July 26, 2016 | Vol. 66, No. 14
Dear PEI Member:
The vast majority of the estimated 100,000 federally-regulated underground diesel fuel tanks in the United States may be at risk of leaking due to troubling corrosion levels, the Environmental Protection Agency (EPA) said in a 62-page report released July 20. In addition to the report, EPA also released a notice about corrosion risks in underground storage tanks (USTs) storing diesel fuel.
EPA’s research showed that 83 percent—35 of 42—of the USTs they studied exhibited moderate or severe corrosion, but less than 25 percent of owners were aware of corrosion prior to EPA’s research inspections, according to Carolyn Hoskinson, director of EPA’s Office of Underground Storage Tanks (OUST). The study concluded that corrosion inside UST systems “could result in an increased chance of releases of fuel to the environment and subsequent groundwater contamination.”
EPA found “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.” EPA’s findings will not come as a surprise to most PEI members, who were among the first to report evidence of corrosion of this sort in 2007. In fact, EPA’s report acknowledges that visual observations of the 35 USTs showing moderate or severe corrosion “were consistent with observations of corrosion reported from PEI’s 2010 industry corrosion study and CDFA’s [Clean Diesel Fuel Alliance’s] 2012 study as well as general anecdotes from the UST industry.”
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Although EPA’s research population “was geographically, materially, and operationally diverse,” the number of USTs studied represent a small percentage of USTs in diesel service across the nation, and EPA’s report acknowledges “the types of USTs and maintenance practices by owners in the research population may differ from those in the national population of USTs storing diesel. Therefore, EPA cannot predict if the presence of moderate or severe corrosion in diesel USTs across the United States will be higher or lower than identified in our research.”
The EPA study did not conduct any research into possible causes for accelerated corrosion in diesel fuel UST systems. Indeed, currently no definitive research has yielded conclusive evidence of the corrosion mechanism(s) involved. However, the combination of study results and industry field experience suggests that microbiologically-influenced corrosion (MIC) linked to the production of low molecular weight organic (e.g., acetic and glyceric) acids is a leading mechanism of corrosion in USTs. The Coordinating Research Council (CRC), a non-profit industry research organization, is in the process of evaluating proposals from contractors who would utilize controlled laboratory testing to address the unanswered questions raised by investigations and studies from EPA and other organizations. The laboratory study conducted by the CRC later this year is expected to focus on 11 potential factors influencing or contributing to accelerated corrosion. EPA will cooperate and contribute to the CRC study, according to Carolyn Hoskinson.
Until a widely-accepted solution to the problem is found, EPA’s notice recommends “actions tank owners can take now to minimize the corrosion and the associated risks while stakeholders look for a solution.” They include:
EPA’s website explains that corrosion in USTs storing fuels like diesel does not violate federal UST requirements. However, the website goes on to say that “UST owners and operators must ensure corrosion does not affect the functionality of their equipment. If UST equipment does not function as intended, it may violate the federal UST regulation or lead to releases into the environment.” EPA also states that owners and operators should contact their state implementing agencies because they may impose requirements more stringent than the federal regulations.
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The TulsaLetter (ISSN 0193-9467) is published two or three times each month by the Petroleum Equipment Institute. Robert N. Renkes, Executive Vice President, Editor. Opinions expressed are the opinions of the Editor. Basic circulation confined to PEI members.