Sample filtering, revisited
In response to September 13th’s edition of Abandoned Mine Posts, “Filtering in the Field,” a number of experts sent us their advice and experiences about filtering water samples.
George Watzlaf, an Environmental Engineer with the U.S. Department of Energy, clarified that a 0.45 micron filter is used to separate dissolved and suspended elements, meaning the holes are about the size of a single wavelength of light! Our newsletter had also said that acid is consumed if ferrous iron oxygenates into ferric iron en route to the analysis laboratory; this is correct, but Mr. Watzlaf points out that “the oxidized ferric iron will precipitate immediately with the net effect of producing acid.”
Finally, Penn State Professor Emeritus Art Rose notes that filtering can even help determine what mine drainage treatment methods should be employed for a given discharge. If a water sample analysis still shows metals after being filtered, these metals are dissolved and treatment requires chemical treatment before a settling pond. Alternatively, if the water only contains suspended particulates, which the filter removes, a settling pond alone is sufficient.