Which data layers are commonly overlaid in GIS to support site characterization?

• A. Soils, Geology, and Receptors
• B. Population density and traffic patterns
• C. Meteorological data only
• D. Land ownership maps

Answer: (A)

Overlaying multiple data layers in GIS is used to assess how contaminants might move and where they could have an impact by combining subsurface information with potential receptors. Soils tell you how water and solutes move through the ground—permeability, porosity, sorption, and infiltration rates—which determine transport speed and pathways. Geology shows the subsurface structure—layers, faults, aquifers, and fracture networks—that shape groundwater flow directions and contaminant retardation, helping identify where plumes are likely to travel or be blocked. Receptors map the targets at risk—humans, drinking-water sources, and ecological or environmental receivers—so you can see where exposure could occur if a plume reaches them.

Putting these together highlights the priority areas for characterization and mitigation: places where a transport pathway through favorable soils and geological features leads toward sensitive receptors. Other data layers, like population density and traffic patterns, can inform social exposure in some analyses but don’t define the physical transport pathways. Meteorological data alone doesn’t reveal subsurface movement, and land ownership maps address access and rights rather than the physics of transport or the location of receptors.