Cleaning Up Construction Runoff

Soil scientists are using a non-toxic chemical at construction sites to remove dirt from muddy stormwater before it reaches streams.


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Inside Science Buzzwords

  • Stormwater - Moving water that results from the accumulation of rain, snowfall or melting ice or snow on the ground.
  • Sediment - Tiny pieces of rock and other naturally occurring debris transported by water, wind or ice.
  • Silt - A specific class of sediment categorized by its grain size; a natural material with a texture smoother than sand but rougher than clay.
  • Polyacrylamide - A non-toxic chemical that, when added to stormwater, can cause sediment particles to stick together to form a heavy clump that sinks to the bottom of the water and can be easily removed.

Ask Inside Science

How does polyacrylamide attract soil particles when soil isn't electrically charged?

Though soil as a whole is electrically neutral, the clay in it has an electrically charged surface. In addition, soil is made up of many different elements, such as cadmium, iron and aluminum, many of which are present in the form of ions, or electrically charged particles. As the video shows in simplified form, polyacrylamide is electrically charged, and it attracts these particles and clumps together with the clay so as to remove large amounts of sediment from the water in the construction runoff.

What happens to the polyacrylamide after it clumps in water? Is it removed?

The polyacrylamide binds to the sediment particles and settles in sediment collection areas such as sediment basins. Periodically the accumulated sediment is removed and spread somewhere on the construction site as fill material. Polyacrylamide is non-toxic so this sediment is no different than any other sediment they would remove from a basin. It slowly breaks down over time through the action of microbes.