Agriculture Reference
In-Depth Information
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how much ground water is being withdrawn by pumping.
The Soil Conservation Service can provide valuable information on the
geology of an area and on the potential for groundwater contamination on your
property.
Spring and fall generally are the times when the water table is closest to
the soil surface. The water table often moves downward during the summer
when evaporation and plant uptake are high and when larger than normal
amounts of groundwater are being used for irrigation and other hot weather
needs. The water table also moves downward in winter if surface water cannot
move down through the frozen soil to recharge the ground water.
The permeability of geological layers between the soil and ground water is
also important. If surface water can move down quickly, pesticides are more
likely to reach groundwater. Gravel deposits are highly permeable. They al-
low water and any pesticides in it to move rapidly downward to groundwater.
Regions with limestone deposits are particularly susceptible to groundwater
contamination, because water may move rapidly to the groundwater through
caverns or "rivers" with little filtration or chemical breakdown. On the other
hand, layers of clay may be totally impermeable and may prevent most water
and any pesticides in it from reaching the ground water.
Sinkholes are especially troublesome. Surface water often flows into
sinkholes and disappears quickly into the groundwater. If a pesticide is re-
leased into an area that drains into a sinkhole, even a moderate rain or irriga-
tion may carry some of the pesticide directly to the groundwater.
Some pesticides or certain uses of some pesticides may be classified as re-
stricted use because of groundwater concerns. The user and applicator of these
pesticides has a special responsibility to handle all pesticides safely in and near
use sites where groundwater contamination is particularly likely. Take extra
precautions when using techniques that are known to be likely to cause con-
tamination of groundwater, such as chemigation and soil injection.
When a pesticide product has been found in groundwater or has character-
istics that may pose a threat of contamination of ground water, the pesticide
product labeling may contain statements to alert you to the concern. Typical
pesticide labeling statements include:
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This chemical has been identified in limited groundwater sampling
and there is the possibility that it can leach through the soil to
groundwater, especially where soils are coarse and groundwater is near
the surface.
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This product is readily decomposed into harmless residues under most
use conditions. However, a combination of permeable and acidic soil
