With the growing popularity of both water-based cleaning chemistries and new solvent technologies, the debate between water-based and solvent cleaners rages on. Companies that have cleaning requirements for industrial, precision, and specification-driven applications must decide which material is best for their applications and their business. Having and understanding the facts is the first step. In this post, we’ll explore the differences in properties, performance, cost, safety and regulatory implications for these two cleaning materials to help you make an easy and informed decision for your application.
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For our discussion, a solvent cleaner or solvent degreaser uses a liquid to dissolve a soil. It can utilize one solvent, a variety of solvents, or a combination of several solvents and compounds to maximize performance parameters for a specific application. Solvents can be broken down into their basic functional compounds, such as alcohols, ketones, aliphatic hydrocarbons, etc. Each chemical category has specific characteristics that lend to different solvency profiles. The addition of different compounds and mixtures provides the range of solvency seen in commercial products. These different solvents and cleaning solutions can be tuned to remove a specific soil while leaving other materials relatively untouched. Some familiar solvents include acetone and butyl acetate, which can be found in local hardware stores. Other familiar solvents include alcohols such as isopropanol and ethanol, and even gasoline due to its hydrocarbon composition.
Water is also a solvent and is a subsection of the solvent category. Water-based degreasers utilize water as the primary solvent, but can also include any of the solvents mentioned above, plus detergents, pH modifiers, builders, chelating agents, and a variety of other compounds. When these other compounds are used, water-based cleaners can either be very strong cleaners or mild cleaners. They can be dangerous or relatively nontoxic, but they usually require a rinse step. The variety and complexity of water-based cleaners is enormous. The two cleaners are used in a variety of applications which include, but are not limited to, degreasing, precision cleaning, ultrasonic cleaning, and medical device assembly cleaning.
All solvents work by dissolving the soil; breaking it down into smaller particles and carrying it into the solution and away from the surface being cleaned. Many solvents offer the advantage of quick cleaning, so the soils dissolve and flow off of the substrate without needing extended prep time, processing time, or drying time.
Solvent-based cleaners remain popular in industrial applications due to their cleaning power; they remove thick, baked on oils, dirt, containments, solder flux, and greases. Some examples of strong cleaning solvents are acetone, methyl ethyl ketone, toluene, nPB, and trichloroethylene (TCE). Common mild solvents include isopropyl alcohol, glycerin, and propylene glycol. In this case, the terms “strong” and “mild” are arbitrary designations. Solvent strength depends not only on the nature of the soils being removed, but also on the amount of soil to be removed and the level of cleanliness that is required.
Solvent-based cleaners can be fast evaporating or slow evaporating, high in odor or low in odor, plastic safe or very aggressive. The wide array of solvents has allowed the creation of very specific cleaning chemistries for removing specific soils from substrates. For example, some cleaners are capable of removing a specific ink on a plastic substrate while leaving others completely untouched.
When choosing a solvent cleaner, one of the first questions is, “should I use a flammable or nonflammable solution?” If flammable solvents can be safely used and there are no ignition sources, there is good air turnover, and all safety protocols can be followed, flammable solvents tend to be significantly less expensive than nonflammable solvents. However, if any of the aforementioned safety concerns are an issue, there are many nonflammable solvents to choose from.
Solvent evaporation rates vary -- some are immediately volatile at room temperature, while others may only evaporate at elevated temperatures. Those which evaporate immediately may be better suited to minimizing process downtime, while those that evaporate much more slowly are better suited to elevated temperature soak applications. There is not a single solvent that works for all applications. Also, those that evaporate more slowly are less likely to be volatile organic compounds (VOCs) but may need an additional drying process.
Surface tension is the measurement of a liquid’s ability to pull together into a cohesive droplet. The lower the surface tension of a material, the harder it is for that material to pull together into a droplet, thus allowing the material to spread out and wet a surface, and ultimately lay down a thin even coat. When the surface tension is high, the liquid tends to pull together to form droplets. In general, solvents tend to offer lower surface tension than water-based cleaners, providing the ability to permeate into tight clearance areas to remove soils, without being entrapped.
All solvents and cleaners should be handled while using personal protective equipment in well-ventilated areas to minimize exposure. Follow the recommendations offered by the manufacturer’s SDS.
A growing concern with many solvents is whether they contain Volatile Organic Compounds or VOCs. VOCs are materials that readily evaporate and turn into the gaseous state at normal room temperatures, and their ability to contribute to smog formation and the environmental and personal health impacts associated with them. This is one reason why low or no VOC solvents are becoming such an important issue as companies are using them to both meet air quality standards and improve worker safety.
