Standards vary from state to state for reasons which I find impossible to explain. For example, Pennsylvania has set an iron limit of 7 mg/liter (7 ppm) on the discharge from a treatment plant. West Virginia, on the other hand, has adopted 10 mg/liter (10 ppm) in the receiving stream as a satisfactory iron level, thus giving proper credit for the dilution effect of the stream. As you all know, public hearings are currently being held in all fifty states, attempting to develop stream standards which will be satisfactory to both the states and the Federal Water Pollution Control Administration. So, we still are aiming at a moving target.
Now, let’s consider the fate of the ferrous iron and the acid in the water as it moves—miles, in many cases—from its point of formation to its point of discharge. As all of you know, substantial amounts of limestone or calcium carbonate are associated with coal deposits.
The first reaction (Equation 1)—which occurs rapidly—is the reaction of the acid with, say, limestone. Bicarbonate ion is formed and acid in the mine water is neutralized.
After, or simultaneously with neutralization of the acid, another important reaction begins. You will remember that I stated that ferrous,