An initial office-based survey of a representative group of 199 groundwater production wells that are completed within the upper Tertiary aquifers in the Northern Adelaide Plains Prescribed Wells Area found that 34 of these wells had abnormally high salinity levels. A field assessment of these 34 wells, using geophysical well logging, down hole camera and site surveys, was then undertaken to determine the possible causes of the high salinity levels. An extra six wells were visited during the site surveys and subsequently these were added to the list of those being probed, as it was believed that they may be contributing to the increasing salinity levels of certain of the surveyed wells. Of the total 40 wells investigated so far, 8 are considered to have leaking casings, 3 have heavily corroded casings and are considered to be potentially leaking, 13 are considered to be contaminated by high salinity plumes emanating from neighbouring wells, and one could not be tested due to the refusal of the well's owner. Produced groundwater samples from another 7 wells with suspect past salinity readings were re-analysed, with the conclusion made that the Tertiary aquifer waters being tapped in these wells should now be considered to possess native salinity. Technical conclusions concerning the contamination status of the remaining 8 wells could not be made at the time of compiling this report, due to the inability to geophysically log the wells while they were being used for irrigation. The field procedure used in this initial study has been found to be effective, and should be applied to the rest of the investigation.