There are a variety of tradeoffs that can accompany the use of solvents that do not contain VOCs. One downside is the possible increase in the drying time of the cleaners. This is the case for both water-based and solvent-based systems. One way to decrease the VOC impact of a cleaner is to add slow-evaporating solvents to the mixture that minimize the VOC contribution to the environment. This can be the addition of certain materials that act like oils, or in some cases adding water mixtures to the cleaner. In either case, additional processes including rinsing, drying heat tunnels, or reclamation procedures may be required to meet the required process parameters.
Another tradeoff can be the use of VOC exempt materials, such as acetone, siloxanes, and PCBTF. While these solvents are generally strong cleaners, they are flammable and the acetone and PCBTF have high odor levels. Acetone is a relatively inexpensive material, but the PCBTF and siloxanes solvents are much more costly. Other VOC exempt materials, such as HFC-43-10mee, do not have sufficient cleaning ability to remove most soils when used by itself and must be mixed with other stronger solvents to increase the cleaning ability.
Water-based cleaners remove soils not only by dissolving contaminants, but also by chemically reacting with the contaminants to make them more readily dissolvable in water. For example, some materials will react with or dissolve more readily into an acidic solution (pH of 7 or lower). Some common acidic materials can be found in lemons (citric acid), vinegar (acetic acid), soft drinks (carbonic and phosphoric acid) and car batteries (sulfuric acid). Other materials are more readily reacted with or dissolved into a solution with a pH above 7. These solutions are caustic, or alkaline. Some common caustic materials are ammonia, bleach (sodium hypochlorite), lye (sodium hydroxide), and oven cleaners (more sodium hydroxide).
Most aqueous cleaners contain a variety of other components to enhance the cleaning profile. These other materials can include[2]:
Detergents or surfactants – materials that have wetting and emulsifying properties, and can carry soils into a solution that they would not otherwise dissolve into.
Builders – materials that increase the efficacy of detergents in water by adding alkalinity to solutions.
Emulsifiers – liquids that can carry oils into water solutions, creating a liquid in liquid solution.
Saponifiers – materials that will react with fatty acids and other carboxyl groups to form water-soluble soaps that can dissolve into the water solution.
Sequestering agents – bind with calcium, magnesium and other metals in hard water that detract from the overall cleaning ability of the cleaner. Sequestering agents can bind with more than one metal ion at a time.[3]
Chelating agents – similar to sequestering agents, but bind to one metal ion only.
The combination of water, solvents, surfactants, and saponifiers can be as effective as solvent cleaning, but often requires a change in the cleaning process. In a high precision application where residues cannot be tolerated, a rinsing process is often required with water-based chemistries. Batch or in-line cleaning systems generally have rinse and dry cycles to overcome these issues.
Aqueous cleaners can achieve very similar cleaning levels as solvent-based cleaning chemistries, but there are certain differences:
Evaporation: Water-based cleaners function in a much narrower range of evaporation time when compared to solvent cleaners. While solvent cleaners evaporation time can range from milliseconds to months, water-based degreasers usually operate in a much narrower range. They typically are not left to evaporate on their own, and can normally be used in a cold or hot soak application.
Temperature profile: Cleaning temperatures for water-based chemistries can range from room temperature up to about 80C, depending on the specific cleaner and its formulation. Although this provides a great deal of process variability, this is much more limited when compared to solvent cleaners. Solvent temperature cleaning range can be much wider just based on the variety of solvents available, from below 0C to above 200C.
Higher surface tension: In general, water-based cleaners have higher surface tensions when compared to solvents. Raising the temperature, using different surfactants and emulsifiers, and incorporating spray and drying systems can overcome much of this shortcoming. However, for the tightest clearance areas, solvents with low surface tension are superior in their abilities to wet into and evaporate out of tight spaces.
Reactive additives: Some of the reactive additives incorporated into aqueous cleaners can be very aggressive to different metals, plastics, or inks. Once the part is cleaned, validation of material compatibility with the parts must be checked. This includes making sure no reactive material is left behind from the rinse process, and verifying that the product will function in the expected manner and in all expected environments. Trace quantities of some of these reactive materials may contribute to electrical leakage, coating dewetting, and a variety of other defects.
Rinse and Drying: As noted above, rinsing and drying removes any cleaner components and solubilized contaminants. While some solvent cleaning systems also require a rinse and dry process, water-based systems are usually more involved with respect to the rinse and dry process in the context of vapor degreasing applications.
