In 1979 a landowner in the Waterloo Corner area of the Northern Adelaide Plains Groundwater Basin (Fig. 1) reported that groundwater in his well had turned saline. The well had been drilled into Aquifer 'A1 (Fig. 2) a short while previously, when salinity of the water was reported as 820 mg/1 Total Dissolved Solids (TDS). Salinity had risen subsequently, under the influence of pumping, to around 2 500 mg/1 TDS - a level unsuitable for vegetable irrigation. Inquiries showed that the area contains a number of abandoned wells, and local people say that the whole region is contaminated by saline water. It is well known that sandy gravels occurring as lenses within the alluvial sediments which overlie the deep Tertiary confined aquifers can contain water of high salinity. It is for this reason that the gap between the well casing and the hole wall must be pressure cemented to prevent saline water from percolating downwards and contaminating the deeper aquifers. It was thought that faulty well construction could be the cause of contamination in this particular case. However, similar cases have been reported from the Virginia area where geophysical investigation was carried out by McPharlin in 1979, who suggested that a possible cause could be downward leakage from the shallow aquifers as a result of heavy pumping from confined aquifer A. It was decided to test this hypothesis by drilling and testing an experimental well in the Waterloo corner area. Drilling was carried out with a cable tool rig to provide reliable samples of the strata, so that the depth and potentiometric level of each aquifer could be recorded. Well casing was first carefully pressure cemented into Aquifer A to ensure that the well would be effectively sealed from the overlying shallow aquifers. Discharge testing was carried out from open hole in Aquifer A with regular water samples taken for salinity determination by the conductivity method. The well was then deepened and casing driven into Aquifer B with a cement plug to ensure a tight seal. Discharge testing was then carried out from open hole in Aquifer B.