24401-16
BACKGROUND DOCUMENT
i
RESOURCE CONSERVATION AND RECOVERY ACT
SUBTITLE C - HAZARDOUS WASTE MANAGEMENT
SECTION 3001 - IDENTIFICATION AND LISTING
OF HAZARDOUS WASTE?
SECTION 261.24 - EP TOXICITY CHARACTERISTIC
ENVIRONMENTAL PROTECTION AGENCY
OFFICE OF SOLID WASTE
May 2, 1980
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Index to Extraction Procedure Toxicity Characteristic
Background Document
Page
I. Proposed Regulation 1
II. Development and Rationale for the Characteristic 7
A. Need for Toxicity Characteristic 7
B. Nature of Toxicity Regulated Under the Subtitle C 8
Regulat ions
C. Scope of the Toxicity Characteristic 12
1. Aspects of Toxicity Outside the Scope of the 13
Toxicity Characteristic
a. Chronic Toxicity of Wastes Containing 13
Contaminants Other than those Included in
the National Interim Primary Drinking Water
Standards
b. Careinogenicity 14
c. Mutagenicity 15
d. Teratogenicity 16
e. Chronic Toxicity to Fish 17
f. Phytotoxicity 18
D. Major Postulates Contained in the Characteristic 18
1. Choice of Groundwater Exposure Pathway 18
2. Choice of Particular Disposal Environment Model 20
a. Choice of Landfill Disposal 20
b. Choice of Degree of Simulated Leaching Activity 22
1) The Leaching Simulation Test 22
2) Arguments That the Leaching Test is Overly 24
Aggres s ive
3) Arguments That the Leaching Test is 29
Insufficiently Agressive
c. Remaining Features of the Waste Disposal Model 31
3. Thresholds to Determine Unacceptable Levels of 33
Cont aminat ion
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Page
III. Rationale for the Extraction Procedure 37
A. Genesis of the Extraction Procedure 37
B. Choice of a Batch Test 40
C. Maximum Concentration Versus Cumulative Release 41
D. Explanation of How the EP Models Physical Factors 43
Which Influence Leachate Formation in the Assumed
Disposal Environment
1. Sample Preparation 44
a. Liquid - Solid Separation 44
1) Sample Filtration 45
b., Sample Homogeniz at ion/Part ic le Size Reduction 47
(including Structural Integrity Procedure)
2. Leaching Media Composition 52
3. Sample to Extractant Ratio 56
4. Agitation Methods, Number of Elutions and 58
Extraction Contact Time
a. Agitation Methods 58
b. Extraction Contact Time 60
c. Number of Elutions 63
5. Post - Extraction Sample Handling 64
IV. Basis for Attenuation Factor Used in Relating National 66
Interim Primary Drinking Water Standards to EP Extract
Values
A. Attenuation of Constituent Concentrations in Leachate 67
B. EPA's Choice of An Attenuation Factor 75
V. Response to Comments Received on the Proposal and on 81
the Noticed Reports
A. Adopt Existing Regulations 81
B. Suitability of EP As A Regulatory Tool 84
• •
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Page
1. Appropriateness as a General Tool for Determining 85
Whether a Waste is a Hazardous Waste
2. Acceptance by Scientific Community 86
3. Reproducibility of Test Procedure 89
4. Accuracy of Test Procedure 103
5. Propriety of Requiring Excercise of Scientific 105
Judgment
C. Failure to Distinguish Between Chromium III & 109
Chromium VI
D. Operational Problems 113
1. Liquid-Solid Separation Procedure 114
2. Structural Integrity Procedure/Grinding 119
3. Agitation 123
4. Adjustment of Extract pH 126
5. Sample to Extractant Ratio 127
6. Final Volume Adjustment 129
7. Analysis of Multiphasic Extracts 130
8. Extract Toxicity 131
E. Economics of Testing 132
F. Specific Comments on the Noticed Reports 133
VI. Promulgated Regulation 148
VII. Bibliography 158
in
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I. Proposed Regulation
(1) Definition
A solid waste is a hazardous waste if, according to
the methods specified in paragraph (2), the extract obtained
from applying the Extraction Procedure (EP) cited below
to a representative sample of the waste has concentrations
of a contaminant that exceeds any of the following values:
Extract level
Contaminant: milligrams per liter
Arsenic 0.50
Barium 10.0
Cadmium 0.10
Chromium 0.50
Lead 0.50
Mercury 0.02
Selenium 0.10
Silver 0.50
Endrin (l,2,3,4,10,10-hexacloro-6,7-
epoxy-l,4,4a,5,6,7,8,8a-octahydro-l,
4-endo, endo-5,8-dimethanonaph-
thalene) 0.002
Lindane (1,2,3,4,5,6 hexachlorocyclo hexane
gamma isomer) 0.040
Methoxychlor (1,1,1-Trichloroethane)
2,2-bis ( p-methoxypheny ) 1.0
Toxaphene (C H CL - technical chlorinated
camphene, 67-69 percent cholrine) 0.050
2,4-D, (2,4-Dichlorophenoxyacetic acid 1.0
2,4,5-TP (Silvex) (2,4,5-
Trich lorophenoxypropionic acid 0.10
NOTE: - Extract levels specified for the above substances
equal ten times the EPA National Interim Primary Drinking
Water Standards for these substances. These standards
are being revised. Extract levels specified above will
be changed to reflect revisions to these standards. Also,
EPA is considering use of the Water Quality Criteria under
the Clean Water Act as a basis .for setting extract levels,
in addition to the EPA National Interim Primary Drinking
Water Standards.
(2) Identification Method
(i) Extraction procedure. (2) Identification method.
(A) Take a representative sample (minimum size 100 gms)
of the waste to be tested and separate it into its
component phases using either the filtration method or
the centrifugation method described in this section.
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Reserve the liquid fraction under refrigeration at 1-5°C
(34-4l°F) for use as described in paragraph (F) of this
section.
(1) Filtration Method.
Equipment: Millipore YY22 142 30 filter holder (Millipore
Corp., Beford, MA, 01730) equipped with an XX42 142 08 necessary
1.5 liter reservoir, or Nuclepore Corp., Pleasanton, CA 94566)
equipped with a 1.5 liter reservoir, or equivalent filter holder.
Procedure: 1. Using the filter holder place a 0.45 micron
filter membrane (Millipore type HAWP142, Nuclepore type 112007,
or equivalent) on the support screen. On top of the membrane
(upstream) place a prefilter (Millipore AP25124, Nuclepore
P040, or equivalent). Secure filter holder as directed in
manufacturer's instructions.
2. Fill the reservoir with the sample to be separated,
pressurize to no more than 75 psi (7 kg/cm^), and filter
until no significant amount of fluid (o.5 ml) is released
during a 30 minute period.
3. After liquid flow stops, depressurize and open the top
of the reservoir, invert the filter unit, replace filter pads
as in step 1. above, and resume filtering. Save pads for
later use. Repeat this step until no more fluid can be removed
from the waste at a pressure of 75 psi (7kg/cm2).
4. Take the solid material, and any pads used in filtration,
and extract as described in paragraph (B). Subtract tare
weights of filter pads in calculating the amount of solid
material.
(2) Centrifugation Method
Equipment: Centrifuge (e.g. Damon-IEC catalog no. 7165,
Damon-IEC Corp., Needham Heights, MA, or equivalent) equipped
with a rotor for 600 ml to 1 liter containers (Damon-IEC
catalog no. 976, or equivalent). For flammable material
containing wastes, explosion proof equipment is recommended.
Procedure 1. Centrifuge sample for 30 minutes at 2300 rpm.
Hold temperature at 20-40°C (68-104°F).
2. Using a ruler, measure the size of the liquid and solid
layers, to the nearest mm (0.40 inch). Calcuate the liquid
to solid rat io.
3. Repeat 1 and 2 above until the liquid: solid ratio calculated
after two consecutive 30 minute centrifugations is within 3%.
4. Decant or siphon off the layers and extract the solid as
described in paragraph B.
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(B) Take the solid portion obtained in paragraph (i), and
prepare it for extraction by either grinding it to pass
through 9.5 mm (3/8) standard sieve or by subjecting it
to the following structural integrity procedure.
STRUCTURAL INTEGRITY PROCEDURE
Equipment: Compaction tester having a 1.25 inch diameter
hammer weighing 0.73 Ibs. and having a free fall of 6 inches
(Figure 1) (one suitable device is the Associated Design and
Manufacturing Company, Alexdria, Va. 22314, catalog no. 125).
Procedure: 1. Fill the sample holder with the material to be
tested. If the waste sample is a monolithic block, then cut
out a representive sample from the block having the dimensions
of a 1.3" dia. x 2.8" cylinder.
2. Place the sample holder into the Compaction Tester and
apply 15 hammer blows to the sample.
3. Remove the now compacted sample holder and transfer it
do the extraction apparatus for extraction.
(C) Take the solid material from paragraph (B), weight it
and place it in an extractor. A suitable extractor will not
only prevent stratification of sample and extraction fluid
but also insure that all sample surfaces are continuously
brought into contact with well mixed extraction fluid. When
oprated at greater than or equal to 40 rpm, one suitable device
is shown in figure 2 and available as Part No. 3736 produced by
Associated Design and Mfg. Co., Alexandria, Va. 22314)
(D) Add to the extractor a weight of deionized water equal to
16 times the weight of solid material added to the extractor.
This includes any water used in transferring the solid material
to the extractor..
(E) Begin agitation and adiust the pH of the solution to 5.0+ 0
using 0.5N acetic acid. Hold the pH at 5.0+0.2 and continue
agitation for 24+0.5 hours. If more than 4 ml of acid for each
gm of solid is required to hold the pH at 5, then once 4 ml of
acid per gm has been added, complete the 24 hour extraction
without adding any additional acid. Maintain the extractant
at 20-40°C (68-104°F) during extraction. It is recommended that
a device such as the type 45-A pH Controller manufactured by
Chemtrix, Inc. Hillsboro, OR 97123, or equivalent, be used for
controlling pH. If such a device is not available then the
following manual procedure can be employed.
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MANUAL pH ADJUSTMENT
1. Calibrate pH meter in accordance with manufacturer's
specificat ions.
2. Add 0.5N acetic acid and adiust pH of solution to 5.0 + 0.2.
If more than 4 ml of solution to 5.0 + 0.2. If more than 4 ml
of acid for each gm of solid is required to hold the pH at 5,
then once 4 ml of acid per gm has been added complete the 24
hour extraction without adding any additional acid. Maintain
the extractant at 20-40°c (68-104° F) during extraction. -
3. Manually adjust pH of solution at 15,-30, and 60 minute
intervals moving to the next longer interval if the pH did
not have to be adjusted more than 0.5 pH units since the
previous adjustment.
4. Continue adjustment procedure for a period of not less than
6 hours.
5. Final pH after a 24 hour period must be within the range
4.9-5.2; unless 4 ml of acid per gram of solid has already
been added.
6. If the conditions of 5 are not met, continue pH adjustment
at approximately one hour intervals for a period of not less
than 4 hours.
(F) At the end of the 24 hour extraction priod, separate the
material in the extractor into solid and liquid phases as in
paragraph (A). Adjust the volume of the resulting liquid phase
with deionized water so that its volume is 20 times that occupied
by a quantity of water at 4° C equal in weight to the initial
quantity of solid material charged to the extractor (e.g., for
an initial weight of 1 gm, dilute to 20 ml). Combine this
solution with the original liquid phase from paragraph (A).
This combined liquid, and any precipitate which may later
form, is the Extraction Procedure Extract.
(ii) Analysis - Analyses conducted to determine conformance with
Section 250.13(b)(l) shall be made in accordance with the
following or equivalent methods:
(A) Arsenic - Atomic Absorption Method, "Methods for Chemical
Analysis of Water and Wastes," pp. 95-96, Environmental Protection
Agency, Office of Technology Transfer, Washington, D. C. 20460,
1974.
(B) Barium - Atomic Absorption Method, "Standard Methods for
the Examination of Water and Wastewater" latest edition, or
Methods for Chemical Analysis of Water and Wastes, "pp. 97-98,
Environmental Protection Agency, Office of Technology Transfer,
Washington, D. C. 20460, 1974.
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(C) Cadmium - Atomic Absorption Method, "Standard Methods
for the Examination of Water and Wastewater", latest edition,
or "Methods for Chemical Analysis of Water and Wastes".
pp. 101-103, Environmental Protection Agency, Office of
Technology Transfer, Washington, D. C. 20460, 1974.
(D) Chromium - Atomic Absorption Method, "Standard Methods
for the Examination of Water and Wastewater", latest edition, or
"Methods for Chemical Analysis of Water and Wastes", pp. 112-112,
Environmental Protection Agency, Office of Technology Transter,
Washington, D. C. 20460, 1974.
(E) Lead - Atomic Absorption Method, "Standard Methods for
the Examinations of Water and Wastewater", latest edition, or
"Methods for Chemical Analysis of Water and Wastes", pp. 112-
113, Environmental Protection Agency, Office of Technology
Transfer, Washington, D. C. 20460, 1974.
(F) Mercury - Flameless Atomic Absorption Method, "Methods
for Chemical Analysis of Water and Wastes," pp. 118-126,,
Environmental Protection Agency, Office of Technology Transfer,
Washington, D. C. 20460.
(G) Selenium - Atomic Absorption Method, "Methods for
Chemical analysis of Water and Wastes," p. 145, Environmental
Protection Agency, Office of Technology Transfer, Washington,
D. C. 20460, 1974.
(H) Silver - Atomic Absorption Method, "Standard Method for
the Examination of Water and Wastewater," latest edition, or
Methods for Chemical Analysis of Water and Wastes", p. 146,
Environmental Protection Agency, Office of Technology Transfer,
Washington, D. C. 20460, 1974.
(I) Endrin, Lindane, Methoxychlor, or Toxaphene - as
desribed in "Method for Organochlorine Pesticides in Industrial
Effluents", MDOARI, Environmental Protection Agency, Cincinnati,
Ohio, November 28, 1973.
(J) 2,4-D and 2,4,5-TP Silver-as described in "Methods
for Chlorinated Phenoxy Acid Herbicides in Industrial Effluents,"
MDQARI, Environmental Protection Agency, Cincinnati, Ohio,
November 28, 1973.
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Figure 1
COMBINED
WEIGHT
.73 Lb:
•U5D
/-SAMPLE
/ /-POLYURETHANE
L—^SAMPLE HOLDER
1.3D
28
1
COMPACTION TESTER
ft , ' • -'
Polyurethane foam shall conform to requirements
for Grade 21, performance Grade AD or BD,
established In ASTM Standard D3453.
Figure 2
NON CLOGGING SUPPORT BUSHING
1 inch BLADE AT 30° TO HORIZONTAL
vo
EXTRACTOR
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II. DEVELOPMENT AND RATIONALE FOR THE CHARACTERISTIC
A. NEED FOR A TOXICITY CHARACTERISTIC
Subtitle C of the Solid Waste Disposal Act, as
amended by the Resource Conservation and Recovery Act
(RCRA) creates a regulatory framework for controlling
the management of hazardous waste. Section 3001 of RCRA
requires the U.S. Environmental Protection Agency (referred
to herein as the Agency) to identify the characteristics
of and to list hazardous wastes. Those wastes so
identified are then included in the waste management
control system set forth in Sections 3002 to 3006 and
3010 of RCRA.
This Background Document describes the process by
which the Agency identified and defined one such charac-
«
teristic, the "Extraction Procedure Toxicity Characteristic",
and presents the rationale, assumptions, models, and
scientific studies employed in defining the characteristic.
This document also discusses the comments received on
the proposed characteristic and the changes made
in response to those comments.* For clarity the name
for this characteristic has been changed from the
proposed "Toxicity Characteristic to the Extraction
Procedure Toxicity Characteristic in the final regulations.
*The distinction between a waste which is hazardous because
it possesses the characteris tic of toxicity, and a waste which
is listed as hazardous because it meets the criteria of toxicity,
is explained in detail in the background document on Identifica-
tion and Listing of Hazardous Waste.
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B. NATURE OF TOXICITY REGULATED UNDER THE SUBTITLE C REGULATIONS
Section 1004(5) of RCRA defines a hazardous waste as
one that may:
(A) cause or significantly contribute to an increase
in mortality or an increase in serious irreversi-
ble, or incapacitating reversible, illness; or
(B) pose a substantial present or potential hazard
to human health or the environment when improperly
treated, stored, transported, or disposed of, or
otherwise managed.
The usual conception of "toxicity" certainly meets this
standard.* Furthermore, section 3001(a) requires that
toxicity be taken into aeccount in determining which wastes
are hazardous.
As used in these regulations, "toxicity" includes a wide
range of hazardous effects. Acute toxicity upon exposure
is one such effect. Toxicity is also used to encompass the
specific properties of aquatic and mammalian chronic toxicity,
carcinogenicity, mutagenicity, teratogenicity, and phytotoxicity.
Another property of toxicity deemed of regulatory significance
is the potential to bioaccumulate in animal tissue (see
section 300l(a)). The following properties of toxicity are
of particular regulatory concern:
*Websterfs New Collegiate Dictionary, for example, indicates
that toxic is synonomous with poisonous.
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~ serious harm to humans resulting from long term
subacute exposure to chemicals released from the waste (i.e.,
death, incapacitat ion, cancer, birth defects, damage to future
generations through changes in the gene pool);
- serious diminution of fishing resources resulting from
contamination of surface water bodies; and
- serious harm to agricultural resources resulting from
use of water contaminated by waste management practices for
irrigat ion.
These choices are easily justifiable. In addition to
the obvious need to regulate wastes which may result in death
or incapacitat ion, wastes posing a threat of carcinogenicity
are of special concern. Chemicals present in the environment,
*
combined with dietary and societal influences, have been
implicated in the high incidence of cancer in humans. In
order to lessen human exposures to carcinogens, it is necessary
to handle and dispose of wastes containing significant quantities
of carcinogens in a manner appropriate for hazardous materials.
An additional danger from which society requires stringent
protection is exposure to chemicals capable of damaging
genetic material (i.e., mutagens). As a recent review in the
American Chemical Society's Chemical and Engineering News stated:
The relationship between mutagenicity and carcinogenicity
debated by many, up to 90% of the chemicals so far tested
and identified as mutagens in one or more short term
tests are carcinogens as well.
Cancer is only one consequence of genetic mutation,
but the tragedy of its human dimension attracts public
attention. Another potential serious threat from
mutagens may lie in store for future generations:
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the insidious accumulation of subtle, irreversible
mutations in the gene pool conceivably could have
horrific consequences for the human race. By the
time the effects of such mutations become apparant
it'll be too late. (1)
Protection of the unborn fetus is another important
goal of the hazardous waste program under RCRA. In order to
lessen the likelihood of birth defects occurring as a
consequence of improper management of waste materials, it
is important to identify and regulate management of wastes
containing teratogenic substances.
Protection of fishing resources is also an important
goal of the hazardous waste program. Fishing is both a
major source of income and food to many people and serves an
important recreational purpose as well.
Congress cited several instances of fish kills
in describing the types of substantial harm caused by
hazardous waste mismanagement (2), indicating an intent to
protect this resource from improper hazardous waste management
Furthermore, the Act requires the Agency to consider and
protect not only "human health" but "the environment" in
determining which wastes are hazardous (section 1004(5)).
Serious harm to fishing resources due to mismanagement
of wastes can occur in two important ways. Discharge of
toxic chemicals to waterways can result in the immediate
death of large numbers of fish. This has occured many times
during the past decade as a consequence, most notably, of
transportation accidents. A second, more insidious threat,
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is posed by long term, low level discharge of chemicals to
surface waters via groundwater transport. These chronic
exposures can interfere with growth and reproduction,
as well as cause death, and can lead to long term dis-
appearence of aquatic resources of a water body. The
Agency believes it is important to regulate wastes posing
such a risk in order to safeguard this important national
resource.
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Protection of agricultural resources is an additional
goal of the hazardous waste program, inasmuch as large amounts
of ground and surface water are used in the United States
for crop irrigation. According to the U.S. Geologic Survey,
"The quantity of water withdrawn for irrigation
in the United States, Puerto Rico, and the Virgin
Islands in 1975 was estimated at 160 million acre-
feet. .. This was an average rate of 140 billion
gallons per day, and the water was used on approxi-
mately 54 million acres of farmland. This represents
an increase in water use of about 10.9 percent
over the 1970 estimate and an increase in acreage
of about 9.4 percent."(3)
Plants often absorb harmful materials from their environment.
It is therefore extremely important, given the critical
importance of agriculture, that the sources of water available
for irrigation be kept safe for this use. Furthermore,
human exposure to waste contaminants may result from ingestion
of food-chain crops exposed to contaminated water. Again,
the threat to human health and the environment is plain, and
warrants regulatory protection.
C. SCOPE OF THE TOXICITY CHARACTERISTIC
After identifying the various aspects of toxicity that are
of concern, the Agency attempted to develop a definition
for the "Extraction Procedure Toxicity Characteristic" which
would encompass all of these aspects. Detailed discussions
of the approach employed in attempting to develop such a
broad characteristic have been detailed previously in materials
made available to the public. (4,5,6,7)
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However, the Agency was unsuccessful in developing
such a definition. The EP Toxicity Characteristic promulgated
today is limited to wastes which present a hazard to human
health due to propensity to leach significant concentrations
of those toxicants for which drinking water thresholds have
been established. It should be noted, however, that although
the EP Toxicity Characteristic regulates only those wastes
containing toxic constituents for which National Interim
Primary Drinking Water Standards (8) have been established,
other wastes may still be regulated as toxic via the listing
mechanisms under §§261.31 through 261.33 of the regulations.