Environmental Impact: Here again, environmental impact concerns apply to both solvent and aqueous cleaners. Global, national, state and municipal regulations continue to limit the cleaning choices available to manufacturers:
Montreal and Kyoto protocols limit categories of substances like CFC’s (chlorofluorocarbons), HCFC’s (hydrochlorofluorocarbons), and HFC’s (hydrofluorocarbons) due to ozone depletion, global warming, and other environmental concerns.
EPA (Environmental Protection Agency) and state agencies like Cal-OSHA (California OSHA) limit personnel exposure to toxic chemicals.
CARB (California Air Review Board) restricts smog-producing VOCs (volatile organic compounds) in cleaners based on specific cleaning categories.
Hazardous Air Pollutants (HAPs). Hazardous air pollutants (HAPs) are those pollutants that are known or suspected to cause either environmental damage or other serious health effects (i.e. reproductive complications,birth defects, and cancer).[4] Some solvents are considered a HAP, and in general water-based chemistries do not contain HAPs.
Priority Pollutant List[5]. These are a set of chemicals that the EPA regulates, and has analytical test methods for detecting under the Clean Water Act. Once again, several solvents are on this list, while aqueous cleaning chemistries are not.
These regulatory pressures force manufacturers to evaluate new cleaners and cleaning processes to overcome policy-related hurdles. As a result, water-based cleaners are becoming more common in the industry.
Both cleaning technologies have the potential to be very effective in terms of performance – however, the cleaning ability depends on what is being cleaned off of the surface, the substrate being cleaned, and both the process constraints and requirements. All three parameters must work in tandem for the best cleaning results.
To choose between an aqueous cleaner vs. a solvent, one must evaluate your unique application, requirements, and goals. Then, you must consider safety, performance, and cost of the solution. A good cleaning agent that is made specifically for removing handling soils may not remove machine greases, a cleaner that works well on stainless steel may not be compatible with glass lenses, and a cleaner that removes machining oil may not be clean enough for a liquid oxygen line.
The bottom line is that it’s impossible to make an overall credible judgment of the superiority of either solvent or water-based cleaners without evaluating the unique situation of the user. Luckily, even with the ever-mounting regulations, there's an array of choices that include both solvents and water-based cleaners.
There you have it - our comparison of solvent and aqueous cleaners. Be sure to post your questions and comments below. And if you still need assistance choosing between a solvent cleaner and water base, speak with one of our product specialists. They’ll help you get the right product for your application.
[1] From ACGIH website, https://www.acgih.org/about-us/history, accessed 07-20-.
[2] Adapted from pages 14-16, “The Aqueous Cleaning Handbook”, McLaughlin and Zisman, ISBN 0--7-X, published .
[3] https://www.researchgate.net/post/Is_there_a_difference_between_chelant_and_sequestrant_agents, Accessed 07-31-.
Contact us to discuss your requirements of Thinning Cleaning Agent. Our experienced sales team can help you identify the options that best suit your needs.
[4] https://www.epa.gov/compliance/national-emission-standards-hazardous-air-pollutants-compliance-monitoring. Accessed 08-01-.
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A CERCLA hazardous substance is not a RCRA hazardous constituent. CERCLA defines "hazardous substance" as those substances designated pursuant to CERCLA section 102(a) and by reference to the following authorities:
CERCLA section 102(a) gives EPA authority to designate hazardous substances, in addition to those substances listed or identified under the statutory provisions cited above.
There are currently more than 800 CERCLA hazardous substances. In addition, CERCLA includes about 1,500 known radionuclides, approximately 760 of which are listed individually. The CERCLA list of hazardous substances can be found at Title 40 of the Code of Federal Regulations Section 302.4 in Table 302.4 “List of Hazardous Substances and Reportable Quantities.”
Appendix VIII in 40 CFR Part 261 is EPA's list of RCRA hazardous constituents. The Appendix VIII list is comprised of chemicals that have toxic, carcinogenic, mutagenic, or teratogenic effects on humans or other life forms. Appendix VIII currently includes approximately 500 chemicals or classes of chemicals.
EPA uses the Appendix VIII list to identify the universe of chemicals of concern under RCRA. EPA also uses Appendix VIII to determine if a waste contains hazardous constituents and should be considered for listing as a hazardous waste under 40 CFR section 261.11(a)(3). Additionally, hazardous constituents listed on Appendix VIII are routinely assessed for and may be addressed as part of the RCRA corrective action process.
