Common Causes
Dissolved gases in water (methane, ethane, carbon dioxide) from natural sources or from mining/gas drilling. There are no standards for these gases. Methane concentrations above 28 mg/L are most likely to cause these symptoms.
Possible Solutions
Continue routine testing of methane if concentration is below 7 mg/L. Install vented well cap above about 7 mg/L and use aeration system for higher concentrations (above about 28 mg/L).