United States Solid Waste and EPA530-R-99-030b
Environmental Protection Emergency Response NTIS: PB99-156 093
Agency (5305W) June 1998
Petroleum Refining
Process Waste Listing
Determination
Proposed Rule
Response to
Comments Document;
Part II
Printed on paper that contains at least 30 percent postconsumer fiber
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III. HEALTH AND RISK ASSESSMENTS
A. TRIMETHYLBENZENE: The Agency requested comments on the appropriateness
of the provisional RfD and the availability of any additional data on the toxicity of 1,3,5-
trimethylbenzene. The Agency also requested comments on the appropriateness of using a
surrogate (SAR) analysis for constituents with no health effects data, and requested any
toxicity data on these constituents.
No specific comments were submitted in response to these requests.
B. PAH POTENCY ESTIMATION: The Agency requested comment on the
uncertainties and limitations of two methods for estimating the potency of PAHs.
Comment 1: The inclusion of 7,12-dimethylbenz(a)anthracene and 3-methyl cholanthrene in the
CSO risk assessment significantly overestimates the risk posed by PAH-containing wastes.
Inclusion of these compounds in the risk analysis is inappropriate because, even if these
compounds are present in the waste as generated, they would be chemically and biologically
degraded so quickly in the environment that they are unlikely to reach a receptor and contribute
to the risk. Because 7,12-dimethylbenz(a)anthracene and 3-methyl cholanthrene have high
cancc - slope factors; their inclusion in the risk analysis causes the risk to be substantially
overestimated. (EEI, 00026)
Response: EPA agrees that biodegradation may be a significant removal process for PAHs and
should be considered in analysis of PAH fate and transport. While biodegradation of PAHs
within land treatment units was considered in the analysis for the proposed listing,
biodegradation that may occur during transport and at the receptor location was not.
Accordingly, in response to comments, the non-groundwater risk analysis was been expanded to
include biodegradation of PAHs outside the LTUs for the waste streams of concern. Detailed
results of this analysis were provided in the Supplemental Background Document;
NonGroundwater Pathway Risk Assessment; Petroleum Process Waste Listing Determination in
the docket for the April 8, 1997, NOD A. While the half-life of 7,12-dimethylbenz(a)anthracene
is relatively short at 28 days (Park et al., 1990), the half life for 3-methyl cholanthrene is reported
to be from 1.67 to 3.84 years (Howard et al., 1991). The following table (Table III.B-1) presents
the data available for estimating the biodegradation of PAH in soil. These rates are dependent on
the soil type, soil biota, and meteorologic parameters at the site. EPA has chosen to use the
lowest value for this parameter in order to assure that biodegradation is not over-estimated when
soil and meteorologic conditions are not ideal. However, biodegradation rates were included as
variable parameters in the quantitative uncertainty analysis conducted in support of this listing
decision The inclusion of biodegradation did not affect the listing decision. In addition, a risk
level of 1E-05 is estimated at the 90th percentile for the home gardener living near a petroleum
refinery where CSO sediment is disposed in an on-site LTU even if 7,12-
dimethylbenz(a)anthracene and 3-methylcholanthrene are removed from consideration entirely.
June 29, 1998 III-l
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Table III.B-1 Biodegradation Rates of PAHs
Constituent
Biodegra
dation
Rates
(1/yr)
Benz(a)
anthracene
2.48
1.56
0.969
0.372
Benzo(a)
pyrene
4.44
1.11
1.10
0.819
0.607
0.478
0.307
Benzo(h)
fluoranthene
1.20
0.861
0.858
0.703
0.415
Benzo(k)
fluoranthene
0.278
0.118
0.0797
Chrysene
46.0
1.13
0.771
0.682
0.654
0.253
Dibenz(a.h)
anthracene
1.75
0.701
0.602
0.269
7.12-Dimethyl
benz
(a)anthracene
12.6
9.04
Indeno
(1.2.3-cd)
pyrene
0.422
0.347
3-Methvl-
cholanthrene
0.415
0.181
Comment 2: The commenter is concerned about the analytical methodology used to identify
7,12-dimethylbenz(a)anthracene and 3-methyl cholanthrene, which are extremely difficult to
identify conclusively. (EEI, 00026)
Response: These two compounds are appropriately included in the risk assessment analysis
because they were identified as waste stream constituents in the waste sampling and analysis.
The sampling and analysis protocol is provided in the Quality Assurance Project Plan for Record
Sampling Under the 1992-1996 Petroleum Refining Listing Determination and Industry Study,
September 22, 1993, Docket// F-95-PRLP-S0011.
The CSO sediment samples were analyzed using EPA approved methodology outlined in SW-
846, 3rd edition and as documented in the September 1993, QAPjP, site-specific sampling and
analysis plans, and analytical data reports. Each sample was extracted according to Method
3550A (sonication) followed by Gel-Permeation Chromatography (GPC) cleanup according to
Method 3640B. Extracts were then analyzed with GC/MS instrumentation according to Method
8270B. Due to the large number of semivolatile target analytes requested and potential problems
associated with reference standard compatibility, the contract laboratory performed three separate
initial calibration curves for all samples associated with the petroleum refining listing, one for the
majority of target analytes specified in Method 8270, and two additional curves using the
industry specific, non-routine target analytes. Therefore, 7,12-dimethylbenz(a)anthracene and 3-
methyl cholanthrene were calibrated to develop a second curve using a mixture of seven similar
PAH compounds in the concentration range of 20 to 160 ppb. The laboratory was successful in
meeting all method-specific instrument calibration, extraction efficiency, and analytical precision
and accuracy requirements for the two samples in which the PAH compounds in question were
detected. In addition, the validity of each calibration curve was evaluated with the analysis of a
laboratory control standard containing representative target analytes prepared independently of
the calibration standards. The reported concentrations of 7,12-dimethylbenz(a)anthracene and 3-
June29, 1998
III-2
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C. PLAUSIBLE MANAGEMENT: The Agency requested comments on its choice of
plausible management scenarios and the possibility of using alternative scenarios.
Comment 1: The commenters support the common sense approach to base listing determinations
on plausible management practices. (Valero, 00051, Mobil, 00033)
Response: The Agency acknowledges the commenters' support.
Comment 2: Waste management practices (e.g., surface impoundments, onsite cover for landfill
or land treatment units, use as road bed material, storage in a pile) potentially posing substantial
human health and environmental risks were not evaluated by the agency. (EOF, 00036, Section
II.A; ETC, 00038)
Response: The commenter cited waste-specific examples of its concern regarding the Agency's
choice of management scenarios of concern in the context of its specific comments on the
individual wastes. EPA's detailed responses to these concerns are provided in Section IV on a
waste-by-waste basis. The Agency's decisions not to model certain scenarios in its risk
assessment were sound for the reasons discussed in these responses. See IV.F.2, Comment 1 for
a discussion of storage piles for off-specification product and fines from thermal treatment. See
IV.H.2, Comment 1 for a discussion of surface impoundments associated with HF alkylation
units. See IV.E.2, Comment 1 for a discussion of surface impoundments associated with spent
caustics. See IV. A.5, Comment 2 for a discussion of the use of crude oil tank sediment as
landfill cover. See IV. B 2, Comment 4 for a discussion of the use of CSO as onsite road bed
material.
D. BIODEGRADATION: The EPA requested comments on the benzene
biodegradation rates determined by the Agency; and requested submission of any
biodegradation data that can be used for nationwide modeling analyses.
Comment 1: The commenter believes that the biodegradation of benzene should be considered
to estimate the potential risks from Subtitle D landfilling of spent hydrotreating catalyst, spent
hydrorefining catalyst, and crude oil storage tank bottom sediment. The commenter further
contends that if biodegradation had been considered, the estimated risks from such management
of those residuals would have been substantially lower and recommended that EPA should give
significant weight to biodegradation as an additional factor in the final listing decisions for the
residuals of concern. This belief is supported by the following points:
1) There is adequate evidence in the recent literature that indicate both anaerobic and
aerobic biodegradation processes play key roles in limiting the groundwater transport of
benzene.
2) Multiple independent research efforts have confirmed the anaerobic biodegradability of
benzene.
June 29, 1998 III-4
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biodegradation, biodegradation of benzene was not considered directly in the 1995 analysis or in
the April 8, 1997 NODA analysis51.
Comment 2: EPACMTP-simulated groundwater exposure concentrations for the onsite
landfill hydrorefming and hydrotreating catalyst scenarios are too high because biodegradation of
benzene was ignored. An EPACMTP simulation conducted by API using a worst case decay rate
resulted in groundwater concentrations approximately equal to the MCL for benzene. (API,
00046)
Response: See response to Comment 1.
Comment 3: Although EPA recognizes that biodegradation may be a significant removal
process, they discounted the process in the groundwater pathway analysis by citing that the
literature data are not consistent with EPA's protocol. This decision seems to be very arbitrary
and inconsistent with the selection of other parameters. Simulations were performed using the
EPACMTP model and peak receptor well concentrations were nine orders of magnitude below
the no biodegradation results when a reasonably conservative decay rate of 0.004/day was
employed. (Shell, 00047)
Response: See response to Comment 1.
