This section describes the off-site disposal categories in Taking Stock Online that, to the extent possible, represent the waste disposal practices employed by North American industrial facilities and reported to each country’s PRTR program. It also provides information on the risks associated with some of these disposal practices.
The selection or use of a given waste disposal practice depends on various factors such as the existing regulatory framework, the type of industry and the characteristics of the waste generated. Not all waste types generated by industrial activities are hazardous (for example, as described in section 2.3.3, certain substances on the US TRI list are not considered to be hazardous as defined under the Resource Conservation and Recovery Act, the legislation that regulates hazardous waste). However, as described in this section, many waste streams have at least one hazard characteristic (i.e., they are toxic, inflammable, etc.). In the absence of other means of managing waste, the selected disposal method must consider the need to prevent negative impacts on human health or the environment.
Disposal in landfills or surface impoundments
This category includes a wide variety of containment practices and reflects key differences among the three countries relative to terminology, definitions, and related regulations. For the purposes of this report, the terms “landfill,” “surface impoundment,” and “controlled confinement” refer to sites or installations intended for the disposal of hazardous waste and designed to prevent releases of hazardous substances to the environment, subject to standards and regulations specific to each country.
For example, in the United States, surface impoundments are very similar to landfills in that both are either a natural topographic depression, excavation, or diked area and require a liner, leachate, and groundwater monitoring system. However, surface impoundments are generally used for temporary storage or treatment, whereas a landfill is designated for final waste disposal. Nevertheless, if a surface impoundment cannot be “clean-closed” (i.e., removing or decontaminating all wastes), the wastes left in place are stabilized, free liquids are removed, and a cap or cover is placed on top of the waste. The owner/operator must take precautions for a set period following closure, known as post-closure care.[12]
In Canada, disposing of waste substances in a regulated surface impoundment is also permitted. For example, tailings (the residual materials remaining after minerals or other mined materials have been processed) are disposed of in tailings management areas, which consist of dams and dikes designed to store tailings from oilsands production and other mining operations. These sites are seen as part of a comprehensive management system and represent the final stage in the hazardous waste treatment and/or management process, during which hazardous waste is confined or subject to long term control, for as long as it remains hazardous (CCME 2006).
In Mexico, surface impoundments are not regarded as a final waste disposal method and a distinction is made between “controlled confinement” and “landfills.” In effect, the regulation of confinement sites for hazardous waste control and neutralization is stricter than the regulation of landfills intended for residential and special management waste (with the latter regulated less stringently as regards controlling the substances and types of waste deposited therein). As explained in section 2.3.3, the regulation and control of the disposal of hazardous waste is the responsibility of the General Directorate for Comprehensive Management of Hazardous Materials and Activities (Dirección General de Gestión Integral de Materiales y Actividades Riesgosas—DGGIMAR), as disposal is considered one of the stages or activities in the comprehensive management of hazardous waste. Thus, hazardous waste regulation is parallel with and independent of the regulation of PRTR listed substances.
Hazardous waste management in Canada is a shared responsibility of the federal and provincial/territorial governments. National data from 2016 indicate that 14.7 million of the 24.9 million metric tons of solid waste (both hazardous and non-hazardous materials) generated and sent for disposal were from non-residential activities (Statistics Canada 2021; Government of Canada 2018). This waste includes materials generated by primary and secondary manufacturing sectors, as well as by the retail sector, construction projects, offices, and institutions such as schools and hospitals, and accounts for 59% of the waste disposed of (mostly in landfills, with a small amount incinerated).
In the United States, according to the data available from the 2019 biennial report of the Resource Conservation and Recovery Act (RCRA), which principally concerns waste generated by large scale industrial facilities (not including non-hazardous industrial waste), over 34.9 million tons of hazardous waste were reported in 2019. According to estimates for the 2001–2017 period, over 16 million tons were disposed of in or on land, including 4% to 10% in landfills or surface impoundments and at least 90% by means of underground injection (EPA 2021f, h).[13]
In Mexico, PRTR listed substances and mixed waste must undergo stabilization (and thus, the companies that perform this treatment are the ones identified in the PRTR reports). However, when these PRTR listed substances are treated and mixed with other substances and waste, traceability is lost when they are transferred to their final destination, such as a controlled confinement site.[14]
According to the data for the 2000–2017 period, disposal of hazardous wastes in confinement sites accounted for 8.1% (1.7 million tons) of Mexico’s authorized and installed capacity for hazardous waste recycling, reuse, treatment, incineration, and confinement activities (Semarnat 2019). It is important to highlight the fact that the authorization for confinement activities is granted to only three companies (Semarnat 2020), which raises the question of whether there is sufficient infrastructure to provide sound waste management solutions to the range of generators.
