Table of Contents
- Secondary Containment - Breaking Down the Terminology
- Massachusetts Regulatory Requirements for Secondary Containment
- Best Management Practices – Storage Tank Containment
- Best Management Practices – Fuel Pipe Containment
- Managing Rainwater Accumulation in Release Prevention Barriers
AST Located Inside Containment Dike with Rain Shield
Secondary Containment - Breaking Down the Terminology
Secondary Containment as defined by the Massachusetts Department of Environmental Protection is a set of techniques that may include impervious liners, double-walled tanks, or equivalent methods approved by the fire marshal. A containment system for double-wall tanks means the tank has an inner and outer barrier with an interstitial space that is monitored for leaks.
Owners of field erected tanks may be more familiar with the term “Release Prevention Barrier” or RPB. The containment barrier must have a dike, berm or retaining wall that is sufficiently impervious to the stored liquid and is installed under the aboveground storage tank. The regulations do not define “sufficiently impervious” but examples of acceptable materials include steel, concrete, asphalt, clay and plastic. According to the American Society of Civil Engineers a sand-organoclay mixture with at least 50% organoclay will ensure low hydraulic conductivity to gasoline and jet fuel while a mixture of at least 70% is required for diesel and fuel oil. A soil based liner system should be sufficiently impervious if it meets EPA SW-846 Test Method 9100: Saturated Hydraulic Conductivity, Saturated Leachate Conductivity, and Intrinsic Permeability. An example of permeability requirements as defined by New Hampshire’s administrative code specify containment systems must be constructed so that spills will not penetrate into the soil at a rate greater than one foot per 72 hours.
The following are examples of containment types:
- Double-walled steel ASTs
- Dike Tanks
- Horizontal Shelter Tanks
- Containment sumps
- Rooms with a sealed floor
- Elevator pits
- Containment pallets
All double-wall tanks with secondary containment must have an interstitial space monitor as specified in Massachusetts 527 CMR 9.02. The Head of the Fire Department may require release prevention barriers or dikes around exterior storage tanks that are larger than 10,000-gallons if they are concerned about risks to the environment or public health. Containment systems or equivalent protection may be required for new installations where groundwater below the facility is within Zone II (Zone of Contribution) of municipal water wells, or where private potable water wells or a water supply reservoir is within 300 feet of the tank installation. Construction plans for release prevention dikes must be reviewed and sealed by a Physical Engineer (PE).
Secondary containment is also required for new and replacement piping. Double-wall piping, impervious liners or equivalent methods approved by the Marshall may be used. This piping must be monitored for product loss by a fuel detection system. The exception is suction piping that is pitched back to the storage tank. Construction, maintenance and installation of above ground storage tanks must be done in accordance with 527 CMR 9.00 and 502 CMR 5.00.
Containment systems must retain 100% of the capacity of the largest tank within the enclosure. Uncovered tank release prevention barriers located outdoors must be able to contain 100% of the stored quantity of the largest tank. This rule takes into account precipitation (including ice, snow and rain) and storm water runoff.
It is not necessary for aboveground storage tanks located indoors to meet the same requirements if the floor is impervious and does not have floor drains or cracks that would allow fuel to flow through. The total capacity of the tank must be contained and the installation must meet NFPA 30 or 31 to be exempt from needing a containment enclosure.
An aboveground storage tank used for less than 6 months from the installation date is called a temporary tank. Temporary storage tank must meet the same requirement as permanent tanks. These include mobile or portable oil bulk storage containers.
Closed Top Dike Construction Provides Protection for the AST and Piping
Best Management Practices – Storage Tank Containment
According to EPA estimates 84 percent of facilities with aboveground storage tanks do not have spill prevention with liquid tight liners. Containment areas were originally designed to contain a hypothetical spill in a horizontal direction. Since 30 percent of oil discharges were to containment areas, having a liquid tight liner is an important step to preventing fuel from reaching the environment.
Aboveground oil storage tanks should be stored within concrete block, brick, or steel containment systems that are epoxy coated. Leaked fuel can penetrate mason and create an expensive cleanup project if you have a spill. Even untreated steel will soak up small amounts of fuel and could off-gas vapors for years. By applying an epoxy coating to all surfaces you will ensure that any leaked fuel is fully contained.
Corrosion of tank bottom plates is the most common cause of releases from ASTs. Pinholes develop and release small amounts of fuel over time. Draining, cleaning and inspecting the tank interior are the only methods of locating this type of leak when it’s installed on a solid concrete pad. You can avoid this expense by installing aboveground tanks on a grooved cement pad. The channels will allow any leaked fuel to travel out the channels, to a visible location inside the containment, so that detection can be found during monthly walkthrough inspections.
