Interpretation of stereo-paired aerial photographs is NOT helpful when evaluating a site for

• A. contaminant plume migration in a confined aquifer
• B. contaminant plume migration in an unconfined aquifer
• C. surface water drainage patterns
• D. topographic features

Answer: (A)

Stereo-paired aerial photographs provide a three-dimensional view of the surface, making them excellent for mapping topography and surface drainage patterns. They let you see hills, valleys, streams, and how water moves across the landscape, which helps identify recharge areas and surface features that influence groundwater behavior at the surface. However, a contaminant plume in a confined aquifer is controlled by underground conditions—the thickness and properties of the confining layer, the hydraulic conductivity of the aquifer, and subsurface gradients or barriers. Those factors lie beneath the surface and aren’t revealed by surface stereo imagery, so this method isn’t directly useful for evaluating plume migration in a confined aquifer. For such assessments, subsurface data from boreholes, aquifer tests, and geophysical surveys are needed. In contrast, surface water drainage patterns and topographic features are exactly the kinds of information stereo photos readily provide.