EJScreen Indicators Overview – Underground Storage Tanks (UST)

What is the UST indicator?

The “UST indicator” measures how many underground storage tanks and UST release sites are near where people live. EJScreen presents this relative density of USTs using percentile rank, ranging from 0 (lowest) to 100 (highest) with higher scores representing higher relative densities.

Why are underground storage tanks important?

• There have been over 2.5 million USTs installed in the US, over 530,000 of which are active tanks, or currently in use. Relatedly, there have been over 570,000 reported UST releases, including 58,000 that have not reached the cleanup completed milestone. The greatest potential threat from an UST release is contamination of groundwater, the source of drinking water for nearly half of the US. UST releases can also contaminate soil, surface water, and indoor air.
• Until the mid-1980s, most USTs were made of bare steel, which is likely to corrode over time and allow UST contents (typically oil, diesel, and gasoline) to leak into the environment. Faulty installation, human error, or inadequate operating and maintenance procedures also can cause USTs to release their contents into the environment.
• Petroleum products, such as gasoline or diesel, are of primary concern as these releases can spread through the groundwater and contaminate private drinking well water, travel into public drinking water intakes, and migrate underneath building foundations, causing petroleum vapor intrusion.
• Petroleum products from UST releases can make air unsafe to breathe and water unsafe or unpleasant to drink. Benzene, a constituent of fuels, is a known carcinogen. The current maximum contaminant level (MCL) of benzene is .005 mg/L; however, the taste threshold is approximately 4.5 mg/L. This is of particular concern for the more than 15% of the US population who get their drinking water from private domestic wells which are not regulated under the Safe Drinking Water Act.

How does EJScreen create the underground storage tanks indicator?

• The UST indicator scores are provided by the EPA’s Office of Research and Development and Office of Underground Storage Tanks and can be accessed through the EPA UST Finder.
• EJScreen’s UST indicator is calculated using the sum of UST releases (multiplied by a factor of 7.7) and the number of USTs within a 1,500-foot buffered block group. That number is then divided by the area of the buffered block group in km². The 7.7 multiplier is derived from the average number of active USTs divided by the average number of UST releases (cleanups remaining). A 1,500-foot buffer is used as a radius of influence for the benzene plume migration to encompass USTs/UST releases near block groups that could potentially be affected by a release.
• For technical details on the calculations and source data, visit the EJScreen Technical Documentation.  

Moving Forward – What You Can Do

• Learn more about USTs and UST releases on the EPA Underground Storage Tanks site.
• Access the EPA’s resources on UST Regulatory Requirements, Preventing and Detecting UST Releases, and Cleaning Up UST Releases.
• Reach out to your UST State Contacts for state-specific inquiries.
• Search for UST locations and details with the UST Finder. UST Finder contains information about proximity of UST facilities and UST releases to surface and groundwater public drinking water protection areas, private domestic wells, and flooding and wildfires areas.