pathways, interaction between the groundwater and volcanic gas has occurred in the past and is ongoing, and consequently mineral dissolution persists at deep levels; the origin of high salinity of brackish groundwater in all Tertiary aquifers and aquitards is concentrated solutes from water rock interaction and cyclic deposition.