(1) Aspects of Toxicity Outside the Scope of EP Toxicity
Characteristic
(a^ Chronic Toxicity of Wastes Containing Contaminants
Other Than Those Included in the National Interim
Primary Drinking Water Standards
In addition to the 14 substances for which National
Interim Primary Drinking Water Standards have been established,
there exist thousands of other chemicals which possess a signi-
ficant toxicity. The Agency has wrestled unsuccessfully with
the problem of setting definitional thresholds for these diverse
potential toxicants. While one possible approach was outlined
in the proposed Part 250.15 delisting requirements, adoption
of this approach was found to suffer from a number of problems,
principally the lack of a recognized means of setting a
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threshold to measure these compounds1 chronic toxicity.
In addition, there is believed to be insufficient laboratory
capacity to analyze generators' wastes or waste extracts for
the thousands of toxic species involved. At the present
time, therefore, only wastes containing the drinking water
contaminants are within the scope of the characteristic.
(b) Carcinogenicity
A number of groups are active in identifying chemicals
which are carcinogenic to humans. EPA's Cancer Assessment
Group has taken the lead for the Agency in evaluating
available information in order to determine which chemicals
show substantial evidence of carcinogenicity.
The Cancer Assessment Group has evaluated the available
information on a large number of such chemicals. They have
concluded (10) that for approximately 150 compounds the
information was sufficient for the compounds to be considered
suspect human carcinogens.
This list was not made part of the se1f-regulating EP
Toxicity Characteristic because of:
a. the lack of laboratory capacity to analyze
all wastes for the presence and concentration
of these compounds, and
b. the absence of the necessary dose-response
and mobility relationships with which to derive
general waste threshold levels which would
withstand scientific challenge.
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In addition to doing reasearch on methodology for specific
compound identification and quantification, the Agency is
conducting research to develop rapid, inexpensive biological
screening methods to identify wastes containing carcinogenic
materials. However, until such time as these methods are
available, the Agency will identify specific carcinogen
containing wastes through the listing mechanism.
c. Mutagenicity
There are a variety of mechanisms by which chemicals
can act to cause damage to DNA. A program of waste control
aimed at identifying and eliminating human exposure to such
materials requires rapid, inexpensive procedures to pinpoint
dangerous materials. In response to this problem, a number
of rapid and potentially inexpensive bacterial and in vitro
cellular tests have been developed. These tests are designed
to identify mutagenic substances by detecting genetic damage
in the test species. Because of the variety of types of
DNA damage that are possible, no one test is sufficient to
identify all mutagenic substances.
Although test procedures of this type are in general
use for identifying potentially hazardous chemicals, the
Agency has decided not to require their general use by the
regulated community for two reasons:
(1) Research to date has not been sufficient to
develop and validate experimental methodologies
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for using these tests to evaluate the potential
hazard posed by wastes;
(2) There is significant scientific uncertainty as
to the degree to which such screening test
results correlate with human toxicity.
There are currently a number of large scale programs being
conducted to determine the applicability and validity of
short term mutagenicity test systems. Foremost among these
are the International Program for the Evaluation of Short-Term
Tests for Carcinogenicity, the Genetox Program and the National
Toxicology Program. The "International Program" is approximately
three years old, while the other two programs have been underway
for about two years and one year respectively. Detailed con-
clusions relative to the utility of short-term tests for
mutagenicity are not yet available.-
The Agency therefore has decided to postpone use of such
tests pending the results of further studies. Wastes found to
contain compounds posing a mutagenic threat to humans or the
environment will be regulated through the listing mechanism.
d. Teratogenicity
There are at present no suitable testing methods capable of
identifying teratogenic wastes. Consequently, in order to lessen
the likelihood of birth defects occurring as a consequence of
improper management of waste materials, the Agency will rely
in the listing mechanism to reach such wastes.
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e' Chronic Toxicity to Fish
The Agency encountered two problems in developing a
toxicity test protocol for protection of fisheries resources.
The first of these problems was the selection and development
of a scenario to relate waste management to contamination of
surface waters in which fish live. The second problem was
in then establishing thresholds to determine what an unaccep-
table level of surface water contamination would be.
While a possible solution to the first of these problems
(i.e., relating disposal to exposoure) was presented in the
December 15, 1978 Draft Toxicity Background Document (6), the
contamination model did not account for exposure occurring
through either direct discharge or surface runoff. In addition
to its incompleteness, the model suffered from the fact that
the mixing zone dilution was not based on actual environmental
data.
The second major problem relates to the unavailability of
thresholds analogous to the drinking water standards. The
Agency currently has a program underway to develop water
quality guidelines. These guidelines will reflect the Agency's
best scientific judgment as to maximum levels of toxic species
in waters consistent with protection of the aquatic resources.
However, until such time as these guidelines are available,
the Agency does not believe it is in a position to complete
development or propose a toxicity characteristic for protection
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of fishery resources. Thus, identification of wastes posing
a significant hazard to fish will be made using the listing
mechanism.
f. Phytotoxicity
Besides not having threshold values to measure
chronic exposure levels for fish, the Agency lacks threshold
toxic exposure levels for plants as well. Thus, in order to
protect against harm to agriculture resources, the listing
mechanism will be used to bring phytotoxic wastes into the
hazardous waste control system.
D. MAJOR POSTULATES CONTAINED IN THE CHARACTERISTIC
As noted above, the Extraction Procedure Toxicity
Characteristic is limited to evaluation of the substantiality
of hazard to human health posed by leachable waste constituents
for which National Interim Primary Drinking Standards exist.
The major postulates underlying the characteristic, and the
reasons therefor are set out below.
1. Choice of Groundwater Exposure Pathway
For wastes defined as toxic by Section 1004(5),
the hazard posed by a waste is dependent primarily on two
factors:
a. the intrinsic toxic properties of the constituents
in the waste (e.g., acute toxicity, chronic
toxicity, genetic activity, bioaccumulation); and
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b. the propensity of the constituents in the waste
to migrate from the waste during management and
result in environmental exposure.
The first factor, the intrinsic hazard, defines the actual
health effect posed by the waste when exposure to the public
or environment occurs. For the compounds identified in the
characteristic promulgated today, sufficient toxicological
information (i.e., National Interim Primary Drinking Water
Standards) was available for EPA to determine not only intrinsic
toxicity but safe exposure levels as well.
The second factor was not as well defined. That is, no
test procedures were available to relate concentrations of
toxic species in a waste to migration into the environment
during waste management. Therefore, in order to develop the
Extraction Procedure Toxicity Characteristic, the Agency
found it necessary to develop a procedure to evaluate the
propensity of a toxic material present in a waste to enter
the environment and result in human exposure.
In considering the various exposure pathways of concern,
the Agency concluded (not surprisingly) that the most probable
ones were groundwater, surface water, and air. The ground-
water pathway is believed to be the most serious for a number
of reasons:
(1) Protection of groundwater from leachate contamination
was one of Congress1 principal objectives in enacting
RCRA. (2)
19
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(2) Grbundwater serves as a source of drinking water for
at least half of the propulation of the United States,
and almost one-fifth obtains drinking water directly
from groundwater wells. (11)
(3) Once contaminated, groundwater aquifers tend to remain
contaminated for extended periods of time since their
renewal times are very long.
(4) Groundwater aquifer contamination is difficult to
detect, particularly in its early stages. Significant
human exposure may thus occur before remedial action
can be taken.
(5) Numerous incidents of groundwater contamination
resulting from improper waste management have actually
occurred.*
2. Choice of Particular Disposal Environment Model
a. Choice of Landfill Disposal
In considering the various forms of industrial waste
management likely to occur which would lead to exposure via a
*The prevalence of the problem of groundwater contamination
is illustrated by a 1977 study (12) of 50 land disposal sites
that had received industrial wastes. At 13 sites, the study
was able to obtain evidence that organic chemicals had migrated
from the disposal site to groundwater, and that organic
contamination of groundwater had occurred. Similarily, at 30
of the sites, inorganic contaminants were found to have
migrated to groundwater. At 26 of these sites, hazardous
inorganic constituents in the water at one or more monitoring
wells was found to exceed the EPA drinking water limits.
This study is but one indication of the potential for groundwater
contamination posed by existing waste management. Other
damage incidents are collected in open files of the EPA Office
of Solid Waste, Hazardous and Industrial Waste Division, and are
in the Subtitle C rulemaking record.
20
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groundwater pathway (e.g., 1andfilling, land treatment, surface
impounding, biological treatment), landfill disposal was
believed to offer the greatest potential for mismanagement.
The Agency reached this latter conclusion after considering
the following factors:
(1) Land disposal of wastes results in the concentration
of toxic species into a relatively small area,
(2) Concentrating waste into a small area results
in the population exposed to toxicants emitted from
the waste receiving a higher dose;
(3) Since the degree of harm posed by exposure to toxic
chemicals is a function of the level of exposure,
•
concentrating wastes into a small area is potentially
more dangerous to human health and the environment;
(4) Leaching or leakage of toxic chemicals present in a
waste disposed of in a landfill can result in
contamination of potable groundwater supplies;
(5) Landfilling is believed to be the most prevalent
waste disposal method and therefore the method most
appropriate for modelling;
(6) The Agency believes that due to the lower cost of
disposal, industrial waste not brought under Subtitle
C control will likely be disposed of along with
municipal trash and refuse in landfills.
21
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The Agency thus concluded that since landfill disposal
appeared to be the most common method of disposal and appeared
to present a great potential for groundwater degradation,
it would be the management scenario to model in these initial
regulat ions.
• b. Choice of Degree of Simulated Leaching Activity
1) The Leaching Simulation Test
After determining that the toxicity characteristic
should evaluate the potential hazards posed by improper waste
landfilling and subsequent environmental release via a
groundwater exposure pathway, the Agency next had to decide
how to measure wastes' potential to release hazardous constituents
to groundwater under these circumstances, i.e., wastes' capacity
to leach hazardous constituents if improperly landfilled.
The key question thus became what degree of leaching activity
the test should induce.
In devising this test, the Agency was guided by the
statutory definition of hazardous waste, which commands
implicitly that any test to determine hazardousness be aggressive,
since all wastes potent ially capable of causing substantial
hazard if improperly managed are to be regulated as hazardous.
At the same time, there must be some upward limit on the
aggressiveness of a test, since virtually any substance can be
hazardous if sufficiently mismanaged (for instance, dumped
directly into a drinking water supply), yet the statute doe
not contemplate Subtitle C regulation of all wastes. The
Agency thus determined that a test which simulates a degree
22
s
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of leaching activity very unlikely to occur in most waste
management practice is overly aggressive.
The leaching test, contained in the characteristic,
known as the Extraction Procedure (EP), is designed to satisfy
these competing considerations. As will be explained in
greater detail below, the test assumes wastes will be exposed
to an acidic leachate medium with pH of 5. This leachate
medium tends to leach waste constituents (particularly
metals) relatively aggressively, yet, as discussed below, is
not so aggressive as to simulate a level of leaching activity
beyond that which could realistically occur.
The choice of the leachate medium selected was premised
on a specific physical model, which is described below.
Importantly, however, the Agency believes that the predicted
degree of contaminant concentrations in leachate could reasonably
occur in the course of most waste management, whether or not
the specific waste management conforms to this physical
model.
The specific environment contemplated by the Agency in
developing a leachate test is an improperly designed and
managed municipal landfill. This type of landfill generally
becomes acidic during its lifetime at which time the degree
of leaching induced is relatively high.* The Agency's
*Specific features of this model are,
the landfill receives predominantly domestic refuse
or, if not domestic refuse, material with similar chemical,
biological, and toxicological properties (i.e., only 5% of
the fill is industrial in nature).
— the character of the leaching fluid that the waste
will be exposed to is predominantly a function of the
nonindustrial material in the landfill.
23
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concern is that potentially hazardous wastes, if not brought
within the Subtitle C system, may be sent to municipal land-
fills, with a resulting high level of leaching activity and
environmental insult if the landfill was not designed specifi-
cally to prevent migration of leachate into the environment.
This concern was shared by the Congress in promulgating
Subtitle C:
Even more threatening are the present
disposal practices for hazardous waste ...
In many instances these hazardous wastes
are disposed of in the same manner and
location as municipal refuse — in the
local landfill. H. Rep. No. 94-1491, supra,
at 12.
These wastes' potential to cause harm in this environment
therefore should be evaluated.*
2) Arguments That The Lea'ching Test is Overly Agressive
A great many comments were received attacking this
portion of the characteristic as being overly aggressive
because the commenters1 wastes are not placed in municipal
landfills. To the extent that these comments stated only
that individual generators chose not to send their wastes to
municipal landfills the comments are misplaced since the
wastes may still potentially be managed in municipal landfills
(absent Subtitle C regulation).
*A specific discussion of how the leaching test simulates
municipal landfill waste management conditions appears later
in this document.
24
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Certain generators,* however, stressed that their wastes
are not managed in municipal landfills, and are highly unlikely
ever to be so managed whether or not the wastes are regulated
under subtitle C. The Agency remains convinced ^that the
degree of contamination indicated by the EP is nevertheless
sufficiently predictive of what may occur even in purely
industrial waste management practice to be a regulatorily
valid means of evaluating hazardousness of these wastes.
First, even wastes such as these may reasonably come in
contact with mildly acidic leaching media (i.e., pH of approxi-
mately 5) during their management histories. For example,
waste acid streams are often disposed along with large volume
waste streams. (13) Acid rainfall and water passing through
acidic soils may be other sources of acidic leaching solution.
Other wastes, although normally considered to be neutral or
basic, may contain acidic constituents which can be released
on contact with water or air to create acidic leaching condi-
tions. Many mining wastes, for example, contain pyritic
sulfur, which upon exposure to air and rain forms sulfuric
acid, resulting in acidic leachate. Other types of improper
*Among these generators are a number of large volume waste
generators, such as electric utilities and mining wastes.
25
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waste management may also result in exposure of waste to
acidic leaching conditions.*
Furthermore, large volume wastes may cause an equivalent
degree of contamination even if not subiect to acidic leaching
conditions. The large volume of waste present in the site
tends to lead to increased toxicant concentrations. This
\
effect comes about because the water (e.g., rain) acting
on the waste travels through a larger amount of waste before
entering the environment. The leachate thus tends to become
saturated with the contaminants. By contrast, in municipal
landfills, the small volume of industrial waste present
limits the contact time in which toxicants can act to
saturate the leachate.
The Agency therefore believes there is at least the
potential for most wastes to come in contact with an acidic
*A number of commenters agreed that their wastes could come
in contact with acidic leachate media even though not managed
in municipal landfills, but argued that the acidic leachate
would be buffered (i.e., neutralized) to a greater degree
than would acidic leachate in a municipal landfill, which
would in turn result in a lesser degree of waste constituent
solubilization. The degree of buffering in particular waste
management settings is, however, very difficult to quantify,
and the Agency believes its leachate test strikes a reasonable
balance. The test in the first instance uses a relatively
mild acid and further takes buffering capacity into account
by limiting the amount of acid used in performing the extrac-
tion. In the case of wastes with high buffering capacities,
therefore, the waste itself largely determines the leaching
media composition. The degree of buffering predicted, while
obviously not precisely accurate for every waste management
situation, is believed to be sufficiently representative for
use in the protocol.
26
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leachate medium, or to cause equivalent degrees of contami-
nation, so that the wastes' potential to cause harm if
improperly managed can reasonably be measured by assuming
©
the presence of acidic conditions. It should be noted further,
that the Agency is not legally obliged to model precisely
the circumstances of individual waste management sites, or
classes of waste management sites, in making determinations
of hazardousness. Not only does the statutory definition of
hazardous waste itself afford the Administrator great leeway,
but courts in other contexts have upheld national environmental
standards based upon physical models which did not conform
precisely to physical circumstances of affected facilities.
See, e.g., Sierra Club v. EPA, 540 F.2d 1114, 1136 (D.C.
-------
established on the basis of a "simplistic" physical model is
upheld; use of the model is not an arbitrary or capricious
exercise of authority); Hercules, Inc. v. EPA, 598 F.2d 91,
104-106 (D.C. Cir. 1978) (toxic effluent standard for
toxaphene established on the basis of toxaphene's effect on
/
an aquatic species not found in the receiving waters of the
sole discharger).*
It should also be mentioned that the phenomenon of
leaching over the life of a waste management facility is
incompletely understood, and can be characterized legitimately
as "on the frontiers of scientific knowledge . . ."
Industrial Union Department, AFL-CIO v. Hodgson, 499 F.2d
467, 474 (D.C. Cir. 1974). There is also no consensus within
»
the scientific community as to an appropriate short-term
extraction test to measure this phenomenon. Health-based
regulations addressing such areas of uncertainty have tradi-
tionally been accorded considerable judicial deference.
Hodgson, supra, 499 F.2d at 474-76; Ethyl Corp. v. EPA, 541
F.2d 1, 24-29 and cases there cited (D.C. Cir. 1976, en bane).
Again, under these circumstances, some imprecision in the
leaching test is not only acceptable, but eminently justifiable
As the court stated in Ethyl Corp., supra;
*It should be noted further that in each of these cases,
the physical model was used to establish a quantitative
discharge standard, as compared to the present situation
where a model is used only to make a screening determinati
of wastes which must be regulated to ensure proper management,
a less precise undertaking. This situation is consequently
a fortiori from the cited cases.
.on
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Questions involving Che environment
are particularly prone to uncertainty. Tech-
nological man has altered his world in ways
never before experienced or anticipated. The
health effects of such alterations are often
unknown, sometimes unknowable. While a con-
cerned Congress has passed legislation provid-
ing for protection of the public health against
gross environmental modifications, the regulators
entrusted with the enforcement of such laws
have not thereby been endowed with a pre-
science that removes all doubt from their
decision making. Rather, speculation, con-
flicts in evidence, and theoretical extra-
polation typify their every action. How
else can they act, given a mandate to protect
the public health but only a slight or non-
existent data base upon which to draw?
Sometimes, of course, relatively certain proof
of danger or harm from such modifications can
be readily found. But, more commonly, rea-
sonable medical concerns and theory long pre-
cede certainty. Yet the statutes—and common
sense—demand regulatory action to prevent
harm, even if the regulator is less than
certain that harm is otherwise inevitable.
Ethyl Corp. , supra, 541 F.2d at 24-25.
9
3) Arguments That the Leaching Test
is Insufficiently Aggressive
The Agency's proposed leaching test (and the EP Toxicity
Characteristic as a whole) was also criticized as being
insufficiently aggressive because the test was not "designed
on the assumption that the waste will be disposed of in the
worst possible environment."* As noted above, however, the
Agency does not believe it is iustified, nor is it advisable
to base a determination of hazardousness upon waste mismanage-
*Report on Hazardous Waste Disposal, Subcommittee on Oversight
and Investigations of the House Committee on Interstate and
Foreign Commerce, 96th Cong. 1st Sess. 53; see also Comments
of Environmental Defense Fund, March 16, 1979, pp. 9-10.
29
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ment assumptions — including assumptions as to leachate
medium composition -- which are very unlikely to occur in
practice.
Moreover, it should be remembered that the Extraction
Procedure Toxicity Characteristic (of which the leaching
test is a part) is not the sole means of bringing solid
wastes within the subtitle C regulatory framework. The
other mechanism, listing of hazardous wastes, allows the
Agency to interpret leachate data in a more individualized
way, and to take into consideration additional factors, such
as indications of actual waste mismanagement or unusual
waste management practices, which are not measured by the
characteristic.* Thus, the Agency has not ignored all
waste mismanagement situations beyond the situation modeled
»
in the toxicity characteristic; it has chosen to take them
into account in a more individualized manner.
The Agency believes this "Course preferable to basing a
test upon an assumption of absolute worst-case mismanagement.
If a generator's waste fails the test, the waste is irrevocably
within the subtitle C system. In the Agency's view, this
requires some safeguard in the test against indiscriminate
overinclusion, which overinclusion might result from a leaching
*See, for example, Listing Background Documents for Chromium
Pigments, Secondary Smelting and Refining of Lead, and Primary
Smelting and Refining of Lead, all of which list wastes which
conceivably might not fail the toxicity characteristic
but still pose a substantial potential hazard because of the
presence of additional factors not evaluated by the extraction
procedure.
30
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test based upon assumptions of unusually deficient waste
management.* The Agency therefore chose what it regards as
a plausibly-occurring type of mismanagement model on which to
base its leaching test and toxicity characteristic.
c. Remaining Features of the Waste Disposal Model
Once a constituent is leached from the waste matrix,
there remains the question of its environmental fate: does
the constituent have sufficient mobility to pass through
soils and reach groundwater, and if it reaches groundwater,
is It persistent enough to reach environmental receptors in
concentrations sufficient to create a potential substantial
hazard. In evaluating these considerations, it is assumed
that disposal will occur in an environmentally sensitive
area, and that waste constituents will undergo some
attenuation in both soil and groundwater before reaching
environmental receptors. The postulated features of the
hypothetical model which reflect these assumptions are:
— The waste landfill is situated over an
aquifer that serves as the sole source of
drinking water for a significant number of
people;
— The soil below the site is composed of
material with limited attenuative capacity;
-- Persons using the aquifer as a source of
drinking water are being supplied from wells
which are situated 150 meters (500 feet)
downplume of the disposal site and draw
water from the plume of contaminated water.
*By contrast, a listing determination is not irrevocable
since individual generators may petition the Administrator
to have their waste delisted. See §261.39.
31
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As is discussed later in this background document, a rate of
leachate constituent attenuation is then projected based
upon this model.
As with the leachate simulation test, a plausibly
occurring type of worst-case mismanagement is assumed.
With respect to the assumption that disposal occurs in an
environmentally sensitive area, no other assumption would be
warranted in light of the statutory mandate to protect against
groundwater degradation (as well as to protect human health
and the environment). Obviously, any characteristic must be
designed not only to protect against mismanagement occurring
in areas of relatively low mismanagement potential but also
in areas of high potential. Indeed, the assumption of mis-
management in environmentally sensitive areas was not seriously
challenged by any commenter.
