IV. C. Eligibility for Exclusions To be eligible for the proposed exclusions, a facility must meet a number of conditions. As long as the specified conditions are met, the Agency proposes that both exclusions apply to the following:

( 1) Industrial wipes exhibiting a hazardous waste characteristic ( i. e., ignitability, corrosivity, reactivity, or toxicity) 8 due to use with solvents; and 51 ( 2) Industrial wipes contaminated with F001 F005 spent solvents or comparable P and Ulisted commercial chemical products that are spilled and cleaned up.

This proposal would not affect the regulatory status, under federal regulations, of conditionally exempt small quantity generators ( CESQGs)   those that generate no more than 100 kilograms of hazardous waste or no more than one kilogram of acutely hazardous waste in a month and who accumulate no more than 1000 kilograms of hazardous waste or no more than one kilogram of acutely hazardous waste at one time.

EPA's concern surrounding the use of both disposable and reusable industrial wipes is based on the hazardous solvent contained in the used wipes, not the industrial wipes themselves. This proposed rule would not apply to industrial wipes contaminated with solvents that, when spent, are not hazardous wastes. EPA recommends that generators examine the feasibility of substituting non hazardous solvents for hazardous solvents in order to avoid concerns regarding management of hazardous waste.

IV. D. Proposed Conditions for Exclusion from Definition of Hazardous Waste for Disposable Solvent Contaminated Industrial Wipes IV. D. 1. Proposed Conditions for Initial Storage and Accumulation Proposal The proposed conditional exclusion from the definition of hazardous waste would apply to solvent contaminated disposable industrial wipes at the point when the wipes are discarded by the generator. If the wipes are managed according to the proposed conditions, they will not be considered hazardous waste. EPA's proposal establishes a condition for the on site accumulation and storage of solvent contaminated wipes that requires the use of non leaking, covered containers. Generators must accumulate and store solvent contaminated wipes in covered containers that do not allow solvent to be released from the container. The container must not leak liquids and must protect against fugitive air releases of solvents when not in use. These conditions provide flexibility while reducing the threat of fire and protecting the environment and health and safety of workers.

Discussion Site visits conducted by EPA in 1997 provided evidence that both open and closed containers are used for the accumulation of solvent contaminated industrial wipes. The most common management practices involved the use of a wide variety of containers, ranging from approximately five gallons in size ( e. g., safety cans) to 55 gallon drums. Some sites also used safety cans as satellite accumulation units from which the wipes were later transferred to a centralized accumulation unit. Many facilities stored solvent contaminated industrial wipes in screen bottom drums to reduce the amount of free liquids in the materials. Some facilities also used plastic bags as on site accumulation units. The performance based condition proposed by EPA accommodates the needs of workers constantly needing to open the drum and provides flexibility by allowing generators to accumulate solvent contaminated industrial wipes in any of 52 these containers that prevent air releases when not being used. Under the proposed rule, generators may take innovative approaches to meet the performance standard being sought rather than being required to use a specific design. A performance standard also provides a degree of flexibility in terms of allowing different approaches that minimize the length of time required for workers to place a used industrial wipe in a storage container. This requirement also reflects the spirit and intention of OSHA regulations. Generators who already meet OSHA container standards should meet the proposed requirement for the safe on site storage of solventcontaminated industrial wipes.

Requiring the use of covered containers during on site accumulation and storage of solvent contaminated wipes should significantly reduce any health and safety risks associated with worker exposure to vapors through volatilization from solvent contaminated wipes. Many trade associations encourage their clients to use covered containers for the on site storage of solventcontaminated industrial wipes. Similarly, some states require the use of closed containers and may specify more stringent container management standards. In the case of disposable solventcontaminated industrial wipes, almost all states currently regulate these materials as hazardous waste; therefore, containers used to accumulate these wipes at generator facilities are currently subject to the hazardous waste container standards in 40 CFR part 265, subpart I.

Alternate Option   Accumulation Time Limit EPA is considering including a condition that establishes a time limit for accumulation of solvent contaminated disposable wipes at a generator facility, so they cannot be kept on site indefinitely without management. This condition would be that solvent contaminated disposable wipes being accumulated at the generator under the conditions proposed must also follow the accumulation time limits in 40 CFR 262.34 that are applicable for their generator category ( i. e., 90 days for large quantity generators ( LQGs) and 180 days for small quantity generators ( SQGs)). In addition to following the time limits in 262.34, generators would have to mark any container in which solvent contaminated disposable industrial wipes were being accumulated with a label stating that it holds excluded solvent  contaminated wipes and stating the date accumulation started. Although this option would require generators to follow the appropriate time limit for their generator size, because the industrial wipes are excluded from the definition of hazardous waste from the point of generation, they would not have to be added to the generators counting of hazardous waste. In other words, generating solvent contaminated wipes under the conditions of the proposal would not cause a facility to move from being an SQG to being an LQG.

Alternate Option  No RCRA Specific Condition The Agency also is considering not establishing a specific accumulation condition under RCRA, but relying on other regulatory statutes, like the Occupational Safety and Health Act ( OSHA).

OSHA's occupational health and safety standards, found under 29 CFR part 1910, provide both general and specific requirements for the storage of hazardous materials in the workplace. The following discussion provides an overview of OSHA regulations and the applicability of each 53 regulation to solvent contaminated wipes.

OSHA's Hazard Communication Standard, 29 CFR 1910.1200 OSHA's Hazard Communication Standard ( HCS) was promulgated to ensure that pertinent information regarding the risks from hazardous materials in the workplace is conveyed to the workers whose responsibility it is to handle or come in contact with these hazardous materials. 29 CFR 1910.1200( d)( 1) requires " chemical manufacturers and importers to evaluate chemicals produced in their workplaces or imported by them to determine if they are hazardous. Employers are not required to evaluate chemicals unless they choose not to rely on the evaluation performed by the chemical manufacturer or importer for the chemical to satisfy this requirement." Similarly, 29 CFR 1910.1200( d)( 2) states that " chemical manufacturers, importers or employers evaluating chemicals shall identify and consider the available scientific evidence concerning such hazards."

29 CFR 1910.1200( e)( 1) requires employers to develop, implement, and maintain a written hazard communication program at each workplace. The program, at a minimum, must describe how the criteria associated with labeling, Material Safety Data Sheets ( MSDSs), and employee information and training shall be met. The premise of this regulation is that workers who understand the hazards associated with a material will be more likely to handle the material in a safe manner.

Each chemical product used in a facility, whether it is hazardous or contains hazardous chemicals, has an MSDS associated with it. MSDSs give detailed information about products, chemicals in the products, hazards, and handling specifications. Chemicals must be handled in accordance with MSDS information, and under the HCS, employees are required to be educated about the MSDS information. MSDSs may require that particular chemicals or products be stored in closed containers and/ or stored in a cool place. Almost all solvents that are RCRA listed or characteristic hazardous wastes when they are spent would probably require an MSDS.

All facilities that use hazardous chemicals are required to conduct employee hazard training. The comprehensive hazard communication programs disseminate any health or physical hazard information associated with chemicals and products used at the facility. These programs also include information about container labeling requirements, MSDSs, and other employee safety training. According to the OSHA interpretation of the HCS regulations, all containers of hazardous chemicals in the workplace must be labeled either as hazardous or with a description of the specific contents of the container.

OSHA Permissible Exposure Limit Regulations OSHA regulations under 29 CFR 1910 subpart Z support and reinforce the HCS. These regulations address exposure to numerous chemicals that pose unacceptable health risks to workers ( usually based on an 8 hour shift in a 40 hour work week). OSHA currently has 470 permissible exposure limits for various forms of approximately 300 chemical substances. Facilities managing solvent contaminated industrial wipes may be subject to these requirements and exposure limits. 9 Flammable liquids are defined as any liquids having a flash point below 100 ° F ( 37.8 ° C).

10 Combustible liquids are any liquids having a flash point at or above 100 ° F ( 37.8 ° C).

11 Discussion with Mr. Matt Stein of OSHA's Hotline on January 22, 2002.

54 OSHA 29 CFR 1910.106  Management Standards for Flammable and Combustible Liquids 29 CFR 1910.106 requires the proper management and storage of flammable9 and combustible10 liquids in the workplace. The requirements for flammable and combustible liquids are based on the National Fire Protection Association's Flammable and Combustible Liquids Code  NFPA 30.

According to OSHA standards, flammable liquids must be stored in approved containers which meet the requirements of 29 CFR 1910.106( d). Metal containers and portable tanks meeting Department of Transportation standards ( see 49 CFR part 173 and 178) are acceptable. Section § 1910.106 also specifies standards for the areas where containers holding flammable liquids will be stored, including requirements for storage cabinets, rooms, buildings, storage outside of buildings, and industrial plants. 11 However, the management of solvent contaminated wipes is most likely subject to container regulations under 29 CFR 1910.106( e)( 9)( iii), which state that " combustible waste material and residues in a building or unit operating area shall be kept to a minimum, stored in covered metal receptacles and disposed of daily."

Industry Specific OSHA Standards OSHA also has developed specific industry regulations for the protection of worker health and safety. For example, 29 CFR part 1926 provides health and safety standards for construction. The standards apply to activities associated with " construction, alteration, and/ or repair, including painting and decorating." OSHA mandates that, when disposing of waste materials, " all solvent waste, oily rags, and flammable liquids shall be kept in fire resistant, covered containers until removed from the worksite."

Similarly, 29 CFR part 1915 provides Occupational Safety and Health Standards for Shipyard Employment. subpart F regulates General Working Conditions and, specifically, " Housekeeping." These standards mandate that for ship repairing and shipbuilding, " all oils, paint thinners, solvents, waste, rags, or other flammable substances shall be kept in fire resistant, covered containers when not in use."

Finally, OSHA Section 4( b)( 1) defers to other statutes the storage and management of hazardous materials or hazardous waste when regulations are in place. Thus, DOT and RCRA regulations supersede OSHA regulations, where applicable.

EPA believes there may be gaps in coverage if the proposed regulation were to rely strictly on the OSHA regulations. For example, the OSHA container standards may not apply to contaminated wipes with no free flowing liquids or when wipes are contaminated with solvents 55 that would be RCRA hazardous but not meet the OSHA definition of flammable or combustible. Many facilities either generating or handling solvent contaminated wipes should already be subject to these standards and, as a result, deferring to OSHA standards would be simple. For them, however, the OSHA regulations might mandate that containers be sealed, removing some of the flexibility of EPA's proposal.

IV. D. 2. Proposed Conditions for Containers Used for Transportation EPA is proposing a container condition for generators who transport solventcontaminated industrial wipes off site under the conditional exclusion. This condition will ensure that transporting the wipes without full RCRA hazardous waste requirements will still protect against risks posed by these materials to human health and the environment. Under this proposal, generators must transport industrial wipes in containers that are designed, constructed and managed to minimize loss to the environment. In proposing this condition, EPA envisions containers that do not leak liquids and that provide for control of air emissions.

EPA would consider hazardous solvents that are spilled or leaked during transportation to be disposed. Therefore, the party managing the industrial wipes at the time the spill occurred would be responsible for cleaning up the spill and managing those materials appropriately.

Discussion This condition is designed to minimize loss of solvent to the environment during transportation and, therefore, to minimize environmental risk as well. Minimizing loss through evaporation or leakage also makes it more likely that larger quantities of solvent will be recycled or otherwise properly managed. This provision, implementation questions, and other options are discussed in the preamble to this proposal.

IV. D. 3 Proposed Labeling Condition for Containers Used to Transport Disposable Wipes Proposal EPA is proposing a labeling requirement that would require the use of specific language or a pre made label, such as " Excluded Solvent Contaminated Wipes," to be applied to each container used to accumulate and/ or store solvent contaminated industrial wipes, unless the wipes are being recycled. This type of requirement is comparable to the used oil labeling requirement in 40 CFR part 279.

Discussion 56 A label also informs workers of what materials they are handling, so that they can use proper handling procedures. To accomplish this at the point of generation, during transport, and during management, the container in which the wipes are placed and transported should be labeled. In addition to accumulation at the point of use, wipes may also come in contact with other containers at the generator location or in subsequent handling, on site or off site. Labeling containers helps ensure that the materials inside can be easily identified and, therefore, managed properly.

This option provides a simple solution to labeling while allowing generators to indicate that the condition is met. It would allow handlers to differentiate between regulated and excluded industrial wipes and handle them accordingly. However, the " excluded" designation added to the containers raises a question of whether a hazardous waste stigma would remain attached to the industrial wipes, regardless of their status, and still render them subject to more expensive waste management and handling after they leave the generator site.

