Elise Bekele

Use of static Quantitative Microbial Risk Assessment to determine pathogen risks in an unconfined carbonate aquifer used for Managed Aquifer Recharge.

Managed Aquifer Recharge (MAR) is becoming a mechanism used for recycling treated wastewater and captured urban stormwater and is being used as a treatment barrier to remove contaminants such as pathogens from the recharged water. There is still a need, however, to demonstrate the effectiveness of MAR to reduce any residual risk of pathogens in the recovered water. A MAR research site recharging secondary treated wastewater in an unconfined carbonate aquifer was used in conjunction with a static Quantitative Microbial Risk Assessment (QMRA) to assess the microbial pathogen risk in the recovered water following infiltration and aquifer passage. The research involved undertaking a detailed hydrogeological assessment of the aquifer at the MAR site and determining the decay rates of reference pathogens from an in-situ decay study. These variables along with literature data were then used in the static QMRA which demonstrated that the recovered water at this site did not meet the Australian Guidelines for recycled water when used for differing private green space irrigation scenarios. The results also confirmed the importance of obtaining local hydrogeological data as local heterogeneity can influence of residence time in the aquifer which, in turn, influences the outcomes. The research demonstrated that a static QMRA can be used to determine the residual risk from pathogens in recovered water and showed that it can be a valuable tool in the preliminary design and operation of MAR systems and the incorporation of complementary engineered treatment processes to ensure that there is acceptable health risk from the recovered water.

Managed aquifer recharge of treated wastewater: Water quality changes resulting from infiltration through the vadose zone

Secondary treated wastewater was infiltrated through a 9 m-thick calcareous vadose zone during a 39 month managed aquifer recharge (MAR) field trial to determine potential improvements in the recycled water quality. The water quality improvements of the recycled water were based on changes in the chemistry and microbiology of (i) the recycled water prior to infiltration relative to (ii) groundwater immediately down-gradient from the infiltration gallery. Changes in the average concentrations of several constituents in the recycled water were identified with reductions of 30% for phosphorous, 66% for fluoride, 62% for iron and 51% for total organic carbon when the secondary treated wastewater was infiltrated at an applied rate of 17.5 L per minute with a residence time of approximately four days in the vadose zone and less than two days in the aquifer. Reductions were also noted for oxazepam and temazepam among the pharmaceuticals tested and for a range of microbial pathogens, but reductions were harder to quantify as their magnitudes varied over time. Total nitrogen and carbamazepine persisted in groundwater down-gradient from the infiltration galleries. Infiltration does potentially offer a range of water quality improvements over direct injection to the water table without passage through the unsaturated zone; however, additional treatment options for the non-potable water may still need to be considered, depending on the receiving environment or the end use of the recovered water.

Behaviour and fate of nine recycled water trace organics during managed aquifer recharge in an aerobic aquifer

The fate of nine trace organic compounds was evaluated during a 12month large-scale laboratory column experiment. The columns were packed with aquifer sediment and evaluated under natural aerobic and artificial anaerobic geochemical conditions, to assess the potential for natural attenuation of these compounds during aquifer passage associated with managed aquifer recharge (MAR). The nine trace organic compounds were bisphenol A (BPA), 17β-estradiol (E2), 17α-ethynylestradiol (EE2), N-nitrosodimethylamine (NDMA), N-nitrosomorpholine (NMOR), carbamazepine, oxazepam, iohexol and iodipamide. In the low organic carbon content Spearwood sediment, all trace organics were non-retarded with retardation coefficients between 1.0 and 1.2, indicating that these compounds would travel at near groundwater velocities within the aquifer. The natural aerobic geochemical conditions provided a suitable environment for the rapid degradation for BPA, E2, iohexol (half life <1day). Lag-times for the start of degradation of these compounds ranged from <15 to 30days. While iodipamide was persistent under aerobic conditions, artificial reductive geochemical conditions promoted via the addition of ethanol, resulted in rapid degradation (half life <1days). Pharmaceuticals (carbamazepine and oxazepam) and disinfection by-products (NDMA and NMOR) did not degrade under either aerobic or anaerobic aquifer geochemical conditions (half life >50days). Field-based validation experiments with carbamazepine and oxazepam also showed no degradation. If persistent trace organics are present in recycled waters at concentrations in excess of their intended use, natural attenuation during aquifer passage alone may not result in extracted water meeting regulatory requirements. Additional pre treatment of the recycled water would therefore be required.

Modeling secondary oil migration with core-scale data: Viking Formation, Alberta basin

The Viking Formation in the Alberta basin contains approximately 88.7 x 106 m3 (5.579 x 108 bbl) of recoverable oil, which migrated more than 200 km, as indicated by oil-source rock correlation. Simulating the mechanisms controlling secondary oil migration (hydrodynamics, buoyancy, and permeability heterogeneity) is beneficial for exploration, but it remains extremely difficult to predict oil occurrences. Although core-scale petrophysical data for the Viking Formation are abundant (> 69,000 core plugs), the extent of fracture permeability and permeability alteration due to diagenesis are unknown. Moreover, sampling bias may affect the permeability distribution in unpredictable ways. Numerical simulations of oil migration were conducted using the highest core-plug measurement of permeability from each borehole to obtain an upper bound on oil migration velocities. This permeability model is not appropriate for simulating stratigraphic entrapment of oil, but it does reveal that core-scale data are in the appropriate range of magnitude to have allowed significant oil migration. Regional groundwater flow was essential for charging several of the largest and most distant oil fields in the Viking Formation. Maximum core-plug permeability data are useful for modeling the extent of secondary oil migration and may have applications to fluid flow and transport modeling in other foreland settings.