The decision to take attenuation into account also appears
to be both straightforward and desirable. There is clearly
sufficient physical evidence of environmental attenuation for
the Agency to assume that waste constituents will undergo
some degree of attenuation before reaching environmental
receptors. This type of approach has in fact been adopted
by EPA in other environmental programs, with judicial acceptance
See, e.g., Hercules, Inc. v. EPA, supra, 598 F. 2d at 115-17
(mixing zone factor used in establishing toxic effluent
discharge standard).
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3. Thresholds to Determine Unacceptable Levels of
Contamination
The final major assumption contained in the toxicity
characteristic is the choice of thresholds to determine
unacceptable levels of contamination. Obviously, if a test is
used to measure toxicity, contamin'ant concentrations in the
test extract need to be related to a numerical standard, viz.,
what concentrations of what contaminants give rise to a sub-
stantial potential hazard. For these values to be defensible,
they should be based on recognized human exposure health
effect thresholds.
When the Agency evaluated the available toxicological
information it was found that the only available established
benchmarks for toxic contamination of drinking water which
were both scientifically recognized and which address
chronic exposure were the National Interim Primary Drinking
Water Standards (NIPDWS).* These standards were developed
pursuant to §1412 of the Public Health Service Act as amended
by the Safe Drinking Water Act to protect the nation's supply
of potable water. They reflect the best available scientific
information relative to safe levels for 14 potentially toxic
species in drinking water.
*The current approach used in the California hazardous waste
program, which ha's been recommended as a model for the Federal
regulations (see, e.g. , Report on Hazardous Waste Disposal,
supra at 40), is not based upon contaminant thresholds, and
thus provided no guidance in developing such thresholds.
33
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The comment was made that the Agency should broaden the
coverage of the Toxicity Characteristic by incorporating the
"Water Quality Criteria" in addition to the Interim Primary
Drinking Water Standards. As was described in the Proposed
Regulation, this approach was initially considered but
rejected. The principal reasons for not using the
criteria are:
(1) The unavailability of the needed guidelines, and
(2) the lack of available resources in the regulated
community to implement such an approach if adopted.
During the time regulations under section 3001 were being
developed, Water Quality Criteria for the 65 pollutants listed
as toxic under the Clean Water Act were first being formulated.
The preliminary drafts then available received substantial
negative comment from the scientific community, both from
within and from outside the Agency. The Agency thus believed
that it would be a long time before the final Water Quality
Criteria were available, and further felt that it was inadvis-
able to delay proposal of RCRA regulations until the criteria
were available.*
The second reason why use of the Water Quality Criteria
*As it turned out, the first group of criteria were eventually
proposed on March 15, 1979, a full three months after the
RCRA section 3001 regulations were proposed. The last of
the 65 were proposed on October 1, 1979. Final promulgation
of the first group is presently scheduled for this summer.
34
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was not believed to be viable relates to the insufficient
scientific resources to implement such a regulatory approach.
In order to implement a self-determinative regulatory program
which requires generators to test all wastes for a list of
toxic species, reliable, standardized testing protocols are
required. Secondly, the regulated community has to have
available to it sufficient testing capability (i.e. , in-house
or through contractors) to conduct the required tests. At
the time the section 3001 regulations were proposed, and to
a great extent still today, such reliable standardized methodology
was not available. Furthermore, the personnel and laboratory
facilities to perform the analyses that would be required under
such a regulatory approach are not available.
In summary, the Agency believed the suggested approach
(i.e., expand the characteristic by including threshholds
for the 65 toxics for which Water Quality Criteria are being
developed) was impossible to carry out and thus the present
listing approach was adopted. It should also be emphasized
that the Agency may still bring into the hazardous waste
control system any wastes that contain toxicologica1ly signi-
ficant quantities of any of the 65 toxicants for which Water
Quality Criteria are being developed by listing specific
waste streams. Many of the waste streams listed in today's
Federal Register in fact are based upon the presence of many
35
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of these 65 toxicants, as well as upon the presence of other
toxicants not included within either the list of Water Quality
Criteria pollutants or the pollutants measured by the Extraction
Procedure Toxicity Characteristic.
36
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III. RATIONALE FOR THE EXTRACTION PROCEDURE
For purposes of easier comprehensibility of the following
discussion, a description of the proposed Extraction Procedure
(EP) is given at this point. The background document then goes
on to decribe the genesis of the EP, the decision to use batch
tests in the protocol, the issue of whether the test should
be designed to measure maximum concentration or cumulative
B
release of waste contaminants, and the physical justification
for the various steps of the EP.
The proposed EP consisted of a series of steps. First
a representative sample of the waste was obtained. The solid
portion of the waste was then separated from the liquid por-
tion by means of filtration and centrifugation. Next, the
solid portion was ground, or subjected to a compaction force
test for structural stability, and placed in an extractor
where it was extracted with water acidified with acetic acid.
This mixture was agitated and extracted for a period of 24
hours. At the end of the 24 hours the mixture was again
filtered and the resulting liquid extract was combined with
the liquid portion which was originally separated out. The
combined extract was then analyzed for its constituent contami-
nants. If analysis revealed that the extract contained NIPDWS
contaminants in concentrations greater than 10 times those
specified in the National Interim Primary Drinking Water
Standards, the waste was considered hazardous.
A. GENESIS OF THE EXTRATION PROCEDURE
When the Agency embarked on the devlopment of a testing
37
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procedure to detect wastes capable of leaching toxic consti-
tuents into groundwater, there were no standard methods for
measuring the leaching potential of a waste. For that matter,
the processes governing the formation of leachate in landfills
were only partially understood. Accordingly, EPA initiated
two parallel research efforts to develop a standardized testing
procedure to measure leaching potential. The first was a grant
awarded to researchers at the University of Wisconsin in July 1976.
This study, referred to hereafter as the Ham study, was commissioned
to study the process of leachate generation from landfilled wastes,
to evaluate the factors which influence leachate generation and to
develop a leaching test suitable for .assessing the leaching chara-
acteristics of such wastes. This study was completed in July 1978
«
and the results published in a May 1979 report entitled Background
Study on the Development of a Standard Leaching Test (14).
The second research effort was a grant awarded to the Mitre
Corporation to compile information on existing leaching tests and
to evaluate the usefulness of these tests in assessing the leach-
ing potential of a waste. Work on this grant was completed in
February 1978, and the results published in a report entitled
the Compilat ion and Evaluation of Leaching Test Methods (15).
This report discussed the environmental factors which influence
leachate generation and evaluated 26 different leaching tests
for their utility in assessing the leaching characteristics
of a waste. The Mitre report recommended that EPA single
out for further evaluation the leaching test developed by IU
Conversion Systems, the leaching test developed by the State
38
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of Minnesota, and the leaching test being developed by Ham, et. al
at the University of Wisconsin. A study of these three tests was
conducted by Ham as an adjunct to his other study and the
results published in a July 1979 report entitled Comparison
of Three Waste Leaching Tests (16).
While these studies were going on, EPA — as a consequence
of the time constraints mandated by Congress for promulgating
the regulations — entered into an agreement with the Department
of Energy's Oak Ridge National Laboratory (ORNL) to conduct
research into the toxicity of the extracts or leachates
generated by the test procedure then under development by
Ham. It soon became apparent that the extraction fluid
developed by Ham was too toxic to permit its use in bioassay
tests to determine whether toxic materials were leaching from
the wastes. EPA was concerned because it wanted to be able
to assess the toxicity of the waste leachate through bioassay
procedures as well as through analytical detection of the
leachate constituents.* [See the Draft Toxicity Background
Document prepared in support of the proposed regulations.(6)]
An additional concern with the Ham test was that it might be
too site-specific.
Consequently, in the fall of 1977, EPA modified the
agreement with ORNL to allow work to be performed in developing
a leaching procedure suitable for use with bioassays (although
still relatively agressive). Relying heavily on the work
already done by Ham and Mitre and on the work done by other
*Although the finally promulgated test does not provide for
bioassay tests on the waste extract, EPA envisions possibl
incorporation of such tests into the EP in the fut —
39
e
ure .
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groups, such as the American Society for Testing and
Materials (ASTM), ORNL assisted the Agency in developing the
Extraction Procedure set forth in the proposed regulations.
B. CHOICE OF A BATCH TEST
While a number of aspects of aspects about the EP,
as finally proposed, were not settled until relatively late
in the development process, some were settled early. As
noted in the Ham study there are two general approaches to
evaluating the leaching potential of a waste: (1) a very
intensive study of the leaching characteristic of both the
waste and its desposal or (2) a quick test using standardized
procedures (14). Clearly, the intensive study — which is
very expensive and takes a great deal of time -- is unsuitable
for use in the laboratory regime contemplated by the Act.
Consequently, EPA decided early on to utilize a short-term
standardized test as the device for assessing the leaching
potential of a waste.
There are two tvpes of short-term tests commonly used
to assess the leaching potential of a waste: (1) batch or
shake tests and (2) column tests. Batch tests are performed
by placing a representative sample of the waste to be tested
in a container along with the leaching solution. The mixture
is then generally agitated for a specific period of time and
the resulting elutriate or leachate separated from the re-
maining solid and analyzed for its constituents. Such tests
are cheaper, faster and more reproducible than column tests,
40
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but the test procedures must be carefully modeled upon actual
landfill conditions if the information obtained is to be at
all meaningful. Column tests are performed by placing the
waste in a column and passing the leaching solution through.
Such tests can give a better simulation of landfill conditions
than batch tests. However, these tests suffer from a number
of disadvantages, including:
--channeling and nonuniform packing
--unnatural clogging
--unnatural biological effects
—edge effects
--lengthy time requirements for running the
test (months to years)
.--lack of reproducibility (17).
In light of the above difficulties, particularly the
lengthy time requirements for running column tests, EPA chose to
employ a standardized batch test as the means for assessing waste
leaching potential.
C. MAXIMUM CONCENTRATION VERSUS CUMULATIVE RELEASE
Ham considered it important for a leaching test to provide
an indication of both the maximum concentration of toxic con-
stituents likely to be attained in the leachate and the
cumulative release of toxic constituents from the waste over
time (14). EPA on the other hand, considers the maximum
concentration of toxic constituents in the leachate to be the
factor which primarily identifies the environmental hazard
presented by the waste. This is because the concentration of
41
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toxic constituents in the groundwater rather than the aggregate
quantities released thereto determines the health hazard
posed by groundwater contamination, although of course the
two are related.
EPA also considers maximum concentration to be more import-
ant than cumulative release because of the lengthy residence time
of contaminants in the groundwater. Unlike surface waters, ground-
water is not continually flushing itself out; consequently, the
aggregate contribution of pollutants is not as important as in
surface water pollution. Accordingly, EPA has structured the EP
so as to concentrate on the maximum concentration of contaminants
in the leachate.
42
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D. EXPLANATION OF HOW THE EP MODELS PHYSICAL FACTORS WHICH
INFLUENCE LEACHATE FORMATION IN THE ASSUMED DISPOSAL
ENVIRONMENT
The Extraction Procedure is 4esisned to evaluate a waste's
capacity to release hazardous constituents to the environment
if the wastes are improperly landfilled in a plausibly
occurring manner, and to gauge the resulting risk of substantial
potential hazard. It thus becomes important to identify and re-
plicate reasonably the principal physical processes and environ-
mental factors influencing leachate formation and subsequent en-
vironmental contamination. These processes and factors include:
(1) Leaching medium composition;
(2) The amount of leachate medium to which the waste is
exposed;
(3) Surface area, particle size, and composition of the
material being leached;
(4) Contact time between the leachate medium and Che
waste and;
(5) Attenuative capacity of the soil and of the underlying
aquifer.
The operative aspects of the extraction procedure (both the
proposed and the final EP) — i.e. , the aspects of the
procedure which model these factors — are:
(1) Solid material particle size reduction;
(2) Phase separation;
(3) Leaching medium composition;
(4) Ratio of waste to extractant (solid-
liquid ratio);
(5) Aggressiveness of agitation;
(6) Waste-extractant contact time;
(7) Assumed level of environmental attenuation.
43
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A full discussion of the EP's component parts and how
these parts relate to the physical processes which the EP attempts
to model is set forth in the following pages.
^
1. Sample Preparation
•
a. Liquid-Solid Separation
Ham surmises that after a waste is deposited in a landfill the
solid and liquid components of the waste will separate independent
of any leaching action. (14) The liquid component of the waste might
flow downward due to gravity, be absorbed by surrounding materials,
or flow away from the waste by capillary action. After separation,
only the solid material left behind will be subjected to leaching
action by available leaching media.
EPA therefore believes that it is most appropriate to subiect
only the solid component of the waste to simulated leaching.
Consequently, EPA has provided that the initial step in the EP is
to separate the solid and liquid components of the waste. After
extraction, the extract of the solid is combined with the original
liquid phase of the waste to gauge the full extent of potential
contamination posed by the waste.* This step models the situation
*EPA recognizes that the separation of liquid and solid compo-
nents in the waste will depend on site-specific conditions,
and so might not occur invariably. Nevertheless, it believes
that utilization of the solid-liquid separation technique
recommended by Ham is justified. The Agency, as stated, is
attempting to model worst case conditions, and separating
the phases prior to extraction of the solid phase is the
more aggressive test. Secondly, under this approach liquid
wastes would tend to be rated as more hazardous than solid
wastes containing the same concentration of a given toxicant.
This result is believed reasonable since liquids are more
mobile than solids and would tend to migrate more rapidly,
and in a more concentrated manner than solids.
44
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a
where the liquid portion of the waste separates from the solid
e
portion, flows downward and becomes absorbed onto other material in
the fill. Later, leachate generated from the remaining solid
migrates downward, displacing and mixing with the absorbed liquid
phase and carrying it into the aquifer.
1) Sample Filtration
The Agency considered several techniques in performing the
solid-liquid separation step, including filtration, sedimentation,
centrifugation and screening. EPA considered filtration and centri-
fugation to be the most appropriate techniques and elected to make
filtration the final step in the separation process, with centrifug
tion as a supplemental aid in separating wastes which cannot easily
be separated by filtration alone.
The choice of a filter pore size has an important bearing on
the ultimate concentration of toxic contaminants subjected to
analysis, because the filter operationally defines both the liquid
which is presumed to separate out from the waste and the leachate
which is produced by the leaching process. In conformity with
Ham's suggestion, EPA has selected a filter pore size of 0.45
microns because particles larger than 0.45 urn are usually removed
by passage through the soils, as indicated by the low suspended
solids content of most groundwaters (14). It is therefore not
unreasonable to assume that particles larger than .45 urn will be
filtered out by the soil and will not reach groundwater.
45
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The separation procedure can be described as follows.
If the sample is not obviously a solid, an attempt should be
made to filter it through a 0.45 urn filter under a pressure
differential of <_ 75 psi. If clogging occurs, centrifugation
is employed as an aid to the separation. Pressure filtration
acts to accelerate the filtration process without changing
the nature of the separation. Centrifugation is particularly
useful where the nature of the mixture is such that even
pressure filtration would require a large expenditure of
time. Although at the time of the proposal the Agency believed
that centrifugation could be used as a direct replacement for
filtration, later information indicates that using centrifugation
alone results in a carryover of particles greater than 0.45 urn.
Consequently, the final regulation provides that centrifugation
is only to be used as an aid to the filtration process. After
centrifugation a final filtration must be performed to remove
particles greater than 0.45 um from the liquid phase and remove
residual liquid from the solid phase. Anything that cannot be
readily separated by filtration and centrifugation is considered
a solid and is subjected to the leaching aspect of the test.*
A number of commenters said they encountered severe
operational problems running the extract procedure on
*Such wastes might include the thixotropic materials such as
drilling muds and paints which were found to cause difficulty
during evaluation of the separation procedure. (17,18). Since^it
is reasonable to assume that such wastes will not separate out in
actual landfill conditions, such wastes should be treated as solids
and extracted without separation.
46
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liquid wastes which contain a very low percentage of solids
v*
(e.g., <1% solids). To accomodate this problem, EPA has
elected to amend the proposed regulation to provide that a
sample which contains less than 0.5% solids need not undergo
the leaching procedure. Rather, such a sample, after filtra-
tion, should be considered the extract and should be analyzed
directly fqr its toxic constituents. (Filtration is necessary
because of the assumption that only particles less than 0.45
urn in size will appear in the leachate.) This change will
make the EP considerably easier to perform for liquid wastes
with very low solids content, while not appreciably altering
total concentrations of toxic constituents in the extract,
since extractions performed on the small amounts of solid
present in such solutions are not likely to generate much in
the way of toxic contaminants.*
b. Sample Homogenization/Particle Size Reduction
(Including the Structural Integrity Procedure)
To insure reproducibi1ity of the leaching test performed
on the solid portion of the waste, a homogenous portion is required
*During evaluation of the separation procedure by Ham, ORNL,
and EMSL-LV, very few operational problems were encountered,
although one potentially serious problem has been noted by
ORNL (6). Preliminary work indicates that the filtering of
aqueous solutions containing polyaromatic hydrocarbons (PAH),
using either Millipore, type HAWP, or Nuclepore, polycarbonate
membrane filters, results in the solutions losing a substantial
amount of their PAH content. If this effect is found to be the^
case generally for organics , it suggests that the non-polar toxi-
cants may not show up in the extract in as large a concentration
as they might in the real world. Unfortunately, the magnitude
of the problem is not yet known and further work must be done
before attempting to remedy the problem. If a solution turns
out to be needed it will be incorporated into these regulations
in the future.
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0
This can best be accomplished by reducing the particle size
f the waste through subdivision (e.g., grinding, cutting) —
a process which tends to equalize the surface area, geometry,
and other such properties of the waste making up the sample.
As a general matter, the more finely ground the waste, the
more reproducible the test results are likely to be. At the
same time, because grinding increases the surface are which
comes into contact with the leaching medium, the finer the
waste is ground, the higher the concentrations of contaminants
in the extract.
It is difficult to gauge the extent to which reduction
of waste particle size duplicates actual landfill conditions.
The arguments that can be made on behalf of very fine grinding
include the fact that wastes will eventually degrade in a
landfill, and that fine grinding probably comes closest to
representing the saturated conditions which occur when the
leaching medium percolates slowly through a column of waste.
However, very fine grinding tends to yield results which are
probably not representative of wastes which have been treated
for the purpose of reducing the mobility of the toxic species.
A variety of these treatment processes have been developed
— including the incorporation of the waste into a solid
matrix, the encapsulation of the waste in an impervious
coating, and the addition of binders. These management tech-
niques are designed expressly to prevent breakdown during
disposal and need special consideration with regard to sample
preparat ion.
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To accomodate wastes which have been treated in an attempt to
reduce 'the mobility of the toxic species or naturally are in a
bound form, EPA has promulgated alternative sets of requirements.
Wastes which have not been subjected to cementing processes or are
otherwise not found in a monolithic or block form are required to
be ground or otherwise subdivided such that they pass through a 9.5
mm (3/8 in) standard sieve. This requirement represents a compromise
between the very fine grinding specified by the tests being developed
by the states of Illinois (20) and California (21) and the use of
a monolithic mass specified by ASTM (22) and IUCS (15).* Wastes
which have been subjected to special encapsulation or fixing processes
— and are thus monolithic in form — may instead be demonstrated
to be structually stable and exempt from testing in a subdivided
form through use of a special procedure called the Structural
Integrity Procedure (SIP). The SIP is designed to be a moderately
severe approximation of the disintegration that might be expected
if heavy equipment passes over the waste.
Mahlock et al (23) have determined that a compaction test
identical to the procedure of ASTM D-698-70, but using only 15
hammer blows, simulates the corapactive effort that might be expected
from passing earthmoving equipment over a placed landfill. Their
*A few commenters complained that the requirement of passage
through a 9.5 mm sieve is insufficiently flexible because it fails
to accomodate certain waste particles which fail to pass through
the sieve yet exhibit a surface area equivalent to waste particles
which do pass through the sieve. EPA has taken care of this pro-
blem by specifying that the waste either be passed through a 9.5
mm (3/8") sieve or have a surface area equal to or greater than
3.1
49
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15-blow test uses a (5.5-lb) hammer impacting on a (.0333 ft3)
cylinder of sample after dropping (12 in). This apparatus would
exert an impact of (165 ft-lb/ft3) on the sample:
v2 » 2 (acceleration of gravity) (distance)
= 2 (32.2 ft/sec2) (1 ft)
= 64.4 ft2/sec2
Kinetic energy
volume of sample
1/2
m v
(1/30)
= (.5) (5.5/32) (64.4)
.0333
« 165 ft-lb/ft3
EPA has decided to employ a modification of this procedure.
The procedure selected is one based on a scaled down verion of
Mahlock's 15-blow compaction procedure. The scaled down procedure
uses a .32 Kg (0.73 Ib) hammer acting on a (0.0022 ft3) sample
with a (6-in) free fall. This device (Figure 1) has approximately
the same compaction action as the larger unit, as demonstrated by
the equation below.
Kinetic energy
volume of sample
2 a x
(2) (32.2) (0.5)
32.2
1/2 m v2
(.0022)
(0.5) (0.73/32) (32.2)
( .0022)
165 ft lb/ft3
50
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The sample size designated by this procedure will be approximately
100 gms, which corresponds nicely with the minimum sample size
required for extraction. To account for the cushioning or energy
dissipation resulting from the compressibility of surrounding
wastes, a resilient sample holder has been incorporated in the design
Weeter and Phillips (24) evaluated this procedure using a flue
gas dusulfurization sludge fixated by the addition of varying
amounts of water. Three samples were used in an attempt to repre-
sent a full range of unconfined compressive strengths.
Table 1
Sludge Density 21 day UCSa
Sample No. (lb/ft3) (lb/in2)
A 50 81
B 120 586
C 101 1450a
a Unconfined Compressive Strength
When subjected to a series of blows by the .32 Kg (0.73 Ib)
hammer, sample A cracked throughout the upper half of the cylinder,
and the bottom half remained intact. The pulverized particles
formed in the upper half of the cylinder seemed to dissipate much
of the energy exerted by the hammer after the third or fourth blow.
