Major Aquifer Systems Research Articles

HYDRODYNAMIC ANALYSIS OF FLOW SYSTEMS AND FAULT SEAL INTEGRITY IN THE NORTH WEST SHELF OF AUSTRALIA

The North West Shelf hydrodynamics pressure database, developed as part of the North West Shelf Hydrodynamics Project, currently contains 7,780 pressure data points and hundreds of stress, temperature and water salinity data. All data have been ranked using a newly developed quality-control system. Equivalent hydraulic head mapping (fluid potential energy analysis) to interpret fluid migration pathways, hydraulic barriers and conduits was shown to be a valid technique despite lateral and vertical fluid density variations. Pressureelevation analysis identified six major aquifer systems (hydrostratigraphic units) in the regional North West Shelf. On a regional scale, the general flow direction in the North West Shelf is from the basins’ depocentres towards the onshore and upwards to the shallower aquifer systems. Compaction-driven flow is the main driving force for fluid flow in the North West Shelf. Overpressured compartments in the Carnarvon Basin are leaking, not hydraulically isolated from the regional flow field, thus generating their own local flow system. In general, fluid flow within the hydrostratigraphic units is parallel to the trend of major fault systems, which act as barriers in the horizontal plane of the aquifer. However, local-scale hydrodynamic analysis has shown that faults can act as fluid conduits between hydrostratigraphic units providing vertical hydraulic communication (e.g. Mardie to Barrow aquifers). Case studies in the Harriet, Gorgon, Griffin, Goodwyn and Vulcan areas have shown that the migration paths can be very complex due to the hydraulic nature of the faults and the presence of overpressured compartments

The Role of Hydrogeology in Petroleum Development Oman

ABSTRACT A hydrogeological study of the South Oman Salt basin in particular, and the Oman basin in general, was carried out by Petroleum Development Oman to support basin modelling. The study focused on major aquifer systems: the Tertiary Umm Er Radhuma aquifer and the Paleozoic Haima-Haushi aquifers. Temperature, water quality, radiocarbon age dating and potentiometric data was used to determine the flow, thermal and salinity regimes of the systems. The resulting models were then used to define areas where oil biodegradation due to meteoric water influx can be expected. A review of oil chemistry data confirmed that fields in these areas have the highest API gravity oil demonstrating that hydrogeological modelling can be beneficial in predicting oil quality for prospect evaluation. An additional benefit of this study was the development of a formation water resistivity model for enhancing log analysis techniques.

Assessing impacts of basin management and environmental change in the Eastern Murray Basin

The Lower Murrumbidgee groundwater model was developed to improve the understanding of the regional flow system, and to evaluate the impact of large scale land management options and climate change on the water and salt balance for the major regional aquifers within the Eastern Murray Basin (Punthakey et al., 1994). The model covers approximately 39,000 km 2 equivalent to 13% of the Murray Geological Basin, and comprises three layers. Each layer represents a major regional aquifer system, the Shepparton, Calivil and Renmark. The model was calibrated using observed potentiometric data from 1980 to 1985. Comparison of contours of observed heads and modelled heads for the Shepparton, Calivil and Renmark showed that the modelled heads matched the observed head contours closely. The Lower Murrumbidgee groundwater model has shown that large areas of the current irrigation areas and districts will be affected by rising groundwater by 2020 under the ‘Do nothing’ scenario. The ‘Deep groundwater pumping’ scenario appeared to offer the best long-term option for controlling high water tables while at the same time offering the possibility for trading existing surface water entitlements. The use of groundwater models to investigate the impacts of environmental change within the Basin such as planting trees along riverine corridors and their impact on shallow water tables in the Shepparton aquifer was investigated. The ‘Shallow groundwater pumping’ scenario appeared to control the rate of rise in water table in the Shepparton, although the disposal of large quantities of saline groundwater pumped from the Shepparton presents a major disposal problem. An increase in irrigation recharge in the Irrigation Areas and Districts, and on Private Irrigation Properties would result in unacceptably high water tables in the CIA, Wah Wah, and in the northeastern part of the model domain. Any proposal for increased irrigation would therefore have to be evaluated closely for impacts. The model can be used to provide a window into the future of likely impacts to the area under a range of scenarios. The implementation of a specific option will however depend on its economic merit to the community and the area.

