The casings of abandoned wells eventually develop leaks, which, if not properly plugged, can allow pollutants to reach freshwater aquifers that supply drinking water. Sources of pollutants include brine ponds, landfill sites, agricultural activities, industrial activities, illegal disposal sites, or accidental spills. The problem is particularly acute in regions where there are old petroleum fields or where water wells have been extensively used for agricultural irrigation. Even urban areas can contain wells that were abandoned and concealed during development.
White symbols represent wells located on aerial photographs.
The aeromagnetic data have been corrected for latitude-dependent effects under the assumption that all induced magnetization is parallel to the regional magnetic field. This correction brings most anomalies directly over their sources. There is good correspondence between the wells and the positive magnetic anomalies. Positive anomalies that do not correspond to identified wells may be due to tanks, metal buildings, or concealed wells. Wells that do not correspond to positive anomalies may be uncased.