As a result, the succeeding blows had little effect on the remaining
structure of the cylinder. No visible change in structure was
noted in specimens B and C after the SIP procedure.
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0
One shortcoming of the SIP as currently formulated is the lack
f any measure of weatherabi1ity. Wastes deposited in or on the
land will be subjected to the effects of water, freeze-thaw cycles,
and seasonal and daily temperature changes. EPA intends to explore
these factors to determine if a testing procedure can be devised
which incorporates these additional factors.
2. Leaching Media Composition
It has been demonstrated empirically that the leaching media
to which a waste is exposed, whether it be water, an acidic solution
or whatever, has an important influence on the ultimate concentrations
of toxic contaminants in the leachate. Consequently, the choice
of a leaching medium (extractant) has an important bearing on the
aggressiveness and ultimate shape of any leaching test.
As was explained previously in this document, EPA chose to
model the leaching medium employed in the EP upon the leaching
medium likely to be found in an actively decomposing municipal
landfill. This was based on several considerations. First, given
the considerable uncertainty and lack of information concerning
the phenomenon of long term leaching, as well as its statutory
mandate, the Agency believed it should be reasonably conservative
in its choice of a leaching environment to model. Second, the
Agency was convinced that most categories of waste have the potent-
ial of being disposed in municipal landfills. Third, the Agency
believed that even wastes which are unlikely to be disposed of in
municipal landfills are reasonably likely to come into contact
52
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with a mildly acidic leaching medium at some point in their
management histories. Finally, the level of leaching activity
predicted could also occur even if acidic leachate was not
present.
The following discussion explains how the composition of
the extraction medium simulates leaching media which could be
present in municipal landfill.
There is ample evidence that pH of the extracting solution
is the most important factor in modeling an expected level of
leaching activity relative to metal migration (14).* Further,
the pH of the leaching media of a decomposing municipal land-
fill leachate will generally be acidic sometime during its
lifetime, due to the presence of biodegrading refuse (14).
The Agency therefore chose an acidic leachate composition,
consisting of an acetic acid solution with a pH of 5.
Acetic acid was chosen because it is the most prevalent
acid found in municipal landfill leachate (14). The pH
value selected is well within the reported ranges of pH levels
for municipal landfills, as shown in the following table:
*0ther important factors include solution buffering capacity,
complexing capacity, redox potential, organic solvency and
ionic strength (14).
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Table 2. pH RANGES REPORTED BY VARIOUS AUTHORS FROM
LANDFILL OR LITERATURE SURVEYS (14)
pH
Source Range
Chianetal. 3.7 -8.5
Steiner et al. 4.0 - 8.5
£/
Clark et al. 1.5 - 9.5
Encom Associates 3.0 - 8.5
Pohland 4.9 - 8.4
ji/ Site received acidic industrial wastes.
Furthermore, the pH value selected promotes relatively
aggressive leaching of elemental waste constituents, and so
furthers the Agency's statutory mandate of protection of human
health and the environment.
Another important physical feature influencing toxicant
concentrations in leachate is buffering capacity. The ultimate
buffering capacity of real world leachates is a consideration
which has received little attention from the research community.
Data gathered at EPA's Boone County Field Site (25) over a
period of 7 years indicates that the leachate generated by
decomposing municipal waste contains approximately 0.14
equivalents of acidity per kilogram of dry refuse. Applying this
54
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data Co the hypothetical disposal environment (containing 5%
industrial waste and 95% organic refuse), EPA concluded that
1 gram of industrial waste could potentially be acted upon
by approximatley 2 milliequivalents of acid. Translating
this into the terms of the test, EPA determined that it
should set a limit on total acid added to the extraction
solution of 2.0 mi 1liequivalents of acid per gram of solid
material or 4 ml of 0.5 N acetic acid per gram of waste
being extracted.
Certain other chemical parameters, notably extractant
convplexing capacity and redox potential, are not incorporated
in the EP leaching medium (or are incorporated only to a
limited degree). However, the Agency's -.failure to exactly
replicate municipal landfill leachate is not necessarily a
shortcoming. The ultimate regulatory objective is not to
precisely model leachate from a municipal landfill, but to
devise a protocol which is reasonably predictive of ultimate
levels of leaching activity of a great variety of wastes.
EPA believes that the present protocol largely achieves
this objective relative to mobilization of metals and, to a
limited extent, organics, and is thus promulgating the EP in
the present form. EPA is studying this issue further, however
and if it appears that the protocol requires modifications
in order to remain reasonably representative, appropriate
revisions will be made.
55
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The Agency is aware of one potentially serious regulatory
deficiency in its choice of leachate medium composition.
Studies performed by ORNL demonstrate that EPA's leaching
solution (and Ham's synthetic solution) are deficient in
their ability to adequately model the organic solubilizing
ability of real world leaching media (7).* Since the charac-
teristic is at present designed principally to evaluate
leaching propensity of elemental,rather than organic
contaminants, this deficiency is not deemed severe enough to
warrant additional delay inplementing the characteristic.
EPA is, however, working to develop a leaching media which
reflects more accurately wastes' capacity to leach organic
toxicants .
3. Sample to Extractant Ratio
The solid-liquid ratio, that is, the ratio of the quantity of
solid waste to the quantity of leaching solution used, can be an
important factor in assessing the leachability of a waste, since
the greater the amount of waste present in the liquid, the more
toxic species there are to be dissolved and the higher their
concentration.**
*This is probably attributable to the failure of EPA's
leaching solution and possibly Ham's as well to include
species such as fatty acids, alcohols and humic acids which
have a great deal of organic character (7).
**This dependency of concentration on solid-liquid ratio is
particularly characteristic of species whose concentration
is not controlled by a solubility equilibrium. On the other
hand, where the concentration of the toxic species is control-
led exclusively by solubility equilibrium, the concentration
of the species will not vary with the solid-liquid ratio,
although Ham's experience suggests that there are very few
such species (14).
56
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A high solid-liquid ratio is probably better representative
«
of actual landfill conditions, inasmuch as the solid-liquid
ratio encountered by a drop of leachate percolating through a
landfill is likely to be very high. In addition, a high
solid-liquid ratio is more likely to reflect the maximum
attainable concentrations which are the principal focus of
EPA's concern. At the same time, a. high solid-liquid ratio
can cause difficulties with stirring or separation and can
cause the system to become saturated with readily soluble
salts -- with the result that the less soluble but more toxic
species are left behind in the waste. A low solid-liquid
ratio will promote greater ease of operation but will tend to
magnify sampling and analytical errors.
After considering the above factors,- EPA has elected to
use a 1:20 solid-liquid ratio. EPA believes this ratio will
attain reasonably high concentrations while preserving
operational precision. Furthermore the ratio selected is
well within the bounds of the ratios used in other comparable
leaching tests, as shown in the following table, and is
therefore believed to be an acceptable value.
57
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Table 3. SOLID - LIQUID RATIO LEVELS UTILIZED IN OTHER
LEACHATE TESTS (15)
Test
IUCS
University of Wisconsin
Standard Leaching Test
State of Delaware
State of Minnesota
Solid - Liquid Ratio
1:4
1: 10
1: 25
1:40
4. Agitation Methods, Number of Elutions, and Extraction
Contact Time
Apart from the solid-liquid ratio, already discussed, the
remaining parts of the EP which have the greatest bearing on the
concentration of toxic constituents in the leachate are the agita-
tion method, the number of elutions performed, and the contact
time between leaching solution and the waste. These are discussed
below.
a. Agitation Method
To ensure that the surface area of the waste is sufficiently
exposed to the synthetic leaching solution to replicate the effects
of a leaching medium percolating slowly through a landfill, and to
ensure reproducibile results, it is important to employ a uniform,
non-destructive, efficient agitation. Ham evaluated the following
five agitation methods:
58
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1. Continuous shaking (Gyrotory/Shaker, New
Brunswick Scientific Co.)
2. Continuous mechanical paddle stirrring
(Phipps and Bird, Inc. Richmond va.)
3. Intermittent shaking by hand
4. Swing-type shaking
5\ Rotating at two different angles
Ham concluded that none of these methods resulted in ap-
preciably greater release of toxic constituents, although the
rotating method gave the highest release. On the basis of
the higher release figures for the rotating method and visual
observtions which suggested that rotating at two different
angles gave the best solid-liquid contact, Ham recommended
use of the rotating method (14).
The Agency has, on its own, developed a stirring method
e
which is useable with a wide variety of wastes and will permit
the pH of the solution to be continuously monitored and
adjusted using automated equipment. This device is illustrated
in Figure 1 (see p.6). ORNL found that this device gave adequate
agitation when rotational speeds greater than 40 rpm were
employed. (7,19)
Rather than require use of this or any other particular
equipment, EPA has decided, to simply specify that a suitable
agitator or extractor is one which "will not only prevent
stratification of sample and extraction fluid but also insure
that all sample surfaces are continuously brought into contact
59
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with well mixed extraction fluid." This is being done with
the intention of providing the regulated community with the
greatest flexibility in obtaining a suitable extractor. A
number of commenters interpreted the proposed regulations to
require that agitation be performed with a particular piece
of equipment manufactured by the Associated Design and
Manufacturing Co. (i.e., the equipment EPA employed in many
of its own laboratory studies). This is not the case. The
proposed regulation and the final regulation allow the use
of any piece of equipment that meets the general objective
of insuring sufficient agitation so that stratification of
the sample and extractant fluid does not limit the extraction
of potential contaminants. This will give the regulated
community the greatest flexibility in the choice of extraction
equipment .
Extractors other than the one developed by EPA have been
developed for use in evaluating wastes. One additional device
that deserves mention (26) (Figure 3) uses a simple jig to
hold and rotate a number of jars containing samples of waste
and extractant fluid. Other extractors or agitation devices
are under study. The results of these evaluations will be
made public as they become available.
b. Extraction Contact Time
Ideally waste should be kept in contact with the leaching
solution long enough to insure that maximum concentrations
of the toxic contaminants are obtained. Unfortunately,
however, this is not always possible because small amounts
60
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2-liter plastic or glass bottles
1/15 horsepower electric motor
.screws for holding bottles
£LvA
(XrStJ
Rotary Extractor
-------
of material may continue to leach from the waste for years.
Ham conducted research into the effects of elution time
on cumulative contaminant release. He ran four elutions of
varying duration on the waste—i.e., durations of 2 hours, 24
hours, 48 hours and 72 hours. After each elution, the liquid
was filtered and analyzed for its constituents and the waste
was contacted with an elution of fresh leaching solution.
The results showed that cumulative release after three elutions
is lower with a two hour contact time. For contact times
over 24 hours the results were variable and in no instance
were equilibrium conditions apparently reached. Ham suggested
that a leaching contact time of between 24-72 hours be chosen,
largely for practical considerations (14).
The Mitre survey indicates that there is no consensus
.among the available leaching tests as to the appropriate
contact time required to simulate landfill conditions (15).
This survey indicates that the contact times used in the
various tests can be broken down as follows:
Less than 24 hours - 39 percent
24 hours - 39 percent
Longer than 24 hours - 21 percent
In view of the above, EPA has chosen to employ a leaching
contact time of 24 hours for the EP, based largely on practical
considerations. The Ham research--although it dealt with the
influence of contact time on cumulative release rather than
maximum concent rat ion—would appear to be applicable to maximum
62
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concentration-oriented procedures in its conclusion that the
effect of employing an elution time longer than 24 hours is
inconsistent. Consequently, the Agency has chosen a 24 hour
contact time to for the convenience of the laboratory personnel.
A number of comments were received in relation to the EP
contact time. Some thought the time to be too long and others
thought it to be too short. The Agency acknowledges that, in
some instances, at extraction time of longer than 24 hours
might yield more information. It also recognizes that in
some instances a longer extraction contact time might result
in a somewhat more conservative test. It believes, however,
that concentrations obtained during the 24 hour contact time
for one elution sufficiently approximates the maximum obtainable
concentrations to justify selection of this figure.
c. Number of Elutions
Ham's procedure for measuring maximum concentrations
of toxic contaminants in the leachate consists of running
successive extractions or contacts of the same leaching
solution on fresh waste. His study of this procedure showed
that in some cases, steady state maximum concentrations were
obtained after a very few extractions while in other cases
steady state concentrations were not obtained even after 28
extractions performed over the course of eleven weeks. The
most rapid increase in concentration occurred in the first
extraction. Ham concluded that there is no ideal number
63
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of extractions capable of generating maximum concentrations
of all toxic species in the waste. Consequently, he recommended
three contacts—primarily on the basis of practical
considerations. (14)
EPA has determined that only one extraction need be
performed for the EP. It recognizes that a greater number
of contacts might result in higher concentrations. In the
absence of any demonstration that one number is clearly
better than another, however, and in view of the fact that
the first contact gives the highest concentrations for any
one elution, the Agency has elected to go the less conservative
route and require only one extraction.
5. Post-Extraction Sample Handling
As noted above, EPA has made the assumption that the
toxic species present in the liquid phase of the waste will
migrate from the solid and eventually reach the underlying
aquifer independent of any leaching action which takes place
on the solid. In order to model this situation, the extract
obtained from the solid phase of the waste is combined with
the waste's original liquid phase prior to testing. While it
usually is more convenient to analyze the combined liquids as
one solution, in certain cases where a multiphasic mixture is
obtained analysis may be more conveniently performed on the
separate phases. In such situations the analytical results
are mathematically combined, relative to the ratio of the
phases, to determine the integrated Extraction Procedure
64
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extract concentrations.
Once wastes are extracted, the extract should be preserved
in order to prevent changes in the extract which might result
in spurious analytical or bioassay results. When extracts
are to be subjected to conventional chemical analysis only,
the applicable preservation methods described in the EPA
publication "Test Methods for Evaluating Solid Wastes" (27)
are employed. In the event bioassay test are performed on
the extracts, they should only be preserved by refrigeration
at 4°C. This will prevent the introduction of potentially
toxic preservatives. Irrespective of what sample preservation
technique is employed, extracts should be analyzed as soon as
possible after generation to prevent possible problems. One
such problem relates to the formation of precipitates. In
some cases the Agency has found that precipitates form when
the extract sits for a period of time. While problems relating
to precipitate formation are readily overcome when the extract
is to be analyzed (i.e., through employment of the digestion
procedures described in the test methods specified for use
in evaluating solid wastes) (27), precipitate formation can
present a problem when bioassay procedures are used. The
Agency will be conducting further studies to determine the
magnitude of these potential problems.
65
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IV. BASIS FOR ATTENUATION FACTOR USED IN RELATING NATIONAL
INTERIM PRIMARY DRINKING WATER STANDARD TO EP EXTRACT
VALUES
The Extraction Procedure is designed to predict* the
potential concentrations of toxic constituents which will
leach from the waste matrix itself. There remains the question
of what will happen to the leachate after it leaves the waste
matrix and before it reaches the point of environmental
exposure. To accomodate the attenuation in concentration
that can be expected to occur as the waste passes through the
soil barrier beneath the landfill into the groundwater aquifer
and ultimately to a drinking source, the Agency formulated a
dilution factor designed to acccount for expected attenuation
in groundwater. This attenuation or dilution factor was
calculated against the backdrop of the following fairly
conservative assumptions:
(1) The waste landfill is situated over an aquifer
that is a source of drinking water;
(2) The soil below the site is composed of material
with limited attenuative capacity; and
(3) Persons using the aquifer as a source of drinking
water are supplied from wells situated 150 meters
(500 feet) downgradient from the landfill.
The choice of an attenuation factor reflecting real-
world conditions has proven to be one of the most difficult
tasks faced by the Agency in formulating the EP Toxicity
66
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Characteristic. Although the various attenuation mechanisms
themselves are understood reasonably well, the actual rate of
attenuation is highly s i t e-specifHc . Moreover, there is very
little empirical data on attenuation occurring during actual
waste management, compounding the difficulty of generalization.
Under these circumstances, it is the Agency's view that the
choice of an attenuation factor is at the present time as
much a question of regulatory policy — i.e. what should the
scope of coverage of the toxicity characteristic be — as of
regulatory judgment relative to the expected degree of
attenuation that might occur during any specific type of
waste management. The Agency believes its initial choice of
a dilution factor of 10, and its final choice of an attenuation
factor of 100 are both justifiable by reference to physical
processes—that is, available data supports either choice. The
discussion below sets forth the physical data bearing on
attenuative mechanisms affecting constituent concentrations
in leachate. The policy considerations which determined the
Agency's decision to increase the proposed dilution factor
are then described.
A. ATTENUATION OF CONSTITUENT CONCENTRATIONS IN LEACHATE
Changes in the composition of leachate from a landfill
are usually achieved through a series of reactions. As the
leachate migrates, constituent concentration may be affected
by passage through various media. During percolation through
67
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Che landfill interior, some components will be removed by
adsorptive and complexing reactions, and others wij.1 be added
by waste solubllization. At the interface between the landfill
and the underlying strata, some further components may be
removed by precipitation, filtration of particles, and
absorption on gel precipitates. The existence below the
landfill of an unsaturated zone with a liquid and a gas phase
increases the possibility of attenuation or delay of
contaminants. In this zone, permeability is lower than that
of an all-liquid environment, and flow rates will probably
not be uniform, thereby allowing some solute dispersion. Some
insignificant attenuation by chemical or biochemical processes
may also occur depending on the thickness of the unsaturated
zone. (28)
At the boundary between the unsaturated and saturated
zones, leachate movement changes from vertical to predominantly
horizontal flow. This is in keeping with the fact that water
entering the ground first moves vertically through the
unsaturated zone then enters the saturated zone and travels
in a hydraulic gradient. (28) Groundwater flow is normally
laminar (i.e., characterized by parallel adjacent flow paths),
although mixing can occur during movement through large
fissures or in the immediate vicinity of a pumping well which
alters the flow pattern of the groundwater. (29)
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Leachate does not mix readily with groundwater but tends
to move as a slug, a plume, or a mass of degraded water in a
manner governed by the groundwater flow pattern, although
differences in density and miscibility can cause variation in
behavior between the plume of contaminated water and native
water. The velocity of this slug or plume of contaminated
water may be less than, equal to, or greater than that of
groundwater. (30)
Pollutants entrained in groundwater flow tend to
become attenuated with time and distance. The attenuation
mechanisms involved include dilution, adsorption, dispersion,
diffusion, precipitation, and degradation. The most significant
of these mechanisms in the saturated zone may be dilution of
the leachate as it follows flow paths through the aquifer.
The rate of attenuation will be dependent on the local
hydrogeologic framework. Leachate will tend to be contained
at sites underlaid by fine grained, compact materials with
low hydraulic conductivities (slate, shale, soft clays).
Migration with attenuation is favored in formations exhibiting
intergranular flow (sands, sandstones, sandy clays, gravels)
and formations displaying marked fissure flow with an element
of intergranular storage (chalk) if the intergranular conductivity
is greater than the maximum recharge rate. Rapid leachate
69
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migration through coarse, unconsolidated gravel formations
and fissured jocks such as limestone and granite allows little
attenuation of pollutants. (30)
Where groundwater flow is rapid, leachate from a point
source will form a long thin plume. Where groundwater flow
is low, leachate may tend to disperse laterally. Distortion
of the shape of the plume can also be caused by variations in
permeability, the operation of a pumping well, and changes
in the groundwater flow, recharge, and waste disposal rates,
(which can cause the plume to expand or contract.) The plume
of a leachate containing constituents having a greater
susceptibility to attenuation will be smaller than that of
one containing persistent contaminants. Additionally, a
plume supported by constant input of leachate will ordinarily
stabilize.
As can be seen from the above, the degree of pollutant
attenuation within an aquifer basically depends on site-
specific conditions; therefore it is impossible to choose
a dilution factor that will be appropriate in all cases.
While some sites may exhibit attenuations of 1,000-fold,
others may show no attenuation at all. In some cases, with
time, a site that originally exhibited a 1,000-fold attenuation
may become saturated and begin to flush at the identical
rate at which it is being charged.*
*A recent EPA - sponsored synposium on assessing attenuation
likewise reached the conclusion that leachate attenuation is
difficult to quantify outside of site-specific conditions.
See "Pollution Prediction Techniques for Waste Disposal
"sTFing, a State-of-the-Art Assessment" (31)
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The Agency has utilized mathematical models in formulating
i
an attenuation factor for regulatory use (32). A mathematical
model is a simplified representation of a real system, and
while difficulties are often encountered in quantifying
parameters and testing and verifying results under specific
field conditions, the model can supply information on potential
groundwater effects, A model to estimate leachate dilution
in groundwater and downgradient well discharge has been
devised at the Water Research Center of Medmenham Laboratory
in England (33). This model also suggests that there may be
a wide range of dilution factors even if only a relatively
few variables are considered. The model is based on the
following assumptions:
1. Leachate of consistent composition is discharged
from the entire landfill at a constant rate. (Lehr, Jay;
Combined Media Report (34).
2. There is no chemical change in the leachate as it
migrates through the aquifer.
3. The unsaturated zone is considered a delay mechanism
only.
4. In the saturated zone, the aquifer is uniform and
the natural groundwater gradient is constant.
