Figure 2From: Modeled nitrate levels in well water supplies and prevalence of abnormal thyroid conditions among the Old Order Amish in Pennsylvania Principle aquifers in the three study area counties in southeastern Pennsylvania. Data from Principal Aquifers of the 48 Conterminous United States, Hawaii, Puerto Rico, and the U.S. Virgin Islands: U.S. Geological Survey. Madison, WI; 2003Back to article page