Listing chemicals as RCRA hazardous constituents does not make them, or the wastes containing them, RCRA hazardous wastes.
Simply defined, a hazardous waste is a waste with properties that make it dangerous or capable of having a harmful effect on human health or the environment. Under RCRA, there are two ways to designate a waste as hazardous: a hazardous waste listing or characteristic determination. A hazardous waste listing determination, as specified under the third listing criterion in 40 CFR Section 261.11(a)(3), is a lengthy process that requires EPA to collect and consider information on 11 regulatory factors.
Hazardous waste is generated from many sources, ranging from industrial manufacturing process wastes to batteries and may come in many forms, including liquids, solids, gases, and sludges. A hazardous waste listing triggers all cradle to grave requirements in RCRA (meaning from the time it is created, while it is transported, treated, and stored, and until it is disposed). These requirements ensure that the waste is managed safely, which protects human health and the environment.
In order for a material to be classified as a hazardous waste, it must first be a solid waste. So, the first step in the hazardous waste identification process is determining if a material is a solid waste. Refer to 40 CFR Section 261.2. The second step in this process examines whether or not the waste is specifically excluded from regulation as a solid or hazardous waste.
Once a generator determines that their waste meets the definition of a solid waste, they investigate whether or not the waste is a listed or characteristic hazardous waste. Listed wastes are wastes from common manufacturing and industrial processes, specific industries and can be generated from discarded commercial products. Characteristic wastes are wastes that exhibit any one or more of the following characteristic properties: ignitability, corrosivity, reactivity or toxicity.
Aqueous solutions containing less than twenty-four percent alcohol by volume are excluded from the characteristic of ignitability (Section 261.21(a)(1)). EPA originally intended for the alcohol exclusion to exempt alcoholic beverages and some types of latex paints that exhibit low flash points due to the alcohol content, but do not sustain combustion because of the high water content (Volume 45 of the Federal Register (FR) starting on page , guidance on page ; May 19, ). Nevertheless, the alcohol exclusion is not limited to alcoholic beverages or paints. The exclusion applies to all aqueous solutions containing less than twenty-four percent alcohol, even if additional non-alcoholic components are present. The term "alcohol" refers to any alcohol or combination of alcohols (55 FR , ; June 1, ). However, if the alcohol has been used for solvent properties and is one of the alcohols specified in EPA hazardous waste codes F001-F005, the waste must be evaluated to determine if it should be classified as an F-listed spent solvent waste (Monthly Call Center Report Question; July (RCRA Online #)).
Additional guidance on the alcohol exclusion is available in the following documents:
Memo, Skinner to Walter; February 26, (RCRA Online #)
Monthly Call Center Report Question; August (RCRA Online #)
No generator, transporter, handler, or owner or operator of a Treatment, Storage and Disposal Facility (TSDF) shall dilute a hazardous waste as a substitute for adequate treatment.
However, dilution of wastes that are hazardous only because they exhibit a characteristic and are subsequently discharged under the Clean Water Act or Safe Drinking Water Act (e.g., Class I underground injection well) is not impermissible, unless a treatment method other than DEACT is specified.
In all cases, the Agency has determined that for non-toxic hazardous characteristic wastes, it should not matter how the characteristic property is removed so long as it is removed. Thus, dilution is an acceptable treatment method for such wastes.
Any solid waste is not a hazardous waste if it does not exhibit any of the characteristics of hazardous waste identified in Title 40 of the Code of Regulations (CFR) Part 261 Subpart C. However, wastes that exhibit a characteristic at the point of generation may still be subject to the LDR requirements in Part 268, even if they no longer exhibit a characteristic at the point of land disposal.
Characteristic wastes that are exempt from the dilution prohibition and which are managed and disposed of on-site, are not subject to the full Section 268.7 requirements for waste analysis and record keeping.
References: 40 CFR Section 268.3(a)
40 CFR Section 268.3(b); 55 FR , , June 1,
40 CFR Section 261.3(d)
Monthly Call Center Report Question, October (RCRA Online #)
66 FR , , May 16,
The Hazardous Waste Identification Process
40 CFR Section 268.7(a)(7)
A solid waste derived from a hazardous waste listed solely for exhibiting a characteristic of ignitability, corrosivity, and/or reactivity is not a hazardous waste when it no longer exhibits any characteristic of hazardous waste (40 CFR Section 261.3(g)(2)(ii)). However, a waste listed solely for exhibiting the characteristic of ignitability, corrosivity, and/or reactivity that exhibits the characteristic at the point of generation and subsequently loses the characteristic is still subject to the land disposal restrictions requirements in Part 268 (66 FR ; May 16, ).
