Chronic ingestion of water containing elevated levels of arsenic can cause a variety of health problems, including skin, lung, bladder, and kidney cancer, and skin discoloration and thickening.
In 2006 the U.S. Environmental Protection Agency lowered the Maximum Contaminant Level for arsenic from 50 to 10 μg/L for public-water systems and newly constructed domestic wells. Several community water systems in Maryland, particularly in Southern Maryland and the Delmarva Peninsula, were known from previous sampling to have ground-water arsenic concentrations that exceed the new standard, especially in the Aquia and Piney Point aquifers.
Arsenic in the Coastal Plain aquifers of Maryland (MGS Report of Investigations 78)
Interactive map of arsenic in the Aquia and Piney Point aquifers
Arsenic in Drinking Water (U.S. Environmental Protection Agency)