The regulatory requirements for hazardous waste disposal facilities vary among the three countries. Nevertheless, there does exist a minimum of design elements which must be considered, along with strict control in operations and monitoring to ensure their effectiveness, such as: a leachate capture system, a system of waterproof membranes, a rainwater management system, and a venting system. Likewise, site selection is a key issue, in which climate, hydrology and hydrogeological aspects must be assessed. All these factors must be considered to ensure sound design engineering and operations of waste disposal sites, as well as their adequate monitoring, closure, and decommissioning plans.
Underground injection
Underground injection is generally defined as the controlled placement of fluids in selected geological formations through specially designed and monitored wells. The history of this practice dates to the 1930s when the petroleum industry developed and used underground injection to dispose of oil and gas brines. This practice was later applied to waste from other industrial sectors (e.g., the steel industry and chemicals industry) (EPA 2003).
The viability of underground injection in deep wells depends on factors such as the selection of an area with favorable geological and hydrological conditions; and on sound injection well design and monitoring to minimize potential groundwater contamination (DENR 1989; EPA 2021e, h). Thus, a rock formation is a suitable site if its integrity and low permeability are sufficient to ensure containment of the injected waste in the injection site; if the waste does not chemically react with the rock formation; and if there are no nearby geological fault lines.
Underground injection of hazardous waste accounts for a significant proportion of off-site transfers to disposal in Canada, due mainly to the large volumes of transfers by the oil and gas sector. In Canada, the provincial and territorial governments are responsible for regulating the installation and operation of injection wells. For example, the Alberta Energy Regulator (AER) has defined and regulates four classes of injection wells.[15] Data on underground injection are compiled in various databases, such as the commercially available AccuMap database by S&P/IHS Markit.[16] With the development of industrial activities and the oil and gas sectors, a total of 700,000 wells have been drilled in the Western Canadian Sedimentary Basin, which is located under an area of nearly 1.5 million square kilometers extending from southwestern Manitoba to northeastern B.C. and which also includes parts of the northern United States (Government of Canada 2021a). Fifty thousand of these wells have been used as injection wells at some time during their operational lifespan (Ferguson 2014).
The technology required for an injection well depends on the relevant regulations. For example, in the United States, the more than 740,000 injection wells regulated under the Underground Injection Control (UIC) program are classified in six categories, in accordance with the type of fluid injected, the purpose of the injection, and the required well depth (EPA 2020c). All six classes of injection wells must comply with conditions guaranteeing the isolation of injected fluids. For example, Class I wells, used by industry to inject hazardous and non-hazardous wastes into deep, confined rock formations below underground sources of drinking water, are strictly regulated under the Resource Conservation and Recovery Act (RCRA) and the Safe Drinking Water Act (SDWA).[17]
In Mexico, underground injection is considered a waste treatment process rather than a final disposal method. Furthermore, no authorization is required if the waste in question is classified as non-hazardous (Semarnat 2015). Mexican law defines the concept of “hazardous waste treatment via deep underground injection technology” as the introduction of hazardous waste in the subsoil, where it is expected that the characteristics of the geological strata will neutralize, reduce, or eliminate the toxicity of the injected waste, while at the same time guaranteeing the integrity of aquifers and surface water (DOF 2006). Therefore, although this activity is recognized as a confinement or disposal technique, it represents a hazardous waste treatment process designed to reduce waste toxicity and not as a technique for final disposal per se. This category is therefore regulated under hazardous waste management law and not under Mexico’s RETC, which is why there are no PRTR data for underground injection activity.
Disposal through land application
Land application is the most frequently reported disposal activity for water treatment sludges or biosolids, which are most often generated by municipal or industrial wastewater treatment facilities and pulp and paper mills. However, a number of other industry sectors (e.g., oil and gas extraction, electric utilities, dairy product manufacturing) also send their wastes for land application. Before these wastes can be landfilled, they must be stabilized through physico-chemical and/or biological treatment[18] and otherwise comply with the exisitng regulatory framework.
Stabilization processes include anaerobic digestion, aerobic digestion, and chemical treatment, which consists of adding lime to the sludge to induce oxidation and avoid fermentation (Rojas and Mendoza 2011). There are, in fact, a variety of disposal methods for biosolids, including composting, landfills, and land application for soil improvement. The latter is one of the most common as it offers several benefits, including added nutrients, improved soil structure and reduced demand for non-renewable resources such as phosphorus and artificial fertilizers. However, unsound management may lead to harmful environmental impacts such as excess nutrients in groundwater from filtration and migration, accumulation of heavy metals in soils, and foul odors.
In Mexico, an estimated 640 million dry tons of wastewater sludges are produced per year (Semarnat 2016). These materials are considered an alternative to soil impoverishment caused by intensive agriculture (in crops such as chiles, onions, oats, and corn) and for use in forest soils (Conagua 2015; Barrios 2009). However, this disposal practice is not considered a final disposal method for the purposes of Mexico’s RETC.
