In general, leak detection rules require that a leak detection device be installed on a storage or disposal unit. Leak detection should be part of the overall system design, since secondary containment structures prohibit visual inspection of the main hazardous waste unit (whether a tank, surface impoundment, landfill, or container) for leaks. An alarm system could also be incorporated into the planning of any leak detection system. Computer leak detection programs are also available to simplify monitoring remote storage facilities. The specific leak detection system standards vary, depending on the type of unit or facility.
Hazardous Waste Tanks
A leak detection system on a hazardous waste storage tank is referred to as secondary containment. Secondary containment for tanks must include one or more of the following devices: a liner (external to the tank), which must include placement of the liner under the tank (according to guidance) to ensure that the base of the tank is not leaking; a vault; a double-walled tank; or an equivalent device as approved by EPA.
Note: Many large quantity generators (LQGs) of hazardous waste do not realize that the secondary containment requirements for tanks DO APPLY to LQG storage tanks. Small quantity generators (SQGs) of hazardous waste, however, are not subject to the same tank regulations as LQGs. While the special SQG tank requirements at 40 CFR 265.201 do not require secondary containment for SQG tanks, SQGs that choose to have secondary containment for their tanks are allowed to inspect their tanks less frequently.
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In addition, to ensure that hazardous waste stored in tanks does not contribute to air pollution, EPA requires hazardous waste storage tanks to have airtight coverings and vapor control devices. The rules are part of EPA’s organic air emissions regulations under 40 CFR 264 and 40 CFR 265, Subparts AA, BB, and CC. Note: tanks managed by SQGs are not subject to these air emissions regulations.
Many LQGs may be able to demonstrate that their equipment (because of the periodic nature of the operation) is exempt from the Subpart BB air emissions standards for equipment leaks if the equipment contains or contacts hazardous waste with an organic concentration of at least 10 percent by weight for less than 300 hours per year. However, if the generator makes this determination, identification of the equipment is required in the operating record under 40 CFR 265.1064(g)(6).
Depending on the maximum organic vapor pressure limit of the waste in the tank, differing levels of tank controls are necessary. If a tank meets certain conditions, Level 1 tank controls can be as simple as ensuring that the tank’s fixed roof (which can be removed in certain circumstances) is properly designed and installed to form a continuous barrier over the entire surface area of the hazardous waste in the tank, such that there are no visible cracks, holes, gaps, or other open spaces between roof section joints or between the interface of the roof edge and the tank wall. Openings in the fixed roof must be equipped with closure devices, or connected by a closed vent system that is vented to a control device. Level 2 tank controls are more demanding.
Hazardous Waste Containers
Containers, such as 55-gallon drums or barrels storing hazardous waste, storing hazardous waste at hazardous waste treatment, storage, and disposal facilities (TSDFs) and LQGs may also be subject to the air emissions standards previously identified. Containers at permitted TSDFs are required to have a containment system as leak detection. LQGs and SQGs accumulating hazardous waste in containers in compliance with 40 CFR 262.34 may not realize that their containers are not required to have secondary containment for their containers (although it would be a best management practice to have it).
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The containment system for containers at permitted TSDFs must be designed and operated:
- On an impervious, sloped base that is free of cracks and gaps.
- So that the containment system can contain 10 percent of the total volume of all of the containers, or the volume of the largest container.
- So that provisions are made to prevent or contain any run-on that might enter the system.
- So that any spilled or leaked waste and accumulated precipitation is removed from the sump or collection area in a timely manner.
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