Hazardous wastes listed in accordance with the criteria in 40 CFR Section 261.11(a)(2) are designated as "acute" hazardous wastes. Acute hazardous wastes are assigned the hazard code (H) (Section 261.30). Specifically, a waste is classified as an acute hazardous waste if it is any P-listed waste (Section 261.33) or one of the following F-listed wastes: F020, F021, F022, F023, F026, and F027 (Section 261.31).
The as-generated waste would not be considered a hazardous waste even though it meets the listing description for K045. A waste listed solely for the characteristic of ignitability, reactivity, and/or corrosivity is excluded from regulation as a hazardous waste once it no longer exhibits a characteristic of hazardous waste (Section 261.3(g)(1)). The same rationale applies when a waste meets such a listing description but does not exhibit a characteristic of hazardous waste at the point of generation. In the Hazardous Waste Identification Rule, EPA stated that extending this exclusion to as-generated wastes that do not exhibit a characteristic of hazardous waste remains protective of human health and the environment (66 FR , ; May 16, ). Additionally, the as-generated waste would not be subject to the LDR requirements in Part 268 (51 FR , ; November 7, ). EPA has clarified that when a waste has been listed solely because it exhibits a characteristic of ignitability, corrosivity and/or reactivity and that waste does not exhibit any hazardous waste characteristic at the point of generation, then that waste is not subject to the LDR requirements (66 FR , ; May 16, ). If, however, the waste exhibits a characteristic at the point of generation and subsequently becomes decharacterized, then it would be subject to the LDR requirements (Section 261.3(g)(3)).
Elementary neutralization units are tanks, tank systems, containers, transport vehicles, or vessels used for neutralizing wastes that are hazardous only because they exhibit the corrosivity characteristic or because they are listed solely for the characteristic of corrosivity (Section 260.10). A tank, tank system, container, transport vehicle, or vessel that meets the definition of an elementary neutralization unit is exempt from permitting requirements under RCRA Subtitle C (Sections 264.1(g)(6), 262.1(c)(2), and 270.1(c)(2)(v)). In addition, generators managing hazardous waste immediately upon generation in an on-site elementary neutralization unit are not required to count those wastes toward their monthly generator status (Section 262.1(c)(2)).
An elementary neutralization unit is a device which:
(1) is used for neutralizing wastes that are hazardous only because they exhibit the corrosivity characteristic defined in Section 261.22, or they are listed in Part 261 Subpart D only for this reason; and
(2) meets the definition of tank, tank system, container, transport vehicle, or vessel (Section 260.10).
Treatment means any method, technique, or process, including neutralization, designed to change the physical, chemical, or biological character or composition of any hazardous waste so as to neutralize such waste, or so as to recover energy or material resources from the waste, or so as to render such waste non-hazardous, or less hazardous; safer to transport, store, or dispose of; or amenable for recovery, amenable for storage, or reduced in volume (40 CFR Section 260.10). Some forms of treatment are not regulated under RCRA, including treatment of hazardous wastes in an elementary neutralization unit.
The unused solvent removed from the spray can may meet a hazardous waste listing. If the remaining solvent in the spray can is located on either the P list or the U list in Section 261.33(e) or (f), the residue could be a listed hazardous waste. Specifically, Section 261.33(b) states that, "any residue remaining in a container or in an inner liner removed from a container that has held any commercial chemical product or manufacturing chemical intermediate having the generic name listed in paragraphs (e) or (f) of this section, unless the container is empty as defined in Section 261.7(b) of this chapter" is a hazardous waste.
However, if the residue is not on the P list or the U list, it may still be hazardous if it exhibits any of the characteristics of a hazardous waste as defined in Part 261, Subpart C. It is the responsibility of the generator to make this determination. The unused solvent removed from the spray cans would not be classified as a spent solvent waste as listed in Section 261.31. The solvent waste F-listings apply to spent solvents, which are particular chemicals used for their solvent properties, that is, to solubilize, dissolve or mobilize other constituents, but are no longer useable as solvents (50 FR , : December 31, ). The product paint thinner remaining in the aerosol can was not used as a solvent, nor was it spent because it was never used in the first place. Therefore, the spent solvent F-listings would not apply to the discarded product.
