Response to Comments on the SolventContaminated Wipes 2003 Risk 

Screening Analysis

December, 2011

Office of Resource Conservation and Recovery

U.S. Environmental Protection Agency

Prepared with the support of RTI International

EPA Contract Number EP-W-09-004

RTI Project Number 0212041.002.024
Response to Comments on the Solvent Contaminated Wipes 2003 Risk Screening Analysis

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Table of Contents

1. Introduction ............................................................................................................................................1

2. Summary of Comments by Reviewers...................................................................................................1

2.1 Preferential Treatment of Laundered Wipes and Sludge.............................................................5

2.1.1 Applied Different Modeling Assumptions (comment theme 1)...................................5

2.1.2 Established “5 gram limit” (comment theme 2)...........................................................5

2.2 2003 Modeling Assumptions Overestimate Risk ........................................................................6

2.2.1 Overall Modeling Framework (comment theme 3)......................................................7

2.2.2 Landfill Characteristics and Environmental Setting (comment theme 4) ....................7

2.2.3 Groundwater Leachate Concentration (comment theme 5)..........................................8

2.2.4 Distance to Receptors (comment theme 6)...................................................................8

2.2.5 Centrifuge Removal Efficiencies (comment theme 7).................................................8

2.2.6 Solvent Loadings for Non-Laundered Wipes (comment theme 8)...............................9

2.3 2003 Modeling Assumptions Underestimate Risk ......................................................................9

2.3.1 Solvent Limits, Loading Rates, and Wipe Usage (comment theme 9).......................10

2.3.2 Exposure Parameters (comment theme 10)................................................................11

2.3.3 Use of Dilution and Attenuation Factors (DAFs) (comment theme 11) ....................13

2.3.4 Ecological Risk and Human Food Chain Risk (comment theme 12).........................13

2.3.5 Advective Transport (comment theme 13).................................................................15

2.3.6 Meteorological Conditions (comment theme 14).......................................................15

2.3.7 Soil Characteristics (comment theme 15)...................................................................15

2.3.8 Biodegradation (comment theme 16).........................................................................16

2.3.9 Peer Review Comments (comment theme 17)...........................................................16

2.3.10 Solvent Impact on Liners (comment theme 18) .........................................................18

2.4 Sufficiency of Data and Model..................................................................................................19

2.4.1 Laundry Sludge (comment theme 19)........................................................................19

2.4.2 Use of Delisting Risk Assessment Software (DRAS) (comment theme 20)..............19

2.5.1 Laundering Operations (comment theme 21).............................................................20

2.6 Not Specific to Screening Assessment ......................................................................................21

2.6.1 Combustion of Wipes (comment theme 22)...............................................................21

2.6.2 Consideration of Other Contaminants Including Metals (comment theme 23)..........22

2.6.3 Solvent Wipes Evaluated Separately (comment theme 24)........................................23

2.6.4 Complexity of the Proposed Rule (comment theme 25) ............................................25

2.6.5 Groundwater Monitoring and Corrective Action Controls (comment theme 

26)...............................................................................................................................25

2.6.6 Banning Based on Toxicity Characteristics (TC) (comment theme 27) ....................26

2.6.7 Lifecycle Analysis and Recycling (comment theme 28)............................................27

2.6.8 Concern Over Health of the U.S. Population (comment theme 29)...........................28

3. References............................................................................................................................................29

Appendix A: Risk-Related Comments
Response to Comments on the Solvent Contaminated Wipes 2003 Risk Screening Analysis

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Response to Comments on the Solvent-Contaminated Wipes 

Proposed 2003 Screening Risk Analysis 

1. Introduction

On November 20, 2003, Environmental Protection Agency (EPA) published a notice of 

rulemaking on industrial wipes that proposed a conditional exclusion from the definition of solid waste 

for reusable wipes and a conditional exclusion from the definition of hazardous waste for disposable 

wipes. During the comment period on the November 2003 proposed rule, we received substantive 

comments on the risk screening analysis and the solvent loading calculations. In addition to public 

comments, we received comments from external peer reviewers. Both the public and the peer reviewers 

questioned aspects of the risk screening analysis and the modeling assumptions. In response to comments 

on the risk screening analysis, the Agency undertook a more robust risk analysis to determine the 

potential risk from disposal of solvent-contaminated wipes and laundry sludge in both unlined and lined 

non-hazardous waste landfills. This revised risk analysis was subjected to external peer review and 

presented for public comment, along with the peer review comments and EPA’s response to those 

comments, in a Notice of Data Availability (NODA) on October 27, 2009 (74 FR 55163).

The revised risk analysis is probabilistic in nature and used Monte Carlo methods to characterize 

the variability and uncertainty associated with the modeling. The revised risk analysis results included 

solvent-specific, risk-based mass loading limit (RB-MLL) estimates for both unlined and composite-lined 

landfill scenarios. In addition, the Agency developed and used a new landfill coupled reactor model 

(LFCR), which allowed the modeling to account for solvent biodegradation and partitioning between air, 

water, and solid phases while in the landfill. The probabilistic approach used in the revised risk analysis 

addresses to a great extent the potential to overestimate, or underestimate, the risks from disposal of 

solvent-contaminated wipes and sludges in landfills.

This comment review and response report focuses on the technical themes highlighted by the 

public comments received on the 2003 screening analysis. The subject of this review is the risk-related 

comments. These comments are presented in Appendix A and may also be found in the docket for the rule 

making (EPA-HQ-RCRA-2003-0004). As applicable, the responses discuss how the comment issues were 

addressed in the 2009 revised risk analysis; see Risk-Based Mass Loading Limits for Solvents in Disposed 

Wipes and Laundry Sludges Managed in Municipal Landfills (U.S. EPA, 2009). Note that responses to 

comments on the risk-based mass loading limits (RB-MLL) used in the 2009 revised risk analysis are 

provided in Response to Comments on the Solvent Contaminated Wipes 2009 Risk Analysis: Risk-Based 

Mass Loading Limits, which is located in the docket for this rule. Also, see the docket for Response to 

Comments on the 2003 Proposal on the Landfill Loadings Calculations for Solvent-Contaminated Wipes 

for responses to comments on the landfill loading calculations.

2. Response to Comments Received on the 2003 Risk Screening Analysis

Review of the public comments revealed a consistency in themes across comments. As a result, 

the technical issues noted by the comments were grouped into general themes as follows:

 Preferential Treatment of Laundered Wipes and Sludge (Section 2.1)

1. Applied Different Modeling Assumptions

2. Established “5 gram limit”

 2003 Modeling Assumptions Overestimate Risk (Section 2.2)

3. Overall Modeling Framework

4. Landfill Characteristics and Environmental Setting 
Response to Comments on the Solvent Contaminated Wipes 2003 Risk Screening Analysis

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5. Groundwater Leachate Concentration 

6. Distance to Receptors

7. Centrifuge Removal Efficiencies

8. Solvent Loadings for Non-Laundered Wipes

 2003 Modeling Assumptions Underestimate Risk

9. Solvent Limits, Loading Rates, and Wipe Usage

10. Exposure Parameters

11. Use of Dilution and Attenuation Factors (DAFs)

12. Ecological Risk and Human Food Chain Risk

13. Advective Transport 

14. Meteorological Conditions

15. Soil Characteristics

16. Biodegradation

17. Peer Review Comments 

18. Solvent Impact on Liners

 Sufficiency of Data and Model (Section 2.4)

19. Laundry Sludge

20. Use of Delisting Risk Assessment Software (DRAS)

 Potential Exposures before Landfilling (Section 2.5)

21. Laundering Operations

 Not Specific to Screening Assessment (Section 2.6)

22. Combustion of Wipes

23. Consideration of Other Contaminants Including Metals 

24. Solvents Wipes Evaluated Separately 

25. Complexity of the Proposed Rule

26. Groundwater Monitoring and Corrective Action Controls

27. Banning Based on Toxicity Characteristics (TC)

28. Life Cycle Analysis

29. Concern Over Health of the U.S. Population.

The comments grouped in Section 2.6 capture and identify issues that were not specific to the risk 

screening analysis, but were generally related to the overall risk evaluation. 

The remainder of this section is organized according to the above themes and presents EPA’s 

response to each area of interest. To facilitate linking these response themes to the actual comments 

shown in Appendix A, Table 1 provides a cross-walk between the themes and comments.
Response to Comments on the Solvent Contaminated Wipes 2003 Risk Screening Analysis

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Table 1. Comment Summaries for the 2003 Screening Risk Assessment

Commenter Identifier

Comment Themes

Preferential 

Treatment 

of 

Laundered 

Wipes and 

Sludges

Modeling 

Assumptions 

Overestimate 

Risk

Modeling 

Assumptions 

Underestimate 

Risks

Sufficiency 

of Data and 

Model

Potential 

Exposures 

before 

Landfilling

Not Specific

to Screening 

Assessment

0199-Hearing Transcript, Art Abell, Cando Co. 1 21

0199-Hearing transcript-Ralph Solarski-Kimberly Clark. 1 25

0199-Hearing Transcript- David Dunlap, Uniform and Textile 

Service Association 

21

0199-Hearing Transcript-David Case, ETC 4 18

0199-Hearing Transcript-David Case, ETC 23

0223-Mervyn M. Dymally, California State Assembly 21 23

0257-Kimberly Clark 1

0271-CTDEP 19 22

0272-George H. Larson 1, 2

0272-George H. Larson 21

0281-Graphic Arts Coalition 27

0281-Graphic Arts Coalition 7

0283-INDA/SMART 1, 2 7 25,27

0283-INDA/SMART 1, 2 7

0283-INDA/SMART 1, 2 7

0283-INDA/SMART 1, 2 4,7 27

0283-INDA/SMART 2 3, 4,5,6,7 17 26

0283-INDA/SMART 1, 2 6,7,8 19 21

0288-ETC 9 through 18 19,20 21

0289-AMEC 9,10,11,12,18 23,24

0312-JR Simplot NA – Commenter agrees with EPA’s risk screening analysis 

0316-VT Hazardous Waste Management Program 4 18

0319-American Reusable Textile Association 29

0320-National Paint & Coating Association 2 4, 8
Response to Comments on the Solvent Contaminated Wipes 2003 Risk Screening Analysis

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Commenter Identifier

Comment Themes

Preferential 

Treatment 

of 

Laundered 

Wipes and 

Sludges

Modeling 

Assumptions 

Overestimate 

Risk

Modeling 

Assumptions 

Underestimate 

Risks

Sufficiency 

of Data and 

Model

Potential 

Exposures 

before 

Landfilling

Not Specific

to Screening 

Assessment

0323-Cement Kiln Recycling Coalition 17, 21

0325-ASTSWMO 12 20 21

0330-AR DEQ 12

0330-AR DEQ 12

0330-AR DEQ 22

0330-AR DEQ 12

0330-AR DEQ 20

0346-USWAG by Piper Rudnick 1,2 27

0348-Uniform and Textile Services Association-Textile Rental 

Services Association 

21

0348-Uniform and Textile Services Association-Textile Rental 

Services Association 1 19

0350-Tennessee Valley Authority 4

0353-American Trucking Associations NA – Commenter agrees with EPA’s risk screening analysis

0357-Phelps Dodge Corporation 12 27

0357-Phelps Dodge 21
Response to Comments on the Solvent Contaminated Wipes 2003 Risk Screening Analysis

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2.1 Preferential Treatment of Laundered Wipes and Sludge

2.1.1 Applied Different Modeling Assumptions (comment theme 1)

Comment: Several of the commenters express concern that the 2003 deterministic 

screening analysis applied different assumptions for reusable (laundered) and disposable (nonlaundered) solvent-contaminated wipes and seemingly provided preferential treatment for 

reusable wipes. In particular, there is concern that two very different sets of assumptions were 

applied in evaluating the potential risks from the management of the solvent-contaminated wipes 

in landfills. For example, it was noted that high-end parameter assumptions were applied for 

disposable wipes and central-tendency assumptions were applied for reusable wipes. 