Alternate Option  No RCRA Specific Labeling Condition Another option EPA is considering is not to impose a specific labeling requirement. Under this approach, designation of the disposable industrial wipes as hazardous materials under DOT regulations might still require placarding or other marking for transportation of some fraction of these materials, as described previously. However, for the reasons explained above, we do not expect that the DOT provisions would apply to all solvent contaminated industrial wipes covered by the proposal. This option is simple to implement and easy for generators to understand because it follows current labeling requirements without introducing a new designation for the wastes. Once the contaminated materials meet the performance standards and the materials are excluded from regulation as a hazardous waste, RCRA labeling requirements would no longer apply.

Existing regulatory programs administered by DOT and OSHA already prescribe labeling requirements for container storage and transportation. Title 40 CFR ( Environmental Protection) parts 260 264, Title 49 ( Transportation) parts 171 173, and Title 29 ( Labor) section 1910.1200 all contain regulations pertaining to management of hazardous materials, including labeling requirements. Most of the labeling requirements ( e. g., 40 CFR 262.31) relate to conditions for hazardous waste transportation and many refer to the DOT regulations found in 49 CFR 172, which require marking ( written information that varies depending on the characteristics of the waste), labeling ( where the specific wording and/ or label is provided) and placarding ( where specific placards are used on the outside of vehicles).

The OSHA standards in 29 CFR 1910.1200 require containers in the workplace to be marked with the identity of the hazardous chemicals contained within and appropriate hazard warnings that clearly convey the risks that the chemicals pose before the containers are offered for transport. Some states also require that containers with solvent contaminated wipes be marked with the date of the beginning of accumulation. In addition, OSHA standards state that " Unlabeled drums and containers shall be considered to contain hazardous substances and handled 12For the purposes of this proposal, EPA uses the term other non hazardous landfill to denote part 257 subpart B compliant non hazardous waste landfills. If a non hazardous landfill that is not a municipal landfill accepts this waste, it must meet the minimum standards of 40 CFR part 257 subpart B.

57 accordingly until the contents are positively identified and labeled" ( 29 CFR 1910.1200( j)( 1)( ii)).

EPA could emphasize this regulation in its proposed rulemaking, which would avoid the establishment of duplicative regulations. On the other hand, DOT's regulations for all non bulk hazardous materials being transported require the following:

A generator who offers hazardous waste for transportation must mark each package, freight container, and transport vehicle in a specific manner. Many pre made stickers and placards describe the dangerous characteristics of hazardous materials. The labels must be displayed prominently and clearly, and to the specifications laid out for each container or vehicle in 49 CFR 172.

The proper shipping and ID number must be included with each package for the hazardous material being transported as shown in the table in 49 CFR 172.101. If more than one hazardous substance is being carried in the same package, at least two materials, those with the lowest reportable quantities, must be identified. Technical names of the hazardous materials must be included.

Exempt packages must be marked " DOT E," along with the assigned exemption number.

The cosigner or cosignee's name and address must be marked on the package, except for in certain circumstances ( see 49 CFR 172.301( d)).

A generator must mark each hazardous waste container of 110 gallons or less with a warning, the generator's name and address, and the manifest number before transport off site.

° All vehicles transporting hazardous materials, except those materials classified as " Other Regulated Materials," must have placards in specified places in accordance with the characteristics of the transported hazardous wastes. A vehicle used to transport two or more hazardous materials that require different placards may instead use a DANGEROUS placard, so long as a total of less than 2,268 kg ( 5,000 lbs.) of hazardous material is carried. Vehicles carrying less than 454 kg ( 1,000 lbs.) aggregate gross weight of hazardous materials are not required to have a placard.

IV. D. 4. Proposed Condition for Transportation to a Municipal or Other Non Hazardous Landfill Proposal This proposed rule allows solvent contaminated wipes to be disposed in a municipal subtitle D landfill or other non hazardous waste landfill12 if they meet a condition for being " dry," meaning that each wipe contains less than 5 grams of solvent. Because of the risks of certain 58 Benzene* 2 Nitropropane Carbon tetrachloride* Nitrobenzene* Chlorobenzene* Pyridine* Cresols ( o, m, p)* Tetrachloroethylene* Methyl ethyl ketone ( MEK)* Methylene chloride Trichloroethylene*

Ethyl Ether Acetone Methanol Butanol Toluene Carbon Disulfide Xylenes Cyclohexanone 2 Ethoxyethanol Ethyl benzene Isobutyl Alcohol Ethyl Acetate Trichlorofluoromethane Methyl Isobutyl Ketone Dichlorodifluoromethane 1,2 Dichlorobenzene 1,1,2 Trichlorotrifluoroethane 1,1,1 Trichloroethane 1,1,2 Trichloroethane highly toxic F listed solvents, however, EPA is proposing to make 11 F listed solvents ineligible for this option, meaning that wipes containing these constituents cannot be disposed in a municipal landfill even if they meet the " dry" condition. Because of these concerns, EPA is proposing that industrial wipes that are contaminated with the F listed solvents specified in Table 8 cannot be disposed in municipal or other non hazardous waste landfills.

Table 8 F Listed Solvents That May Not Be Disposed in Municipal or Other Non Hazardous Waste Landfills * Solvent meets the toxicity characteristic.

Table 9 contains the 19 F listed solvents that were evaluated in EPA's risk screening analysis and that would be allowed, under this proposal, to be disposed in a municipal or nonhazardous waste landfill if they meet the " dry" condition. See section 5 for additional details on the results of EPA's risk screening analysis.

Table 9 F listed Solvents That May Be Disposed in a Municipal or Other Non Hazardous Waste Landfill Discussion In developing this option, EPA realized that the hazardous constituents present in F listed solvents each have different toxic effects, as detailed in the risk screening analysis presented in Section 5 of this technical background document. This risk screening suggests to EPA that materials contaminated with certain solvents can be disposed safely in municipal landfills, that additional caution is required for others, and that a third category of contaminants is sufficiently toxic that solvents containing them should be ineligible for disposal in municipal landfills. 59 The results of the risk screening analysis suggest that situations exist where disposable wipes contaminated with some F listed hazardous waste solvents could be managed in a municipal solid waste or other non hazardous waste landfill without posing a risk to human health, particularly if some level of solvent removal is achieved prior to disposal. However, other F listed solvents used in conjunction with disposables ( see Table 8) pose potential health risks even in small amounts. EPA has tentatively concluded that the solvents listed in Table 8 may pose an unacceptable risk to human health and the environment when disposed in such landfills.

Nine of the solvents in Table 8 are toxicity characteristic constituents, as defined in 40 CFR 261.24. EPA's analysis finds that the levels of these solvents in contaminated industrial wipes, even when they have been through solvent extraction and contain less than five grams of solvent per wipe, are likely to be higher than the regulatory levels indicated in 40 CFR 261.24. Therefore, these TC solvents are ineligible for disposal in municipal and other non hazardous waste landfills because of their potential risk, as determined when they were originally identified by EPA as TC wastes. Six of these nine are ineligible just due to their status as TC wastes. The other three ( methyl ethyl ketone, nitrobenzene, and pyridine), in addition to being TC, triggered an ineligible rating on EPA's risk screening analysis. If land disposed, industrial wipes contaminated with these 11 solvents would have to continue to be managed in full compliance with RCRA subtitle C hazardous waste management standards, including the land disposal restrictions.

EPA is proposing that disposable wipes contaminated with F listed solvents other than those in Table 8 can be managed in municipal solid waste landfills once the wipes meet the " dry" condition. However, if the wipe is contaminated by a listed hazardous waste other than F001 through F005, the wipe cannot be disposed in a non hazardous waste landfill. EPA is limiting the exclusion because insufficient data exists at this time to show that wipes contaminated with such materials would not pose a significant threat to human health and the environment if managed in a municipal solid waste landfill.

" Dry" Condition Generators transporting their disposable industrial wipes to a municipal or other nonhazardous waste landfill must ensure that the wipes are dry. For purposes of this proposed rule, an industrial wipe is considered " dry" when it contains less than five grams of solvent. EPA chose five grams because it falls within the range found in our risk screening analysis to be protective of human health and the environment. Five grams is also within the range of what is achievable through use of advanced solvent extraction processes. Generators can meet this condition either by using less than five grams of solvent on each wipe or by putting used industrial wipes through a solvent extraction process capable of removing sufficient solvent to meet the 5 gram condition.

EPA considered requiring centrifuging as the only method to meet the dry condition. However, EPA was concerned that simply requiring centrifuging could allow poorly operated or poorly constructed units to be used to meet the requirements. EPA's data on centrifuges indicates that, in general, they allow for high solvent extraction. EPA has analyzed data demonstrating removal efficiencies for hand wringing, mechanical wringing, screen bottom drums, and centrifuging. Centrifuging was found to remove the greatest quantity of solvent. EPA's 13 Descriptions of these technologies in the Technical Background document are for descriptive purposes only and is not an endorsement of the products themselves.

60 demonstration data showed that a properly operated centrifuge results in removal efficiencies of 76 to 99 percent. This is much more efficient than the next most efficient technology tested by EPA, mechanical wringing, where removal efficiency seldom exceeded 30 percent. However, EPA only observed centrifuges in use in the printing industry, with only a small percentage of generators using the technology. Additionally, although centrifuging is reported to be used for both launderable and disposable wipes, EPA lacks specific data on all of the types of disposable wipes that could be used by industry. However, based on site visits, EPA is confident that a welloperated centrifuge will meet the 5 gram condition in this proposal.

The Agency also recognized that there may be other high efficiency solvent removal technologies currently on the market or under development that could achieve removal efficiencies similar to or better than centrifuging. The Agency wants to provide generators with flexibility to employ effective technologies and is proposing to allow the use of other technologies that can achieve high rates of solvent removal. Generators who do any of the following will be considered to have met the " dry" condition:

° Remove excess solvents by centrifuging or other high performance solvent extraction or removal technology, for example, microwave solvent recovery processes or the Petro Miser or Fierro processes; 13 ° Use normal business records, such as the amount of solvent used per month for wiping operations divided by the number of wipes used per month for solvent wiping operations, to show they are under the threshold;

° Conduct sampling to measure the amount of solvent applied per wipe before use; or ° Sample to measure the amount of solvent remaining on wipes when use is completed.

Testing and extraction technologies are described in greater detail in Section IV. F. 5, in discussion of the free liquids condition.

IV. D. 5. Proposed Condition for Transportation to Non Land Disposal Facilities Proposal EPA is proposing a " no free liquids" condition for solvent contaminated industrial wipes sent for disposal at a non land disposal unit such as a municipal waste combustor ( MWC) or other combustion unit, including use as a fuel. This condition would also apply to solvent contaminated industrial wipes sent to an intermediate handler for further processing to meet the " dry" condition before disposal in a municipal or other non hazardous waste landfill. This condition is meant to minimize the likelihood of solvent loss into the environment, as well as to encourage solvent recovery and pollution prevention by generators. 61 To meet the " no free liquids" condition, no liquid solvent may drip from the wipes before they are sent off site or while they are in transit to a handler or disposal site and there may be no free liquids in the drum. In this proposal, EPA intends for compliance with the " no free liquids" condition to be determined by a practical test. That is, does liquid drip from a wipe when it is held for a short period of time ( e. g., when being transferred from one container to another)? This and other tests are described in detail below.

The proposed rule contains the provision that, if free liquids are discovered at the handling/ combustion facility, the solvent contaminated wipes would remain excluded from the definition of hazardous waste as long as the handler either removes the solvent and manages it properly or returns the shipment to the generator as soon as reasonably practicable, as described in Section V. B. 10. a. of the preamble.

Note that handlers would be required to determine whether the solvent which has been removed from the industrial wipes is listed as a hazardous waste or exhibits a characteristic as defined in 40 CFR part 261. Any hazardous waste solvent removed from the wipes would have to be managed in accordance with hazardous waste requirements found at 40 CFR parts 260 268 and 40 CFR part 270. However, for purposes of this proposed regulation, techniques or technologies used by generators to remove solvent from the wipes would not be considered treatment and would not be subject to permitting.

Discussion One concern certain stakeholders have expressed with this proposed condition is that once in a container, either at the generator site or in transit, industrial wipes can compress and solvent can percolate through them, collecting at the bottom of a container. This means that, while there may not have been free liquids in the container at the generator site, some may be generated during transportation. EPA acknowledges that compression can result in free liquids percolating to the bottom of a container.

Determining Whether the " No Free Liquids" Condition Has Been Met Under the option proposed, the " no free liquids " condition can be met by employing any of the following practices: hand wringing; use of a properly operated screen bottom drum; mechanical wringing; centrifuging; use of an enclosed, controlled air dryer with exhaust vents to recycle the recovered solvent; solvent removal and/ or recycling using low pressure evaporation; microwave or elevated temperature technology; combinations of these techniques/ technologies; or any technology or process that assures free liquids will not be released from the wipes or released into the environment during the process. These technologies are more thoroughly described below. In addition, generators who know, in their best professional judgement, that their processes do not use enough solvent per wipe to produce free liquids can rely on that knowledge. The use of air drying to pass the test is not allowed. If alternative technologies are used, the generator is responsible for determining that no solvent drips from the wipe and that containers do not have free liquids in them, as described above.