Process wastes containing solvents where the solvent is used as an ingredient in the formulation of a CCP do not fall within the scope of the spent solvent listings. Additionally, the products themselves do not meet the listings (50 FR , ; December 31, ). Thus, when unused solvent is added to a product (e.g., paint or ink) as an ingredient, any unused product being disposed of would not carry an F listing. However, if the solvent served as the sole active ingredient for the function of the product (e.g., solvent), then the disposed unused product may be a P- or U-listed hazardous waste. (Call Center Monthly Report Question; June (RCRA Online )).
The solvent constituents listed in Section 261.31 apply to hazardous wastes when they are used as solvents and have become contaminated with physical or chemical impurities and are no longer fit for use without being regenerated, reclaimed, or otherwise re-processed. Solvent constituents are considered used as a solvent when they are used for their solvent properties (i.e., to solubilize (dissolve) or mobilize other constituents) (50 FR , ; December 31, ). For example, solvents used as cleaning or degreasing agents, mediums for chemical reactions, extraction agents, and diluents are covered under the F001 though F005 listings in Section 261.31 (Memo, Straus to Harvey; May 2, (RCRA Online )). Opens a New Window.
Additional guidance regarding the spent solvent hazardous waste listings is available in the following documents:
Memo, Shapi to Dolce; March 1, (RCRA Online )
Memo, Bussard to Wilson; June 14, (RCRA Online )
Memo, Lowrance to Diehn; May 3, (RCRA Online )
Memo, Barnes to Stockli; April 12, (RCRA Online )
Memo, Barnes to Moretta; December 6, (RCRA Online )
Memo, Barnes to Lindberg; May 5, (RCRA Online )
Memo, Sales to Czigler; May 20, (RCRA Online )
Memo, Straus to Skoufis; March 6, (RCRA Online )
Memo, Straus to Hemker; February 19, (RCRA Online )
Memo, Straus to McAdams; August 4, (RCRA Online)
The U223 waste code may apply to toluene diisocyanate (TDI) if it is an unused commercial chemical product (CCP) that is being discarded. A CCP is a substance that consists of the commercially pure grade of a chemical listed in 40 CFR Section 261.33, any technical grades of the chemical, and all formulations in which the chemical is the sole active ingredient (Section 261.33(d))(54 FR , ; July 28, ).
The pure form of a chemical is a formulation consisting of one hundred percent of that chemical. The technical grade of a chemical is a formulation in which the chemical is almost one hundred percent pure, but contains minor impurities (Memo, Lowrance to Wayland; May 3, (RCRA Online #)).
A chemical is the sole active ingredient in a formulation if that chemical is the only active ingredient serving the function of the formulation. However, if a formulation contains more than one active ingredient, the formulation would not fall within the scope of the listing in Section 261.33, regardless of whether only one or both of the active ingredients are listed (Monthly Call Center Report Question; March (RCRA Online #)).
A mixture of a solid waste and a hazardous waste listed solely for the characteristic of ignitability, corrosivity, or reactivity is no longer a hazardous waste if the mixture does not exhibit the hazardous characteristic (Section 261.3(g)(2)(i)). The same rationale applies when a waste meets a listing description, but does not exhibit a characteristic of hazardous waste at the point of generation (Monthly Call Center Report Question; October (RCRA Online #)).
There are currently twenty-nine wastes codes within the RCRA program listed solely for the characteristic of ignitability, corrosivity, or reactivity (66 FR , ; May 16, ). However, U223 is not one of these twenty-nine wastes codes because it was not listed solely for exhibiting the characteristic of reactivity. It was listed because it is both reactive and toxic (Section 261.33(f)). Therefore, the U223 waste code would apply to the discarded toluene diisocyanate if it is an unused CCP even when its reactive properties have been removed or neutralized.
Additional guidance regarding the applicability of P and U listed waste codes is available in the following documents:
Monthly Call Center Report Question; August (RCRA Online #)
Memo, Dellinger to Smith; March 18, (RCRA Online #)
Memo, Barnes to Mastalerz; August 21, (RCRA Online #)
Memo, Barnes to Fox; May 19, (RCRA Online #)
The reason for the different regulatory requirements is that the EPA created a specific hazardous waste exemption for the petroleum-contaminated media and debris caused by leaking USTs because of potentially significant impacts related to the Agency's comprehensive program to prevent leaking underground storage tanks, under Subtitle I of RCRA, including impacts to the cleanup of USTs that have leaked in the past.
