Fertilizer application and manure use practice in agriculture has become one of the most common sources of dissolved nitrogen species to both ground and surface waters. Nitrogen, released as nitrate (NO3-), ammonium (NH4+) and/or organic nitrogen (DON) is subject to a variety of transformation and attenuation processes in groundwater, including sorption, nitrification, denitrification, dissimilatory nitrate reduction to ammonium (DNRA), ammonification and anaerobic ammonium oxidation (anammox). Of these, only denitrification and anammox represent complete attenuation of nitrogen, releasing nitrogen gas (N2). This study examines the occurrence and mechanisms of nitrogen attenuation in groundwater affected by a manure lagoon. Lagoon effluent is in strong contrast to background water with elevated chemical constituents including NH4+ (mean = 121 mg N/L) and DON (218 mg N/L), which are transported through a fast moving groundwater flow system. The NH4+ rich plume interacts with NO3- rich background water at an interface ~3 m below ground surface. Over 100 m of groundwater transport from the source, total nitrogen (TN) was consistently reduced by 90% over two years of study. This reduction can be largely attributed to dilution (~ 80%), but the remaining 10% reflects a component of nitrogen loss due to attenuation, reflecting 32 mg N/L in attenuation and a TN degradation rate of 0.4 mg/L/day. Localized zones of nitrification and denitrification are evidenced by loss of NO3- accompanied by elevated N2O emissions. Anammox is implicated by localized enrichment of δ15N with according decreases in both NO3- and NH4+ at the plume-background interface and through corroborating microbiological study. Ammonification of DON along the flow path, something not observed in similar studies, is conjectured to have a confounding effect on a detailed isotopic investigation by introducing a second source of NH4+ that is depleted in δ15N-NH4+.

This study aims to evaluate the ability of high-frequency (450 and 900 MHz) ground-penetrating radar (GPR) to monitor the effects of an ethanol release over an existing gasoline-contaminated zone. In September 2009, 184L of denatured ethanol mixture (E95) was released into an unconfined sand aquifer directly over gasoline residuals (E10) released the previous year. GPR profiling prior to the ethanol release indicated that the residual gasoline-contaminated zone was largely confined to its initial release point. The GPR profiling performed post ethanol release observed strong shallow reflection events which propagated laterally away from the trench over a one-month period, at which point the maximum extent was established. The effects of the ethanol were also observed with the 450MHz frequency, in the form of an apparent “velocity pull-up” of a stratigraphic reflector. After the initial expansion, reduction in reflection amplitude and increasing traveltimes within the trench, were observed until the onset of winter conditions and the development of frozen soil. Over the winter the presence of ethanol inhibited the freezing process of the pore water in the contaminated zone, thus resulting in a difference in the dielectric properties of the unfrozen verse frozen zone. The unfrozen zone was significantly greater than the spatial extent of the strong reflection events that were monitored through GPR prior to winter. The spatial extent and depth of the unfrozen zone imaged by the GPR profiling was confirmed by a physical impedance depth survey. After thaw, evidence of the ethanol or gasoline was absent until mid-summer, when the water table dropped to approximately 80cm. At this point strong reflection events were again observed throughout the contaminated zone.

<p>The focus of this work was to monitor and evaluate the hydrochemical characteristics of the groundwater in the Incomati Estuary for a period of one year. The aims of this work were to evaluate the groundwater chemistry data for any spatial and temporal variations and to evaluate the suitability of the groundwater for drinking and irrigation purposes.</p>