Comment 4: The groundwater risk analysis is also overly conservative in that it does not
adequately account for benzene biodegradation which occurs naturally. (Mobil, 00033)
Response: See response to Comment 1.
Comment 5: Although adequate peer-reviewed investigations show that benzene biodegrades in
groundwater, this accepted phenomenon was not considered in this listing proposal. Ideally EPA
should quantitatively include a biodegradation factor in its risk calculations for CSO sediment,
and spent hydrotreating and hydrorefming catalysts. (Phillips, 00055)
Response: See response to Comment 1
E. UNCERTAINTY ANALYSES: The Agency requested comments on how best to
factor uncertainty into the Agency's listing determinations, and specifically requested
comments on if a risk estimate has a high degree of uncertainty, should the Agency
consider listing the waste only if the calculated risk is near the high end of the risk range of
106 to 104? Should the calculated risk estimate be even higher? The Agency also asked
51 Supplemental Background Document, Groundwater Pathway Risk Analysis, Petroleum
Refining Process Waste Listing Determination. 1997.
June 29, 1998 III-6
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In this rulemaking EPA has performed an estimate of the magnitude of the interindividual
variation in risk estimates by developing scenarios for both typical and high-end exposed
individuals. However, these scenarios do not provide adequate insight into the impact of many
of the most uncertain exposure parameters - namely, biotransfer factors, food consumption rates,
biodegradation, land application rates, and physical transport processes. Thus, EPA should
include a quantitative analysis of these important sources of uncertainty in the final estimates of
risk for the residuals proposed for listing in this rulemaking. (API, 00046)
Response: A quantitative uncertainty and variability analysis has been conducted in support of
this listing decision. This analysis addresses the uncertainty associated with constituent
concentration, geographical location, size of unit, waste quantity, distance to receptor, ingestion
rates, and exposure duration. A detailed description of this analysis is presented in the
Supplemental Background Document for the Uncertainty Analysis: NonGroundwater Risk
Assessment; Petroleum Refining Waste Listing Determination. These results support the results
of the deterministic analysis presented in the Notice of Data Availability (NODA) (62 FR
16747).
In response to commenter's concerns regarding the degree of uncertainty inherent in the
groundwater risk assessment, the Agency has conducted two parameter sensitivity analyses for
the critical wastestream scenarios and has implemented a Monte-Carlo approach which
incorporates a range of values for parameters which exhibit a high degrees of variability, and
therefore, uncertainty. In a Monte-Carlo analysis, parameters with a significant degrees of
uncertainty are randomly generated or selected from distribution curves. A large number of
simulations are performed with a different set of parameters (i.e., individual realizations) for each
simulation which results in a range of risk values or receptor well concentrations. This differs
from the determination of risk based on one simulation with one set of parameter values. Details
of these updated analyses and results are given in the April 8, 1997 NODA docket53.
F. SOIL TRANSPORT
Comment 1: The procedures used to compute the exposure from ingestion of soil and above and
below ground produce grown in these soils is flawed. The transport of soil from the land
treatment area to the receptors is not physically possible as described by EPA, therefore, there is
no direct or indirect exposure to these subpopulations from soils. (NPRA, 00015; Valero, 00051)
Response: The procedures used to compute the exposure from ingestion of soil and above and
below ground produce grown in these soils has been substantially revised to reflect soil erosion
in an integrated setting approach. This method was described in detail in the Supplemental
"Supplemental Background Document, Groundwater Pathway Risk Analysis, Petroleum
Refining Process Waste Listing Determination. 1997.
June 29, 1998 III-8
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of drainage area, topography, channel density, and relief. None of these factors are included in
the analysis (NPRA, 00015; Valero, 00051)
Response: The method for estimating soil erosion from land treatment units has been revised to
reflect the integrated approach to soil erosion. This method was described in detail in the
Supplemental Background Document for the NonGroundwater Risk Assessment; Petroleum
Waste Listing; Interim Notice of Data Availability which was prepared in support of the NODA
(62 FR 16747) published April 8, 1997. The "soil delivery factor" does not appear in the revised
methodology. The revised method estimates the sediment delivery ratio for the nearest water
body and assumes that the soil eroded from the source that does not reach the stream is deposited
evenly over the subbasin. The basic assumptions in this analysis for the sediment delivery ratio
are:
• The sediment delivery ratio (SDSB) and the soil loss rate per unit area (Xc sub-
basin) are assumed to be constant for all areas within the sub-basin, but may be
different for the watershed outside of the sub-basin.
• The amount of the soil deposited onto the field is estimated by assuming that the
fraction of soil that does not reach the water body (1-SDSB) remains in the sub-
basin
It is assumed in the integrated setting that all receptor sites are downgradient from the source and
within the same defined subbasin as the LTU. The home gardener or subsistence farmer scenario
represents only a single individual at a site. Population risk is discussed in Section IV.B of the
NODA response to comments document.
Comment 4: EPA uses an equation in Table E-17 Appendix E Indirect Exposure Model to
calculate the rate the contaminants are deposited at the receptor site. Again, there is no citation
for this equation. A similar equation is defined in the Applied Handbook of Hydrology, Chapter
l~ (pp. l~-2~) to determine the rate of sedimentation. However, in comparing the two equations,
two parameters have been omitted from EPA's equation E-17. The trap efficiency of the
receptor, i.e., the ability of the receptor location to trap the sediment from flowing beyond the
receptor site, and the specific weight of the sediment are not included in EPA's calculation. The
weight of the sediment is probably such that it would fall out in a short distance in the channel
carrying the runoff away, or in any wide spots in the channel. Thus, again it is unlikely that any
receptor would receive any soil. (NPRA, 00015; Total, 00039; Valero, 00051)
Response: The equations used to estimate soil erosion have been revised to reflect the integrated
settings approach. This method was described in detail in the Supplemental Background
Document for the NonGroundwater Risk Assessment; Petroleum Waste Listing; Interim Notice
of Data Availability which was prepared in support of the NODA (62 FR 16747) published April
8, 1997. This approach does not include channeling because insufficient site specific
June 29, 1998 111-10
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The oral bioavailability of PAHs in rats, hamsters, or humans from diet or oil is approximately
92 percent55. A recent abstract report presented the bioavailability of PAH from soil in terms of
Relative Absorption Fraction (RAF). RAF represents the fraction of the BaP in soil that is
absorbed relative to the BaP in the diet.
_ fraction of BaP absorbed soil
RAF —
fraction of BaP absorbed diet
RAFs reported in this abstract varied from 0.07 to 0.75 with an average of 0.29 based on 3
animal studies56. This variability in the bioavailability soil-bound PAHs may be expected based
upon soil type because PAH sorption to soil increases with increasing soil organic carbon content
and particle surface area (Southworth, 1979; Sullivan and Mix, 1985; Karickhoff et al., 1979;
Gardner et al., 1979). The gastric absorption of PAH may be inhibited by sorption to soil
particles with high organic content or may be enhanced by the presence of oils and fat in the
gastrointestinal tract. In fact, the sorption of PAHs to organic soil may be minimized (practically
neutralized) by the emulsifying action of bile (lipolysis) in gastrointestinal absorptions.
However, sorption of PAHs to organic soil has been demonstrated to be minimized and
bioavailability increased by the emulsifying action of bile (lipolysis) in the gastrointestinal tract
(Rahman et al. 1986). In addition, when mixtures of PAHs (pyrene, benz[a]anthracene,
chrysene, benzo[b]fluorene, benzo[k]fluorene, benzo[a]pyrene, indeno[l,2,3-cd]pyrene,
dibenz[a,h]anthracene, benzo[g,h,i]perylene) were fed to mice in different diet matrices results
indicated that the matrix had little effect on the bioavailability of the PAHs (Wu et al. 1994).57
Due to uncertainty regarding the bioavailability of PAHs the Agency believes it is appropriate to
assume PAHs to be 100 percent bioavailable in order to be protective of human health regardless
of soil characteristics. However, in the case of the risk assessment conducted in support of the
petroleum refining waste listing decision, direct ingestion of soil is not a driving pathway and
even if the risk from soil ingestion were reduced by an order of magnitude or more it would not
affect the total indirect risk to individuals raising home produced fruits and vegetables near
petroleum refineries managing CSO sediment in onsite LTUs.
Comment 7: EPA used an adaptation of the USLE to calculate the concentration of constituents
at an offsite receptor location from run-off from a land treatment unit. As part of the
55Ruby, M.V. 1997. Determining the oral bioavailability of PAHs from soil. Preprints
of Papers Presented at the 214th ACS National Meeting, Las Vegas NV. September 7-11, 1997.
American Chemical Society. 37(2):237-238.
56Magee, B., P. Anderson, and D. Burmaster, 1996. Absorption adjustment factor (AAF)
distributions for polycyclic aromatic hydrocarbons (PAHs) Human and Ecological Risk Assess.
2(4):841-873.