Response: This concern was addressed in the 2009 risk analysis, which makes no 

distinction between solvent-contaminated wipe types. Using a probabilistic national-level 

modeling framework, the 2009 analysis evaluated the management of solvent-contaminated 

wipes and industrial laundry sludge in “nonhazardous waste landfills.” Modeling was performed 

for solvent-contaminated wastes (i.e., wipes and sludge) using an assumed unitized mass loading 

rate (i.e., 1 kg per year) for each liner type, exposure pathway, and receptor. The revised risk 

analysis estimated risk-based, mass loading limits (RB-MLLs) for each F-listed solvent that, if 

contained on any industrial wipe or in laundry sludge, would not exceed EPA’s risk criteria if 

these materials were disposed of in unlined or composite lined nonhazardous waste landfills. 

These RB-MLLs were compared to estimated landfill loading rates (ELLRs). These rates 

estimate the annual quantities of solvents remaining in wipes and laundry sludge when disposed 

in landfills within the United States. The ELLRs were developed using the best available data 

gathered from a variety of sources using a Monte Carlo approach designed to account for 

uncertainty and variability in the input parameters.

2.1.2 Established “5 gram limit” (comment theme 2)

Comment: Under the proposed rule, the constituents shown below in Table 2 were identified 

based on the 2003 risk screening analysis to be eligible for disposal in a municipal or non-hazardous 

waste landfill if they meet the “dry” condition (i.e., contains less than five grams of solvent). As stated in 

the proposed rule, EPA chose five grams to be the standard for this condition because it falls within the 

range found in the risk screening analysis to not pose a substantial hazard to human health and the 

environment and it is also within the range of what is achievable through use of advanced solventextraction processes (e.g., centrifuging or other high-performance solvent-extraction or -removal 

technology). [68FR 65598]

Table 2. 19 Listed Solvents that May Be Disposed of in a Municipal Landfill

under the 2003 Proposed Rule

1,1,1-Trichloroethane Acetone Ethyl Acetate

1,1,2-Trichloroethane Butanol Ethyl benzene

1,1,2-Trichlorotrifluoroethane Carbon Disulfide Ethyl Ether

1,2-Dichlorobenzene Cyclohexanone Isobutyl Alcohol

2-Ethoxyethanol Dichlorodifluoromethane Methanol

In response to the five gram limit, commenters noted that they believe that this limit is unjustified 

from a human health and environmental risk standpoint and therefore is arbitrary and capricious and 

should be eliminated. Of particular concern is the practicality of generators of disposable wipes meeting
Response to Comments on the Solvent Contaminated Wipes 2003 Risk Screening Analysis

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this standard by having access to centrifuging or other advanced solvent extraction equipment needed to 

comply. As a preferred alternative to the five gram limit, commenters supported hand-wringing, which 

EPA has found will remove a meaningful amount of solvent (up to 68 percent according to the Technical 

Background Document).

Response: Under the 2009 analysis, the five gram limit is not considered explicitly. 

Alternatively, the analysis developed solvent-specific RB-MLLs for unlined and lined landfills using a 

unitized mass loading approach. For most solvents, EPA used empirical data from measurements of 

the amount of solvents found on disposed wipes; for other solvents the Agency used data on the 

amount of solvent applied to the wipes and made conservative assumptions of the fraction that 

remains in the disposed wipes. The resulting solvent-specific limits were then compared to solvent 

specific ELLRs to determine whether current industry practices could potentially result in exceeding RBMLLs for the F001 – F005 solvents. The results of the final risk analysis demonstrate that wipes 

contaminated with certain solvents and laundry sludge may be sent to lined landfills without 

posing significant risks to human health and the environment. Because target risk thresholds in 

the risk analysis were not exceeded when accounting for levels of solvent contained in wipes, 

EPA finds that the five gram limit for disposable wipes that are sent to landfills is not necessary 

to protect human health and the environment and, moreover, would be impossible to implement 

and enforce. Instead, solvent-contaminated wipes that are sent to landfills must meet the same 

“no free liquids” condition for wipes that are sent to laundries, dry cleaners, and combustors. 

This "no free liquids" condition reduces human exposure to free liquid spent solvent during 

transport, handling, and final disposition of the wipes and ensures that solvent-contaminated 

wipes contain no free liquids in compliance with the municipal solid waste regulations.

2.2 2003 Modeling Assumptions Overestimate Risk

Several commenters expressed concern that the 2003 screening approach was overly 

conservative. Table 3 identifies key comments received on 2003 analysis and summarizes how the 

revised 2009 probabilistic analysis addressed these concerns. In addition, each of these key areas is 

discussed in greater detail below.

Table 3. Modeling Assumptions Overestimated Risk in Screening Analysis

Parameter Comment on 2003 Screening Analysis 2009 NODA Probabilistic Analysis

Overall Modeling 

Framework

Deterministic approach Probabilistic modeling was implemented 

using Monte Carlo methods to characterize 

variability and uncertainty 

Landfill Characteristics  Small landfill in a wet climate

 Unlined landfill

 Failure to adequately consider 

naturally occurring binding and 

removal mechanisms (e.g., 

degradation).

 Performed national-level modeling that 

included landfills of varying geometry and 

located throughout the contiguous U.S. 

 Modeling scenarios included both unlined 

and lined landfills. 

 The modeling approach was revised and 

a new landfill coupled reactor (LFCR) 

model was developed. 

Groundwater leachate 

concentration

 Use of 5th (rather than the 10th) 

percentile leachate concentrations to 

well concentrations;

 Unexplained use of the highest nineyear average leachate concentrations

Probabilistic modeling was performed with 

EPACMTP using distributions of leachate 

output by the LFCR model.

Distance to receptors Inhalation risks evaluated at 75 meters 

from the landfill

Receptor distance and direction were 

varied.
Response to Comments on the Solvent Contaminated Wipes 2003 Risk Screening Analysis

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Parameter Comment on 2003 Screening Analysis 2009 NODA Probabilistic Analysis

Centrifuge removal 

efficiency

Centrifuging would remove only 90% of 

the solvent even though EPA Technical 

Background Document reveals that 

properly conducted centrifuging of 

disposable wipes results in 95-100% 

removal efficiencies

Not applicable – Applied a two-phased 

probabilistic approach to develop RB-MLL 

and ELLRs.

Solvent Loadings for 

Non-Laundered Wipes

Overly conservative assumptions about 

the wipe market and its contribution to 

solvent loadings.

ELLRs were developed using a Monte Carlo 

approach designed to account for 

uncertainty and variability.

2.2.1 Overall Modeling Framework (comment theme 3)

Comment: Comments were received on overall use of a “deterministic” approach to evaluate 

solvent-specific risks from landfilling (e.g., use of a “worst-case” small landfill size and wet climate 

rather than incorporating landfill size and climate into a probabilistic Monte Carlo analysis). 

Response: The revised 2009 risk analysis did not use a deterministic approach. The revised 

analysis was probabilistic and was implemented using Monte Carlo methods to characterize the 

variability and uncertainty associated with the modeling. The implemented framework and data 

development approach applied in support of the 2009 analysis generally followed major Agency guidance 

documents, including, for example, the Risk Assessment Guidance for Superfund Volume 3 Part A: 

Process for Conducting Probabilistic Risk Assessment (RAGS 3A) (U.S. EPA, 2001a) and the Guiding 

Principles for Monte Carlo Analysis (U.S. EPA, 1997b). For more details, see section 2.2.4 Data 

Development of the revised risk document (U.S. EPA, 2009).

2.2.2 Landfill Characteristics and Environmental Setting (comment theme 4)

Comment: Several comments were received that expressed concern that the modeled landfill 

characteristics resulted in overly conservative risk estimates that were not representative of actual 

management conditions. The characteristics most frequently noted as overly conservative included the 

following:

 Modeling a small landfill in a wet climate: It was noted by the commenters that the EPA 

employed “high-end” (highly conservative) assumptions that included the modeling of a small 

landfill in a wet climate for purposes of analyzing risks from landfilled non-laundered wipes.

 Assuming an Unlined landfill: Comments were received on the fact that the 2003 analysis 

considered releases from an unlined landfill scenario. The commenters charge that this scenario 

was too conservative because most sanitary landfills are equipped with liners and leachate 

collection systems.

 Failure to consider naturally occurring constituent removal mechanisms (e.g., degradation):

Commenters were concerned that the 2003 analysis failed to adequately consider degradation 

effects of organic constituents in media transport pathways, failed to adequately consider the 

effect of evaporation of solvents on landfill loading rates, and assumed that all solvents in a wipe 

were available for release, rather than being irreversibly bound to the wipe.

Response: 

 Small landfill in a wet climate: In the revised risk analysis, a probabilistic approach was applied 

because solvent-contaminated wipes and laundry sludge can be disposed of in landfills of varying 

geometry (e.g., surface area), with varying operating conditions (e.g., operating life), and located 

in many different parts of the country. Thus, each realization in the theoretical distribution of 

10,000 risk outputs represents a unique set of input values that were randomly selected with 
Response to Comments on the Solvent Contaminated Wipes 2003 Risk Screening Analysis

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respect to the landfill characteristics, location, hydrogeology, receptor location, exposure factors, 

etc.

 Unlined Landfill: Under the 2009 risk assessment, modeling was performed using both an 

unlined scenario and a composite liner scenario. The liner modeled under the latter scenario was 

assumed to consist of a geomembrane layer and soil. The liner leakage rates applied under these

scenarios were based on monthly average leak detection system (LDS) flow rates collected from 

empirical data; see section 3.1.2.1 Infiltration and Liner Leakage Rates, in the 2009 risk 

document (U.S. EPA, 2009). Modeling results were used to develop solvent-specific estimates for 

each liner condition. 

 Naturally Occurring Constituent Removal and Binding Mechanisms: In the 2009 analysis, 

the modeling approach was revised and a new landfill coupled reactor (LFCR) model was 

developed and applied. Biodegradation within the LFCR model was accounted for using a single, 

most conservative available value for the biodegradation rate. Mass transfer of volatile 

contaminants to the atmosphere was modeled through evaporation and advective flow within 

landfill gas (primarily methane generated from waste degradation). In addition, the revised risk 

modeling accounted for the partitioning between air, water, and solid phases using standard, 

accepted modeling approaches. The modeling thus accounted for adsorption to solid phases 

within the landfill, including the potential adsorption to disposed wipes material.

2.2.3 Groundwater Leachate Concentration (comment theme 5)

Comment: Comments were received that question the use of the 5th (rather than the 10th) 

percentile value from the distribution of ratios of leachate concentrations to well concentrations and the 

unexplained use of the highest nine-year average leachate concentrations as input to the groundwater 

modeling. 

Response: This concern was addressed under the 2009 revised risk assessment using a nationallevel, probabilistic modeling approach. Within this framework, the LFCR model was run to develop 

distributions of leachate estimates which were used as input to the EPA’s Composite Model for Leachate 

Migration with Transformation Products (EPACMTP) groundwater model (U.S. EPA, 2003a,c). The 

output of EPACMTP is a database of annual peak and time-averaged solvent concentrations arriving at 

randomly selected downgradient groundwater receptor well locations. The time-averaged solvent 

concentrations were used as input to the downstream exposure model.

2.2.4 Distance to Receptors (comment theme 6)

Comment: Comments were received on the fact that inhalation risks were evaluated at 75 meters 

from the landfill rather at a distance based on a national distribution, as was used for groundwater well 

distance. 

Response: The 2009 revised analysis addresses this concern by varying receptor distances and 

directions to simulate locating individuals in any of 36 directions at any of 8 different distances from the 

edge of the unit. See section 3.2 of the risk document (U.S. EPA, 2009).

2.2.5 Centrifuge Removal Efficiencies (comment theme 7)

Comment: Comments were received that pointed out that the assumption that centrifuging would 

remove only 90% of the solvent was overly conservative. EPA’s own Technical Background Document 

(at page 67) reveals that properly conducted centrifuging of disposable wipes results in 95-100% solventremoval efficiencies. 
Response to Comments on the Solvent Contaminated Wipes 2003 Risk Screening Analysis

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A specific comment relating to removal efficiencies for methyl ethyl ketone (MEK)

recommended removing MEK from the listing of banned solvents since EPA’s own risk assessment did

not justify its inclusion and the EPA’s report “Evaluation of the Solvent Extraction Efficiency of an 

Industrial Centrifuge on a Variety of Shop Towels and Wipes,” states, “that the solvent that seemed to be 

most easily extracted was MEK” and notes that MEK’s removal efficiency was 99 percent. Based on the 

removal efficiency of MEK of 99 percent rather than 90 percent, the commenter requests the Agency to 

reevaluate the inclusion of MEK as one of the banned solvents.

