Localised sea water intrusion has been identified as a potential problem particularly in the McLaren Vale Prescribed Wells Area (PWA; Martin and Hodgkin 2005). In the McLaren Vale PWA, salinity monitoring in the northeast of the Port Willunga formation suggests some sea water intrusion may be occurring (Martin 1998). The volume of sea water intrusion during 2009–10 could not be quantified due to the lack of both data and a suitable quantification approach.