57
June 29, 1998 111-12
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with run-off controls, much less with controls achieving 50% efficiently. The commenter
referenced a 1995 EPA report on state requirements for industrial non-hazardous waste
management facilities from which they conclude that 61 refineries are in states that do not
required run-off controls on any land treatment units. (EOF, 00036)
Response: EPA conservatively assumed that no runoff controls were present in its high-end
analysis of risk to individuals residing near land treatment facilities managing petroleum waste
streams because the presence and effectiveness of such controls could not be verified. EPA
believed this is appropriate for the high end scenario. The central tendency scenario, however,
assumed that controls were in place that were 50 percent effective. The basis for this assumption
is two-fold. First, the Agency's 1992 survey asked that refineries characterize whether run-on or
run-off controls were in place at land treatment units used in 1992.58 Based on the information
currently available to the Agency, of the 18 facilities with land treatment units, all reported
controls. While it was not possible to quantify the effectiveness of these controls due to the very
general nature of the questions and responses, it was obvious that the majority of the facilities
provided some level of control. Secondly, EPA conducted site visits at 7 refineries that operated
land treatment units as part of its field study. At the four facilities where EPA toured the land
treatment units, EPA observed controls designed to divert run-on and collect runoff.
EPA recognizes that the effectiveness of control is dependant on any factors (level of engineering
design, operation and maintenance practices, regulatory oversight and minimum standards,
weather conditions, etc.), and that the actual effectiveness of the runon/runoff controls at these
sites varies, in part because of the lack of Federal land treatment unit standards. As a result, EPA
assumed only partial effectiveness, 50 percent controls, for the central tendency analysis, and no
controls for the high end analysis. EPA agrees that there is no specific basis for using "50
percent" effectiveness; EPA does not have available to it data that would allow for quantification
of effectiveness. This value, however, was selected in order to characterize releases from LTUs
where controls known to be widely used have some effect in mitigating releases.
EPA has recognized that no controls are mandated (although the survey indicated that some level
of controls are common) and assumed zero controls in the high end analysis and only partial
control in the central tendency analysis.
Comment 2: There is ample evidence in the RCRA §3007 Petroleum Refinery database that
land treatment units do have erosion controls. Moreover, even where there are no Subtitle C or
mandatory state Subtitle D regulatory requirements for these controls, numerous other factors are
motivating their use, as evidenced by the fact that most facilities currently use them. LTUs
581995 Listing Background Document for the 1992-1996 Petroleum Refining Listing
Determination, Appendix C. In response to comments, EPA examined these units further,
including the evaluation of data submitted by industry, telephone contact with the facilities, and
consideration of permit status data reported in the survey.
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The TCLP is very conservative. The underlying model assumes that the waste is disposed of in a
municipal solid waste landfill, where it is leached by acidic landfill liquids, emerges from the
landfill bottom into underlying groundwater, and migrates to a hydraulically down-gradient
drinking water well. While this may have constituted a plausible worst-case disposal practice in
the past, co-disposal of potentially hazardous industrial wastes in a municipal landfill is not a
likely mismanagement scenario today.
The TC method for determining risks couples the TCLP, the EPACMTP and a toxicological
model. The TCLP was designed to be a water phase model, not a multi-phase model. To apply
the TCLP as a realistic multi-phase model of contaminant leaching requires acceptance of the
following conservative assumptions:
• The bottom of the landfill is in direct contact with groundwater;
• Disposed nonaqueous liquids (i.e., oily liquids) and groundwater are equally mobile in
the subsurface;
• The nonaqueous liquids (i.e., oily liquids) are not leached. They elute directly from the
landfill into the groundwater;
• The continuous release of these liquids proceeds forever (i.e., the source is not finite);
• The solids in the residual are leached with a 20:1 volume of acidic landfill leachate;
• The constituent concentrations in the leachate do not decrease over time (i.e., infinite
source);
• The nonaqueous liquids and the leachate travel together at the same rate through the
subsurface. Attenuation and dilution reduce concentrations by a factor of 0.01;
• Constituent concentration reach steady state in the drinking water well and never decrease
over time; and
• The well owner drinks 2 liters/day for 70 years - nonaqueous liquids and all.
The above assumptions ensure that the TCLP will provide extremely conservative estimates of
leachate concentrations, contaminant mobility, and contaminant risks. Thus the commenter
believes that EPA should be confident that any risks estimated by use of this procedure are likely
to be substantially overstated.
Moreover, use of the TCLP in this case to estimate risks from oil-bearing residuals (e.g., CSO
and crude oil storage tank sediment) would produce even greater overestimates of potential risks.
(API, 00046)
Response. EPA does not agree that the TCLP overestimates leaching levels for these wastes.
The commenter's concern that the TCLP was used to model "multi phase" leaching (i.e.,
leaching of organic and aqueous phases together from wastes) are unfounded. EPA did not, as
asserted by the commenter, assume oily liquids elute directly from the landfill to groundwater,
June 29, 1998 III-16
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b. In the 1990 listing determination for petroleum refinery wastewater treatment
sludges, EPA expressly rejected relying upon the TCLP as the appropriate
measure of potential oily waste teachability, because the "...newly developed
TCLP tends to underestimate the teachability of hazardous constituents from oily
wastes."61
c. In the 1992 listing determination for coke byproduct wastes, the Agency again
rejected TCLP results as the basis for measuring waste teachability. The Agency
cited the filtration and other technical difficulties associated with use of the
procedure on oily or tarry wastes, and thus "...maintained] its belief that the
TCLP results may underestimate the concentrations of constituents in
leachates...."62
d. The 1990 refinery waste listing determination references an EPA contractor report
prepared for the Agency on oily and other wastes that are difficult to filter63 The
report describes several aspects of the TCLP which result in significant
underestimates of teachability using the procedure.
i. Wastes can clog the filter before all waste liquids have passed.
ii. Errors in the TCLP can cause inaccurate liquid/solid leaching ratios
resulting from percent solids determinations that are too high.
e. The Agency requires a different procedure than Method 1311 in the delisting
context to measure metals teachability in wastes containing greater than 1% oil
and grease, thereby acknowledging the deficiencies of the TCLP for metals in oily
wastes as well.64
615 FR 46376 (November 2, 1990).
6257 FR 37294 (August 18, 1992). See also 57 FR 37296 ("The Agency does not believe
that the TCLP can be used to determine the teachability of wastes such as K148 that are difficult
to filter.").
"Evaluation and Modification of Method 1311 for Determining the Release Potential of
Difficult-to-Filter Wastes, Prepared by RTI and Dr. Peirce of Duke University, April 1990
(hereafter "EPA TCLP Report"). By letter dated March 1, 1996, EPA submitted a copy of this
report for inclusion in the instant rulemaking record.
"Petition to Delist Hazardous Wastes: A Guidance Manual (Second Edition), prepared
for EPA by SAIC, March 1993, p. 6-11.
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As a second means of assessing the potential for free or mobile oil content in the residuals of
concern, EPA evaluated the reported oil and grease content of landfilled and land treated wastes,
based on data reported in Section VII of the questionnaire submitted by the industry:65
In assessing any waste that was disposed in an onsite nonhazardous landfill in 1992, the
highest reported oil and grease concentration was 10 percent, with the median value less
than 1 percent.66
For residuals disposed in offsite non-hazardous waste landfills in 1992, 8 individual
wastes were reported to have oil and grease levels over 10 percent, but the median level
was approximately 1 percent (oil and grease data were reported for only 120 out of the
621 residuals disposed in offsite nonhazardous waste landfills).
• EPA conducted further verification of the 8 wastes disposed in offsite landfills
with reported oil and grease levels above 10 percent. The two highest levels, for a
crude oil tank sludge (80%) and a residual oil tank sludge (99%) appear to
represent oil levels prior to deoiling (i.e., the residuals underwent an onsite
removal step prior to being landfilled, and the oil content of the landfilled material
was not provided). The remaining 6 wastes had oil & grease levels ranging from
12 to 30 percent. Only one of these wastes was one of the 14 residuals considered
for listing under this rulemaking (CSO sediment with 20 percent total oil &
grease); the other 5 were residuals identified for study under the EOF consent
decree. Two of these study residuals, both with 20 percent oil and grease levels,
were accompanied by lab results. One sample was described as having no free
liquids as determined by the paint filter test67, and another was described as
having 93 percent solids and 7 percent liquids (which indicates that most of the oil
is bound to the solid matrix).
• Removing the 2 highest data points (80 and 99 percent) from the data set (because
they do not reflect oil levels in wastes actually landfilled) reduced the average oil
and grease level in these wastes with the highest oil and grease content to 19
65 Supplemental Background Document for Listing Support Analyses, 1997, Appendix
A.
66EPA notes that it has such data for only one-third of the residuals disposed in this
manner; oil and grease data for the other two-thirds of the residuals were not reported. The
limitations of these data are discussed further in response to the public comments on the NODA
in Section I.C. 1.
"EPA. "Test Methods for Evaluating Solid Wastes, Physical and Chemical Methods.:
Third Edition, Update 3. SW-846, 9096A. 1997.
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The record sampling and analysis program proceeded smoothly with minimal problems
associated with the conduct of the prescribed methodologies. The contract laboratory was
generally able to achieve the targeted quantitation limits and QA/QC limits were generally met.