Response: Under the 2009 analysis, these concerns were addressed in that specific removal 

technologies were not explicitly considered in estimating risks. Instead, a two-phase probabilistic 

approach was applied to estimate risk-based, mass loading limits and ELLRs for each F-listed solvent.

The ELLRs were then used to determine whether current industry practices could potentially result in 

exceeding the RB-MLLs for the 20 F001 – F005 solvents considered in the analysis. The ELLR analysis 

did not include a ‘what if’ analysis regarding the increase in use of solvent extraction technology for 

disposable wipes. The purpose of the analysis was to estimate landfill loading based on current wipes 

management methods without additional use of technologies such as a centrifuge. Regarding MEK, EPA 

notes that, based on the revised risk analysis, MEK is now included in the exclusion in the final rule.

2.2.6 Solvent Loadings for Non-Laundered Wipes (comment theme 8)

Comment: Commenters stated that under the 2003 analysis, EPA applied an arbitrary “high-end”

parameter of 35 percent as the percentage of solvent-soiled non-laundered wipes (SSNWs) assumed to 

contain one or more F-listed solvents. 

Response: To address concerns related to solvent loadings, the EPA conducted a thorough analysis and 

developed representative ELLRs using the best available data gathered from a variety of sources using a 

Monte Carlo approach designed to account for uncertainty and variability in the input parameters. The 

new approach applied in developing these rates is presented in EPA’s Landfill Loading Calculations for 

Disposed Solvent-Contaminated Wipes and Laundry Sludge Managed in Municipal Landfill (U.S. EPA, 

2008; referred to the “Landfill Loading Report” in this document). The Landfill Loadings Report no 

longer includes a separate factor (such as 35 percent) for estimating the percentage of wipes containing Flisted solvents. Instead, the number of facilities assumed to generate F-listed solvent-contaminated 

disposable wipes was estimated from the Economics Background Document (Estimate of National 

Economic Impact of Conditional Exclusion of Solvent Industrial Wipes from RCRA Hazardous Waste 

Regulation (RCRA-2003-0004-0004), updated to 2002 data). The updated version of the Landfill Loading 

Report is in the docket for the final rule Landfill Loadings Calculations for Solvent-Contaminated Wipes, 

January 2012. Also, see the docket for Response to Comments on the 2003 Proposal on the Landfill 

Loadings Calculations for Solvent-Contaminated Wipes for responses to comments on the landfill loading 

calculations.

2.3 2003 Modeling Assumptions Underestimate Risk

Comments were received that expressed concern that the 2003 screening approach

underestimated risk. Table 4 identifies key technical issues identified by these commenters and 

summarizes how the revised 2009 probabilistic analysis addressed these concerns. Each of these key 

issues as well as others as others are discussed in greater detail below.

Table 4. Modeling Assumptions Underestimated Risk in Screening Analysis

Parameter Comment on 2003 Screening Analysis 2009 NODA Probabilistic Analysis
Response to Comments on the Solvent Contaminated Wipes 2003 Risk Screening Analysis

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Parameter Comment on 2003 Screening Analysis 2009 NODA Probabilistic Analysis

Solvent Limit, Loading 

Rates and Wipe Usage

 5 gram solvent limit will not be met

 Wipe usage assumption is low

 Adjustment factors applied regarding 

percentage of F-solvents used and 

present on wipes are arbitrary and not 

appropriate.

Applied probabilistic modeling 

approaches to develop distributions of 

solvent-specific RB-MLLS and ELLRs

Exposure Parameters  High-end values are not used, as 

required by EPA itself in its 1992 

Exposure Assessment Guidance for 

Inhalation Rates, Exposure Duration 

and Drinking Water Ingestion Rate

 The exposure period of an adult is 

assumed at only 10 years.

 Child exposure is assumed at 7 years.

Data distributions for exposure factors 

were developed based on the EPA 

Exposure Factors Handbook (EFH, U.S. 

EPA, 1997a) and the review draft of the 

Child-Specific Exposure Factors 

Handbook (Child-Specific EFH, U.S. EPA, 

2006a). 

Use of Dilution and 

Attenuation Factors 

(DAFs)

Use of Dilution and Attenuation Factors 

(DAFs) used to estimate exposure point 

concentrations are inappropriate

Probabilistic modeling performed with 

EPACMTP

Ecological Risk and 

Human Food Chain Risk

 Ecological risk is not fully evaluated.

 No food chain risk is evaluated

Consistent, with the 2003 analysis, the 

2009 analysis focused on significant 

pathways that would drive the risk-based 

mass loading rates

Advective Transport Advective transport was not evaluated Using the newly developed LFCR model, 

advective flow within landfill gas was 

modeled 

Meteorological

Conditions 

Air emissions, groundwater and other 

meteorological risk factors were based 

on Houston, TX and Lincoln, NE, when 

other areas could be higher in risk

National-level modeling was performed 

using data from 57 representative 

meteorological regions cross-referenced

with data from the EPACMTP climate 

centers 

Soil Characteristics Use of national averaged soil data 

characteristics without any consideration 

of more complex geologies will 

underestimate risks for many regions.

National-level modeling was performed 

using EPACMTP regional soil types

Biodegradation The assumption of degradation 

understates risk by as high as a factor of 

7.

Biodegradation within the LFCR model 

was accounted for using a single, most 

conservative available value for the 

biodegradation rate.

Peer Review Comments Peer review issues were not addressed. The modeling approach was revised, 

input data sets were created, and a new 

landfill coupled reactor (LFCR) model was 

developed. The 2009 analysis was peer 

reviewed.

2.3.1 Solvent Limits, Loading Rates, and Wipe Usage (comment theme 9)

Comment: Comments were received that indicated that the five gram criterion will not be met 

and the EPA needs to recognize the limitations of the extraction processes. A review of removal 

efficiency data in the docket indicates that no extraction technology can be routinely relied upon to yield 

less than five grams, with the possible exception of centrifuging which EPA is not mandating. The more 

commonly applied techniques of hand wringing or use of a screen bottom drum will result in as high as 

75 grams of solvent remaining on a wipe. The commenter believes that the risk must be modeled based on 

the maximum level expected following extraction, other than centrifuge, which is 75 grams.
Response to Comments on the Solvent Contaminated Wipes 2003 Risk Screening Analysis

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Concerning wipes usage, the commenter points out that the risk assessment assumes 120 wipes 

per day for large quantity generators (LQGs) and 30 wipes per day for small quantity generators (SQGs). 

However, docket data indicates wipe usage rates of 400 to 1,000 per day for many LQGs (e.g., printing 

and aerospace sectors), “several hundred” per day for automobile manufacturers, and 50 to 100 wipes per 

day for a typical auto body repair shop.

In addition, the approach used in the 2003 screening risk assessment appears to be modeling a 

certain amount of solvent contaminant with no reduction of the overall results based on assumptions 

regarding the percentage of F-solvents likely to be used in industry or present on the wipe. However, the 

docket data indicate that weighting factors of 35% were applied for F-solvent constituents and 10% for 

characteristic solvents. This is based on an assumed probability that a given wipe user would only apply 

an F- listed solvent 35% of the time and a characteristic solvent 10% of the time. As a result, the 

commenter states that such an arbitrary assumption is not appropriate.

Response: Under the 2009 revised risk analysis, the five gram limit is not considered explicitly. 

Alternatively, probabilistic national-level modeling was performed for solvent-contaminated wastes (i.e., 

wipes and sludge) using an assumed unitized mass loading rate (i.e., 1 kg per year) for each liner type, 

exposure pathway, and receptor. As discussed previously, the resulting RB-MLLs were then compared to 

estimated landfill loading rates (ELLRs). These rates represent the annual quantities of solvents remaining 

in wipes and laundry sludge when disposed in landfills within the United States. The ELLRs were 

developed using the best available data gathered from a variety of sources using a Monte Carlo approach 

designed to account for uncertainty and variability in the input parameters.

Concerning wipe usage, the landfill loadings calculations in the new Landfill Loading Report 

include the number of wipes used per year per generator. Rather than using a fixed value, the Landfill 

Loading Report used a range of values to correspond to the range of usage rates by sites. In addition, 

different usage rates were prepared for different generator types. This is discussed in Section 2.3.1 of the 

Landfill Loadings Report. These usage rates were based on data in the record, such as those sources cited 

by the commenter.

Regarding weighting factors used for the usage of F-listed solvents, the new Landfill Loading 

Report no longer includes a separate factor (such as 35 percent) for estimating the percentage of wipes 

containing F-listed solvents. Instead, the number of facilities assumed to generate F-listed solventcontaminated disposable wipes was estimated from the Economics Background Document (Estimate of 

National Economic Impact of Conditional Exclusion of Solvent Industrial Wipes from RCRA Hazardous 

Waste Regulation (RCRA-2003-0004-0004), updated to 2002 data).

See the docket for Response to Comments on the 2003 Proposal on the Landfill Loadings 

Calculations for Solvent-Contaminated Wipes for responses to comments on the landfill loading 

calculations. Also, see the docket for the final landfill loading report Loadings Calculations for SolventContaminated Wipes, January 2012.

2.3.2 Exposure Parameters (comment theme 10)

Comment: EPA received comments on the 2003 risk screening analysis stating that 

recommended high end exposure values are not used, as required by EPA in its 1992 Exposure 

Assessment Guidance for Inhalation Rates, Exposure Duration and Drinking Water Ingestion Rate. In 

addition, it was noted by a commenter that the exposure period of an adult was assumed to be only 10 

years. However, for other risk assessments periods of 30 to 70 years are required. Furthermore, it was 

noted that child exposure is assumed at 7 years with no justification. The commenters stated that the risks 

numbers provided for the child scenario are therefore inadequate.
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Response: The revised risk analysis presented in the 2009 NODA addresses these comments 

primarily through the use of data distributions for exposure factors which were developed based on the 

EPA Exposure Factors Handbook (EFH, U.S. EPA, 1997a) and the review draft of the Child-Specific 

Exposure Factors Handbook (Child-Specific EFH, U.S. EPA, 2006a). For this analysis, exposure duration 

was assumed to correspond with the receptor’s residence time in the same house as determined using EFH 

data on residential occupancy. Because the data used to develop parameter information for resident 

receptors were age specific, separate distributions were developed for adult and child residents. Exposure 

durations used in this probabilistic analysis are provided in Appendix I of the revised risk analysis (U.S. 

EPA, 2009).

In the revised risk analysis, for the critical groundwater pathway, we estimated risks for each 

individual exposure route for the adult (ingestion of drinking water, inhalation during showering, dermal 

contact during showering). Because these exposure routes can occur during the same time period for 

carcinogens, we calculated a combined cancer risk by summing the risks for these three exposure routes. 

Note that this approach may slightly overestimate combined risk because the model does not subtract the 

solvent mass available for one shower exposure route (e.g., inhalation) from the mass available for the 

other shower exposure route (e.g., dermal contact). For children, we estimated the combined cancer risk 

due to ingestion of drinking water and dermal contact during bathing by summing the route-specific risk 

estimates. 

For the child receptor, we did not simulate volatilization from the bath and subsequent inhalation 

for two reasons. First, by definition, the RfC is derived to be protective of all human population including 

sensitive subgroups for noncancer risks. Because we assume that the solvent mass that enters the air 

during showering is likely to be greater than the solvent mass that could enter the air during bathing, the

concentration to which adults are exposed during a shower event is likely to be higher than that of

children during bathing. For example, the bath water temperature for children is expected to be somewhat 

lower than the water temperature for showers, which would reduce the potential for volatilization of 

chemical solvents into the air. Second, for cancer endpoints, adult exposures have been shown to drive the 

risks. This is typically the case because the calculated risk is based on the ratio between exposure duration 

and averaging time, which is almost always higher for adults than for children.

