What contaminates Groundwater

What Could Contaminate Groundwater?

Groundwater not only contains the hydrogen and oxygen atoms that form water (H₂O), but it also contains naturally dissolved gases from the atmosphere and dissolved minerals and gases from the soil and rock through which it passes.

The soil filters the water and absorbs and removes many contaminants though some will pass through unimpeded. But if the soil layer is thin, has high permeability, or if the water table is close to the land surface, then the soil is less likely to adequately treat contamination. The excess contaminants may pass through the zone of aeration and enter the groundwater in the zone of saturation.

If this happens, a plume forms. A plume is an underground pattern of contaminant concentrations created by the movement of groundwater beneath a contaminant source. The contaminant spreads mostly laterally in the direction of groundwater movement. The site of original contamination has the highest concentration of contaminant and the concentration decreases as it moves further away from the source.

(Modified from C.W. Fetter, 2)

"Because the top of the sand and gravel aquifer is also the land surface for most of Wisconsin, it is highly susceptible to human-induced and naturally occurring pollutants."¹ A partial list of human sources of groundwater contaminants includes:

Place of Origin	Potential Groundwater Contamination Sources
	Municipal	Industrial	Agricultural	Individual
At or Near the Land Surface	air pollution municipal waste landspreading salt for de-icing streets streets & parking lots	air pollution chemicals: storage & spills fuels: storage & spills mine tailing piles	air pollution chemical spills fertilizers livestock waste storage facilities & landspreading pesticides	air pollution fertilizers homes cleaners detergents motor oil paints pesticides
Below the Land Surface	landfills leaky sewer lines	pipelines underground storage tanks (Simmons Environmental Services, Inc., 62)	underground storage tanks wells: poorly constructed or abandoned	septic systems wells: poorly constructed or abandoned

How many possible contaminants or sources of contamination can you think of that were not included on the above list?

Portage County has made significant advances in protecting groundwater, especially in the areas of municipal wellhead protection, regulation of septic systems, removal of underground petroleum storage tanks, and proper storage and application of manure. The groundwater challenges now facing the County include quantity concerns, and quality concerns with respect to nitrate and pesticide contamination, and unused wells providing contaminants with direct access to the groundwater.⁷

To learn more about soil, click here.

(Italicized words defined in the glossary.)