TOSC ENVIRONMENTAL BRIEFS FOR CITIZENS

Understanding Groundwater

Groundwater becomes contaminated when human-made substances, or in some cases naturally-occurring substances, enter the groundwater. These contaminants include the chemicals found in gasoline and oil, and in road salts, and can cause groundwater to become unsafe for human consumption. Sources of contaminants include leaking storage tanks, hazardous waste sites, uncontrolled landfills, septic systems and both illegal and legal discharges to the environment.

Contamination of groundwater also occurs through natural means. For example, arsenic and lead in rock formations can migrate into groundwater. Radon gas, which occurs from the radioactive decay of uranium, naturally found in some rocks, can also contaminate groundwater.

Groundwater becomes contaminated as contaminants move from a source, through the soil and into the groundwater. Due to the slow move-ment of water through groundwater aquifers, contaminants tend to remain in groundwater longer than in lakes and streams.

Contaminants vary in their ability to move through soil. For example, one class of chemicals, polychlorinated biphenyls (PCBs) tend to "stick" to soil particles and do not pass readily into groundwater. Gasoline components, such as ben-zene, will tend to stay in the air pock-ets in the soil but can also move into the groundwater if sufficient amounts of gasoline are present.

Back
More information
Click here for printable version of the whole fact sheet