This option will allow generators to select the most appropriate solvent removal 62 technology for their particular solvent contaminated industrial wipes. Generators would be able to demonstrate that their solvent contaminated wipes do not contain free liquids through   ° Physical examination of wipes stored in containers prior to being sent off site;

° Examination of on site technologies; or ° Inspection of contractual agreements with outside parties who travel to work sites and use solvent extraction technologies on wipes.

Promulgation of this option is consistent with existing state guidance, which often requires generators to ensure that shipments of solvent contaminated wipes do not contain free liquids, although some states require the use of the Paint Filter Liquids Test ( SW 846 Method 9095) or other state developed tests.

Existing Tests for Determining " No Free Liquids"

RCRA regulations include a number of definitions which rely on the term " liquid." One definition is set forth within the context of the hazardous waste identification criteria of 40 CFR part 261. In using the Toxicity Characteristic Leaching Procedure ( TCLP)( Method 1311), generators can determine whether their waste is a " liquid" by evaluating certain results of SW 846 Method 1310. " Liquid" refers to the portion of the waste sample that is expressed from the waste. If the solid residue obtained after the separation step is less than 0.5 percent of the original weight of the sample, then the generator must treat the liquid portion of the waste as the extract. Under 40 CFR 258.28, wastes are prohibited from disposal in a municipal solid waste landfill if the waste contains free liquids. 40 CFR Section 258.28 directs generators to use the Paint Filter Liquids Test to determine whether a waste contains free liquids. RCRA also prohibits the placement of hazardous wastes containing free liquids in a hazardous waste landfill and prohibits the use of sorbents to solidify a liquid waste if the solidified waste releases the contained liquids under landfill pressures. 40 CFR Sections 264.314 and 265.314 require the use of the Paint Filter Liquids Test as the determinative method for releasable liquids.

With respect to reusable wipes, the states have different policies on what constitutes no free liquids; however, the majority of states require the Paint Filter Liquids Test for such determinations. Other specified methods include the Liquids Release Test ( SW 846 Method 9069) and the TCLP. The following sections describe these analytical tests for determining " no free liquids," and provide some discussion on the applicability of these tests to solvent contaminated wipes.

Physical Examination The simplest technique that many facilities use is to examine a sample of wipes stored in the bottom of the container immediately prior to subsequent handling   either on site or off site. If the amount of solvent applied to the wipe is small ( five to ten grams), then there is a very good chance that no free liquids will be present on the wipe or in the container. Therefore, generators using small amounts of solvent can check their compliance with physical examination of their 63 wipes.

Paint Filter Liquids Test The Paint Filter Liquids Test, SW 846 Method 9095, is a laboratory method used to determine the presence of free liquids in a waste sample. The waste sample is placed in a conical paint filter suspended in a ring stand. The paint filters are typically fine meshed size. To test for the removal of free liquids, the waste sample is weighed prior to testing to determine the amount of absorbed liquid and then placed in the paint filter. If liquid begins to drip from the waste sample in less than 5 minutes, the sample fails and the test is terminated.

To gain accurate and dependable results, tests must be conducted at temperatures above the freezing point of all liquids in the sample. Tests may also be performed above room temperature, 25  C. Exposure to alkaline materials may cause the filter media to separate from the filter cone. However, if the sample is not disturbed, results remain accurate.

If the test is performed long in advance of shipment off site, free liquids may percolate through the container because of the weight of the wipes on top, and this may result in free liquids at the bottom of the container. Because there must be no free liquids in the containers at the time they are sent off site, the generator would be in violation of the no free liquids condition if free liquids were found in the container ready to be shipped, even if those wipes had previously passed the no free liquid test.

Liquids Release Test The Liquids Release Test is a laboratory method that determines whether or not liquids will be released from a waste sample when subjected to the overburden pressures of a landfill. The waste sample is placed between two stainless steel screens supported by two stainless steel grids on opposite sides. The grids are followed by absorptive filter paper while a piston presses down on the top screen with a force of 50 pounds per square inch. Any release of liquid to the filter paper underneath the bottom supporting grid or above the top supporting grid indicates potential release if the waste were subjected to landfill conditions.

Although this test simulates landfill conditions, there are several sources of error. Effects of liquids from external sources, such as rain and snow, have not been estimated and, therefore, are not considered. Also, because some waste samples contain volatile solvents that may quickly evaporate after migrating to the filter paper, samples must quickly be examined as soon as tests are completed. In a limited study, EPA found that many disposable paper wipes pass this test even when considerable amounts of solvent are applied to samples. When solvent is applied at 50 percent of the wipe weight, most samples passed this test. When solvent is applied at 25 percent of the wipe weight, all samples passed this test. For solvents applied at 100 percent of the wipe weight, 88 percent ( 15 out of 17) of samples passed this test ( SAIC 1997). Experiments yielded varying results when they tested disposable cloth wipes due to the method of and materials used in cloth wipe construction.

One Drop Test 64 The One Drop Test was developed by the Massachusetts Department of Environmental Protection and is used by generators in Massachusetts to determine whether industrial wipes contaminated with waste oil are saturated and/ or hazardous. To pass the one drop test, the wipe must not release " one drop" of solvent when hand wrung. Use of a mechanical wringing machine is also recommended to guarantee meeting this standard. If one drop occurs, the solventcontaminated industrial wipes must be managed as a hazardous waste, in accordance with 310 CMR 30.000 until samples pass the One Drop Test. Air drying of wipes to satisfy the one drop test is prohibited.

Solvent Removal Techniques to Meet the " No Free Liquids" Condition In the course of developing this proposed rule, EPA found numerous techniques and technologies that can be used to meet the " no free liquids" condition and the " dry" condition discussed in Section IV. F. 4. The decision to apply these techniques and technologies depends on several site specific factors, including ° The amount of solvent placed on wipes;

° The number of wipes used daily;

° The amount of capital investment available to purchase advanced technologies; and ° The need to comply with other environmental regulations, such as Clean Air Act ( CAA) National Emissions Standards for Hazardous air Pollutants ( NESHAPs), and Clean Water Act ( CWA) effluent guidelines.

The following sections describe physical and mechanical wringing methods and other nonthermal treatment technologies that are currently used, or can be used, to remove solvents from industrial wipes. These sections also provide some discussion on the applicability and efficiency of these treatment methods. Table 10 summarizes the experiments conducted with these technologies, as well as with combinations of these technologies. 14Hand wringing may only be needed for wipes stored in the lower portion of the container if, because of percolation effects, the wipes in the higher portions of a drum do not contain much solvent.

15 Descriptions of companies or technologies found in this Technical Background document are for descriptive purposes only and are not an endorsement of the products themselves.

65 Table 10 Summary of Experiments with Solvent Removal Technologies ( Solvent Weight Two Times Dry Weight of Wipe)

Technology Screen bottom drum Mechanical wringing Hand wringing Mechanical wringing + hand wringing Hand wringing + mechanical wringing Mechanical wringing + screen bottom Hand wringing + screen bottom drum Centrifuging Percent Solvent Removal 4 28 12.9 55.8 4.6 68 9.8 43.8 5.8 42.3 10.8 51.5 8.8 52.7 76 99 Source: SAIC, Use and Management Practices of Solvent Contaminated Industrial Shop Towels and Wipes, December 23, 1997 Hand Wringing Hand wringing can be used to remove any free liquids or contaminating solvents from reusable wipes and disposable paper and cloth wipes. Wipes are twisted by hand until no solvent appears. To test removal efficiency, the wipe can be weighed before and after twisting or wringing. Because of varying factors, such as the strength of the person wringing the wipe and the fabric type of the cloth wipe, solvent removal will not be as consistently effective as other techniques or technologies. Hand wringing can be very inexpensive unless large numbers of wipes must be hand wrung, in which case labor costs must be considered. 14 This technique requires the use of personal protective equipment.

Based on the results of a 1997 study, mean removal efficiency ranged from 5 percent to 24 percent for reusable wipes and disposable paper wipes when the applied solvent was 2 times the weight of the wipe. For reusable wipes specifically, mean removal efficiency was 3.45 percent when the applied solvent was half the weight of the wipe and 11.3 percent when the applied solvent weighed twice as much as the wipe. Removal efficiency ranged from 1.6 percent to 68 percent for disposable cloth wipes when the applied solvent weighed twice as much as the wipe. Studies also show that mean removal efficiency is usually greater when more solvent is on the wipe ( SAIC 1997).

Screen Bottom Drums15 Screen bottom drums can be used to remove free liquids from both reusable and 16Prices referenced in this section reflect costs at the time EPA did research on these technologies in 1998 1999 and have not been updated to reflect 2003 costs.

66 disposable wipes. Screen bottom drums are steel drums equipped with a screen or sieved plate near the drum bottom. The screen or sieved plate supports the contents of the drum, and is used to separate the industrial wipes from the liquids that have percolated to the bottom of the drum.

From site visits and experiments, EPA has found that wipes stored immediately above the screen tend to be saturated with large amounts of solvent as they can act as a dam and hold back solvent moving downward. Handlers must be careful to address this situation. This can be accomplished by hand wringing the relatively small number of wipes sitting immediately above the screen or by transferring the wipes to another container with wipes already stored in it to start the percolation process again. This technology requires use of personal protective equipment for those handling the wipes.

Efficiency of screen bottom drums appears to be dependent on the solvent being used and the type of wipe. Based on a 1997 study, mean removal efficiency ranged from 4 percent to 28 percent for all types of industrial wipes. A linear increase in wipe weight also exists as wipes from top to bottom are re weighed after 24 hours of packing. Although this technology is not very efficient, it may be more useful if employed along with mechanical wringing or hand wringing technologies.

Mechanical Wringing Explosion proof mechanical wringers can be used to remove any free liquids or contaminating solvents from reusable wipes and disposable paper and cloth wipes by using a mechanical device in a similar manner as the hand wringing method. Mechanical wringers should have squeeze rollers made of materials that will not deteriorate when exposed to solvents. To test removal efficiency, wipes can be weighed before and after wringing. This technology requires use of personal protective equipment for persons handling wipes.

Removal efficiencies for mechanical wringing vary depending upon the type and makeup of disposable paper or reusable wipes. Based on the results of a 1997 study, mean removal efficiency ranged from 13 percent to 30 percent when solvent applied was twice the weight of the reusable wipes or disposable paper wipes. Removal efficiency ranged from 11 percent to 56 percent for disposable cloth wipes. Mean removal efficiency ranged from 7.5 percent to 19 percent when solvent applied was half the weight of the disposable paper wipe. Mechanical wringing removed as much as 30% of solvent from spent disposable paper wipes and reusable wipes and as much as 50% of solvent from some types of disposable cloth wipes ( SAIC 1997).

Hand operated mechanical wringers require a small capital investment and may, therefore, be most valuable for small quantity generators. EPA found these models priced from $ 600 to $ 2700.16 Centrifuging 67 Centrifuging is another solvent removal technology appropriate for disposable and reusable cloth wipes. Specially designed centrifuges remove solvent from wipes; over a hundred wipes are placed in a container and the centrifuge is operated for a few minutes, removing the solvent and leaving a dry wipe. Due to their complexity, centrifuges have a much higher capital cost and a generator can either purchase the unit directly or use a contract centrifuge service. Centrifuging machines should be explosion proof. Also, this technology requires use of personal protective equipment for those handling the industrial wipes. Centrifuges are manufactured with a self balancing, perforated basket allowing solvents to drain through the outer containment shell. It is estimated that a four minute cycle can extract between 2.5 and 3.5 gallons of solvent for every load of 225 wipes processed.

EPA collected data on removal efficiencies of centrifuges, some of which is presented in Use and Management Practices of Solvent Contaminated Industrial Shop Towels and Wipes, EPA, December 1997, found in the docket for the proposed rule.

One set of EPA tests led the Agency to estimate solvent removal efficiency to be about 50 percent. During these tests, the weight of the used wipe prior to centrifuging ranged from 2.3 to 3.9 times the weight of the unused wipe. Subsequent discussions with the company conducting the test found that the centrifuge was not operating properly and that removal efficiencies were regularly about 75 percent.

Other removal efficiency data supplied to EPA includes the following: ( 1) a centrifuge vendor, Maratek, indicates solvent removal efficiency of 85 percent ( Newspaper Association of America TechNews, January 1997); ( 2) a Wisconsin printer indicates a removal efficiency of 76 percent. EPA also conducted controlled tests of a centrifuge operation with a Minnesota printer, John Roberts, and obtained solvent removal efficiencies of 95 to 100 percent using a variety of disposable wipes and various solvents. Results of experiments conducted by Bock Engineering, a manufacturer of centrifuges, also found solvent removal efficiencies in the 95 to 100 percent range.