Overall, the quality and reliability of the Agency's data were excellent. These findings were
confirmed by the comparison of split samples collected and independently analyzed by API.71
The reliability of the waste characterization extended to the TCLP results. Each of the samples
collected by the Agency was subjected to both total and TCLP constituent analyses (except those
residuals which were liquid by nature such as spent caustic and did not require aqueous
extraction). In no cases did the laboratory report any difficulties in the conduct of the TCLP.
EPA reviewed the analytical data reports and laboratory logs for 38 samples of the 8 residuals
expected to be the most oily. No filtration difficulties were reported. In the Supplemental
Background Document to the NODA, Table 1 summarizes these findings. The commenter's
concerns regarding problems previously reported with the filtration step of the TCLP were not
observed in the familiarization or record sampling and analysis program. Table 1 also
demonstrates that none of the samples subjected to the TCLP were reported to exhibit
heterogeneous layers or emulsions The commenter's concern regarding the potential for two-
phase flow and the formation of NAPLs was not substantiated by the Agency's observation and
laboratory analyses of over 100 samples of the residuals of concern.
a. The HWIR proposal
The HWIR proposal has broad applicability and is designed to provide regulatory relief to any
hazardous waste that meets its generic criteria. To address concerns that the program might be
overly broad, EPA raised a number of issues in the HWIR proposal that were associated with
specific types of wastes where the generic exemption criteria might not address waste-specific
characteristics. One of these issues was the effectiveness of the TCLP in predicting leaching
from the general category of oily wastes, based in part on the operational problems documented
in the RTI report (discussed further below). In conducting the petroleum refining field
investigation supporting this rulemaking, EPA kept these considerations in mind throughout the
sampling and analysis program. As documented elsewhere in this response, the specific
concerns raised in the HWIR rule associated with the broad class of oily wastes were not found
to be warranted with the specific subset of oily wastes investigated in this rulemaking.
b. The 1990 listing determination for petroleum refinery wastewater treatment
sludges
these matrices, the laboratories attempted to quantify benzene at levels at least this low.
71See Appendix B to the 1995 Listing Background Document, "Comparison of EPA and
API Laboratory Results as Part of the J 992-1996 Petroleum Refinery Listing Study \ July, 1996,
in the docket to today's rule.
June 29, 1998 111-22
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liquid and considered to be homogeneous wastes. For this reason the RTI report is not
considered directly applicable to the petroleum listing residuals.
/. Wastes can clog the filter before all waste liquids have passed.
The RTI report suggests that the current TCLP Method 1311 underestimates the release potential
of toxic constituents when difficult-to-filter wastes are characterized according to the existing
filtration procedure. The report indicates that the glass fiber filter media recommended in
Method 1311 easily clogs using oily matrices thereby inhibiting the determination of analytes in
the filtrate or primary leachate. RTI evaluated several potential changes to the TCLP in an
attempt to address this problem. The leachate results along with the percent solids retained using
a modified filter apparatus were compared to those from soil column experiments and the current
Method 1311 procedure. There were no statistical differences in API separator sludge percent
solids retained and leachate results using the modified and current Method 1311. However, less
solids were retained and additional analytes were detected in the slop oil emulsion using a
modified procedure. The RTI report concluded that the current Method 1311 was adequate for
filterable wastes, but not as accurate as modified filtration procedures for the difficult-to-filter
wastes (see p. 79 of the RTI report).
//. Errors in the TCLP can cause inaccurate liquid/solid leaching ratios
resulting from percent solids determinations that are too high.
The RTI report noted that certain difficult-to-filter wastes may cause TCLP Method 1311 filter
clogging and thereby overestimate the waste percent solids used to calculate the liquid leaching
volume. The report concluded that the resulting excess leaching fluid may dilute the final
leachate concentrations if the solubility equilibrium is not achieved during the 18-hour leaching
period. The Agency agrees that multiphasic and difficult-to-filter wastes that fail to produce a
filtrate upon filtration could potentially result in excess leachate volume since these wastes are
considered to be 100 percent solids for leaching purposes.
After carefully examining the data developed by RTI, EPA concludes that, except for perhaps
API separator sludge, three of the wastes evaluated by RTI are dramatically different from the
listing residuals of concern in this rulemaking. The slop oil emulsion and used motor oil samples
had 40-100 percent oil content (see p. 41 of RTI's report). All four of the wastes were called
''multiphasic" in the report (see p. 7 of RTI's report), indicating the apparent presence of free oil.
All exhibited filter clogging and underestimation of liquid fraction. The conclusions that can be
drawn from RTI's data for API separator sludge support EPA's use of the TCLP to characterize
the petroleum residuals of concern. The conclusions drawn from the RTI report regarding the
other three wastes are not applicable to the wastes of concern in the current rulemaking.
e. The Delisting method
June 29, 1998 111-24
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While cosolvency effects may exist, the Agency has never been able to develop an adequate
means of assessing any potential increases in toxicant mobility in refinery landfills. However,
this is offset by several factors First, the TCLP does measure mobility due to cosolvency within
a given residual, i.e., the TCLP results reflect any "cosolvency" leaching caused by the organic
chemicals in the waste samples themselves. Secondly, the listing determination finalized in this
rule focused on those residuals originally examined in OSW's 1983 survey of the refining
industry and subsequently identified in the EOF consent decree as the petroleum residuals of
most concern (e.g., those posing potential leaching or co-solvency risk). These residuals have
been thoroughly evaluated over the course of the Agency's industry study and risk assessment
The Agency has no reason to conclude that other residuals, not characterized as one of the 29
consent decree residuals, would exert much risk or potential for increasing co-solvent effects
EPA found that very few of the 29 residuals of concern with significant oil content are sent to
landfills; the Agency is not convinced that these limited oily wastes present a significant
potential for increasing co-solvent effects. Third, the promulgation of the Toxicity Characteristic
is likely to have removed many of the wastes containing highly mobile solvents from Subtitle D
landfills, reducing the potential for co-solvent effects. The TC rule regulates many chemicals
that were commonly used as solvents (e..g, trichloroethylene, tetrachloroethylene, carbon
tetrachloride, methyl ethyl ketone; see 261.24) in addition to benzene, a common constituent in
petroleum wastes. Thus, wastes containing appreciable concentrations of these chemicals would
thus be regulated as hazardous and can no longer be codisposed with nonhazardous waste.
Fourth, the promulgation of 1990 sludge listing also removed significant volumes of multiphasic
oily wastes from Subtitle D landfills, further reducing co-solvency risks.
a. Previous petroleum refinery listing determination
As the commenter noted, in an earlier listing of other petroleum refinery wastes (primary and
secondary pile/water/solids separation sludge, F037 and F038 respectively), EPA argued that the
toxic constituents in the wastes (PAHs) may be expected to become mobilized by cosolvency
effects because they "typically contain high concentrations of oils" (55 FR 46369). However, as
noted earlier in this response (as well as in Section I.C. 1 of the NODA Response to Comments),
the existing information indicates that the wastes under examination in the current rulemaking do
not typically contain high levels of free oil, and that the wastes sent to landfills typically do not
have high oil content. Furthermore, the listing of F037/F038 sludges also relied on damage cases
and noted that much of the sludge was generated and stored/disposed of in surface
impoundments, resulting in groundwater contamination (55 FR 46370). In the current
rulemaking, EPA could not find any convincing damage cases (i.e., environmental risks caused
by the residuals under examination), nor were the oily wastes of concern disposed of in surface
impoundments.
b. No evidence that the solvents and oils of concern are no longer present in the
same refining sector land disposal units.
June 29, 1998 111-26
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associated with material placed in a landfill. One refinery73 reported generation of crude oil
storage tank (COST) sediment with oil content of 80 percent directly after removal from the tank.
The facility subsequently conducted oil recovery on this residual, but neglected to report the oil
content of the residual after the recovery step. The 80 percent value was inappropriately carried
over to the de-oiled secondary residual, giving the commenter the erroneous impression that
extremely high oil content residuals were being land disposed.74 The Agency continues to assert
that the oil content of 27 percent assumed by the Agency in its assessment of free phase flow for
the proposal is reasonable, if not high, in terms of actual reported values in the survey and the
Agency's observations during sampling and analysis. See Section III.K, Comment 1 of this
response to comment document for additional discussion.
6. If EPA had not relied on the TCLP, at least 6 wastes would have been listed.
To summarize the discussion presented above, EPA has closely evaluated the appropriateness of
the TCLP to characterize the mobility of toxicants from the petroleum refining residuals of
concern:
• These residuals differ from the oily wastes characterized by the commenter because they
are generally solid, homogenous, and do not contain free oil, as confirmed by field and
laboratory observation.
• The high level of oil and grease content referenced by the commenter of 80 percent was
incorrectly associated with landfilled residual, reflecting levels prior to de-oiling and
subsequent disposal at that facility.
• The contract laboratory did not encounter complications or QA/QC problems during the
conduct of the TCLP.
• The results of the NODA OWEP analyses confirm the adequacy of the TCLP, showing
no significant increases in leaching due to the use of a much more aggressive leaching
media.
• The calculation of percent teachability also confirms that the TCLP results are reasonable
and that matrix effects were not evident.
In conclusion, EPA continues to believe that the TCLP results adequately predict leaching from
the residuals of concern.
"Facility Number 19, ARCO, Los Angeles Refinery, Carson, CA.
