A recent report from the U.S. Environmental Protection Agency’s (EPA) Office of Underground Storage Tanks suggests that corrosion is a widespread problem that threatens the integrity of many underground tanks storing diesel.
EPA undertook the study to gain a better understanding of the rapid and severe corrosion of metal components in underground storage tanks (USTs) storing diesel fuel. UST owners first began reporting this corrosion to UST industry servicing companies in 2007.
The following information is excerpted from the EPA report.
The major finding from our research is that moderate or severe corrosion on metal components in UST systems storing diesel fuel in the United States could be a very common occurrence. Observations suggest that corrosion may be commonly severe on metal surfaces in the upper vapor space of UST systems, an area that before 2007 was not known to be prone to corrosion. Furthermore, it appears many owners may not be aware of the corrosion, nor are they aware that corrosion, which could affect the operability of their UST systems, could already be at an advanced stage.
We observed 83 percent of the inspected tanks had moderate or severe metal corrosion. Prior to our research inspections, 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 contamination. 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.
Problems for Tank Owners
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). However, there are numerous other types of bacteria that could also be consuming chemical components of the fuel or fuel contaminants found in USTs. In addition to bacteria, there are also a number of other microorganisms that could cause or contribute to the corrosion attacks, including fungi, archaea, and eukaryotic organisms. A combination of one or more of these factors could also be responsible, but we did not test for those factors in our research.
Because only limited scientific research was available, EPA assumed from the beginning of our research that, within our research scope, it was not feasible to definitively pinpoint a cause of the corrosion. Therefore, while previous research hypotheses about the role of specific species of a genus oxidizing biofuel components were not disproven by the results of our research, validation would be speculative.
Watch the Tank
EPA recommends owners check their diesel UST systems for corrosion and take steps to ensure the proper operability of their UST systems. EPA is recommending this, because the 83 percent of USTs in the study affected by moderate or severe corrosion is a very high number. Also, most of the owners were not aware of the extent of the corrosion in their USTs, and it appears that corrosion could potentially affect equipment functionality and potentially lead to a release of fuel to the environment.
Our research provided us with key takeaways that, by increasing the knowledge around corrosion, may help prevent releases of diesel fuel from UST systems. Below we list our key takeaways.
- 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.
- MIC could be involved as hypothesized by previous research.
- EPA recommends owners visually inspect USTs storing diesel as part of routine monitoring.