Petroleum contaminated media and debris is excluded from the definition of hazardous waste when the media or debris, such as soil and groundwater, is generated from petroleum UST corrective action activities and fails the toxicity characteristic for hazardous waste codes D018 through D043 (Section 261.4(b)(10)). At the time of promulgation of the final Toxicity Characteristic (TC) rule, EPA made a determination to temporarily defer applicability of the TC rule to media and debris contaminated with petroleum from USTs subject to the corrective action requirements of Subtitle I of RCRA. EPA had little information regarding the full impact of the TC rule on UST cleanups; however, a preliminary assessment indicated that the number of UST cleanup sites and the amount of media and debris at each site that would exhibit the toxicity characteristic would be extremely high. EPA reasoned that subjecting all, or even a portion, of these sites to Subtitle C requirements could overwhelm the hazardous waste permitting program and the capacity of existing hazardous waste treatment, storage, and disposal facilities. In addition, imposition of the requirements could delay UST cleanups significantly (58 FR , ; February 12, ).
On December 24, , EPA proposed a similar exclusion for contaminated media and debris contaminated by petroleum products from non-UST sources (57 FR ), however, EPA never finalized that proposal. EPA later stated in the HWIR-media proposal that finalization was unnecessary because a final HWIR-media rule would solve the problems that the non-UST TC suspension was intended to address (63 FR , ; November 30, ).
It is important to note that a generator must still determine if petroleum contaminated media and debris is hazardous for the hazardous waste codes D001 through D017 (Memo, Lowrance to Bevington; November 9, (RCRA Online #)). In addition, the definition of an UST includes those tanks or combinations of tanks whose volume, including the volume of underground connected piping, is ten percent or more beneath the surface of the ground (Section 280.12). Any tank that does not meet this definition is not a UST for the purposes of Part 280, would not be subject to comprehensive requirements for the reporting and cleanup of soil and groundwater contaminated from USTs, and thus would not qualify for the exclusion in Section 261.4(b)(10).
Refer to Underground Storage Tanks for more information.
Additional guidance regarding the petroleum contaminated media and debris exclusion in Section 261.4(b)(10) is available in the following documents:
Monthly Call Center Report Question; January (RCRA Online # )
Monthly Call Center Report Question; November (RCRA Online #)
Monthly Call Center Report Question; October (RCRA Online # )
Personal protective equipment (PPE), including contaminated clothing and similar debris, are not solid wastes but may be regulated under the contained-in policy. Under the contained-in policy, the PPE contains hazardous waste if it exhibits a characteristic or contains listed hazardous waste. If contamination cannot be removed, PPE must be treated to land disposal restrictions (LDR) treatment standards prior to disposal (Memo, Lowrance to Fields; January 3, (RCRA Online #)).
Additional guidance is available in the following documents:
Memo, Bussard to Colby; July 27, (RCRA Online #)
Memo, Lowrance to Ullrich; June 14, (RCRA Online #)
The contained-in policy is a more flexible version of the mixture and derived-from rules that applies to contaminated environmental media. EPA uses the term environmental media to describe soil, sediments, and ground water (61 FR , ; April 29, ). Environmental media are usually contaminated through accidental spills of hazardous waste or spills of product chemicals that, when spilled, become hazardous wastes. Environmental media is not inherently a solid or hazardous waste and, generally, is not subject to regulation under RCRA. Environmental media that are contaminated can become subject to regulation under RCRA if they “contain” hazardous waste (Management of Remediation Waste Under RCRA; October 14, (RCRA Online #)).
EPA’s contained-in policy states that environmental media contaminated with a hazardous waste must be managed as if they were hazardous wastes until they no longer contain the listed waste, no longer exhibit a characteristic, or are delisted. In order for environmental media contaminated with a listed waste to no longer be considered hazardous, the handler of those media must demonstrate to EPA's or the authorized State's satisfaction that the media no longer poses a sufficient health threat to merit RCRA regulation. EPA has not issued guidelines as to when or at what levels environmental media contaminated with hazardous wastes are no longer considered to contain those hazardous wastes. The levels for media are most appropriately determined on a site-specific basis by the EPA Region or authorized State overseeing the cleanup of such materials under Superfund response actions or RCRA corrective action. These levels are generally determined by the implementing agency according to risk (57 FR 958, 986; January 9, ).
Additional guidance on the contained-in policy is available in the following documents:
Memo, Shapiro to Wright; September 15, (RCRA Online #)
Memo, Lowrance to Warren; October 15, (RCRA Online #)
Memo, Lowrance to Ely; March 26, (RCRA Online #)
Land disposal means placement in or on the land, except in a corrective action management unit or staging pile, and includes but is not limited to, placement in a landfill, surface impoundment, waste pile, injection well, land treatment facility, salt dome formation, salt bed formation, underground mine or cave, or placement in a concrete vault or bunker intended for disposal purposes.