74 Supplemental Background Document for Listing Support Analyses, 1997, Appendix
A
June 29, 1998 111-28
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In addition, EPA reviewed API's "Generation and Management of Residual Materials, 1992-
1993" Appendix C, which provides trends of waste generation from 1987-1993. Generally, 1992
was representative when comparing waste generation and management for the API waste
categories and the residuals under review. Only hydroprocessing catalysts showed a slight
increase in production that year possibly due to the new low-sulfur diesel regulations.
In developing reasonable management scenarios for subsequent risk assessment modeling, EPA
considered some potential shifts in management practices. These considerations are discussed in
the context of each specific waste (see Section IV of this response to comment document). For
the remaining residuals, EPA considered the industry to be stable, and thus assumed that 1992
provided a reasonable picture of the petroleum refining industry's practices. EPA's approach
was not "forever fixed," but used 1992 as a reasonable starting place for assessing the industry's
waste generation and management practices.
Finally, EPA notes that its survey of refineries was a complete census of the industry, and
gathered information from all active petroleum refineries in the United States. It is reasonable
for the Agency to conclude that the large amount of information gathered in its 1992 survey of
petroleum refineries related to waste generation, management, and disposal practices is
representative of such practices in any year. While individual refineries may change practices in
any given year, the overall pattern of these practices, including waste volumes and the potential
environmental risks posed, are unlikely to change significantly for the industry as a whole.
Comment 3: In addition, the commenter noted that the volumes do not reflect either the actual or
potential co-disposal of the wastes included in EPA's data base, or co-disposal with other refinery
wastes managed at onsite and offsite units receiving refinery wastes. Instead, EPA has modeled
the factually false and completely unrealistic scenario of forever fixed 1992 volumes of wastes
managed in units that contain only one of the refinery wastes covered by this rulemaking and
nothing else except materials of a completely benign nature. (EDF, 00036; ETC, 00038)
Response: In response to the commenter's concern regarding co-disposal of refinery residuals,
EPA has conducted a co-disposal analysis, described in detail in the docket for the April 8, 1997,
NODA. The universe of residuals considered in this analysis included all of the 29 residuals of
concern reported in the 1992 survey of petroleum refineries. For example, in assessing the
landfills reported to be used for management of crude oil tank sediment, EPA also compiled the
volumes of CSO sediment and other residuals of concern that were reported to be co-disposed
with these wastes. While other residuals are generated by refineries, they were assumed to not be
of concern to the co-disposal scenario because (1) they are already listed as hazardous (i.e., the
wastewater treatment residuals covered by the existing K. and F listings), or (2) they were low
toxicity residuals not included in the consent decree list of 29 residuals of concern. For off-site
disposal scenarios it was not possible to determine what non-refinery wastes could be co-
disposed with the residuals of concern. From the data set of refinery residuals for which the
Agency had data, EPA eliminated those wastes promulgated as hazardous listed waste through
this rulemaking because they will no longer be eligible for Subtitle D disposal.
June 29, 1998 111-30
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assumptions. A summary of the conservative nature of the Agency's evaluation follows. For
each scenario modeled, the full range of wastes reported to be subjected to that type of waste
management (e.g., landfilling or land treatment) was included in the distribution of wastes of
concern. For the indirect pathways, the 2-high end risk assessment methodology used 90th
percentile values for those scenarios where volume was selected as one of the high end
parameters76. The ground-water pathway, as described in the April 8, 1997 NODA, was based on
a 2-high end methodology, as well as a Monte Carlo analysis that drew from the full range of
reported waste volumes. Thus, the Agency's analysis considers "present hazard" by using
characterizations of wastes and management units associated with the scenarios of concern as
reported in 1992, and considers "potential hazard" by the evaluation of the 90th percentile
volumes in the indirect pathway analysis and the full range of factors affecting releases in the
ground-water pathway analysis.
Comment 5: The methodology is also inconsistent with previous Agency practice and policy
According to EPA's recently described listing determination policy, management scenarios "need
not be in use currently to be considered plausible by EPA since disposal practices can and do
change over time. Potential future waste management practices are projected and considered in
the risk analysis, if appropriate." Thus, in the recently finalized carbamates listing, EPA
computed landfill waste volumes according to the quantity of wastes that could be landfilled, not
just the quantity that happened to be landfilled in the reporting year. Similarly, EPA considered
the co-disposal of solvents and other oily wastes in petroleum refining waste management units
as part of its 1990 listing determination for wastewater treatment sludges. This inconsistency
with previous practice had significant impacts on the modeling results.
The commenter gave specific examples:
• EPA incorrectly chose the "high end" waste volumes for on- and offsite land treatment
units. This is because the Agency picked the high end volumes only from those volumes
that, in fact, were land treated in 1992. Larger generators landfilled much higher
volumes. Since there would be no legal barrier to landtreating these landfilled wastes in
the absence of a hazardous waste listing, EPA should have chosen the landfilled volumes
as the high end waste volume. This would have resulted in increases in land treatment
volumes ranging from factors of 3 (for HF alkylation sludge) to 21 (for crude oil tank
sludge).77
76See the 1995 Assessments of Risks from the Management of Petroleum Refining
Waste: Background Document for a complete description of the risk assessment methodology
and definition of terms.
77Nor can EPA justify different volumes for onsite and offsite land treatment, since
wastes currently managed onsite may be managed offsite at some future time and vice versa.
Once onsite and offsite land treatment or landfilling is established as a plausible mismanagement
scenario, EPA must assume the same wastes can be managed either onsite or offsite, absent some
June 29, 1998 111-32
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only comprised 23 facilities. The carbamates industry actually was subdivided further into
manufacturers of carbamates/carbamoyl oximes (8 facilities), thiocarbamates (1 facility), and
dithiocarbamates (14 facilities) that generated the specific wastes of concern for this industry.
The large number of refineries provided a much broader distribution of management practices,
allowing EPA to rely on actual practices reported and not requiring extensive consideration of
practices not reported.
While EPA believed that the sheer size of the petroleum refining industry provided a
representative characterization of reasonable management scenarios, the 1992 distribution of
management practices was not the Agency's sole consideration in selecting management
practices of concern. Prior to the proposal, EPA also evaluated the reported distribution of
management practices to ascertain whether additional practices were likely. The express purpose
of this exercise was to identify "potential" plausible management practices that were not reported
in 1992. As a result of this evaluation, EPA added several scenarios to its risk assessment
supporting the proposed rule78:
• For FCC catalyst and fines, a monofill scenario was added. The questionnaire was not
designed in a fashion that allowed EPA to determine whether landfills were in fact
monofills. EPA, however, observed during the field study that some refineries did
segregate this waste in monofills or discrete cells to allow for potential future recycling
for its aluminum content. A bounding monofill scenario was evaluated for FCC fines,
showing no significant risk associated with this material.79
• For hydrotreating, hydrorefming and tail gas treating catalysts, EPA evaluated a scenario
where all the residual volumes would be landfilled. This was done for two reasons. First,
both refineries and catalyst recyclers indicate that management practices change over
time. For example, one refinery sent its hydroprocessing catalyst to metals reclamation
or to a special waste landfill depending on market conditions (95-PRLP-S0041, page 11),
while a catalyst recycler reports that greater quantities of spent catalyst are recycled when
metals prices are high, translating to lower costs for catalyst reclamation
(95-PRLP-S0057, page 6). Secondly, discussions with other refineries have indicated
that they recycle due to corporate policy. If these wastes were to be "stamped" as non-
hazardous as a result of a no-list rulemaking, the liability concerns of the refineries might
have been somewhat mitigated, reducing their incentives to recycle and increasing their
78See the 1995 Listing Background Document for the 1992-1996 Petroleum Refining
Listing Determination, subsections "Management Practices Targeted for Risk Assessment"
provided in each chapter
791995 Assessments of Risks from the Management of Petroleum Refining Waste:
Background Document, pp. 12-3 through 12-5.
June 29, 1998 111-34
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Table III. I- 1 . Parameters Affecting Transferability of Petroleum Wastes
Oil & Grease (%)
% Water
% Organic Liquid
% Solid
All Land Treated Residuals
Average
50th Percentile
90th Percentile
13.8
5
30.7
17.2
2
50
9.1
0
31.2
769
96
100
All Landfilled Residuals
Average
50th Percentile
90th Percentile
5.9
1
18
7.5
0
25
4.2
0
10
91.6
100
100
These findings may explain why the volume distributions for land treated wastes appear to result
in higher 50th and/or 90th percentile volumes than those identified for landfilling (i.e., these
wastes contain more oil and more water). In addition, these findings indicate that waste
characteristic (oil and water content) are correlated to refinery waste management choices. EPA
believes that transferability between management practices is likely to be limited by these waste
characteristics.
The second important consideration regarding the transferability of wastes between landfills and
land treatment units is that land treatment is a rather limited and specialized management
practice, particularly with respect to Subtitle D units. As described in the docket to the April 8,
1997 docket, EPA's database only identified one facility with a co-located on-site landfill and
land treatment unit (see S0021, p. 15) and only 6 non-hazardous land treatment units (ibid., p.
30).