The use of centrifuging is relatively uncommon. An industry survey of printing facilities indicated that about three percent use centrifuging ( SGIA 1994b). This is consistent with observations made during EPA's site visits in 1997. Centrifuges can require a substantial capital investment. EPA found centrifuges processing 35, 60, 100, or 130 pounds per load to cost between $ 21,000 to $ 30,000. They are also available as a contracting service. Some services charge about $ 65/ hour; about 1,500 to 1,800 wipes can be processed during this time. One contractor who uses a mobile centrifuging technology charges between 3 and 11 cents per wipe, depending upon the volume of wipes treated.

High Volume Air Drying The High Volume Air Drying method uses laboratory hoods with high velocity air transport to achieve removal of contaminating solvents from disposable and reusable wipes. This technology, however, requires the use of expensive, carbon canister devices or other solvent vapor absorption devices and requires use of personal protective equipment for those handling 68 wipes.

High volume air drying is extremely efficient, regardless of wipe type or solvent, resulting in nearly 100 percent efficiency with the use of a control device like a carbon canister to absorb solvent vapors. This technology is restricted, however, since inexpensive commercial devices needed for solvent vapor absorption are not readily available.

Microwave Technology MicroChem, L. L. C. has developed a microwave technology similar in principle to household microwave ovens. With this system, solvent contaminated industrial wipes are exposed to microwave power under a vacuum. The solvent is vaporized off of the wipes and captured as clean solvent which is returned to the generating facility for reuse. This process has a solvent recovery efficiency of 98 percent. Generating facilities using several hundred wipes per day can recover their investment costs by substituting recovered solvents for new solvent purchases. The cost of this system was unavailable but MicroChem is examining the feasibility of building mobile units.

Maratek Shop Towel On Site Recycling System The Shop Towel On Site Recycling System is an integrated on site dry cleaning/ solvent recovery system designed primarily for organizations using at least 1,000 industrial wipes per day and large amounts of solvent on each wipe. At a cost of $ 177,000, this system can clean wipes and recover and reuse over 95 percent of the solvent contained on them. Again, cost savings are obtained by reusing solvent, thereby reducing purchasing costs for new solvents.

Industrial Laundry Solvent Recovery Systems Brent Industries and Industrial Towel and Uniform, Inc. ( ITU), among others, use petroleum based solvents to process the industrial wipes, as well as to extract solvents contained on them for recovery and reuse. In both cases, any excess solvent recovered is either reused on site or sold to external customers.

Fierro Technologies Fierro has developed a patented process in which totally enclosed vacuum extractors vaporize solvents out of woven and non woven products to be recycled. Once the solvent is vaporized, the solvents are recondensed back into a liquid state for reuse by the generating facility. Solvent recovery rates are almost 100 percent, based on data generated by Fierro at the request of EPA.

IV. D. 6. Exotic Solvents Proposal In the proposed rule, EPA requests information and comments on " exotic" solvents, such 69 as terpenes and citric acids, and how they are presently managed. Specifically, EPA asks for information and comments on the following to help the Agency develop a final rule.

° Which solvents that would currently be considered hazardous wastes are viewed as " exotic?"

° For which solvents do commenters believe a " no free liquids" condition would be problematic?

° Information on documented cases of combustion caused by a lack of free liquids.

° Comments on whether the final rule should give special consideration to wipes contaminated with exotic solvents, particularly allowing the solvents to be wetted down with water during accumulation and transport.

Discussion In the process of developing this proposed rulemaking, the Agency learned that there are new, " exotic" solvents on the market, such as terpenes and citric acids, which, while labeled as non hazardous, could actually be flammable.

Although the solvents do not exhibit the ignitability characteristic in 40 CFR 261.21, stakeholders have told us that, under certain conditions that have yet to be determined, oxygen can mix with the industrial wipes that contain these exotic solvents and spontaneously combust. According to some fire marshals and representatives of industrial laundries, resulting fires have caused major damage to facilities. Some stakeholders have suggested that EPA propose that generating facilities be allowed to transport their industrial wipes off site with free liquids if the facility is using one of these " exotic" solvents that could react or spontaneously combust, so that generators can wet down the wipes with water prior to sending them off site.

IV. D. 7. Proposed Condition for Generators who Remove Solvent from Industrial Wipes Proposal Any solvent removed from an industrial wipe may be subject to regulation as a hazardous waste. Therefore, the generating facility would be required to determine whether the solvent removed from the industrial wipe, if it is not reused, is listed as a hazardous waste or exhibits a characteristic of hazardous waste and, if so, manage the solvent according to prescribed RCRA regulations under 40 CFR parts 260 268 and 270.

Under EPA's proposed exclusion from the definition of hazardous waste, the solventcontaminated industrial wipes would not be hazardous waste at the time they undergo solvent removal. Therefore, solvent removal technologies would not be considered treatment of hazardous waste under RCRA and such operations, whether they are conducted by generators or handling facilities, would not be considered to be treating hazardous waste and would not require a RCRA permit. 70 Discussion A number of facilities generating solvent contaminated wipes that meet the definition of hazardous waste perform solvent extraction processes, such as hand wringing, mechanical wringing or centrifuging, all of which separate the spent solvent from used wipes. The resulting spent solvent is then sent to be recycled or disposed in compliance with RCRA subtitle C, if applicable.

EPA's proposed regulatory structure, which, if conditions are met, makes solventcontaminated industrial wipes not hazardous waste at the time of solvent removal, thereby makes the solvent recovery process not treatment of hazardous waste. This structure is meant to encourage removal and recycling of solvents. Because the proposed rule does not impose RCRA requirements on solvent extraction, generators may be more likely to recover solvent for reuse and reduce the amount of solvent that they purchase. The provisional also makes the rule a more realistic option for smaller businesses which may be unwilling to undertake the RCRA permit process, but would like to be able to remove solvents from industrial wipes to meet the conditions of the proposed rule.

IV. D. 8. Proposed Conditions for Intra Company Transfers Proposal To encourage recovery and recycling of the solvents in the wipes, EPA is proposing to allow generators to continue to qualify for the exclusion from the definition of hazardous waste if they transfer solvent contaminated industrial wipes containing " free liquids" between their own facilities and if the receiving facility has a solvent extraction and/ or recovery process that will remove sufficient solvent to ensure the wipes meet either the " dry" condition or the " no free liquids" condition before being sent off site.

To be eligible for the exclusion, generators must meet the other conditions described in this notice. Specifically, the generator would be required to accumulate the wipes and solvents in non leaking covered containers and to transport the industrial wipes in containers that are designed, constructed and managed to minimize loss to the environment and labeled " Excluded Solvent Contaminated Wipes." EPA is proposing the same performance standard for intracompany transfers of wipes as for wipes meeting the " dry" and the " no free liquids" conditions. Note that because of the free liquids transported with these wipes, not all types of containers are likely to be appropriate ( e. g., cloth bags are not likely to minimize loss for wipes containing free liquids). The solvent, once extracted, would have to be managed as a RCRA hazardous waste if going to disposal. EPA believes this option would result in substantial savings for generators of solvent contaminated industrial wipes as well as in increased solvent recovery by generators.

Discussion Several stakeholders, particularly those who use large numbers of wipes daily with large amounts of solvent on each wipe, would like to transfer their wipes to an intra company facility that would extract the solvents from the wipes without meeting the " no free liquids" condition. 71 Several states already allow these kinds of transfers to be made when both the generating facility and the extracting facility are part of the same company. Under the proposed condition, the solvent extracted at this point could either be returned to the originating customer or sold to another manufacturer for reuse as a feedstock in a manufacturing or service operation. Alternatively, when the economics of solvent recycling are not favorable, the extracted solvents could be disposed as hazardous wastes.

The potential benefits to allowing such shipments under the conditional exclusion from the definition of hazardous waste include additional opportunities for increased recycling, because some generating facilities would find it more profitable to recycle solvents when not having to meet the " no free liquids" condition before sending industrial wipes to a facility with extracting capability. In this case, it is inefficient to remove the free liquids and then ship them to the centrifuge for more solvent extraction. As a result, many wipes go untreated. EPA hopes that, by taking advantage of the proposed provision, the companies in this situation would be able to reduce total solvent use through recovery and reuse, and, therefore, save money. As stated elsewhere in this proposal, several technologies already exist to extract and recover the spent solvent contained on industrial wipes both economically and safely. In addition, there are likely to be environmental benefits because solvent that would have been sent to combustion or disposal in a landfill would be recovered and reused.

A potential disadvantage of allowing intra company transfers without assuring that the containers do not contain free liquids is that it increases the risk of a hazardous waste incident during transportation. Companies taking advantage of this would be required still to transport their wipes in DOT approved, non leaking containers and would not, as EPA sees it, be transporting the wipes very far. EPA is not proposing a specific distance that wipes can be transported under this provision, but is requesting comment on the issue.

Other Options The specifics of other options for this provision aer laid out in the preamble for this rule.

IV. D. 9. Proposed Conditions for Management at Handling Facilities Proposal Of all the handlers, generators have the primary responsibility for assuring that the industrial wipes they transport off site meet the conditions for the exclusion, but non landfill facilities that receive disposable industrial wipes, such as combustors or handling facilities that perform further solvent removal, would also need to meet certain minimum conditions for the wipes to remain excluded from the definition of hazardous waste. First, during the time between when the wipes arrive and when the facility first introduces them into their process ( e. g., when the wipes are removed from their container and placed in a solvent extractor), these facilities must store solvent contaminated industrial wipes either   ( a) In containers that are designed, constructed and managed to minimize loss to the environment ( i. e., that would meet the transportation condition in the proposed rule); or 72 ( b) In non leaking covered containers that would meet the generator conditions in the proposed rule.

The second condition is that if facilities ( other than those intra company facilities where solvent is removed) receive solvent contaminated industrial wipes with free liquids, in order to retain the exclusion from the definition of hazardous waste, they would have to   ( a) Recover and properly manage any liquid solvent that arrives at the facility under federal or state hazardous waste regulations, as applicable; or ( b) Return the container ( with the wipes and liquid) to the generator as soon as reasonably practicable ( e. g., with the next scheduled delivery). When returning the wipes and liquid to the generator, the facility would have to transport them in containers that meet the original shipment conditions, but would not need to use a hazardous waste manifest.

Discussion The objective of this condition is to address situations where free liquids arrive with industrial wipes at a handling facility through no fault of the handling facility. Rather than subject these materials to RCRA hazardous waste requirements, EPA is proposing that these materials be allowed to be further processed to ensure that the conditions of the exclusion are met. We believe this can be done safely and we also believe that this will provide additional incentive for solvent recovery. At any time that hazardous solvents are spilled or leaked, we would consider this to be disposal and the handling facility managing the solvents would be responsible for cleaning up the spill.

EPA believes there is no reason for handlers to open containers with solvent contaminated wipes before the wipes enter the handling process. By not opening these containers, the potential for fires, exposure to workers and the general public decreases considerably. If free liquids are found once the container is opened, EPA would provide flexibility in what the handler can do. Currently, the handler is managing a hazardous waste if containers holding free liquids arrive. Under the proposal, EPA would provide flexibility to handlers in that they have two options to avoid a hazardous waste classification. They can either remove the solvent from the container themselves, continue to send the wipes through their process, and manage the solvent as a hazardous waste, or they can send the container with all materials enclosed back to their customer for them to manage properly.

This proposed condition fosters compliance without creating unnecessary burdens on either the generator or handler. Whether the handler removes the free liquids or sends the container back to the generator, additional costs are incurred that should be passed back to the generator S hopefully fostering changes in their process so that free liquids no longer arrive at the handling facility.

IV. D. 10. Management of Industrial Wipes Containing Co Contaminants Proposal 73 Solvent contaminated industrial wipes that exhibit a characteristic of hazardous waste due to co contaminants also are not eligible for the exclusion, unless the characteristic is ignitability. Specifically, EPA is proposing that industrial wipes that exhibit the characteristics of toxicity, corrosivity, or reactivity because of wastes with which they are co contaminated are not eligible for the conditional exclusion. On the other hand, because the industrial wipes are already likely to be ignitable because of the nature of the solvents on them, and because this risk is managed by the conditions of the exclusion, wipes co contaminated with ignitable waste would remain eligible for the exclusion if they meet the other conditions of the exclusion.

Discussion The proposed rule is not intended to override EPA's mixture rule regarding contaminants on industrial wipes other than the solvents specified in this proposal. In addition to these solvents, spent wipes from industrial applications may be contaminated with material removed during the industrial process S anything from dirt and grease to listed hazardous wastes. The presence of these co contaminants may make the industrial wipes subject to the hazardous waste mixture rule ( 40 CFR part 261.3( a)( 2)( iv)), which states that a mixture made up of any amount of a nonhazardous solid waste and any amount of a listed hazardous waste is a listed hazardous waste. Therefore, if the wipe contains a listed waste other than the identified solvents, it will be considered a listed hazardous waste and will no longer be eligible for the exclusion from the definition of hazardous waste being proposed.

