Hazardous Waste Management System; Identification and Listing of Hazardous Waste; Chlorinated Aliphatics Production Wastes; Land Disposal Restrictions for Newly Identified Wastes; and CERCLA Hazardous Substance Designation and Reportable Quantities
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Federal Register › Vol. 64 › 64 FR 46476
Text
Part II
Environmental Protection Agency
_______________________________________________________________________
40 CFR Parts 148, 261, 264, 265, 268, 271, and 302
Hazardous Waste Management System; Identification and Listing of
Hazardous Waste; Chlorinated Aliphatics Production Wastes; Land
Disposal Restrictions for Newly Identified Wastes; and CERCLA Hazardous
Substance Designation and Reportable Quantities; Proposed Rule
Proposed Rules
ENVIRONMENTAL PROTECTION AGENCY
40 CFR Parts 148, 261, 264, 265, 268, 271, and 302
[SWH-FRL-6413-4]
RIN 2050-AD85
Hazardous Waste Management System; Identification and Listing of
Hazardous Waste; Chlorinated Aliphatics Production Wastes; Land
Disposal Restrictions for Newly Identified Wastes; and CERCLA Hazardous
Substance Designation and Reportable Quantities
AGENCY: Environmental Protection Agency (EPA).
ACTION: Proposed rule.
-----------------------------------------------------------------------
SUMMARY: The EPA is proposing to list three of six wastes from the
chlorinated aliphatics industry as hazardous wastes under the Resource
Conservation and Recovery Act (RCRA), which directs EPA to determine
whether certain wastes from the chlorinated aliphatics industry present
a hazard to human health or the environment. The effect of listing
these three wastes will be to subject them to stringent management and
treatment standards under RCRA and to subject them to emergency
notification requirements for releases of hazardous substances to the
environment. EPA is proposing a contingent-management listing approach
for one of these wastes, and as one of two options for another of these
wastes, such that waste generators will have the option of their waste
not being listed if it is sent to a specific type of management
facility.
CRA and to subject them to emergency
notification requirements for releases of hazardous substances to the
environment. EPA is proposing a contingent-management listing approach
for one of these wastes, and as one of two options for another of these
wastes, such that waste generators will have the option of their waste
not being listed if it is sent to a specific type of management
facility.
DATES: EPA will accept public comments on this proposed rule until
November 23, 1999. Comments postmarked after this date will be marked
``late'' and may not be considered. Any person may request a public
hearing on this proposal by filing a request by September 8, 1999.
ADDRESSES: If you wish to comment on this proposed rule, you must send
an original and two copies of the comments referencing docket number F-
1999-CALP-FFFFF to: RCRA Docket Information Center, Office of Solid
Waste (5305G), U.S. Environmental Protection Agency Headquarters (EPA,
HQ), 401 M Street, SW, Washington, D.C. 20460. Hand deliveries of
comments should be made to the Arlington, VA, address listed in the
fourth paragraph of SUPPLEMENTARY INFORMATION. You also may submit
comments electronically by sending electronic mail through the Internet
to: [email protected]. See the beginning of SUPPLEMENTARY
INFORMATION for instructions on electronic submission.
You should not submit electronically any confidential business
information (CBI). You must submit an original and two copies of CBI
under separate cover to: RCRA CBI Document Control Officer, Office of
Solid Waste (5305W), U.S. EPA, 401 M Street, SW, Washington, D.C.
20460. See the beginning of SUPPLEMENTARY INFORMATION for information
on viewing public comments and supporting materials.
Address requests for a hearing to Mr. David Bussard at: Office of
Solid Waste, Hazardous Waste Identification Division (5304W), U.S.
Environmental Protection Agency, 401 M Street, SW, Washington, D.C.
20460, (703) 308-8880.
), U.S. EPA, 401 M Street, SW, Washington, D.C.
20460. See the beginning of SUPPLEMENTARY INFORMATION for information
on viewing public comments and supporting materials.
Address requests for a hearing to Mr. David Bussard at: Office of
Solid Waste, Hazardous Waste Identification Division (5304W), U.S.
Environmental Protection Agency, 401 M Street, SW, Washington, D.C.
20460, (703) 308-8880.
FOR FURTHER INFORMATION CONTACT: For general information, contact the
RCRA Hotline at (800) 424-9346 or TDD (800) 553-7672 (hearing
impaired). In the Washington, D.C., metropolitan area, call (703) 412-
9810 or TDD (703) 412-3323. For information on specific aspects of the
rule, contact Ross Elliott of the Office of Solid Waste (5304W), U.S.
Environmental Protection Agency, 401 M Street, SW, Washington, D.C.
20460. [E-mail addresses and telephone numbers:
[email protected], (703) 308-8748.]
SUPPLEMENTARY INFORMATION: You should identify comments in electronic
format with the docket number F-1999-CALP-FFFFF. You must submit all
electronic comments as an ASCII (text) file, avoiding the use of
special characters and any form of encryption. If you do not submit
comments electronically, EPA is asking prospective commenters to
voluntarily submit one additional copy of their comments on labeled
personal computer diskettes in ASCII (text) format or a word processing
format that can be converted to ASCII (text). It is essential to
specify on the disk label the word processing software and version/
edition as well as the commenter's name. This will allow EPA to convert
the comments into one of the word processing formats utilized by the
Agency. Please use mailing envelopes designed to physically protect the
submitted diskettes. EPA emphasizes that submission of comments on
diskettes is not mandatory, nor will it result in any advantage or
disadvantage to any commenter. Supporting documents in the docket for
this Notice are also available in electronic format on the Internet
one of the word processing formats utilized by the
Agency. Please use mailing envelopes designed to physically protect the
submitted diskettes. EPA emphasizes that submission of comments on
diskettes is not mandatory, nor will it result in any advantage or
disadvantage to any commenter. Supporting documents in the docket for
this Notice are also available in electronic format on the Internet.
Follow these instructions to access these documents.
WWW: http://www.epa.gov/epaoswer/hazwaste/id
FTP: ftp.epa/gov
Login: anonymous
Password: your Internet address
Files are located in /pub/gopher/OSWRCRA.
EPA will keep the official record for this action in paper form.
Accordingly, we will transfer all comments received electronically into
paper form and place them in the official record, which will also
include all comments submitted directly in writing. The official record
is the paper record maintained at the address in ADDRESSES at the
beginning of this document.
EPA responses to comments, whether the comments are written or
electronic, will be in a notice in the Federal Register or in a
response to comments document placed in the official record for this
rulemaking. We will not immediately reply to commenters electronically
other than to seek clarification of electronic comments that may be
garbled in transmission or during conversion to paper form, as
discussed above.
You may view public comments and supporting materials in the RCRA
Information Center (RIC), located at Crystal Gateway I, First Floor,
1235 Jefferson Davis Highway, Arlington, VA. The RIC is open from 9
a.m. to 4 p.m., Monday through Friday, excluding federal holidays. To
review docket materials, we recommend that you make an appointment by
calling (703) 603-9230. You may copy a maximum of 100 pages from any
regulatory docket at no charge. Additional copies cost $0.15/page. For
information on accessing paper and/or electronic copies of the
document, see the first paragraph of the SUPPLEMENTARY INFORMATION
section.
hrough Friday, excluding federal holidays. To
review docket materials, we recommend that you make an appointment by
calling (703) 603-9230. You may copy a maximum of 100 pages from any
regulatory docket at no charge. Additional copies cost $0.15/page. For
information on accessing paper and/or electronic copies of the
document, see the first paragraph of the SUPPLEMENTARY INFORMATION
section.
Customer Service
How Can I Influence EPA's Thinking on This Proposed Rule?
In developing this proposal, we tried to address the concerns of
all our stakeholders. Your comments will help us improve this rule. We
invite you to provide different views on options we propose, new
approaches we haven't considered, new data, how this rule may affect
you, or other relevant information. We welcome your views on all
aspects of this proposed rule, but we request comments in particular on
the items indicated at the end of each section. Your comments will be
most effective if you follow the suggestions below:
Explain your views as clearly as possible and provide a
summary of the reasoning you used to arrive at your
conclusions, as well as examples to illustrate your views, where
possible.
Provide solid technical and cost data to support your
views.
If you estimate potential costs, explain how you arrived
at your estimate.
Tell us which parts you support, as well as those with
which you disagree.
Offer specific alternatives.
Reference your comments to specific sections of the
proposal, such as the sections or page numbers of the preamble, or the
regulatory citations.
Remember that your comments must be submitted by the
deadline in this notice.
Include the name, date, and docket number with your
comments.
Contents of This Proposed Rule
The contents of the preamble to this proposed rule are listed in
the following outline:
I. Overview
specific sections of the
proposal, such as the sections or page numbers of the preamble, or the
regulatory citations.
Remember that your comments must be submitted by the
deadline in this notice.
Include the name, date, and docket number with your
comments.
Contents of This Proposed Rule
The contents of the preamble to this proposed rule are listed in
the following outline:
I. Overview
A. Who Potentially Will Be Affected by This Proposed Rule?
B. Why Does This Rule Read Differently From Other Listing Rules?
C. What Are the Statutory Authorities for This Rule?
II. Background
A. Schedule Suit
B. Existing Chlorinated Aliphatics Listings
III. Today's Action
A. Summary of Today's Action
1. Scope of the Listing Determination
2. Summary of the Proposed Listing Determinations
3. Summary of the Remainder of This Preamble
B. Description of the Industry
C. Overview of EPA's Information Collection Activities
1. Field Investigations and Sampling
2. RCRA Section 3007 Survey
D. What Are the Risks Associated With Management of Wastewaters and
Wastewater Treatment Sludges From the Production of Chlorinated
Aliphatic Chemicals?
1. What Are the Risks for Potential Human Receptors?
2. What Are the Potential Risks for Ecological Receptors?
3. Did EPA Conduct a Peer Review of the Risk Assessment?
E. Waste-Specific Listing Determination Rationales
1. Chlorinated Aliphatics Wastewaters
2. EDC/VCM Wastewater Treatment Sludges
3. VCM-A Wastewater Treatment Sludges
4. Methyl Chloride Wastewater Treatment Sludges
5. Allyl Chloride Wastewater Treatment Sludges
F. Constituents Proposed for Addition to Appendix VIII to 40 CFR
Part 261
IV. Economic Analysis
Peer Review of the Risk Assessment?
E. Waste-Specific Listing Determination Rationales
1. Chlorinated Aliphatics Wastewaters
2. EDC/VCM Wastewater Treatment Sludges
3. VCM-A Wastewater Treatment Sludges
4. Methyl Chloride Wastewater Treatment Sludges
5. Allyl Chloride Wastewater Treatment Sludges
F. Constituents Proposed for Addition to Appendix VIII to 40 CFR
Part 261
IV. Economic Analysis
A. What Is the Purpose of the Economic Analysis?
B. How May the Public Participate in the Economic Analysis?
C. How Are Chlorinated Aliphatic Chemicals Used in the Economy?
D. Where Are CAHCs Manufactured in the United States?
E. Have CAHCs Been Produced Historically in Other Locations in the
United States?
F. What Are the Estimated Potential Industry Costs of This Listing?
V. Proposed Treatment Standards Under RCRA's Land Disposal Restrictions
A. What Are EPA's Land Disposal Restrictions (LDRs)?
B. How Does EPA Develop LDR Treatment Standards?
C. What Kind of Treatment Standards Are Proposed?
D. Other LDR-Related Provisions
E. What Standards Are Proposed for K173?
F. What Standards Are Proposed for K174?
G. What Standards Are Proposed for K175?
H. What Other Land Disposal Restrictions Aspects Are There to the
Proposal?
I. Is There Treatment Capacity for the Proposed Wastes?
VI. Compliance Dates
A. Notification
B. Interim Status and Permitted Facilities
VII. State Authority
A. Applicability of Rule in Authorized States
B. Effect on State Authorizations
VIII. Designation of Chlorinated Aliphatic Wastes (K173, K174 and K175)
Under the Comprehensive Environmental Response, Compensation, and
Liability Act (CERCLA)
s There Treatment Capacity for the Proposed Wastes?
VI. Compliance Dates
A. Notification
B. Interim Status and Permitted Facilities
VII. State Authority
A. Applicability of Rule in Authorized States
B. Effect on State Authorizations
VIII. Designation of Chlorinated Aliphatic Wastes (K173, K174 and K175)
Under the Comprehensive Environmental Response, Compensation, and
Liability Act (CERCLA)
A. What Is the Relationship Between RCRA and CERCLA?
B. Is EPA Proposing To Add Chlorinated Aliphatic Wastes to CERCLA?
C. How Does EPA Determine Reportable Quantities?
D. When Do I Need to Report a Release of K173, K174 or K175 Under
CERCLA?
E. What if I Know the Concentration of the Constituents in My Waste?
F. How Did EPA Determine the RQs for K173, K174 and K175 and Their
Hazardous Constituents?
G. How Do I Report a Release?
H. What Is the Statutory Authority for This Program?
I. How Can I Influence EPA's Thinking on Regulating K173, K174 and
K175 Under CERCLA?
IX. Administrative Assessments
A. Executive Order 12866
B. Regulatory Flexibility Act
C. Paperwork Reduction Act
D. Unfunded Mandates Reform Act
E. Executive Order 12875: Enhancing the Intergovernmental
Partnership
F. Executive Order 13084: Consultation and Coordination With Indian
Tribal Governments
G. Executive Order 13045: Protection of Children From Environmental
Risks and Safety Risks
H. National Technology Transfer and Advancement Act of 1995
I. Executive Order 12898: Environmental Justice
I. Overview
A. Who Potentially Will Be Affected by This Proposed Rule?
cing the Intergovernmental
Partnership
F. Executive Order 13084: Consultation and Coordination With Indian
Tribal Governments
G. Executive Order 13045: Protection of Children From Environmental
Risks and Safety Risks
H. National Technology Transfer and Advancement Act of 1995
I. Executive Order 12898: Environmental Justice
I. Overview
A. Who Potentially Will Be Affected by This Proposed Rule?
Beginning January 1, 1999 all documents related to USEPA's
regulatory, compliance and enforcement activities including rules,
policies, interpretive guidance, and site-specific determinations with
broad application, should properly identify the regulated entities,
including descriptions that correspond to the applicable SIC codes or
NAICS codes (source: 09 October 1998 USEPA memo from Peter D.
Robertson, Acting Deputy Administrator of USEPA). Today's action, if
finalized, could potentially affect those who handle the wastes that
EPA is proposing to add to the Agency's list of hazardous wastes under
the RCRA program. This action also may affect entities that may need to
respond to releases of these wastes as CERCLA hazardous substances.
These potentially-affected entities are described in the Economics
Background Document placed in the docket in support of today's proposed
rule; a summary is shown in the table below.
Summary of Facilities Potentially Affected by the USEPA's 1999 Chlorinated Aliphatics Manufacturing Waste
Listing Proposal According to Applicable SIC and NAICS Codes
----------------------------------------------------------------------------------------------------------------
Number of
Parent U.S. Parent
Item company Industry sector name relevant company NAICS
SIC code CAHC mfg. code
facilities* equivalent**
----------------------------------------------------------------------------------------------------------------
1............................. 1311 Mining: Crude petroleum and natural 3 211111
gas.
2............................
------------------------------
Number of
Parent U.S. Parent
Item company Industry sector name relevant company NAICS
SIC code CAHC mfg. code
facilities* equivalent**
----------------------------------------------------------------------------------------------------------------
1............................. 1311 Mining: Crude petroleum and natural 3 211111
gas.
2............................. 1400 Mining: Nonmetallic minerals, except 2 212300
fuels.
3............................. 2295 Manufacturing: Coated fabrics, not 1 31332
rubberized.
4............................. 2800 Manufacturing: Chemicals & allied 3 325000
products.
5............................. 2810 Manufacturing: Chemicals & allied 1 325000
products.
6............................. 2812 Manufacturing: Alkalies & chlorine 1 325181
manufacture.
7............................. 2821 Manufacturing: Plastics materials & 8 325211
resins.
8............................. 2851 Manufacturing: Paints & allied 1 32551
products.
9............................. 2869 Manufacturing: Industrial organic 1 32511
chemicals, nec.
10............................ 2911 Manufacturing: Petroleum refining..... 1 32411
11............................ 3600 Manufacturing: Electronic & other 1 335000
electric equipment.
-------------
Total Applicable Facilities....... 23
----------------------------------------------------------------------------------------------------------------
*The number of relevant facilities is based on the (a) type of CAHC products manufactured, (b) types of wastes
generated, and (c) baseline waste management practices, in relation to the terms and conditions of the
proposed listing options. However, all CAHC manufacturing facilities in each industrial sector code may not be
affected by the proposed listing options
-------------------------------
*The number of relevant facilities is based on the (a) type of CAHC products manufactured, (b) types of wastes
generated, and (c) baseline waste management practices, in relation to the terms and conditions of the
proposed listing options. However, all CAHC manufacturing facilities in each industrial sector code may not be
affected by the proposed listing options.