Thus, to project that large volumes of waste would shift between landfills and land treatment unit
seems implausible. Any changes that do occur in future years are likely to be offsetting given the
size of the industry and the lack of identified trends toward any given management practice.
Assuming for the sake of argument that such shifts did occur, it is possible that any change in
waste management practice for one refinery would be offset by the opposite change by another
refinery, in effect balancing out any changes from year to year.
As discussed above in Comment 3, EPA has evaluated the potential effect of co-disposal to
respond to the commenter's concerns. After removing the wastes with listings promulgated
under this action, the residual effect of co-disposal appears to be negligible.
June 29, 1998
IH-36
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upon a leaching method for organic constituents. EPA has since gained considerable experience
with the application of the TCLP, and while it is not perfect, the analyses described in Section H
of this document support EPA's conclusion that the TCLP is an adequate tool for predicting
leaching from the listing residuals of concern.
With respect to the groundwater codisposal modeled for the April 8, 1997 NODA analysis82,
volumes of all 29 petroleum wastestreams (both study and listing wastestreams) were summed
for each landfill based on actual 1992 disposal as reported in the 1992 RCRA §3007 Survey
responses. Results showed that although the total waste fraction increases due to codisposal, the
effective leachate concentration and total waste concentration for a particular contaminant
decrease. As a consequence, individual single-waste stream scenarios were actually more
conservative for many wastestreams. The use of a uniform waste fraction of 1.0 for all wastes
(i.e., assuming a monofill scenario for each residual) would have been overly conservative and
would not have been representative of actual waste disposal as reported in the 1992 RCRA
§3007 Survey responses.
Comment 7: In the instant rulemaking, the high-end analysis for the groundwater pathway uses
a waste fraction calculated from the 90th percentile 20-year waste quantity for individual waste
streams divided by the mean landfill volume. For all but four of the waste streams, the
cak ilated waste fraction is at least an order of magnitude less than the minimum value of 0.036
recommended in the user's guide for the model, based upon the assumption that the receiving
unit contains a minimum of 3.6% hazardous material. (EOF, 00036)
Response: The minimum value of 0.036 reported in the EPACMTP 1995 User's Guide is a
lower bound obtained from an analysis of waste composition in municipal landfills83 and its use
as a lower bound applies only to the database used for HWIR modeling. Waste fraction is
dependent on both waste quantity disposed and unit size, as the commenter implies. The RCRA
§3007 survey provides reliable data for waste quantity and onsite unit area, while the suitability
and source of offsite unit areas is discussed elsewhere in these comments (i.e., Section III.J).
These input data are specific to the industry under study. In contrast, the minimum waste
fraction data cited by the commenter and used for HWIR is based on an analysis of waste
composition to municipal waste landfills (as stated in the EPACMTP User's Guide). In
summary, the derived waste fraction value used for refining wastes is more appropriate than the
HWIR value because (1) it is derived from refining industry-specific data rather than the more
general data used for HWIR, and (2) it represents a different disposal assumption than that used
for HWIR (i.e., refinery wastes are assumed to be continued to be disposed in Subtitle D
^Supplemental Background Document, Groundwater Pathway Risk Analysis, Petroleum
Refining Process Waste Listing Determination. 1997
"Scats, R. and Salhotra, 1992. Subtitle D (Municipal) Landfill Characteristics. Center
for modeling and risk assessment, Woodward-Clyde Consultants, Oakland CA.
June 29, 1998 111-38
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based on actual petroleum waste management practices in 1992. Assumptions were not made in
the modeling analyses about potential disposal practices other than those reported in the RCRA
§3007 Survey responses. Offsite landfill sizes were selected from the USEPA's Database of
Industrial Subtitle D Landfills"5 and were reasonable estimates based on available information.
Furthermore, for finite waste sources, it is not necessarily true that the larger the landfill, the
higher the resulting receptor well concentration. The modeled receptor well concentration is a
function of a number of parameters, such as waste volume, leachate concentration, and various
chemical transport properties. For a given waste volume, a larger landfill area will not
necessarily produce higher well concentrations.
EPA believes that there are indeed reasons why a facility would not dispose all its generated
waste in an onsite landfill, including permit limitations and liability considerations. Based on its
review of engineering site visit reports, EPA found that four facilities operated onsite
nonhazardous landfills. Two facilities manage FCC catalyst and fines, but no other listing or
study wastes, in their landfills.. The two other refineries operate onsite nonhazardous landfills for
disposal of only some of their generated wastes; other wastes are disposed offsite or recycled
EPA believes its approach of calculating different unit areas for different wastes was reasonable
because they are reflective of actual operating practices, and another approach may result in
unrealistic or unreasonable assumptions regarding waste management practices.
Comment 2: The methodology employed for deriving high-end waste unit areas ignores the
present and potential co-disposal of refinery wastes in onsite facilities. EPA's underlying
assumption that some refinery wastes will not be managed in the larger landfills sharply contrasts
with the reality that onsite refinery landfills routinely receive refinery wastes of all kinds. (EOF,
00036)
Response: The Agency recognrzes the commenter's concern for the representativeness of the
modeling scenarios. In response to the above and several other comments regarding codisposal
practices, on- and off-site codisposal modeling scenarios were included in the April 8, 1997
NODA analysis86. It should be noted, however, that landfill areas are not a sensitive parameter in
consideration of codisposal. Total waste volume and/or mass is the parameter that could
possibly produce higher risk in a codisposal scenario. As discussed above, for a given waste
volume, a larger landfill area will not necessarily produce higher concentrations at receptor wells
85U.S. EPA. Background document for EPACMTP: Finite Source Methodology for
Degrading Chemicals with Transformation Products. 1996.
86c
Supplemental Background Document, Groundwater Pathway Risk Analysis, Petroleum
Refining Process Waste Listing Determination. 1997.
June 29, 1998 111-40
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municipal landfill area distributions. The revised and expanded analyses are presented in
"Additional Groundwater Pathway Analyses; Supplemental Background Document; Petroleum
Refining Process Waste Listing Determination, USEPA, " 1998.
The off-site landfills used in the revised groundwater risk were derived from EPA's 1988 Survey
of Municipal Landfills.87 The high end area (90th percentile) used was 420,888 square meters.
This is somewhat smaller than the high-end area assumed by EPA in its analysis for the
carbamate listing, which was 949,317 square meters. EPA believes that the areas used in the
present rulemaking are more realistic in that they are derived from actual landfill data. The area
used in the carbamates rule was simply projected from the total volume of all carbamate wastes.
Furthermore, the full distribution of unit areas from surveys of off-site landfills were used in the
Monte Carlo assessment of the potential risks associated with off-site landfilling. Thus, EPA
believes that its approach in the current rule represents the evolution of risk assessment
methodology.
Comment 5: In selecting a plausible mismanagement scenario for dissolved phase contaminant
flow, EPA should develop a volume size that reflects the quantity of all refinery wastes that
could be landfilled over the unit's active life, taking into account the potential for co-disposal of
other wastes in these units. (EDF, 00036)
Response: The co-disposal scenario considers the volumes of the 29 residuals of concern
identified in the EDF/EPA consent decree (see Section III.I, Comment 3). EPA did not collect
information regarding the composition or volumes of other refinery residuals.
For the Groundwater Pathway Analysis, an active landfill lifetime of 20 years was assumed (see
Section III.L). Therefore, a total 20-year volume of waste was modeled for each single
wastestream scenario conducted in the 1995 analysis as well as for the single-wastestream and
codisposal scenarios conducted for the April 8, 1997 NODA. The codisposal scenario is
included in the current analysis in response to several comments. EPA notes, however, that it
revised its assumption of active landfill life to 30 years for off-site units, as described in the
response to comments document for the NODA (see Section I. A of that document).
See also responses to comments 1, 2, and 3 in this section, above for additional responses on the
issue of co-disposal.
K. POTENTIAL FOR FREE-PHASE FLOW
"Draft National Survey of Solid Waste (Municipal) Landfill Facilities, EPA/530-SW-88-
034, USEPA, 1988.
June 29, 1998 111-42
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saturate the material in the landfill beyond the 10% residual saturation limit. Below this limit the
oil will not migrate as a NAPL If the oil does not escape the landfill, the NAPL cannot saturate
the soil beneath the landfill, nor can NAPL-facilitated transport in the subsurface occur.
Beyond the results of the EPACMOW, EPA believes the commenter's concerns about NAPL or
free-oil release from landfills are unwarranted, since the residuals of concern are not oily in the
manner anticipated by the commenter While the sampled residuals may contain oil, this
observation is not equivalent with concluding, as the commenter does, that free oil is present in
these residuals. The method used to estimate oil content in the samples, the Total Oil and Grease
(TOG) method, will overestimate "free" oil because it uses a strong organic solvent to extract
various organic material, including waxes, greases, and higher molecular weight oils that are not
mobile. During EPA's observation and handling of crude oil tank sediment during sampling and
laboratory analysis, a discrete oily phase, or NAPL, was not observed. None of the samples
analyzed via the TCLP in this investigation were found to have oily phases. In addition, as noted
elsewhere, reported oil and grease content of landfilled wastes support EPA's conclusion that
wastes with high oil content (whether free oil or not) are not typically land disposed. This result
is consistent with EPA's belief that oil concentrations in a landfill will not reach the levels the
commenter suggested, since refineries have economic incentives to recover free oil as much as
possible, and minimize the amount of recoverable oil that is disposed in residual material.