The objective of the revised risk evaluation was to determine the lowest mass loading that would 

not exceed the target risk, not to analyze all possible exposures. EPA believes that the adult shower 

inhalation pathway provides a sufficiently protective estimate of potential risk/hazard from inhalation 

while bathing for all receptors. The revised risk analysis presented in the 2009 NODA included a variety 

of conservative assumptions to ensure that potential risks from landfill disposal were assessed 

protectively. Furthermore, our evaluation was based on the risks at the upper end of the risk distributions, 

i.e., the 90th percentile in the probabilistic analyses. In any case, the final risk analysis indicates that the 

risks for the solvent-contaminated wipes in composite-lined landfills are well below the target risk criteria 

for all of the solvents (except for trichloroethylene, which is not eligible for the exemption); the solvent 

landfill loadings are below one tenth of the risk-based mass loading limits.1

Regarding comments that the Combustion Risk Assessment Guidance suggests that infant 

scenarios should be addressed including impacts from nursing, the revised risk analysis did not evaluate 

this type of infant exposures for the landfill scenario because dioxins, furans, and dioxin-like 

polychlorinated biphenyls (PCBs) were not constituents of concern. The Human Health Risk Assessment 

Protocol for Hazardous Waste Combustion Facilities (U.S. EPA, 2005) only provides guidance for 

 1 See the risk results in F001-F005 Solvent-Contaminated Wipes and Laundry Sludge: Comparison of Landfill 

Loading Calculations and Risk-Based Mass Loading Limits” in the docket for the final rule.
Response to Comments on the Solvent Contaminated Wipes 2003 Risk Screening Analysis

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evaluating these specific constituents of concern and does not provide guidance for evaluating infant 

exposures to other constituents (such as solvents) via the ingestion of breast milk.

2.3.3 Use of Dilution and Attenuation Factors (DAFs) (comment theme 11)

Comment: Comments were received on the 2003 approach that applied universal DAF factors 

derived using general soil characteristics and a generic CMTP model, without any consideration for the 

behavior of the actual contaminants of concern. In one case, it was noted that the commenter felt the 

DAFs were inflated by a factor of 10.

Response: This comment was addressed under the 2009 probabilistic analysis, which included 

national-level modeling using the EPA’s Composite Model for Leachate Migration with Transformation 

Products (EPACMTP) groundwater model (U.S. EPA, 2003a,c). This model was used to perform solventspecific modeling using the leachate estimates produced by the LFCR model. Generic DAFs were not 

used in the revised risk analysis. EPACMTP has been the subject of multiple peer reviews and has been 

through a formal review process with EPA’s SAB. In addition, the EPACMTP and supporting databases 

have been used in at least eight risk analyses that have been through a combination of peer and SAB 

reviews (e.g., the Dyes and Pigments listing determination, EPA, 2003b). The output of EPACMTP is a 

database of annual peak and time-averaged solvent concentrations arriving at randomly selected 

downgradient groundwater receptor well locations. The resulting time-averaged solvent concentrations 

were used as input to the downstream exposure models.

2.3.4 Ecological Risk and Human Food Chain Risk (comment theme 12)

Comment: Commenters believe that the 2003 ecological screening analysis is deficient because

it included only 10 of the 34 solvent constituents. Contrary to EPA’s conclusion on page 118 of 

Document-0003, all of the constituents fail the aquatic benchmarks, showing that there is substantial 

ecological risk from the proposed rule. As it stands, EPA’s ecological screening analysis was not 

conservative because it left out most of the solvent constituents and assumed excessive stream flow and 

dilution.

In addition, comments were received that stated that the 2003 screening risk assessment failed to 

consider other important human indirect exposure pathways that are required by other programs, such as 

Superfund and Hazardous Waste Combustors. For example, there is no assessment of food chain risks. 

The commenters also pointed out that the risk assessment also fails to address runoff and erosion and to 

address particulate emissions because a daily cover is assumed. Yet volatilization of the solvent can occur 

into the daily cover soil layer and dispersed by wind. Also of concern is lint or dirt saturated with solvent

or metal particles dispersed by the wind.

Response: As discussed above, EPA received comments on the lack of conservatism in the 2003 

risk screening analysis; these comments covered certain modeling assumptions and gaps in available data. 

To address peer review and public comments regarding the importance of exposure pathways in 

determining the protective risk-based mass loading limits, EPA reevaluated the potential for risk via 

indirect exposure pathways as well as the potential for significant impacts on valued ecological attributes. 

On October 27, 2009, EPA published a NODA that presented the revised methodology and results. As 

discussed below, EPA believes that the revised methodology has substantively addressed the above 

comments on the 2003 risk assessment. 

Indirect human health exposure pathways – During the problem formulation stage of the 2009

risk analysis, EPA decided that the risk-based mass loading rates should be developed for the exposure 

pathways that posed the greatest potential concern. In other words, the risk-based rates would be 

protective of all exposure pathways including those that represent relatively minor contributions to the 
Response to Comments on the Solvent Contaminated Wipes 2003 Risk Screening Analysis

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overall risk. As such, EPA considered the physical and chemical properties of the chemicals of interest 

and decided to focus primarily on direct exposure pathways. As discussed in section 2 of the RB-MLL 

report, the 20 solvents evaluated include a wide range of volatile and semi-volatile organic chemicals, 

most of which have relatively short environmental half-lives (as compared to persistent organic 

chemicals). As with most organic solvents, diffusion and advection into the air are the primary release 

mechanisms into the environment and are the main reason many of these solvents can be used only with 

adequate ventilation. Moreover, a number of these solvents (e.g., benzene, toluene, and xylene) have been 

identified as groundwater contaminants at Superfund RCRA Corrective Action sites. Consequently, the 

leaching-to-groundwater pathway was also considered a primary release mechanism. The generally low 

values for partition coefficients for these solvents (e.g., the tendency for the solvent to volatilize) strongly 

suggests that indirect exposure pathways (e.g., plant uptake of vapors and subsequent ingestion of 

contaminated produce) will either be incomplete or contribute negligibly to total exposure.

The conclusion that volatile and semi-volatile organic solvents are insignificant contributors to 

risk via indirect exposure pathways (for a landfill source) is consistent with other risk analyses of landfill 

waste management scenarios (see for example, the risk analysis performed for the Paint and Coatings 

Hazardous Waste Listing Determination [U.S. EPA, 2001b]). Thus, direct exposure pathways to air and 

groundwater were the primary focus of the risk modeling for wipes and laundry sludge. Furthermore, 

landfills maintain controls for particulate air releases and for soil erosion and runoff; regulations for 

municipal solid waste landfills include run-on/runoff controls (40 CFR 258.26), daily cover (§ 258.21), 

and compliance with the CAA requirements (§ 258.24). Thus, the primary focus of the risk modeling was 

to assess direct exposure pathways to the air and groundwater. EPA is not aware of information 

suggesting that including these indirect exposure pathways would alter the RB-MLLs, nor did the 

commenter provide any such information.

Soil erosion and runoff – As noted above, existing regulations for MSWLFs are designed to 

minimize the likelihood of run-on and runoff. For example, under 40 CFR Section 258.26, the owner or 

operator is required to prevent run-on to the active portion of the landfill units and to collect and control 

run-off from the active portion for a 25-year storm. In addition, runoff controls are a legal requirement of 

the EPA’s National Pollutant Discharge Elimination System (NPDES) under the Clean Water Act. 

Therefore, based on existing regulations issued to control runoff and erosion, EPA eliminated runoff 

pathways from the risk assessment. 

Ecological Risk - The 2009 RB-MLL report explains that potential exposures to aquatic life 

associated with surface water contamination due to groundwater interactions were not modeled because 

this would have required site-specific information on nearby waterbodies to determine

 that there is a receiving waterbody capable of sustaining aquatic life

 the waterbody provides habitat for valued ecological attributes

 the dilution/attention attributable to the

− hydrogeological characteristics of the subsurface

− distance between the landfill and the waterbody, and

− capacity of a lake/pond or flow rate for a stream/river.

For chemical constituents that are potentially persistent and/or bioaccumulative in aquatic 

environments, the EPA would typically conduct a quantitative screening analysis to better understand the 

potential for adverse ecological effects. However, the solvents evaluated have low octanol-water partition 

coefficients (i.e., these chemicals are relatively water soluble and tend not to bioaccumulate) and tend to 

degrade rapidly in aqueous environments, especially in surface water (e.g., see, for example, 

biodegradation rates for the solvents as shown in Appendix B, U.S. EPA, 2009). Given the chemical-
Response to Comments on the Solvent Contaminated Wipes 2003 Risk Screening Analysis

15

physical properties of solvent constituents, the opportunity for dilution and attenuation prior to any 

ecological exposure, and the localized nature of any sort of ecological impact, the EPA does not believe 

that potential risks to aquatic ecosystems would drive the RB-MLLs. That is, the predicted risk to human 

health for individuals living in proximity to a landfill that manages industrial rags and wipes will be 

greater than the risks to aquatic ecosystems. As a matter of policy, EPA chose the upper end of the risk 

distribution (i.e., the 90th percentile) to establish the RB-MLLs; this approach to protecting human health 

builds an additional layer of conservatism into these limits. Therefore, EPA chose to focus on the most 

significant risks, as appropriate, to establish RB-MLLs that would be protective of human health and the 

environment with a high degree of certainty.

2.3.5 Advective Transport (comment theme 13)

Comment: Comments were received on the 2003 screening expressing concern that advective 

transport was not considered. The failure to consider advective transport of solvent contaminants through 

landfill gas was viewed as a major flaw that underestimates risk associated with the air pathway. In fact, 

these losses would continue even after a landfill cover is applied and also throughout the post closure 

period.

Response: In the 2009 revised risk analysis, advective transport was addressed. The revised 

modeling approach used a new landfill coupled reactor (LFCR) model, which included algorithms for 

considering advective transport. As part of this model, mass transfer of volatile contaminants to the 

atmosphere was modeled through evaporation as well as through advective flow within landfill gas 

(primarily methane generated from waste degradation). Furthermore, the revised risk analysis modeled 

releases after the landfills are closed.

2.3.6 Meteorological Conditions (comment theme 14)

Comment: Comments were received on the fact that air emissions, groundwater and other 

meteorological risk factors were based in 2003 exclusively on conditions in Houston, Texas, and Lincoln,

Nebraska, while other locations in the country could be higher in risk. As a result, the screening could 

understate risk for major regions of the United States. As an alternative, the EPA should evaluate areas 

with high industrial density for which heavy wipe usage is likely. For example, MSW landfills located in 

Detroit, Michigan, should be evaluated to evaluate risk for the auto industry wipes.

Response: This concern was addressed under the 2009 analysis by evaluating air exposures based 

on national-level air dispersion modeling using surface and upper air meteorological data obtained from a 

dataset of 57 representative meteorological regions. These representative meteorological regions were

then cross-referenced with the EPACMTP climate regions to develop national-level data sets used as 

inputs the landfill and groundwater models. The air dispersion modeling is described in section 3.2 of the 

2009 risk document (U.S. EPA, 2009).

2.3.7 Soil Characteristics (comment theme 15)

Comment: Comments were received on the use of national averaged soil data characteristics 

without any consideration of more complex geologies. It was noted that the 2003 assessment assumed

favorable geology based on a national averaged soil composition designated as “silt loam” with properties 

assigned.

Response: Under the 2009 assessment, this comment was addressed under the implemented 

national-level probabilistic approach. Under this approach, databases developed to support the 

EPACMTP groundwater model were used as the primary source for the correlated environmental 

parameters including soil type as well as other parameters such as aquifer type, climate center, and aquifer 

temperature. The EPACMTP and supporting databases have been used in at least eight risk analyses that 
Response to Comments on the Solvent Contaminated Wipes 2003 Risk Screening Analysis

16

have been through a combination of peer and SAB reviews (e.g., the Dyes and Pigments listing 

determination, EPA, 2003b). Thus, we used these data with a high level of confidence that the methods 

used to collect and develop this information were consistent with Agency guidance and best practices 

with respect to probabilistic risk analysis. See section 3.3.2 of the 2009 risk document (U.S. EPA, 2009) 

on model inputs for details on soil and other subsurface data were used.

2.3.8 Biodegradation (comment theme 16)

Comment: Comments were received that stated that the assumption of degradation applied in the 

2003 analysis understates risk by as much as a factor of 7. The assessment assumes degradation of solvent

contaminants occurs as part of the partitioning model of the landfill. However, the risk report notes that 

this may not be an appropriate assumption.

