Are The Dredge Spoils Contaminated?

And people ask why is everything so expensive...because our opponents force us to spend money on items that we are forced to address.....

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I've conferred several times with Tomas Roa, who is vice president for sales and manufacturing at Soil Net, LLC.  Here is some additional discussion of the Wisconsin State Laboratory of Hygiene memo dated December 2 that we sent you yesterday.

To summarize the results presented:

1. The test for aquatic toxicity characterization was done using standard protocol on two aquatic species, Ceriodaphnia dubia and fathead minnows.  The result was that the median lethal concentration, LC50, was greater than a concentration of 4 g/L of Soil Net TRIPAM in water. 

2. Because it was physically impossible to increase the concentration of the polymer solution due to the high viscosity that the polymer would produce, the laboratory calculated a half maximal effective concentration for the polymer solution, EC50, with effectiveness defined as the limitation of movement and 50% of the test population of Daphnia and fathead minnows.  The result of this the EC50 was 1230 mg/L for Daphnia and 1370 mg/L for fathead minnows, for TRIPAM dissolved in water.

How do these results apply to the PAM powder application to dredge spoil sediment proposed for this project?

1. The polymer applied to the sediment surface will have a very strong tendency to bind with soil particles and not dissolve into the water column, because of the binding of the anionic charge of the polymer and the cationic charge of the sediment particles.  That is the main characteristic of the polymer employed in its use as an erosion control agent.  The polymer will adhere to the soil particles in the sediment much more than it will tend to dissolve into the water that may appear above the sediment surface.

2. The proposed surface soil application rate of 54 pounds per acre corresponds to 0.56 grams of polymer per square foot.   In order for the polymer in the sediment to even come near to the water solution EC50 of approximately 1.4 g/L, approximately 1/3 of a liter of water would need to be in permanent contact with one square foot of sediment surface (corresponding to an inch or two of water above the soil), without mixing or greater water depths (very unlikely at this location).  Even more importantly, even approaching the EC50 concentration would require complete dissolution and transfer of the polymer from the sediment to the water above the sediment, which will not happen due to the bonding of the polymer to the soil particles.

3. Note that the 54 pounds per acre application rate is based on performance in standard tests (ASTM and Wisconsin DOT) for control of soil erosion in a sloped soil test plot subject to high rainfall rates.  The test procedure is designed to produce a lot of raindrop impact energy at the soil surface that could cause soil particle detachment.  This application rate is much, much lower than application rates that would even approach the EC50 water column concentrations to matter what the circumstances.

Based on this discussion of the results of the Wisconsin State Laboratory of Hygiene testing, it is our opinion that the TRIPAM polymer will not endanger the environment in this application.