5. Steady-state conditions exist.
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This model calculates dilution factors using the following
equation:
C (ground water) = IC(leachate)
I + (UB/L)
wh e r e :
C = pollutant concentration
I = leachate infiltration rate
U = groundwater flow rate
B = depth of mixing
L « length of landfill in the direction of groundwater
flow (35)
With the use of this equation, assuming average aquifer
characteristics and a constant leachate production rate of
0.3 m/annum, dilution factors were calculated for three
types of aquifers (Table 4). Results are given below:
Table 4 Dilution Factors For Three Types of Aquifers
Distance from landfill
Aquifer 50meters (164 ft) 300 meters (984 ft)
Chalk 15 - 50 100 - 250
Sandstone 3-10 15-50
Gravel 100 - 200 200 - 500
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The lowest dilution factor obtained by these calculations
(3x) was for a contaminant migrating through a sandstone aquifer
beneath a landfill 50 m long. A well directly downgradient
from the landfill would thus be expected to contain water
(landfill leachate) exhibiting this degree of attenuation
Any additional dilution that may occur would depend on how
fast water was withdrawn from the well. If high pumping
rates were employed water from outside the plume might be
drawn into the well thus diluting the contaminated water (33).
Existing empirical data (and there is not a great deal)
likewise indicates considerable variability in pollutant
dilution factors in groundwater. The behavior of chloride
\
graphically illustrates this. The chloride ion is a highly
mobile and persistent contaminant. It is readily leached
from waste and is resistant to ion exchange, chemical re-
actions and adsorption. Attenuation of chloride during
migration is due to dispersion and dilution. Some observed
dilution factors for chloride at various distances from
waste disposal sites are listed in Table 5.
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TABLE 5. Chloride Dilution Factors (14)
Site
Illinoi
Llangol
Connect
Fly ash
DuPage
Winnetk
Tythegs
s landf il 1
len, Delaware landfill
icut. landfill
settling pond
County, Illinois landfill
a, Illinois landfill
ton landfill, England
Distance D
650
650
200
500
32
800
330
ft.
ft.
ft.
ft.
ft.
ft.
ft.
ilution Factors
4-5
27
2
8-9
2
13
2-3
Attenuation factors for hazardous constituents of leachate
also vary widely. Table 6 illustrates data from field
analyses of several waste disposal sites.
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TABLE 6 - Pollutant Attenuati
on
(14)
Site
Iowa landfill
Fly ash settling pond
Kings Kettle landfill,
England
Coatham Stob landfill
Pollutant
B**HM>IB^^BIMB^I^^MMMMI^m
Arsenic
Arsenic
Cyanide
From Disposal
Site Distance
At tenuat ion
Factor
400 ft.
500 ft.
430 ft.
12 - 13
4
50
England
Mitco
Mitco
Mitco
Mitco
Chromium
Phenol
Nickel
Phenol
Zinc
500 ft.
ad j acent
ad i acent
ad j acent
ad i acent
100
>23
>170
>1000
>14
The results illustrate the current rudimentary understanding
of leachate attenuation and the difficulty in arriving at a
dilution factor which reasonably reflects the dilution in
concentration from the point at which the contaminated leach-
ate leaves the disposal site to the point of human or environ'
mental exposure. In sum, there exist no widely accepted
criteria for gauging this diminution in concentration.
B. EPA'S CHOICE OF AN ATTENUATION FACTOR
In the proposed regulation, EPA chose a dilution factor
of 10 as a conservative, but reasonable figure. EPA based
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this dilution factor on (1) the figures computed from "the
mathematical model—figures which incorporated EPA's original
assumptions of no attenuation between waste matrix and
groundwater aquifer, and, (2) the empirical analyses of
attenuation experienced at actual landfill sites. EPA does
not believe that this factor of 10 represented the minimal
level of dilution that could be expected. For instance,
leachate migrating from a disposal site in Islip, New York
was not attenuated by that amount until it had migrated 805
meters (0.5 mile)(28). It did, however, believe that a
dilution factor of 10 provided a reasonable degree of protection
to the public health and the environment while at the same
time acknowledging the broad range of hydrogeologica1 conditions
at waste disposal sites across the country and the variety
of contaminants likely to be released.
A large number of comments were received concerning the
proposed dilution factor. Most argued that the factor of 10
was arbitrary and far too conservative. Others argued that
the factor of 10 was not conservative enough and that only a
factor of zero would ensure adequate protection to public
health and the environment.
EPA has carefully reevaluated its original choice of a
10-fold dilution factor and has decided that a 100-fold
dilution factor would be more appropriate. A number of
considerations have motivated EPA to make this alteration.
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Probably the most important consideration is the relative
absence of empirical data upon which to base an attenuation
factor, and strong suggestions that choice of any of a wide
range of attenuation levels could be supported by what data
is available. This absence of empirical data is particularly
troubling because the dilution factor plays an exceptionally
important role in defining the breadth of the EP's coverage.
A second consideration involves a shift in current
regulatory strategy. The EP was initially viewed as the
principal mechanism for bringing hazardous wastes into the
Subtitle C regulatory system. However, when it proved
impossible to develop suitable characteristics for carcino-
genicity and other aspects of toxicity, (see pp. 12-18 above),
the Agency decided, at least -for the present, to use the
listing mechanism as the chief means of coverage. The overall
scope of coverage of the EP thus became somewhat less critical,
and a less conservative attenuation factor more appropriate
(particularly since the listing mechanism encompasses wastes
containing EP contaminants).
-Another consideration is the absence of a variance
procedure for wastes which exhibit the property of EP Toxicity
(i.e., wastes which fail the EP are conclusively deemed to
be hazardous). The effects of a waste being anomalously
brought into the system by the EP are greatly aggravated by
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this lack of a variance procedure, thus dictating the need
«
for some caution.
A further consideration is that the EP is a necessarily
less precise instrument than Che flexible listing procedure
for determining whether a waste which straddles the line is
in fact hazardous. For instance, the EP fails to take into
account the quantity of a waste generated—a factor which
could make a difference in determining whether a marginally
hazardous waste belongs in the system or out. Similarly,
the EP fails to take into account mismanagement scenarios
specific to the waste which might argue for including the
waste in the system even though it passed the EP. Conse-
quently, EPA believed that marginal determinations of hazard
might better be entrusted to the listing mechanism.
EPA is also concerned that its assumption of zero soil
attenuation may have been unduly conservative, since soil
attenuation may play a role in many waste management situations.
A decision to take soil attenuation into account also suggests
some need to increase the attenuation factor.
EPA has therefore decided to adopt a 100-fold factor.
It is convinced that waste which fails the EP at the 100-fold
factor has the potential to present a substantial hazard,
regardless of the waste's management circumstance, so that
coverage will certainly not be over-inclusive. In order to bring
into the system wastes which present a potential substantial
78
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hazard but do not fail the EP at the 100-fold dilution factor,
EPA. has listed and will continue to list wastes which do not
fail the EP at this 100-fold factor. Its adoption of the
100-fold factor will thus shift to the listing mechanism
some of the burden for capturing wastes containing EP
contaminants.
EPA emphasizes that the change to the 100-fold dilution
factor is provisional. If forthcoming studies demonstrate
that another attenuation factor is more appropriate, EPA
will switch to that factor. In taking the cautionary step
of moving to the 100-fold factor, EPA recognizes it is empowered
to forge ahead in the face of scientific uncertainty. By the
same token, however, it is empowered to act cautiously—
especially when there is another means (here the listing
mechanism) of accomplishing its goal.
The Agency is cognizant of the fact that for four of the
organochlorine compounds for which thresholds have been
established, the threshold exceeds the published water
solubility for the compounds. However, the Agency does not .
believe this presents a problem.
The primary purpose of the EP Toxicity Characteristic is
to iden-tify manufacturing or process wastes containing
leachable contaminants in toxicologically significant levels.
When present in process wastes or as formulated products, the
compounds are normally present in admixture with other organic
79
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compounds which tend to act as cosolvents to increase the
apparant water solubility. Thus the Agency believes that the
water solubility is not a true measure of potential solubility
in the EP extract.
A second factor leading the Agency to conclude that this
potential problem may not be a serious one relates to the
specific pesticides involved. Several of them enjoy only
limited use and thus are unlikely to actually be present in
any significant number of wastes.
However, the Agency is studying this apparant problem
and if it is determined that corrective action is needed,
such changes will be incorporated into future revisions of
the regulations.
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V. RESPONSE TO COMMENTS RECEIVED ON THE PROPOSAL AND ON THE
NOTICED REPORTS
A. Adopt Existing Regulations
The Agency received several comments questioning
EPA's need to develop a new method of identifying toxic wastes
since there are already a number of states with regulations
which address this problem. These states include Washington
(39), California (40), and Minnesota" (41). Some commenters
specifically suggested that EPA model the Federal regulations
on the California and Washington regulations.
The Agency believes that the hazard posed by a waste is
primarily dependent both on the intrinsic toxic properties of
the waste constituents and the propensity of constituents in
the waste to migrate from the waste to the "point of environmental
exposure. Except in the case of direct discharge to sewers or
surface water bodies, contamination of ground and surface
water appears to be a function of not just what is in the
waste, but also the likelihood of the toxic constituents
migrating from the paint of disposal. Therefore, in formulating
its leaching test, the Agency has attempted to comprehensively
incorporate into the test consideration of the waste's
migration (i.e., leaching) potential. Inasmuch as many of
the outstganding state regulations fail to give consideration
to migration potential, EPA has not adopted their approaches
in constructing the EP.
EPA has, however, to some extent based its Hstin* approach
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states whose regulatory approaches most resemble EPA's in this
regard are Minnesota and California. In both the Minnesota and
California approaches, wastes are considered to be hazardous
based on the presence in the waste of a designated toxic
specie (40,41). In the Minnesota regulations, the waste must
contain a given concentration of the toxic species. In the
California regulations, the mere presence of any one of a long
list of chemical species is presumed to make the waste hazardous,
unless the generator proves otherwise. EPA's newly formulated
criteria for listing come very close to incorporating this
California approach. Under these criteria, the presence of a
hazardous constituent is deemed to make the waste hazardous
•
unless the Administrator, after considering any of a number of
factors concludes that the waste is not hazardous. Most of
these factors have a direct bearing on migration potential.
EPA has elected to adopt this approach in the Extraction
Procedure Toxicity Characteristic in recognition of the
differences between the two mechanisms. The EP Toxicity Charac-
teristic is a one-shot mechanism for bringing wastes into
the system; there is no opportunity for generators to present
mitigating data nor is there any variance procedure. Conse-
quently, it is incumbent on the Agency to fully incorporate
consideration of migration potential into the test protocol
accompanying the characteristic. The listing mechanism, on
the other hand allows for some generator input into the
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Agency's determination and is accompanied by a variance
procedure. Consequently it is permissible to create what is
in effect a presumption for listing based on the mere presence
of the toxic constituent in the waste (as California does (4-°)
in view of the opportunities provided for subsequent consider-
ation of migration potential and the opportunities for more
individualized consideration of hazard.
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B. Suitability of EP As a Regulatory Tool
A number of comments were received concerning the
suitability of using the Extraction Procedure as a regulatory
test. These comments, many of them similar, addressed the
reproducibility, validity, accuracy, and scientific defensi-
bility of the procedure. The comments came from all factions
of the affected community including industry, government,
X
environmentalists, academia and citizens in general.
The comments addressed one or more of the following
five areas:
1. Appropriateness of using a single test procedure,
based on a single model of assumed management, to determine
the hazardous potential of wastes which are disposed of in a
wide variety of disposal environments.
2. Acceptability of using for regulatory purposes a test
procedure that has not been fully accepted by the scientific
community.
3. Whether the EP is reproducible enough for it to be
acceptable for regulatory use.
4. Accuracy of the Extraction Procedure.
5. Propriety of having a hazardous waste definition employ
a test procei
judgement.
idure which requires the exercise of scientific
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1. Appropriateness of Using a Single Test, Based on a
Single Model of Assumed Mismanagement, to Determine
whether a Waste is Hazardous
The vast majority of comments revolved around the
Agency's use of a single test procedure, based on a single
model of assumed mismanagement, to determine whether a waste
is hazardous. Many of these comments specifically questioned
the appropriateness of the Agency's utilization of a co-
disposal scenario. Others expressed the view that because
they handle their waste in a manner very different from that
described in the scenario on which the Extraction Procedure
is modeled, the EP should not apply to them and a means should
be given to permit them to disprove the results of the EP.
Some commenters were especially critical of the Agency's use
of one test to measure environmental mobility in light of
the comments expressed by Ham et. al. (14,16). Some specific
statements of Ham that were pointed to are:
"A standard leaching test provides a reproducible set of
numbers that are a function of the interaction of waste with a
specific leaching solution under a specific set of conditions.
It is up to the decision maker to evaluate those numbers and
make a prediction regarding the behavior of the waste in a
landfill. Unfortunately, the multiplicity of factors affecting
the leaching characteristics of a waste, both in the test and
in the landfill? and the variability of landfill conditions
dictate that interpretation be done with «re "%-^^-JJ^"-
tion of the waste and landfill characteristics. Test results
should not be interpreted rigidly, -g.,Developing or, e.ia
statins that a certain concentration of a given parameter
in the test leachate automatically and without further
in tne cesc ie h t the waste is hazardous in the
consideration indicates tnatcne h factors
landfill. Rather, ""^"'^ '*™ ]* £ *nnual net infiltration
as the amount of waste to be ^sposed affecting the
of water in the area of th e land fill, t d from the
leaching of the *"te (« f ^e,^ e interactions, and the
mi iri^l^i^^i ^ ;t i.sr - waste
passes through wastes or soil. (16, p. -3, &,
85
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"Because of the major differences in a waste's leaching
characteristics as a result of the leaching media composition
no one media can give results adequate to describe properly the
leaching characteristics of a waste." (14,p.2)
"The importance of using different leaching media was
indicated by the results." . . . "Without the use of several
leachates, test results could be very misleading and have no
relation to the actual landfill for a particular waste." (16, p.2)
Proper interpretation of the results from the recommended
procedure is critical to its usefulness. The test was designed
to be aggressive; the numbers obtained are expected to be maximum
values which will not be attained normally in an actual land-
fill." (14, p.3)
"Whatever standard test is used, interpretation of test
results is the crucial factor in determining the test's ultimate
value in predicting whether a waste is hazardous when placed
in landfill. Virtually any leaching test which is properly
interpreted would be more useful in making such a prediction
than would be a well designed leaching test which is poorly
interpreted." (16, p.7)
"Unfortunately, the multiplicity of factors effecting the
leaching characteristics of a waste, both in the test and in
the landfill, and the variability of landfill conditions dictate
that interpretation be done with care and with consideration of
the waste and landfill characteristics. Test results should
not be interpreted rigidly, e.g., developing criteria stating
that a certain concentration of a given parameter in the test
leachate automatically and without further consideration indicates
that the waste is hazardous in the landfill." (16, p.6)
"One obvious way to interpret the leachate composition
results is to compare the concentrations of the various chemical
species to some standard, for example, drinking water standards.
This is dangerous, however, and is difficult to defend for the
leaching test developed in this study." . . . "It was not designed
to provide realistic concentrations of the various species for
a specific situation." (14, 127)
"Thus, once a standard leaching test has been designed,
interpration of the test results becomes a crucial factor
in determining the applicability of the test." . . . "It is up
to the decision maker to evaluate ... and make a prediction
regarding the behavior of the waste." (16, p. 3)
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"It may be possible to correlate test conditions with
landfill concentrations by running extensive verification
tests, correlating a waste's behavior in the test with the
behavior of the same waste in a carefully monitored landfill.
Correlation coefficients could then be developed for parameters
and conditions similar to those in the verification study and
the test result used to estimate landfill concentration."
(Background)(14, p. 124)
"There is a lack of data regarding leachate generation
at fullscale industrial waste landfills with which results
from the laboratory leaching procedure can be compared.
Field verification studies are needed in which unattenuated and
indiluted leachate from specific industrial wastes in mono- as
well as co-landfill situations can be compared with appropriate
leaching test results, preferably on a long term basis."
(Background)(14 , p. 4)
As was discussed earlier in this document, EPA believes
it has the authority to base the EP Toxicity Characteristic
on a single plausibly-occurring scenario of mismanagement
even if this mismanagement scenario does not precisely
correspond to the circumstances of a particular generator's
management practices. Those who quoted Ham on this point
failed to appreciate that Ham's goals differed somewhat from
the Agency's goals. Ham was interested in designing a test which,
insofar as possible, evaluated the leachability of particular wastes
as they are actually managed in particular landfill environments.
Recognizing that the leachability of a waste, and thus its ability to
cause a hazard, is a situation-specific phenomenon, Ham counseled
caution in applying the results of the test to specific landfill
situations. EPA, on the other hand, is not as interested in the
leachability of a waste as it is actually managed as it is in the
leachability of the waste under some plausibly-occurring mismanagement
situation. Thus, while EPA recognizes that its test will not predict
the leachability of particular wastes as they are actually managed,
85-B
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it believes that its test is reasonably predicitve of the hazard
which a waste could present if mismanaged. EPA has intention-
ally refrained from making its definition of hazard dependent
on the actual management to which a waste is subjected, because
it believes that the Act contemplates defining hazard in terms of
some assumed level of improper management. Making the definition
of hazard completely dependent on situation-specific management
practices would have the effect of excluding from the hazardous
waste management system those wastes which are properly managed,
with a consequent sacrifice of the continuing oversight and
assurance of proper management provided by the system.
The above does not, however, fully respond to those who
argued that, in constructing its scenario of assumed mismanage-
ment, EPA should to the extent possible take into account the
actual mismanagement practices to which particular wastes
are likely to be subjected. One of the principal comments
along this line was that EPA should use a variety of leaching
media in the EP to take into account the fact that many wastes
are not likely to be disposed of in municipal landfills, even
if improperly managed.
The Agency recognizes this concern but believes, as arti-
culated in greater detail above, that the single leaching medium
it has elected to employ, when considered in light of the other
aspects of the test, is reasonably predictive of the the leach-
ability of mismanaged wastes, even if those wastes are not disposed
of in municipal landfills. The Agency also believes that its de-
cision to employ a single model of improper management is
85-C
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justified by concerns about the administrative feasibility
of employing more sophisticated multiple models. In any
event, to the extent the commenters are concerned that, by
failing to tailor the model of improper management to specific
management conditions, EPA is making its test too aggressive,
these concerns are put to rest by EPA's switch to the 100-fold
dilution factor. EPA is fully convinced that anything which
fails the EP at the 100-fold factor has the potential to
cause a hazard, no matter what leaching medium, etc., it is
actually exposed to.
85-D
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2. Acceptance by Scientific Community
A number of comments questioned the acceptability of
using a test procedure which has not fully been accepted by
the scientific community. Before addressing the acceptability
of using a test procedure for regulatory purposes that has
not been fully accepted by the "scientific community," one
must first define what is meant by the "scientific community".
There are two groups making up membership in this
community; those scientists working for industry, government,
and other entities who will be directly affected by the
regulations and scientists whose only interest is academic.
The first group has a direct financial or institutional
interest in seeking to exempt from the system waste(s) their
organization or constituency generates. Obviously, these
members of the regulated community are concerned with the
economic implications of any test methodology employed in
defining a hazardous waste. The second group of scientists
are basically motivated by a desire to assist the Agency in
developing regulations utilizing the "best" information
that the scientific community possesses.
In the main, it was the regulated community that commented
that methodology should receive scrutiny and acceptance by
the "scientific community" prior to regulatory use. The
Agency agrees with this comment. Toward this end, EPA
developed the proposed test procedures in open view of
all interested parties in hope that scientists would then
86
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apply the procedures being developed to wastes of concern
and, with the data so obtained, assist the Agency in correcting
any problems with the proposed procedures. With few notable
exceptions (35, 37, 42, 43) this did not happen. Scientists
from the regulated community have, in the main, concerned
themselves with trying to convince the Agency to modify the
test procedures. Their go.al was to make the test procedures
less aggressive and, thus, less likely to identify their
particular waste as a hazardous waste, rather than to determine
if the procedures were scientifically valid (i.e., accurately
identify wastes needing controlled management). Even though
the Agency extended the comment period on March 12, 1979,
for an additional sixty days (44 F_R 13548)^4)^ industry did not
submit significant amounts of data.
While many comments were received commenting on the invalid-
ity of the test procedures, few commenters supplied the necessary
scientific data to justify their concern. The chemical industry
was especially unresponsive. Studies sponsored and conducted
by the Agency(18 , 19 ), the Electric Power Research Institute(37),
and others (35,36) have indicated that the Extraction Procedure
is of acceptable reproducibility ' for regulatory use. Given
the lack of convincing data to the contrary from the affected
groups, the Agency has decided to employ the Extraction
Procedure in the regulations being promulgated today. If
future research uncovers better test procedures for use in
§3001 regulations, the regulations will be amended.
87
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probably more germane to the issue of the adequacy of the EP
and the analytical techniques. Third, the studies were not
designed for comparison with other studies. Thus, even when
results are presented on similar phenomena, e.g., the intra-
laboratory reproducibility of analyses results for barium and
chromium, the statistics reported are not always sufficient to
make good comparisons. For example, some of the studies (19,18)
use coefficients of variations (the same as the relative standard
deviations, RSD) to indicate the degree of variability in the
measures, while others (36) use a relative standard error (RSE).
Thus, when the specific means and standard deviations are not
reported, it is not possible to calculate uniform measures of
reproducibility that can be used across studies.
Fourth, none of the studies were designed to focus
e
specifically on the questions of reproducibility. The exception
might be the complex design in the study conducted by the Electric
Power Research Institute (37), but the use of geometric analyses
makes the study incompatible with research results in the other
studies. Also, no interpretation of the results from this
study (37) are offered in the report which was available.
Along this line also, none of the studies presented data on
analytical technique reproducibility for all of the toxic metals
included in these regulations. This leaves open the question of
whether different levels of reproducibility are characteristic
of different toxic metals. This limitation is important because
it cannot be assumed that the analytical precision of measures on
one element could be equally precise for another element.
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Apparent Reproducibility of the EP
With the above in mind, we turn to a review of these
studies insofar as they bear on the reproducibility of the EP.
