Sources of Pollutant Chemicals to the Subsurface Environment

Groundwater can become contaminated in numerous ways (Fig. 3-4). Disposal of chemicals by burying them in drums or by ponding them in lagoons (shallow depressions on the soil surface) has led to groundwater contamina- 

FIGURE 3-4 A representative water table aquifer of sand and gravel with fractured bedrock beneath it. Several paths by which chemicals can enter the subsurface environment are shown. 

Subsurface chemical pollutants also come from septic tanks, which are widely used for the disposal of nonindustrial wastewater in much of suburban and rural North America. The pollutants of concern from septic tanks include pathogens as well as nutrients such as nitrogen and phosphorus. Sometimes, other toxic materials are thoughtlessly disposed of via septic systems in 

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