Naturally occurring arsenic (As) in Holocene aquifers in Bangladesh have undermined a long success of supplying the population with safe drinking water. Arsenic is mobilised in reducing environments through reductive dissolution of Fe(III)-oxyhydroxides. Several studies have shown that many of the tested mitigation options have not been well accepted by the people. Instead, local drillers target presumed safe groundwater on the basis of the colour of the sediments. The overall objective of the study has thus been focussed on assessing the potential for local drillers to target As safe groundwater. The specific objectives have been to validate the correlation between aquifer sediment colours and groundwater chemical composition, characterize aqueous and solid phase geochemistry and dynamics of As mobility and to assess the risk for cross-contamination of As between aquifers in Daudkandi and Matlab Upazilas in SE-Bangladesh. In Matlab, drillings to a depth of 60 m revealed two distinct hydrostratigraphic units, a strongly reducing aquifer unit with black to grey sediments overlies a patchy sequence of weathered and oxidised white, yellowish-grey to reddish-brown sediment. The aquifers are separated by an impervious clay unit. The reducing aquifer is characterized by high concentrations of dissolved As, DOC, Fe and PO43--tot. On the other hand, the off-white and red sediments contain relatively higher concentrations of Mn and SO42- and low As. Groundwater chemistry correlates well with the colours of the aquifer sediments. Geochemical investigations indicate that secondary mineral phases control dissolved concentrations of Mn, Fe and PO43--tot. Dissolved As is influenced by the amount of Hfo, pH and PO43--tot as a competing ion. Laboratory studies suggest that oxidised sediments have a higher capacity to absorb As. Monitored hydraulic heads and groundwater modelling illustrate a complex aquifer system with three aquifers to a depth of 250 m. Groundwater modelling illustrate two groundwater flowsystems: i) a deeper regional predominantly horizontal flow system, and ii) a number of shallow local flow systems. It was confirmed that groundwater irrigation, locally, affects the hydraulic heads at deeper depths. The aquifer system is however fully recharged during the monsoon. Groundwater abstraction for drinking water purposes in rural areas poses little threat for cross-contamination. Installing irrigation- or high capacity drinking water supply wells at deeper depths is however strongly discouraged and assessing sustainability of targeted low-As aquifers remain a main concern. The knowledge gained here can be used for developing guidelines for installing safe wells at similar environments in other areas of Bangladesh. / QC 20111227

