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Competency Area 6: Watershed hydrology AEM

PO 64. Understand the relationship between geologic conditions and the potential for groundwater and surface water contamination.

Soil layering and varying subsoil geologic conditions will significantly affect water movement. Layers that are permeable allow water to flow in any direction. However, layers that are impermeable impede water movement, and the flow of water is then redirected through more permeable layers. The depths, separation distance between layers of differing permeability, and the slope of impermeable layers all affect water movement and the direction in which it moves. Different combinations of depths and separation between layers also affect water movement in different ways, and whether water flows primarily to surface or groundwater.

Groundwater is most easily contaminated when the soil is permeable to great depths. The deep unconsolidated permeable materials of alluvial valley-fill common to Central NY and NY's Southern Tier valleys or in the Coastal Plain area of Long Island, NY are examples where leaching of nitrates and soluble pesticides can contaminate the groundwater. In contrast, an impermeable layer that lies just below the surface, such as in soils with fragipans, impedes downward water movement, and excess water is forced to move laterally (interflow). If the soil is sloping and the fragipan is not, the water is forced back to the surface. This will show up as a seep in the landscape, and the runoff from this may cause surface water contamination. These types of soils are common in the Catskills region of New York, where surface runoff contaminated with phosphorus facilitates the eutrophication of reservoirs.