movement of water and contaminants.

Chemistry Plays a Role

The characteristics of an individual pesticide affect its
ability to reach groundwater. The most important
characteristics are solubility in water, adsorption to soils,
and persistence in the environment.
Pesticides that are highly soluble in water have a
higher potential for contaminating groundwater than
those, which are not. The water solubility of a chemical
indicates how much chemical will dissolve in water and
is measured in parts per million (ppm). Chemicals which
have a water solubility greater than 30 ppm are ones
which may create problems.
A chemical's ability to adhere to soil particles,
measured by values called K_d, plays an important role.
Those which have a high affinity for soil adsorption (low
K_dvalue) are less likely to reach the aquifer. Adsorption
is also affected by the amount of organic matter in the soil
which is measured by K_oc. Soils with high organic
contents (high K_oc) are less vulnerable than those with low
organic contents (low K_oc).
Finally, how persistent a chemical is in the
environment may affects its ability to reach groundwater.
Those that persist for long periods of time may be more
likely to cause contamination than materials which
breakdown quickly. Persistence is measured by how
quickly half of a given amount of pesticide takes to
degrade. These measurements, called half-lifes, are
determined for a pesticide's degradation by water
(hydrolysis) and light (photolysis). Chemicals with an
overall estimate of half-life longer than three weeks pose a
threat to groundwater.

Table 4.7. K
Persistence Values for Selected Pesticides^{d, Koc, Water Solublility and}

persistence, lower water solubility or higher potential
for soil adsorption. The following table will assist
you with these decisions.

[!]Determine your local soil and geologic
circumstances. If you are in an area with a shallow
water table or your soil is low in organic matter or
sandy in nature you have a greater risk of
contaminating your groundwater. In these cases,
choose a pesticide that has a low water solubility and
is not persistent.

[!]Evaluate your management practices. They
may be the most important factor in determining your
risk of contaminating your groundwater. If you use
the same materials year after year or many times a
season you can increase the potential for
contamination due to the amount of pesticide in your
soil. When you apply a material also has an effect. If
you make applications during periods of high rainfall
or heavy irrigation it is more likely that
contamination may occur. Also, the water table in the
spring may be higher than at other times. Early
season applications, therefore, may pose a greater
chance for groundwater contamination. Finally, the
method of application may have an affect. Direct
injection, incorporation and chemigation all increase
the chance of contamination. If you use these
techniques, be sure to follow the procedures listed on
the material's label.

[!]The location of your wells can be important. If
your sprayer loading area or pesticide storage
building is too close to your well, the risk of
contamination may be greater. Wells used for
drinking water or other purposes should be at least 50
feet away from pesticide storage buildings and
loading areas. In the event of an accident, this
distance should prevent contamination. This
minimum distance should also be followed for field
irrigation wells. If they are too close to application
areas, contamination might occur.

[!]Check the condition of any wells in the
vicinity of sprayerloading areas, pesticide storage
areas or field applications. If they have cracked
casings you are inviting trouble. Cracks in a well
casing provide a direct point of entry for pesticide
contaminated water in the soil around the well.

[!]Use some type of anti back-flow device in any
system used for chemigation or to fill your sprayer
with water. In the event of a pump shutoff or other
event, if any back-flow into the water system occurs,
these devices will prevent pesticides from entering
your well. In New Jersey these devices are now
required for sprayers by state law. New Jersey law
requires that anti back-flow devices be placed on all
sprayer water intake systems prior to the water
entering the tank. The use of an air gap only, is no
longer acceptable.

How to Prevent Contamination of Your Ground
Water

[!]Examine the chemical properties of the pesticide that you use. If you are using materials which persist for long periods of time, are very water soluble, or are not tightly held by the soil then you may be contaminating your groundwater. You may wish to select another material that has a shorter

1998 New Jersey Commercial Tree Fruit Production Guide

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