The study by the American Electroplating Society (35) examined
twelve wastes (sludges) generally representative from wastewater
treatment systems in the electroplating industry. The study as
a whole consists of thirteen experiments, some of which are
still in progress. Two major deviations from the EP were
incorporated in the study. First, lumps of solids in the waste
samples were broken up by stirring prior to the initial
centrifugation or filtering of the sample. As stated in the
report, this stirring could possibly cause a higher level of
toxic metals in the final EP extract (35, p.2-2). The second
deviation from the EP was involved when, after agitation, the
o
beakers with the solid waste material were removed, covered
with a parafin cover, and allowed to stand and settle overnight
(35, p. 2-4). Both of these deviations from the EP standard
invalidate any good estimate of the general reproducibility of
the EP. It was noted in the report that filtering vs.
centrifugation in the EP can make the difference between passing
or failing the threshold values for toxic metals established by
the EPA (35, p.2-5). However, the experiment involved only two
metals, lead and chromium, and two levels of pH, pH 5 and pH 7.
At the specified pH 5 level in the EP, the threshold value for
lead was surpassed when centrifugation was used to separate the
solid material from the sample. The threshold value was not
reached when filtration was used.
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The NUS Corporation (36) subjected samples of four waste
materials to the EP and analysis using the AA techniques. Few
comments in the report related specifically to the reproducibility
of the EP, except that the specified EP was used. The NUS
study also compared Toxic Extraction Procedures (TEP) with the
EP. The TEP is the precursor to EPA's current EP. One statement
from the NUS report (36), however, deserves special comment.
The report states that sampling error is a factor in the (inter-
laboratory) reproducibility test. Even though the report makes
the distinction between "repeatability" (intra-laboratory
consistency) and "reproducibility" (inter-laboratory concurrence),
the statement is not appropriate if aliquots of the same EP
extract are used. Specifically, sampling error relates to the
overall representativeness of the waste material to be charac-
o
terized, not to the precision of the EP or of the analytical
techniques.
The Oak Ridge National Laboratory (19) employed the EP
and analyzed eighteen different wastes, including arsenic-
contaminated ground water. The standard EP was followed, except
that extractors made of different materials or combination of
materials were used. The report states that "no significant
problems were encountered in extracting or analyzing wastes for
inorganic species"(19, p.2), but several suggestions were
offered with regard to various aspects of the EP. For example,
stirring problems, e.g., binding and sampling grinding, were
encountered with some of the wate material during extraction.
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Also, the report recommended that a nonmetallic extractor should
be used to lessen the possibility of contamination occurring
during waste extraction. In general, however, this report (19)
suggests that the EP is relatively reproducible. One statement
(19, p.15) suggests that reported values of chromium, nickel
and calcium indicate an EP variability trend that exceeds that
expected for analytical determinations. This statement applies
only to the situation when extractors made of different materials
are used. Out of context, the statement would suggest that the
EP is unreproducible in either intra- or inter-laboratory stiuations
A total of twenty-five wastes from eleven different
sites were examined in the study by Environmental Monitoring
Systems Laboratory in Las Vegas (18). One specific deviation
from the EP was employed in the study. All waste materials
were screened by inductively coupled plasma emission spectroscopy
(ICM) to select those wastes for EP and analyses by AA methods
(18,p.22). Also, different kinds of agitation, the wrist-arm
shaker and the extractor device, were used in the study. The
report states that preliminary results suggest good agreement
(from the analyses) between the two types of agitation. Like
the Oak Ridge National Laboratory Study (19), this study (18)
also suggests that steel containers not be used in the EP
because of its possible contamination in tests for chromium.
Also, the report states that the variation in the tests for
barium are due to the analytical method (not the EP). Other
studies are planned which will address the issue of the
reproducibility of the EP more directly, but there is little in
94
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the interim report to suesest t-hai- »•>,« v-a • - ,
r w ouggest cnat the EP is not generally
reproducible.
Finally, the study by the Electric Power Research
Institute (37) is the only investigation which clearly separates
out the question of reproducibility of the EP and the analytical
techniques. Further, the complex design partitions (through
analysis of variance (ANOVA) techniques) variation of the EP
and analysis techniques which can be attributed to inter- and
intra-laboratory results. Four types of utility wastes were
subject to the EP and analyzed in the study. The design included
all the toxic metals except silver. Also, the basic design of
the study was intended to compare flame and furnace AA methods
of analysis. Unfortunately, because of incomplete data and
values for toxic matal content which were sometimes below
detection limits, a variety of adjustments were incorporated
into the overall statistical analyses. For example, simulation
methods were used to produce enough observations to complete
the ANOVA design. Geometric techniques were employed because of
the highly skewed observations, i.e., results from the test of
toxic metals in the waste materials. In all, the results of
the study should be given a very conservative interpretation.
As noted previously, no interpretation of the results is offered
in the study report. However, examination of the data presented
and communication with those persons who conducted the analyses
suggest two major findings:
First, as might be expected, intra-laboratory reproducibility
/ . „ ^ f^ u^fh the EP and the analytical techniques tended
(consistency) for ootn cne ^r
95
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to be better than inter-laboratory reproducibility (concurrence).
Secondly, the reproducibi1ity of the EP overall (both intra-
laboratory and inter-laboratory) appears to be better than the
overall reproducibility of the analytical techniques. This latter
finding suggests that the overall reproducibility of the analytical
techniques may be more of a problem than the EP itself. This
is contrary to assumptions which have been made in some studies
(36) and further questions the use of the analytical results of
EP extracts as an uncontrolled criterion to assess the
reproducibi1ity of the EP.
Apparent Reproducibility of the Analytical Technique
Most of the five studies reviewed addressed, to some
extent, the general reproducibi1ity of the analytical techniques.
The data reported, however, is sometimes too incomplete to make
any comparisons among the different studies. Consequently,
caution has to be exercised in generalizing about the
reproducibility of the analytical techniques. Some discussion
about the statistical measures used to indicate reproducibility
is in order before proceeding to the separate research studies.
The measures mentioned or employed across the studies have
included the following:
0 standard deviations
0 relative standard deviation, i.e., the standard
deviation expressed as a percentage of the mean
0 the coefficient of variability, i.e., the same as the
relative standard deviation
0 the range of values, i.e., the difference between the
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highest and lowest value
standard error (unspecified), and
relative standard error, i.e., the standard error of
the mean expressed as a percentage of the mean.
Each of these measures can be used to assess relative
reproducibility under certain circumstances. In some cases,
however, the measures can be misapplied. For example, the best
indicator of reproducibility when replications are made of the
same test and the values are averaged is the standard error of
the mean or the relative standard error, not the coefficient of
variability, i.e., the relative standard deviation. The
advantage of the standard error of the mean is that probability
statements can be made about hypothetical true values, e.g.,
the threshold values, or different mean values obtained from
other tests of the same waste material. The only study to employ
the standard error of the mean (specifically the relative standard
error) was the NUS Corporation study (36). The relative standard
error (RSE) indicates that one can be 95% confident that the
true value, e.g., level of toxic metal, is within +_! RSE of the
mean value obtained. There is no direct way of comparing the
coefficient of variability and the RSE. The advantage of the
relative standard deviation or the relative standard error is
that variation is expressed as a percentage of the mean, thereby
facilitating relative comparisons of the variation around the
mean, i.e., reproducibility.
The study by the American Electroplating Society (35)
presents data on the intra-laboratory reproducibility (consistency)
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of duplicate analyses for three wastes on toxic levels of
cadmium, lead and chromium (35, p. 2-20). The results for lead
are probably not representative since the values for lead con-
tent were near or below the detection limits of the analytical
technique. The other results of the analyses of the extracts
at pH 5 are presented below in mg/1:
Waste ' Cadmium Chromium
2
7
9
Mean
120
1.7
— _
SD
6
.45
— —
RSE
+ 7%
+ 38%
_ —
Mean
3.3
.33
.40
SD
1.4
.09
.08
RSE
+ 60%
+ 39%
+ 28%
The RSE employed above as the indicator of reproducibi1itv
indicates the 95% confidence interval as a percentage of the mean.
For example, there would be the probability of only 5 times out
of 100 that the true mean for cadmium in waste 2 would be out-
side of the range of 111.6 to 128.4. The RSE also permits
comparisons by the calculation of the 95% confidence intervals
for each measure. For example, the 95% confidence intervals on
chromium levels in wastes 2, 7, and 9 would be 1.32 to 5.28,
0.20 to 0.46, and 0.28 to 0.512, respectively. Thus, one could
say that the chromium level in waste 2 is significantly (p <.05)
different from the chromium levels in either waste 7 or waste 9.
On the other hand, because the confidence intervals overlap, it
cannot be said that the chromium levels between wastes 7 and 9
are significantly (p <.05) different. Further, it cannot be
stated that the chromium level in waste 9 is significantly
(p <.05) below the threshold value of .50 mg/1 proposed in 43
FR 58956(9). However, one can state, with confidence that it
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less, but range from 1.01 to 1.41. These ranges exclude analyses
where "the number of values reported as 'below the detection limit'
was not so large as to preclude statistical analyses, but large
enough to make the results less reliable" (3, p. 3 of Phase I Report)
The effect of the simulated values on the CMs is not known
exactly. Consequently, only tentative conclusions, or hypotheses,
about reproducibility seem justified from the report.(37)
In conclusion, the above reports, while not complete enough
to permit any firm conclusions, do contain data which is
suggestive on the issue of reproducibility. Of particular
interest is the suggestion in the EPRI data that the EP is at
least as reproducible, if not more reproducible, than the
analytical techniques. In as much as these analytical techniques
•
have generally been accepted by industry and others as being
sufficiently precise for regulatory use, the EP should also
prove acceptable.
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4. Accuracy of Test Procedure
A number of commenters questioned whether the EP
was sufficiently accurate for use in a regulatory regime. By
this they apparently meant one of two things: either that
the EP inadequately predicts the -leaching which might occur
under the disposal conditions postulated in the EP's definitional
model or that the EP is not sufficiently precise to enable
one to be confident in the results obtained from a given
testing.
In response to the first criticism, the Agency
believes, based on its hypotheses noted above, that the EP
(not including the attenuation factor) is an accurate prediction
of the levels of leaching which could occur in a relatively
aggresive leaching environment. The Agency concedes however,
that it may have fallen somewhat short of fully modeling the
leaching which could occur in a actively decomposing municipal
landfill — in part, bacause its leaching medium fails to take
into account the various chemical, biological and physical
factors whicli bear on the aggres s ivines s of municipal landfill
leaching media. The Agency further concedes that it had little
empirical data upon which to base its assumptions about the
accuracy of leachability on site specific considerations.
Obtaining such empirical data may be an ephemeral goal.
Nevertheless, the Agency hopes to assemble data on leachate
concentrations observed at actual landfill sites in an attempt
to gauge the representativeness of the EP.
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In response to the second criticism, the Agency believes
that the EP is sufficiently precise to enable one to obtain
reasonable confidence in the results of the test—especially
given the fact that one can always obtain greater confidence
in the results by running further replicates of the test.
The width of the confidence interval has an inverse relationship
to the number of tests run on a given sample. Consequently,
if there is a question whether a given test is reflective of
the "true" result, it becomes a simple matter to run additional
samples until the desired confidence is obtained.
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5' Propriety of Requiring Exercise of Scientific Judgement
A number of comments argued that the Extraction Procedure,
as published in 43 JFR 58956<9>, was not well enough defined to
permit the unambiguous interpretation of how the procedure
should be followed. Furthermore, problems arose in conducting
the liquid-solid separation and in agitating the sample during
the extraction phase of the procedure.
The Agency agrees with these comments and has taken steps
to eliminate the difficulties. Some of the specific changes that
have been made relate to:
1. specification of filtration as the final stage in
sample preparation prior to measurement,
2. specification that the purpose of centrifugation is
to aid in liquid-solid separation, not as the final means of
separat ion,
3. use of a generic specification of the agitation equipment
4. codification of under what conditions the sample contains
so little solid that it can be considered to be a liquid for testing
purposes .
In addition to changes that have been made in the pro-
cedure description* the Agency is making available to the public
a methodology manual (27) to present additional descriptive
information on the sampling and testing methodologies used
in the evaluation of wastes. The purpose of this manual is
to give more specific operational information than would be
practical to put in the regulation itself.
* Appendix II of the §3001 regulations.
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This manual will contain information about testing
specific wastes, including clarification of any procedural
steps needed to correct interpret ational difficulties.
The Agency intends to keep the manual current by updating it
on a regular basis.
However, the Agency believes that no laboratory procedure
for waste testing can ever by written that unambiguously addresses
all potential interferences. The testing methods have been written
for use by experienced scientific personnel. It is felt that
such persons will be able to overcome potential problems and
obtain acceptable data, given an adequate understanding of the
intent of each phase of the testing procedures.
Specific examples of how this philosophy would work can
be gleaned from an examination of some of the comments. One
organization subjected oak and maple leaves to the Extraction
Procedure and experienced significant difficulty in attempting
to separate the extractant liquid from the leaves. The intent
of the liquid-solid separation step is to remove all particles
of the extracted sample having a particle size greater than
0.45 micrometer from the extract. Thus, an experienced scientist
would know to allow the leaf particles to settle, under the in-
fluence of either gravity or centrifugal force, decant off
and filter the bulk of the liquid, then transfer the remaining
mass of leaves to the pressure or vacuum filter for removal
of the small amount of free liquid that remains. This
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change, though not significant from the standpoint of the final
results, would have eliminated the long filtration time experi-
enced by the commenter.
A second example which serves to illustrate this point re-
lates to the large number of comments the Agency received on the
agitation apparatus described at 43 £R 58961 . These comments
concerned problems with the specific extractor described in
a
the proposed regulations. These problems consisted primarily
of jamming when an attempt was made to extract hard, granular
wastes, and potential extract contamination caused by using
a metallic extractor.
As described in the proposed regulation:
"A suitable extractor will not only prevent strati-
fication of sample and extraction fluid but also
insure that all sample surfaces are continuously
brought into contact with well mixed extraction
fluid."(9)
The Agency believes that with this description a competent
scientist can eliminate any problems, of the above types, en-
countered with specific wastes or agitators. If the sample is
of such a size and consistency that jamming occurs due to the
spacing between the extractor blade and the container, then
either an agitator with a different spacing should be used or,
if this does not eliminate the difficulty, a different type of
agitator should be employed. This latter approach was used
by several commenters in determining the leachability of
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materials such as coal combustion ash. Though the studies
conducted at Oak Ridge National Laboratory (7,19) and Las Vegas
(18) indicated that contamination of the extract by an extractor
fabricated of Type 316 Stainless Steel was not a significant
problem, the Agency feels that if this problem actually mani-
fests itself, scientist conducting the tests will know to
employ an extractor fabricated of either plastic or glass,
since neither material would hinder attainment of the agitation
conditions specified in the regulation.
The most significant problem encountered by commenters in
applying the Extraction Procedure to a specific waste, occurred
when filtering samples of drilling mud. Due to the thixotropic
and pore clogging properties of such materials, neither filtra-
tion nor centrifugation was able to effect separation of the
liquid and solid phases. It is the Agency's position that, in
such cases, the whole waste should be treated as a solid and run
cx>
through the extraction procedure. If, after performing the ex-
traction procedure, no extract is obtainable, the waste should
not be considered hazardous.
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C* Failure to Distinguish Between Chromium III and Chromium VI
A number of comments argued that, basing an Extraction
Procedure Toxicity threshold on total chromium in the extract
^k
was improper . These commenters argued that the two oxidation
states of chromium present very different toxicity and environ-
mental problems and therefore the threshold should be based
only on the concentration of chromium in the +6 oxidation
state.
In support of this position the following was cited.
Cr(VI) is significantly more toxic than Cr(IIl).
Oxides and salts of Cr(VI) are very soluble in water
while those of Cr(IIl) are relatively insoluble.
Cr(VI) has been shown to be a potent carcinogen in
humans while Cr(lll) on the o'ther hand has not been
shown to be carcinogenic in either humans or animals.
0 Monitoring of groundwater below a landfill receiving
tannery waste containing chromium in the reduced +3
state has shown only limited migration after a period
of 10 years. (45)
0 There is no data to indicate that under conditions of
land burial Cr(IIl) can be converted to Cr(Vl).
* The maior group affected by the application of thresholds,
appears to be the leather tanning industry. According to a
study conducted for the E.P.A.U6) and comments received in
response to the proposed regulations(47), the tanning industry
generates and disposes of approximately 200x10* Kg of waste^
per year containing approximately 1000 metric tons of chromium.
109
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In formulating both the National Interim Primary Drinking
Water Standards and these regulations, the Agency has chosen
not to adopt separate thresholds for the various oxidation
states of chromium. The reason for this is the Agency's
concern about the possibility of the conversion of chromium
from the relatively nontoxic +3 form to the toxic +6 oxidation
state after disposal occurs. This concern is based on studies
and observations reported by researchers of the California
Department of Health (48) and conditions known to occur in
municipal waste disposal environments.
A great deal of controversy exists about the environmental
and health effects of chromium. The two most important oxidation
states of chromium for environmental purposes, are chromium III
•
and chromium VI. There is general agreement, as to the hazards
posed by the chromium VI state since it exhibits toxic effects
to humans and animals by every route of exposure and is reported
OB
to be relatively mobile in the environment(48). On the other
hand, available evidence indicates a generally low oral toxicity
for chromium(III) compounds. The reason for the controversy
over the hazard posed by wastes containing Cr(III) revolves
around its possible conversion into the more toxic Cr(Vl) form
under conditions that might reasonably be expected to occur in
the environment.
The California researchers(48) found that upon exposure to
artificial ultra violet light or sunlight, significant oxidation
of Cr(lll) to Cr(Vl) takes place in water within a pH range
110
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V
of 7 to 10. Exposing an aqueous suspension containing both
soluble Cr(lll) and precipitated Cr(OH)3, to ultraviolet
light and air for 5 days resulted in oxidation of approxiraatel
20% of the total chromium to the Cr(vi) state. After 7 days
the percentage of chromium in the Cr(Vl) state approached
50% and after 41 days the percentage approached 90%. Definitive
evidence of the photo-oxidation of Cr(lll) in actual chromium
bearing tannery wastes has not been obtained. According to
the California researchers:
"Analysis of these wastes for Cr(Vl) has proven unreliable
using any of the published methods. These analytical
methods all involve acidification of the Cr(Vl) solution
prior to final analysis because the tannery wastes all
contain relatively high concentrations of dissolved organics,
and because Cr(Vl) is quickly lost by reduction by the
organics. We have found that this redox reaction takes place
very rapidly and results in irreproducible results for Cr(Vl)
concentrations. It is commonly held that chromium tannery
wastes do not contain hexavalent chromium and the basis for
this belief is negative analytical results based on the EPA or
Standard Methods procedures(49). Close examination indicates
that these negative chromium(VI) data may well be an artifact
of the method and do not reflect the true hexavalent chromium
content of the tannery wastes."(48)
Given the fact that the oxidation of Cr(lll) to Cr(Vl)
has been demonstrated to occur under relatively mild conditions,
and that this demonstration is consistent with the observation
that the predominant form of chromium in the surface layers
of the sea is the hexavalent form (48), the possibility that
Cr(lll) in wastes may undergo oxidation after disposal cannot
be ruled out.
In summary, the Agency believes that pending further studies
to determine the extent to which this conversion does or does
not occur under environmentally significant conditions, the
only prudent course of action is to consider all forms of
111
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chromium potentially toxic. The Tanners' Council of America
in their comments on the proposed regulations echoed this
conclusion. To quote:
"A study conducted in California found that ultra-
violet light and sunlight promoted the oxidation of
chromium. It is appropriate, therefore, that the
disposal of waste's containing trivalent chromium be
regulated so that these wastes are quickly and adequately
covered at the disposal site to minimize their exposure
to sunlight ."(5)
If future research indicates that such a course of action
is not warranted, then the Agency will revise the definition
of a hazardous waste accordingly.
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D. Operational Problems
Introduct ion
The comments previously discussed, dealt with what
could be termed philosophical disagreements with the
proposed toxicity characteristic. In addition to these philoso-
phical questions, a number of comments were received concerning
the actual operation of the Extraction Procedure. These
comments can be grouped into the following areas:
1. Liquid - solid separation procedures
2. Structural integrity procedure/ Grinding of sample before
extract ion
3. Problems with the extraction equipment/agitat ion
4. Adjustment of extract pH
5. Sample: extractant ratio
6. Final volume adjustment
7. Analysis of multiphasic extracts
8. Extractant toxicity as it affects testing of the extract.
This section will address those changes made in the proposed
procedure as a consequence of these comments, and explain other
suggested changes that were not made.
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1. Liquid-solid Separation Procedure
As was briefly discussed earlier, significant problems
were en countered by a number of commenters in separating
the liquid phase of the sample from the solid phase using
either the filtration or the centrifugation procedure. In
the case of thixotropic materials such as drilling fluid and
paint these difficulties were severe.
As discussed above, the Agency believes that if no liquid
phase can be generated using the separation procedure, the
whole waste should be treated as a solid and subjected to
the extraction. If, after the extraction procedure
is performed, no liquid is produced, the waste should be
considered nonhazardous.
The separation problems encountered with the wastes other
than paint and drilling fluid appeared to be readily overcome
using standard laboratory techniques although, possibly because
of the manner in which the test procedures were written, the
availability of these solutions may not have been readily ap-
parent to the laboratory personnel. In the main, these problems
consisted of either clogging of the filter membrane pores or
lack of a centrifuge which met the specifications described
in the proposed regulation.
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In order to overcome these problems, the following
changes have been made.
a. The centrifugation procedure is now defined in terms
of goals and no specific equipment is specified. This change
clarifies the concept that centrifugation is actually more
a tool for prefiltration sample preparation than a final
separation technique itself.
b. The filtration step is no longer defined in terms of
specific equipment. The procedures manual(27) will contain all
references to specific equipment to make it clear that specific
pieces of equipment are not being mandated. The procedures
manual(27) will also clarify for the operator what procedural
changes one may make without invalidating the test.
