Soil Facts:  Chemical Treatment to Control Turbidity on Construction Sites
(McLaughlin, R.A. Professor and Soil Extension Specialist, Department of Soil Science, North Carolina State University)

"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." 
"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."

Polyacrylamide, PAM, is a term describing a wide variety of chemicals based on the acrylamide unit.  PAM is available as a crystalline powder, an emulsion, a solid block, or effervescent tablets.  It is non-toxic to humans and other species in the environment.  PAM is a flocculant used to cause the small, or fine, suspended  sediments to stick together, forming flocs.  Flocculating the sediment how we achieve cleaner water in a very short amount of time.