Stable isotopes in the sulfate evaporites from southeastern Iowa, U.S.A.: Indications of postdepositional change

Sulfate evaporites of mid-Paleozoic age are exposed or can be found within several hundreds of meters below the surface across much of southeastern Iowa. In addition, Mesozoic (Jurassic?) evaporites have been mined from thick beds in north-central Iowa. This study reports stable isotope analyses performed on twenty-four samples, representing each of the major evaporite units in the state. Values of δ 34S in all samples are consistent with those of sulfates of the same age on the global sulfur “time line”, defined by previous investigators. Some samples, however, have δ 18O-values that are as much as 6‰ lighter than sulfates of the same age on the global oxygen “time line”. These anomalies were observed in both Devonian and Mississippian samples, but only in a small region near Ottumwa. The cause of the anomalous values is not clear, although circumstances suggest a chemical interaction with migrating fluids. In this part of Iowa. Devonian and Mississippian strata host major aquifer systems whose waters may have disturbed the isotopic compositions of the evaporites, or may have served in the past as conduits for other migrating fluids. Results of this survey suggest, therefore, that δ 34S-values of Iowa evaporites carry an undisturbed record of the isotopic composition of Paleozoic seawater, but that δ 18O has been affected by postdepositional changes and is no longer a reliable measure.

Aqueous Geochemistry of the Sand‐and‐Gravel Aquifer, Northwest Florida

AbstractThe aqueous geochemistry of the sand‐and‐gravel aquifer in northwest Florida was characterized as part of the Florida Ground‐Water Quality Monitoring Network Program, a multiagency cooperative study delineating baseline and/or background water quality for the major aquifer systems throughout the State. The aquifer is the principal source of water in northwest Florida and consists predominantly of quartz sand with smaller amounts of andesine, chlorite, calcite, kaolinite, and illite. Water from 42 wells in the sand‐and‐gravel aquifer sampled during 1986 and 1987 was characteristically low in dissolved solids (median value of 72 milligrams per liter) and of nondistinct water type, although relative concentrations of magnesium and sulfate tended to be lower than those of other major ions. Nonparametric statistical tests of major‐ion concentration variations with depth and relative distance along flow paths indicate that the water chemistry does not change significantly (0.05 significance level) as the water moves vertically and laterally through the aquifer. Mass‐balance calculations indicate that dissolved solids from rainfall and saline‐water sources each account for 13 percent of the concentration of dissolved solids in ground water. Incongruent dissolution of andesine, chlorite, and muscovite to form kaolinite accounts for 94 percent of the neutralization of the total hydrogen ion input from rainfall and from carbonic acid weathering in the subsurface. The remaining neutralization is accounted for by the dissolution of calcite.

Modelling nitrate from agriculture into public water supplies

A wide range of models and techniques are briefly reviewed within the context of the Thames nitrates study in which models were developed to assess impacts of agricultural practices on nitrate levels in the river system. Here a semi-distributed approach was adopted in which a series of component models was developed to simulate hydrological and chemical behaviour of the Thames River basin. These components included: ( a ) a daily hydrological model for the Thames basin, which included 17 tributary sub-catchments and several major aquifer systems. The model provided input flows such as tributaries, groundwater, surface runoff, effluent returns as well as abstraction flows; ( b ) a soil zone and aquifer model for calculating the nitrate concentrations of surface runoff and groundwater given a particular land-use and fertilizer application rate; ( c ) An integrated model of flow and water quality for the main river, which provided a mass balance along 22 reaches of the main river, allowed for denitrification processes and incorporated all inputs from the non-point sources derived by ( a ) and ( b ) above. Model results will be presented together with an assessment of the major problems of nitrate modelling and predictions, which occur within the hydrologically active soil zone.