**OSW-EMRAD derived the NAICS code equivalents above from the SIC-to-NAICS conversion tables provided by the US
Department of Commerce, Bureau of the Census, at the following website: http://www.census.gov/epcd/www/
naicstab.htm. There is no direct match in the SIC-NAICS conversion tables for SIC codes 1400, 2800, 2810, and
3600, so a generalized six-digit NAICS code is provided above for these four cases.
The list of potentially affected entities in the above table may
not be exhaustive. Our aim is to provide a guide for readers regarding
entities likely to be regulated by this action. This table lists those
entities that EPA is aware potentially could be affected by this
action. However, this action may affect other entities not listed in
the table. To determine whether your facility is regulated by this
action, you should examine 40 CFR 260 and 261 carefully in concert with
the proposed rules amending RCRA that are found at the end of this
Federal Register notice. If you have questions regarding the
applicability of this action to a particular entity, consult the person
listed in the preceding section entitled FOR FURTHER INFORMATION
CONTACT.
B. Why Does This Rule Read Differently From Other Listing Rules?
ld examine 40 CFR 260 and 261 carefully in concert with
the proposed rules amending RCRA that are found at the end of this
Federal Register notice. If you have questions regarding the
applicability of this action to a particular entity, consult the person
listed in the preceding section entitled FOR FURTHER INFORMATION
CONTACT.
B. Why Does This Rule Read Differently From Other Listing Rules?
Today's proposed listing determination preamble and regulations are
written in ``readable regulations'' format. The authors tried to use
active rather than passive voice, plain language, a question-and-answer
format, the pronouns ``we'' for EPA and ``you'' for the owner/
generator, and other techniques to make the information in today's rule
easier to read and understand. This new format is part of the Agency's
efforts at regulatory reinvention, and it makes today's rule read
differently from other listing rules. The Agency believes that this new
format will increase readers' abilities to understand the regulations,
which should then increase compliance, make enforcement easier, and
foster better relationships between EPA and the regulated community.
C. What Are the Statutory Authorities for This Rule?
These regulations are being proposed under the authority of
Sections 2002(a), 3001(b), 3001(e)(2) and 3007(a) of the Solid Waste
Disposal Act, 42 U.S.C. 6912(a), 6921(b) and (e)(2), and 6927(a) as
amended several times, most importantly by the Hazardous and Solid
Waste Amendments of 1984 (HSWA). These statutes commonly are referred
to as the Resource Conservation and Recovery Act (RCRA), and are
codified at Volume 42 of the United States Code (U.S.C.), Sections 6901
to 6992(k) (42 U.S.C. 6901-6992(k)).
Section 102(a) of the Comprehensive Environmental Response,
Compensation, and Liability Act of 1980 (CERCLA), 42 U.S.C. 9602(a) is
the authority under which the CERCLA aspects of this rule are being
proposed.
II. Background
A. Schedule Suit
servation and Recovery Act (RCRA), and are
codified at Volume 42 of the United States Code (U.S.C.), Sections 6901
to 6992(k) (42 U.S.C. 6901-6992(k)).
Section 102(a) of the Comprehensive Environmental Response,
Compensation, and Liability Act of 1980 (CERCLA), 42 U.S.C. 9602(a) is
the authority under which the CERCLA aspects of this rule are being
proposed.
II. Background
A. Schedule Suit
In 1989, the Environmental Defense Fund (EDF) sued the
Environmental Protection Agency (EPA), in part for failing to meet the
statutory deadlines of Section 3001(e)(2) of RCRA (EDF vs. Browner;
Civ. No. 89-0598 D.D.C.). To resolve most of the issues in the case,
EDF and EPA entered into a consent decree, which has been amended
several times to revise dates. The consent decree sets out deadlines
for promulgating certain RCRA rules and for completing certain studies
and reports. Paragraph 1. m. of the consent decree obliges EPA to
propose a hazardous waste listing determination for wastewaters and
wastewater treatment sludges generated from the production of specified
chlorinated aliphatic chemicals. The wastewater and wastewater
treatment sludges subject to the consent decree are those from the
production of chlorinated aliphatics for which other process wastes
already have been designated as hazardous waste F024 in 40 CFR 261.31.
According to the consent decree, EPA must propose listing
determinations by July 30, 1999 and promulgate final listing
determinations on or before September 30, 2000. Today EPA is proposing
listing determinations for these wastes in accordance with the consent
decree.
B. Existing Chlorinated Aliphatics Listings
ss wastes
already have been designated as hazardous waste F024 in 40 CFR 261.31.
According to the consent decree, EPA must propose listing
determinations by July 30, 1999 and promulgate final listing
determinations on or before September 30, 2000. Today EPA is proposing
listing determinations for these wastes in accordance with the consent
decree.
B. Existing Chlorinated Aliphatics Listings
Today's proposal does not affect the scope of the chlorinated
aliphatics process wastes that already have been listed as hazardous in
prior EPA rulemakings. These wastes include wastes designated as
hazardous waste code F024 as well as a number of other chlorinated
aliphatic wastes listed below in Table II-1. EPA is not soliciting
comment on these existing hazardous waste listings and does not intend
to respond to such comments, if received.
Likewise, EPA is not soliciting comments in today's rule on the
applicability of the existing chlorinated aliphatics listings to the
provisions of CERCLA. Wastes listed as hazardous
under RCRA are by definition hazardous substances under CERCLA, and are
included in the list of hazardous substances in 40 CFR 302.4, along
with their corresponding reportable quantities (``RQs''). Hazardous
substance RQs are those quantities of the designated chemical or waste
that trigger certain reporting requirements if released to the
environment. The previously listed hazardous wastes from chlorinated
aliphatics production and their corresponding RQs are listed below in
Table II-1.
zardous substances in 40 CFR 302.4, along
with their corresponding reportable quantities (``RQs''). Hazardous
substance RQs are those quantities of the designated chemical or waste
that trigger certain reporting requirements if released to the
environment. The previously listed hazardous wastes from chlorinated
aliphatics production and their corresponding RQs are listed below in
Table II-1.
Table II-1.--List of Currently-Regulated Chlorinated Aliphatic Process
Wastes and Corresponding Reportable Quantities as CERCLA Hazardous
Substances
------------------------------------------------------------------------
Hazardous substance RQ pounds (KG)
------------------------------------------------------------------------
F024--Process wastes, including but not limited to, 1 (0.454)
distillation residues, heavy ends, tars, and reactor
cleanout wastes from the production of certain
chlorinated aliphatic hydrocarbons, by free radical
catalyzed processes. These chlorinated aliphatic
hydrocarbons are those having carbon chain lengths
ranging from one to and including five, with varying
amounts and positions of chlorine substitution. [This
listing does not include wastewaters, wastewater
treatment sludges, spent catalysts, and wastes listed
in 40 CFR 261.31 or 261.32.]...........................
F025--Condensed light ends, spent filters and filter 1 (0.454)
aids, and spent dessicant wastes from the production of
certain chlorinated aliphatic hydrocarbons, by free
radical catalyzed processes. These chlorinated
aliphatic hydrocarbons are those having carbon chain
lengths ranging from one to and including five, with
varying amounts and positions of chlorine substitution.
K016--Heavy ends or distillation residues from the 1 (0.454)
production of carbon tetrachloride.....................
K018--Heavy ends from the fractionation column in ethyl 1 (0.454)
chloride production...................................
phatic hydrocarbons are those having carbon chain
lengths ranging from one to and including five, with
varying amounts and positions of chlorine substitution.
K016--Heavy ends or distillation residues from the 1 (0.454)
production of carbon tetrachloride.....................
K018--Heavy ends from the fractionation column in ethyl 1 (0.454)
chloride production....................................
K019--Heavy ends from the distillation of ethylene 1 (0.454)
dichloride in ethylene dichloride production...........
K020--Heavy ends from the distillation of vinyl chloride 1 (0.454)
in vinyl chloride monomer production...................
K028--Spent catalyst from the hydrochlorinator reactor 1 (0.454)
in the production of 1,1,1-trichloroethane.............
K029--Waste from the product steam stripper in the 1 (0.454)
production of 1,1,1-trichloroethane....................
K030--Column bottoms or heavy ends from the combined 1 (0.454)
production of trichloroethylene and perchloroethylene..
K095--Distillation bottoms from the production of 1,1,1- 1 (0.454)
trichloroethane........................................
K096--Heavy ends from the heavy ends column from the 1 (0.454)
production of 1,1,1-trichloroethane....................
------------------------------------------------------------------------
III. Today's Action
A. Summary of Today's Action
1. Scope of the Listing Determination
Aliphatic hydrocarbons are compounds composed of the atoms of
hydrogen and carbon, where the carbon atoms are linked by covalent
bonds in an open-chain (straight and branched) structure, and those
cyclic compounds that resemble the open-chain compounds. Aliphatics are
distinguished from aromatic hydrocarbons, which are defined as benzene
and compounds that resemble benzene in chemical behavior. For an
aliphatic to be chlorinated, one or more hydrogen atoms have been
chemically replaced with chlorine atoms
by covalent
bonds in an open-chain (straight and branched) structure, and those
cyclic compounds that resemble the open-chain compounds. Aliphatics are
distinguished from aromatic hydrocarbons, which are defined as benzene
and compounds that resemble benzene in chemical behavior. For an
aliphatic to be chlorinated, one or more hydrogen atoms have been
chemically replaced with chlorine atoms. The chlorinated aliphatic
chemicals, the wastes of which are described in the (existing) F024
listing description, and identified in the consent decree, are those
produced by free-radical catalyzed processes with carbon chain lengths
ranging from one to five.
EPA performed an initial review and investigation of the waste
categories identified in the consent decree, as well as a review of
chlorinated aliphatics production processes and the wastewaters and
wastewater treatment sludges generated by these processes. The Agency
decided, for the purpose of studying chlorinated aliphatic wastes, to
divide the wastestreams into several distinct waste groupings. Waste
groupings were defined to differentiate between unique residuals, as
well as to differentiate between unique management practices (e.g., on-
site land treatment) and/or particular constituents (e.g., mercury).
The Agency segregated chlorinated aliphatics wastewaters into two
groupings, with one group being wastewaters generated from the
production of vinyl chloride monomer using mercuric chloride catalyst
in an acetylene-based process. These wastewaters were evaluated as one
group due to the unique nature of this production process, the fact
that these wastewaters are treated in a dedicated wastewater treatment
system, and the presence of mercury in the wastestream. All other
chlorinated aliphatic wastewaters were included in a second group and
evaluated collectively
ercuric chloride catalyst
in an acetylene-based process. These wastewaters were evaluated as one
group due to the unique nature of this production process, the fact
that these wastewaters are treated in a dedicated wastewater treatment
system, and the presence of mercury in the wastestream. All other
chlorinated aliphatic wastewaters were included in a second group and
evaluated collectively. The Agency found that many producers of
chlorinated aliphatics manufacture several different chlorinated
aliphatic products at a single facility and commingle the wastewaters
generated by all processes prior to treatment in a single wastewater
treatment system.
The Agency identified four waste groupings for wastewater treatment
sludges generated by the chlorinated aliphatics industry. These waste
groupings were defined based primarily upon the particular management
practices used to manage the wastes, but also based on particular
production processes. The Agency identified four waste groups for
chlorinated aliphatics wastewater treatment sludges. These waste groups
include sludges generated from the treatment of wastewaters from the
production of:
Ethylene dichloride and/or vinyl chloride monomer (EDC/
VCM);
Vinyl chloride monomer using mercuric chloride catalyst in
an acetylene-based process (VCM-A);
Methyl chloride; and
allyl chloride.
The scope of today's notice does not include any other process
residuals generated by the chlorinated aliphatics industry. In
particular, the Agency is not re-evaluating previous listing
determinations concerning wastes generated by chlorinated aliphatics
production processes
onomer using mercuric chloride catalyst in
an acetylene-based process (VCM-A);
Methyl chloride; and
allyl chloride.
The scope of today's notice does not include any other process
residuals generated by the chlorinated aliphatics industry. In
particular, the Agency is not re-evaluating previous listing
determinations concerning wastes generated by chlorinated aliphatics
production processes.
The Agency also points out that the consent decree specifies that
this listing determination ``shall include wastewaters and wastewater
treatment sludges generated from the production of chlorinated
aliphatics specified in the F024 listing'' (a listing which is limited
to wastes from chlorinated aliphatic production using the ``free
radical catalyzed process'' but does not include wastewaters or
wastewater treatment sludges). However, for today's proposed rule the
Agency did not restrict its evaluation of wastewaters and wastewater
treatment sludges to only those generated from chlorinated aliphatics
manufacturers using the free radical catalyzed process. In the
rulemaking for the F024 listing (which includes process wastes such as
distillation residues, heavy ends, and tars, but not wastewaters and
wastewater treatment sludges) we found that there were distinct
differences in the amount and type of chemical constituents present in
these production wastes as a direct result of the production process
used. For example, the free radical catalyzed reactions tended to
produce unwanted organic compounds, as well as the desired chemical
product, because this type of reaction is less specific (in terms of
desired product) than other types of processes used. As a result, the
chemical constituents that were the basis for listing F024 includes
many organic compounds that are more prevalent in process wastes
(again, tars, heavy ends, etc.) generated from the free radical
catalyzed process
mpounds, as well as the desired chemical
product, because this type of reaction is less specific (in terms of
desired product) than other types of processes used. As a result, the
chemical constituents that were the basis for listing F024 includes
many organic compounds that are more prevalent in process wastes
(again, tars, heavy ends, etc.) generated from the free radical
catalyzed process.
However, in developing the information for today's proposed
listing, EPA was concerned that limiting the scope of the investigation
to free radical catalyzed processes might not be appropriate because of
the different nature of wastewaters and wastewater treatment sludges as
compared with the F024 process wastes. Wastewaters may be generated in
different ways, including from scrubber waters, cooling waters, as well
as reaction media, etc. Ultimately, our primary reason for not
restricting our evaluation of wastewaters and wastewater treatment
sludges to those generated by free radical catalyzed processes is that
our preliminary analysis of these wastes indicated that the
constituents of concern (i.e., dioxins, chloroform, arsenic) were not
the same as the constituents of concern associated with the previously-
listed F024 and F025 wastes. In those previous listing determinations
(which did not include wastewaters or wastewater treatment sludges) the
Agency was able to distinguish risk levels of concern based upon
particular production processes.
In the case of today's proposed listing determination, we were not
able to make such a distinction. The primary constituents of concern in
the wastes we are proposing to list as hazardous in today's notice are
dioxins, whereas dioxins were not a basis for listing the F024 and F025
wastes
s) the
Agency was able to distinguish risk levels of concern based upon
particular production processes.
In the case of today's proposed listing determination, we were not
able to make such a distinction. The primary constituents of concern in
the wastes we are proposing to list as hazardous in today's notice are
dioxins, whereas dioxins were not a basis for listing the F024 and F025
wastes. Data currently available to the Agency does not support a
conclusion that wastewaters and wastewater treatment sludges generated
by free radical catalyzed processes have significantly different
concentrations of dioxins than other types of production processes used
to manufacture chlorinated aliphatics. However, EPA requests comment
and data addressing the issue of whether one type of manufacturing
process (e.g., free radical catalyzation) versus all other potential
processes (e.g., ionic catalyzed processes) would result in different
levels of dioxins in the resulting wastestream. The Agency will
consider modifying the listing description proposed in today's
rulemaking as appropriate to account for distinctions identified in
information available to EPA at the time of the final rule.
2. Summary of the Proposed Listing Determinations
In today's notice, EPA is proposing to add three wastes generated
by the chlorinated aliphatics industry to the list of hazardous wastes
in 40 CFR 261.32. Below are the wastestreams EPA is proposing to list
as hazardous with their corresponding proposed EPA Hazardous Waste
Numbers.
n
information available to EPA at the time of the final rule.
2. Summary of the Proposed Listing Determinations
In today's notice, EPA is proposing to add three wastes generated
by the chlorinated aliphatics industry to the list of hazardous wastes
in 40 CFR 261.32. Below are the wastestreams EPA is proposing to list
as hazardous with their corresponding proposed EPA Hazardous Waste
Numbers.
K173 Wastewaters from the production of chlorinated aliphatic
hydrocarbons, except for wastewaters generated from the production
of vinyl chloride monomer using mercuric chloride catalyst in an
acetylene-based process. This listing includes wastewaters from the
production of chlorinated aliphatic hydrocarbons that have carbon
chain lengths ranging from one to, and including five, with varying
amounts and positions of chlorine substitution.
K174 Wastewater treatment sludges from the production of ethylene
dichloride or vinyl chloride monomer (EDC/VCM).