Spent wipes from industrial applications are not only contaminated with solvents ( some listed and/ or characteristically hazardous), but they are also often contaminated with material removed during the industrial process. This material may be specific to the industry or process ( e. g., inks and printing sludges; lacquers and other coatings from auto body repair; stains, shellacs and other coatings from the furniture production and refinishing industry), or they may be generic in nature ( e. g., dirt, metal shavings, waxes and spent lubricating oils). In either case, these cocontaminants may pose a hazard to human health or the environment if they are disposed with spent wipes in a non hazardous waste landfill or incinerator.

Previous investigations have identified the following industries as likely to produce significant quantities of spent wipes contaminated with listed or characteristically hazardous solvents:

 printing  auto body repair  furniture refinishing The materials used in each of these industries and the tasks for which solvents and wipes are used suggest contaminants that are likely to be found on spent wipes. These contaminants are discussed below, in categories by industry. The information presented here is based on information gathered during site visits, literature research, and Internet searches. 74 Printing The printing industry encompasses diverse processes for transferring images to a wide range of substrates, including coated and uncoated paper, polymer films, and fabrics. These diverse processes include lithographic, flexographic, offset, rotogravure and screen printing. All of these industrial printing processes generate waste ink and ink sludges that are frequently codisposed with spent wipes. While actual ink formulations differ from process to process, they are generally composed of   ° A colorant ( either pigment [ insoluble colorant] or dye [ soluble colorant]); ° A vehicle ( which disperses the colorant); and ° A modifier ( added to control ink or coating viscosity, slickness of the surface, drying time, stability to exposure to light and humidity, and rub resistance).

Colorants represent the most chemical diversity in the ink system, and pose the greatest potential for hazard. Colorants may be generally classified as   ° Organic pigments  based primarily on carbon but may contain metallic elements necessary to make the compound insoluble. They include azo compounds, triphenylmethane salts, rhodamines, and phthalocyanines. ° Inorganic pigments  including salts and oxides of lead, chromium, cadmium, barium, titanium, and iron; calcium carbonate, aluminum silicates, magnesium carbonate, and alumina hydrate; aluminum powders for silver inks and bronze powders for gold inks. ° Carbon black pigments  very small particle size and structural complexity in relation to all of the other pigment types. ° Acidic dyes  these have limited applications and are rarely used. ° Basic dyes  primarily aniline compounds. ° Azo metal complexes ( dyes)  azo dyes complexed with inorganic constituents, most commonly chromium. ° Disperse dyes  low molecular weight organic compounds that sublimate at relatively low temperatures.

Little specific information could be found on the vehicles ( dispersants) used in ink formulations. Ink MSDSs obtained on the Internet usually claimed the information to be proprietary or did not include any information at all. Anecdotal information indicates that the vehicles are usually solvents ( at least for liquid inks), and that these solvents primarily consist of toluene, acetone, varnish maker's and painter's naphtha, xylenes, and various aliphatic hydrocarbons. Inadequate data is available to assess the relative proportion of solvent burden on the contaminated wipe at the time of disposal that can be attributed to solvent in the waste ink or sludge versus the amount of solvent applied directly to the wipe.

Modifiers are added to ink systems to control process and wear characteristics. The majority of these additives fall into one of the following categories:

° Phenolic resins 75 ° Acrylic resins ° Hydrocarbon ( petroleum based) resins ° Cellulose and modified cellulose resins.

MSDSs indicate that glycol ethers and vinyl chloride monomer are also added as modifiers ( vinyl chloride is a known human carcinogen).

No data could be found on the volumes of inks or specific colorants sold or used in any given time period that would allow one to draw even preliminary conclusions about the amounts of any of these components that are disposed of during a given time period, nor to estimate possible risks to human health and the environment posed by specific disposal scenarios. However, observations made during site visits conducted earlier indicate that the total amounts of waste inks and ink sludges disposed on contaminated wipes may be significant. As demonstrated by MSDSs, many of the colorants used include toxic compounds or elements, some of which are toxicity characteristic constituents. Insufficient data is available to estimate the fate of contaminated wipes in the TCLP.

Auto Body Repair Site visits indicate that industrial wipes are one of auto body repair shops' multiple waste streams. Outside of general housekeeping activities, wipes appear to be used with listed or characteristically hazardous solvents for surface preparation. Some applications are   ° Wax and grease removal; ° Dust and particulate removal, including metal shavings and epoxy, acrylic and urethane resins; and ° Removal of lacquers and coatings. The colorants present in automotive paints appear to be the same as many of those used in ink formulations. No data could be found on the volumes of automotive body fillers, paints and finishes, or specific colorants that would lead to conclusions about the amounts of these materials co disposed with spent wipes or to estimate possible risks to human health and the environment posed by specific disposal scenarios. However, observations made during site visits indicate that the total volume of co contaminants on spent wipes generated in body shops is not significant. As demonstrated by MSDSs, many of the colorants used include toxic compounds or elements, some of which are toxicity characteristic constituents. Insufficient data is available to estimate the fate of contaminated wipes using the TCLP. Additionally, reactants used in epoxy and urethane resin formation and curing are known to be toxic. Whether any significant amount of unreacted material is present on spent wipes is not known.

Furniture Refinishing Furniture finishing and refinishing processes involve the application of solvents, stains, and finishes ( lacquers, shellacs, urethane coatings), which generate spent wipes that are cocontaminated with all of these materials. Through anecdote, EPA found that production of spent wipes in these processes is significant. Insufficient data was available to make conclusive judgements about these materials, as most of the formulations are considered proprietary. MSDSs 17 As used here, destruction compares the composition of the exiting ash to the composition of the incoming municipal solid waste. For comparison, hazardous waste combustors require 99.99 percent destruction, when comparing the composition of the exiting air to the composition of the incoming waste. Because the constituents of concern are largely volatile, larger quantities of the unreacted constituent are expected to be present in exhaust gas rather than in ash residue.

76 do indicate that the formulations are solvent based ( primarily acetone, methyl ethyl ketone, isopropyl alcohol, aliphatic hydrocarbons and aromatic hydrocarbons), and that some finishes also may contain nitrocellulose. No information was located on the types of colorants used in wood stains. Insufficient information is available to estimate either the volume or composition of the waste stream, or to evaluate any potential hazard posed by co disposal with spent wipes.

IV. D. 11. Proposed Conditions for Burning Solvent Contaminated Industrial Wipes in Combustors Proposal EPA is proposing that municipal and other waste combustors be allowed to burn solventcontaminated industrial wipes that meet the proposed conditions for the exclusion. Facilities managing these wipes would have to ensure that the wipes remain in containers that meet either the proposed generator or transportation condition until they enter the combustion process. Also, if a combustion facility finds industrial wipes with free liquid solvents when it initiates processing of the wipes, for industrial wipes to retain the exclusion, the facility would have the choice of removing the free liquids and managing them as a hazardous waste or closing the container and sending the wipes back to the originating generator. When returning the wipes and liquid to the generator, the combustor would have to transport them in containers that meet the original shipment conditions, but would not need to use a hazardous waste manifest.

Discussion The proposed rule would allow solvent contaminated wipes to be managed at MWCs regulated under subtitle D and applicable state specific controls, provided neither the wipes themselves, nor the containers they are in, contain free liquids and that they are shipped to the MWC in closed containers that are appropriately labeled. Destruction rates for solvents are expected to be at least 99.99 percent in MWCs, when comparing the incoming waste concentration to the ash concentration. 17 These rates are expected because constituents would be destroyed and/ or would volatilize to the exhaust air. Based on the Agency's analysis of the potential risks associated with this proposal, the Agency found that given the rate of destruction expected to occur in MWCs, ash from burning solvent containing wipes is not likely to exceed these limits.

The advantages of this approach include

Greater regulatory relief for generators;

Decreased costs for treatment and disposal;

Emissions controls stringent enough to ensure protection against potential releases 77 of solvent constituents; and

Greater potential for residues to remain under subtitle D controls.

The disadvantages of this approach include

Potential confusion due to variation in state specific requirements for the management of wastes at MWCs; and

Some MWCs may refuse to ever accept exempted hazardous waste.

Municipal Waste Combustors MWCs do not obtain RCRA permits, do not operate under subtitle C management requirements, and therefore are prohibited from managing hazardous wastes, per 40 CFR 270.1( b). As proposed, however, solvent contaminated wipes meeting the conditions of a regulatory exclusion would be excluded from the definition of hazardous waste. MWCs burning such wipes would be managing a " solid waste" rather than a " hazardous waste" and consequently would not be required to obtain a RCRA hazardous waste permit or meet the operating requirements or performance standards applicable to hazardous waste combustors ( HWCs). MWCs are already subject to stringent performance standards that may be considered comparable to those applicable to HWCs regulated under 40 CFR part 264, subpart O. Thus, MWCs are capable of burning excluded wipes in a manner that is protective of human health and the environment.

Although the requirements for MWCs are generally promulgated at the state level, there are basic guidelines for thermal processing of solid wastes established at the federal level under 40 CFR part 240. These requirements delineate the minimum levels of performance required of any thermal processing operation. However, the addition of any further controls beyond the emissions standards established under the Clean Air Act ( CAA) would be done through an individual state's municipal solid waste program. The guidelines or recommendations provided in 40 CFR part 240 also include   ° Designation of wastes acceptable for burning at facilities; ° Assurance that the facility has been designed to handle such wastes; ° Exclusion of wastes from being handled at a combustion facility based on certain criteria ( i. e., facility's capabilities, alternative methods available, chemical and biological characteristics of the waste); ° Recommendations for general design, site selection, water and air quality, control of vectors, aesthetics, management of residues, and safety measures; and ° General operating procedures which specify that the facility should be operated and maintained in a manner that assures the facility will meet the design requirements. Recommended procedures include providing adequate personnel training, determining alternate disposal and operating procedures for emergencies, and creating routine maintenance schedules.

EPA promulgated revised air emission requirements for MWCs under the New Source Performance Standards ( NSPS) on December 19, 1995 ( 60 FR 65387). The standards and 18 New MWCs are defined as those for which construction is commenced after September 20, 1994.

78 guidelines establish emission levels for   ° MWC organics ( dioxins and furans only); ° MWC metals ( cadmium, lead, mercury); ° MWC acid gases ( hydrogen chloride, sulfur dioxide, and nitrogen oxides); ° MWC fugitive ash emissions from both new and existing MWCs; 18 and ° Other parameters, such as particulate matter and opacity.

In addition, operating conditions are specified, including carbon monoxide levels, load restrictions, and flue gas temperature at the PM control device inlet. Numerous other requirements concerning " good combustion practices" apply as well for MWCs ( see 40 CFR part 60, subpart Eb). These requirements include feed rate limits, continuous emissions monitoring, annual stack testing, and certification of facility operators.

EPA has promulgated revised air emission requirements under the New Source Performance Standards for large new MWCs ( facilities managing more than 250 tons of waste per day) under subparts Ea and Eb of 40 CFR Part 60 and large existing MWCs under subpart Cb of Part 60. There are 167 large MWCs in the US and all of these facilities now meet these standards. Similarly, EPA has promulgated revised NSPS air emission requirements for smaller MWCs ( facilities managing less than 250 tons of waste per day) under Subparts AAAA and BBBB of 40 CFR part 60. All 39 existing smaller units should be retrofitted to meet these new standards by 2005. As described in the TBD, these NSPS standards provide a level of protection comparable to hazardous waste incinerators and should be able to burn solvent contaminated wipes without any difficulty.

Hazardous Waste Combustors Hazardous waste managed prior to burning in a boiler or industrial furnace ( BIF) or incinerator is subject to all applicable RCRA regulations, including   ° The hazardous waste manifest system; ° The use of hazardous waste transporters; and ° Storage in hazardous waste management units meeting the standards of part 264/ 265 ( e. g., container standards of subpart I, tank standards of subpart J).

BIFs and incinerators are regulated as hazardous waste treatment, storage, and disposal facilities, so they also must comply with the additional general management requirements of 40 CFR part 264/ 265, as follows:

° Hazardous waste general facility standards ( subpart B); ° Preparedness, prevention, and emergency response standards ( subparts C and D); ° Groundwater monitoring requirements ( subpart F); ° Closure and post closure requirements ( subpart G); and 79 ° Financial assurance requirements ( subpart H).

HWCs also must obtain RCRA hazardous waste operating permits, a process which involves public participation procedures.

EPA has updated the air emission standards for hazardous waste combustors, which are co promulgated under RCRA and the CAA. This rule ( 64 FR 52828, September 30, 1999) establishes stringent air emission regulations for hazardous waste incinerators, hazardous wasteburning cement kilns, and lightweight aggregate kilns. The standards include limits on emissions of chlorinated dioxins and furans, mercury, particulate matter, semivolatile and low volatile metals, hydrogen chloride and chlorine gas, carbon monoxide, hydrocarbons, and destruction and revomal efficiency, in lieu of standards for nondioxin/ furan organic hazardous air pollutants.

