Interesting case of being too good - from The Sacramento Bee:
Purified wastewater triggers release of arsenic within aquifer, study finds
When it comes to the science of transforming sewage into tap water - or potable reuse - engineers say there's no question the product is clean enough to drink.
The trouble is, researchers are now learning that this drinking water may be too clean to store underground without special treatment.
A study published this week in the journal Environmental Science & Technology found that when highly purified wastewater was stored in an Orange County aquifer, the water caused arsenic to escape from clay sediments in a way that naturally infiltrating water did not.
In some instances, researchers said that arsenic concentrations exceeded the drinking water limit of 10 micrograms per liter, although the increases were only temporary and levels eventually returned to normal. None of the affected water entered the public tap system, officials said.
The root of the problem, according to researchers at Stanford University and the Orange County Water District's Groundwater Replenishment System, was that the purified, recycled water lacked the minerals that native water acquires as it soaks into the earth or flows along rivers.
"Basically the water was too pure," said senior author Scott Fendorf, a Stanford geochemist. "It was devoid of everything other than water molecules."
The solution, according to the researchers, was to add quicklime or another calcium-rich substance to the purified water before adding it to the aquifer - essentially dirtying it up a bit.
Fortunately, our aquifer is in limestone so no problems there. Tastes really good too and great for home-brewing.