K175 Wastewater treatment sludges from the production of vinyl
chloride monomer using mercuric chloride catalyst in an acetylene-
based process.
EPA is proposing to list these wastes because these residuals meet
the criteria set out in 40 CFR 261.11(a)(3) for listing a waste as
hazardous. EPA assessed and considered these criteria for all six
wastestreams through the use of risk assessments and risk modeling, as
well as a consideration of other pertinent factors. Today's proposed
listing determination follows the elements of the Agency's listing
decision policy that was presented in the proposed listing for wastes
generated by the dye and pigment industries published in the Federal
Register on December 22, 1994 (see 59 FR 66073). This policy uses a
``weight-of-evidence'' approach in which calculated risk information is
a key factor considered in making a listing determination
determination follows the elements of the Agency's listing
decision policy that was presented in the proposed listing for wastes
generated by the dye and pigment industries published in the Federal
Register on December 22, 1994 (see 59 FR 66073). This policy uses a
``weight-of-evidence'' approach in which calculated risk information is
a key factor considered in making a listing determination.
Upon promulgation of these proposed listings, wastes meeting the
listing descriptions will become hazardous wastes and need to be
managed in accordance with RCRA subtitle C requirements. Residuals from
the treatment, storage, or disposal of the wastewater treatment sludges
proposed to be listed as hazardous also will be classified as hazardous
wastes pursuant to the ``derived-from'' rule (40 CFR 261.3(c)(2)(i)).
1 Also, with certain limited exceptions, any mixture of a
listed hazardous waste and a solid waste is itself a RCRA hazardous
waste (40 CFR 261.3(a)(2)(iv), ``the mixture rule'').
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\1\ As explained later in this notice, residuals generated from
the management of wastewaters proposed to be listed as hazardous
(i.e., wastewater treatment sludges) will not be subject to the
derived-from rule due to the fact that EPA conducted separate
investigations of these residuals and they are the subject of
independent listing determinations.
---------------------------------------------------------------------------
tice, residuals generated from
the management of wastewaters proposed to be listed as hazardous
(i.e., wastewater treatment sludges) will not be subject to the
derived-from rule due to the fact that EPA conducted separate
investigations of these residuals and they are the subject of
independent listing determinations.
---------------------------------------------------------------------------
In today's notice, the Agency is proposing an alternative approach
to listing two of the wastes from chlorinated aliphatics processes as
hazardous, rather than proposing to list these wastes in accordance
with the Agency's traditional listing approach. The Agency is proposing
a conditional listing approach for one waste, and as one of two
alternative approaches for a second waste, because the Agency has
evaluated the ways in which the wastes are likely to be managed and has
determined that certain waste management activities would present
significant risks but that others would be protective of human health
and the environment. Under a contingent management approach, EPA is
proposing to list particular wastes as hazardous only if the wastes are
managed in a way other than the manner in which the Agency has
determined is protective of human health and the environment. In
implementing a conditional-listing approach, the Agency is proposing
that wastes that fall outside the scope of the listing description
(e.g., are destined for the appropriate type of disposal) are non-
hazardous when generated. However, if it turns out that the waste
actually is not handled in accordance with the conditions of the
listing at any point in its management, the generators or other
handlers of the waste would be subject to various enforcement actions
or, depending on the violations, the waste could become a hazardous
waste and may even be considered hazardous from the point of
generation
when generated. However, if it turns out that the waste
actually is not handled in accordance with the conditions of the
listing at any point in its management, the generators or other
handlers of the waste would be subject to various enforcement actions
or, depending on the violations, the waste could become a hazardous
waste and may even be considered hazardous from the point of
generation. The Agency's proposed conditional-listing approach for
wastes generated from chlorinated aliphatics processes is further
discussed in section III.E of today's notice.
Today's action also proposes not to list as hazardous the following
three wastes:
Process wastewaters from the production of vinyl chloride
monomer using mercuric chloride catalyst in an acetylene-based process,
Wastewater treatment sludges from the production of methyl
chloride, and
Wastewater treatment sludges from the production of allyl
chloride.
3. Summary of the Remainder of this Preamble
Section III.B. describes the chlorinated aliphatics industry.
Section III.C. describes how the information was gathered in support of
today's proposed rule. Section III.D. is a description of the risk
assessment performed for three of the wastes evaluated in today's rule,
including chlorinated aliphatic wastewaters, EDC/VCM sludges, and
methyl chloride sludges, and the results of these assessments. Section
III.E provides the rationale for the proposed listing decisions for all
six wastes analyzed in today's rule. Because full risk analyses were
not necessary for VCM-A wastewaters, VCM-A wastewater treatment
sludges, or allyl chloride sludges, we discuss our assessment of risks
attributable to each of these wastes in the same sections where we
describe our listing decisions for the wastes. Section IV contains the
economic assessment of the industry and the estimated impact of today's
proposed listing determinations
isk analyses were
not necessary for VCM-A wastewaters, VCM-A wastewater treatment
sludges, or allyl chloride sludges, we discuss our assessment of risks
attributable to each of these wastes in the same sections where we
describe our listing decisions for the wastes. Section IV contains the
economic assessment of the industry and the estimated impact of today's
proposed listing determinations. Section V describes the proposed land
disposal restriction requirements for those wastes we propose to list
as hazardous, along with determinations of whether there is adequate
treatment and disposal capacity for these wastes. Sections VI
(compliance dates), VII (state authority), VIII (designating CERCLA
hazardous substances) and IX (administrative assessments) discuss other
analyses required by statute and various executive orders.
B. Description of the Industry
In 1992, when EPA began gathering information about the U.S.
chlorinated aliphatics industry, it consisted of 27 facilities owned by
20 corporations. However, as a result of information updates in 1997,
we determined that two chlorinated aliphatics facilities had closed and
two additional facilities manufacture de minimis quantities of
chlorinated aliphatics, lowering the number of facilities affected by
today's proposed rulemaking to 23 and corporations to 19.
Chlorinated aliphatics production facilities are located primarily
in and around the petroleum/petrochemical industry which generally is
located along the Gulf Coast. The majority of facility locations are
fully integrated petrochemical processing facilities. A few facilities
are co-located with other chemical manufacturing and/or petroleum
refining facilities. These integrated facilities often manage wastes
generated across different production processes within the same waste
management systems. For example, these facilities often combine
chlorinated aliphatic wastewaters with non-chlorinated aliphatics
wastewaters prior to treatment
facilities. A few facilities
are co-located with other chemical manufacturing and/or petroleum
refining facilities. These integrated facilities often manage wastes
generated across different production processes within the same waste
management systems. For example, these facilities often combine
chlorinated aliphatic wastewaters with non-chlorinated aliphatics
wastewaters prior to treatment. The combined wastewater treatment
system generates a commingled sludge. In addition, there are facilities
that manage chlorinated aliphatics wastewaters in separate or dedicated
wastewater treatment systems. For the purpose of this listing
determination, the Agency refers to these treatment systems, and
resulting sludges, as ``dedicated'' systems and ``dedicated'' sludges.
Nearly 10 million metric tons of chlorinated aliphatics were
produced in 1996. More than 85 percent of the chlorinated aliphatic
products manufactured in 1996 was ethylene dichloride and vinyl
chloride monomer (EDC/VCM) manufactured via the ``balanced process.''
This process involves the production of EDC as an intermediate product
using direct chlorination and oxyhydrochlorination of ethylene,
followed by cracking to produce VCM. Other chlorinated aliphatics
production includes chlorinated methanes, methyl chloride, and a
variety of other products.
C. Overview of EPA's Information Collection Activities
EPA's investigation of the wastes generated by the chlorinated
aliphatics industry can be characterized in terms of two major
information collection efforts: field investigations and survey
evaluation. The Agency's field investigations included engineering site
visits, ``familiarization sampling'' (sample collection and analysis to
gain a preliminary understanding of the nature and concentration of
potential constituents of concern), and ``record sampling'' (sample
collection and analysis to provide data to use in assessing the
potential risks posed by the wastes)
ns and survey
evaluation. The Agency's field investigations included engineering site
visits, ``familiarization sampling'' (sample collection and analysis to
gain a preliminary understanding of the nature and concentration of
potential constituents of concern), and ``record sampling'' (sample
collection and analysis to provide data to use in assessing the
potential risks posed by the wastes). The survey effort included the
development, distribution, and assessment of an extensive industry-wide
RCRA Section 3007 survey. Each of these efforts is summarized below.
1. Field Investigations and Sampling
EPA initiated its work activities with a series of engineering site
visits. The primary purpose of the site visits was to gather
information on chlorinated aliphatic manufacturing processes and the
generation, management, and characterization of the consent decree
wastes. In addition, the field teams identified potential record
sampling locations. The Agency conducted site visits at 16 facilities
prior to record sampling; site visit facilities were selected based on
a goal of obtaining first hand information from a representative
sampling of all chlorinated aliphatic manufacturers as well as all
relevant manufacturing and waste management processes, including an
investigation of dedicated wastewater treatment units.
Concurrently, the Agency initiated the analytical phase of this
listing determination with the development of a Quality Assurance
Project Plan (QAPjP) for sampling and analysis, followed by collection
of 15 familiarization samples from three different manufacturing
facilities (collected during the engineering site visits). The purpose
of collecting familiarization samples is to assess the effectiveness of
the analytical methods identified in the QAPjP for the analysis of the
residuals of concern.
Upon successful completion of the familiarization sampling and
analysis effort, the Agency initiated record sampling and analysis of
the consent decree wastes
facilities (collected during the engineering site visits). The purpose
of collecting familiarization samples is to assess the effectiveness of
the analytical methods identified in the QAPjP for the analysis of the
residuals of concern.
Upon successful completion of the familiarization sampling and
analysis effort, the Agency initiated record sampling and analysis of
the consent decree wastes. The Agency sampled wastewaters and
wastewater treatment sludges from twelve facilities. During a four-
month period beginning in April of 1997, the Agency collected 52
samples, excluding additional blanks and matrix spike/matrix spike
duplicates(MS/MSD) collected for quality assurance purposes. Of these
52 samples, 41 were wastewater samples, and 11 were wastewater
treatment sludge samples.
2. RCRA Section 3007 Survey
EPA developed an extensive questionnaire under the authority of
Section 3007 of RCRA for distribution to the chlorinated aliphatics
manufacturing industry. The purpose of the survey was to gather
information about solid and hazardous waste generation and management
practices in the U.S. chlorinated aliphatics manufacturing industry
necessary to support the listing determination. The questionnaire
covered topics such as chlorinated aliphatic product information,
facility and unit process flow diagrams, process descriptions, residual
generation and residual management profiles.
The Agency distributed the survey in November of 1992 to 57
facilities and/or corporations identified as potential chlorinated
aliphatics manufacturers from the most recent information available at
the time. Of the 57 surveys distributed, completed surveys were
received from 27 facilities. These facilities represent 20 companies
that reported that they had manufactured chlorinated aliphatics in
1991. The remaining facilities notified EPA that they had either
stopped operations or
identified as potential chlorinated
aliphatics manufacturers from the most recent information available at
the time. Of the 57 surveys distributed, completed surveys were
received from 27 facilities. These facilities represent 20 companies
that reported that they had manufactured chlorinated aliphatics in
1991. The remaining facilities notified EPA that they had either
stopped operations or
did not manufacture chlorinated aliphatic products.
We also conducted an exhaustive engineering review of the submitted
surveys for accuracy and completeness. Data from the survey responses
was then entered into a data base known as the Chlorinated Aliphatics
Industry Studies Data Base (ISDB). We conducted quality assurance
reviews of the ISDB to identify any inappropriate entries and missing
data links. The exhaustive engineering review of each facility's
response resulted in follow-up letters and/or telephone calls to
facility representatives seeking clarifications, corrections, and
additional data where needed. The responses to these requests for
clarification, along with additional information gathered during
engineering site visits and familiarization and record sampling
activities were entered into the data base.
In 1996 we conducted a review of data collected previously, and re-
contacted facility representatives to verify the status of chlorinated
aliphatics manufacturing operations. In June of 1997, the Agency sent
requests for updated data (for calendar year 1996) regarding consent
decree wastes generated to each facility. We processed the data
received from this request in the same manner as the original RCRA
surveys, and entered the new information into the ISDB. Between 1993
and 1996, two chlorinated aliphatics manufacturers ceased operations,
resulting in a universe of 23 chlorinated aliphatics manufacturing
facilities owned and operated by 19 different companies
t
decree wastes generated to each facility. We processed the data
received from this request in the same manner as the original RCRA
surveys, and entered the new information into the ISDB. Between 1993
and 1996, two chlorinated aliphatics manufacturers ceased operations,
resulting in a universe of 23 chlorinated aliphatics manufacturing
facilities owned and operated by 19 different companies. Each of the 23
current manufacturers of chlorinated aliphatics generate at least one
wastestream identified in the consent decree. All 23 facilities
generate at least one wastewater residual, while 14 facilities reported
that they generate wastewater treatment sludges.
D. What Are the Risks Associated With Management of Wastewaters and
Wastewater Treatment Sludges From the Production of Chlorinated
Aliphatic Chemicals?
As discussed in Section III.A.2. of this preamble, EPA considers
the Listing criteria set out in 40 CFR 261.11, as well as any other
information relevant to the criteria, in making listing determinations.
The criteria provided in 40 CFR 261.11 include eleven factors for
determining ``substantial present or potential hazard to human health
and the environment.'' Nine of these factors, as described generally
below, are directly incorporated into EPA's completion of a risk
assessment for the wastestreams of concern:
Toxicity (Sec. 261.11(a)(3)(i)) is considered in
developing the health benchmarks used in the risk assessment modeling.
Constituent concentrations and waste quantities
(Sec. Sec. 261.11(a)(3)(ii) and 261.11(a)(3)(viii)) are used to define
the initial conditions for the risk evaluation.
Potential to migrate, persistence, degradation, and
bioaccumulation of the hazardous constituents and any degradation
products (261.11(a)(3)(iii), 261.11(a)(3)(iv), 261.11(a)(3)(v), and
261.11(a)(3)(vi)) are all considered in the design of the fate and
transport models used to determine the concentrations of the
contaminants to which individuals are exposed
onditions for the risk evaluation.
Potential to migrate, persistence, degradation, and
bioaccumulation of the hazardous constituents and any degradation
products (261.11(a)(3)(iii), 261.11(a)(3)(iv), 261.11(a)(3)(v), and
261.11(a)(3)(vi)) are all considered in the design of the fate and
transport models used to determine the concentrations of the
contaminants to which individuals are exposed.
We consider two of the remaining factors, plausible mismanagement
and other regulatory actions (Sec. Sec. 261.11(a)(3)(vii) and
261.11(a)(3)(x)) in establishing the waste management scenario(s)
modeled in the risk assessment.
EPA conducted analyses of the risks posed by wastewaters and
wastewater treatment sludges from the production of chlorinated
aliphatic chemicals to assist in the determination of whether the
wastes meet the criteria for listing set forth in 40 CFR 261.11(a)(3).
This section (III.D.) discusses the human health risk analyses and
ecological risk screening analyses EPA conducted to support our
proposed listing determinations for chlorinated aliphatics wastewaters
(other than VCM-A wastewaters), EDC/VCM wastewater treatment sludges,
and methyl chloride wastewater treatment sludges. We consider the risk
analyses in developing our listing decisions for each of the
wastestreams (described in Sections III.E.1.a. for chlorinated
aliphatics wastewaters, III.E.2. for EDC/VCM sludges, and III.E.4. for
methyl chloride sludges). The risk analyses we describe in this section
(III.D.) are presented in detail in the Risk Assessment Technical
Background Document for the Chlorinated Aliphatics Listing
Determination which is located in the docket for today's proposed rule
treams (described in Sections III.E.1.a. for chlorinated
aliphatics wastewaters, III.E.2. for EDC/VCM sludges, and III.E.4. for
methyl chloride sludges). The risk analyses we describe in this section
(III.D.) are presented in detail in the Risk Assessment Technical
Background Document for the Chlorinated Aliphatics Listing
Determination which is located in the docket for today's proposed rule.
Because full risk analyses were not necessary for VCM-A
wastewaters, VCM-A sludges, or allyl chloride sludges, we discuss our
assessment of risks attributable to each of these wastes in the same
sections where we describe our listing decisions for each of the
wastes, that is, Sections III.E.1.b., III.E.3, III.E.5, respectively.
1. What are the Risks for Potential Human Receptors?
a. What was EPA's Approach to Conducting the Human Health Risk
Assessment?
EPA's human health risk analyses for chlorinated aliphatics
wastewaters and EDC/VCM and methyl chloride sludges provide estimates
of the incremental human health risks resulting from exposure to
contaminants detected in these wastes. The incremental human health
risks are expressed as estimates of excess lifetime cancer risk for
individuals (``receptors'') who may be exposed to carcinogenic (cancer-
causing) contaminants and hazard quotients (HQs) for those contaminants
that produce noncancer health effects. Excess lifetime cancer risk is
the incremental probability (chance) of an individual developing cancer
over a lifetime as a result of exposure to a carcinogen. A hazard
quotient is the ratio of an individual's chronic daily dose of a
noncarcinogen to an acceptable daily dose for chronic exposures to the
noncarcinogen.
