According to the Environmental Protection Agency (EPA), subtitle C of the Resource Conservation Recovery Act (RCRA), creates a cradle-to-grave management system for hazardous waste. The purpose of this law is to ensure the treatment, storage, and disposal of hazardous waste is done in ways that human health and the environment are not harmed.
Under the RCRA the EPA regulate the design and operation for land disposal units (LDUs). There are nine types of LDUs for hazardous waste disposal:
- Surface impoundment
- Waste pile
- Land treatment unit
- Injection well
- Salt dome formation
- Salt bed formation
- Underground mine
- Underground cave
Specific regulations have been developed for the first four types of land disposal units. The following is an overview of these:
1. Hazardous Waste Disposal - Landfills
Landfills are either excavated or engineered sites where non-liquid hazardous waste is placed for permanent disposal. After it is deposited it is covered. Landfill sites are selected and designed to minimize the potential for the release of hazardous waste into the environment. Design standards for hazardous waste landfills require:
- A double liner
- Redundant, double leachate collection and removal systems (LCRS)
- A leak detection system
- Run on, runoff, and wind dispersal controls
- Construction quality assurance (CQA) program
There are limits on what may be deposited in a hazardous waste disposal landfill. For example, liquid wastes may not be placed into a hazardous waste landfill.
Hazardous waste disposal landfill operators must comply with inspection, monitoring, and release response requirements. Since landfills are permanent disposal sites and are closed with waste buried in place, closure and post-closure care and maintenance requirements include:
- Installing and maintaining a final cover
- Continuing operation of the LCRS until leachate is no longer detected
- Maintaining and monitoring the leak detection system
- Maintaining ground water monitoring
- Preventing storm water run on and runoff
- Installing and protecting surveyed benchmarks
2. Hazardous Waste Disposal - Surface Impoundments
A surface impoundment uses natural topographic depressions, man-made excavations, or diked areas for temporary storage or treatment of liquid hazardous waste. Examples include ponds, pits and lagoons such as:
- Holding ponds
- Storage pits
- Settling ponds
- Aeration pits
Hazardous waste surface impoundments are constructed using a double liner system, a leachate collection and removal systems (LCRS), and a leak detection system. To ensure they are installed and constructed properly, EPA regulations require surface impoundments to have and follow a construction quality assurance (CQA) program.
EPA regulations also outline monitoring, inspection, response action, and closure requirements for surface impoundments.
3. Hazardous Waste Disposal - Waste Piles
Waste piles are used for the temporary storage and treatment of non-containerized piles of solid, non-liquid hazardous waste.
In addition to the standard double liner and leachate collection and removal systems (LCRS), waste piles are required to have a second LCRS above the top liner. Waste piles must also have run on and runoff controls, be managed to prevent wind dispersal of waste, and they are subject to inspection, monitoring, and release response requirements.
Since waste pile are temporary they will be closed. When closing a waste pile all wastes must be removed. This includes all waste residue. Contaminated soil and equipment must be either removed or decontaminated.
4. Hazardous Waste Disposal - Land Treatment Units
Land Treatment Units use naturally occurring microbes in the soil, plus sunlight to accomplish hazardous waste decomposition and disposal. The way the land treatment unit process works is:
The hazardous waste is spread directly on the soil surface, or it is mixed it into the upper layers of the soil. Microbes in the soil, and sunlight, will decompose, degrade, transform or immobilize the hazardous constituents of the waste.
Land treatment units rely upon the physical, chemical, and biological processes naturally occurring in the soil to contain the waste. Because of this, land treatment units are not required to have liner systems or a leachate collection and removal systems (LCRS).
Before hazardous waste can be placed in a land treatment unit, operators must complete a treatment demonstration to show the unit's ability to fully treat the hazardous waste. Once it is operational, operators must monitor the unit (unsaturated zone monitoring) to ensure that all hazardous constituents are being treated adequately.
The closure of a land treatment unit is accomplished by placing a cover of vegetation over the unit and certifying that hazardous constituent levels in the treatment zone do not exceed background levels.
5. Hazardous Waste Disposal - Injection Wells
Injection wells are regulated primarily under the Safe Drinking Water Act (SWDA) and the Underground Injection Control (UIC) Program.
Congress passed the Safe Drinking Water Act in 1974. In part, it required the EPA to develop minimum federal requirements for UIC Programs, as well as other safeguards to protect public health by preventing injection wells from contaminating underground sources of drinking water.
Hazardous Waste Disposal LDU Types 6 thru 9 - Salt Dome Formations, Salt Bed Formations, Underground Mines, and Underground Caves
Salt dome formations, salt bed formations, underground mines and underground caves are used as geologic repositories. Because these types of hazardous waste disposal locations vary greatly, they are subject to environmental performance standards instead of prescribed technology-based standards such as liners, leachate collection systems and leak detection systems. The standards require that these miscellaneous types of waste disposal locations be located, designed, constructed, operated, maintained, and closed in a manner that ensures the protection of human health and the environment.