From a recent CBS CHANNEL 2/KCAL 9 report:
Heavy rains in Southern California have washed away a chemical that had contaminated a proposed luxury-home development in the San Fernando Valley.
Just days before an official cleanup project was to begin, state toxic officials have found that all the perchlorate is gone.
Last fall, inspectors found the chemical that is used in rocket fuel was in Dayton Canyon Creek at a concentration about 166 times higher than the state allows.
After the New Year's storms drenched the site with water, they found none.
Reminds one of the old saying, "the solution to pollution is dilution".