Comment 2: EPA's dismissal of the possibility of NAPL migration to the water table has a
domino effect in that, based on its analysis of multi-phase transport in the soil zone, EPA
chooses to forego an evaluation of the impact of saturated-zone NAPL on receptor well
concentrations. (EOF, 00036)
Response: EPA has concluded that the NAPL flow, if any, from these residuals will not reach
the underlying aquifer and thus further modeling is not necessary. As discussed in Section III H,
the Agency has no information that indicates that the residuals of concern are likely to exhibit
free phase flow.
Comment 3: EPA concludes that the NAPL will not exit the base of the landfill because the
fraction of oily liquid in the waste unit is so small that all of the oil will be retained in the waste
unit as immobile residual. The basis for this conclusion is a calculation indicating that the
fraction of the landfill occupied by the NAPL will be only 0 00387 percent.
The fraction of NAPL in the landfill is calculated by dividing the 20-yr 90th percentile crude oil
tank sludge waste stream volume by the 90th percentile landfill volume and taking 27% of the
resulting waste fraction. This combination of parameters does not represent a high-end scenario
for NAPL release.
For example, in evaluating the potential for NAPL release, a smaller landfill provides the
reasonable worst-case management scenario, because the potential for NAPL release increases
with the waste fraction as explained below. Since there is no legal or technical bar precluding
June 29, 1998 111-44
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disposal practices are expected to be similar to 1992 disposal practices and the wastes are
expected to be similar in nature. Refineries have economic incentives to recover free oil as much
as possible and minimize the amount of recoverable oil that is disposed in residual material.
Again, EPA argues that the 27% value is not relevant and the physical nature of all the crude oil
tank sediment samples was such that the percentage of free oil is probably close to zero in all
cases
Comment 5: EPA falsely assumes that the waste will be uniformly mixed with benign material
in the landfill. Uniform mixing of the waste is not a plausible mismanagement scenario. It is
highly unlikely that the other wastes received by a landfill over its operational period will be
benign. The implications for co-disposal for NAPL transport are that the oil-retention capacity
of a substantial portion of the landfill matrix will be taken up by co-disposed oils and organic
liquids, and free-phase NAPL in the modeled waste stream will be more likely to exit the waste
unit. (EOF, 00036)
Response: As discussed in response to Comment 1 above, EPA has further analyzed the
residuals of concern and EPA contends that the residuals of concern are not oily in the manner
anticipated by the commenter; therefore, any concern over exceeding the residual saturation of
the landfill through codisposal with other wastes is unfounded. EPA has no basis for assuming
that these wastes, which contain virtually no free oil, will be placed in a landfill with a large
amount of free oil which will then mobilize the constituents.
Comment 6: When NAPL enters an unsaturated soil column, vertical migration dominates. For
a given volume of mobile NAPL, the smaller the infiltration area, the narrower the soil column
through which the NAPL travels, and the less soil volume available for NAPL retention. For the
50th percentile offsite landfill, the unsaturated zone beneath the waste is 6.1 meters thick. Given
the previous assumptions about the NAPL, including the holding capacity of the unit itself, the
threshold quantity of crude oil storage tank sludge producing NAPL at the water table is 161
MT/yr, or 52% of the landfill volume. (EOF, 00036)
Response: EPA responds to the commenter's concerns of NAPL leaving the landfill in
comment 3 above.
Comment 7: Although the thickness of the unsaturated zone did not emerge as a highly
sensitive parameter in the analysis of aqueous-phase transport from the modeled waste streams,
the distance of the oily waste above the water table is crucial in controlling whether or not NAPL
will reach the groundwater zone. In the modeled scenario, the thickness of the unsaturated zone
(6.1 m) was determined using the median value from the OSW modeling database. A true high-
end analysis of the potential for NAPL migration to ground water would also consider the 10th
percentile depth to the water table. (EOF, 00036)
June 29, 1998 111-46
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not an issue. 100% of the solid residuals will be retained by the landfill and contaminants will
only be transported in the aqueous phase.
Comment 9: Even if the migrating oil body contains insufficient oil to reach the well in the free
phase, the groundwater zone will still contain a zone of laterally distributed immobile residual
This zone of residual can exist substantially beyond the bounds of the landfill in the direction of
groundwater flow, effectively reducing the distance between the "source" and the receptor well.
Dilution and attenuation mechanisms in the groundwater become the only controls on receptor
well concentrations during the active life of the saturated-zone source. (EDF, 00036)
Response: The basis of the comment is an assumption that free-phase oil will saturate the soil
around the landfill. However, both EPA's 1995 free-phase flow modeling analysis and the
laboratory analysis described in Section HI.H demonstrate that its assessment of the potential for
free phase flow was adequate and that these wastes in general should not contain sufficient free
oil to exit the landfill, enter the unsaturated zone, and travel to the water table.
The distance between the source and the receptor well will only be reduced if sufficient
quantities of free-phase oil are present in the waste. The free-phase flow analysis conducted in
1995 showed that for a multi-high-end (more than two high-end parameters) scenario sufficient
oil was not present and more importantly as stated above, EPA's laboratory analysis of the
residuals showed that the samples were not multiphasic or heterogeneous. These materials were
generally solid at room temperature, with a tarry or granular consistency.
Comment 10: Contaminants flowing from the oil will dissolve into groundwater flowing
through the residual zone at their effective solubility levels. Accordingly, the chemical
concentration at the groundwater zone will be higher than any scenario modeled in this •
rulemaking because the contaminant-attenuation capacity of the unsaturated zone column is
unavailable. The combination of reduced distance between the receptor well and source, and the
higher initial concentrations, can be expected to significantly increase receptor well
concentrations. (EDF, 00036, II.£.3.^23)
Response: EPA fundamentally disagrees with the commenter regarding the presence of free oil
in these materials. As stated in response to comments 1 and 7 of this section, EPA does not
believe that free oil will exit the waste management unit.
Comment 11: Leachate exiting the base of the landfill is likely to contain oil emulsions because
of co-disposal of other wastes. Micro-emulsions increase the effective aqueous solubility of
compounds present in the oil, leading to higher chemical concentrations in groundwater near the
emulsion. Hydrophobic contaminants such as PAHs will preferentially partition to the oil
droplets in micro-emulsions, providing a mechanism for facilitated transport of these
compounds. The oil droplets that form micro-emulsions in the groundwater zone tend to travel
in the larger pore spaces of a hydro geological medium, so their transport paths are less dispersed
than those of compounds dissolved in water. Given the high potential for co-disposal with other
June 29, 1998 111-48
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Comment 2: In the carbamates listing determination, EPA assumed a 30 year active life for all
landfills and surface impoundments. No explanation is provided as to why carbamate waste
facilities are assumed to operate longer than petroleum refinery waste facilities. (EOF, 00036)
Response: EPA conducted a review of the active lives of landfills as reported in the 1992 RCRA
§3007 surveys. This review is presented in the Supplemental Background Document for Listing
Support Analysis, March 1997. EPA looked only at refinery landfills managing petroleum
wastes of concern. Based on this analysis, EPA determined that the median active life is
approximately 20 years. Therefore, EPA is confident that the 20 year value is appropriate for
onsite landfills managing petroleum wastes because it is based on industry-specific information.
Also see Response to Comment 1 above.
Comment 3: There is a substantial body of evidence demonstrating many refinery waste
management units have extremely long active lives. For example, EPA recently proposed a
treatability variance to address sludge from a refinery surface impoundment operating since the
late 1940s. In the course of reviewing a very small number of refinery RFAs, EOF found many
surface impoundments and landfills operating for longer than 20 years. These data demonstrate
the inadequacy of the 20 year active life assumption for refinery waste land disposal units. A
plausible mismanagement scenario should take into account the potential for refineries to manage
wastes in land disposal units for very long periods of time, as indicated by previous and current
practices. (EOF, 00036)
Response: See Response to Comment 1 above. Concerning impoundments, EPA notes that
"active life" concept is of limited use in projecting volumes of waste disposed, due to a variety of
reasons. First, as noted elsewhere (Section IV.E.2, Comment 1 of this document), most
impoundments are part of a wastewater treatment train and do not accept the waste as generated,
i.e., waste wasters flow to these impoundments only after some treatment. Other impoundments,
as documented in the October 1995 Listing Background Document (page 63) for FCC catalyst
fines, are typically used to settle solids from aqueous waste mixtures prior to wastewater
treatment. For such settling impoundments, solids that collect in the unit are typically removed
periodically for dewatering and disposal, thus waste volumes in such units are difficult to project
EPA believes that the 20-year assumption for on-site impoundments is quite conservative as a
basis for estimating the volume of the waste that might be present in the unit. Furthermore, EPA
notes that impoundments were modeled only for one waste, FCC catalysts and fines, and the
risks for this waste were negligible. Therefore, any changes in assumptions to waste volume in
the unit for this waste are unlikely to result in any significant change in risks or alter EPA's
decision not to list this waste.
