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www.fueloilnews.com | FUEL OIL NEWS | SEPTEMBER 2016 39 less than 25 percent of owners reported knowledge of corrosion in their UST systems. It appears from our research that corrosion inside of UST systems could result in an increased chance of releases of fuel to the environment and subsequent groundwater con- tamination. Across the sample population, EPA observed corrosion occurring on all types of UST system metal components, including submersible turbine pump shafts, automatic tank gauge probe shafts, risers, overfill equipment like flapper valves and ball valves, bungs around tank penetrations, inner walls of tanks, and fuel suction tubes. Many of these UST system components are designed to prevent overfilling the tank or to identify leaks, and the components must be able to move and function as designed. Corrosion of some metal components could hinder their proper operation and possibly allow a release of fuel to occur or continue unnoticed. Anecdotal reports since EPA began our research suggest that other metal components in UST systems, such as tank walls, could also eventually fail by corroding completely through the metal if corrosion is not stopped. This would most likely occur in the bottom of an UST where aqueous phase and tank sludge collect. Corrosion through the bottom or wall of a tank could potentially allow fuel to leak into secondary containment areas or release to the environment. EPA has heard anecdotes of functionality failures of release prevention equipment and leak detectors, as well as failures of metal walls resulting in leaks into secondary contain- ment areas. Outside of anecdotes, however, very little verifiable data exists about how equipment functionality and integrity are being affected by corrosion in USTs storing diesel fuel. However, that information should become more available as owners become more aware of the findings of our research and corrosion in USTs storing diesel becomes more visible. Even absent a release of fuel to the environment, severe corrosion poses concerns for owners. Corrosion increases servicing and equipment maintenance costs for UST system owners. Anecdotes suggest that dispenser filters may become clogged with corrosion debris that resembles coffee grounds, resulting in filters needing to be changed more frequently. Other equipment may need to be repaired more often and sometimes may need to be prematurely replaced. The data and analyses could not pinpoint a cause of corrosion that UST owners began reporting in 2007. It appears multiple underlying factors and corrosion mechanisms could be contributing to the corrosion; one such mechanism is microbiologically- influenced corrosion (MIC). Previous research on the recent corrosion phenomenon is limited, but suggests that the reduced sulfur in diesel could be allowing microbial life to proliferate in ultra-low sulfur diesel tanks and, through MIC, cause corrosive conditions that were less possible in USTs storing low sulfur diesel. Several independent organiza- tions have produced publicly available resources that suggest following certain enhanced maintenance practices when storing diesel fuel in USTs. If followed, these practices can likely minimize MIC risks by reducing bacterial populations or preventing an environ- ment where microbial life can thrive. Key Takeaways from EP A study Corrosion of metal components in UST systems storing diesel appears to be common. Many owners are likely not aware of corrosion in their diesel UST systems. The corrosion is geographically widespread, affects UST systems with steel tanks and with fiberglass tanks, and poses a risk to most internal metal components. Ethanol was present in 90 percent of 42 samples, suggesting that cross-contamination of diesel fuel with ethanol is likely the norm, not the exception. The quality of diesel fuel stored in USTs was mixed. Particulates and water content in the fuel were closest to being statistically significant predictive factors for metal corrosion, but causation cannot be discerned. Microbiologically-influenced corrosion could be involved as hypothesized by previous research. EPA recommends owners visually inspect USTs storing diesel as part of routine monitoring. Source: EPA study released July 20, 2016