Secondary Containment Structures for SPCC Regulated Marine Facilities

SPCC requires that all storage containers have secondary containment for the entire contents of the largest single container within the containment area, and if outside they must have sufficient freeboard to allow for precipitation.  Alternative systems are allowed.  An Alternate system might consist of a drainage trench that completely encloses the storage tanks and  arranged so that a spill would enter the drainage trench and terminate in a catchment basin.  Containment structures must be sufficiently impervious to the types of oil products stored at a facility.  Diked areas should be free of pooled oil; spills should be removed promptly.

 The volume of freeboard should be based on regional rainfall patterns. Facilities in states with large amounts of rainfall (e.g., Washington, Alaska, and Hawaii, and the Commonwealth of Puerto Rico) will require secondary containment to accommodate greater amounts of water.

Precipitation data is available from the National Oceanic and Atmospheric Administration's (NOAA) National Climatic Data Center (NCDC). 

The following table describes the most common secondary containment systems.

Types of Secondary Containment 

  •     Concrete Structures
  •     Containment Curbing
  •     Concrete Masonry Unit (CMU) walls
  •     Earthen Berms
  •     Trench and Sump Systems

Concrete Structures

Concrete containment structures are typically steel reinforced and cast in place.  Concrete structures are usually the cheapest route when constructing a permanent facility, especially where vehicle traffic is an issue.  However, keep in mind that concrete cracks.  Problems with cracks can be avoided by using ACI (American Concrete Institute) Environmental Standards, ACI 350.  

Many containment structures that we have inspected are essentially useless, and many do not meet regulations leaving the owner in a risky position.  Even some containment structures made out of concrete that look good on the out side are worthless for containing the liquids they were intended to hold because of cracks.   In containmentconcrete pour.jpg (12639 bytes) structures, the amount of cracking that is normally permitted in a standard structure or ordinary pavement may constitute a significant failure if it occurs in a containment structure.  As a result, alternative concrete design and construction standards which have been developed specifically for environmental concrete structures should be applied, ACI 350.  These alternative standards are not included in typical engineering design curricula and, therefore, are widely unknown by most site design engineers.    Building it right the first time will save you money over the long term.

A common misconception is that large, monolithic concrete pours which minimize the number of construction joints will result in improved containment integrity.  In fact, studies of these large, monolithic pours have demonstrated a reduced containment integrity due to shrinkage cracking during the concrete cure and differential settlement after the concrete has cured.

  • Conventional concrete is not totally impervious to liquids including petroleum; any spill left inside a concrete containment area may eventually penetrate the concrete and could contaminate groundwater sources.  Concrete sealants and coatings may used.  

  • The expansion and contraction of piping which runs through concrete containment walls can create areas of weakness and potential leaks.
  • Grout or sealants in expansion joints requires maintenance to prevent weak points, which may allow petroleum penetration.   Grout and sealants should be selected to be resistant to the stored material.

Containment Curbs

 

Containment curbs work well in outside areas and in areas where trucks or other vehicle traffic is present.  

Containment curbs are similar to speed bumps and are constructed of concrete.  They can also be easily installed on existing paving.  
  • Since the area is usually larger, they fill up with rainwater more rapidly than higher containment or walled areas.
  • Collected storm water must be managed.

Concrete Masonry Unit (CMU) walls

CMU or  block walls are also commonly used for containment structures.   CMU walls should be constructed on level concrete paving to avoid cracks in mortar between the blocks that destroys the integrity of the wall.

In addition CMUs are very porous and they do not form liquid-tight seals between mortared joints.  A sealant or coating is recommended on all CMU containment walls.

The open top of the blocks should also be sealed.  Water and ice penetrate the blocks and can eventually break them apart.

Earthen Berms

Earthen berms containing clay or bentonite mixtures are commonly used at very large oil storage facilities and in oil field operations.  Earthen berms are subject to erosion and require frequent rebuilding.  Sandy soil does not effectively contain oil spills; groundwater contamination may result.  Impervious liners of clay or synthetic membranes may be required to contain oil spills.

Vegetation inside bermed areas is a fire hazard and restricts the operator's ability to detect spills or defective equipment and should not be allowed.

Trench and Sump Systems

Trench and sump systems are below-grade containment structures typically covered with metal grates and installed in concrete paved areas and constructed of concrete with a liner or sealant..  

Earthen trenches are not recommended and  have the potential for groundwater contamination unless constructed with appropriate materials and lined.  

Trenches must be properly constructed are supported or they will deteriorate quickly, especially in traffic areas.  

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