Fluid pressure implications of erosional unloading,basin hydrodynamics and glaciation in the Alberta Basin, Western Canada

Abstract Subhydrostatic fluid pressures in the Alberta Basin produce groundwater flow directions that directly oppose regional topography-driven flow, but the processes that contributed to the formation of large underpressures remain equivocal. Previous studies have largely neglected the influence of glacial unloading and focused primarily on erosion; however, the amount of underpressuring simulated by basin models that incorporate long-term erosion is insufficient. Moreover, conflicting rates and timing of erosion have been postulated for the study area. To address these problems, numerical simulations of regional groundwater flow were conducted along a 700-km-wide transect to test competing hypotheses of subnormal fluid pressure generation in the Alberta Basin. Results based on modeling erosion since the Early Eocene and unloading of the Late Wisconsin ice sheet correlate betterwith fluid pressure data from Cretaceous strata than results based on rapid erosion since the Late Pliocene. The effects of glacial unloading should be considered in paleohydrologic studies where recent glaciations have occurred. Subnormal fluid pressures have significance for the timing of major groundwater flow reversals and possible implications for hydrocarbon migration and entrapment.

On-line groundwater velocity probe: Laboratory testing and field evaluation

An automated on-line instrument has been developed to rapidly measure groundwater velocity within a screened well. The instrument consists of a carbon dioxide gas tracer that is periodically delivered to a permeable chamber located within a screened well. The rate of diffusion of the tracer through the wall of the permeable chamber was rapid and the effective diffusion into the groundwater was controlled by the mass transfer limitations at the groundwater/chamber interface with gas entrainment proportional to the groundwater velocity past the chamber. By periodically delivering the gas tracer and monitoring the reduction in concentration of the tracer from the permeable chamber, the groundwater velocity was determined multiple times daily. Laboratory experiments undertaken within a calibrated flow chamber have demonstrated that the instrument can be used to accurately and reliably determine groundwater flow velocities at 3h intervals for flow rates between 25 and 300 m y(-1). Field testing of the velocity probe at multiple well locations in a sandy aquifer gave velocities consistent with another monitoring technique (passive flux meter) and site modelling.

Impact of change in vegetation cover on groundwater recharge to a phreatic aquifer in Western Australia: assessment of several recharge estimation techniques

Groundwater levels in a deep phreatic aquifer in the northern Perth Basin, Western Australia have risen between 10 and 55 cm/y over the last three decades due to the replacement of deep-rooted native vegetation with pasture and annual crops. This has sparked debate over increasing groundwater allocation limits to meet growing demand. Estimates of recent and historical rates of groundwater recharge are needed to manage the resource effectively. The Parmelia Formation, composed predominantly of sandstone, supplies domestic, stock and production bores for rural towns. Groundwater recharge was estimated using several recharge estimation techniques including the water-table fluctuation method and tracer techniques; groundwater chloride, chlorofluorocarbons (CFCs) and C-14. Vertical fluxes of soilwater under pasture and native vegetation were determined using chloride as a tracer. Apparent groundwater ages determined using CFCs and carbon-14 are generally younger than 40 years in piezometers that are screened within a few metres of the water-table from recharge under pasture, while groundwater is older than several thousand years in bores that are screened well below the water-table, and mixed waters occur at discharge areas. Recharge-rate estimates obtained under native vegetation are mainly <12 mm/y, whereas after replacement with pasture and annual crops, recharge rates are generally 20 – 50 mm/y. The presence of thick clay lenses in some areas may be responsible for observed delays of approximately one decade in the water-table response to land-use change. The study highlighted the fact that several recharge estimation techniques are required for better understanding of recharge processes and evaluation of recharge.

Transient fluid flow in the Timor Sea, Australia: implications for prediction of fault seal integrity

Abstract A variety of geochemical techniques have been used to identify vertical remigration of oil and saline formation water from Mesozoic hydrocarbon traps in the Timor Sea, Northern Australia. This transient fluid flow event is thought to have been initiated by the Mio-Pliocene fault reactivation and has a major impact on the seal integrity of fault dependant hydrocarbon traps. Significant thermal anomalies appear to accompany brine flow and together with the highly saline nature of the fluids and absence of a shallow salt source suggest that these originate from deeply buried Palaeozoic evaporites. Numerical simulations have been utilised to test this hypothesis, and in combination with the empirical observations seek to provide an enhanced prediction of fault seal integrity for future exploration.

Using treated wastewater to save wetlands impacted by climate change and pumping.

Wetlands occur where the watertable which underlies much of Perth intersects the land surface. Regional groundwater levels have been falling since the 1970s as a result of lower rainfall and increased extraction causing a loss of environmental and social values. This paper examines a scheme to add almost 2 GL/yr of treated wastewater to infiltration galleries immediately down-gradient of Perry Lakes so that the wetlands may be restored. Modelling suggest that groundwater levels would be raised up-gradient of the galleries, increasing both lake levels and groundwater supplies in the vicinity. It is not envisaged that wastewater will enter the lakes. Adding treated wastewater to nearby trial galleries has shown that phosphorus, pathogens and organic carbon are greatly reduced within 5 to 50 m. Nitrogen levels are less reduced but are similar to those in the lakes and nearby aquifer. It is estimated that the wetlands add about

Hydrogeology and hydrochemistry of the Parmelia aquifer, northern Perth Basin, Western Australia

54 m to land prices near the lakes and would add more than