EPA used two different methods of analysis to estimate risks. These
methods are called ``deterministic risk analysis'' and ``probabilistic
risk analysis.'' A deterministic risk analysis produces a point
estimate of risk or hazard for each receptor based on using a single
value for each parameter in the analysis
arcinogen to an acceptable daily dose for chronic exposures to the
noncarcinogen.
EPA used two different methods of analysis to estimate risks. These
methods are called ``deterministic risk analysis'' and ``probabilistic
risk analysis.'' A deterministic risk analysis produces a point
estimate of risk or hazard for each receptor based on using a single
value for each parameter in the analysis. A probabilistic analysis
calculates risk or hazard by allowing some of the parameters to have
more than one value, consequently producing a distribution of risk or
hazard for each receptor. A parameter is any one of a number of inputs
or variables (such as waste volume or distance between the waste
management unit and the receptor) required for the fate and transport
and exposure models and equations that EPA uses to assess risk. (In
some cases EPA treats multiple parameters as a single parameter for the
purpose of conducting our analyses. We do this to prevent inadvertently
combining parameters in our analyses in ways that are unrealistic. For
example, EPA treats environmental setting [location] parameters such as
climate, depth to groundwater, aquifer type as a single set of
parameters. We believe that, for example, allowing the climate from one
location to be paired with the depth to groundwater for another
location could result in a scenario that would not occur in nature.)
EPA conducts both ``central tendency'' and ``high end''
deterministic risk assessments to attempt to quantify the cancer risk
or non-cancer hazard for the ``average'' receptor in the population
ameters. We believe that, for example, allowing the climate from one
location to be paired with the depth to groundwater for another
location could result in a scenario that would not occur in nature.)
EPA conducts both ``central tendency'' and ``high end''
deterministic risk assessments to attempt to quantify the cancer risk
or non-cancer hazard for the ``average'' receptor in the population
(the central tendency risk) and the risk or hazard for individuals in
small, but definable ``high end'' segments of the population (the high
end risk). For central tendency deterministic risk analyses, we set all
parameters at their central tendency values. For the chlorinated
aliphatics risk assessments, the central tendency values generally are
either mean (average) or 50th percentile (median) values.
We use high end deterministic risk analysis to predict the risks
and hazards for those individuals exposed at the upper range of the
distribution of exposures. EPA's Guidance For Risk Characterization
(EPA 1995) 2 advises that ``conceptually, high end exposure
means exposure above about the 90th percentile of the population
distribution, but not higher than the individual in the population who
has the highest exposure,'' and recommends that ``* * * the assessor
should approach estimating high end by identifying the most sensitive
variables and using high end values for a subset of these variables,
leaving others at their central values.'' For the chlorinated
aliphatics high end deterministic risk analyses, EPA set two parameters
at their high end values (generally 90th percentile values), and set
all other parameters at their central tendency values. We used a
``sensitivity analysis'' to identify the two parameters that we set at
high end. A sensitivity analysis is an iterative procedure in which an
analysis is performed by alternately setting different parameters at
high end to identify the parameters that most influence the analysis'
outcome
nerally 90th percentile values), and set
all other parameters at their central tendency values. We used a
``sensitivity analysis'' to identify the two parameters that we set at
high end. A sensitivity analysis is an iterative procedure in which an
analysis is performed by alternately setting different parameters at
high end to identify the parameters that most influence the analysis'
outcome. EPA compares the different results generated by the
sensitivity analysis and selects the two high end parameters to which
the analysis was ``most sensitive,'' that is, the two parameters that
are expected to generate the greatest estimate of risk or hazard.
---------------------------------------------------------------------------
\2\ EPA. 1995. Guidance for Risk Characterization. U.S.
Environmental Protection Agency Science Policy Council. February.
---------------------------------------------------------------------------
EPA used probabilistic risk assessment to support the results of
the deterministic risk analyses and to allow EPA to quantify individual
risk at selected percentiles of the risk distribution (for example,
50th percentile, 90th percentile, 95th percentile). EPA conducted
probabilistic risk analyses for those combinations of receptor,
contaminant, and pathway for which risk or hazard estimated using a
deterministic analysis exceeded the following criteria: a cancer risk
of 1 x 10 -6 or a hazard quotient of 1. In a probabilistic
analysis, each parameter may have more than one value. EPA develops
``probability density functions'' (PDFs), distributions that describe
the full range of values that the various input parameters may have
nant, and pathway for which risk or hazard estimated using a
deterministic analysis exceeded the following criteria: a cancer risk
of 1 x 10 -6 or a hazard quotient of 1. In a probabilistic
analysis, each parameter may have more than one value. EPA develops
``probability density functions'' (PDFs), distributions that describe
the full range of values that the various input parameters may have.
Some of the parameters in the probabilistic analysis are set as
constant values because (1) there are insufficient data to develop a
PDF; (2) EPA made assumptions to simplify the analysis in cases where
such simplifications would improve the efficiency of the analysis
without significantly affecting the results; (3) site-specific
constants are available; or (4) the analysis has not been shown to be
sensitive to the value of the parameter, that is, even if the parameter
varies, the resulting risk estimate does not vary significantly. The
Risk Assessment Technical Background Document for the Chlorinated
Aliphatics Listing Determination describes the input parameters used in
the probabilistic analysis. In the probabilistic analysis, risk is
approximated through repetitive calculation of the fate and transport
and exposure equations and models using input parameters randomly
selected from the PDFs. The result of the probabilistic analysis is a
distribution of the risks or hazards for each of the receptors
isting Determination describes the input parameters used in
the probabilistic analysis. In the probabilistic analysis, risk is
approximated through repetitive calculation of the fate and transport
and exposure equations and models using input parameters randomly
selected from the PDFs. The result of the probabilistic analysis is a
distribution of the risks or hazards for each of the receptors.
The human health risk assessments that EPA conducted to support the
chlorinated aliphatics listing determination included four primary
tasks: (1) establishing that there are constituents in the wastes that
are of concern to the Agency and that warrant analysis to determine
their risk to human health; (2) establishing a scenario under which
contaminants are released from a waste management unit and subsequently
are transported in the environment to a human receptor; (3) estimating
the concentrations of contaminants to which the receptor might be
exposed; (4) quantifying the receptor's exposure to contaminants and
the contaminants' toxicity to the receptor; and (5) describing the
receptor's predicted risk. The following sections discuss how EPA
completed each of these tasks for the risk assessments conducted to
support the chlorinated aliphatics listing determination.
b. How Did EPA Determine Which Waste Constituents and Waste Volumes
Would Be Evaluated in the Risk Assessments?
To support the chlorinated aliphatics listing determination, EPA
collected and analyzed samples of wastewaters from the production of
chlorinated aliphatic chemicals, wastewater treatment sludges from the
production of EDC/VCM, and wastewater treatment sludges from the
production of methyl chloride (see Section III.E of today's preamble,
as well as the Background Document for Identification and Listing of
Chlorinated Aliphatics Production Wastes, for further discussion of
EPA's waste characterization efforts)
production of
chlorinated aliphatic chemicals, wastewater treatment sludges from the
production of EDC/VCM, and wastewater treatment sludges from the
production of methyl chloride (see Section III.E of today's preamble,
as well as the Background Document for Identification and Listing of
Chlorinated Aliphatics Production Wastes, for further discussion of
EPA's waste characterization efforts). We used the results of these
waste analyses to establish the ``constituents of potential concern''
(COPCs) in the wastes. We derived waste volume information from data
provided by facilities in their RCRA Section 3007 questionnaire
responses.
EPA collected and analyzed 41 samples of wastewaters generated from
the production of chlorinated aliphatic chemicals. EPA collected six of
these samples at the influent (or ``headworks'') of wastewater
treatment systems that manage only wastewaters derived from the
production of chlorinated aliphatic chemicals. We call these samples
``dedicated'' chlorinated aliphatics wastewater samples,3
and we chose to use these samples in our assessment of the risks and
hazards attributable to the management of chlorinated aliphatic
wastewaters. (The assessment of dedicated sample data allows us to
evaluate without question what risks are attributable to the wastes of
concern to the Agency.) Because we used analytical data for dedicated
chlorinated aliphatics wastewater samples in our analysis, we also used
dedicated chlorinated aliphatic wastewater volumes in our analysis. We
identified eight wastewater volumes that represent the volumes of
dedicated chlorinated aliphatics wastewaters discharged to the
headworks of chlorinated aliphatics facility wastewater treatment
systems.
---------------------------------------------------------------------------
ewater samples in our analysis, we also used
dedicated chlorinated aliphatic wastewater volumes in our analysis. We
identified eight wastewater volumes that represent the volumes of
dedicated chlorinated aliphatics wastewaters discharged to the
headworks of chlorinated aliphatics facility wastewater treatment
systems.
---------------------------------------------------------------------------
\3\ ``Dedicated'' chlorinated aliphatic wastewaters are those
that are comprised only of chlorinated aliphatics process
wastewaters, that is, wastewaters generated from the production of
the chlorinated aliphatic chemicals of concern to this listing
determination.
---------------------------------------------------------------------------
EPA collected and analyzed seven samples of nonhazardous EDC/VCM
sludge. (Some sludges generated by this industry already are designated
as hazardous because they include material derived from wastes that EPA
previously listed as hazardous waste.) Four were samples of sludges
that were derived from wastewater treatment systems that manage only
EDC/VCM process wastewaters. These samples are ``dedicated'' EDC/VCM
sludge samples. Three were samples of sludges that result from the
treatment of EDC/VCM process wastewaters combined with wastewaters from
non-EDC/VCM processes and sources. EPA chose to use only the dedicated
EDC/VCM sample data in our analysis. Because we used
were derived from wastewater treatment systems that manage only
EDC/VCM process wastewaters. These samples are ``dedicated'' EDC/VCM
sludge samples. Three were samples of sludges that result from the
treatment of EDC/VCM process wastewaters combined with wastewaters from
non-EDC/VCM processes and sources. EPA chose to use only the dedicated
EDC/VCM sample data in our analysis. Because we used
analytical data for dedicated EDC/VCM sludge samples in our analysis,
we also used ``dedicated'' EDC/VCM sludge volumes. EPA divided the
volume of wastewater attributable to EDC/VCM processes by the total
volume of wastewater influent, and applied the resultant ratio to the
total sludge volumes to obtain the volume of wastewater treatment
sludge attributable to EDC/VCM processes (that is, the ``dedicated ``
EDC/VCM sludge volume).
The methyl chloride sludge, generated by only one facility, results
from treatment of the combined wastewaters from the facility's methyl
chloride production process and other facility processes and sources.
The facility reports that approximately 18 percent of the wastewater
that generates the sludge is from the methyl chloride process. The
remainder of the wastewater is from other processes. Because the
sludge, as generated, is not dedicated, and there is no means to obtain
a dedicated sample of the methyl chloride sludge, we conducted our risk
assessment using the sample data for the nondedicated methyl chloride
sludge sample, and, comparably, the nondedicated (total) methyl
chloride sludge volume.
Using the results of the analysis of the waste samples, EPA
developed a list of ``chemicals of potential concern'' (COPCs) for the
chlorinated aliphatics wastewaters, EDC/VCM sludges, and methyl
chloride sludges. The COPCs are the constituents which were the subject
of EPA's risk assessment
thyl chloride
sludge sample, and, comparably, the nondedicated (total) methyl
chloride sludge volume.
Using the results of the analysis of the waste samples, EPA
developed a list of ``chemicals of potential concern'' (COPCs) for the
chlorinated aliphatics wastewaters, EDC/VCM sludges, and methyl
chloride sludges. The COPCs are the constituents which were the subject
of EPA's risk assessment. EPA developed the COPC lists by taking the
complete list of detected constituents in the wastes and eliminating
constituents from the list that occurred at concentrations clearly
below levels of concern, based on screening analyses developed to
maximize risk estimates. For chlorinated aliphatics wastewaters and
EDC/VCM sludges, EPA also eliminated constituents when a constituent
was detected in only one of the samples and the concentration of the
constituent in the one sample was qualified with the ``J'' qualifier,
indicating that the constituent was detected below the quantitation
limit and the reported value was estimated. Specifically, the
laboratory detected 69 constituents in chlorinated aliphatics
wastewater samples of which we eliminated 28; 53 constituents in EDC/
VCM sludges of which we eliminated 16; and 19 constituents in methyl
chloride sludges of which we eliminated 11.
Six polychlorinated dibenzodioxin (``dioxin'') congeners and ten
polychlorinated dibenzofuran (``furan'') congeners were among the
constituents detected in samples of the chlorinated aliphatics
wastewaters, EDC/VCM sludges, and methyl chloride sludges and evaluated
in the risk assessment. EPA classifies the furan congeners and certain
polychlorinated biphenyl (PCB) congeners as ``dioxin-like compounds''
because of their structural similarity to the dioxins (EPA 1994a
4). In today's preamble we use the term ``dioxins'' to
represent both the dioxin and furan congeners
ated aliphatics
wastewaters, EDC/VCM sludges, and methyl chloride sludges and evaluated
in the risk assessment. EPA classifies the furan congeners and certain
polychlorinated biphenyl (PCB) congeners as ``dioxin-like compounds''
because of their structural similarity to the dioxins (EPA 1994a
4). In today's preamble we use the term ``dioxins'' to
represent both the dioxin and furan congeners. Our use of the term
``dioxins'' does not refer to dioxin-like PCBs because we did not
analyze for PCBs in our waste samples from the chlorinated aliphatics
industry since we do not expect PCBs to be constituents of the
chlorinated aliphatics wastes that are the subject of today's listing
determination.
---------------------------------------------------------------------------
\4\ EPA. 1994a. Estimating Exposure to Dioxin-Like Compounds,
Volume I: Executive Summary. Review Draft. EPA/600/6-88/005Ca.
Office of Research and Development. June.
---------------------------------------------------------------------------
c. What Exposure Scenarios Did EPA Evaluate?
Prior to conducting the risk assessments, EPA had to establish that
there is a plausible scenario under which a receptor might be exposed
to contaminants in the wastewaters and sludges. Establishing this
scenario required that EPA determine:
How the waste is managed or is likely to be managed;
How contaminants could be released from the waste
management unit;
How contaminants could be transported in the environment
to a point of contact with a receptor; and
How a receptor could be exposed to the contaminants.
One respondent to EPA's Sec. 3007 questionnaire reported that they
discharge a portion of their nonhazardous chlorinated aliphatics
wastewaters to nonhazardous underground injection wells. Section
III.E.1.a.i. discusses EPA's evaluation of the underground injection
waste management scenario. Twenty-three respondents reported that they
manage their nonhazardous or exempt chlorinated aliphatics wastewaters
in tanks
s Sec. 3007 questionnaire reported that they
discharge a portion of their nonhazardous chlorinated aliphatics
wastewaters to nonhazardous underground injection wells. Section
III.E.1.a.i. discusses EPA's evaluation of the underground injection
waste management scenario. Twenty-three respondents reported that they
manage their nonhazardous or exempt chlorinated aliphatics wastewaters
in tanks. Because management of wastewaters in tanks is the dominant
wastewater management practice in the chlorinated aliphatics industry,
EPA chose to evaluate tanks in our risk assessment for chlorinated
aliphatics wastewaters. For reasons discussed in III.E.1.a.i., EPA
chose to evaluate risks attributable to management of chlorinated
aliphatics wastewaters in uncovered aerated biological treatment tanks.
One respondent to EPA's Sec. 3007 questionnaire reported that they
manage their EDC/VCM wastewater treatment sludges in an onsite land
treatment unit. All other respondents reported that nonhazardous EDC/
VCM sludges are managed in landfills. Eight facilities send EDC/VCM
sludges to offsite nonhazardous waste landfills, two facilities manage
EDC/VCM sludge in onsite nonhazardous industrial waste landfills, and
one facility manages their nonhazardous EDC/VCM sludge in an onsite
hazardous waste landfill (see section III.E.2.a. in today's preamble
for a description of current methods for managing EDC/VCM sludges). For
this assessment, EPA evaluated the risks associated with management of
EDC/VCM sludges in unlined municipal landfills and in a land treatment
unit. Because the only facility that generates methyl chloride sludges
manages them in an onsite nonhazardous industrial waste landfill, EPA
evaluated this management scenario in our risk assessment for methyl
chloride sludges. The Risk Assessment Technical Background Document for
the Chlorinated Aliphatics Listing Determination provides a complete
discussion of the parameters that define the characteristics of the
waste management units
methyl chloride sludges
manages them in an onsite nonhazardous industrial waste landfill, EPA
evaluated this management scenario in our risk assessment for methyl
chloride sludges. The Risk Assessment Technical Background Document for
the Chlorinated Aliphatics Listing Determination provides a complete
discussion of the parameters that define the characteristics of the
waste management units.
