1. Quality of Water in Public-Supply Wells in Modesto, California Karen Burow, Bryant Jurgens, and Sandy Eberts National Water-Quality Assessment (NAWQA) Program

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3. Old water Young water Not to scale affected water water table 400 feet

4. Old water Young water Not to scale affected water PCE uranium nitrate 400 feet water table

5. Photo credits: Tulare Public Library; Carmen Burton, USGS Irrigated crops Dryland farming

6. Old water Young water Not to scale High Uranium (30  g/L) Low Uranium (1  g/L) 200 feet 400 feet water table

7. Old water Young water ` ` High Uranium water table High Uranium (30  g/L) Low Uranium (1  g/L) Not to scale 200 feet 400 feet

8. Old water Young water ` ` High Uranium water table High Uranium (30  g/L) Low Uranium (1  g/L) Not to scale 200 feet 400 feet

9. Implications for Management  Water providers often have to manage multiple contaminants from a variety of sources  Wellhead protection may be of benefit for well- defined sources, but of less value to widespread sources and/or natural contaminants  Necessary to understand the interaction between human activities, the physical and chemical properties of the aquifer, and the mechanics of the well itself 9

10. For more information on this study:  http://oh.water.usgs.gov/tanc/NAWQATANC.htm  Karen Burow, krburow@usgs.gov