Response: EPA finds that degradation should be considered as part of the landfill modeling. In 

the revised risk analysis presented in the 2009 NODA, biodegradation within the newly developed LFCR 

model was accounted for using a single, most conservative available value for the biodegradation rate.

EPA finds that this approach reflects the degradation process that occurs and is appropriately 

conservative.

2.3.9 Peer Review Comments (comment theme 17)

Comment: Even though EPA had noted that they were deferring the issues identified during peer 

review until the final risk assessment was performed, public comments were received noting the peer 

review comments had not been addressed. The below list highlights key technical issues noted by the peer 

reviewers. 

 Groundwater transport was understated.

 Inadequate waste stream characterization..

 Tetrachloroethylene was not evaluated.

 Applied parameter values do not meet the requirement for a “high end” exposure scenario 

important to making regulatory decisions.

 Many additional transport pathways exist and would increase risk.

 Other types of receptors must be evaluated, included a worker at the landfill.

 Advective transport of air contaminants must be addressed.

 Degradation, if assumed, must also consider risks from toxic degradation products, such as vinyl 

chloride.

 Other factors besides climate and geology and landfill size need to be considered in the risk 

model.

 The use of generic DAF’s is inappropriate.

 No prediction of upset conditions due to unusual concentrations at a particular location in the 

landfill, or unusual preferential transport conditions (e.g. macropores in the landfill or 

surrounding soils).

 No consideration of NAPL effects, which could underestimate risk substantially both for the air 

pathway and the groundwater pathway.

 Partitioning methodology treats other MSW waste in the unit as if it were a soil, which is clearly 

erroneous.

 Too much information is based on “verbal” discussion or limited documentation making much of 

the data suspect and the risk conclusions questionable.

 More comparison to actual cases is needed to validate the risk conclusions.
Response to Comments on the Solvent Contaminated Wipes 2003 Risk Screening Analysis

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Response: As discussed throughout this document, EPA completely revised the risk analysis and 

presented the analysis for comment in the 2009 NODA. These peer comments on the original risk 

screening analysis from 2003 proposal have essentially been addressed in the 2009 revised risk analysis 

either through the development of the new LFCR model, national-level datasets, or through the 

implementation of the probabilistic national-level modeling approaches used to develop the RB-MLL and 

ELLRs. EPA presented the revised risk analysis for peer review and has responded to the peer review 

comments on the revised analysis. See the docket for responses to peer review comments on the 2009 

revised risk analysis (ELLR calculations -- EPA-HQ-RCRA-2003-0004-0432; RB-MLL calculations --

EPA-HQ-RCRA-2003-0004-0433). EPA has also responded to public comments on the 2009 revised risk 

analysis; see the docket for Response to Comments on the Solvent Contaminated Wipes 2009 Risk 

Analysis: Risk-Based Mass Loading Limits.

In response to some of the specific peer review comments on the risk screening analysis 

mentioned by the commenter, EPA notes that the 2009 revised risk analysis addresses most of these 

concerns in the revised modeling (RTI, 2009). The revised analysis included:

• modeling for tetrachloroethylene;

• “high-end” risk results, i.e., EPA 90th percentile ELLR and RB-MLL values;

• advective flow of gas within the landfill using the new landfill model (LFCR);

• modeling of multiple pathways, including inhalation exposure from air releases and exposure 

from groundwater releases through drinking water ingestion, showering, and dermal 

absorption; 

• modeling of the fate and transport of the specific solvent chemicals (not generic DAFs).

Regarding predictions at particular locations, the 2009 revised risk assessment used a nationallevel, probabilistic modeling approach. The modeling was not designed to attempt to assess site specific 

factors. However, the data distributions used represented a wide range of possible conditions across the 

country. EPA finds that this is a conservative approach, especially in conjunction with use of the 90th 

percentile results for our final evaluation.

Concerning degradation products, the model used in the revised risk analysis does not simulate 

the formation of daughter products from the degradation of chemical constituents in the landfill.

However, any degradation products will themselves be subject to degradation, making any assessment of 

the practical effect of this extremely difficult to quantify. In the case of vinyl chloride, we note that this 

chemical is a gas at room temperature and is likely to volatilize from the landfill rather readily. Given that 

the revised risk analysis showed that the high-end (90th percentile) risk pathway of most concern was

release to groundwater, it seems unlikely that air risks from formation of vinyl chloride would present 

higher risks than the groundwater risks evaluated in the revised analysis. 

The Agency finds the formation of NAPL (non-aqueous phase liquids) from the disposal of 

solvent-contaminated wipes to be highly unlikely. As a condition for the exclusion, the final rule requires 

that there be no free liquids in containers used for shipment and disposal. Also, the regulations for 

municipal solid waste landfills restrict the acceptance of any wastes with free liquids. Furthermore, the 

levels of solvents in the wipes are unlikely to be sufficient to promote formation of a non-aqueous phase, 

especially considering the properties of the solvents. For example, most of the solvents are relatively 

water soluble and volatile, properties that make formation of a separate NAPL layer unlikely.

To address concerns related to the use of limited documentation for waste characterization and

solvent loadings, the revised risk analysis included a thorough analysis and development of representative 

ELLRs using the best available data gathered from a variety of sources. The analysis using a Monte Carlo 
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approach designed to account for uncertainty and variability in the input parameters. EPA’s revised 

methodology for estimating solvent loadings is described in Landfill Loading Calculations for Disposed 

Solvent-Contaminated Wipes and Laundry Sludge Managed in Municipal Landfill (U.S. EPA, 2008) and 

the updated version of the document in the docket for the final rule Landfill Loadings Calculations for

Solvent-Contaminated Wipes, January 2012.

In response to the comment that more comparison to actual cases is needed, as noted above, the 

revised analysis did not attempt to model particular locations. Rather, the 2009 revised risk analysis used 

a national-level, probabilistic modeling approach. The modeling was not designed to attempt to assess site 

specific factors. There are significant uncertainties concerning how exposure and environmental 

assumptions will change over time. However, the fate and transport model used (EPACMTP, and its 

predecessors), have been verified extensively at each of the developmental stages. The model has been 

verified, in numerous cases, by comparing the simulation results against both analytical and numerical 

solutions. Additionally, EPACMTP and its predecessors have been validated using actual site data from 

four different sites. The relevant verification and validation history is discussed in detail in Appendix D of 

the EPACMTP Technical Background Document (U.S. EPA, 2003c). See the discussion on the model in 

section 4.2.2.3 of the risk documentation for the 2009 analysis (U.S. EPA, 2009). EPA finds that the 

modeling approach used in the 2009 revised risk assessment (a national-level, probabilistic modeling 

approach), is appropriate. 

See responses in this document regarding other pathways (section section 2.3.4) and responses to 

comments on potential worker exposure (section 2.5).

2.3.10 Solvent Impact on Liners (comment theme 18)

Comment: In response to the 2003 screening approach, comments were received on the unlined

landfill scenario and recommended that EPA should consider the risk of wipe disposal on lined landfills 

and the potential for solvent impacts on liner integrity.

Response: EPA recognizes that there are uncertainties associated with modeling the fate and 

transport of the chemicals in the environment. To address uncertainties highlighted by comments received 

in response to the 2003 risk screening analysis, EPA revised the analysis and developed a landfill coupled 

reactor (LFCR) model to simulate the dominant release mechanisms from a landfill, including vapor 

diffusion, advection, and leaching. The revised analysis also considered liner leakage rates that are based 

on measured, empirical data (Tetra Tech, 2001) that reflect existing conditions in landfills. In addition, 

the landfill source model accounts for liner leakage by sorption to the geomembrane surface and 

diffusion through the geomembrane. As a result, the approach used in the revised risk analysis provides 

a reasonable representation of anticipated behaviors and supports the development of protective RBMLL. Given the low expected concentrations resulting from the application of the RB-MLLs, it is 

unlikely that liner impacts will be significant. The most commonly used plastic for landfill liners, HDPE, 

has excellent resistance to most chemicals, particularly at low concentrations typically present in landfills.

While it is true that high concentrations of some solvents can lead to swelling and decreased integrity of 

some plastics, solvent concentrations are much lower in a landfill setting than levels known to lead to 

such effects. As an EPA-sponsored study indicates, the published leachate chemistry data show that 

leachate from municipal solid waste landfills contains trace concentrations of synthetic organic chemicals 

(see Appendix E to Assessment and Recommendations for Improving the Performance of Waste 

Containment Systems, EPA/600/R-02/099 , December 2002).
Response to Comments on the Solvent Contaminated Wipes 2003 Risk Screening Analysis

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2.4 Sufficiency of Data and Model

2.4.1 Laundry Sludge (comment theme 19)

Comment: To ensure that land disposal of laundry sludge is appropriate in all circumstances, 

commenters recommended that sufficient data be used in the risk analysis to account for laundry 

variability (e.g., variations due to customer mix and specific types of items being processed). This type of 

variability can result in differences in constituents and concentrations. Of particular concern is the 

discussion in the preamble where EPA notes that the data used to analyze potential risks associated with 

the disposal of laundry sludge consisted of “a very limited number of wastewater concentrations collected 

from industrial laundries by the Office of Water as part of their effluent guidelines development process 

[68FR65609].”

Response: This comment was addressed under the revised analysis using a two-phased 

probabilistic modeling approached. To address variability in disposal environments, probabilistic 

national-level modeling was performed to develop RB-MLLs using a mass loading rate approach (i.e., kg 

per year). These RB-MLLs were then compared to estimated landfill loading rates (ELLRs). EPA 

completely revised the landfill loading calculations and presented our new analysis in the October 2009 

NODA. The ELLRs were estimated as described in detail in the Landfill Loading Calculations for 

Disposed Solvent-Contaminated Wipes and Laundry Sludge Managed in Municipal Landfills (U.S. EPA, 

2008). These rates represent the annual quantities of solvents remaining in wipes and laundry sludge 

when disposed in landfills within the United States. The ELLRs were developed using the best available 

data gathered from a variety of sources using conservative assumptions and a Monte Carlo approach 

designed to account for uncertainty and variability in the input parameters. For response to comments 

specific to the ELLR calculations, see the docket for Response to Comments on the 2003 Proposal on the 

Landfill Loadings Calculations for Solvent-Contaminated Wipes.

2.4.2 Use of Delisting Risk Assessment Software (DRAS) (comment theme 20)

Comment: A commenter recommended that the EPA use the Delisting Risk Assessment 

Software (DRAS) as a comparison to the EPA’s screening analysis. It was noted that when DRAS is used 

to evaluate risk associated with the disposal of solvent-contaminated industrial wipes, the outcome 

appears to be inconsistent with the conclusions of EPA’s risk screening analysis. 

Response: The DRAS model was designed to evaluate delisting petitions submitted under 40 

CFR 260.22 to determine the potential risks arising from land disposal of a specific wastestream. Thus, 

the delisting process uses characterizations and volumes of waste generated by a particular generator. 

Rather than performing additional modeling with the DRAS delisting model, EPA developed the revised, 

robust risk analysis using models that reflect conditions at landfills nationally and updated estimates of 

the quantity of solvents on wipes and in laundry sludge. The revised risk analysis is included in the docket 

for the final rule. The revised risk analysis used a state-of the art landfill model, national-level datasets, 

and a probabilistic national-level modeling approach to develop the Risk-Based Mass Loading Limits 

(RB-MLL) and Estimated Landfill Loading Rates ELLRs. The Agency believes that the revised risk 

analysis is a more up-to-date and comprehensive evaluation of risk and is more appropriate for a nationallevel listing decision compared to the DRAS model. The DRAS model uses leaching data (TCLP) as 

input for the model. The revised risk analysis uses a new landfill model (LFCR) rather than TCLP 

leachate data for modeling solvent releases, which presents several advantages. EPA needed to perform a 

comprehensive national-level assessment and the limited TCLP data available were not adequate for that 

purpose. The RB-MLL methodology allowed EPA to capture a broad variety of conditions needed to 

back-calculate acceptable levels of solvents for a national rule. In addition, the model allowed EPA to 

consider the potential risk for many solvent chemicals based on their properties and transport 

characteristics, regardless of whether empirical release data such as TCLP were available. Finally, the 
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revised risk analysis modeled disposal in a composite-lined landfill, an option not included in the DRAS 

model. EPA presented the revised risk analysis for peer review and has responded to the peer review 

comments. EPA has also responded to public comments on the revised risk analysis presented in the 2009 

NODA; see the docket for Response to Comments on the Solvent Contaminated Wipes 2009 Risk 

Analysis: Risk-Based Mass Loading Limits.

