Chemistry of Treatment

If you have not yet gone over the section on the Carbonate Buffering system, you should do so now.

It is a common practice to add calcium carbonate (CaCO₃) to the stream in order to increase the water's buffering capacity, or alkalinity. This is a measure of the amount of acidity the stream can absorb. By increasing this capacity, the acid in the stream is removed (eq 4).

This has a number of effects.

1. The waters of the stream are no longer toxically acid, thus life can begin to recolonize.

2. The heavy metals precipitate out, normally, effectively removing them from the aquatic environment. Aluminum will fall out of the water after the stream has increased to about pH 5.

3. The first two were positive changes; however, the aluminum that has precipitated out combines with the yellow boy. This reaction produces an iron-aluminum-sulfur-hyrdoxide complex that armors the rocks. In streams with large amounts of yellow-boy, this creates a permanent unsightly yellow-orange coating on the rocks. Otherwise, it covers the rocks in a silvery-grey coating. Either way, the coating prevents algae recolonization of the river bed.

Go on to the next stop to Form a Hypothesis about how Highland Park's rivers might be affected by Acid Mine Drainage.