Comparison of Air Emission Standards presents a side by side comparison of the key air emission standards for new MWCs and HWCs. presents a side by side comparison of the key air emission standards for existing MWCs and HWCs.

Table 11 80 Comparison of Key Air Emission Standards for New Combustion Units Parameter New Municipal Waste Combustors ( MWCs) New Hazardous Waste Combustors ( HWCs)

1. Carbon monoxide ( CO) 50 150 ppmv, depending on unit type 100 ppmv 2. Particulates ( PM) 24 mg/ dscm ( 0.010 gr/ dscf) 34 mg/ dscm ( 0.015 gr/ dscf)

3. Cadmium ( Cd) 0.02 mg/ dscm ( 8.7 gr/ mil dscf) 24 µ g/ dscm 4. Lead ( Pb) 0.20 mg/ dscm ( 87 gr/ mil dscf) 24 µ g/ dscm 5. Mercury ( Hg) 0.08 mg/ dscm ( 35 gr/ mil dscf), or an 85% reduction 45 µ g/ dscm 6. Dioxins/ Furans 13 ng/ dscm ( or 7 ng with less frequent testing) ( measured as total mass dioxins/ furans) 0.20 ng/ dscm ( TEQ)

7. Sulfur Dioxide ( SO 2) The higher of 80% reduction or 30 ppmv N. A.

8. Hydrochloric Acid ( HCl) The higher of 95% reduction or 25 ppmv 21 ppmv ( HCl/ Cl 2)

9. Hydrocarbons ( HC) N. A. 10 ppmv 10. Low Volatile Metals ( As, Be, Cr, Sb) N. A. 97 µ g/ dscm 11. Nitrous Oxide ( NOx) 150 ppmv ( large plants (> 225 Mg/ day) only) N. A.

12. Fugitive Dust Emissions ( fly ash/ bottom ash) Visible emissions < 5% of time N. A.

13. Opacity < 10% ( 6 minute average) N. A.

Table 12 81 Comparison of Key Air Emission Standards for Existing Combustion Units Parameter Existing MWCs Existing HWCs 1. Carbon monoxide ( CO) 50 250 ppmv, depending on unit type 100 ppmv 2. Particulates ( PM) 27 mg/ dscm ( 0.012 gr/ dscf) for large plants; 70 mg/ dscm ( 0.03 gr/ dscf) for small plants 34 mg/ dscm ( 0.015 gr/ dscf)

3. Cadmium ( Cd) 0.04 mg/ dscm ( 18 gr/ mil dscf) for large plants; 0.10 mg/ dscm ( 44 gr/ mil dscf) for small plants 240 µ g/ dscm 4. Lead ( Pb) 0.49 mg/ dscm ( 200 gr/ mil dscf) for large plants; 1.6 mg/ dscm ( 700 gr/ mil dscf) for small plants 240 µ g/ dscm 5. Mercury ( Hg) 0.08 mg/ dscm ( 35 gr/ mil dscf), or an 85% reduction 130 µ g/ dscm 6. Dioxins/ Furans 60 ng/ dscm ( if ESP based controls) ( 30 ng/ dscm otherwise) for large plants; 125 ng/ dscm for small plants 0.20 ng/ dscm ( TEQ)

7. Sulfur Dioxide ( SO 2) The higher of 75% reduction or 31 ppmv for large plants; 50% reduction or 80 ppmv for small plants N. A.

8. Hydrochloric Acid ( HCl) The higher of 95% reduction or 31 ppmv for large plants; 50% reduction or 250 ppmv for small plants 77 ppmv ( HCl/ Cl 2)

9. Hydrocarbons ( HC) N. A. 10 ppmv 10. Low Volatile Metals ( As, Be, Cr, Sb) N. A. 97 µ g/ dscm 11. Nitrous Oxide ( NOx) 200 250 ppmv ( large units (> 225 Mg/ day) only) N. A.

12. Fugitive Dust Emissions ( fly ash/ bottom ash) Visible emissions < 5% of time N. A.

13. Opacity < 10% ( 6 minute average) N. A. 19In fact, the Agency identified incineration as the basis for the LDR treatment standard for all organic constituents regulated in nonwastewaters with the exception of seven constituents: disulfoton, famphur, methyl parathion, parathion, phorate, diphenylamine, and diphenylnitrosamine ( EPA 1994, 4 10).

82 A comparison of the applicable air emissions standards for municipal waste combustors and hazardous waste combustors shows that the standards applicable to municipal waste combustors are similar or somewhat more stringent than the standards that apply to hazardous waste combustors, with the exception of hydrocarbons. Therefore, an evaluation of the potential effectiveness of municipal waste combustors in treating solvent contaminated wipes, based solely on the basis of the technology and the emissions standards ( and without a thorough evaluation of handling practices) leads to a conclusion that these units are as effective in treating or destroying the wastes.

It should be noted that, regardless of whether a municipal combustion facility manages solvent contaminated wipes, the ash generated by these facilities is a newly generated waste and is subject to the waste identification requirements of 40 CFR parts 261 and 262. Owners and operators of MWCs must determine whether or not the ash generated at their facilities exhibits one or more of the characteristics of hazardous waste. If the ash generated at a MWC exhibits the toxicity characteristic, the ash must be managed as a hazardous waste in compliance with all applicable subtitle C management requirements, including the land disposal restrictions requirements.

Land Disposal Restriction Issues Related to Incineration of Wipes or Burning Wipes for Energy Recovery EPA considered various options for modifying current RCRA rules to exclude industrial wipes contaminated with hazardous waste solvents from hazardous waste management regulations. This section discusses issues associated with the current applicability of the Land Disposal Restrictions ( LDRs) at 40 CFR part 268 to these materials and with the combustion of solvent contaminated wipes in MWCs.

Under the current RCRA regulations, hazardous wastes destined for land disposal must meet the LDR treatment standards. It can be reasonably assumed that thermal treatment technologies would be selected only for the treatment of nonwastewater forms of F001 F005. The nonwastewater LDR treatment standards for all organic solvent wastes are based on incineration. 19 However, any technology can be used so long as it meets the treatment standard. For organic wastes, the technologies selected typically involve combustion, such as incineration in a hazardous waste combustor or fuel substitution for energy recovery. For the purposes of the LDRs, combustion is defined at 40 CFR 268.42 as High temperature organic destruction technologies, such as combustion in incinerators, boilers, or industrial furnaces operated in accordance with the applicable requirements of 40 CFR part 264, subpart O, or 40 CFR part 265, subpart O, or 40 CFR part 266, subpart H, and in other units operated in accordance with applicable operating requirements; and certain non combustive 83 technologies, such as the Catalytic Extraction Process.

Thus, combustion units receiving hazardous wastes must be permitted or have interim status under RCRA subtitle C to handle hazardous wastes. Municipal waste combustors, therefore, do not meet the LDR requirements for combustion.

IV. D. 12 Disposal of Treatment Residues from Municipal Waste and Other Combustion Facilities Proposal and Discussion Under the proposed rule, when solvent contaminated industrial wipes meet the conditions of the exclusion before being combusted, they would not be considered hazardous wastes. Therefore, the derived from rule does not apply to the ash derived from the burning of these materials. In other words, as stated above, the ash generated by a MWC or other combustion facility is a newly generated waste and is subject to the waste identification requirements of 40 CFR parts 261 and 262. Owners and operators of MWCs and other combustion facilities must determine whether or not the ash generated at their facilities exhibits one or more of the characteristics of hazardous waste. They may do so by using knowledge of the wastes they receive and/ or generate, coupled with a knowledge of the capability of their combustor facility, or by testing the ash. If they determine that MWC ash exhibits a hazardous characteristic, the ash must be managed as a hazardous waste in compliance with all applicable subtitle C management requirements, including the LDRs.

IV. E. Proposed Conditions for Exclusion from the Definition of Solid Waste for Reusable Solvent Contaminated Industrial Wipes This section details a number of proposed conditions designed to ensure that reusable solvent contaminated industrial wipes are handled as valuable commodities.

IV. E. 1. Proposed Conditions for Initial Storage and Accumulation Proposal The proposed conditional exclusion from the definition of solid waste would apply to solvent contaminated industrial wipes at the point where the generator ceases using them. If the wipes are managed according to the proposed conditions, they are not considered solid waste.

For the exclusion from the definition of solid waste, EPA is proposing the same performance based on site management condition as for the exclusion of disposable industrial wipes from the definition of hazardous waste. For reusable industrial wipes, when wipes are discarded, the user must place them in a non leaking, covered container. This condition is described more fully in Section IV. F. 1. above.

Discussion 84 Management standards for accumulation of reusable industrial wipes differ from state to state due to varying state policies. However, some trade associations and industrial laundries already encourage their members and customers to use closed or sealed containers during storage and transportation of solvent contaminated wipes.

EPA believes that the proposed condition ensures responsible management of the wipes in a manner that is commodity like by preventing the loss of wipes, preventing the loss of solvent which could be recovered and reused, and protecting against risks from fires. The primary type of damage incident identified by EPA as a result of the mismanagement of solvent contaminated wipes is fire related damage due to the ignitability or flammability of these materials. The proposed condition also allows for a wide variety of containers to be acceptable for accumulation of reusable wipes.

Site visits conducted by EPA in 1997 provided evidence that both open and closed containers are used for the accumulation of solvent contaminated wipes. The most common management practices involved the use of a wide variety of containers, ranging from approximately five gallons in size ( e. g., safety cans) to 55 gallon drums. Some sites also used safety cans as satellite accumulation units from which the wipes were later transferred to a centralized accumulation unit. As with the exclusion, the performance based requirement proposed by EPA provides flexibility by allowing generators to accumulate solvent contaminated wipes in any of these containers, including spring bottomed drums, which prevent air releases when not being used, but accommodate the needs of workers constantly needing to open the drum. Under the proposed rule, generators may take innovative approaches to meet the performance standard rather than being required to use a specific design. A performance standard also provides a degree of flexibility in terms of allowing different approaches that minimize the length of time required for workers to place a used wipe in a storage container. This requirement also is in keeping with the spirit and intentions of OSHA regulations. Generators who already meet OSHA container standards should meet the proposed requirement for the safe on site storage of solvent contaminated wipes.

IV. E. 2. Proposed Conditions for Containers Used for Transportation Proposal For transportation of reusable industrial wipes, EPA is proposing that facilities which transport reusable solvent contaminated industrial wipes off site to an industrial laundry, a dry cleaner, or a facility that removes solvents from industrial wipes prior to cleaning, must do so in containers that are designed, constructed and managed to minimize loss to the environment; this is the same condition we are proposing for disposable industrial wipes that are conditionally excluded from the definition of hazardous waste. We believe this condition reflects the manner in which a commodity would be transported because it minimizes the possibility that valuable material would be spilled, lost or damaged during transportation.

Discussion 85 This condition is more fully described above in Section IV. F. 2. In addition, implementation questions, as well as other options being considered, are discussed in the preamble to this proposal.

IV. E. 3. Proposed Conditions for Transportation to Laundry, Dry Cleaner, or Handler Proposal EPA is proposing that generators be required to remove all free liquids prior to sending solvent contaminated reusable industrial wipes off site to be cleaned for reuse. This condition is the same as the condition for disposable industrial wipes being transported for disposal at a nonland disposal facility, such as a municipal solid waste combustor, which is discussed in IV. F. 5 above. Note, however, that there is no labeling condition for reusable industrial wipes.

Discussion This condition and background information on this condition are discussed in the preamble of this proposal.

IV. E. 4. " Exotic Solvents"

Proposal In the proposed rule, EPA requests information and comments on " exotic" solvents, such as terpenes and citric acids, and how they are presently managed. EPA asks for information and comments to help the Agency develop a final rule.

Discussion For a more detailed discussion of exotic solvents, see Section IV. F. 6 of this technical background document.

IV. E. 5. Proposed Conditions for Generators who Remove Solvent from Industrial Wipes Proposal Any solvent removed from an industrial wipe by a generator when using solvents in conjunction with industrial wipes may be subject to regulation as a hazardous waste. Therefore, the generating facility must determine whether the solvent removed from the industrial wipe is listed as a hazardous waste or exhibits a characteristic of a hazardous waste as defined in 40 CFR part 261 and, if so, manage it according to prescribed RCRA regulations under 40 CFR parts 260 268 and 270.

Discussion 86 Under the proposed exclusion from the definition of solid waste, the solvent contaminated wipes would not be a solid or a hazardous waste at the time they undergo solvent removal. Therefore, solvent removal technologies would not be considered treatment under RCRA and such operations, whether they were conducted at generating or handling facilities, would not require a RCRA permit. Further discussion of this issue can be found above in Section IV. F. 7.