2.5 Potential Exposures before Landfilling

2.5.1 Laundering Operations (comment theme 21)

Comment: Comments were received that pointed out that the EPA has not considered exposures 

resulting from wipes and laundering processes, other than to evaluate sludge and wipe disposal in a MSW 

landfill. The following lists the exposure pathways recommended by commenters for evaluation:

 Worker exposure at both the laundering facility and the Publicly Owned Treatment Works 

(POTW) receiving contaminated groundwater.

 Fate and transport of hazardous constituents not treated at the POTW that pass through to the 

water discharge and impact receiving water bodies.

 Air emission pathways from the laundering process, and impacts on nearby residences.

 Runoff issues and fire potential resulting from the storage and accumulation of wipes.

Response: The purpose of the screening analysis was to characterize the potential risk from the

disposal of solvent-contaminated wipes and laundry sludge in MSW landfills. Occupational exposures, 

such as exposures resulting from the partitioning of solvents to air and wastewater during laundering 

operations, were not considered as part of the analysis. With regard to exposures to solvents during 

laundering operations, EPA assumes that workers are appropriately protected by regulation and guidance 

provide by the U.S. Labor Department's Occupational Safety and Health Administration (OSHA). For 

example, worker exposures to an airborne contaminants are limited based on 1910.1000 Tables Z-1 and 

Z-2 (http://www.osha.gov/pls/oshaweb/owadisp.show_document?p_table=STANDARDS&p_id=9992

and http://www.osha.gov/pls/oshaweb/owadisp.show_document?p_table=STANDARDS&p_id=9993). In 

addition, the final rule establishes a closed container standard that addresses fugitive air emissions from 

the solvent-contaminated wipes, which will protect laundry employees. The final container standard 

applies to accumulation and storage at the generating facility, transportation either on-site or off-site, and, 

finally, storage and management at the handling facility, such as a laundry.

Concerning exposure to residents living in close proximity to laundering/dry cleaning facilities,

given the range of exposures captured by the modeling scenarios in the revised risk analysis presented in 

the October 2009 NODA, and the fact that ambient air exposures were not significant, any ambient air 

impacts from laundering/dry cleaning operations should be less significant than those considered under 

our landfill disposal scenario. The revised risk analysis assumed that ambient air exposure could occur as 

close as 25 meters from the landfill, a fairly conservative assumption. Despite this, none of the 90th

percentile RB-MLLs were based on ambient air exposures. Indoor air exposures resulting from showering 

with contaminated groundwater and groundwater ingestion were found to be the key exposures 

considered, and these risks drove the analysis. 

Furthermore, in response to comments from the peer review of the landfill model used in the 

2009 risk analysis, EPA considered what the mass loading rates would be if all of the leachate mass 

volatilized and the air pathway was the only pathway of concern. The results from this effort are presented 

in Table 4-8 in the revised risk analysis document (U.S. EPA, 2009). This table presents the mass loading 

rates associated with the greatest estimated risk for the air and groundwater pathways, respectively, at the 

90th percentile of the risk distribution. The table also includes an estimate of the mass loading rate 
Response to Comments on the Solvent Contaminated Wipes 2003 Risk Screening Analysis

21

associated with the air pathway if all leachate mass volatilized. In short, this analysis determined that, 

even if all of the solvent mass from landfill leachate was released into the air (i.e., no transport to 

groundwater occurred), the resulting mass loading limit for the solvents would not change significantly 

(see Section 4.2.2.1, U.S. EPA, 2009)

With regard to partitioning of solvents to wastewater and sludges, EPA’s Office of Water 

regulates wastewater discharges through the National Pollutant Discharge Elimination System (NPDES). 

The NPDES permit program controls water pollution by regulating point sources that discharge pollutants 

into waters of the US (http://cfpub.epa.gov/npdes/). Also, local POTW pretreatment standards may apply 

to many laundries. Therefore, risks associated with these discharges are currently managed by the EPA. 

Similarly, risks associated with solvents that partition and persist in municipal sewage sludge are also 

managed by EPA’s Office of Water under the Clean Water Act (referred to as the 503b standards), which 

routinely evaluates the potential risks associated with pollutants in sludge, and established risk-based safe 

levels for selected pollutants based on the predicted risk to human health and the environment 

(http://water.epa.gov/scitech/wastetech/biosolids/biosolids_index.cfm). 

Lastly, runoff issues associated with temporary storage practices were not evaluated as part of the 

assessment given that runoff controls are a legal requirement of the EPA’s National Pollutant Discharge 

Elimination System (NPDES) under the Clean Water Act. Most states are authorized to implement the 

NPDES storm water program (http://cfpub.epa.gov/npdes/stormwater/authorizationstatus.cfm and 

http://cfpub1.epa.gov/npdes/stormwater/swbasicinfo.cfm ). The NPDES regulations establish best 

management practices (BMPs) for stormwater and runoff pollution control practices designed to reduce 

the pollutants contained in discharges to the storm drain system and/or receiving waters. Based on 

existing regulations issued to control stormwater runoff, EPA assumed that BMPs would reduce exposure 

pathways associated with runoff to levels well below concern. In addition, the final rule establishes a

closed container standard that should address potential releases during storage.

2.6 Not Specific to Screening Assessment

This section identifies other technical issues noted by commenters that were not specific to the 

2003 risk screening analysis. 

2.6.1 Combustion of Wipes (comment theme 22)

Comment: In support of the 2003 proposed rule, combustion of contaminated wipes was 

considered and evaluated as a management option. EPA proposed to conditionally exclude from the 

definition of hazardous waste solvent-contaminated disposable wipes that are sent to a municipal waste 

combustor (MWC) or other combustion facility. As a result, comments were received on this management 

practice.

One commenter stated that the MWC analysis assumes 99.99% destruction efficiency; however,

this is the minimum efficiency for hazardous waste combustors, and is not necessarily the case with 

MWCs. The commenter noted that MWCs are not required to demonstrate destruction efficiency and can 

operate at significantly lower combustion temperatures than hazardous waste incinerators. The 

commenter stated that the MACT standards for MWCs allow higher levels of dioxin emissions than 

HWCs, reflecting their poorer operating conditions and lower destruction efficiency. Commenters

suggested that wipes contaminated with chlorinated F001 and F002 listed solvents may pose a significant 

hazard for the generation of dioxin emissions from combustors and/or contamination of combuster 

residues.

Commenters also stated that the solvent-contaminated wipes could pose a risk to the environment, 

either through volatilization or release of free liquids, or potential fire. Commenters urged EPA to specify 
Response to Comments on the Solvent Contaminated Wipes 2003 Risk Screening Analysis

22

some minimum standards for management of solvent-contaminated wipes to be burned in combustors to 

address risk from fugitive emissions during the storage and processing of these wipes prior to and during 

combustion.

Response: In support of the November 2003 proposed rule, the Agency analyzed the risks posed 

from combustion of disposable wipes in municipal waste combustors. Based on this information, EPA 

made the conservative estimate that 99.99 percent of the incoming contaminant would be destroyed, with 

the remainder ending up in the ash (68 FR 65609). These combustors are easily capable of destroying the 

solvent, as described in Section IV.F.11 of the Technical Background Document (68 FR 65602). EPA 

went on to explain that EPA has promulgated revised air emission standard requirements under the New 

Source Performance Standards for municipal waste combustors and commercial and industrial solid waste 

incinerators, which provide a level of protection comparable to the National Emission Standards for 

Hazardous Air Pollutants (NESHAP) for hazardous waste incinerators (68 FR 65602). 

The New Source Performance Standards, which are promulgated under section 129 of the CAA, 

already require that municipal waste combustors and other solid waste combustion facilities comply with 

numerical emission limitations and performance standards that address emissions of dioxin and furans, as 

well as other air pollutants, such as mercury, particulate matter, sulfur dioxide, nitrogen oxides, semivolatile metals, lead, cadmium, hydrogen chloride, and carbon monoxide. To eliminate confusion 

regarding how the New Source Performance Standards apply to municipal waste combustors and other 

solid waste combustion facilities, we are clarifying in the regulatory language that we are allowing 

disposable wipes that meet the conditions of today’s rule to be sent to municipal waste combustors and 

other combustion facilities that are regulated under the New Source Performance Standards in section 129 

of the CAA. Generators may also continue to send solvent-contaminated wipes to a hazardous waste 

combustor regulated under 40 CFR parts 264 or 265, or a hazardous waste boiler and industrial furnace 

regulated under 40 CFR part 266 subpart H which also control for dioxin and furan emissions.

EPA shares some of the commenters’ concerns about the management of solvent-contaminated 

wipes prior to combustion. EPA has addressed these concerns in the final rule. Specifically solventcontaminated wipes must not contain free liquids when transported to a municipal waste combustor or 

other combustion facility. EPA has clarified this standard by defining “no free liquids” using the Paint 

Filter Liquids Test. The use of this test enables proper implementation of the “no free liquids” condition 

and, combined with today’s requirement that generators document how they are meeting this condition, 

should minimize the possibility of free liquids occurring after the solvent-contaminated wipes leave the 

generator. If, however, free liquids do reach the combustor, they must be removed and managed under the 

applicable hazardous waste regulations. In addition, EPA is requiring that solvent-contaminated wipes be 

accumulated, stored, and transported in non-leaking, closed containers that are labeled as “Excluded 

Solvent-Contaminated Wipes.” This container standard will reduce the potential releases of the solvent to 

the air or through spills while being managed by the combustor.

2.6.2 Consideration of Other Contaminants Including Metals (comment theme 23)

Comment: The commenters pointed out that the EPA neglected to consider contamination of 

wipes from the materials that the solvent removes from the equipment. Testing by a national 

environmental company indicated that even after processing by a professional laundering service, cloth 

shop towels contain harmful levels of chemicals including lead and cadmium. However, another comment 

was received that dismissed this point stating that claims about residual metals in clean, laundered shop 

towels are entirely without merit. 

Response: We first note that solvent-contaminated wipes that exhibit a characteristic (except for 

ignitability) due to constituents other than one of the excluded F- and corresponding P- and U- listed 
Response to Comments on the Solvent Contaminated Wipes 2003 Risk Screening Analysis

23

solvents (e.g., co-contaminant metals) are not eligible for the conditional exclusions. Similarly, wipes 

contaminated with other listed hazardous wastes would not be eligible for the conditional exclusions. 

Regarding other possible contaminants, we note that the F-, P-, and U-code solvent listings are based on 

the toxicity and/or ignitability hazards presented by the specific solvents included in the listing 

descriptions. The language in the listings illustrates EPA’s concern with the solvent chemicals. Other 

potential constituents in the solvent wastes vary widely across industries, such that it would be 

exceedingly difficult, if not impossible, to categorize and evaluate risks associated with these wastes if we 

considered all other hazardous constituents and characteristics. Because of the wide variability in 

constituents that might be present in wastes from use of the solvents and the identified hazards posed by 

the solvents, we focused our evaluation on the solvent chemicals themselves. We find that this is the most 

practical approach to evaluating risks posed by solvent-contaminated wipes. 

Regarding the potential for laundered towels to contain residual metals, we note that the study 

cited by the commenter was limited to metal contaminants, not listed solvents. As described in the above 

paragraph, EPA did not attempt to evaluate possible co-contaminants on the wipes. The exclusion is for 

wipes contaminated with F-listed solvents, not metal-contaminated wipes. The solvent-contaminated 

wipes are still subject to the TC for metals, which would help to address any potential metal residuals in 

the laundered wipes. In addition, any residual metals still on the towels after laundering would likely be 

tightly bound to the fibers, making any transfer from laundered towels to workers unlikely.

