The availability of good quality groundwater from two Tertiary confined aquifers (T1 and T2) under the Northern Adelaide Plains (NAP) has encouraged the development of over 3000 hectares of horticulture in the area since the 1950s. At present, approximately 3500 ML of groundwater is extracted annually from aquifer T1, and between 13 500 and 14 000 ML from aquifer T2. Before the 1950s, the piezometric water levels of both aquifers were approximately 10 m above ground level. Most groundwater extraction in the southern part of the NAP occurs from aquifer T1, and has resulted in the formation of cones of depression in the Waterloo Corner irrigation area and the Penrice Soda Products industrial area. In the northern part of the NAP, groundwater extraction from aquifer T2 is concentrated within a relatively small area where the water salinity is below 1500 mg/L, and aquifer transmissivity is relatively low. Consequently, depletion of elastic storage and the development of a pronounced cone of depression (with up to a 75 m decline in piezometric water level in the centre of the cone) is occurring during summer. This cone of depression does not recover completely during the winter. The latter cone of depression is a result of the inability of the T2 aquifer to freely transmit water into the cone's centre where a high concentration of pumped wells are extracting large volumes of groundwater. It is evident that due to high groundwater extraction rates being practised over approximately the last 50 years, the Tertiary confined aquifers of the NAP have suffered a massive reduction in potentiometric pressure, and therefore water levels have declined steeply in the middle of the cones of depression. Currently, during summer, the base of the cone of depression in the T2 aquifer in the Virginia area reaches the depth of the top of the aquifer, creating an unconfined hydrodynamic situation. If current well pumping rates are maintained, it is expected that the continued decline in groundwater level will persist to a minor degree in the Virginia area, but that also, a major more rapid decline will begin to occur outside of the centre of the cone. As the cone progressively expands, the unconfined hydrodynamic situation will spread laterally, covering a large portion of the NAP irrigated area. Such continually declining ground water levels have and will result in reduced well yields and increased pumping costs. Produced groundwater salinity in some wells has of late increased significantly, primarily due to inter-aquifer leakage via old and poorly constructed wells. In other wells it is possibly caused by lateral flow from the surrounding saline aquifer margins. The prime source of recharge to the Tertiary aquifers is from the rainfall-fed fractured rock Precambrian bedrock aquifers in the Adelaide Hills. This groundwater mass held at higher elevation in the Hills appears to act as a source of pressurised water to the less elevated Tertiary aquifers. The hydrogeological conceptual model of the NAP indicates that effective lateral flow occurs via preferential paths through the fractured rock aquifers into the Tertiary aquifers. Several strategies to combat the declines in water level and the salinity increases within the T1 and T2 aquifers have been proposed, including: eliminating winter extraction, implementing aquifer storage and recovery (ASR) technology in the area during winter months (particularly in the centre of the cone), and using other water sources such as surplus mains water and/or treated, reclaimed sewage water from Bolivar. It is anticipated that the elective use of treated effluent water delivered by the new pipeline from Bolivar, particularly during the winter months, will reduce the irrigators' reliance on groundwater. Use of effluent water and implementation of ASR technology will be the most effective approaches in improving the condition of the basin. Several modelling scenarios to enable the selection of the most appropriate management option are now being examined.