Around here the perchlorate is found in water samples from wells adjacent to a onetime munitions manufacturer.
Halifax Explosives and later, Bermite Powder, both manufactured munitions, dynamite, and just about everything else that goes flash and bang. In those days residue was just dumped in a hole out yonder and all that stuff has just percolated through the soil until it reached the water table.
There are other areas however, where perchlorate contamination is widespread and unattributed to any particular source.
We do know that perchlorate turns up in breast milk and we know that it can cause irreversible problems. What we don't know is how much will it take to cause those problems in the unborn babies that the lovely young ladies in the neighborhood are carrying.
I suppose it's kind of like the problem of arsenic contamination in wells. I may decide it's not worth the hassle to deal with the arsenic in my well but I should at least have the knowledge of it's presence in my area and if I sell, the prospective buyer should know.
What is it you ask?
The bottled water industry...a gallon of their filtered water cost you more than a gallon of gasoline, yet few complain.
No doubt that "hotspots" with extremely high industrial concentrations of perchlorate should be addressed, but probably by cheaper containment methods than the current expensive pump and treat water treatment plants. Yes we now know that perchlorte shows up in human breast milk, but it is in water in the breast milk. Perchlorate reportedly does not accumulate in the human body and it is unproven that very low doses pose a significant health risk sufficient to warrant the hundreds of billions we are spending on it. In Chile nearly everyone has been exposed to perchlorate at similar levels to those in Southern California for decades with no measurably significant higher levels of mental retardation or learning deficits. WL