Tertiary butyl alcohol plumes in southern california groundwater from leaking underground storage tank sites

Abstract

Tertiary butyl alcohol in the groundwater was evaluated using closed leaking underground storage tank sites in Southern California between 2016 and 2019. Tertiary butyl alcohol is not regulated and lacks a maximum contaminant level in California. The current level of 12 µg per liter in drinking water (notification level) is advisory and not enforceable. As high as 88% of sites during 2018–2019 fiscal year were closed with tertiary butyl alcohol higher than its notification level in groundwater. Twenty-five percent of the time, the maximum tertiary butyl alcohol concentrations in the groundwater at closure were higher than 2,300 µg per liter during 2016–2017, 7,600 µg per liter during 2017–2018, and 4,400 µg per liter during 2018–2019, respectively. The plume length of the maximum tertiary butyl alcohol increased from 649 feet in 2016 to 1,128 feet in 2019. Considering the proximity of drinking water wells to the leaking underground storage tank sites in California, this points to an increase risk of impact on the drinking water resources. Tertiary butyl alcohol remained above 12 µg/L in a substantial percentage (70% in 2016–1017, 72% in 2017–2018, and 88% in 2018–2019) of sites. Site closure practices at Los Angeles Regional Water Quality Control Board should be more stringent toward tertiary butyl alcohol contamination. Despite documented health hazards, tertiary butyl alcohol has not received sufficient attention from government agencies. The toxicological evaluation of tertiary butyl alcohol indicates significant human health concerns. Based upon the toxicological evidence, an MCL should be considered for tertiary butyl alcohol in drinking water.