What are the sources of groundwater contamination and how can it be remediated?

Sources include: industrial discharges, agricultural runoff (nitrates, pesticides), septic tanks, landfill leachate, underground storage tank leaks, and saltwater intrusion. Remediation methods: pump-and-treat extracts contaminated water for surface treatment; air sparging introduces air to volatilize contaminants; bioremediation uses microorganisms to degrade pollutants; permeable reactive barriers treat groundwater in-situ; and soil vapor extraction removes volatile organics. Method selection depends on contaminant type and site hydrogeology.