EPA determined that releases from all of the waste management units
(tank, land treatment unit, and landfill) could occur through release
of vapor emissions to the air. In addition, for the land treatment unit
and the landfill, EPA determined that releases could occur through
leaching of the waste into the subsurface. We assumed that the
chlorinated aliphatics industry's tanks retain sufficient structural
integrity to prevent wastewater releases to the subsurface (and
therefore to groundwater), and that overflow and spill controls prevent
wastewater releases to the ground surface. For the land treatment unit,
releases also could occur through release of particulate emissions to
the air and runoff and erosion of waste from the unit. EPA assumed that
wastewater would entrain any particulate matter such that particulates
would not be released from the tanks. EPA did not evaluate particulate
emissions from the landfills because the moisture content of the
sludges (41 to 74 percent moisture) would prevent generation and
release of particulates to the air in the time between placement of the
waste in the landfill and application of daily cover or a new day's
waste addition. EPA also assumed that runon/runoff controls would
prevent releases from the landfills due to erosion and runoff.
EPA also evaluated the mechanisms and pathways by which
contaminants
(41 to 74 percent moisture) would prevent generation and
release of particulates to the air in the time between placement of the
waste in the landfill and application of daily cover or a new day's
waste addition. EPA also assumed that runon/runoff controls would
prevent releases from the landfills due to erosion and runoff.
EPA also evaluated the mechanisms and pathways by which
contaminants
might be transported to the points where receptors are exposed. The
mechanisms and pathways we evaluated are as follows:
Eroded waste can be transported by runoff and deposited
onto the soil and into surface water bodies.
Leachate can migrate through the unsaturated 5
zone to the saturated 6 zone, where contaminants are
transported in groundwater to drinking water wells and to points of
discharge to surface water bodies.
---------------------------------------------------------------------------
\5\ The unsaturated (vadose) zone is a subsurface zone in which
the pore spaces contain both water and air.
\6\ The saturated zone is a subsurface zone in which all pore
spaces are full of water.
---------------------------------------------------------------------------
Vapor emissions can remain dispersed in the air, or can be
deposited through wet and dry deposition. Specifically, EPA models:
The concentration of vapor phase contaminants in air,
The diffusion of vapor phase contaminants into plants,
The diffusion of vapor phase contaminants into surface
water,
Wet deposition of vapors onto soils and surface water (for
example, due to wash-out [scavenging] by precipitation).
Dry deposition of vapors onto soils (for example, due to
density).
Although we do not evaluate wet and dry deposition of
vapors onto plants, we do assume that wet and dry deposition of vapors
onto soils increase the contaminant concentrations in the soil and
result in additional uptake of contaminants into plants via soil-to-
plant uptake
mple, due to wash-out [scavenging] by precipitation).
Dry deposition of vapors onto soils (for example, due to
density).
Although we do not evaluate wet and dry deposition of
vapors onto plants, we do assume that wet and dry deposition of vapors
onto soils increase the contaminant concentrations in the soil and
result in additional uptake of contaminants into plants via soil-to-
plant uptake.
Particulate emissions can remain dispersed in the air or
be deposited through wet deposition (in precipitation) or dry
deposition (particle settling). We assume that particulates may be
deposited onto soil and surface water through both wet and dry
deposition, and onto plants through dry deposition.
Human receptors indirectly may come into contact with vapors that
diffuse into vegetation, particulates that are deposited on vegetation,
or contaminants that are taken up by vegetation from the soil through
exposure to contaminated home-grown fruits and vegetables, as well as
exposure to contaminated beef and dairy products derived from cattle
which have ingested contaminated forage, silage, grain, and surface
soil. Receptors that ingest fish also indirectly may come into contact
with contaminants in air-borne vapors and particulates (through vapor
diffusion into surface water, vapor deposition onto surface water, and
particulate deposition onto surface water), contaminated groundwater
(through groundwater discharge into surface water), and runoff and
eroded soil that enter surface water.
EPA determined that the following receptors reasonably represent
the types of individuals that could be exposed to contaminants in
chlorinated aliphatics wastes, and were the receptors evaluated in our
risk analyses:
an adult resident
the child of a resident
a home gardener
a farmer
the child of a farmer
a fisher
into surface water), and runoff and
eroded soil that enter surface water.
EPA determined that the following receptors reasonably represent
the types of individuals that could be exposed to contaminants in
chlorinated aliphatics wastes, and were the receptors evaluated in our
risk analyses:
an adult resident
the child of a resident
a home gardener
a farmer
the child of a farmer
a fisher
The following sections describe briefly EPA's primary assumptions
regarding the characteristics and activities of each of the receptor
types, and the routes by which each receptor is exposed.
Adult Resident and Child of Resident--We assume that an adult and
child reside near the waste management unit. The residential receptors
inhale vapors and particulate matter that are dispersed in the ambient
air. EPA assumes that household water is supplied to the residential
receptors by a domestic groundwater well that is located near their
home. The adult resident and child of the resident drink water that
comes from the well. We assume that the adult resident inhales vapors
that are emitted from the water that they use in their house (for
example, during showering), and that the adult resident's skin also is
exposed to groundwater when he/she bathes. The residential receptors do
not ingest foods that are grown in the vicinity of their home, however
they do incidentally ingest surface soil from their yard.
Home Gardener--We assume that the residential receptor may have a
home garden. The home gardener grows fruit, exposed vegetables
(vegetables with edible parts that are exposed at land surface), and
root vegetables. Approximately 23 percent of the exposed vegetables, 11
percent of the root vegetables, and 12 percent of the fruits eaten by
the gardener are grown in his/her garden (EPA 1997a, Table 13-71)
7. The gardener's other characteristics and activities are
the same as those of the adult resident.
---------------------------------------------------------------------------
rface), and
root vegetables. Approximately 23 percent of the exposed vegetables, 11
percent of the root vegetables, and 12 percent of the fruits eaten by
the gardener are grown in his/her garden (EPA 1997a, Table 13-71)
7. The gardener's other characteristics and activities are
the same as those of the adult resident.
---------------------------------------------------------------------------
\7\ EPA. 1997a. Exposure Factors Handbook, Volumes I, II, and
III. Office of Research and Development, Washington, D.C., EPA/600/
P-95/002Fa, b, c. August 1997; www.epa.gov/ordntrnt/ord/webpubs/
exposure/index.html.
---------------------------------------------------------------------------
Fisher--We assume that the residential receptor may be a
recreational angler. Approximately 32 percent of the fish eaten by the
fisher are from a stream located near the waste management unit (EPA
1997a, Table 13-71). The fisher's other characteristics and activities
are the same as those of the adult resident.
Adult Farmer and Child of Farmer--We assume that a farmer raises
fruits, exposed vegetables, root vegetables, beef cattle, and dairy
cattle in an agricultural field located near the waste management unit.
Approximately 42 percent of the exposed vegetables, 17 percent of the
root vegetables, 33 percent of the fruits, 49 percent of the beef, and
25 percent of the dairy products eaten by the farmer and the child of
the farmer are grown/raised on the farmer's agricultural field (EPA
1997a, Table 13-71). We assume that the farmer incidentally ingests
soil from the agricultural field, and that the child of the farmer
incidentally ingests soil from his/her yard. The farmer's and child's
exposure to groundwater via ingestion, inhalation, and dermal contact
are the same as that for the adult resident and child of the resident.
EPA establishes the locations of receptors relative to waste
management units based on information obtained from national surveys
e agricultural field, and that the child of the farmer
incidentally ingests soil from his/her yard. The farmer's and child's
exposure to groundwater via ingestion, inhalation, and dermal contact
are the same as that for the adult resident and child of the resident.
EPA establishes the locations of receptors relative to waste
management units based on information obtained from national surveys.
Exposure to groundwater occurs through the use of water from drinking
water wells, and exposure via nongroundwater pathways occurs through
runoff/erosion and releases to air. Therefore, ``distance to receptor''
for groundwater exposure pathways actually is the distance to the
drinking water well that the receptor is using (the ``receptor well'').
``Distance to receptor'' for nongroundwater pathways is the distance to
the residence where the receptor is inhaling air or contacting soil,
the distance to the garden where the receptor is growing fruits and
vegetables, or the distance to the field where the receptor is growing
crops or raising livestock. Consequently, EPA uses different databases
to establish ``distance to receptor,'' depending on whether we are
evaluating a groundwater or a nongroundwater pathway.
For analysis of the nongroundwater pathway (air pathways and
erosion/runoff) risks in the deterministic analysis we assume that the
receptors live either 75 meters (m) (high end) or 300 m (central
tendency) from the waste management unit. The distance of 250 feet (ft)
(approximately 75 m) is based on the actual measured distance to the
nearest resident for the worst-case facility evaluated in the risk
assessment conducted to support the ``Hazardous Waste Treatment,
Storage, and Disposal Facilities--Organic Air Emissions Standards for
Process Vents and Equipment Leaks Final Rule'' (55 FR
endency) from the waste management unit. The distance of 250 feet (ft)
(approximately 75 m) is based on the actual measured distance to the
nearest resident for the worst-case facility evaluated in the risk
assessment conducted to support the ``Hazardous Waste Treatment,
Storage, and Disposal Facilities--Organic Air Emissions Standards for
Process Vents and Equipment Leaks Final Rule'' (55 FR
25454), and was used as distance to the nearest resident for that
rulemaking. In the same risk assessment, EPA identified the receptor
distance of 1000 ft (approximately 300 m) as the median distance in a
random sample of distances to the nearest residence. For the
probabilistic analysis, we assume the receptors live either 50, 75,
100, 200, 300, 500, or 1000 m from the waste management unit. For air
pathway analyses, we always assume that the receptors (including
cattle) are located along the centerline of the area most greatly
impacted by air releases from the waste management units. However, at
distances of a few hundred meters from the waste management unit, the
air concentrations within about a 100 meter lateral distance do not
vary appreciably.
For deterministic analyses we assume that a receptor well is
located 102 m (high end) or 430 m (central tendency) from the waste
management unit, and that the receptor well is located on centerline of
the contaminant plume (high end) or halfway between the centerline and
the edge of the contaminant plume (central tendency). The 102 m
distances is the 10th percentile value in the distribution of distances
derived from EPA's 1988 survey of Solid Waste (Municipal) Landfill
Facilities (DPRA 1993 8). The 430 m value is the 50th
percentile value in that same distribution
ocated on centerline of
the contaminant plume (high end) or halfway between the centerline and
the edge of the contaminant plume (central tendency). The 102 m
distances is the 10th percentile value in the distribution of distances
derived from EPA's 1988 survey of Solid Waste (Municipal) Landfill
Facilities (DPRA 1993 8). The 430 m value is the 50th
percentile value in that same distribution. For the Monte Carlo
analysis, the distance from the waste management unit to the receptor
well is based on the complete distribution of distances to receptor
well reported by the survey respondents, and ranges from 0.02 m (the
location of the closest reported well was 0 m) to 1604 m (the maximum
distance for which EPA requested receptor well information was 1 mile).
For the Monte Carlo analysis we assume that the receptor well is
located anywhere within the contaminant plume.
---------------------------------------------------------------------------
\8\ DPRA. 1993. Parameter Values for Developing Nationwide
Regulations with the EPA's Composite Model for Landfills (EPACML).
EPA Contract Number 68-WO-0029. July.
---------------------------------------------------------------------------
The Risk Assessment Technical Background Document for the
Chlorinated Aliphatics Listing Determination provides a complete
discussion of the values of additional parameters that define the
characteristics of each receptor, such as the amounts of contaminated
food and water they ingest, their inhalation rates, and how long they
live near the waste management unit.
d. How Did EPA Predict What Contaminant Concentrations Are at the
Points Where Receptors Are Exposed?
EPA conducts contaminant fate and transport modeling and indirect
exposure modeling to determine what the concentrations of contaminants
will be in the media (for example, groundwater, air, soil, food items)
that the receptor comes into contact with
they
live near the waste management unit.
d. How Did EPA Predict What Contaminant Concentrations Are at the
Points Where Receptors Are Exposed?
EPA conducts contaminant fate and transport modeling and indirect
exposure modeling to determine what the concentrations of contaminants
will be in the media (for example, groundwater, air, soil, food items)
that the receptor comes into contact with. These concentrations are
called ``exposure point concentrations'' (that is, they are the
contaminant concentrations at the point where the receptor is exposed
to the contaminants). There are a number of computer-based models and
sets of equations that EPA uses to predict exposure point
concentrations. In the following sections we briefly discuss these
models and equations and their application in the risk analyses.
i. Partitioning Model
For the landfill and the land treatment unit, EPA uses a series of
``partitioning'' equations to determine how much contaminant mass is
retained in the waste management unit and how much is released into the
environment. These equations are based upon equations presented in a
series of articles by Jury et al. (Jury et al. 1983, 1984, and 1990
9). EPA used the partitioning equations to estimate the mass
of a contaminant that will be lost from the land treatment unit due to
volatilization into the air, contaminant leaching into the subsurface,
runoff from the land treatment unit, and degradation. For the landfill
scenarios, EPA used the partitioning equations to determine how much of
the contaminant mass would be lost due to volatilization into the air;
EPA assumed that the remainder of the mass would be available to leach
into the subsurface. We assumed that volatilization losses could occur
prior to the landfill being covered with daily cover or daily waste
addition, through the daily cover or daily waste addition, and through
the cap that is placed on the landfill after closure
minant mass would be lost due to volatilization into the air;
EPA assumed that the remainder of the mass would be available to leach
into the subsurface. We assumed that volatilization losses could occur
prior to the landfill being covered with daily cover or daily waste
addition, through the daily cover or daily waste addition, and through
the cap that is placed on the landfill after closure. For the landfill,
we used toxicity characteristic leaching procedure (TCLP) analytical
results (rather than the partitioning equations) as the predictor of
leachate concentration. The TCLP is an analytical procedure that
``leaches'' a waste sample in a way that mimics the leaching of waste
in a municipal landfill. Thus, TCLP results are a proxy for the
concentrations of contaminants that would be generated in leachate if
the waste were placed in a municipal landfill.
---------------------------------------------------------------------------
\9\ Jury, W.A., W.F. Spencer, and W. J. Farmer. 1983. Behavior
assessment model for trace organics in soil: i. model description.
J. Environ. Qual. 12(4):558-564.
Jury, W.A., W. J. Farmer, and W.F. Spencer. 1984. Behavior
assessment model for trace organics in soil: ii. chemical
classification and parameter sensitivity. J. Environ. Qual.
13(4):567-572.
Jury, W.A., D. Russo, G. Streile, and H.E. Abd. 1990. Evaluation
of volatilization by organic chemicals residing below the soil
surface. Water Resources Research. 26(1):13-20.
---------------------------------------------------------------------------
Behavior
assessment model for trace organics in soil: ii. chemical
classification and parameter sensitivity. J. Environ. Qual.
13(4):567-572.
Jury, W.A., D. Russo, G. Streile, and H.E. Abd. 1990. Evaluation
of volatilization by organic chemicals residing below the soil
surface. Water Resources Research. 26(1):13-20.
---------------------------------------------------------------------------
ii. Tank Emissions Model
EPA modeled emissions from aerated biological wastewater treatment
tanks using the CHEMDAT8 model (EPA 1994b 10). We used the
emissions estimates in conjunction with the air dispersion modeling
results (see Section D.1.d.iii) to estimate constituent-specific air
concentrations and deposition rates. CHEMDAT8 accounts for most of the
competing removal pathways that might limit air emissions, including
adsorption, biodegradation, and hydrolysis. Chemicals that sorb to
solids or decompose due to either biodegradation or hydrolysis have
lower potential for emission to the air. CHEMDAT8 is considered to
provide reasonable to slightly high estimates of air emissions.
---------------------------------------------------------------------------
\10\ EPA. 1994b. CHEMDAT8 User's Guide, EPA-453/C-94-080B.
Office of Air Quality Planning and Standards, US Environmental
Protection Agency, Research Triangle Park, NC, November. This model
is publicly available from EPA's Web page at http://www.epa.gov/ttn/
chief/software.html.
---------------------------------------------------------------------------
---------------------------------------
\10\ EPA. 1994b. CHEMDAT8 User's Guide, EPA-453/C-94-080B.
Office of Air Quality Planning and Standards, US Environmental
Protection Agency, Research Triangle Park, NC, November. This model
is publicly available from EPA's Web page at http://www.epa.gov/ttn/
chief/software.html.
