This Record was originally issued as a BMR Engineering Geology Technical Note dated 11 March 1977. The original document was admitted as evidence in the Canberra Coroner's Enquiry into the explosion and fire at the Center Cinema, at hearings in August 1977. Minor amendments have been made to the original. Following an explosion at the Center Cinema in Canberra City on 10 February 1978, groundwater seepage into the building was found to be contaminated with hydrocarbons. This report discussess hydrocarbon pollution of groundwater in general and the hydrogeology of Canberra City. Hydrocarbon pollution makes groundwater unfit for drinking, and gas may accumulate in buildings and constitute a fire hazard.

This Record describes the scope of the Great Artesian Basin (GAB) Automatic Data Processing System and outlines Stage 1(Data Transcription), and describes Stage 2, the checking of coded data. The subject of this record is the permanent storage, updating, and retrieval for processing of the data passed through Stages 1 and 2. The system described was developed for application to drill stem test (DST; Formation Test) data by G.E. Seidel (BMR) and then extended to suit the general GAB data by G. Krebs (BRGM).

How much easier it would be to map and quantify the key elements of the hydrological cycle if the Earth's surface was transparent! Unfortunately, this is not the case and it is this very inability to penetrate to sufficient depths to map and quantify groundwater components of the hydrological cycle that currently necessitates the integration of satellite- airborne- and ground observations. In Australia, important advances have been made in the last 3 years in quantifying key elements of the hydrological cycle. This has been achieved in part through the increased use of Landsat, MODIS, SPOT, hyperspectral, NOAA and LiDAR datasets to improve the mapping and quantification of surface water, evapotranspiration, soil moisture and recharge and discharge. However, significant limitations remain in using satellite-based platforms alone for quantifying catchment water balances, surface-groundwater interactions, groundwater resource estimation and managing groundwater dependent ecosystems. Increasingly, the need to map the key elements of the hydrological cycle to calibrate water balance models and for environmental management, is leading to the development of more holistic systems approaches, involving the integration of satellite-, airborne and ground-based techniques and measurements. One example is in the River Murray Corridor (RMC) in SE Australia, where previous attempts to assess the water needs for iconic floodplain wetland ecosystems, based largely on satellite-based measurements, did not adequately take into account sub-surface soil conditions and groundwater quality and processes. In floodplain environments such as the River Murray Floodplain, the factors that govern tree health are invariably complex, and include a wide range of biophysical and biogeochemical factors.

The Steering Committee met on 3rd June in Canberra, and one of the matters agreed upon was that a field inspection of parts of the Basin should be held for geologists and hydrogeologists working on the Project, mainly to discuss stratigraphic correlation problems and, as well, hydrogeological aspects. Detailed planning for the field inspection, scheduled to begin early in October, and preceded by a one-day seminar, was completed. Work on a preliminary groundwater model of the whole Basin at the Geological Survey of Victoria has resulted in the development of a model to the operational stage. At BMR the compilation of available geological and geophysical data has continued steadily, and by the end of the year it is expected that all bores from which stratigraphic information has been obtained will have been plotted, and preparation of structure contour maps can begin.

During the period Bureau of Mineral Resource staff completed a compilation of the 1:1 000 000 scale Cainozoic geology map and associated figures, and drawing for publication of a preliminary edition of the map was in progress. The hydrogeological phase of the Project gained momentum, with data for six 1:250 000 scale map sheets being compiled, and a program of water sampling in collaboration with participating organisations begun.

Hydrogeological investigations in two pediplain basins at Lanyon, in the southern Tuggeranong Valley of the ACT, have identified areas which require remedial drainage for urban development. The rocks of the central Lanyon area consist of faulted Silurian dectic to rhyolitic ash-flow tuffs and interbedded sediments. Significant storage and transmission of groundwater occurs in well developed sets of open tensile fractures which formed in response to at least two reversals in regional principal stress directions during epeirogenic uplift and erosional unloading. Hydrogeological parameters measured in the field and laboratory included infiltration capacities, effective proosities, and hydraulic conductivities. From these data a predictive model for drain spacings is developed for all hydrogeological populations and for any given rainfall event. Constraints on locations of drains are also identified. It is recommended that a sufficient number of bores and piezometers be preserved after urban development to adequately assess changes to the groundwater regime.

Steady progress with the first phase of the Projectcontinued. Two highlights during the period described in this report are first, the design and implementation of a preliminary groundwater model of the whole Basin, and second, the field inspection of parts of the Basin in South Australia, Victoria and New South Wales undertaken by Project workers during October 1981 mainly to discuss stratigraphic correlation problems. The Steering Committee met in Sydney on 5th November, 1981.

In this study, 3D mapping using airborne electromagnetics (AEM) was used to site a monitoring bore network in the Darling River floodplain corridor. Pressure loggers were installed in over 40 bores to monitor groundwater levels primarily in the shallow unconfined Coonambidgal Formation aquifer, deeper (semi)confined Calivil Formation and confined Renmark Group aquifers. In 2010-11, the network provided the opportunity to monitor the groundwater response to flooding of the Darling River and the replenishment of the Menindee Lakes storages, following a period of prolonged drought. In this event, the Darling River at Menindee (Weir 32) rose from 1.59m in October 2010 and peaked at 7.16m in March 2011. A synchronous rise in groundwater levels varying between 0.5-3.4m was observed in the shallow unconfined aquifer near the river. Shallow groundwater levels also declined following the flood peak. Near-river groundwater levels in the Calivil aquifer rose between 0.2-1.3m and also by 4.0 m at a site near Lake Menindee. The latter confirms lake leakage into the aquifer at this particular site, as previously inferred by the AEM data. There was also a pressure response of 0.1-0.9m evident in certain Renmark aquifer bores near the river. The monitoring confirms the importance of episodic flood events to the recharge of the alluvial aquifers, as supported by groundwater chemistry and stable isotope data. Although some of the confined aquifer response may relate to transient hydraulic loading associated with the flood, the inference is that in places there is a degree of hydraulic connectivity between the aquifers.

This report covers the period during which a joint BMR-BRGM team prepared and started the computer based simulation of the Great Artesian Basin. Geological and hydrologic data were first collected from Federal and State authorities and then processed either manually or automatically. Processed data were then used to prepare input and calibration documents, including geological documents (geometry of system) and hydrologic documents (potentiometry). The first run of the mathematical model was obtained for the initial steady-state, and results appeared very encouraging.

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