2.6.3 Solvent Wipes Evaluated Separately (comment theme 24)

Comment: Comments were received that the analysis only considered a single solvent 

constituent from a single source going to a single landfill, and the landfill is assumed to receive wipes 

from no other sources. Furthermore it was noted that the benchmarks (risk criteria) used are inadequate to 

allow margins for contaminants migrating from other sources in the landfill. The commenter suggested 

that a non-cancer hazard index of 1.0 and cancer risk of 1E-05 do not provide a margin for other exposure 

impacts from other sources, and suggested using lower HQ and cancer risk targets.

Response: The Agency revised its analysis for the October 2009 risk analysis to evaluate 

multiple facilities disposing of solvent-contaminated wipes in one landfill. We used a Monte Carlo 

analysis to represent the variability of generator and landfill locations; the distribution used ranged from 2 

to 67 generators per landfill. In addition, the overall loadings assumed were conservative estimates, as 

described in the Landfill Loading Report (see Landfill Loadings Calculations For Solvent-Contaminated 

Wipes; January 2012, in the docket for the final rule.)

In using the data from the Biennial Report (BR), for example, the Landfill Loading calculations 

assumed that all of the waste reported in the BR category used was rags and wipes, even though the BR 

waste form (code W002, contaminated debris) includes, for example, certain paper, clothing, rags, wood, 

empty fiber or plastic containers, glass, piping, or other solids.

2 Furthermore, the solvent landfill loading 

analysis was scaled up to account for other industries that may generate wipes (increasing the number of 

facilities by about 80%), and also included an additional factor to account for possible growth in the use 

of disposable wipes in the future.3

The calculation of the risk-based mass loading limits (RB-MLLs) also used conservative 

assumptions, e.g., the revised risk analysis presented in the October 2009 NODA used conservative 

receptor locations for groundwater and ambient air pathways. In addition, the final risk evaluation was 

based on the risks for the upper end of the risk distributions, i.e., the 90th percentile in the probabilistic 

 2 See Biennial Report instructions: http://www.epa.gov/wastes/inforesources/data/br11/br2011rpt.pdf 3 See section 2.3.4 of Landfill Loadings Calculations for Solvent-Contaminated Wipes; January 2012, in the docket 

for the final rule.
Response to Comments on the Solvent Contaminated Wipes 2003 Risk Screening Analysis

24

analyses. Therefore, based on the conservative assumptions used to calculate both the solvent landfill 

loadings and RB-MLLs, the solvents present in the wipes and sludge are unlikely to present a significant 

risk when disposed in a composite lined landfill.

EPA does not agree with the commenter’s suggestion that EPA use more restrictive target risk 

criteria to address other possible sources of the solvents of concern. The Agency believes that the risk 

criteria used (1E-5 cancer risk and HQ less than 1.0 for non-cancer risk) are appropriate for a listing 

decision, especially in light of the conservative approach used in the overall risk evaluation. However, the 

risk documentation also presented results for the 1E-06 cancer risk level (see Table 5 in F001-F005 

Solvent-Contaminated Wipes and Laundry Sludge: Comparison of Landfill Loading Calculations and 

Risk-Based Mass Loading Limits, January 2012, in the docket for the final rule). These results show that, 

even if the Agency used the 1E-06 criterion, the carcinogenic solvents would still not present risks above 

this level, except for trichloroethylene, which is not eligible for the exemption in any case due to noncancer risks. Furthermore, for the solvent RB-MLLs based on non-cancer risks, all of these solvents 

(except trichloroethylene) had HQ levels below 0.1, i.e., 10-fold below the risk criteria used. Therefore, 

even using more restrictive criteria as suggested by the commenter, the disposal of solvent contaminated 

wipes and sludge in composite lined landfills does not appear to present significant risk. 

The Agency also considered other potential sources for solvents in municipal landfills. These 

include: solvent-contaminated wipes from conditionally exempt small quantity generators (CESQGs), 

other industrial wastes that may contain the solvent chemicals, and solvents contained in household 

hazardous waste. The Agency does not believe these sources would significantly affect the overall risk 

results as described below.

Under federal regulations, CESQGs may dispose of hazardous waste in MSW landfills subject to 

§258 regulations (see 40 §CFR 261.5(g)(3)). However, many states have requirements that are more 

stringent. For example, based on information collected in 1990, at least 22 states require all or some 

CESQGs to manage their hazardous waste at a permitted Subtitle C facility, thus prohibiting disposal at a 

municipal solid waste facility (more states may have adopted similar restrictions since 1994).

4 In any 

case, solvent loadings associated with wipes from CESQGs are expected to be relatively small. For 

example, Large Quantity Generators generate over 1000 kg per month of hazardous waste, compared to 

CESQGs which cannot generate more than 100 kg per month (220 lbs, or about 1⁄2 of a drum) of 

hazardous waste (which includes all hazardous waste generated at the facility).

Concerning other industrial wastes, wastes not associated with wipes that arise from solvent use 

of these chemicals will continue to be regulated under the F-code listings and the hazardous waste 

characteristics (Part 261, Subpart C). Non-solvent related wastes will be regulated under the hazardous 

waste characteristics, which include the Toxicity Characteristic for many of the more toxic solvents, as 

well as the ignitability characteristic for the more flammable chemicals.5 Therefore, beyond the CESQG 

waste discussed above, there are regulations in place to restrict disposal of other sources of the solvent 

chemicals. Furthermore, existing hazardous waste regulations would continue to provide pollution 

prevention incentives toward decreasing the use of F-listed solvents in general, because their use would 

continue to result in the generation of listed hazardous waste, such as spent solvents. In addition, many Flisted constituents are hazardous air pollutants (HAPs). Various NESHAP regulations (e.g., such as those 

identified in Appendix C of the Landfill Loadings Report) provide incentives for a facility to decrease its 

use of HAP-containing solvents.

 4 Generation and Management of CESQG Waste, July 1994, EPA. 5 Six of the 20 solvents evaluated in the risk analysis are TC chemicals and 12 are included in the F003 or F005 

listing, indicating that they are ignitable.
Response to Comments on the Solvent Contaminated Wipes 2003 Risk Screening Analysis

25

Regarding household hazardous waste, households are not generally expected to be using 

industrial hazardous waste solvents. In addition, many communities in the United States offer a variety of 

options for safely managing household hazardous waste. Some communities have permanent facilities

that collect hazardous household waste year-round, including leftover paints, solvents, pesticides, and 

cleaning and automotive products.

6 Other communities have special collection days for such wastes.

Therefore, these waste collection programs will help divert this hazardous waste stream from MSW 

landfills.

2.6.4 Complexity of the Proposed Rule (comment theme 25)

Comment: Commenters stated that the 2003 proposed rule had different conditions for reusable 

wipes and disposable wipes destined for landfills. There are different regulatory exclusions, different 

labeling requirements, different limits on solvents and prohibitions. The commenters noted that

complexity of the regulation is unnecessary because the risks to human health and the environment are the 

same.

Response: EPA agrees the risks from release of solvent from wipes are the same for both 

reusable and disposable wipes, thus it makes sense to apply the same conditions during 

accumulation, transportation, and management of both types of wipes. The conditions in the final 

rule ensure that the solvent-contaminated wipes are being managed appropriately, regardless of 

whether they are being laundered or disposed. Furthermore, by finalizing conditions that are as 

similar as possible for both exclusions, EPA has reduced the burden of compliance with the rule, 

especially for facilities that use both types of wipes. 

2.6.5 Groundwater Monitoring and Corrective Action Controls (comment theme 26)

Comment: Commenters stated that the proposed rule gave no consideration to groundwater 

monitoring and corrective action controls, even though all MSWLFs and 40 C.F.R. Part 257, Subpart B 

landfills operating today are required to have such controls. The commenter noted that EPA must take 

these regulatory conditions into account in determining whether disposable wipes disposed of in such 

units are properly classified as hazardous waste. See, e.g., 40 C.F.R. § 261.11(a)(3)(x) (consideration of 

the impact of other regulatory programs in determinations of whether solid waste should be identified and 

characterized as listed hazardous waste); Dithiocarbamate Task Force v. EPA, 98 F.3d 1394 (D.C. Cir. 

1996) (determination of whether wastes pose a substantial hazard to human health or the environment 

when mismanaged requires consideration of all factors in 40 C.F.R. § 261.11(a)(3)).

Response: EPA disagrees with the commenter’s assumption that, in an unlined landfill scenario, 

comprehensive monitoring is being done to assess potential impacts to groundwater, and that such 

monitoring would prevent potential risk. While monitoring is required for many landfills, there are 

exceptions to this requirement (e.g., for smaller landfills, as defined in § 258.1(f)(1)). Furthermore, the 

commenter is assuming that groundwater monitoring would identify landfill releases in a timely fashion 

in all cases, which is not certain.

In any case, protectiveness should not rely on groundwater monitoring to protect nearby 

residents from potential exposures. Rather, our risk analysis seeks to estimate risks to highly exposed 

individuals that rely on groundwater sources near landfills. If we rely on well monitoring, then 

groundwater releases might not be detected until aquifers have been contaminated. That approach would 

be inconsistent with the preventive intent of RCRA to prospectively avoid releases into the environment 

that may threaten human health and the environment. Therefore, relying on monitoring is not appropriate 

 6 For example, see the programs in Minnesota at http://www.pca.state.mn.us/index.php/living-green/living-greencitizen/household-hazardous-waste.html and New York at http://www.dec.ny.gov/chemical/8778.html .
Response to Comments on the Solvent Contaminated Wipes 2003 Risk Screening Analysis

26

in our risk analysis. Finally, EPA has considered the impact of other regulatory programs in evaluating 

wastes from solvent-contaminated wipes. We considered the regulatory programs in place for municipal 

landfills and municipal waste combustors. The final exclusion is conditioned upon disposal of the spent 

wipes in landfills subject to regulation under 40 CFR 258 and combustors that are regulated under section 

129 of the CAA.

2.6.6 Banning Based on Toxicity Characteristics (TC) (comment theme 27)

Comment: In the proposed 2003 rule, EPA proposed that industrial wipes contaminated with the 

specified F- or U-listed solvents in Table 5 (Table 4 in the preamble to the 2003 proposed rule) or that are 

characteristically hazardous for other hazardous constituents, such as metals, cannot be disposed in 

municipal or other non-hazardous waste landfills. As further discussed in the proposed rule, nine of the 

solvents in Table 5 are characteristically toxic (TC), as defined in 40 CFR 261.24. Of these nine, six (as 

noted by an asterisk: ‘‘*’’) were ineligible for disposal in a municipal or other non-hazardous waste 

landfill because they met the toxicity characteristic, not because of the results of EPA’s risk screening 

analysis. The remaining five solvents (three of which are also characteristically toxic) in Table 5 were

restricted from disposal in municipal or other non-hazardous waste landfills because the 2003 risk 

screening analysis indicated that they may pose an unacceptable risk to human health and the 

environment when disposed of at levels lower than the five-gram condition. [68FR65597 -68FR65598] 

Table 5. 2003 Proposed Rule: Listed Solvents Not Allowed in Municipal Landfills

Benzene* 2-Nitropropane

Carbon tetrachloride* Nitrobenzene

Chlorobenzene* Pyridine

Cresols (o,m,p)* Tetrachloroethylene*

Methyl ethyl ketone (MEK) Methylene chloride

Trichloroethylene*

In response to this proposal, commenters expressed concern over the inability to achieve and 

verify a zero concentration of these 11 solvents given the potential for trace contaminants or slight crosscontamination of materials. Instead of banning these solvents entirely, it was recommended that the EPA

clearly state in the final rule language that the toxic characteristic concentrations, as found in Table 1 of

40 CFR 261.24 for each of the solvents listed in this table, should be considered the de minimis level. 

In addition, it was noted that EPA has no statutory authority to prohibit non-hazardous waste 

landfill disposal of wipes containing the solvents for which the EPA’s own risk screening analysis 

demonstrated no substantial hazard from landfilling. Furthermore, it was stated that the EPA’s use of the 

Toxicity Characteristic (“TC”) to ban the landfilling of certain additional solvents is unwarranted for 

several reasons:

1. TC modeling makes assumptions and uses parameters that are unsuitable for purposes of this 

rulemaking;

2. It is inappropriate and illogical to apply the anticipated results of a TC hazardous waste test 

designed for a wide universe of wastes in lieu of the risk screening analysis

3. Banning wipes containing any percentage of solvent is not appropriate given that certain wipes 

will contain insufficient amounts of these solvents to exhibit the TC. 