---------------------------------------------------------------------------
CHEMDAT8 requires that the user specify parameters relating to tank
characteristics, waste characteristics, contaminant physical and
chemical properties, and location-specific meteorological conditions
(for example, windspeed and temperature). The tank characterization
data required by the model include both tank physical parameters (for
example, tank dimensions) and tank operating parameters (for example,
the number of aerators in the tank). In the absence of site-specific
data, we developed tank dimensions based on facility-reported
wastewater generation rates, an assumed wastewater depth in the tank of
15 feet, and a retention time in the tank of two days. We selected
operating parameters that we believe represent typical operating
conditions of an aerated tank. The Risk Assessment Technical Background
Document for the Chlorinated Aliphatics Listing Determination provides
a complete list of the parameters used in the CHEMDAT8 model.
iii. Air Dispersion and Deposition Model
We used EPA's Industrial Source Complex Short Term model (version
3;
s. We selected
operating parameters that we believe represent typical operating
conditions of an aerated tank. The Risk Assessment Technical Background
Document for the Chlorinated Aliphatics Listing Determination provides
a complete list of the parameters used in the CHEMDAT8 model.
iii. Air Dispersion and Deposition Model
We used EPA's Industrial Source Complex Short Term model (version
3;
ISCST3 11) to estimate the dispersion and deposition of
vapors emitted from the wastewater treatment tank, the municipal
landfill, the onsite industrial landfill, and the land treatment unit.
EPA also used ISCST3 to estimate the dispersion and deposition of
particulate emissions from the land treatment unit. For the land
treatment unit, EPA used equations documented in EPA's ``Compilation of
Air Pollutant Emission Factors (AP-42)'' (EPA 1985) 12 to
estimate particulate emissions resulting from wind erosion and tilling
activities. Vapor emissions from the landfill and the land treatment
unit were estimated using the partitioning models discussed in Section
III.D.1.d.i. Vapor emissions from the wastewater treatment tank were
estimated using the CHEMDAT8 model discussed in Section III.D.1.d.ii.
ISCST3 was used to estimate the air concentration of vapors, wet
deposition of vapors, the air concentration of particulates, wet
deposition of particulates, and dry deposition of particulates. We
calculate dry deposition of vapors using the air concentration of
vapors and a contaminant deposition velocity.
---------------------------------------------------------------------------
.D.1.d.ii.
ISCST3 was used to estimate the air concentration of vapors, wet
deposition of vapors, the air concentration of particulates, wet
deposition of particulates, and dry deposition of particulates. We
calculate dry deposition of vapors using the air concentration of
vapors and a contaminant deposition velocity.
---------------------------------------------------------------------------
\11\ EPA. 1995. User's Guide for the Industrial Source Complex
(ISC3) Dispersion Models (Draft) (Revised). Volume I. EPA-454/B-95-
003a. Office of Air Quality Planning and Standards, Emissions,
Monitoring and Analysis Division, Research Triangle Park, NC. The
ISCST3 model and meteorological preprocessor, PCRAMMET, and related
user's guides can be accessed and downloaded through the Internet
from the Support Center for Regulatory Air Models (SCRAM) web page
(http://www.epa.gov/scram001). The SCRAM is part of EPA's Office of
Air Quality Planning and Standards (OAQPS) Technology Transfer
Network (TTN).
\12\ EPA. 1985. Compilation of Air Pollutant Emission Factors,
AP-42, Fifth Edition, Volume I: Stationary Point and Area Sources.
Office of Air Quality Planning and Standards, Emissions Inventory
Group, Research Triangle Park, NC. AP-42 can be downloaded through
the Internet at http://www.epa.gov/ttn/chief/ap42.html.
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iv. Overland Transport Model
The Universal Soil Loss Equation (USLE) is an erosion model
originally designed to estimate long-term average soil erosion losses
to a nearby surface water body from an agricultural field having
uniform slope, soil type, vegetative cover, and erosion-control
practices. We used a modified form of the USLE to estimate the mass of
soil lost per year per unit area from the land treatment unit and
deposited directly onto the adjacent receptor site (agricultural field,
residential lot, home garden) and into a nearby stream
s
to a nearby surface water body from an agricultural field having
uniform slope, soil type, vegetative cover, and erosion-control
practices. We used a modified form of the USLE to estimate the mass of
soil lost per year per unit area from the land treatment unit and
deposited directly onto the adjacent receptor site (agricultural field,
residential lot, home garden) and into a nearby stream.
Because the basic USLE equation estimates only soil erosion to
surface water bodies, EPA assumes the receptor location is located
between the land treatment unit and the surface water body. The area
including the land treatment unit, the receptor site, and the
intervening area is considered for the purposes of the analysis to be
an independent, discrete drainage subbasin that is at steady-state. We
estimate the soil erosion load from the subbasin to the surface water
body using a distance-based sediment delivery ratio, and consider that
the sediment not reaching the surface water body is deposited evenly
over the area of the subbasin. Using mass balance equations, EPA
estimates contaminant contributions to the surface water body and the
receptor soil. ``Mass balance equations'' are equations that honor the
law of conservation of mass, that is, the mass of a contaminant that is
present at the beginning of the analysis (for example, the mass of a
contaminant in a waste placed in a waste management unit) is equal to
the mass of the contaminant present at the end of the analysis. Even
though at the end of the analysis the contaminant mass may be
partitioned into a number of environmental ``compartments'' (for
example, the waste management unit, the soil, and the surface water
body), there is in total no more or no less mass than was present at
the start of the analysis.
Contaminated particles are transported from the land treatment unit
to receptor sites via air deposition as well as runoff/erosion
alysis the contaminant mass may be
partitioned into a number of environmental ``compartments'' (for
example, the waste management unit, the soil, and the surface water
body), there is in total no more or no less mass than was present at
the start of the analysis.
Contaminated particles are transported from the land treatment unit
to receptor sites via air deposition as well as runoff/erosion. We
applied mass balance for each area of interest (for example, buffer
area between source and receptor site, receptor site, or surrounding
area). Consequently, the respective air deposition value for each area
of interest is included in the evaluation of the mass balance. We
considered that the air deposition over the entire subbasin area is
uniform and equal to the air deposition modeled for the receptor site.
v. Groundwater Model
We used EPA's Composite Model for Leachate Migration with
Transformation Products (EPACMTP; EPA 1996a, 1996b, 1996c, 1997
13) to model the subsurface fate and transport of
contaminants that leach from the waste management units (the land
treatment unit or the landfill) and migrate to a residential drinking
water well or discharge from groundwater to surface water.
---------------------------------------------------------------------------
\13\ EPA. 1996a. EPA's Composite Model for Leachate Migration
with Transformation Products (EPACMTP) Background Document. Office
of Solid Waste, Washington, DC.
EPA. 1996b. EPA's Composite Model for Leachate Migration with
Transformation Products (EPACMTP) Background Document for the Finite
Source Methodology. Office of Solid Waste, Washington, DC.
EPA. 1996c. EPA's Composite Model for Leachate Migration with
Transformation Products (EPACMTP) Background Document for Metals.
Office of Solid Waste, Washington, DC.
EPA. 1997. EPA's Composite Model for Leachate Migration with
Transformation Products (EPACMTP) User's Guide. Office of Solid
Waste, Washington, DC
ument for the Finite
Source Methodology. Office of Solid Waste, Washington, DC.
EPA. 1996c. EPA's Composite Model for Leachate Migration with
Transformation Products (EPACMTP) Background Document for Metals.
Office of Solid Waste, Washington, DC.
EPA. 1997. EPA's Composite Model for Leachate Migration with
Transformation Products (EPACMTP) User's Guide. Office of Solid
Waste, Washington, DC.
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Precipitation that migrates through the waste management unit
generates leachate, which infiltrates the bottom of the waste
management unit and migrates into the unsaturated zone. The
contaminants dissolved in the leachate subsequently are transported in
the aqueous phase through the unsaturated zone to the underlying
saturated zone and then downgradient to a receptor (drinking water)
well or surface water body located at a specified distance from the
boundary of the waste management unit. EPACMTP accounts for the
following processes affecting contaminant fate and transport:
advection, hydrodynamic dispersion, equilibrium linear or nonlinear
sorption by the soil and aquifer solids (both in the unsaturated and
saturated zones), and contaminant hydrolysis. In the event that the
hydrolysis daughter products are toxic and their chemical properties
are known, the model also accounts for the formation and subsequent
fate and transport of the daughter products.
The landfill analysis employed two simplifying assumptions. First,
we assumed that contaminant leaching from the landfill does not occur
until after the landfill closes (that is, after 30 years). EPA made
this assumption because of complexities associated with linking the
output of the landfill partitioning equations (discussed in Section
III.D.1.d.i.) and the groundwater model, EPACMTP. Second, we assumed
that there are no contaminant losses due to mechanisms other than
leaching after the landfill has been closed (that is, after 30 years)
he landfill closes (that is, after 30 years). EPA made
this assumption because of complexities associated with linking the
output of the landfill partitioning equations (discussed in Section
III.D.1.d.i.) and the groundwater model, EPACMTP. Second, we assumed
that there are no contaminant losses due to mechanisms other than
leaching after the landfill has been closed (that is, after 30 years).
This effectively over-estimates the total mass of volatile contaminants
that would leach to groundwater because it does not allow contaminant
loss due to volatilization from the landfill to deplete the total
contaminant mass available for leaching from the landfill in the years
after closure. EPA determined that if volatile constituents caused
significant risk via the groundwater pathway, we would have to re-
evaluate our methodology for conducting the landfill analysis. This
situation did not occur.
vi. Surface Water Model
EPA assumed that fish are exposed to waste constituents in surface
water. Specifically, we assumed that fish are exposed to contaminants
dissolved in the water column, contaminants sorbed to suspended solids
in the water
column, and contaminants associated with the bed sediment in the
surface water body. The method used to estimate how management of
chlorinated aliphatics wastewaters and wastewater treatment sludges
impacts surface water is based on the methodology presented in Addendum
to Methodology for Assessing Health Risks Associated with Indirect
Exposure to Combustor Emissions (EPA 1993) 14
the water
column, and contaminants associated with the bed sediment in the
surface water body. The method used to estimate how management of
chlorinated aliphatics wastewaters and wastewater treatment sludges
impacts surface water is based on the methodology presented in Addendum
to Methodology for Assessing Health Risks Associated with Indirect
Exposure to Combustor Emissions (EPA 1993) 14. The model
accounts for six ways in which contaminants may enter the surface water
body: (1) contaminants may be sorbed to eroded soils that enter the
surface water body, (2) contaminants may be dissolved in runoff that
enters the surface water body, (3) contaminants may be bound to
airborne particles that are deposited on the surface water body, (4)
vapor phase contaminants in air may be deposited on the surface water
body in precipitation (that is, wet deposition of vapor phase
contaminants), (5) vapor phase contaminants in air may enter the
surface water body through direct diffusion from the air, and (6)
contaminants in groundwater may discharge into the surface water body.
The model also accounts for processes that remove contaminants from the
surface water body. These include: (1) volatilization of contaminants
that are dissolved in surface water and (2) burial of contaminants in
the sediment at the bottom of the surface water body. The model assumes
that the impact to the water body is uniform, which is more realistic
for smaller surface water bodies than for larger ones. The model
estimates the concentrations of contaminants in the water column and
bed sediment. We used the water column or bed sediment concentrations
and bioconcentration factors (BCFs), bioaccumulation factors (BAFs), or
biota-sediment accumulation factors (BSAFs) to estimate contaminant
concentrations in fish tissue.
---------------------------------------------------------------------------
The model
estimates the concentrations of contaminants in the water column and
bed sediment. We used the water column or bed sediment concentrations
and bioconcentration factors (BCFs), bioaccumulation factors (BAFs), or
biota-sediment accumulation factors (BSAFs) to estimate contaminant
concentrations in fish tissue.
---------------------------------------------------------------------------
\14\ EPA. 1993. Addendum to Methodology for Assessing Health
Risks Associated with Indirect Exposure to Combustor Emissions. EPA/
600/AP-93003. Office of Health and Environmental Assessment,
Washington, DC.
---------------------------------------------------------------------------
vii. Indirect Exposure Equations
EPA uses a series of ``indirect exposure equations'' to quantify
the concentrations of contaminants that pass indirectly from
contaminated environmental media to the receptor. For example,
contaminants that are transported in air may be deposited on plants or
onto the soil where they may accumulate in forage, grain, silage or
soil that is consumed by beef cattle and dairy cattle. Individuals may
then ingest contaminated beef and dairy products. Similarly,
contaminants may be transported in groundwater to domestic groundwater
wells where the groundwater is extracted and used for showering. The
water vapor generated in the shower may be inhaled by the receptor. The
indirect exposure equations allow EPA to calculate exposure point
concentrations for these pathways and routes of exposure. The indirect
exposure equations used by EPA to conduct the chlorinated aliphatic
wastewater, EDC/VCM sludge, and methyl chloride sludge risk assessments
are presented in the Risk Assessment Technical Background Document for
the Chlorinated Aliphatics Listing Determination.
e. How Did EPA Quantify Contaminant Exposure and Toxicity?
Exposure is the condition that occurs when a contaminant comes into
contact with the outer boundary of the body, such as the skin, mouth
and nostrils
ater, EDC/VCM sludge, and methyl chloride sludge risk assessments
are presented in the Risk Assessment Technical Background Document for
the Chlorinated Aliphatics Listing Determination.
e. How Did EPA Quantify Contaminant Exposure and Toxicity?
Exposure is the condition that occurs when a contaminant comes into
contact with the outer boundary of the body, such as the skin, mouth
and nostrils. Once EPA establishes the concentrations of contaminants
at the points of exposure, EPA can estimate the magnitude of each
receptor's exposure, or the contaminant dose. Dose is the amount of the
contaminant that crosses the outer boundary of the body and is
available for absorption at internal exchange boundaries (lungs, gut,
skin; EPA 1992 15). For example, for exposure to a
carcinogen through ingestion of contaminated drinking water, dose is a
function of the concentration of the contaminant in drinking water (the
exposure point concentration), as well as certain ``exposure factors,''
such as how much drinking water the receptor consumes each day (the
intake rate), the number of years the receptor is exposed to
contaminated drinking water (the exposure duration), how often the
receptor is exposed to contaminated drinking water (the exposure
frequency), the body weight of the receptor, and the period of time
over which the dose is averaged.
---------------------------------------------------------------------------
\15\ 57 FR 22888. Final Guidelines for Exposure Assessment. U.S.
Environmental Protection Agency, May 29, 1992.
---------------------------------------------------------------------------
d drinking water (the exposure
frequency), the body weight of the receptor, and the period of time
over which the dose is averaged.
---------------------------------------------------------------------------
\15\ 57 FR 22888. Final Guidelines for Exposure Assessment. U.S.
Environmental Protection Agency, May 29, 1992.
---------------------------------------------------------------------------
EPA's primary source of exposure factors is the ``Exposure Factors
Handbook'' published by EPA in August 1997 (EPA 1997a 16).
For probabilistic risk analyses, EPA used the distributions of exposure
factor values provided in the Exposure Factors Handbook to develop PDFs
for exposure factors. The one situation where EPA does not develop an
expression of dose is the case where we use Reference Concentrations
(RfCs) 17 to estimate noncancer hazard for the inhalation
exposure route. In this situation, EPA calculates noncancer hazard from
concentration of the contaminant in air and the RfC, without
considering exposure factors (inhalation rate, body weight) other than
those inherent in the RfC.
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\16\ EPA. 1997a. Exposure Factors Handbook, Volumes I, II, and
III. Office of Research and Development, Washington, D.C., EPA/600/
P-95/002Fa, b, c. August 1997, www.epa.gov/ordntrnt/ord/webpubs/
exposure/index.html.
\17\ Very simply, an RfC is EPA's acceptable concentration in
air for a contaminant that causes non-cancer health effects. An RfC
is an estimate (with uncertainty spanning perhaps an order of
magnitude) of a continuous inhalation exposure to the human
population (including sensitive subgroups) that is likely to be
without an appreciable risk of deleterious noncancer effects during
a lifetime.
---------------------------------------------------------------------------
aminant that causes non-cancer health effects. An RfC
is an estimate (with uncertainty spanning perhaps an order of
magnitude) of a continuous inhalation exposure to the human
population (including sensitive subgroups) that is likely to be
without an appreciable risk of deleterious noncancer effects during
a lifetime.
---------------------------------------------------------------------------
We express the toxicity of contaminants as health benchmarks.