Despite being one of the largest aquifers of its type in Australia, the Burdekin River Delta (BRD) is an area that has received comparatively little research on its groundwater resources. This study conceptualises the hydrogeology of the BRD and characterises the relationships between the stratigraphic elements and the physical and chemical components of the groundwater system that influence the major governing processes. Importantly, a large amount of spatial and temporal groundwater information exists in database form, which enables an integrated conceptual model of the BRD aquifer to be developed from the key hydrogeological and hydrogeochemical relationships. Conceptualisation of the BRD aquifer is achieved by categorising four main aspects of the groundwater resource: 1. Surface characterisation; 2. Geologic characterisation; 3. Hydrogeologic characterisation; and 4. Groundwater System characterisation. The BRD is a large cuspate delta comprising a complex stratigraphy of Pleistocene to Holocene sediments of fluvial, deltaic and marine origin to a maximum depth of about 150 metres. The lower Pleistocene sediments lie predominantly below sea level and are typified by laterally discontinuous sands, silts and clays that have formed in response to fluctuating sea levels. The upper Pleistocene boundary is differentiated from the overlying Holocene sediments by a formerly exposed surface of semiconsolidated oxidised sandy clays and gravel. By contrast, the Holocene sediments comprise loose, uncompacted sequences of fluvial channel sands, interdistributary floodplain silts and marine incursions of estuarine clays and mangrove muds. The anastomosing array of fluvial sand bodies of former Burdekin River channels and levees is the setting for the main shallow aquifer units. Aquifer units of the lower Pleistocene sediments are in hydraulic connection with the Holocene units, effectively categorising the whole BRD as a single unconfined aquifer. Hydraulic gradients from both sides of the river divide the BRD into two broad flow regimes. Interpreted flow zones based on hydrograph patterns further subdivide the flow system based on seasonal recharge response to elevated river heights and flooding, and response to long-term rainfall patterns associated with La Niña episodes of the Southern Oscillation. Stable isotope data (2H and 18O) indicate that the dominant isotopic signature of groundwater throughout the BRD corresponds with intense rainfall activity, however high deuterium-excess values indicate that significant evaporation occurs prior to recharge. This infers dominant recharge by the Burdekin River that drains a massive catchment extending hundreds of kilometres inland. Direct recharge via rainfall infiltration is largely dependant on soil texture. More conductive soils are associated with the major levee systems that comprise the main shallow aquifers. Two evolutionary hydrogeochemical paths exist for the north and south sides of the river, and are constrained by the interpreted flow zones. In the south side, groundwater enters the main aquifer from river recharge and leakage out of weathered granite outcrops (exposed bedrock). Mineral hydrolysis and evaporative concentration of salts initially evolve groundwater in the weathered granite to a combination of Na-Cl and Na-HCO3 type. Leakage through clay-rich hillwash and marginal sediments causes reverse cation-exchange reactions where excess Na replaces Ca and Mg on ion-exchange surfaces. This leads to the formation of Mg,Ca-Cl type groundwaters into the southern parts of the main aquifer (supersaturated with respect to calcite and dolomite). Discharge towards the coast is characterised by seawater mixing where salinity increases with corresponding evolution to Na-Cl type waters. Recharge waters from the Burdekin River are fresh (<250mS/cm) Ca-HCO3 type, undersaturated with respect to calcite, and are easily distinguishable from the ion-exchange groundwater. In the north, only one smaller outcrop of bedrock exists, which hosts similar mineral hydrolysis reactions and base-exchange reactions. An absence of associated Na-Cl type waters means that reverse-cation exchange reactions are negligible, and so water types are predominantly Na-HCO3 type. Aquifer sands in the north are more widespread than in the south, so the fresh Ca-HCO3 recharge waters tend to dominate the overall groundwater composition, with Na-HCO3 types limited to the exposed bedrock areas. Towards the coastline, groundwater mixes with seawater towards Na-Cl type waters, similar to that observed in the south. The mangrove mud sequences that flank the coastline of the BRD are associated with high-Fe and low-pH groundwater formed by the oxidation of Fe-sulphides such as pyrite). SO4 is a product of this reaction, but does not achieve abnormally high concentrations, possibly due to the presence of sulphate-reducing bacteria. Carbonate dissolution is a possible side effect of acid sulphate generation, with possible gypsum dissolution as a secondary source of SO4. This study tested an alternative method to characterising groundwater to determine if the spatial extent of hydrogeochemical processes could be defined and comparable results achieved. This method involved discriminating discrete statistical groups of ionic ratios based on their cumulative frequency distribution. The statistical groups are bounded by critical values that distinguish different chemical processes, referred to as hydrogeochemical indicators. Various tested ionic ratios produced analogous indicators, proving their reliability as a valid method for the characterisation of groundwater chemistry. The significance of this research underlies the importance of groundwater use in the BRD as a primary source of irrigation supplies. Land use expansion and unregulated pumping pose a risk to future groundwater quality and sustainable volumes. The understanding of the relationship between the main geologic elements and the subsequent hydrogeochemical processes provides a scientific basis for conceptualising the groundwater resource. This establishes a framework for initiating future groundwater management options.

