SoilFacts
Using Polyacrylamide (PAM) to
Reduce Erosion on Construction
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Sediment and turbidity have the widest impact on water quality of any pollutants.
Runoff from sites where bare soil is exposed, such as construction sites or tilled farm
fields, often carries high sediment loads into receiving water bodies where some of
the sediment settles, filling channels and lakes and causing habitat destruction. One
approach to reducing this type of erosion is to use chemical treatments to augment
seeding and mulching. The chemical polyacrylamide (PAM) is well suited for erosion
control enhancement, and its use is described below.
Characteristics of PAM
PAM is a term describing a wide variety
of chemicals based on the acrylamide and
acrylate units. When linked in long chains,
these units can be modified to result in a
net positive, neutral, or negative charge
on the PAM molecule. The positively
charged, or cationic, PAMs, are not used
for erosion control because they can be
toxic to fish and other aquatic organisms
if they spill into water bodies in sufficient
concentrations. The negatively charged,
or anionic, PAMs, are much less toxic to
aquatic organisms and are widely used in
furrow irrigation agriculture. This type of
PAM is the focus of this discussion, and
all references to “PAM” are to the anionic
forms.
PAM is available as a crystalline powder
(Figure 1), an emulsion, or a solid block
or “log.” It is nontoxic to humans and
to other species in the environment.
One of the ingredients used to make
PAM is acryamide, which is a suspected
carcinogen, and as a result the PAMs
available for our uses are required to have
less than 0.05 percent free acryamide. This
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quality control allows them to be used in food
processing, drinking water treatment, and
other uses where human exposure is likely.
PAM is water soluble, but dissolves very
slowly and requires rapid agitation and
extended mixing time. Water with more than
0.1 percent dissolved PAM is often noticeably
viscous, and most PAMs have a maximum
concentration of 0.5 to 1 percent in water. A
good rule of thumb is to mix 1 pound of PAM
per 1 00 gallons of water. When dry PAM
becomes wet, it is very slippery and sticky
and can create a slipping hazard.
Erosion Control
The erosion process is initiated when a rain
droplet impacts the soil surface and dislodges
soil particles. Once overland flow begins
during a heavy or prolonged rain, these soil
particles are then washed downslope. It has
long been known that protecting the soil
by maintaining plant cover or by mulching
reduces potential erosion significantly.
Therefore, erosion control should always
begin with protecting the soil from rain
droplets and slowing overland flow by using
mulch and vegetation. PAM does not directly
protect soil from rain droplet impacts, but it