Health benchmarks include cancer slope factors (CSFs, EPA's measure of
cancer potency) 18 for oral exposure carcinogenic
contaminants; reference doses (RfDs, EPA's acceptable contaminant dose
via ingestion) 19 for oral exposure to noncarcinogenic
contaminants; inhalation CSFs for inhalation exposure to carcinogenic
contaminants; and RfCs for inhalation exposure to noncarcinogenic
contaminants. EPA derived inhalation CSFs from Unit Risk Factors (URFs)
for inhalation exposure to carcinogens. EPA uses Toxicity Equivalency
Factors (TEFs) to express the toxicity of specific dioxin congeners in
terms of the toxicity of 2,3,7,8-tetrachlorodibenzo-p-dioxin (2,3,7,8-
TCDD) (see Section III. D.1.g.ii. for an explanation of TEFs). Health
benchmark values are available from a number of sources. For the
chlorinated aliphatics wastewater, EDC/VCM sludge, and methyl chloride
sludge risk assessments, EPA established an order of preference for the
sources of health benchmarks. The order of preference is as follows
(from most preferred to least preferred): (1) the Integrated Risk
Information System (IRIS) online database of verified health benchmarks
(http://www.epa.gov/iris/subst/index.html) 20; (2) the
Health Effects Assessment Summary Tables (HEAST;
hyl chloride
sludge risk assessments, EPA established an order of preference for the
sources of health benchmarks. The order of preference is as follows
(from most preferred to least preferred): (1) the Integrated Risk
Information System (IRIS) online database of verified health benchmarks
(http://www.epa.gov/iris/subst/index.html) 20; (2) the
Health Effects Assessment Summary Tables (HEAST;
EPA 1997b) 21; (3) EPA's National Center for Environmental
Assessment (NCEA) provisional values, and (3) benchmarks developed by
the California Environmental Protection Agency (CALEPA) 22.
The specific health benchmarks used in the analysis are presented in
Appendix C of the Background Document for the Chlorinated Aliphatics
Risk Assessment.
---------------------------------------------------------------------------
\18\ A cancer slope factor is the slope of the dose-response
curve in the low-dose region. When low-dose linearity cannot be
assumed, the slope factor is the slope of the straight line from 0
dose (and 0 excess risk) to the dose at 1% excess risk. An upper
bound on this slope is usually used instead of the slope itself. The
units of the slope factor usually are expressed as 1/(mg/kg-day).
\19\ An RfD is an estimate (with uncertainty spanning perhaps an
order of magnitude) of a daily exposure to the human population
(including sensitive subgroups) that is likely to be without an
appreciable risk of deleterious effects during a lifetime.
\20\ EPA. 1998. Integrated Risk Information System. Online
database. (IRIS) Office of Research and Development (ORD).
Cincinnati, OH.
\21\ EPA. 1997b. Health Effects Assessment Summary Tables:
Annual Update. (HEAST) Office of Emergency and Remedial Response.
Washington, D.C. July.
\22\ California Environmental Protection Agency (CalEPA). 1997.
Air Toxics Hot Spots Program Risk Assessment Guidelines: Technical
Support Document for Determining Cancer Potency Factors. Draft for
Public Comment
elopment (ORD).
Cincinnati, OH.
\21\ EPA. 1997b. Health Effects Assessment Summary Tables:
Annual Update. (HEAST) Office of Emergency and Remedial Response.
Washington, D.C. July.
\22\ California Environmental Protection Agency (CalEPA). 1997.
Air Toxics Hot Spots Program Risk Assessment Guidelines: Technical
Support Document for Determining Cancer Potency Factors. Draft for
Public Comment. Office of Environmental Health Hazard Assessment,
Berkeley, CA, www.oehha.org/ra__guidance/.
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f. What Are the Risks From Exposure to Chlorinated Aliphatics
Wastewaters, and EDC/VCM and Methyl Chloride Sludges?
The following sections discuss EPA's estimates of individual and
population risk for chlorinated aliphatics wastewaters, EDC/VCM
sludges, and methyl chloride sludges.
i. What Are the Individual Risks?
EPA combined estimates of dose and estimates of toxicity (the
health benchmarks) to calculate individual incremental lifetime
carcinogenic risk estimates and hazard quotients for the potential
contaminants of concern in chlorinated aliphatic wastewaters, EDC/VCM
sludge, and methyl chloride sludge. Complete results of these
calculations are provided in the Risk Assessment Technical Background
Document for the Chlorinated Aliphatics Listing Determination. EPA
typically considers a decision to list a waste when carcinogenic risks
are 1x10-5 or greater or when the noncancer HQ is 1 or
greater. None of the contaminants generated noncancer hazards with an
HQ greater than 1, nor did the sum of the contaminant HQs exceed 1. In
summing carcinogenic risk estimates and noncancer hazard quotients, EPA
does not sum those risks or hazards that could not occur within the
lifetime of an individual
a waste when carcinogenic risks
are 1x10-5 or greater or when the noncancer HQ is 1 or
greater. None of the contaminants generated noncancer hazards with an
HQ greater than 1, nor did the sum of the contaminant HQs exceed 1. In
summing carcinogenic risk estimates and noncancer hazard quotients, EPA
does not sum those risks or hazards that could not occur within the
lifetime of an individual. For example, if estimated risks due to
nongroundwater pathways occur during the operating or post-closure life
of the unit (that is, due to releases to air and runoff/erosion) and
risk via the groundwater pathways are not projected to occur for
hundreds, or even thousands, of years due to long times required for
contaminant migration, then these two pathway risks would not be added
together.
The following sections present separately our deterministic and
probabilistic estimates of individual risk for:
Wastewaters from the production of chlorinated aliphatic
chemicals,
Wastewater treatment sludges from the production of EDC/
VCM, and
Wastewater treatment sludges from the production of methyl
chloride.
Chlorinated Aliphatic Wastewaters
Table III-1 summarizes the significant (greater than
1x10-5 risk estimates for chlorinated aliphatic wastewaters
managed in onsite aerated biological wastewater treatment tanks. The
highest deterministic risk estimate, 2x10-5, occurs for the
farmer. The risk is attributable to the farmer's ingestion of dioxins,
which in Table III-1 are expressed as the 2,3,7,8-tetrachlorodibenzo-p-
dioxin (TCDD) toxicity equivalent (TEQ). The farmer's high end
deterministic risk falls slightly below the 90th percentile
probabilistic risk estimate (the 80th percentile risk estimate is
1x10-5). Table III-2 summarizes our deterministic estimates
of risk due to the direct inhalation of chloroform. The high end
chloroform risks are 3x10-6 for the farmer and
2x10-6 for all other receptors
p-
dioxin (TCDD) toxicity equivalent (TEQ). The farmer's high end
deterministic risk falls slightly below the 90th percentile
probabilistic risk estimate (the 80th percentile risk estimate is
1x10-5). Table III-2 summarizes our deterministic estimates
of risk due to the direct inhalation of chloroform. The high end
chloroform risks are 3x10-6 for the farmer and
2x10-6 for all other receptors. The chloroform deterministic
risk estimates for the adult receptors are roughly equal to the 97.5th
percentile probabilistic risk estimates. Although the chloroform risks
are not greater than 1x10-5, they are additive to the risks
that EPA estimated for dioxins because they would occur within the same
timeframe.
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EDC/VCM Sludges
Tables III-3 and III-4 summarize the significant (greater than
1x10-5) risk estimates for EDC/VCM wastewater treatment
sludges managed in an onsite land treatment unit. In all cases, we
estimated that the highest risk occurs for the farmer. Table III-3
presents dioxin (expressed as 2,3,7,8-TCDD TEQ) risk estimates for the
land treatment unit nongroundwater pathways. The high end deterministic
risk estimate for the farmer is 2x10-4, which also
corresponds to the 95th percentile probabilistic risk
estimate. Table III-4 presents arsenic risk estimates for the land
treatment unit groundwater pathways. The high end deterministic risk
estimate for the farmer is 1x10-5, which falls between the
97.5th percentile probabilistic risk estimate
(6x10-6) and the 100th percentile probabilistic
risk estimate (5x10-5). EPA estimates that the groundwater
pathway risks in Table III-4 would occur approximately 1500 years in
the future, whereas the dioxin nongroundwater pathway risks in Table
III-3 would occur during the assumed operating life of land treatment
unit. Table III-5 summarizes the significant risk estimates for EDC/VCM
sludges managed in an offsite municipal landfill
listic
risk estimate (5x10-5). EPA estimates that the groundwater
pathway risks in Table III-4 would occur approximately 1500 years in
the future, whereas the dioxin nongroundwater pathway risks in Table
III-3 would occur during the assumed operating life of land treatment
unit. Table III-5 summarizes the significant risk estimates for EDC/VCM
sludges managed in an offsite municipal landfill. The risk estimates
presented in Table III-5 are arsenic groundwater pathway risks. The
high end deterministic risk estimate for the farmer is
3x10-5, which falls between the 97.5th percentile
(1x10-5) and 100th percentile (3x10-4)
probabilistic risk estimates. We estimate that the arsenic risks
attributable to the landfill (presented in Table III-5) would occur
thousands of years in the future.
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Methyl Chloride Sludges
EPA conducted a deterministic analysis to estimate nongroundwater
(air) pathway risks associated with management of methyl chloride
sludges in an onsite landfill. All nongroundwater pathway carcinogenic
risks were less than 1 x 10-8, and all noncancer HQs were
less than 0.0001.
For groundwater pathways, EPA performed a screening analysis that
maximizes estimates of risk or hazard to human receptors. EPA
calculated the carcinogenic risk for an adult who ingests (drinks) 1.4
liters of leachate from the landfill for 350 days per year for 58
years. EPA also calculated the noncancer hazard for a child who ingests
1.4 liters of leachate from the landfill for 350 days per year for 9
years. None of the noncancer HQs was greater than 1. Arsenic was the
only carcinogen with risk in excess of 1 x 10-5.
Specifically, an adult's risk due to ingesting leachate from methyl
chloride sludges for 58 years was 5 x 10-5 due to arsenic.
EPA discusses our evaluation of this risk in Section III.E.4.b.
ii
d who ingests
1.4 liters of leachate from the landfill for 350 days per year for 9
years. None of the noncancer HQs was greater than 1. Arsenic was the
only carcinogen with risk in excess of 1 x 10-5.
Specifically, an adult's risk due to ingesting leachate from methyl
chloride sludges for 58 years was 5 x 10-5 due to arsenic.
EPA discusses our evaluation of this risk in Section III.E.4.b.
ii. What are the Population Risks?
EPA expects that the population risks resulting from management of
chlorinated aliphatics wastewaters in tanks and EDC/VCM sludges in
onsite land treatment units and landfills are not significant. With
regard to groundwater pathway risks, EPA believes that the number of
domestic drinking water wells (thus the population) potentially
affected by groundwater contaminated with arsenic originating from the
landfill and the land treatment unit would be very small. Furthermore,
we estimate that the arsenic concentrations predicted in receptor
(drinking water) wells will result in risks only slightly above 1
x 10-5 for that very small number of people.
For nongroundwater pathways, EPA performed a screening evaluation
of population risk for the waste management scenario and pathway that
resulted in the greatest individual risk estimate of any pathway
evaluated in the chlorinated aliphatics risk assessment. Specifically,
EPA evaluated risk associated with ingestion of beef and dairy products
contaminated with dioxins derived from the onsite EDC/VCM land
treatment unit. As presented previously, under the land treatment unit
scenario the farmer's total individual excess lifetime cancer risk from
ingestion of beef and dairy was 2 x 10-4 for high end
exposures and 3 x 10-6 for central tendency exposures
fically,
EPA evaluated risk associated with ingestion of beef and dairy products
contaminated with dioxins derived from the onsite EDC/VCM land
treatment unit. As presented previously, under the land treatment unit
scenario the farmer's total individual excess lifetime cancer risk from
ingestion of beef and dairy was 2 x 10-4 for high end
exposures and 3 x 10-6 for central tendency exposures.
Although the individual risk estimates for the farmer exposed to
dioxins from EDC/VCM sludge managed in a land treatment unit are an
order of magnitude greater than those for the farmer exposed to dioxins
from chlorinated aliphatics wastewaters managed in tanks, is possible
that population risks resulting from releases from chlorinated
aliphatics wastewaters would exceed those resulting from releases from
EDC/VCM sludges. This might occur because there is only one land
treatment unit that is used to manage EDC/VCM sludge, and we expect
that there may be many aerated biological wastewater treatment tanks
used to manage chlorinated aliphatics wastewaters. Nevertheless, EPA
believes that it is reasonable to assume that the population risks for
the land treatment unit likely would be greater than those for the
wastewater tanks because there would need to be at least 10 wastewater
treatment tanks with surrounding cattle populations similar to that of
the land treatment unit to produce a population risk estimate
equivalent to that of the land treatment unit.
Results of the population risk analysis for the land treatment unit
indicate that 2 x 10-4 excess cancer cases would be
expected annually in a population of 1,410 individuals ingesting beef
produced from cattle raised within 2 kilometers of the land treatment
unit over a 40-year operational life for the land treatment unit (dairy
cattle are not raised in the county where the land treatment unit is
located, thus we did not evaluate ingestion of dairy products in the
population risk analysis)
cer cases would be
expected annually in a population of 1,410 individuals ingesting beef
produced from cattle raised within 2 kilometers of the land treatment
unit over a 40-year operational life for the land treatment unit (dairy
cattle are not raised in the county where the land treatment unit is
located, thus we did not evaluate ingestion of dairy products in the
population risk analysis). The average individual risk to the
population consuming beef from within the 2-kilometer radius is 2
x 10-7. We calculated the population potentially affected by
a release from the land treatment unit (1,410 individuals) from the
total estimated quantity of contaminated beef and average beef
ingestion rates (that is, we calculated how many people would be
required to consume all of the contaminated beef assuming typical rates
of beef ingestion). It is possible that the contaminated beef would be
distributed more widely throughout the population, such that the total
number of people ingesting the contaminated beef would be greater than
1,410. However, the population risk estimate would not change because
population risk is a function of the number of people who are exposed
(that is, consume contaminated beef) and each person's individual risk
(which is a function of the amount of contaminated beef a person
consumes). Consequently, as the number of people who are exposed
increases, the individual risk must decrease proportionally because
there is only a finite amount of contaminated beef, and the overall
population risk remains the same. The Risk Assessment Technical
Background Document for the Chlorinated Aliphatics Listing
Determination provides a description of the procedure used to estimate
population risks.
EPA did not estimate population risks for the other receptors for
whom we calculated individual risk estimates (residents, children,
gardeners, and fishers)
ed beef, and the overall
population risk remains the same. The Risk Assessment Technical
Background Document for the Chlorinated Aliphatics Listing
Determination provides a description of the procedure used to estimate
population risks.
EPA did not estimate population risks for the other receptors for
whom we calculated individual risk estimates (residents, children,
gardeners, and fishers). Because the high end risk for the land
treatment unit scenario was driven by the ingestion of beef and dairy
products, the population risks for non-farmer receptors are expected to
be considerably lower than 2 x 10-4.
Although the population risks attributable to the management of
chlorinated aliphatics wastes are expected to be very small, EPA does
not believe it is appropriate to allow contamination from waste
management activities to cause substantial risk to nearby residents
simply because there are few individuals in the immediate vicinity of
the waste management units. 40 CFR 261.11 clearly states that wastes
are to be listed if they are ``capable of posing a substantial present
or potential hazard.'' It does not state that a large number of people
must be affected. However, population risk may be a factor that the
Agency could consider under 40 CFR 261.11(a)(3)(xi) (``other factors as
may be appropriate'').
EPA's Guidance for Risk Characterization (EPA 1995) states that
when small populations are exposed, population risk estimates may be
very small, however, ``in such situations, individual risk estimates
will usually be a more meaningful parameter for decision-makers.''
Consequently, EPA's decision to list wastes has been based primarily on
the concern over risks to those individual's who are significantly
exposed, even if there are relatively few such individuals. EPA,
however, requests comment on whether it would be appropriate to give
weight to population risk in deciding whether to list these chlorinated
aliphatic wastes as hazardous
decision-makers.''
Consequently, EPA's decision to list wastes has been based primarily on
the concern over risks to those individual's who are significantly
exposed, even if there are relatively few such individuals. EPA,
however, requests comment on whether it would be appropriate to give
weight to population risk in deciding whether to list these chlorinated
aliphatic wastes as hazardous. EPA further invites comment on the
effect of this approach on the Agency's goals with respect to
environmental justice in rural areas.
g. What Is the Toxicity of COCs Identified by EPA?
The two contaminants for which EPA calculated significant risks are
dioxins (expressed as the 2,3,7,8-TCDD TEQ) and arsenic. The following
sections discuss the ways that these contaminants affect human health.
i. Arsenic
Arsenic is a naturally occurring element in the earth's crust that
usually exists as an inorganic or organic compound, rather than in a
free state. Arsenic that exists in compounds with elements such as
oxygen, chlorine, and sulfur is referred to as inorganic arsenic;
arsenic combined with carbon is referred to as organic arsenic. Organic
forms of arsenic are less toxic than inorganic forms.
