Containment Talk - 110% vs. 25 yr. / 24 hr. – Revisited, Know What is Required

As with many of my articles, today’s stems from recent interactions with Witt O’Brien’s clients. This particular issue comes up regularly, so understand what is required.

To frame up today’s discussion, let’s look at a question that several different people asked at one of our annual Environmental Protection Agency (EPA) and Spill Prevention Control and Countermeasure (SPCC) workshops several years ago.

Question: Containment freeboard requirements, do we use the 110% rule of thumb, 25-year 24-hour method, or xxx?

Today’s topic, in particular, is one that companies must contend with regularly for various reasons. Whether it be new builds, new tanks in existing tank farms that require new containment calculations, or updates to dikes that require new calculations. The conversation can yield different responses depending upon when a facility was constructed, what EPA Region it’s in, who the Professional Engineer (P.E.) is, among a host of other factors. Yes, I know this is an impossibility when dealing with regulations. Hopefully, today’s article will help shine some light and add another tool to your arsenal.

If your facility’s containment is short, here is an article I wrote a while back to help navigate the next steps: If your facility’s containment is short, how does P.E. Seal SPCC Plan?

To today’s main question, does either standard referenced in the subject line mean anything with regards to “Sufficient Freeboard”?

To start this discussion off, let’s first review what the EPA in their Spill Prevention, Control, and Countermeasures (SPCC) Guidance for Regional Inspectors published on December 1, 2013, under chapter 4.3.2 “Sufficient Freeboard” states:

“The SPCC rule does not specifically define the term “sufficient freeboard,” nor does it describe how to calculate this volume. The 1991 proposed amendment to the SPCC rule recommended the use of industry standards and data on 25-year storm events to determine the appropriate freeboard capacity. Numerous commenters on the 1991 proposal questioned the 25-year storm event recommendation and suggested alternatives, such as using 110 percent of storage tank capacity or using other characteristic storm events. EPA addressed these comments in the preamble to the 2002 amendments to the rule:

We believe that the proper standard of “sufficient freeboard” to contain precipitation is the amount necessary to contain precipitation from a 25-year, 24-hour storm event. That standard allows flexibility for varying climatic conditions. It is also the standard required for certain tank systems storing or treating hazardous waste. (67 FR 47117, July 17, 2002)

However, the SPCC rule did not set this standard as a requirement for freeboard capacity. Therefore, the use of precipitation data from a 25-year, 24-hour storm event is not enforceable as a standard for containment freeboard. In the 2002 preamble, EPA further stated:

While we believe that the 25-year, 24-hour storm event standard is appropriate for most facilities and protective of the environment, we are not making it a rule standard because of the difficulty and expense for some facilities of securing recent information concerning such storm events at this time. (67 FR 47117, July 17, 2002)

Ultimately, EPA determined that, for freeboard, “the proper method of secondary containment is a matter of engineering practice so [EPA does] not prescribe here any particular method” (67 FR 47101, July 17, 2002). However, where data are available, the facility owner/operator (and/or certifying Professional Engineer [P.E.]) may want to consider the appropriateness of the 25-year, 24-hour storm event precipitation design criteria for containment freeboard.”

Why is it important that we started here?

I've been involved in more than 2,000 SPCC Plan developments throughout my career, and thousands more have passed through the doors here at Witt O'Brien's. In most cases, the client's perception was that 110% is a written rule for containment volumes. This 110%, just as 25 yr. / 24 hr., is not a regulatory standard. However, they are both only generally accepted guiding methodologies. 

SPCC Plans written before the EPA’s 2013 SPCC Guidance for Regional Inspectors manual generally rely on 110% for dike containment, as many in industry-built containments to this “perceived requirement” as they thought it to be the rule, and not realizing it was just an engineering best practice commonly used. Subsequently, many containments around the U.S. are built to 110% of the largest tank (in addition to other displacement considerations). However, though not completely enforceable, the EPA continues to push the more conservative approach of utilizing 25 yr. / 24 hr.

So, what’s the catch?

One of the main reasons the 25 yr./24 hr. standard cannot be applied as a steadfast rule is that the number is a constantly moving target. For example, rainfall events aren’t consistent each year, so these numbers are forever changing, which, in theory, by law would require regular containment upgrades.

Similar to the EPA, Witt O’Brien’s has also moved towards recommending our clients utilize the 25 yr. / 24 hr. standard. For example, on more than one occasion, our compliance consultants have witnessed firsthand where containments failed during what is considered “normal seasonal weather”, as containments couldn’t hold rain volumes along with product releases – but 110% was met! Additionally, we strive to keep our clients within the restraints of the rule and in step with how the agencies are interrupting and enforcing their rules.

Keep in mind that in some states such as New Mexico and Arizona, 110% is overkill given the limited rainfall. Therefore, not using a blanket standard can save on cost in this case.

Thoughts moving forward:

1. New Containment Builds – Research current 25 yr. / 24 hr. numbers based on NOAA or other reputable publications, and then compare to 110% numbers. The cost should not be the determining factor. The key: ensure the source is documented in the SPCC Plan to show your reasoning in the future.
2. Existing Containments – This can be tricky; one must weigh 110%, which was likely used originally, toward the actual rain amounts in the area. This is when working closely with your P.E. becomes very important – be logical, not emotional. A great example of what I mean by that is a facility in Louisiana that had 142% containment; however, when using the normal annual rainfall amounts, they had only 75%. Meaning, yes, they could hold 110%; however, based on what the area normally received in a typical weekend rain event during the early parts of summer, their containments would not hold a release.

What did Mark Howard say? Bottom line, this is a discussion you must have with your P.E. The P.E. should take into consideration precipitation of the area and decide based upon these factors, not simply a “rule of thumb”. He emphasized the EPA’s SPCC rule is based on freeboard, not an arbitrary percentage. Moreover, if you use 110%, do not be surprised if an EPA inspector asks to see the rationale used for precipitation if not documented in the SPCC Plan. He also noted that for large footprint areas (large tank farms), 110% works due to area in many cases. However, the smaller the footprint, the less rain an area can hold.

Recapping, the SPCC rule does not dictate a standard for “sufficient freeboard.” As with most parts of the SPCC rule, it ultimately leaves the final decision with the facility owner and P.E. At the end of the day, the ultimate goal is to limit offsite impacts that affect the environment. And, frankly, let’s be honest, also come to the table with plenty of monetary expenses. Doing this requires us not to simply use a blanketed standard, i.e., 110%, but to look at the big picture; local precipitation history, topography, drainage, onsite structures, and tank volumes, among other items.

Along these lines, a similarly important discussion I addressed several years back is permeability. You can read more on this topic in the article: What’s meant by “sufficiently impervious” under the SPCC rule?

Other containment discussions, past articles:

• Age-old question: How much containment for Oil-Filled Operation Equipment? - SPCC Discussion
• Transfer Area vs. Rack Secondary Containment (SPCC Discussion)
• Draining containments under the SPCC regulations - REMINDER
• What is a “Mobile Refueler” under the SPCC Regulations?
• Double-walled tanks under the SPCC rule – Post-EPA Conference
• My containment is short, and I can’t build berm up, now what? – SPCC Plan Discussion
• Revisited: Are railcars regulated under the SPCC rule? (SPCC Discussion)

For a complete listing of archived blogs and compliance insights, click here. Past blogs cover training requirements, clarification on additional confusing elements within the above rules, and much more.

We are here to help solve your compliance questions and challenges. Need some compliance assistance, or have a question? Please email John K. Carroll III (jcarroll@wittobriens.com) Associate Managing Director – Compliance Services or call +1 281-320-9796.

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