Response: EPA agrees with those commenters who argued that the TC criteria should not be 

used to prohibit solvent-contaminated wipes from being landfilled as a non-hazardous waste and has 

decided to use the results of the final risk analysis rather than apply the TC regulations to determine 
Response to Comments on the Solvent Contaminated Wipes 2003 Risk Screening Analysis

27

whether solvent-contaminated wipes can be disposed as solid wastes in municipal solid waste landfills 

(MSWLFs). Therefore, wipes contaminated with benzene; chlorobenzene; o-,m-,p-creosols; methyl ethyl 

ketone; and/or tetrachloroethylene are eligible for the conditional exclusion for disposable wipes provided 

they meet the conditions of the exclusion.7 The Agency undertook a comprehensive risk analysis to 

estimate the potential risk from disposal of solvent-contaminated wipes and laundry sludge in MSWLFs. 

This revised risk analysis was subjected to external peer review and presented for public comment in the 

2009 NODA. In support of this analysis, EPA: (1) collected and reviewed information (e.g., current 

industry practices, state programs, landfill loadings) from a wide variety of sources (site visits, data 

collected by EPA for RCRA and other regulatory programs, public comments, and other available 

information); (2) used probabilistic methods to characterize the variability and uncertainty associated with 

the risk modeling; (3) developed and used a state-of-the-art landfill model and examined the exposure 

pathways that pose the greatest potential risk; (4) included updated information for various input 

parameters, when such information was provided in the comments; and (5) recalculated the potential risks 

by using the most up-to-date human health toxicity benchmarks made available after the October 2009 

NODA was published.

The revised risk analysis presented in the October 2009 NODA included a variety of conservative 

assumptions to ensure that potential risks from landfill disposal were assessed protectively. Furthermore, 

our evaluation was based on the risks at the upper end of the risk distributions, i.e., the 90th percentile in 

the probabilistic analyses. Therefore, we are confident that the solvents present in the wipes and sludge 

would not present a significant risk. The 2012 final risk analysis represents a comprehensive 

characterization of the risk posed by these solvent-contaminated wipes and, therefore, EPA concludes that 

this is appropriate information to use in determining whether solvent-contaminated wipes should be 

excluded from the definition of hazardous waste.

The 2012 risk analysis for the six solvents that are also TC chemicals (benzene, chlorobenzene, 

cresols, methyl ethyl ketone, tetrachloroethylene, and trichloroethylene) indicated that five of the 

chemicals have risks well below the target criteria used.8 The one solvent that presents risks above the 

criteria is trichloroethylene, which is therefore ineligible for the conditional exclusion for disposable 

wipes being promulgated today. In addition, the exclusion only applies to disposable wipes; other 

industrial wastes, including solvent wastes not associated with wipes, will continue to be regulated as 

listed or characteristic hazardous waste, as applicable. Therefore, there are regulations in place to restrict 

disposal of solvent chemicals from other sources in municipal landfills. 

2.6.7 Lifecycle Analysis and Recycling (comment theme 28)

Comment: The commenter references a Lockheed study that looked at the raw material 

requirements and pollutant emissions associated with each type of wipe for its entire life cycle, from 

manufacture through usage and to the ultimate disposition. It is noted that the results of the study 

accounted for multiple use cycles for reusable towels. The report stated that reusable shop towels uses 

much less water and energy, and generate less solid waste when compared to an equivalent amount of 

disposable paper towels.

Comments were also received that expressed concern that the proposed rule will not promote 

recycling of solvents and does not adequately support improved solvent handling practices by generators 

 7 However, wipes contaminated with trichloroethylene would still be subject to the TC because the results of the 

final risk analysis demonstrate that these wipes present a significant risk when disposed in a composite-lined 

landfill. See section III.D. for further discussion. 8 Risks for the five solvents in composite-lined landfills were below one tenth of the target risk criteria. See the risk 

results in “F001-F005 Solvent-Contaminated Wipes and Laundry Sludge: Comparison of Landfill Loading 

Calculations and Risk-Based Mass Loading Limits” in the docket for the final rule.
Response to Comments on the Solvent Contaminated Wipes 2003 Risk Screening Analysis

28

and handling facilities. It was noted that the proposed rule may make it easier for generators and handlers 

to mismanage solvent-contaminated industrial wipes and evade regulation by storing contaminated wipes 

in lieu of disposal while claiming intent to dispose at an indefinite future date.

Response: EPA agrees that reusable wipes provide environmental benefits. In the final rule, EPA 

is excluding reusable wipes from the definition of solid waste as the Agency proposed in the November 

2003 proposed rule. The final rule revises the definition of solid waste to conditionally exclude solventcontaminated wipes that are cleaned and reused. The purpose of this final rule is to provide a consistent 

regulatory framework that is appropriate to the level of risk posed by solvent-contaminated wipes in a 

way that maintains protection of human health and the environment, while reducing overall compliance 

costs for industry.

Regarding the impact on recycling, solvent removal and recovery can happen at various points in 

the life cycle of both disposable and reusable wipes. Generators may choose to recover solvent either to 

reduce virgin solvent use and reduce costs, or to reduce their environmental footprint. In addition, 

laundries or dry cleaners may recover solvents from the solvent-contaminated wipes that arrive at their 

facilities. Generators of solvent-contaminated wipes have the potential to capture and recycle spent 

solvent “free liquids.”

Concerning the potential for mismanagement, the final rule requires certain conditions to be met

for reusable and disposable solvent-contaminated wipes to be excluded from regulation. Specifically, the 

wipes, when accumulated, stored, and transported, must be contained in non-leaking, closed containers 

that can contain free liquids and the containers must be labeled “Excluded Solvent-Contaminated Wipes.” 

The solvent-contaminated wipes may be accumulated for up to 180 days prior to being sent for cleaning 

or disposal. At the point of transport for cleaning or disposal, the solvent-contaminated wipes and their 

containers must not contain free liquids. In addition, generators must maintain documentation that they 

are managing excluded solvent-contaminated wipes as required and keep that documentation at their sites. 

Lastly, the solvent-contaminated wipes must be managed by facilities (laundries, landfills, and 

combustors) that are subject to the specified standards in order for the wipes to be eligible for the 

conditional exclusions under the final rule. Therefore, the Agency finds that these conditions address the 

potential for mismanagement.

2.6.8 Concern Over Health of the U.S. Population (comment theme 29)

Comments: One commenter expressed concerns over potential threats posed by landfills, and 

cited possible impacts on certain subpopulations (children and the elderly). The commenter cited reports

suggesting increased incidence of disease in families living near landfill sites and questioned the

operational effectiveness of landfills. The commenter noted many environmental advantages of reusable 

shop towels and urged EPA to exempt reusable shop towels from being classified as hazardous waste.

Response: EPA agrees that reusable wipes provide environmental benefits and the final rule

conditionally excludes reusable wipes from the definition of solid waste. The Agency is also conditionally 

excluding disposable solvent-contaminated wipes, provided the wipes are: (1) disposed in a municipal 

solid waste landfill that is regulated under 40 CFR part 258, including § 258.40, or a hazardous waste 

landfill regulated under 40 CFR parts 264 or 265; or (2) treated in a municipal waste combustor or other 

combustion facility that is regulated under section 129 of the Clean Air Act (CAA). Based on the revised 

risk evaluation the Agency finds that, under these conditions, the disposal of solvent-contaminated wipes 

in composite-lined landfills would not present a significant risk for the solvent chemicals included in the 

exclusion.

The Agency does not believe the environmental health or safety risks addressed by this action 

present a disproportionate risk to children or other subgroups. The commenter did not delineate how a 
Response to Comments on the Solvent Contaminated Wipes 2003 Risk Screening Analysis

29

conditional exclusion for wipes disposed in landfills would impact subgroups, such as children. In any 

case, as noted in response to other comments (see section 2.3.2 Exposure Parameters), health-based 

benchmarks (e.g., RfC) are derived to be protective of all human population including sensitive subgroups 

for noncancer risks. For cancer endpoints, adult exposures have been shown to drive the risks, thus, the 

risk criteria used in the Agency’s revised risk evaluation is protective of the general population and 

subgroups. Also as described previously, the revised risk analysis includes conservative assumptions to 

ensure that potential risks from landfill disposal were assessed protectively (e.g., the revised risk 

evaluation is based on the risks at the upper end of the risk distributions). The final risk analysis indicates 

that the risks for the solvent-contaminated wipes in composite-lined landfills are well below the target 

risk criteria for all of the solvents (except for trichloroethylene, which is not eligible for the exemption).

3. References

U.S. EPA (Environmental Protection Agency). 1997a. Exposure Factors Handbook. EPA/600/P95/002Fa. U.S. EPA, Office of Research and Development, Washington, DC. Available at EFH1997 Final Report

U.S. EPA (Environmental Protection Agency). 1997b. Guiding Principles for Monte Carlo Analysis. 

EPA/630/R-97/001. March. Available at http://www.epa.gov/ncea/pdfs/montcarl.pdf

U.S. EPA (Environmental Protection Agency). 2001a. Risk Assessment Guidance for Superfund Volume 3 

Part A: Process for Conducting Probabilistic Risk Assessment (RAGS 3A). EPA 540-R-02-002. 

Available at http://www.epa.gov/oswer/riskassessment/rags3adt/. December.

U.S. EPA (Environmental Protection Agency). 2001b. Risk Assessment Technical Background Document 

for the Paint and Coatings Hazardous Waste Listing Determination. Office of Solid Waste, 

Washington, DC. January. Available in Docket as document number EPA-HQ-RCRA-2001-

0022-0426.

U.S. EPA (Environmental Protection Agency). 2003a. EPA’s Composite Model for Leachate Migration 

with Transformation Products (EPACMTP) Parameters/Data Background Document. EPA530-R-03-003. 

U.S. EPA, Office of Solid Waste, Washington, DC. Available at

http://www.epa.gov/osw/nonhaz/industrial/tools/cmtp/pd_toc-2.pdf

U.S. EPA (Environmental Protection Agency). 2003b. Risk Assessment Technical Background Document 

for the Dye and Pigment Industry Hazardous Waste Listing Determination. U.S. EPA, Office of 

Solid Waste, Washington, DC. Available in docket as document number EPA-HQ-RCRA-2003-

0001-0005.

U.S. EPA (Environmental Protection Agency). 2003c. EPACMTP Technical Background Document. U.S. 

EPA, Office of Solid Waste, Washington, DC. Available at 

http://www.epa.gov/osw/nonhaz/industrial/tools/cmtp/

U.S. EPA (Environmental Protection Agency). 2005. Human Health Risk Assessment Protocol for 

Hazardous Waste Combustion Facilities. EPA/530/R-05/006. U.S. EPA, Office of Solid Waste 

and Emergency Response. September. Washington, DC. Available at 

http://www.epa.gov/osw/hazard/tsd/td/combust/risk.htm#hhrad

U.S. EPA (Environmental Protection Agency). 2006a.Child-Specific Exposure Factors Handbook 

(External Review Draft). EPA-600/R-06-096a. U.S. EPA, National Center for Environmental 

Assessment, Cincinnati, OH. September. Available at 

http://cfpub.epa.gov/ncea/cfm/recordisplay.cfm?deid=56747.
Response to Comments on the Solvent Contaminated Wipes 2003 Risk Screening Analysis

30

U.S. EPA (Environmental Protection Agency). 2008. Landfill Loadings Calculations for Disposed 

Solvent-Contaminated Wipes and Laundry Sludge Managed in Municipal Landfills. U.S. EPA, 

Office of Solid Waste and Emergency Response. October. Washington, DC.

U.S. EPA (Environmental Protection Agency). 2012. F001-F005 Solvent-Contaminated Wipes and 

Laundry Sludge: Comparison of Landfill Loading Calculations and Risk-Based Mass Loading 

Limits. U.S. EPA, Office of Solid Waste and Emergency Response. August. Washington, DC.

U.S. EPA (Environmental Protection Agency). 2009. Risk-Based Mass Loading Limits for Solvents in 

Disposed Wipes and Laundry Sludges Managed in Municipal Landfills. U.S. EPA, Office of 

Solid Waste and Emergency Response. October. Washington, DC.