The study focuses on the adjacent Tenthill and Ma Ma catchments which converge onto the heavily cultivated alluvial plain of Lockyer Creek. Groundwater extracted from the alluvial aquifers is the primary source of water for intensive irrigation. Within the study the hydrogeology is investigated, a conceptual groundwater model produced and a numerical groundwater flow model is developed from this. The hydrochemistry and stable isotope character of groundwater are also investigated to determine processes such as recharge and evaporation. Examination of bore logs confirms the Quaternary alluvium comprises a laterally continuous gravel aquifer with an average thickness of 4.5 m, overlain by mixed sands and clays which form a semi-confining layer with an average thickness of 22 m. Variations in long term groundwater hydrographs indicate the aquifer changes from confined to unconfined in some locations as water levels drop, while bores adjacent to creek banks display a rapid response to a flood event. Pump testing of bores screened in the gravel produces estimates of hydraulic conductivity ranging from 50-80 m/day and storativity of 0.00166 which are both within realistic bounds for this aquifer material. Major ion chemistry of surface water collected during a flood is Mgdominated, similar to alluvial groundwater in the Tenthill catchment and the Lockyer plain, suggesting a strong connection between surface and groundwater in these locations. Alluvial groundwater salinity in Tenthill catchment is typically less than 3500 ìS/cm but may approach 6000ìS/cm on the Lockyer plain. By contrast Ma Ma catchment alluvial groundwater is Na-dominated with conductivity up to 12000 ìS/cm and more associated with groundwater from the underlying sandstone bedrock. Stable isotope analyses of alluvial groundwater from throughout both catchments and the Lockyer plain are compared with basalt and sandstone groundwater. A range of processes have been identified including recharge to alluvium from basalt groundwater and evaporated surface water; and alluvial-bedrock groundwater mixing at some locations. Integration of the components of the study enabled the production of a conceptual hydrogeological model of the Lockyer alluvial plain, proposing two hydrostratigraphic units; the gravel aquifer and the overlying mixed sand and clay which acts as a semi confining unit. Hydrochemical and stable isotopic evidence suggests seepage from creek channels as the dominant recharge process. A single layer groundwater flow model using MODFLOW was developed, based on groundwater extraction data, to represent flow in the gravel aquifer. The model was calibrated to transient conditions with groundwater fluctuations, incorporating both drought and flood conditions. A sensitivity analysis for each of the aquifer properties demonstrates the model is insensitive to variations within realistic bounds for the gravel aquifer material, however, the model is highly sensitive to changes in the chosen boundary conditions. Predictive simulations with several annual extraction scenarios ranging from 1.75 to 0.5 ML/ha indicate the resulting minimum saturated aquifer thickness ranges from 0.03 to 1.4 m.

Bribie Island is a large, heterogeneous, sand barrier island that contains groundwater aquifers of commercial and environmental significance. Population growth has resulted in expanding residential developments and consequently increased demand for water. Caboolture Shire Council (CSC) has proposed to increase groundwater extraction by a new borefield. Two aquifers exist within the Quaternary sandmass which are separated by an indurated sand layer that is ubiquitous in the area. A shallow aquifer occurs in the surficial, clean sands and is perched on the indurated sands. Water levels in the shallow water table aquifer follow the topography and groundwater occurs under unconfined conditions in this system. A basal aquifer occurs beneath the indurated sands, which act as a semi-confining layer in the island system. The potentiometric surface of the basal aquifer occurs as a gentle groundwater mound. The shallow groundwater system supports water-dependent ecosystems including wetlands, native woodlands and commercial pine plantations. Excessive groundwater extraction could lower the water table in the shallow aquifer to below the root depth of vegetation on the island. Groundwater discharge along the coastline is essential to maintain the position of the saline water - fresh groundwater boundary in this island aquifer system. Any activity that changes the volume of fresh water discharge or lowers the water table or potentiometric surface below sea level will result in a consequent change in the saline water – freshwater interface and could lead to saline water intrusion. Groundwater level data was compared with the residual rainfall mass curve (RRMC) on hydrographs, which revealed that the major trends in groundwater levels are related to rainfall. Bribie Island has a sub-tropical climate, with a mean annual rainfall of around 1358mm/year (Bongaree station). Mean annual pan evaporation is around 1679mm/year and estimates of the potential evapotranspiration rates range from 1003 to 1293mm/year. Flows from creeks, the central swale and groundwater discharged from the area have the potential to affect water quality within the tidal estuary, Pumicestone Passage. Groundwater within the island aquifer system is fresh with electrical conductivity ranging from 61 to 1018ìS/cm while water near the coast, canals or tidal creeks is brackish to saline (1596 to 34800ìS/cm). Measurements of pH show that all groundwater is acidic to slightly acidic (3.3-6.6), the lower values are attributed to the breakdown of plant material into organic acids. Groundwater is dominated by Na-Cl type water, which is expected in a coastal island environment with Na-Cl rainfall. Some groundwater samples possess higher concentrations of calcium and bicarbonate ions, which could be due to chemical interactions with buried shell beds while water is infiltrating to depth and due to the longer residence times of groundwater in the basal aquifer. A steady-state, sub-regional groundwater flow model was developed using the Visual MODFLOW computer package. The 4 layer, flow model simulated the existing hydrogeological system and the dominant groundwater processes controlling groundwater flow. The numerical model was calibrated against existing data and returned reasonable estimates of groundwater levels and hydraulic parameters. The model illustrated that: .. The primary source of groundwater recharge is infiltration of rainfall for the upper, perched aquifer (Layer 1). Recharge for the lower sand layers is via vertical leakage from the upper, perched aquifer, through the indurated sands (Layers 2 and 3) to the semi-confined, basal aquifer (Layer 4). .. The dominant drainage processes on Bribie Island are evapotranspiration (15070m3/day) and groundwater seepage from the coast, canals and tidal creeks (9512m3/day). Analytical calculations using Darcy’s Law estimated that approximately 8000m3/day of groundwater discharges from central Bribie Island, approximately 16% less than the model. .. As groundwater flows preferentially toward the steepest hydraulic gradient, the main direction of horizontal groundwater flow is expected to be along an eastwest axis, towards either the central swale or the coastline. The central swale was found to act as a groundwater sink in the project area.