There is clear evidence that chronic exposure to inorganic arsenic
in humans increases the risk of cancer, and EPA classifies inorganic
arsenic as a Group A--Known Human Carcinogen. Studies report that
inhalation of arsenic results in an increased risk of lung cancer. In
addition, ingestion of arsenic has been associated with an increased
risk of nonmelanoma skin cancer and bladder, liver, kidney, and lung
cancer. No information is available on the risk of cancer in humans
from dermal exposure to arsenic (EPA 1998).
ii. Dioxins
2,3,7,8-Tetrachlorodibenzo-p-dioxin (2,3,7,8-TCDD) belongs to the
class of compounds, chlorinated dibenzo-p-dioxins and chlorinated
dibenzofurans, that are referred to as dioxins. EPA issued a draft
Health Assessment Document for 2,3,7,8-TCDD and Related Compounds in
1994
ncer. No information is available on the risk of cancer in humans
from dermal exposure to arsenic (EPA 1998).
ii. Dioxins
2,3,7,8-Tetrachlorodibenzo-p-dioxin (2,3,7,8-TCDD) belongs to the
class of compounds, chlorinated dibenzo-p-dioxins and chlorinated
dibenzofurans, that are referred to as dioxins. EPA issued a draft
Health Assessment Document for 2,3,7,8-TCDD and Related Compounds in
1994. This document is a three-volume series consisting of a complete
reassessment of the toxic effects of 2,3,7,8-TCDD (EPA 1994a, b \23\).
The document was reviewed by EPA's Science Advisory Board (SAB) but has
not yet been issued in final form.
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\23\ EPA. 1994a. Health Assessment Document for 2,3,7,8-
Tetrachlorodibenzo-p-Dioxin (TCDD) and Related Compounds. Volume II.
(Draft). Office of Research and Development, Washington, D.C.,
www.epa.gov/ord/health.
EPA. 1994b. Health Assessment Document for 2,3,7,8-
Tetrachlorodibenzo-p-Dioxin (TCDD) and Related Compounds. Volume
III. (Draft). Office of Research and Development, Washington, D.C.,
www.epa.gov/ord/health.
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EPA has classified 2,3,7,8-TCDD as a Group B2--Probable Human
Carcinogen (EPA 1997b). An increase in lung cancer risks was observed
among Japanese males exposed to 2,3,7,8-TCDD as a result of an oil
poisoning accident. Human studies have also found an association
between 2,3,7,8-TCDD and soft-tissue sarcomas, lymphomas, and stomach
carcinomas, although for malignant lymphomas, the increase in risk is
not consistent. The increase in risk is of borderline significance for
highly exposed groups and is less among groups exposed to lower levels
of 2,3,7,8-TCDD (EPA 1994b). In animal tests, TCDD is one of the most
potent carcinogens ever evaluated.
Although EPA has not developed an RfD or an RfC for 2,3,7,8-TCDD,
noncarcinogenic health effects have been reported for 2,3,7,8-TCDD
ase in risk is
not consistent. The increase in risk is of borderline significance for
highly exposed groups and is less among groups exposed to lower levels
of 2,3,7,8-TCDD (EPA 1994b). In animal tests, TCDD is one of the most
potent carcinogens ever evaluated.
Although EPA has not developed an RfD or an RfC for 2,3,7,8-TCDD,
noncarcinogenic health effects have been reported for 2,3,7,8-TCDD. The
major noncarcinogenic effect from exposure to 2,3,7,8-TCDD is
chloracne, a severe acne-like condition that develops within months of
first exposure to high levels of 2,3,7,8-TCDD. For many individuals,
the condition disappears after discontinuation of exposure, for others
it may remain for years. There are limited human data to suggest the
doses at which chloracne is likely to occur (EPA 1994a, b).
Epidemiological studies report conflicting evidence on the
immunotoxicity of 2,3,7,8-TCDD in humans. Some studies suggest evidence
of immunotoxicity, such as alterations in lymphocyte populations, cell
surface markers, or lymphocyte proliferative response (ATSDR 1997c
\24\). However, studies have not reported changes in the immune system
directly related to 2,3,7,8-TCDD exposure (EPA 1994a, b). An
association has been reported between levels of male reproductive
hormones and 2,3,7,8-TCDD exposure. Decreased testosterone levels were
detected in several human studies, and animal data are available to
support these findings. Other effects noted in human studies include an
association between 2,3,7,8-TCDD exposure and the following:
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\24\ ATSDR (Agency for Toxic Substances and Disease Registry).
1997c. Toxicological Profile for 2,3,7,8-Tetrachlorodibenzo-p-
dioxin. U.S. Public Health Service, U.S. Department of Health and
Human Services, Atlanta, GA.
---------------------------------------------------------------------------
sure and the following:
---------------------------------------------------------------------------
\24\ ATSDR (Agency for Toxic Substances and Disease Registry).
1997c. Toxicological Profile for 2,3,7,8-Tetrachlorodibenzo-p-
dioxin. U.S. Public Health Service, U.S. Department of Health and
Human Services, Atlanta, GA.
---------------------------------------------------------------------------
An increased risk of diabetes and an elevated prevalence
of abnormal fasting serum glucose levels
The induction of cytochrome P-450 1A1, an enzyme involved
in biotransformation reactions
Elevation of gamma glutamyl transferase, a liver enzyme
A possible increased risk of endometriosis, a disease of
the female reproductive system (EPA 1994a, b).
Animal studies report reproductive and developmental effects from
exposure to 2,3,7,8-TCDD. These studies suggest that altered
development may be among the most sensitive endpoints of 2,3,7,8-TCDD
exposure. Developmental toxicity has been reported to occur in several
animal species at lower levels than male and female reproductive
toxicity effects. 2,3,7,8-TCDD appears to affect a large number of
critical developmental effects at specific developmental stages. These
changes can lead to increases in fetal mortality, disruption of organ
system structure, and irreversible impairment of organ function.
Developmental toxicity from 2,3,7,8-TCDD has been seen in fish, birds,
and mammals (EPA 1994a, b).
EPA assigned 17 dioxin and furan congeners individual toxicity
equivalency factors (TEFs). TEFs are estimates of the toxicity of
dioxin-like compounds relative to the toxicity of TCDD, which is
assigned a TEF of 1.0. We used the TEFs identified as the I-TEFs
(International-TEFs) to conduct the chlorinated aliphatics risk
assessment because, until very recently, this is the TEF scheme EPA
scientists have recommended and used for the last 10 years (EPA 1989)
\25\ \26\. Documentation supporting the use of the TEFs has been placed
in the rulemaking record
the toxicity of TCDD, which is
assigned a TEF of 1.0. We used the TEFs identified as the I-TEFs
(International-TEFs) to conduct the chlorinated aliphatics risk
assessment because, until very recently, this is the TEF scheme EPA
scientists have recommended and used for the last 10 years (EPA 1989)
\25\ \26\. Documentation supporting the use of the TEFs has been placed
in the rulemaking record.
---------------------------------------------------------------------------
\25\ EPA. 1989. Interim Procedures for Estimating Risks
Associated with Exposure to Mixtures of Chlorinated Dibenzo-p-
Dioxins and Furans (CDDs and CDFs) and 1989 Update. EPA/625/3-89/
016. Risk Assessment Forum. March.
\26\ Proposed Rule, ``Addition of Dioxin and Dioxin-Like
Compounds; Modification of Polychlorinated Biphenyls (PCBs) Listing;
Toxic Chemical Release Reporting; Community Right-to-Know,'' 62 FR
24887, (May 7, 1997).
---------------------------------------------------------------------------
The I-TEFs are presented in Table III-6. The I-TEFs are based on a
limited data base of in vivo and in vitro toxicity testing (EPA 1989).
The World Health Organization (WHO) recently reviewed the I-TEFs (Van
den Berg et al. 1998) \27\, and determined that three of the I-TEFs,
those for 1,2,3,7,8-PeCDD (pentachlorodibenzo-p-dioxin), OCDD
(octachlorodibenzo-p-dioxin), and OCDF (octachlorodibenzofuran),
required modification (Table III-6). EPA is in the process of adopting
these modifications, and consequently reviewed the impact that the
revised (WHO-) TEFs would have on the results of the chlorinated
aliphatics risk assessment. 1,2,3,7,8-PeCDD was not detected in
dedicated chlorinated aliphatic wastewaters, dedicated EDC/VCM sludges,
or methyl chloride sludges. Consequently, the difference in the I-TEF
and the WHO-TEF for 1,2,3,7,8-PeCDD has no impact on the results of the
risk analyses presented in this section
ct that the
revised (WHO-) TEFs would have on the results of the chlorinated
aliphatics risk assessment. 1,2,3,7,8-PeCDD was not detected in
dedicated chlorinated aliphatic wastewaters, dedicated EDC/VCM sludges,
or methyl chloride sludges. Consequently, the difference in the I-TEF
and the WHO-TEF for 1,2,3,7,8-PeCDD has no impact on the results of the
risk analyses presented in this section. Because of the TEF differences
for OCDD and OCDF, however, the decision to use either the I-TEFs or
the WHO-TEFs potentially may result in large differences in the
calculated TCDD TEQ concentrations for a given chlorinated aliphatics
waste sample. Nevertheless, because OCDD and OCDF contribute very
little to the actual risk attributable to dioxin compounds, the
decision to use either
the I-TEFs or the WHO-TEFs has negligible impact to the overall risk
results. The Risk Assessment Technical Background Document for the
Chlorinated Aliphatics Listing Determination provides separate risk
results for each of the dioxin congeners detected in the wastewaters
and sludges evaluated.
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\27\ Van den Berg, et al. 1998. Toxic Equivalency Factors (TEFs)
for PCBs, PCDDs, PCDFs for Humans and Wildlife. Environmental Health
Perspectives, v.106, n.12, pp. 775-792. December.
Table III-6. Toxicity Equivalency Factors (TEFs) for Dioxin Compounds
------------------------------------------------------------------------
Compound I-TEF WHO-TEF
------------------------------------------------------------------------
2,3,7,8-TCDD............................ 1 same
1,2,3,4,5,7,8,9-OCDD.................... 0.001 0.0001
1,2,3,7,8,9-HxCDD....................... 0.1 same
1,2,3,4,6,7,8-HpCDD..................... 0.01 same
1,2,3,4,6,7,8,9-OCDF.................... 0.001 0.0001
1,2,3,4,7,8-HxCDD,...................... 0.1 same
1,2,3,7,8-PeCDD,........................ 0.5 1
2,3,7,8-TCDF............................ 0.1 same
1,2,3,4,7,8,9-HpCDF....................
same
1,2,3,4,5,7,8,9-OCDD.................... 0.001 0.0001
1,2,3,7,8,9-HxCDD....................... 0.1 same
1,2,3,4,6,7,8-HpCDD..................... 0.01 same
1,2,3,4,6,7,8,9-OCDF.................... 0.001 0.0001
1,2,3,4,7,8-HxCDD,...................... 0.1 same
1,2,3,7,8-PeCDD,........................ 0.5 1
2,3,7,8-TCDF............................ 0.1 same
1,2,3,4,7,8,9-HpCDF..................... 0.01 same
2,3,4,7,8-PeCDF......................... 0.5 same
1,2,3,7,8-PeCDF......................... 0.05 same
1,2,3,6,7,8-HxCDF....................... 0.1 same
1,2,3,6,7,8-HxCDD....................... 0.1 same
2,3,4,6,7,8-HxCDF....................... 0.1 same
1,2,3,4,6,7,8-HpCDF..................... 0.01 same
1,2,3,4,7,8-HxCDF....................... 0.1 same
1,2,3,7,8,9-HxCDF....................... 0.1 same
------------------------------------------------------------------------
h. What Is the Uncertainty in the Human Health Risk Results?
EPA typically classifies the major areas of uncertainty in risk
assessments as parameter uncertainty, scenario uncertainty, and model
uncertainty. This section identifies the primary sources of each of
these types of uncertainty in the chlorinated aliphatics risk
assessment, and qualitatively describes how each may influence the
results of the risk assessment.
Many of the parameters that we used to quantify contaminant fate
and transport and contaminant exposure and dose either were not
measured or could not be measured precisely and/or accurately. Some of
the most important and sensitive parameters in our analyses include
those that describe waste composition; waste management practices; site
characteristics (for example, hydrogeological, topographical,
meteorological, and soils data); the physiologic and behavioral
exposure characteristics of the receptors; the physical, chemical, and
biochemical properties of the contaminants; and toxicological effects.
We believe that the primary sources of parameter uncertainty include
the following:
position; waste management practices; site
characteristics (for example, hydrogeological, topographical,
meteorological, and soils data); the physiologic and behavioral
exposure characteristics of the receptors; the physical, chemical, and
biochemical properties of the contaminants; and toxicological effects.
We believe that the primary sources of parameter uncertainty include
the following:
The risk analyses were based on a limited set of waste
sample data. It is possible that these data do not represent the
true distribution of contaminant concentrations in the waste
categories evaluated, resulting in either an overestimation or
underestimation of the actual risk to receptors.
EPA obtained little site-specific information regarding
waste management units for the chlorinated aliphatics industry,
necessitating that we make a number of assumptions regarding waste
management in off-site landfills, the land treatment unit, and
wastewater tanks. Many of the facilities reported using offsite
nonhazardous landfills to dispose of EDC/VCM sludges. We assumed
that these landfills are municipal landfills, and modeled typical
municipal landfills based on available data. Our major assumptions
about the municipal landfills that have the effect of decreasing our
risk estimates are that the landfills have daily covers and run-on/
run-off controls. Our major assumptions about the municipal
landfills that have the effect of increasing our risk estimates are
that the landfills are not lined and have no leachate collection
systems. For the land treatment unit, we assumed that no run-on/run-
off controls were present to mitigate risk
ffect of decreasing our
risk estimates are that the landfills have daily covers and run-on/
run-off controls. Our major assumptions about the municipal
landfills that have the effect of increasing our risk estimates are
that the landfills are not lined and have no leachate collection
systems. For the land treatment unit, we assumed that no run-on/run-
off controls were present to mitigate risk. We assumed that the
industry's wastewater treatment tanks are uncovered (which increases
our risk estimates), are aerated (which increases our risk
estimates), employ biological treatment techniques (which decreases
our risk estimates), have structural integrity (which decreases our
risk estimates), and have spill and overflow controls (which
decreases our risk estimates).
We typically used regional databases to obtain the
parameter values necessary to model contaminant fate and transport.
Because the data that we used are not specific to the facilities at
which the actual wastes are managed, the data represent our best
estimates of actual site conditions. Use of these databases in lieu
of site-specific data may result in either overestimates or
underestimates of risk.
Sources of uncertainty in toxicological benchmarks
include one or more of the following: extrapolation from laboratory
animal data to humans, variability of response within the human
population, extrapolation of responses at high experimental doses
under controlled conditions to low doses under highly variable
environmental conditions, and adequacy of the database (number of
studies available, toxic endpoints evaluated, exposure routes
evaluated, sample sizes, length of study, etc.). Toxicological
benchmarks are designed to be conservative (that is, overestimate
risk) because of the uncertainties and challenges associated with
condensing toxicity data into a single quantitative expression.
Therefore, use of the current toxicological benchmarks most likely
overestimated risk for the pathways evaluated
uated, exposure routes
evaluated, sample sizes, length of study, etc.). Toxicological
benchmarks are designed to be conservative (that is, overestimate
risk) because of the uncertainties and challenges associated with
condensing toxicity data into a single quantitative expression.
Therefore, use of the current toxicological benchmarks most likely
overestimated risk for the pathways evaluated.
EPA estimated the risk of developing cancer from the
estimated lifetime average daily dose and the slope of the dose-
response curve. A cancer slope factor is derived from either human
or animal data and is taken as the upper bound on the slope of the
dose-response curve in the low-dose region, generally assumed to be
linear, expressed as a lifetime excess cancer risk per unit
exposure. However, individuals exposed to carcinogens in the first
few years of life may be at increased risk of developing cancer. For
this reason, EPA recognizes that significant uncertainties and
unknowns exist regarding the estimation of lifetime cancer risks in
children. We also note that the analysis of cancer risks in children
has not been externally peer reviewed.
We expect that the various sources of parameter uncertainty in our risk
assessment counterbalance each other, such that parameter uncertainty
will not result in a significant overall increase or decrease in risk.
Scenario uncertainty results from the assumptions we make regarding
how receptors become exposed to contaminants. This uncertainty occurs
because of the difficulty and general impracticality of making actual
measurements of a receptor's exposure. Exposure modeling relies heavily
on default assumptions regarding population activity patterns,
mobility, dietary habits, body weights, and other factors
rio uncertainty results from the assumptions we make regarding
how receptors become exposed to contaminants. This uncertainty occurs
because of the difficulty and general impracticality of making actual
measurements of a receptor's exposure. Exposure modeling relies heavily
on default assumptions regarding population activity patterns,
mobility, dietary habits, body weights, and other factors. Because the
risk estimates presented in today's notice are for hypothetical chronic
exposures and are designed to provide a realistic range of potential
receptor exposure sc
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