These changes in the description of the filtration step
should clear up any uncertainty about the use of vacuum fil-
tration. It is the intent of the Agency that if the solid
phase does not require high (75 psi) pressure to affect
separation, then use of the more readily available vacuum filter
is allowable. The use of the pressure filter offers a means of
operationally defining, at what point a wet solid can be
considered a solid for purposes of extraction. (For example,
when to treat a sludge, though it might actually still contain
85% water, as a solid for extraction purposes.)
The following discussion will address specific criticisms and
operational problems brought out in the comments. The first of these
relates to the potential clogging of the filter pad by wastes having
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low liquid to solid ratios. This situation may result in a
reduced degree of separation and long filtration times. The Agency
believes this potential problem is easily overcome. In such
cases, if the solid tends to clog the filter pores, an initial
centrifugation to compact the solid is recommended. The liquid
thus obtained is then filtered to remove carryover particles, and
the solid remaining is filtered under gradually increasing pre-
ssure. Specific, directions will be given in the methodology
guidance manual(27) for those investigators unfamiliar with such
techniques.
Section 250.13(d)(2)(1)(A)<1) of the proposal(9) called for
filtration to continue until no significant amount of fluid
«0.5 ml) is released during a 30 minute period. Commenters
felt that for many wastes this is unnecessary. In addition,
one commenter, suggested that filtration should be stopped
when gas issues from the filter since allowing gas to
bubble out of the filter for up to 30 minutes can cause the
volatilization of materials from the filtrate.
The Agency agrees with these recommendations and has
made the necessary changes in the regulation. In order to
eliminate confusion on the part of the testing community
without resorting to overspecification, the regulation has been
changed to describe what is intended and to delete speci-
fication of the filtration time. Laboratory personnel can
use whatever filtration time is required for the specific waste.
In addition, the final regulation specifies that filtration
should stop when gas issues from the filter. This should
eliminate any potential problems with gas discharge.
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Section 250.13(d)(2)(i)(A)(l) of the proposal(9) called
for inverting the filter unit when changing the filter pads.
The Agency has been told that filter holders supplied by one
manufacturer cannot be inverted without leaking. Thus, the
regulations have been changed to eliminate this specification.
If membrane changes are necessary to complete the required
separation, instructions from the manufacturer of the specific
filter holder being employed should be followed.
Some of the commenters reported that when the pressure
filtration technique was applied to different wastes, filter
cakes with significantly different amounts of moisture were
obtained. They felt this indicated a problem with the tech-
nique. The Agency disagrees with this interpretation. The
filtration procedure is intended to simulate the separation
that may occur in a landfill. If the liquid refuses to
separate out during pressure filtration, it will also tend
not to drain away from the waste when the waste is placed in
a landfi11.
Comments were received which said that requiring two con-
secutive 30 minute centrifugations without an apparent change
in degree of separation was excessive. The Agency disagrees
with this comment but notes that this concern has been accomodated
by adoption of the more flexible centrifugation procedure. Because
studies indicated that centrifugation alone resulted in carryover
of particles > 0.45 urn, centrifugation is now simply used as
a means of achieving a preliminary separation in order to
117
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speed up filtration. All centrates are to be filtered to remove
fine particles prior to analysis. This change in the
centrifugation procedure addresses the concerns of other
comments relating to addressed:
a. Problems with centrifugation of wastes containing solids
having lower densities than the liquid phase, and
b. The need to define centrifugation conditions in terms of
separation force (g forces) instead of rotor speed
and diameter.
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2. Structural Integrity Procedure/Grinding
In order to accomodate generators whose wastes are not
expected to undergo significant structural degradation after
disposal because of their monolithic structure or subjection
to special "fixing" processes, the Agency developed and
incorporated the Structural Intgrity Procedure into the
proposed regulations(9). This procedure received criticism
from several persons and groups. The specific criticisms
were :
a. any alteration of the test specimen is not representa-
tive of actual field conditions,
b. the specific field conditions used as a model for the
Structural Integrity Procedure are completely contrary to
conditions that actually exist in the field,
c. the equipment specified in the proposed regulations(9)
is unavailable and, thus, industry has not been able to
adequately evaluate the procedure,
d. it is impossible to obtain an undisturbed field speci-
men of the size and shape required,
e. the foam block employed as a sample holder is subiect
to contamination, and
f. the Structural Integrity Procedure lacks sufficient
scientific validation,
Though some of these comments are valid, the Agency does
not believe that the information presented in the comments is
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sufficient to warrant either dropping or substantially modify-
ing the test procedure.
The following states the Agency's reasons for retaining
the proposed Structural Integrity Procedure and the reasons why
changes have not been made.
None of the comments presented any evidence to support
the claim that stabilized, or other monolithic wastes, fail
to undergo degenerative structural changes after disposal.
In fact, studies (51 and 52) indicate that significant
deterioration actually occurs in some cases. One such situation
was found to occur with fly ash stabilized with a popular
commercial fixation process (52). Thus, the Agency believes
that in order to carry out its mandate under RCRA to consider
potential for harm under improper management conditions, it is
reasonable to extract wastes in their degraded form if degrada-
tion is actually going to occur in the field.
A second point raised by commenters concerns the field condi
tions modeled by the Structural Integrity Procedure. While
subjecting stabilized waste to compaction stresses is not
routine practice, it is by no means unknown. Advertisements
have appeared in a number of publications, including the
Washington Post, stressing the beneficial uses to which
stabilized waste can be put. Among the uses suggested was
as a replacement for gravel in construction applications (e.g.,
forming bicycle paths). Since such uses are possible, and, in
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the case of some wastes probable, it appears reasonable to
assume the waste may be subjected to the compaction forces
Sp
imparted by earthmoving equipment such as tractors. Given
such an assumption, the Structural Integrity Procedure,
which is a modification of an established procedure for
simulating the effects compaction machinery has on soils,
appears to be based on reasonable assumptions.
The comments made with respect to the unavailability of
the equipment were due to a misunderstanding on the part of
the commenters. The equipment design belongs to EPA, not to
any one company. The design and specifications were published
at 43 FR 58691(9) and anyone desiring to obtain the equipment
could either fabricate it in their own facilities or obtain
it from a competent machine shop. EPA published the name of
the particular supplier from which EPA purchased its units
solely for the convenience of the public.
The Agency agrees with the concern that obtaining an
undisturbed specimen of an already disposed of monolithic
waste presents a problem. However, the agency envisions
preparing samples of the correct size and geometry by casting
the fresh waste in a suitable mold, allowing it to cure for
the specified time, and then subjecting it to the procedure.
This is analogous to the methodology commonly employed in
the construction industry for testing the strength of concrete
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For those situations where a specimen is required of an already
inplace waste, geological coring equipment (which is
*.
inconvenient and potentially expensive) can be employed.
The Agency recognizes the concern with particles becoming
trapped in the cellular polyurethane sample holder causing
contamination of subsequent samples. To eliminate this potential
problem, the equipment specifications have been broadened to
permit the use of non-cellular sample holders which are
easily cleaned between tests.
EPA believes that even though the reproducibi1ity of the
Structural Integrity Procedure has not been determined, the
advantages of including the test in the regulations outweigh
the potential disadvantages. Elimination of the test would
require everyone testing waste to grind it to pass a 3/8"
sieve. Retention of the Sturctural Integrity Procedure
imposes no additional burden on the regulated community
and, at the same time, allows generators who stabilize their
wastes against leaching a means of demonstrating this property.
Grinding
A comment was received concerning the fact that some wastes
were difficult to grind. The commenter reported that attempting
to grind a waste in a blender resulted in the blender breaking.
The Agency realizes that some wastes may be very hard. A blender
is not designed to be a grinder. If a hard material is to
be ground, then equipment designed for such use should be
employed. Such equipment is readily available from companies
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servicing metallurgical and plastics testing laboratories.
In addition, if the material to be tested is so strong
that ^grinding actually presents a problem, then it is likely
that such a material would not tend to be ground in the environ-
ment and should therefore be evaluated using the Structural
Integrity Procedure.
3 . Agitat ion
A number of comments were received concerning problems
people encountered, or envisioned, while employing the extractor
pictured in Figure 1 of the proposed regulation (43 FR. 58961)(9),
These comments fall into the following groups:
a. The extraction conditions (40rpm) do not prevent
strat ification.
b. In certain cases the extractor blade will iam, with
the result that the motor can burn out.
c. When using very small samples the top blades do not
contact the solution.
d. When solids having a very low density are tested,
there is insufficient room in the extractor to accommodate
all the solution and still agitate the system vigorously.
e. Use of stainless steel as the material of construct-
ion may result in contamination of the extract with various
metals.
f. The extractor is not large enough to permit the pre-
paration of sufficient amounts of extract to allow one to
conduct the test procedures described in the Advance Notice
of Proposed Rulemaking (43 FR 59022)<9>.
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The Agency recognizes the validity of these comments but
believes they are not significant enough to have required a
change in the proposed regulation. This conclusion was
reached because the regulation, as proposed, incorporated
sufficient flexibility to eliminate all these problem areas.
Elimination of these potential problems requires the exer-
cise of scientific judgement on the part of the investigator
conducting the tests. The proposed regulation did not specify
that any one specific extractor is required. The Agency
found that this point was misunderstood by many people. To
eliminate confusion a notice was placed in the Federal Register
on March 12, 1979 at 44 FR 13548(44). This notice sought to
clarify that the Agency's intent in describing the particular
extractor was to illustrate one acceptable type of agitator.
The Agency did not intend the unit so described to be considered
the only one acceptab-le.
The Agency believes that the specific extractor used in any
particular investigation should be determined after considering:
a. the physical characteristics of the waste,
b. the quantity of sample to be extracted,
c. the method of pH adjustment to be employed,
d. the analyses to be performed on the resulting extract, and
e. the number of waste evaluations to be performed concurrently.
Under these conditions, if the analyst is faced with any of the
problems previously mentioned, it becomes a simple matter to select an
extractor suitable for the waste in question. For example,
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if a waste is being examined for leachable metals, it would
o
seem prudent to use an extractor fabricated of a nonmetallic
material if aggressive conditions are to be employed during
extraction. Similarly, if jamming is found to occur, an
extractor with either a different blade clearance or one
which does not require stirring of the particles should be
selected.
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4. Adjustment of Extract pH
Two commenters mentioned problems with the pH adiustment
during the course of the extraction. The first commenter
concerned the potential danger of adding acid to a waste
containing cyanide, sulfide, or other constituent capable
of forming toxic gas. The second comment complained about
the cost of the equipment needed to automate the procedure.
With respect to the danger of toxic gas formation, the
Agency believes it is only common sense to evaluate the
waste for the presence of gas generation contaminants prior
to conducting the Extraction Procedure. This is especially
important since the presence of such constituents can make
the waste hazardous under the Reactivity Characteristic even
if the waste does not contain other extractable toxicants.
With respect to the cost of automating the pH adjustment
step, two points need to be made. The first is that automation
of the adjustment step is not required by the regulations.
Secondly, if a laboratory elects to employ automatic titration
equipment, for purposes of saving labor cos'ts, the cost of
such equipment is much less than the commenter quoted. Spe-
cifically, the equipment described in the proposal, and employed
during much of the developmental research conducted at the
Oak Ridge National Laboratory, retails for $325 (Cole Farmer
Co. Catalog #5997-20) while a similar competing unit
retails for $495 (Fisher Scientific Co., Catalog #13-637-650).
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5. Sample to Extractant Ratio
One commenter commented as follows:
"The solid/liquid ratio used in the EP test is based on "as re-
ceived" (wet) weight. This severely complicates intersample and in-
ter labor at ory testing. Also, diluting from a ratio of 1:16 to 1:20
requires careful quantitative transfer procedures. Why not just use
1:20 or 1:10, since solid to liquid ratios tend to be arbitrary as
shown in the Wisconsin study."
This comment addresses two concerns-problems related
to working with materials whose composition may change if
care in their handling is not taken (e.g., the wet samples
may dry out with a resulting change in percent solid), and
the fact that careful laboratory techniques are required
throughout testing. With regard to the first point, the
Agency has chosen to use wet weight for purposes of computing
the solid/liquid ratio because use of dry weight might not
prove representative of the leachability of the waste. For
instance, if the solid residue obtained after the initial
separation procedure still contained a fairly high percentage
of liquid, drying the solid residue would dramatically increase
the concentration of toxic contaminants in the solid sample
with a possible attendant increase in the quantity of
contaminants leached from the waste. At the same time drying
the solid residue could severely understate the leachability
of the waste, as in the case of electroplating wastes. Data
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in the Agency's possession indicates that, for some unknown
reason drying electroplating wastes results in lower contaminant
concentrations in the leachate (35).
With regard to the second point, the Agency believes
that the need for care in performing the analytical transfers
does not justify changing the regulations inasmuch as it is
in the very nature of analytical chemistry to require such
care.
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6. Final Volume Adjustment
One commenter suggested that for operational convenience
«*>
it may be desirable to perform the extract dilution prior to
the liquid solid separation step. The following formula for
determining the amount of water to add was suggested:
V = (20)(w) - (16)(w) - (a)(HOAc)
wh e r e :
V = ml of water to add
w = weight in gms of solid charged to extractor
a - ml of acetic acid solution added during extraction.
Since this procedural change neither changes the intent
nor results of the dilution step, and does save the laboratory
investigator time, the Agency has adopted the suggestion
and changed the regulations accordingly.
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7. Analysis of Multiphasic Extracts
A number of comments were received concerning the analysis
i*
of multiphasic liquid extracts. These comments and questions
indicated to the Agency that more guidance is needed in this
area.
There are basically two methods for handling multiphasic
liquid extracts. The phases can be separated, their volumes
measured, separately analyzed and then mathematically combined
to determine the original concentration for each species in
question. Alternatively, the operator can mix the multiphasic
mixture, using a high shear mixer (e.g., homogenizer), withdraw
an aliquot, then subject the aliquot to a total extraction
or digestion depending on the species of interest.
In order to eliminate confusion on the part of the regu-
lated community the Agency has added clarifying wording to
the regulation and will give further guidance in the methodology
manual(27).
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8. Extract Toxicity
A large number of comments expressed concern that the
presence of^acetic acid, or acetate ion, would interfere
with bioassay testing of the extract. This concern is parti-
ally valid inasmuch as acetate is known to interfere, in
some cases, with the phytotoxicity bioassay procedures currently
under development by the Agency (19). However, since the
final regulations do not call for any bioassay testing to be
performed on the extract, this potential for interference
is a moot point. Research at ORNL (7,19) indicates that EP
extracts can be evaluated for both mutagenicity and aquatic
toxicity without serious interference from the leaching
medium. As noted, above, the Agency is continuing work on a
leaching medium which will not interfere with bioassay testing.
Some commenters expressed the concern that the acetate
would interfere with chemical analysis of the extracts. The
Agency knows of no data to indicate that this concern is
anything but theoretical and so is not convinced that a
change in the methodology is required. If, in the future,
there is a demonstration of such interference appropriate
changes will be made.
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E. Economics of Testing
A number of comments were received on the cost of the
test procedures required to be performed by the regulated
community. There are two aspects to this concern. The
first is the actual cost for performing the specific tests.
The second relates to the question of what tests the regulated
community will be required to perform on their wastes.
In responding to this comment, it should be noted at the
outset that RCRA does not require EPA to take costs into account
in formulating its regulations. The Agency believes, however,
that the cost of running the EP on one's waste is, by any standard
of judgement, reasonable.
The cost of determining whether a waste meets the Extraction
Procedure Toxicity Characteristic can be divided into the cost for
obtaining the sample and the cost of testing the sample.
Sampling costs are largely dependent on the waste, the gen-
erator, and even the plant involved. The Agency believes that it
is only right to require one who is disposing of a waste to know
what the properties of the waste are. In order to accomplish
this one must have a sample of the waste. Thus, collecting
a sample of one's waste is not felt to be an unjust burden.
The Agency has found that independent laboratories are
quoting prices for testing a specific sample, using the
Extraction Procedure and associated analytical procedures,
to be in the range of $200-600 for the required tests.
These are single sample prices and, for most companies who
have several wastes to test, would actually be at the low
end of this range (approximately $200).
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F. Specific Comments on the Noticed Reports
Q
Since publication of the proposed regulations, the Agency
received and made available to the public a number of reports
dealing with the development of the Extraction Procedure
Toxicity Characteristic. These reports are:
Compilation and Evaluation of Leaching Test
Methods (EPA-600/2-78-095)(l5>
Comparison of Three Waste Leaching Tests (Final
and Executive Summary) (EPA-600/2-79-071)(16)
Toxicity of Leachate, Interim & Final Reports,
Oak Ridge National Labor at ory (? > 19 )
0 Assessment of RCRA/EP Test Results on FBC Residues:
Part II(53^
0 Electroplating Wastewater Sludge Characterization,
EPA-AES Cooperative Agreement, September 12, 1979^35
0 Evaluation of Solid Waste Extraction Procedures and
Various Hazard Identification Tests, NUS Project
Number 6745(36)
0 Proposed RCRA Extraction Procedure: Reproducibility
and Sensitivity, EPRI, November 1, 1979.<37)
0 Evaluation of Procedures for Identification of
Hazardous Waste, Interim Report, EMSL-LV (18)
0 Background Study on Development of Standard Leaching
Test (EPA-600/2-79->107)<14)
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Approximately 30 comments were received in response to
the Agency's notice of these reports. In the main the comments
did not address themselves to the specific scientific results
reported in these studies. Rather they addressed their
interpretation of the meaning of the work in relation to the
proposed toxicity definition as enunciated in the EP Toxicity
characteristic and the criteria for delis ting.(9)
While the comments dealt with a number of issues, most
of these have been discussed previously in this background
document. This section will address the remaining issues as
well as clarify several points made by commenters who had
apparently not availed themselves of the explanatory material
made available in the draft Toxicity Background Document'"'
and thus were not aware of the intent and rationale behind
the work done during these studies.
Comment: No factual basis for defining hazard has been
developed in these studies and no recognized
standard of judgment has been applied to this work.
Response: The basis for the Extraction Procedure developed as
a result of these studies has been described previously
in this document. The basis for the bioassay tests has been
discussed in the aforementioned draft Background Document.'6^
The reason different dilutions of the EP extract were examined
for toxic effects in the various bioassays relates to the
fact that the model of environmental exposure used in developing
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B
the EP Toxicity characteristic postulates different degrees
of dilution for different targets of exposure (e.g., fish,
plants). Chronicly toxic effects toward the aquatic and
terrestrial plant environments were thus studied at the
expected levels of exposure. The organisms employed in these
studies were believed to be sensitive enough for such an
approach to be used.
Comment: "CMA recognizes that an uncomplicated short-term
test is necessary for initial screening of the large
body of wastes to define potential hazard. The single elution,
solid/liquid ratio, and the time per elution of the proposed
EPA are a practical compromise to more complex procedures
such as the SLT reviewed in the subject document. The setting
of a threshold concentration as the basis for defining hazard
makes proper use of the most important data such tests develop".
Response: The Agency appreciates the fact that these commenters
took the time to let EPA know they concur with our
conelus ion.
Comment: Work done by ASTM under Phase II of a study supported
by the U.S. Department of Energy indicated that
the EP is not reproducible.
Response: The Agency is aware of this study but has been unable
to obtain a copy of the results from the sponsoring
ASTM subcommittee. Thus, the results of this work have not
135
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been "included in the data base used to develop the EP charac-
teristic.
Comment: The quality of the work performed at ORNL is
suspect since less than adequate quality assurance
procedures were employed.
Response: The Agency believes the work performed at ORNI/7>9)
to be scientifically valid pending any specific
evidence to the contrary.
Comment: The EP is not reproducible.
Response: While this point was raised in a number of comments,
the comments by two groups, the American Petroleum
Institute (API) and the Utility Solid Waste Activities Group
(USWAG) were the most specific and detailed and thus have been
specifically addressed.
In general, the Agency agrees with many of the criticisms
noted in the API and USWAG comments relative to the incompleteness
of the data base, and its ability to precisely define the
reproducibility of the EP and analytical procedures. However,
as with the studies themselves, the commenters often do not
clearly distinguish in their comments between reproducibility
as it relates to the EP or as it relates to the analytic tech-
niques. Also, there appears to be some expectation that the
EP and analytic techniques should have similar reproducibility
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indicators for each of the eight elements and for each of
many different waste types. This may represent a fundamental
misconception about the reproducibility of both the EP and
the analytic techniques. This expectation is somewhat similar
to expecting that a test battery that measures vastly different
types of abilities should have an overall reliability estimate
that applies equally to all age groups. Further, as in the
studies themselves, the comments do not indicate what would
be an acceptable level of reproducibi1ity. Failure to provide
some guidelines of what general levels of reproducibi1ity
would be acceptable for the EP and the analysis techniques
tends to compromise the criticisms offered. The critical
issue is whether the proposed EPA guidelines and regulations
regarding the EP and analysis techniques have adequate repro-
ducibility to serve as a screening mechanism for identifying
potentially hazardous wastes. It should be borne in mind
that since the Agency has raised the definitional threshold t
100 times the applicable NIPDWS threshold, many of the
criticisms made by the commenters do not apply. This is due
to the fact that at higher thresholds the toxicants are
analytically easier to measure and the percent error would be
expected to decrease significantly.
API Comments
The API comments concern a review and discussion of the
results of the four studies (18,35,36,37) conducted on the
reproducibility of the EP and AA analysis techniques. The
137
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four separate studies were conducted by Electric Power Research
Institute (EPRI),<37) NUS Corporation (36)f the American
Electroplater's Society (AES)<35) and the EPA Environmen-
tal Monitoring Systems Laboratory,^1-8) respectively.