In the United States, data show that 4.75 million dry metric tons of biosolids were generated in 2019 (EPA 2021c). It is estimated that approximately 47% of these biosolids were used in land application to improve and maintain productive soils and stimulate plant growth (EPA 2018a).[19]
In Canada, where over 660,000 tons of stabilized biosolids are produced per year, the provinces and territories have jurisdiction over the processing, use and disposal of biosolids, including via land application (CCME 2012).
Storage prior to disposal
While storage is not a waste disposal action per se, it is considered an intermediate and short-term measure during which decisions must be made about the ultimate disposition of the waste in question. Although each country has developed specific regulations relative to hazardous waste storage, all three countries define storage as the action of temporarily retaining hazardous waste until it is treated, stored elsewhere, or disposed of.
A planned storage site must be designed and constructed in accordance with the technical specifications stipulated by the competent authority, in compliance with strict safety measures, particularly in relation to waste considered as hazardous. Permissible storage times vary in accordance with each country’s regulations. In Mexico and the United States, hazardous waste may not be stored longer than six months. In Canada, except for hazardous waste imports and exports, which are regulated by the federal government, each province or territory is responsible for developing and enforcing regulations relative to the management and storage of waste in its own jurisdiction.
Stabilization or treatment prior to disposal
Stabilization and treatment are different from disposal because they involve changing the nature and volume of the original waste. However, pollutants sent to stabilization or treatment prior to disposal are considered as transfers to disposal in Taking Stock because decisions must be made regarding the final disposal of the waste portions that remain following stabilization or treatment. As described above, stabilization can involve mixing waste or other materials with binding agents to provoke a chemical reaction, which reduces the likelihood of pollutants dispersing in the environment. For example, when soil contaminated with metals is mixed with water and lime, the resulting reaction converts metals into non-water-soluble compounds (EPA 2021b). This technique provides a relatively rapid and economical method for preventing exposure to pollutants, in particular metals and radioactive materials.
On the other hand, treatment enables changing the composition of the waste. Certain treatment processes enable the recovery of waste for reuse in manufacturing processes, while others drastically reduce the volume of the treated waste (EPA 2021d). Waste treatment processes include the following[20]:
In Mexico, waste classified as hazardous must first comply with certain characteristics before it may be transferred to disposal (for example, in a controlled confinement site). Companies that accept hazardous waste for stabilization or treatment purposes must apply the physical and chemical processes to ensure the required characteristics before these materials may be authorized for transfer to confinement sites—and, in so doing, avoid chemical reactions in the disposal cells. This new stabilized mixture, which is no longer considered a PRTR listed substance, is instead regarded as generic waste and, as such, is not subject to reporting under Mexico’s RETC.
Other disposal (unknown)
As indicated in Table 6, facilities in Mexico and the United States can report transfers of waste to “other disposal,” the details of which are not provided in their PRTR reports (but which might be reported under other waste management programs).
[12] Source: EPA 2005. Introduction to Land Disposal Units (40 CFR, parts 264/265, Subparts K, L, M, N)
[13] Deeba Yavrom. 2021. “An Overview of Hazardous Waste Generation”, EPA, April 28, 2021; EPA. 2021. “Quantity of RCRA Hazardous Waste Generated and Managed, 2001-2019”, Report on the Environment (ROE) indicators.
[14] Readers are reminded that under Mexico’s legal framework, “controlled confinement” is the disposal practice for hazardous waste, equivalent to landfill and surface impoundment in Canada and the US.
[15] AER. 1994. Directive 051: Injection and Disposal Wells – Well Classifications, Completions, Logging, and Testing Requirements, Alberta Energy Regulator, March 1994.
[17] The sixth category of underground injection well is used exclusively for the geological sequestration of CO2. A detailed description of all six classes of underground injection wells can be found in EPA’s UIC website: “Protecting Underground Sources of Drinking Water from Underground Injection.”
[18] See, for example: CCME, 2005, “Guidelines for Compost Quality”.
[19] EPA (2018), Cleaning up and revitalizing land: EPA Unable to Assess the Impact of Hundreds of Unregulated Pollutants in Land-Applied Biosolids on Human Health and the Environment, General Report No. 19-P-0002, Environmental Protection Agency, Office of Inspector, November 15, 2018.
[20] Readers are reminded that there are differences in the terminology and definitions used by the three PRTR programs. For example, the Taking Stock category of stabilization or treatment prior to disposal includes data for incineration, thermal treatment, and wastewater treatment. Since the US TRI does not include incineration/thermal treatment within total disposal quantities, the US amounts shown in this report can be somewhat higher than in the national dataset.