Removal of restricted waste from a unit and subsequent placement of the waste, either back into the unit or into another unit, is subject to the land disposal restrictions. In situ treatment or movement of waste within the same unit does not constitute "placement" and does not subject the waste to the land disposal restrictions.
The placement concept is also used in the Area of Contamination (AOC) Policy. Because a designated AOC is equated to a RCRA land-based unit, consolidation and in situ treatment of hazardous waste within an AOC does not create a new point of hazardous waste generation for purposes of RCRA.
Hazardous wastes placed into land disposal units after the effective date are subject to the prohibitions, but wastes disposed prior to the applicable effective date do not have to be removed or exhumed for treatment. If, however, wastes subject to land disposal restrictions are removed from either a storage or land disposal unit after the effective date, subsequent placement of such wastes in or on the land would be subject to the restrictions and treatment provisions.
References:
40 CFR Section 268.2(c)
Memo, Weddle to Vaille, July 19, (RCRA Online #)
Memo, Fields and Herman to RCRA Senior Policy Managers, October 14, (RCRA Online #)
51 FR , , November 7,
PCE contaminated media may be regulated as listed hazardous waste because contaminated environmental media is subject to regulation when it contains hazardous waste. Generally, EPA considers contaminated media to contain hazardous waste when it exhibits a characteristic of hazardous waste, or when it is contaminated with concentrations of hazardous constituents from listed hazardous waste that are above health-based levels (Management of Remediation Waste Under RCRA, EPA530-F-98-026). In addition, spent PCE used in dry cleaning is classified as F002 when the spent solvent formulation meets the ten percent (by volume) criterion in the listing (Call Center Monthly Report Question; October , RCRA Online #). Therefore, contaminated media that contains spent PCE meeting the F002 listing description in Section 261.31 is regulated as F002.
A generator must know the source and the before use concentration of PCE in order to determine if the F002 listing applies. If the source of the PCE is from a product spill (e.g., unused solvent), it could be a U210 listed waste. A facility owner or operator must make a good faith effort to determine if a material is a listed hazardous waste. However, if an owner or operator cannot make such a determination because documentation regarding a source of contamination, contaminant, or waste is unavailable or inconclusive, the owner or operator may assume the source, contaminant, or waste is not a listed hazardous waste and, provided the material in question does not exhibit a characteristic of hazardous waste, that RCRA requirements do not apply (Management of Remediation Waste Under RCRA, EPA530-F-98-026).
Furthermore, media that becomes contaminated with hazardous waste must be managed as if it were hazardous waste until it no longer exhibits a hazardous waste characteristics or no longer contains the listed waste. EPA believes that such levels for contaminated media are most appropriately determined on a site-specific basis by the EPA Region (or authorized state) overseeing cleanup of such materials (Management of Remediation Waste Under RCRA, EPA530-F-98-026).
Additional guidance regarding the applicability of the F002 hazardous waste code is available in the following documents:
Call Center Monthly Report Question; May (RCRA Online #)
Memo, Lowrance to Wassersug; September 22, (RCRA Online #)
Additional guidance regarding contaminated media is available in the following documents:
Memo, Fields and Herman to RCRA/CERCLA Senior Policy Managers; October 14, (RCRA Online #)
Memo, Shapiro to Wright, September 15, (RCRA Online #)
Memo, Lowrance to Ely; March 26, (RCRA Online #)
Memo, Cannon to Jorling; June 19, (RCRA Online #)
Contaminated environmental media can become subject to regulation if they "contain" hazardous waste. EPA generally considers contaminated media to contain hazardous waste: when they exhibit a characteristic of hazardous waste, or when they are contaminated with concentrations of hazardous constituents from listed hazardous waste that are above health-based levels.
Environmental media that contain listed hazardous waste must be managed as hazardous waste as long as they contain listed wastes.
Media that are contaminated with hazardous waste must be managed as if they were hazardous waste until they no longer "contain" the listed waste. EPA believes that such levels for media are most appropriately determined on a site-specific basis by the EPA Region (or authorized State) overseeing cleanup of such materials.
A waste which contains a listed waste remains a hazardous waste until it is delisted.
References:
Memo, Fields and Herman to RCRA/CERCLA Senior Policy Managers, October 14, (RCRA Online #)
Memo, Shapiro to Wright, September 15, (RCRA Online #)
57 FR 958, 986, January 9,
61 FR , , April 29,
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