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- Groundwater[remove]78
- Nitrates18
- Water15
- Water quality15
- Aquifers8
- Pesticides8
- Water resources development6
- Water-supply6
- Geological Survey (U.S.)4
- Groundwater flow4
- Hazardous wastes4
- Nutrient pollution of water4
- Arsenic3
- Environmental law3
- Government information3
- National Water-Quality Assessment Program (U.S.)3
- Volatile organic compounds3
- Agricultural chemicals2
- Agricultural pollution2
- Boring2