The Gippsland Basin of southeastern Australia is the most energy-rich basin of Australia producing petroleum, gas and brown coal. Three-quarters of the Basin lies offshore and the rest onshore. The basin was initiated as a rift valley, caused by the separation of the Australian continent from the Antarctic followed by a number of tectonic events throughout the basin history. Early Cretaceous sedimentary rocks form the basement, which is in turn covered with Late Cretaceous to Recent sediment of sand, clay, limestone, and brown coal seams. The total thickness of the in-filling sediments offshore attains up to 6000 m, but onshore is up to 1200 m. There are three main acquifer systems, the Hydrostratigraphic Units 2, 4, and 7, all of which are confined. The two lower aquifer systems, Units 4 and 7, contain high temperature groundwater. It is generally agreed that the hydrocarbons offshore have been derived from terrestrial matters including brown coal and ligneous clay offshore. In the present study, the author has developed a case that hydrocarbons offshore being derived not only from the offshore source but also from onshore brown coals and coaly matter and in this hydrocarbon forming processes, groundwater has played a significant role. The Central Deep, in particular, provides favourable conditions for hydrocarbon maturation. Throughout the basin history, the Central Deep has experienced the oil window temperatures. In supporting this hypothesis, geochemical studies on groundwater, brown coal, and hydrocarbons as well as hydrodynamics are presented.

Isotopes and hydrochemistry were used to define groundwater flow systems and better understand the hydrogeological setting of the Karijini National Park within the Central Pilbara region, this study was initiated because of the near proximity of the Marandoo iron ore mine to the National Park. Based on the stable isotope composition of the water samples, two main groups of water can be identified. Groundwater is characterised by depleted δD and δ¹⁸O, suggesting no significant evaporation effect. Surface water on the other hand is more enriched in δD and δ¹⁸O due to evaporation. The relatively high concentration of Cl- compared to rainfall and depleted δD and δ¹⁸O values of groundwater indicate that recharge of the aquifers is occurring during intense rainfall events when rapid infiltration occurs. Evapotranspiration then acts to concentrate ionic species prior to recharge. The presence of CFCs in the groundwater indicates the presence of modern recharge water. Relationships between various ionic species has shown that infiltration through the Tertiary sequence and subsquent dissolution of carbonate minerals is main influence on increasing concentrations of Ca²⁺ , Mg²⁺ , HCO₃⁻ . The TDS concentration of the groundwater in the Marra-Mamba Iron Formation that hosts the Marandoo ore body is higher than most of the water bodies surrounding the mining area. This suggests that either significant chemical modification is occuring or it is recharged by different mechanisms to that of the Karijini groundwater. Relationships between the major ion concentration and catchment area, surficial Tertiary cover and distance between recharge and discharge were identified. The results show that the hydrochemistry of the water discharging at each location within the National Park can be justified by groundwater evolution within it’s own catchment.

Thesis (Ph. D.)--University of Arizona, 1991. / Includes bibliographical references (p. 174-179).