Overfills are another source of storage tank fuel releases. They are commonly caused by operator error but can also occur when an overfill device fails. In addition to the vent whistle for overfill protection we also recommend a mechanical overfill prevention device and electronic alarm. Interstitial leak detection devices are required by MassDEP regulations in double-walled tanks so an automatic tank gauge (ATG) is already included in the installation. Adding a leak detection alarm with audible and visual indicators is an inexpensive way to provide additional protection.
A Diesel Fuel Leak Captured in Secondary Containment
Containment systems are not typically present in fuel delivery areas of commercial facilities. Unloading procedures, implemented by oil delivery contractors, are required to meet the requirements and regulations established by the Department of Transportation. Absorbent and spill containment materials, present on each oil delivery truck, would be utilized in the event of an oil spill. To prevent staining or penetration of fuel, the motor vehicle dispensing surface should be coated with an impermeable surface and sized to fit the largest vehicle that will operate in this area. If asphalt is used as a spill prevention material, special measures should be taken to ensure adequate protection. A sealant applied to the asphalt will produce a surface with low permeability or asphalt can be manufactured with fine aggregate to produce a low hydraulic conductivity. Additionally, positive limiting barriers, which are capable of containing up to 5 gallons of fuel, are another good spill prevention tool.
By implementing containment system in indoor fuel storage areas and by maintaining a readily available supply of sorbent materials, facilities can minimize the potential for oil spills to reach the local sewer system or waterways.
Small emergency generator day tanks and elevator hydraulic reservoirs are not typically stored within release prevention berms, but are located in rooms that are constructed in a manner which provides adequate containment (i.e., have no floor drains and are of sufficient size to contain an oil spill). While this may meet the requirements for a Spill Prevention Control and Countermeasure (SPCC) plan it is not the best method for containing a spill. We have seen float switches on a generator day tank fail and continue to pump from the main storage tank. In this scenario, the double-wall containment doesn’t prevent a spill, because the tank will overflow outside the emergency vent pipe. Without a containment berm and fluid sensor, the fuel will continue pumping until the spill is discovered. The installation of fuel return lines with emergency vents set higher than the return piping is the best method to prevent this spill. Furthermore, a release prevention barrier with fluid sensor would contain this type of spill and set off an audible alarm.
Duplex Pump Set Installed Inside Steel Containment Tray
Piping connected to aboveground storage tanks should be pitched so that leaks to the containment system flow back to liquid-tight containment sumps with leak detection monitoring. Transfer pumps should be mounted on a concrete pad that has a metal tray to contain all leaks. Testing transfer pumps annually is an ideal method of exercising an overfill prevention switch and verifying pump seals are working properly.
Installing a gravity drain in spill prevention structures designed for storing fuel and hazardous liquids is not recommended. An employee may forget to close a gravity drain valve which would allow fuel leaks to pass directly into the environment. The most common method for removing rainwater is a manual sump pump that discharges into an oil water separator. The facility manager can visually inspect the water for an oily sheen before discharging it. Oil water separator systems (OWSS) are tanks designed with baffles and coalescers that extract oil from water. Most facilities have separator systems installed in parking areas to capture motor oil from cars so it’s likely you have one available to connect your tank containment system to.
Highland Tank Series J Oil Water Separator
A vacuum pump is another method for removing water from release prevention systems if there is no visible sheen on the water. According to EPA 40 CFR 112.7(e)(2)(iii)(B-D), drainage of rainwater from containment structures will be acceptable if:â€¨
- The bypass valve is normally closed.
- Inspection for the run-off rain water ensures compliance with applicable water quality standards and will not cause a harmful discharge as defined in 40 CFR 110.
- The bypass valve is opened, and resealed following drainage under responsible supervision. The employee discharging the water of the containment structure will remain onsite until all water is drained and reseal the valve after draining the structure.
- Adequate records are kept of such events which include names responsible personnel, date, Tank ID, and condition of contents of basin (i.e. whether or not there was oil sheen present and any methods used to absorb oily materials prior to discharge).
- If an oily sheen is observed, the inspector will insure that petroleum product is removed and properly disposed of prior to discharging water from the basin.
Rainwater or snow accumulation in diked or curbed areas can be a maintenance issue. To avoid these problems facilities will cover the storage tank containment with a roof or canopy. By installing the canopy with open sides the enclosure will not be classified as a building; however there may be other building code requirements.
Aboveground Storage Tank in Secondary Containment with Steel Roof
Steel storage tanks and containment options have changed considerably over the past thirty years. Double-wall tank construction is the lowest maintenance option of any containment system. Since the containment is not open to precipitation, the 110% capacity is sufficient to fully contain product in the event of a leak from the primary tank. By providing adequate containment you reduce your facility’s liability risk and potentially lower your insurance premiums. Secondary containment paired with overfill protection and release detection provides tank owners with optimum protection for their facilities and the environment.
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