IV. E. 6. Proposed Conditions for Intra Company Transfers Proposal EPA is proposing that generators can qualify for the exclusion from the definition of solid waste when transferring solvent contaminated reusable industrial wipes containing " free liquids," provided the transfer is between facilities within the same company, and the receiving facility has a solvent extraction and/ or recovery process that removes enough solvent from industrial wipes for them to meet the " no free liquid" condition. Generators must transport the industrial wipes in containers that are designed, constructed, and managed to minimize loss to the environment.

Discussion A more detailed discussion of this provision, as well as other options EPA is considering, can be found above in Section IV. F. 8. However, reusable industrial wipes being managed under the exclusion from the definition of solid waste would not have to meet the labeling condition that disposable industrial wipes must meet.

IV. E. 7. Proposed Conditions for Management at Handling Facilities Proposal As described for disposable industrial wipes, generators would have the primary responsibility for assuring that their industrial wipes meet the conditions for the proposed exclusion. However, handling facilities which receive and process reusable industrial wipes, such as industrial laundries, would also need to meet certain minimum conditions for the wipes to remain excluded from the definition of solid waste.

The first condition EPA is proposing states that to maintain the exclusion from the definition of solid waste for reusable industrial wipes, between arriving on site and entering a facility's process the wipes would have to be stored either   ( a) In containers that are designed, constructed and managed to minimize loss to the environment that meet the proposed transportation condition, or ( b) In non leaking covered containers that meet the proposed generator accumulation condition.

The process begins when the laundry begins to handle the wipes. For example, at many laundries, the wipes are sent through a counting machine first, before they are cleaned, to record how many 87 wipes the generator has sent to be cleaned. In this example, wipes would enter the handling process when they are counted.

From site visits, we expect that at the laundries, the solvent contaminated industrial wipes will generally remain in the containers in which they were transported. In the case where a facility chooses to transfer the industrial wipes into another container before the wipes enter the handling process, we are proposing that the generator condition, placement in a non leaking covered container, would be sufficient to maintain the exclusion from the definition of solid waste.

Handling facilities would also not be allowed to mismanage free liquids. For example, an industrial laundry may not introduce free liquids into their laundering process. Facilities that happen to receive solvent contaminated industrial wipes in containers with free liquids ( unless they are being transported intra company) would be required to either   ( a) Return the container ( with the wipes and liquid) to the user ( generator) as soon as practicable, or ( b) Recover and properly manage any liquid solvent that arrives at the facility under applicable federal or state hazardous waste regulations.

When returning the wipes and liquids to the user, the laundry would have to transport them in the containers that meet the original shipment conditions, but would not be required to use a hazardous waste manifest.

Discussion The discussion of this provision of the proposed rule is discussed in the preamble of the proposal.

V. Summary of Risk Screening Analysis 88 V. A. Introduction This section describes the approach EPA took to evaluate the risks from disposing of solvent contaminated industrial wipes and their residues in landfills. EPA's risk screening and assessment approach used a series of mathematical models to evaluate the potential risks from landfilling industrial wipes containing hazardous solvents as well as the ash and sludge residues from combustion and waste water treatment processes, respectively. this section is meant as an overview of the risk screening did in developing this proposal. The actual report from the risk analysis is available in the docket to the proposed rule.

V. B. Assessing the Risks from the Landfilling Industrial Wipes Containing Hazardous Solvents EPA conducted an analysis to determine the constituent specific risks from landfilling F listed spent solvents that are contained on industrial wipes used for cleaning and degreasing operations. This analysis addressed the following questions: ( 1) which F listed constituents present the most risk; and ( 2) using reasonable assumptions, do circumstances exist where industrial wipes containing F listed solvents can be managed in landfills without posing unacceptable risk to human health and the environment? For this analysis EPA evaluated disposal in a municipal solid waste landfill.

The overall approach to answering these questions consisted of three separate analyses. First, EPA calculated a risk loading threshold for each constituent, which is the daily solvent loading to a municipal landfill that poses unacceptable risks to human health. Second, using the results from this effort, EPA then compared the risk loading threshold for each F listed solvent to the total solvent loadings disposed of in a landfill on a daily basis to determine whether the quantity of F listed solvent disposed would pose unacceptable health risks. For this analysis, the human health benchmarks were a hazard quotient ( HQ) of 1 for a noncarginogen and a carcinogenic risk of 10 5. Values above these numbers were deemed to pose an unacceptable risk to human health. In conducting these analyses, EPA generally used a deterministic approach ( i. e., discreet values of input parameters were selected).

This section provides some of the background on how solvent from solvent contaminated industrial wipes could pose a risk to human health and the environment. In broad terms, generators use industrial wipes in conjunction with hazardous solvents and become a hazardous waste once the wipes no longer can be used. Once the hazardous waste is disposed in a landfill, the solvent contaminants contained on the wipe may leach, enter the groundwater, and impact an offsite receptor drinking water well. A resident could be exposed to these solvent contaminants through drinking water and non ingestion routes, such as dermal and inhalation exposure. This analysis calculates a unit risk coefficient per day for each solvent, as well as the maximum quantity of contaminant that can be present in the landfill.

V. B. 1. Constituents Evaluated 89 As stated elsewhere in this document, there are an almost infinite number of combinations of solvent blends used by generating facilities for cleaning and degreasing operations. Some generators use blends consisting of three or four constituents; others use pure solvents. Also, many generators use very few wipes a day while many others use thousands. In effect, no two generators are the same in terms of their solvent use practices. Because of this situation, EPA adopted a simplified approach to estimate unit risks from disposing of F listed solvents in a municipal landfill.

For this analysis ( as well as for the analyses associated with ash from combustion facilities and sludges from wastewater treatment processes), EPA evaluated 34 F listed solvents ( consolidated to 30 because of overlapping characteristics associated with cresol and xylene solvents) because the RCRA mixture rule ( 40 CFR 261.3( b)) dictates that any solid waste mixed with RCRA hazardous waste ( e. g., wipes mixed with hazardous solvents) is a hazardous waste, even if only very small amounts of solvent are contained in the wipe. These constituents were selected because they are expected to be present in mixtures of hazardous waste spent solvent ( e. g., F001 to F005) and wipes. Even though RCRA regulates other hazardous solvents ( such as P and U listed commercial chemical products), EPA did not consider them for this analysis because it had no information on the frequency of occurrences for when these solvents might be spilled during production processes, creating a waste comparable to an F listed solventcontaminated wipe. However, EPA believes these spills should occur very infrequently compared to F listed solvents used in normal cleaning operations.

Toxicity benchmarks for these 30 solvents are included in Table 13. Health benchmarks include Reference Doses ( RfDs, for noncarcinogenic effects) and Cancer Slope Factors ( CSFs, for carcinogenic effects) for estimating risk from ingestion and dermal exposures; risks from inhalation were determined using Reference Concentrations ( RfCs, for noncarcinogenic effects) and inhalation unit risk factors ( URFs, for carcinogenic effects). Benchmarks were principally obtained from EPA's Integrated Risk Information System ( IRIS), supplemented with other sources as appropriate ( see Table 13). Most of the compounds had oral benchmarks while a significant number did not have inhalation benchmarks. 90 Table 13 Constituents Present in F001 to F005 Solvents Constituent Solvent Listing Oral Benchmark Inhalation Benchmark Noncarcinogens Nitrobenzene F004 RfD: 0.0005 RfC: 0.002 f Pyridine F005 RfD: 0.001 RfC: 0.007 f Ethyl ether F003 RfD: 0.2   Acetone F003 RfD: 0.1 RfC: 31 f Methanol F003 RfD: 0.5 RfC: 13 f Butanol F003 RfD: 0.1   Carbon disulfide F005 RfD: 0.1 RfC: 0.7 Methyl ethyl ketone F005 RfD: 0.6 RfC: 1.0 Methyl isobutyl ketone F003 RfD: 0.08 f RfC: 0.08 f Cyclohexanone F003 RfD: 5.0   2 Ethoxyethanol F005 RfD: 0.4 RfC: 0.2 Tetrachloroethylene d F002 RfD: 0.01 RfC: 0.3 f Isobutyl alcohol F005 RfD: 0.3   Cresols a F004 RfD: 0.05 ( o, m) RfD: 0.005 ( p) f   Chlorobenzene F002 RfD: 0.02 RfC: 0.02 f Ethyl acetate F003 RfD: 0.9   Trichlorofluoromethane d F002 RfD: 0.3 RfC: 0.7 f Dichlorodifluoromethane b F001 RfD: 0.2 RfC: 0.2 f 1,2 Dichlorobenzene F002 RfD: 0.09 RfC: 0.2 f Ethyl benzene F003 RfD: 0.1 RfC: 1.0 Toluene F005 RfD: 0.2 RfC: 0.4 1,1,2 Trichlorotrifluoroethane d F002 RfD: 3.0 RfC: 30 f 1,1,1 Trichloroethane d F002 RfD: 0.2 f RfC: 1.0 f Table 13 Constituents Present in F001 to F005 Solvents Constituent Solvent Listing Oral Benchmark Inhalation Benchmark 91 Xylenes ( total) c F003 RfD: 2.0 ( o, m, and total) f   ( o, m) RfC: 0.43 ( total) F Carcinogens Methylene chloride d F002 RfD: 0.06 CSF: 0.0075 RfC: 3.0 f URF: 4.7 x 10 7 1,1,2 Trichloroethane F002 RfD: 0.004 CSF: 0.057 URF: 1.6 x 10 5 Carbon tetrachloride F001 RfD: 0.0007 CSF: 0.13 URF: 1.5 x 10 5 f 2 Nitropropane F005   RfC: 0.02 URF: 2.7 x 10 3 F Benzene e F005 CSF: 0.029 e URF: 8.3 x 10 6 e, f Trichloroethylene d F002 CSF: 0.011 f, g URF: 1.7 x 10 6 f Sources of toxicity data are the Integrated Risk Information System ( IRIS), except otherwise noted. RfD ( oral) is in units of mg/ kg/ d. RfC ( inhalation) is in units of mg/ m3. Lower values correspond to more severely acute toxicity properties. CSF ( oral) is in units of ( mg/ kg/ d) 1. URF ( inhalation) is in units of ( µ g/ m3) 1. Higher values correspond to more severe carcinogenic properties. a. The isomers o, m, and p cresols were evaluated; risks from ` total cresols' were not evaluated. The highest risks were from p cresol which were used to represent all ` cresols.' b. The F001 listing identifies ` chlorinated fluorocarbons.' Dichlorodifluoromethane was selected as one such compound. Other chlorofluorocarbons are explicitly identified in the F002 listing. c. The isomers o and m xylene were evaluated along with total xylenes. d. These compounds are listed in both F001 and F002 descriptions. e. Toxicity data for benzene was updated in IRIS subsequent to the risk analysis. The new assessment shows slightly lower carcinogenic properties from inhalation ( i. e., the new inhalation URF is 2.2 to 7.8 x 10 6 ( µ g/ m3) 1 compared to the value of 8.3 x 10 6 used in the risk assessment). Carcinogenic properties from oral properties are approximately unchanged ( i. e., the new oral CSF is 0.015 to 0.055 ( mg/ kg/ d) 1 compared to the value of 0.029 used in the risk assessment). f. Indicates IRIS was not used as a source for toxicity data. See EPA ( 1999) for complete referencing of all benchmarks. g. EPA has recently published a draft health risk assessment for trichloroethylene ( EPA, Trichloroethylene Health Risk Assessment: Synthesis and Characterization ( External Review Draft, August 2001, EPA/ 600/ P 01/ 002A). This source presents a range of CSFs, of 0.02 to 0.4 ( mg/ kg/ d) 1. It also presents an RfD of 0.0003 mg/ kg day. The range of CSFs in the draft health risk assessment is higher than that used in the risk screening assessment for industrial wipes. Additionally the draft health risk assessment presents an RfD; EPA did not assess noncarcinogenic effects of trichloroethylene in its risk screening assessment for industrial wipes. These new toxicity data in the August 2001 draft health risk assessment would result in higher risks from this constituent. However, the August 2001 report is not final and is undergoing external review. 92 V. B. 2. Transport, Fate and Receptor Assumptions Used to Estimate Risk Loading Thresholds The risk loading threshold was derived using the following approach:

° Generators use industrial wipes in conjunction with a certain amount ( 1.3 kg/ day) of hazardous solvents on each wipe to derive a waste once the wipes no longer can be used. This quantity ( 1.3 kg/ day) represents the estimated amount that would be necessary for a generator to become a large quantity generator ( LQG). However, this quantity is used only as a base to derive unit coefficients and does not reflect the more complex loading assumptions detailed later in this report and used in identifying constituents posing unacceptable risks. ° The waste is disposed in a landfill. ° The solvent contaminants contained on the wipe leach, enter the groundwater, and impact an offsite receptor drinking water well. ° A resident is exposed to these solvent contaminants through drinking water and non ingestion routes. ° The risk for each solvent is calculated. ° The maximum quantity of contaminant that can be present in the landfill is calculated using a noncarcingenic Hazard Quotient ( HQ) of 1 or a carcinogenic risk of 10 5. This is the risk loading threshold.

