 The water contains naturally occurring arsenic in excess of the maximum contaminant level adopted by the U.S. Environmental Protection Agency.The federal standard is 10 micrograms of arsenic per liter of water.In a public notice issued to residents on January 29, 2010, the District reported that the average arsenic concentration from these wells during the 4th Quarter of 2009 ranged from 12.7 to 16.1 micrograms per liter.