In coastal southern California the drinking water supply is one of the most important and limited resources. Only 20 percent of San Diego's drinking water is locally derived while the remainder is imported from northern California and the Colorado River. To meet the steadily increasing population of the coastal San Diego area further studies are being conducted to assess the groundwater resources. Several multiple-depth monitoring-well sites installed throughout the San Diego area were used to collect groundwater samples at depth from the different formations that comprise the coastal southern Californian aquifer system. Classifications of groundwater quality were determined using a combination of total dissolved solids (TDS) concentrations, and geophysical logs. By correlating electromagnetic induction (EM) logs collected from the deepest monitoring well at each site with TDS concentrations, zones of saline groundwater were delineated in the coastal southern California aquifer. Finally, by identifying recent changes in major-ion chemistry, TDS concentrations, and geophysical logs from 2006 to 2012, zones where seawater intrusion is occurring and were distinguished from zones of groundwater "freshening" in the coastal aquifer system.