V. B. 2. a. What Type of Landfill Is Used for Disposal of the Waste?

The landfill was assumed to be an municipal solid waste landfill ( MSWLF), with no liner or leachate collection system. This assumption is consistent with the approach used in the proposed rule to list certain inorganic chemical manufacturing wastes as hazardous ( 65 FR 55684, September 14, 2000), as well as other risk assessments for similar decisions regarding regulatory decisions for hazardous and industrial wastes. Even though regulations currently specify design criteria for MSWLFs ( 40 CFR 258.40), including liners and leachate collection, the assumption that the landfill is unlined and has no leachate collection system is made, in part, because older unlined landfills may continue to be operating.

Another important parameter for this assessment is the type of cover used. Many of the solvent components are volatile and can pose potential risks from air as well as leachate exposure pathways. For this analysis, EPA assumed that a daily cover of six inches is used, consistent with federal regulations ( 40 CFR 258.21). A final cover of 30 inches was also assumed ( regulations specify several layers of final cover including 18 inches of earthen material with 6 inches of top soil). Finally, the waste was assumed to be added in layers no more than 2.5 feet deep. The landfill was assumed to be operational for 30 years.

The screening analysis considered four specific scenarios, each corresponding to a different landfill size and climatic condition assuming receipt of industrial wipes from a large quantity generator:

° Median landfill size, high end climatic conditions, LQG 93 ° Median landfill size, median climatic conditions, LQG ° Small landfill size, high end climatic conditions, LQG ° Small landfill size, median climatic conditions, LQG A high end (` small') and central tendency (` median') landfill were assumed to be 8,100 m2 and 60,700 m2, respectively. These correspond to the 10th percentile and 50th percentile sizes determined from EPA's 1988 National Survey of Solid Waste ( Municipal) Landfill Facilities. Larger facilities were not evaluated because a sensitivity analysis showed that larger areas were associated with less risk for both leachate and air releases. As discussed later in this section, the scenario resulting in the highest receptor risks was a small landfill in high end climatic conditions; these results were used in calculating the risk loading thresholds. The quantity of solvent placed in the landfill was also varied, however this variation was not relevant for development of the risk loading thresholds.

Contaminant release corresponding to two climatic conditions were evaluated: those corresponding to Lincoln, Nebraska ( central tendency) and Houston, Texas ( high end). The central tendency site was the same one identified in the proposed 1995 Hazardous Waste Identification Rule. The high end site was selected to attempt to represent a case where releases to both the groundwater and air pathways would be increased. These were selected from a total of 29 meteorological regions identified during the EPA Superfund Soil Screening Level program.

The most important climatic parameters affecting releases to the air are windspeed and temperature, while the most important climatic parameter affecting releases to groundwater is infiltration rate. The infiltration rates associated with these conditions correspond to 25 cm/ yr for the central tendency case and 40 cm/ yr for the high end case.

V. B. 2. b. How Are The Contaminants Assumed to Be Released from the Waste?

The contaminants in the waste were assumed to be available for release and not irreversibly bound to the matrix. A uniform quantity of waste was assumed to be disposed every day for 350 days per year for the entire 30 year operational life of the landfill.

Once in the landfill, the contaminants were assumed to be released from the waste to both the air and the leachate. EPA used a series of partitioning equations to determine how much contaminant mass would be retained in the waste management unit and how much would be released into the environment. These equations are based upon a series of articles by Jury and others ( see EPA 1999). EPA used the partitioning equations to estimate the mass of a contaminant that would be lost from the landfill due to volatilization into the air, contaminant leaching into the subsurface, and degradation. These losses were assumed to occur during the entire 30 year active life of the landfill and for a 40 year post closure period.

EPA assumed that volatilization losses could occur prior to the landfill being covered with daily cover or daily waste addition, through the daily cover, and through the cap that is placed on the landfill ( or individual cells) after closure. The landfill model sums each of these contributions in a dynamic fashion. Note, however, that advective transport was not considered, which is the release of contaminant as landfill gas ( e. g., methane), and in general the post closure losses were 94 assumed to be negligible following the capping of the landfill.

EPA assumed that leachate losses could occur during the pre and post closure periods. In addition, losses as a result of biodegredation and hydrolysis were incorporated as an overall first order degradation rate ( e. g., degradation calculated from a " half life"). Such loss rates were identified from the literature, where most data represent soil.

V. B. 2. c. How Are the Contaminants Transported Through the Environment?

The results of the previously described partitioning were used as inputs to the subsequent groundwater and air transport models. The risk assessment evaluated transport by a groundwater pathway and an air pathway. Specifically, residents living near landfills managing these wastes may be exposed to contaminated groundwater or vapors. For all contaminants, the groundwater pathway was found to be dominant.

Groundwater Pathways For groundwater transport, the highest nine year average leachate concentration was used as input to the groundwater modeling. Contaminant specific modeling was not performed. Instead, an overall Dilution Attenuation Factor ( DAF) was used to estimate the dilution between the landfill and the receptor well; such DAFs were similarly used in EPA's 1995 soil screening analysis ( see EPA 1999). The contaminant was assumed to reach an off site drinking water well which serves as an exposure point to a receptor.

In the soil screening analysis, EPA's Composite Model for Leachate Migration with Transformation Products ( EPACMTP) was used in a Monte Carlo framework. In this framework, values for different parameters affecting fate and transport are randomly selected within the constraints of their range in thousands of iterations, resulting in a corresponding thousands of values for the calculated DAFs. The DAF corresponding to the 95th percentile was selected for each landfill area size. The Monte Carlo analysis varied the receptor well location anywhere within the groundwater transport plume up to one mile from the source. As a result of this analysis, a constant DAF of 11 was used in the solvent contaminated industrial wipes analyses with the median size landfill, and a constant DAF of 27 was used in analyses with the small size landfill. Additional analyses were presented in EPA ( 1999) assuming a very close receptor well ( i. e., more conservative) and assuming a liner was present ( i. e., less conservative), although results are not presented here or used for calculation of the risk loading thresholds.

Air Pathways For air transport, the Industrial Source Complex Short Term Model ( ISCST3) was used to model the dispersion of volatile compounds from the landfill to a receptor located 75 meters from the source. The contaminant was diluted by transport and removed prior to reaching the receptor by deposition. The receptor becomes exposed via inhalation of the contaminant.

Note that while biodegredation of the organic constituents was considered in the landfill, no degradation effects were considered in the media transport pathways. 95 V. B. 2. d. What Receptors Were Considered?

Risks associated with the following exposure pathways were considered for each constituent:

° inhalation of vapors transported off site as vapors ° groundwater ingestion ° indirect exposure of groundwater including inhalation in the shower, bathroom, and whole house, as well as indirect dermal exposure of groundwater.

All of the pathways consider two receptors: adult farmer and child. Appropriate intake assumptions for each receptor were obtained from EPA's 1997 Exposure Factors Handbook ( EPA, 1997a) and are described in detail in EPA ( 1999). In general, average values were used for most of the exposure parameters.

Inhalation risk factors are estimated for a child in Houston exposed for 12 hours to constituents disposed of by a LQG in a small landfill 75 meters from the child's home. Groundwater ingestion risk factors are estimated for a child in Houston ingesting groundwater from a well located downgradient of a small landfill containing constituents disposed of by a LQG ( well distance is determined by national distribution). Indirect exposure factors are determined by adding the HQs for inhalation of the constituent in the shower, bathroom, and whole house. These HQs are calculated using a unit concentration for the constituent's concentration in groundwater. The HQ calculations for dermal exposure were also based on the constituent's concentration in groundwater.

Separate risks were calculated for each of the four landfill management scenarios discussed above. For each scenario, risks were determined for the direct inhalation of the landfill vapors, ingestion of contaminated drinking water, and indirect exposure from household use of water. Both adult and child receptors were considered in the risk screening.

EPA evaluated carcinogens at a risk loading threshold of 10 5, the same level used in the proposed rule to list chlorinated aliphatics wastes as hazardous wastes. In that proposal, EPA considered a decision to list wastes if the carcinogenic risks are 10 5 or higher ( 64 FR 46489, August 25 1999).

For each constituent, the exposure resulting from all sources of groundwater ( i. e., ingestion, inhalation, and dermal exposures) were summed. Additionally, risks resulting from carcinogen exposure were summed ( i. e., this affected each of the six contaminants with carcinogenic effects identified in Table 13).

Carcinogens are assumed to have cumulative effects, such that exposure to multiple carcinogens would present a greater risk than risks to a single constituent. In this analysis, such effects were accounted for by first calculating the risks posed by individual constituents. The cumulative risks were calculated by also adding the risks from all other lower toxicity carcinogens. The risk loading thresholds were subsequently calculated from these cumulative risks. This impact is shown in Table 14 for the six carcinogens. The additional toxicity is 96 calculated by dividing the sum of carcinogenic risks from all other carcinogenic contaminants by the risk from the individual contaminant.

For noncarcinogens, the contaminants are assumed to have independent effects ( i. e., if a receptor is exposed to both methanol and acetone, the compounds are assumed to affect different parts of the body). Therefore, risks from different noncarcinogens are not ` summed.'

Table 14 Carcinogenic Effects of Solvent Constituents For the following contaminant with carcinogenic effects... The additional toxicity due to additive effects is...

2 Nitropropane 1x ( Additional toxicity is negligible due to high toxicity of this contaminant.)

Methylene chloride 1.9 x Benzene 2.6 x 1,1,2 Trichloroethane 1.5 x Carbon tetrachloride 1.1 x Trichloroethylene 1x ( No additional effect because this contaminant is the least toxic)

V. B. 2. e. What Are the Results?

The calculated risk loading thresholds are presented in Table 15. This table presents, for each F listed constituent, the risks from various pathways assuming a loading of 1.3 kg/ day per landfill. The sum of risks from these pathways are determined in the next to last column. The last column presents the calculated risk loading threshold, in kg/ day. This amount is intended to signify the quantity of contaminant that can be placed in a landfill to result in an HQ of 1 or a carcinogenic risk of 10 5. It is calculated by proportion. For example, in the case of acetone, a risk of HQ= 0.75 results from a landfill loading of 1.3 kg/ day. Therefore, by simple proportion, an HQ= 1 is expected to result from a landfill loading of 1.7 kg/ day. This assumes linear performance of all models; the uncertainty and limitation of this assumption are discussed in section V. B. 6.

Groundwater receptor well concentrations were calculated for each of the four different combinations of climatic conditions and landfill size. The highest concentrations were selected for use in subsequent calculations; the highest concentrations resulted from the small landfill in a high end climate ( Houston, TX), although there was very little difference in the results from the two locations.

Risks from groundwater exposure were determined by adding risks from ingesting the water, from various inhalation pathways, and from dermal exposure. Each of these routes of 97 exposure was summed to identify the total risk from a particular contaminant resulting from all pathways.

The results of the last two columns illustrate which F listed solvents could pose a problem if disposed in a landfill. For example, the risk loading threshold derived for nitrobenzene using the above assumptions is only 0.043 kg/ day. Therefore, even very little nitrobenzene disposed in a landfill on a daily basis may pose a risk. Conversely, the risk loading threshold for ethy ether is 4.30 kg/ day. Therefore, larger amounts of this solvent could be disposed without posing an unacceptable risk to human health.

The magnitude of these risk loading thresholds differ substantially, from 0.003 kg/ day ( for 2 nitropropane) to 403 kg/ day ( for 1,1,2 trichlorotrifluoroethane). Additionally, the dominant exposure pathway is different depending on the constituents, split between groundwater ingestion and indirect inhalation from groundwater use. This difference in risk loading thresholds is due to several factors, including the following:

° Differing toxicity between chemicals: as shown in Table 13, the carcinogenic URF for 2 nitropropane is very high, suggesting high toxicity. Both the noncarcinogenic RfD and RfC for 1,1,2 trichlorofluoroethane are very high, suggesting low toxicity.

° Chemical properties: chemical properties such as degradation rates, Henry's Law constant, and solubility affect partitioning between leachate, air, and solid in the landfill waste and/ or between air and water in the receptor's house.

° Differing toxicity between routes of exposure: as shown in Table 13, many compounds do not have inhalation exposure benchmarks, and therefore risks from inhalation pathways were not estimated for these constituents. 98 Table 15 Risk Loading Threshold Results Constituent Relative Risk ( as HQ or carcinogenic risk), based on disposal of 1.3 kg contaminant/ day in a landfill Resulting Risk Loading Threshold ( kg/ d, per landfill) From Direct Inhalation From Ground Water Ingestio n From Indirect Ground Water Exposure ( Inhalation) From Indirect Ground Water Exposure ( Dermal) Sum of Risk from Pathways Noncarcinogens ( Risk expressed as hazard quotient)