Organic Carbon and THM Formation Potential in Kansas Groundwaters

Fifty wells in Kansas were sampled to determine the concentrations of total organic carbon (TOC) and trihalomethane formation potential (THMFP) associated with major aquifer systems. The mean TOC and THMFP concentrations were 1.03 ± 0.76 mg/L and 46.7 ± 39.5 μg/L, respectively; THMFP was very strongly correlated with TOC (r = 0.953). Only 8 percent of the THMFP concentrations exceeded 100 μg/L, but 56 percent exceeded 25 μg/L and 90 percent exceeded 10 μg/L, suggesting that many Kansas water utilities using groundwater might have difficulty meeting a substantially lower THM standard. Efforts to control THMs in Kansas groundwater supplies should focus on alluvial aquifers, particularly those with high concentrations of TOC, ammonium, iron, and manganese.

Trace organic compounds in groundwater: a survey of unpolluted groundwater from three major British aquifer systems

ABSTRACT In view of the increased concern about the occurrence and persistence of organic chemicals in the environment, the Water Research Centre instigated a baseline survey of trace organics in groundwater from representative cross-sections of three major British aquifer systems. A total of 32 public and private supply boreholes in selected areas of the Permo-Triassic Sandstone, Chalk, Lincolnshire Limestone and the Great Oolite aquifers have been sampled. The areas have been chosen with the aim of characterising the organic content of ‘clean’ groundwater from the confined and unconfined zones on each cross-section. The survey was designed to encompass groundwaters of varying ages, from recent recharge in outcrop areas through to ancient waters in deep confined sections. In this way, it was expected that any compounds of anthropogenic origin would be detected only in the younger groundwaters. The total organic carbon content of the groundwaters sampled was generally very low, between 0.2 and 1.4 mg/1; low levels of aromatic halogenated hydrocarbons, which are generally taken to be contaminants, were found in many of the samples at levels above 0.01 µg/1; low levels of aromatic hydrocarbons were often detected. Although the number of compounds detected averaged 20 per sample (range: 7 to 52), few were present at concentrations greater than 0.1 µg/1. Over 100 different compounds were detected altogether but only 75 could be identified positively. Of these, nine occurred in more than half of the samples. There were no obvious differences in either compound types or levels between the confined and unconfined zones of any of the aquifers. Uncontaminated groundwater examined in this survey may be typified as having a TOC level below 0.8 mg/1, and no more than four compounds (none of which are chlorinated hydrocarbons) present at levels above 0.1 µg/1.

Analytical Isolation, Separation and Identification of Mutagens from Nonvolatile Organics of Drinking Water

A general procedure has been developed for the concentration/fractionation of mutagenic residue organics from small, less than 50L, and large, to 1200L, volumes of drinking water obtained from a variety of sources. This procedure features concentration of the residue organics chromatographically by passage of the water through XAD-2 and XAD-7 resins in specially designed columns, details of which are given. The residue organics are eluted from the resins via organic solvents, followed by solvent removal and subsequent bioassay for mutagenicity. Then the residue organics are fractionated via a coupled bioassay/analytical fractionation method which progressively focuses to the bioactive constituents of the complex mixture of residue organics. In this report, results for the optimal operation and validation of the concentration system are given, using drinking water derived from an industrially polluted river system, a wilderness river system and a major aquifer system. The predominant type of mutagenesis observed for the residue organics isolated from these samples was direct-acting to the Salmonella tester strain, TA98, which was decreased by the addition of the metabolic activation system from the livers of rats previously treated with Arochlor 1254. Some TA100 direct-acting mutagenesis was observed for all samples. Fractionation of the residue organics indicated the mutagens to be nonpolar. Samples of residue organics collected over a period of a year from each type of drinking water showed no discernable pattern of mutagenesis versus season. The methodologies described in this paper provide a comprehensive approach for the concentration/isolation of residue organics from drinking water for studies to identify biohazardous compounds and to characterize these compounds biologically.

