Soil Facts
Chemical Treatment to Control
Turbidity on Construction Sites
■ When soil is exposed during construction activities, runoff that occurs during
storm events tends to pick up soil particles and carry them to the nearest body
of water. Larger particles, such as pebbles and sand, quickly settle to the bottom
once the flow rate slows.
Figure 1. A pond adjacent to a construction site shows the effects of turbidity.
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However, clays and fine silts settle much more
slowly and tend to stay suspended. These
suspended particles result in turbidity that can
travel many miles in streams or keep ponds
and lakes looking muddy for a long time after
a storm (Figure 1).
Turbidity reduces the productivity of the
affected waters, decreases their recreational
value, and increases treatment costs for indus¬
trial or drinking water plants. Several chemi¬
cal treatment options are available to reduce
turbidity in impounded water, and they are
described here.
PAM, gypsum, and alum
Polyacrylamides, or PAM, is a term describ¬
ing a wide variety of chemicals based on the
acrylamide unit. When linked in long chains,
some portion of the acrylamide units can be
modified to result in a net positive, neutral, or
negative charge on the PAM molecule. The
positively charged, or cationic, PAMs, usually
are not used for turbidity control because they
can be toxic to fish and other aquatic organ¬
isms if they enter water bodies in sufficient
concentrations. The negatively charged, or
anionic, PAMs, are much less toxic and are
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