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Overview of VOCs

Volatile Organic Chemicals (VOCs) are carbon-containing compounds that evaporate easily from water into air at normal air temperatures. This is why the distinctive odor of gasoline and many solvents can easily be detected. VOCs are contained in a wide variety of commercial, industrial and residential products including fuel oils, gasoline, solvents, cleaners and degreasers, paints, inks, dyes, refrigerants and pesticides. People are most commonly exposed to VOCs through the air, in food, through skin contact, and in drinking water supplies.

Sources of VOCs

VOCs enter private water supplies through accidental spills and leaks, improper storage and disposal, and industrial discharges and runoff. When VOCs are spilled or improperly disposed of, a portion will evaporate, but some will soak into the ground. In soil, VOCs may be carried deeper by rain, water or snow melt and eventually reach the groundwater table. When VOCs migrate underground to nearby wells, they can eventually end up in drinking water supplies.

What factors contribute to VOC contamination of well water?

distance between the well and the source of contamination

One factor is the distance between the well and a source of contamination. Many wells contaminated with VOCs are located near industrial or commercial areas, gas stations, landfills or railroad tracks.

The amount of VOCs dumped or spilled

Some spills are small and localized. Others occur over a long period of time, or involve large quantities of contaminants. When a large quantity of chemicals has leaked or spilled, as may occur with leaking underground tanks or industrial spills, a large geographical area may be affected.

The depth of a well

Shallow wells are often affected sooner and more severely than deep wells when contaminants have been spilled on surface soils.

The local geology surrounding the well

Groundwater covered by thin, porous soil or sand layers is most vulnerable. Dense, thickly layered soils may slow down the movement of contaminants help to absorb them.

The flow of the ground water

Another factor affecting contamination of water is time. Groundwater typically moves very slowly. A spill may take years to reach nearby wells, so wells may not be contaminated until months or years after the spill is discovered.

Health Effects of VOCs in Water

VOCs vary considerably in their toxic (or harmful) effects. VOCs are easily absorbed through the digestive tract and are then carried rapidly throughout the body by the blood. Once ingested some VOCs will collect in and cause damage to the brain, kidney, liver and nervous system. Some VOCs are known or suspected carcinogens (or cancer-causers). Safe drinking water levels called Maximum Contaminant Levels (MCL) have been established by the EPA for many VOCs. MCLs are levels of chemicals in drinking water that the EPA considers to be safe for people to drink, including sensitive people such as the very young or the elderly.

When to Test for VOCs

Testing of private well water for VOCs and petroleum products is indicated if the water has the taste or odor of gasoline or solvents. Wells should also be tested if they are within one to two city blocks (500 to 1000 feet) of a former or existing gasoline service station, or other fuel tanks.

How to Treat Wells Contaminated with VOCs?

Individuals who have received one report of the occurrence of VOCs in their private well may wish to have the well retested before taking action to treat or replace their water supply. If chemical contamination is confirmed, construction of a safe, uncontaminated well, or connection to a safe well or public water system are the best options for private well owners whose water contains VOCs at or above health risk limits. When VOCs are detected at low levels, steps may be taken to prevent further contamination by treating or removing the source. Removal of the source is not always possible, and groundwater treatment is costly and time consuming.