Potential New Sources of Water for Energy Resource Development in Northwestern Colorado: ABSTRACT

Northwestern Colorado contains the largest reserves of shale oil in the world and the coal beds of the area are some of the most extensive in the United States. Development of the oil shale and coal may require large supplies of water and may therefore create additional demands on the surface-water resources of the region. The availability of ground water, however, is not well known. The Eocene Green River Formation in the Piceance basin has been estimated to contain several million acre-ft of ground water that generally is chemically suitable for most uses, and the ground-water resources of all northwestern Colorado probably are much larger. Preliminary studies indicate that large quantities of water may be available in the Mississippian Leadville Limestone on the southern, western, and northern flanks of the White River Uplift. The Leadville is about 200 ft (6 m) thick, has solution openings, and is very permeable at least in places. Much of this permeability, as evidenced by the extensive paleokarst topography throughout most of western Colorado, had developed by the beginning of the Pennsylvanian Period. The Leadville yields water to at least 100 springs and probably forms a major aquifer system that would yield calcium carbonate type water to shallow wells on the flanks of the White River Uplift. The quantity of ground water in storage in the Leadville Limestone in the western one-half of the White River Uplift area m y exceed 10 million acre-ft. Exploratory drilling and testing of the Leadville Limestone to depths of 2,000 ft (600 m) are needed to evaluate the potential of this aquifer for providing large supplies of water. End_of_Article - Last_Page 568------------

The Nature and Source of Arsenic in Northeastern Ohio Ground Watera

ABSTRACTElevated arsenic concentrations were found in ground water near Canal Fulton, Ohio. The hydrologie and chemical properties of the area were studied to determine the source of the arsenic and evaluate the possibility of a similar problem occurring elsewhere. Two major aquifer systems exist within the study area: the Sharon Sandstone of the upland areas; and the outwash sand and gravel deposits of the buried valleys. Ground‐water flow is generally from the north, but local variations are caused by the Tuscarawas River valley on the south and west of the study area. Within the study area, there is no evidence for an anthropogenic source of arsenic to the ground water. Agricultural soils, abandoned underground coal mines, industrial impoundments to the north, and an abandoned industrial dump site within the study area were all eliminated as possible sources for the arsenic. The arsenic in Canal Fulton ground water is entirely inorganic, consisting of about equal parts of arsenate and arsenite. Reduction‐oxidation (redox) considerations suggest that arsenic is controlled by an adsorption equilibrium with ferric hydroxides, and that the reduction of the ferric hydroxides by a recent lowering of Eh and/or pH in the aquifer has liberated both iron and arsenic to solution. A high correlation between ferrous iron and total dissolved arsenic supports this model. It is hypothesized that Eh conditions have been lowered in the aquifer by either the recent introduction of methane gas or the deposition of a thick layer of till during the last glacial retreat. The methane gas could be leaking from deep underground storage at the site and reducing oxidized compounds. The deposition of till would have eliminated local recharge of oxygenated waters.

Application of mathematical modelling techniques to the alluvial aquifer system near Wagga Wagga, New South Wales

Abstract The central part of the Murrumbidgee River meanders across an alluvial plain which is 1.5 km to 5 km wide, and confined between low hills composed of granite and folded lower Palaeozoic rocks. Deposition commenced under humid and reducing conditions during the Miocene, and continued during Pliocene time. Oligomict quartz‐sand and gravel beds are dominant in the sequence, and are interlayered with grey to black clay and silty clay, which contain a prolific pollen fauna. During Pleistocene time, a marked reduction in rainfall and consequent change in vegetation resulted in the deposition of a widespread coarse polymict poorly‐sorted gravel associated with yellow and brown clay and silt. The quartz‐sand and gravel beds within the Pliocene deposits constitute a major aquifer system and contain low salinity water suitable for irrigation and town water‐supply purposes. Since 1968, increasing demand has been made on this aquifer system, and wells sunk for various State and Local Government bodies have a total installed capacity of approximately 1000 litres/sec. The most concentrated exploration and development has been effected east of Wagga Wagga, where a well field was constructed to provide water for a regional water supply scheme. Following a refraction seismic survey, test drilling, and mathematical simulation, four production wells were constructed. Mathematical simulation models developed on a mini‐computer were designed primarily to study the behaviour of the aquifer system in response to pumping from the Pliocene aquifers. An analytical model was used to assist in the location of production wells, and a numerical model was used, after construction of the wells, to determine what additional losses from the Murrumbidgee River would be induced by pumping them. These losses were found to correspond to approximately 90% of the pumping rate during long term pumping.