Comments on the NUS study (36) tend to misinterpret the
relative standard error (RSE) used by the NUS investigators
as an index of reproducibility. For example the comments
include the statement that the standard error which defines
the distribution of the means is related to the standard
deviation (36, p.4). This is true, but the standard error
(of the mean) is also a function of the number of analytic
replications, an important component in determining the size
•
of the standard error (of the mean). In this regard, the
comments state that "API would hesitate to accept any procedure
with such a high analytical error" (+_ 30% RSE) (36, p.4).
With a + 1 RSE representing the 95% confidence interval about
the mean value of lead in BOF slag, one wonders what RSE
would be acceptable to API.
The Agency generally agrees that the NUS report is not a
thorough study and is incomprehensible (36, p.5) but cannot
agree that levels of toxic metals below detection limits
should be reported as 0.000 ppra and included in the analysis
(36, p. 5). EPA believes that values at or near the limit
of detection and which are orders of magnitude below the
threshold levels should not be included in reproducibility
estimates, only those levels near the threshold values or
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above should be included.
Comments regarding the EP and Toxic Extraction Procedure
(TEP) comparisons in the API Comments are irrelevent since
the EPA regulations specify only the use of the EP.
API comments on the EPRI report^37) seem valid generally,
except that the comments regarding the Confidence Multipliers
(CMs) in the EPRI report tend to ignore the study limitations
noted by the authors of the EPRI report. Many of the extreme
confidence intervals include analyses which the authors of
the EPRI study note should be interpreted with caution (because
of variability due to unallocated error or because the number
of values below detection units are large enough to make the
results less • reliable) (p. 3 of Phase I report).(37) Also,
reporting extreme 90% confidence limits as percentage of the
mean is a somewhat misleading way to present reproducibility
data. The percentages reflect both measurement error and 90%
of the area included under a normal distribution.
API comments on the study by the EPA Environmental
Monitoring Systems Laboratory (EMSL)^18^ in Las Vegas tend to
be confusing. For example, ICP was used as a screening device
by EMSL to determine what wastes would be subjected to the
EP and the AA analyses. The API comments, however, discuss
the ICP results as though they were indicators of the EP and
analytical reproducibilities. Specifically, the API comments
state that the ICP analysis results indicate there is something
amiss with the EP or analytical procedure. The ICP has
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nothing to do with EP reproducibility. Also, the EMSL is
criticized by API for being incomplete even though the report^18)
is clearly indicated as an interim report and includes statements
O
about further analyses that are planned.
API comments on the AES study^35) intersperse comments
on the design of AES experiments with issues relating to the
reproducibility of the EP and analytic techniques. For example,
in the AES experiment with different levels of pH used for
the EPA, the unreproducibi1ity of the EP at the standard pH 5
levels is not established simply because different analytical
results were obtained at other pH levels. Even so, the
analytic results at pH 5 seemed somewhat more uniform than the
analytic results at the other pH levels. As indicated earlier,
the API comment regarding the overall reliability of the EP
may reflect a misconception that the EP should be equally
reproducible for all types of solid wastes.
USWAG Comments
The comments submitted by the Utility Solid Waste
Activities Group (USWAG) tend to be more focussed through the
API comments upon the specific research results of three
studies regarding the reproducibility of the EP and AA analytic
methods. In general, the review by USWAG consultants,
Envirosphere, submitted along with the comments is a fairly
thorough evaluation of the methodological and scientific
merits of each of three studies, the EPRI study,<3?) the EPA
EMSL study,CIS) and the NUS Corporation study.<36> The USWAG
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comments regarding the variability of analytic results according
to the types of wastes and toxic metals examined tends to be
supported across the different studies. However, as indicated
earlier, reproducibi1ity estimates need to be established
for each type of waste and for each elemental analysis.
The USWAG comment regarding the appropriateness of the
use of any standardized leaching test to "perform more than
an initial screening function" is somewhat confusing. The EP
and analytic techniques coupled with the threshold levels
serve as a screening mechanism for determining wastes requiring
controlled management. The accuracy of the EP and analytic
techniques to model actual leaching at specific disposal
sites will not be established until studies comparing the
model results with actual disposal site leaching are conducted.
As was discussed previously, the EP is not meant to model any
specific disposal site but is instead a generalized model.
As with the API comments, the measures of the relative
standard error used in the NUS report^36) tends to be
interpreted as a relative standard deviation (RSD) or
coefficients of variability in the USWAG comments. Also, the
USWAG comments on the EPRI report^37) include most of the
Confidence Multiplier (CMs) for each element included in the
EPRI report. If, for example, one only includes those data
which are largely complete for the ANOVA design, a somewhat
different picture emerges of the reproducibi1ity of intra-
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laboratory analyses (consistency) and inter-laboratory
analyses (concurrence). The following distributions of
CMs are found with a more conservative extraction of the EPRI
e
data (37, p. 14) (indicators of inter- and intra-laboratory
reproducibility on the combined AA analysis results).
Inter-Laboratory Intra-Laboratory
Analysis CMs Analysis -CMs
Intervals
1.01-1.25
1.26-1.50
1.51-1.75
1.76-2.00
2.01-2.25
2.26-2.50
2.51 +
Totals
N
13
0
1
2
1
0
8
' 25
1
52
0
4
8
4
0
32
100%
N_
20
4
1
0
0
0
0
25
_%
80
16
4
0
0
0
0
100%
These results suggest that the reproducibi1ities of
intra-laboratory analysis techniques (consistency) are
appreciably better than inter-laboratory analysis reproduci-
bilities (concurrence). A different (and less positive)
picture emerges when all the data results are considered as
in the API comments and the USWAG comments. Also, averaging
all the CMs presented in the EPRI studyO7) tends to present
an inflated picture of the CMs, since the mean is affected
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by extreme values and the extreme values are very large CMs.
The USWAG comments regarding the NUS report,(36) however,
seem justified, except that RSEs are reported as relative
£>
standard deviations (same as coefficients of variation).
The report attached to the USWAG comments, completed by
the Environsphere Company, is a thorough and insightful review
of the three reproducibi1ity studies. However, the Agency
questions the inclusion of sampling techniques as part of
determining reproducibi1 ities in the "Toxic Waste Test." It
is generally understood that the EPA guidelines regarding
sampling techniques for solid waste need further refinement.
At the present time, the precision and reproducibi1ity of the
EP and AA techniques is the central issue. Also, presentation
of the "corrected mean concentrations" of elements from "the
EPRI report (37, pp. 17-19) does not adequately reflect
reproducibi1 ities of the analyt ic procedures, since these
values incorporate variances attributable to both the EP and
to the analytic technique.
The consultant's report addresses the issues of the
incorrect statistical summaries presented in Table 8 of the
EMS!/18) report, yet fails to point out that their corrected
values indicate an increased reproducibi1ity estimate for the
pH levels and percent solid determinations. Also, the Agency
cannot understand why, in both the EMSL^8) study and the
consultants review, ANOVA techniques were used without multiple
comparisons tests. A simple t-test between the highest and
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lowest mean values for chromium in Pond P, 2A, and lead in Pond
0, 2B, did not indicate significant differences within three
replicate analyses of the same samples. The consultants are
not particularly clear about how they conducted their own ANOVAs
analyses .
Comment: Specification of construction materials for extractor
a
must be flexible in order to accomodate different
waste materials.
Response: Neither the proposed nor final regulations specify
materials of construction for the extraction
equipment. The Agency agrees that those evaluating waste
materials should use materials of construction appropriate to
the properties of the waste and to the analyses to be conducted.
Comment: None of the reports evaluated analytical procedures
for the pesticides.
Response: Due to the unavailability to the Agency of wastes
containing significant concentrations of pesticides,
these were not included in the test program. However, no
comments were received indicating problems in analyzing EP
extracts for pesticides.
Comment: Neither vacuum filtration nor mechanical agitation
are appropriate for determining if wastes contain
volatile materials.
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Response: The Agency agrees and is not using the EP to
determine if a waste poses a potential hazard
due to its content of volatile compounds.
Comment: Concentrating extracts prior to analysis is in-
appropriate since it does not simulate what happens
in the real world.
Response: The commenter appears to misunderstand the intent
of the concentration step. The purpose of
concentrating the extract prior to analysis is to improve the
accuracy of the analytical determination. Thresholds for
toxicity are expressed on the basis of concentration in the
original extract. Concentrating the extract prior to analysis
c
does not change the measure of toxicity.
Comment: The fact that a sample of sewage sludge failed the
proposed criteria for cadmium and mercury indicates
the excessive severity of the EP.
Response: The Agency disagrees with this comment. Many municipal
sewage sludges contain concentrations of cadmium and
other metals sufficient to pose a health hazard if improperly
used for soil amendment or fertilization use. Thus these
sludges would be hazardous wastes under RCRA. However, using
the thresholds promulgated today (i.e., 100X NIPDWS), none of
the municipal wastes tested would have met the definition of
hazardous waste.
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Comment: Use of the resin technique for concentrating organic
materials present in the extract as part of the
analytical procedures is not suitable for all types of organic
compounds.
Response: The Agency agrees with this comment. However, this
technique is currently under evaluation and has not
been included in the regulations promulgated today.
Comment: The meaning of the results using the arsenic
contaminated groundwater is in question given the
unknown handling and storage of the sample.
Response: The groundwater sample was not -employed to determine
if any specific waste was a hazardous waste, but
rather served as an investigatory tool. Thus, irrespective
of its history, since its composition prior to biological use
was determined, the results obtained are valid.
A number of comments were received relative to biological
test procedures which had been proposed as part of the de-
listing procedures under Part 250.15. Since these test pro-
cedures have not been included in the regulation promulgated
today, a detailed discussion of these comments will not be
included in this discussion. In general, the Agency agrees
with the commenters who indicated that the EP extractant
liquid seriously interfered with the phytotoxicity test
procedure. However, the Agency believes that this problem
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with the EP extractant fluid does not apply to either the
mutagenicity or Daphnia magna chronic toxicity assays. As
has been discussed previously in this Background Document,
the Agency does not believe, however, that these assays are
ready for general use by the regulated community.
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VI. PROMULGATED REGULATION
§261.24 Characteristic of EP Toxicity
(a) A solid waste exhibits the characteristic of EP
toxicity if, using the test methods described in Appendix II or
equivalent methods approved by the Administrator under the pro-
cedures set forth in §§260.20 and 260.21, the extract from a
representative sample of the waste contains any of the
contaminants listed in Table I at a concentration equal to or
greater than the respective value given in that Table. Where
the waste contains less than 0.5 percent filterable solids,
the waste itself, after filtering, is considered to be the
extract for the purposes of this section.
•
(b) A solid waste that exhibits the characteristic of
EP toxicity, but is not listed as a hazardous waste in Subpart
D, has the EPA Hazardous Waste Number specified in Table I
which corresponds to the toxic contaminant causing it to be
hazardous.
148
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Table I
Maximum Concentration of Contaminants
for Characteristic of EP Toxicity
EPA
Hazardous Waste
Number _
D004
D005
D006
D007
D008
D009.
D010
D011
D012
D013
DO 14
DO 15
D016
DO 17
Contaminant
Maximum
Concentration
(milligrams per lite)
Arsenic »»...„ „._... 5.0
Q
Barium 100.0
Cadmium i.o
Chromium .. . ............ 5.0
Lead - » * , „.... 5.0
Mercury » 0.2
Selenium . . . ^ . . . . 1.0
Silver 5.0
Endrin (1,2,3,4,10,10-hexachloro-l
7-epoxy-l,4,4as 5,6,7,8,8a-octahydro-l
4—endo, endo-5,8-dimethano naph-
thalene -• 0 .02
Lindane (1,2,3,4,5,6-
hexachlorocyclohexane, gamma
isomer ^ 0.4
Methoxychlor (1,1,1-Trichloro-2,2-bis
[p-methoxyphenyl]ethane) . 10.0
Toxaphene (C10Hi0Cl8> Technical
chlorinated camphene, 67-69
percent chlorine) - 0.5
2,4-D, (2,4-Dichlorophenoxyacetic
acid) 10.0
2,4,5-TP Silvex (2,4,5-
Trichlorophenoxypropionic acid) 1.0
149
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APPENDIX II
EP Toxicity Test Procedure
A. Extraction Procedure (EP)
1. A representative sample of the waste to be tested
(minimum size 100 grams) should be obtained using the methods
specified in Appendix I or any other method capable of yielding
a representative sample within the meaning of Part 260. [For
detailed guidance on conducting the various aspects of the EP"
see "Test Methods for the Evaluation of Solid Waste, Physical/
Chemical Methods," SW-846, U.S. Environmental Protection Agency
Office of Solid Waste, Washington, D.C. 20460.*]
2. The sample should be separated into its component
liquid and solid phases using the method described in
"Separation Procedure" below. If the solid residue** obtained
using this method totals less than 0.5% of the original weight
of the waste, the residue can be discarded and the operator
should treat the -liquid phase as the extract and proceed
immediately to Step 8.
3. The solid material obtained from the Separation
Procedure should be evaluated for its particle size. If
the solid material has a surface area per gram of material
* Copies may be obtained from Solid Waste Information, U.S.
Environmental Protection Agency, 26 W. St. Clair Street,
Cincinnati, Ohio 45268
**The percent solids is determined by drying the filter pad at
80°C until it reaches constant weight and then calculating
the percent solids using the following equation:
(weight of pad + solid) - (tare weight of pad) X 100 = % solids
initial weight of sample
150
-------
equal to, or greater than, 3.1 cm2 or passes through a
9.5 mm (0.375 inch) standard sieve, the operator should
proceed to Step 4. If the surface area is smaller or the
particle size larger than specified above, the solid material
0
should be prepared for extraction by crushing, cutting or
grinding the material so that it passes through a 9.5 mm
(0.375 inch) sieve or, if the material is in a single piece,
by subjecting the material to the "Structural Integrity
Procedure" described below.
4. The solid material obtained in Step 3 should be
weighed and placed in an extractor with 16 times its weight
of deionized water. Do not allow the material to dry prior
to weighing. For purposes of this test, an acceptable
extractor is one which will impart sufficient agitation
to the mixture to not only prevent stratification of the
sample and extraction fluid but also insure that all sample
surfaces are continuously brought into contact with well
mixed extraction fluid.
5. After the solid material and deionized water are
placed in the extractor, the operator should begin agitation
and measure the pH of the solution in the extractor. If the
pH is greater than 5.0, the pH of the solution should be
decreased to 5.0 +_ 0.2 by adding 0.5 N acetic acid. If the
pH is equal to or less than 5.0, no acetic acid should be
added. The pH of the solution should be monitored, as
described below, during the course of the extraction and if
151
-------
the pH rises above 5.2, 0. 5N acetic acid should be added to
bring the pH down to 5.0 -f 0.2. However, in no event shall
the aggregate amount of acid added to the solution exceed
4 ml of acid per gram of solid. The mixture should be
agitated for 24 hours and maintained at 20° - 40°C (68°-104°F)
during this time. It is recommended that the operator
monitor and adjust the pH during the course of the extraction
with a device such as the Type 45-A pH Controller manufactured
by Ghemtrix, Inc., Hillsboro, Oregon 97123 or its equivalent,
in conjunction with a metering pump and reservoir of 0.5N
acetic acid. If such a system is not available, the follow-
ing manual procedure shall be employed:
(a) A pH meter should be calibrated in accordance
with the manufacturer's specifications.
(b) The pH of the solution should be,checked and,
if necessary, 0.5N acetic acid should be
manually added to the extractor until the
pH reaches 5.0 + 0.2. The pH of the solution
should be adjusted at 15, 30 and 60 minute
intervals, moving to the next longer interval
if the pH does not have to be adjusted more
than 0.5N pH units.
(c) The adiustment procedure should be continued
for at least 6 hours.
(d) If at the end of the 24-hour extraction period,
the pH of the solution is not below 5.2 and
the maximum amount of acid (4 ml per gram of
solids) has not been added, the pH should be
adjusted to 5.0 +_ 0.2 and the extraction
continued for an additional four hours, during
which the pH should be adjusted at one hour
intervals.
6. At the end of the 24 hour extraction period, deionized
water should be added to the extractor in an amount determined
152
-------
by the following equation:
V= (20)(W) - 16(W) - A
V= ml deionized water to be added
W« weight in grams of solid charged to extractor
A- ml of 0.5N acetic acid added during extraction
7. The material in the extractor should be separated
into it component liquid and solid phases as described under
"Separation Procedure."
8. The liquids resulting from Steps 2 and 7 should be
combined. This combined liquid (or the waste itself if it
has less than 1/2 percent solids, as noted in step 2) is the
extract and should be analyzed for the presence of any of
the contaminants specified in Table I of §261.24 using the
Analytical Procedures designated below.
Separation Procedure
Equipment: A filter holder, designed for filtration media
having a nominal pore size of 0.45 micrometers and capable of
applying a 5.3 kg/cm2 (75 psi) hydrostatic pressure to the
solution being filtered shall be used. "For mixtures
containing nonabsorptive solids, where separation can be
affected without imposing a 5.3 kg/cm2 pressure differential,
vacuum filters employing a 0.45 micrometrers filter media
can be used. (For further guidance on filtration equipment
or procedures see "Test Methods for Evaluating Solid Waste,
Physical/Chemical Methods.")
153
-------
Procedure:*
(i) Following manufacturer's directions, the filter
unit should be assembled with a filter bed consisting
of a 0.45 micrometer filter membrane. For difficult
or slow to filter mixtures a prefilter bed consisting
of the following prefilters in increasing pore size
(0.65 micrometer membrane, fine glass fiber prefilter,
and coarse glass fiber prefilter) can be used.
(ii) The waste should be poured into the filtration unit.
(iii) The reservoir should be slowly pressurized until liquid
begins to flow from the filtrate outlet at which point
the pressure in the filter should be immediately lowered
to 10-15 psig. Filtration should be continued
a
9
until liquid flow ceases.
(iv) The pressure should be increased stepwise in 10 psi
increments to 75 psig and filtration continued until
tti
flow ceases or the pressurizing gas begins to exit
from the filtrate outlet.
*This procedure is intended to result in separation of the "free"
liquid portion of the waste from any solid matter having a
particle size >0.45um. If the sample will not filter, various
other separation techniques can be used to aid in the filtration.
As described above, pressure filtration is employed to speed up
the filtration process. This does not alter the nature of the
separation. If liquid does not separate during filtration, the
waste can be centrifuged. If separation occurs during centrifuga
tion, the liquid portion (centrifugate) is filtered through the
0.45um filter prior to becoming mixed with the liquid portion of
the waste obtained from the initial filtration. Any material
that will not pass through the filter after centrifugation is
considered a solid and is extracted.
154
-------
(v) The filter unit should be depressurized, the solid
material removed and weighed and then transferred to
the extraction apparatus, or, in the case of final
filtration prior to analysis, discarded. Do not
allow the material retained on the filter pad to dry
prior to weighing.
(vi) The liquid phase should be stored at 4°C for
subsequent use in Step 8.
B. Structural Intergrity Procedure
Equipment: A Structural Integrity Tester having a 3.18 cm
(1.25 in.) diameter hammer weighing 0.33 kg (0.73 Ibs.) and
having a free fall of 15.24 cm (6 in.) shall be Used. This
device is available from Associated Design and Manufacturing
Company, Alexandria, VA., 22314, as Part No. 125, or it may
be fabricated to meet the specifications shown in Figure 1.
Procedure:
1. The sample holder should be filled with the material
to be tested. If the sample of waste is a large monolithic
block, a portion should be cut from the block having the
dimensions of a 3.3 cm (1.3 in.) diameter x 7.1 cm (2.8 in.)
cylinder. For a fixated waste, samples may be cast in the
form of a 3.3 cm (1.3 in.) diameter x 7.1 cm (2.8 in.) cylinder
for purposes of conducting this test. In such cases, the
waste may be allowed to cure for 30 days prior to further
testing.
2. The sample holder should be placed into the Structural
Integrity Tester, then the hammer should be raised
155
-------
to its maximum height and dropped. This should be repeated
fifteen times.
3. The material should be removed from the sample
holder, weighed, and transferred to the extraction apparatus
for extraction.
Analytical Procedures for Analyzing Extract Contaminants '
The test methods for analyzing the extract are as
fo1lows:
(1) For arsenic, barium, cadmium, chromium, lead, mercury,
selenium or silver: "Methods for Analysis of Water and Wastes,"
Environmental Monitoring and Support Laboratory, Office of
Research and Development, U.S. Environmental Protection Agency,
Cincinnati, Ohio 45268 (EPA-600/4-79-020, March 1979).
(2) For Endrin; Lindane; Methoxychlor; Toxaphene; 2,4-D;
2,4,5-TP Silver: in "Methods for Benzidine, Chlorinated Organic
Compounds, Pentachlorophenol and Pesticides in Water and
Wastewater," September 1978, U.S. Environmental Protection
Agency, Environmental Monitoring and Support Laboratory,
Cincinnati, Ohio 42568.
as standardized in "Test Methods for the Evaluation of
Solid Waste, Physical/Chemical Methods."
For all analyses, the method of standard addition shall
be used for the quantification of species concentration.
This method is described in "Test Methods for the Evaluation
of Solid Waste." (It is also described in "Methods for Analysis
of Water and Wastes.")
156
-------
15.25cm
IS")
ze'^'Z:
I
,.
•'*>;.-
•&^'0
• ' ^ J » > •
»*•• . '-v • •Jr"
',*•'•< !:'• A •
^;V ^
•?C^^
^V.r--.?s
3.3cm
Cl.a")
9.4cm
(3.7")
COMBINED
r WEIGHT
(.731b)
(3.15cm)
(1.25")
SAMPLE
/- ELASTOMERIC*
SAMPLE HOLDER
/
K
J.
7.1cm
(2.8")
*ELASTOMER!C SAMPLE HOLDER FABRICATED OF
MATERIAL FIRM ENOUGH TO SUPPORT THE SAMPLE
Figure 1
TION TESTER
157
-------
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•
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