EPA reviewed active lives for onsite landfills managing petroleum refining wastes addressed in
the proposed rule, and presented these results in the Supplemental Background Document for
Listing Support Analysis, March 1997. EPA found that some facilities have (or are likely to
have) landfills with a greater than 20 year active life. At the same time, an equal number of
June 29, 1998 111-50
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where:
BCFBEEF = biotransfer factor for beef
Kow ' = octanol-water partition coefficient
BCFSIILK = biotransfer factor for milk
This relationship is a reasonable prediction for a number of chemicals. It is known that PAH
compounds are readily metabolized by mammals by well-developed mixed function oxidase
(MFO) systems95, meaning that actual BAFs would be much lower than predicted using log Kow.
Mammals are capable of metabolizing PAHs even more efficiently than aquatic organisms
(Beaulieu, Steve. Personal communication with Lawrence Burkhard, EPA. Memorandum to the
file. Research Triangle Institute, RTP, North Carolina. Re: telephone contact, 1997.). Asa
result, the body burdens estimated using the estimated biotransfer factors based upon these
equations represent upper bound screening estimates that could occur only in animals with
deficient MFO systems. Therefore, beef, dairy, and fish ingestion pathways are not evaluated in
any analysis except for the initial bounding analysis.
Comment 2: EPA's justification for ignoring subsistence farmer and fisher receptors is the
"high uncertainty" associated with fish and plant-to-animal bioconcentration factors for the
PAHs of concern in this rulemaking. Yet as a condition of obtaining a RCRA permit, EPA
currently requires hazardous waste combustors to evaluate the impacts to subsistence farmers and
fishers of PAH emissions from their facilities along the very same direct and indirect food chain
pathways at issue in the instant rulemaking. Moreover, the HWIR proposal considered potential
impacts to subsistence farmers and fishers from releases of PAHs and many other constituents
along the same exposure pathways. If EPA assumes PAH bioconcentration factors are a source
of uncertainty, EPA cannot then ignore the pathways and risk entirely, thereby dg facto assuming
the pathways present no risks. Instead, EPA should consider the information qualitatively,
and/or present a range of results based upon possible bioconcentration factors. (EDF, 00036)
Response: EPA has not ignored risks to subsistence receptors from indirect exposure to PAHs.
Rather, lacking valid quantitative means of estimating biotransfer factors for PAH for beef and
dairy, the Agency has relied on qualitative knowledge regarding metabolism of PAHs by
mammals. However, no measurement data are available for calculating compound specific
bioaccumulation factors for animals. Subsistence fisher scenarios were evaluated using
measured bioaccumulation/bioconcentration factors (BAF/BCF) where available. BAFs reflect
the transfer of contaminant from the environment to the fish from food sources as well as
dissolved concentration (L/kg body weight) total. Since measured BAFs are usually not
available BCFs are used. BCFs represent the transfer from the dissolved phase to the fish tissue
BCF (L/kg). For those constituents for which neither measured BAFs nor BCFs were available.
95B.A. Rattner, D.J. Hoffman, and C.M. Marn, 1989. Use of mixed-function oxygenase
to monitor contaminant exposure in wildlife. Environmental Toxicology and Chemistry, 8:1093-
1102.
June 29, 1998 111-52
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Response: See response to comment 6, Section III.F of this response to comment document.
_ fraction of BaP absorbed soil
fraction of BaP absorbed diet
Comment 5: The use of ingestion-based toxicity factors for the inhalation pathway is
inappropriate, particularly for benzo(a)pyrene. In evaluating the risk posed by the PAHs
contained in crude oil tank sludge and clarified slurry oil tank sludge the Agency appears to have
calculated a risk from direct inhalation of PAH constituents (particularly benzo(a)pyrene
("BAP")) and used that value in the risk assessment. However, EEI is unaware of any valid
toxicity factor for BAP by the inhalation route. Moreover, EPA's own guidance on PAH risk
assessment states, "There is currently no inhalation unit risk for BAP that has been found
acceptable by the CRAVE. At this time, there is no basis for judgment that BAP or other PAHs
will be equipotent by oral and inhalation routes."96 Yet, despite this statement in its own
guidance document, EPA appears to have utilized the ingestion toxicity factor for BAP in
calculating the inhalation risk. As the Agency's own guidance states, there is simply no support
for the use of the ingestion factor in this route and the Agency should avoid an inhalation risk
until it develops an appropriate risk factor. (EEI, 00026)
Response: The Agency agrees with the commenter. The inhalation CSF for BaP has been
removed from IRIS and HEAST because it was determined that there were not sufficient existing
data to support this benchmark, and thus it was not in concordance with the Agency proposed
cancer guidelines.
Currently, no carcinogenicity assessment is available for BaP via inhalation exposure in IRIS97
and HEAST98. The single study available for inhalation exposure of animals to BaP provided
only questionable evidence of causality. In the study, hamsters exposed to BaP aerosols
developed tumors in the nasal cavity, larynx, and trachea, pharynx, esophagus, and forestomach
96 Provisional Guidance for Quantitative Risk Assessment of Polvcyclic Aromatic
Hydrocarbons. Docket No. PRLP-S0433, p.9.
97U.S. Environmental Protection Agency (EPA). 1997. Integrated risk information
system (IRIS). On-line database. Office of Research and Development (ORD). Cincinnati, OH.
98U.S. Environmental Protection Agency (EPA). 1995. Health Effects Assessment
Summary Tables (HEAST). Office of Research and Development. May. EPA 540/R-95-036.
June 29, 1998 111-54
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soil. EPA used a soil ingestion rate of 100 mg/day for both central tendency and high-end risk
estimates. This parameter should be represented by a distribution (or, at a minimum, a range)
where 100 mg/day falls at the upper end.
A more reasonable scenario accounts for the probability that individuals ingest soil in proportion
to the time spent at each location (i.e., away from home, indoors at home, outdoors at home).
While the concentration of waste-related contaminants in soil ingested while away from the
home should be zero, there is evidence to suggest that soil concentrations outside the home do
influence concentrations inside the home. Calabrese and Stanek have estimated that 313 percent
of indoor dust originates from outdoor soil102. Similarly, Chuang et al. have shown that indoor
dust concentrations are correlated to entryway soil (on inside doormat).103 Although the
percentage of indoor dust from outside sources is not specified, the concentration in indoor dust
was always less than the concentration in entryway soil. (API, 00046)
Response: The soil ingestion rate has been addressed in the uncertainty and variability analysis
conducted in support of the risk assessment for this rule. The distribution of values presented in
the 1997 Exposure Factors Handbook was used and a discussion of the data distribution and the
results are presented in the Supplemental Background Document for the NonGroundwater Risk
Assessment; Uncertainty Analysis.
Comment 8 : The assumptions used in determining the risk to home gardeners are not realistic
and overstate the risk to this subpopulation. First, EPA assumes that 38% of the U.S. population
have gardens. According to the National Gardening Association's 1994-95 survey, there are
three types of home gardens in the United States that are relevant for produce consumption in
this rulemaking: vegetable, fruit, and berry. Their survey indicates that the percentage of the
United States population having vegetable gardens is 3 1, fruit gardens is 14, and berry gardens is
These numbers should not be added to obtain a total percentage of gardens in the United States
for two reasons. Adding the numbers assumes that all home gardeners grow only one type of
produce which is clearly not the case. In addition, each of the garden types have different rates
of produce consumption by the home gardener) and by using an average value or a worst case
number would significantly overstate the amount of produce consumed by a home gardener.
102Calabrese and Stanek, 1992, "What Proportion of Household Dust Is Derived From
Outdoor Soir7 J. Soil Contam. l(3):253-263.
103Chuang et al., 1995, "Monitoring Methods For Polycyclic Aromatic Hydrocarbons And
Their Distribution In House Dust And Track-In Soil " Environ. Sci. Technol. 29:494-500,
U)4National Gardening Survey 1994-95 pp 36, 55, and 64 respectively.
June 29, 1998 111-56
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In Appendix F of RTI (1995) EPA presents its estimates for Bv, the ratio of chemical
concentration in dry weight of produce to concentration in air (mg/g dry weight/mg/g air). Some
of the values for Bv are calculated from Henry's constant and Kow using a relationship reported
by Bacci et al105. Others are apparently calculated from the data provided by Simonich and
Hites106. However, the equations and assumptions used to convert the vegetation-air partition
coefficients (Kv) given by Simonich and Hites (1994) to the uptake coefficient (Bv) used by
EPA are not given. Simonich and Hites (1994) give Kv values for various PAHs in terms of
concentration of PAH in vegetable lipids divided by concentration of PAH in air. To convert
from Kv to Bv (which uses concentration in vegetable dry weight), an assumption must be made
as to the average lipid content of above ground produce. EPA does not provide either the
calculation of Bv from Kv or the lipid content assumed for the calculations.(API, 00046)
Response: The issues concerning consumption rates were previously addressed in response to
comment 9, above. The air-to-plant biotransfer factors used for most constituents in this analysis
are measured values reported in Simonich and Hites (1994). The remaining BCFvs are estimated
from the Kow using the Bacci equation. This may tend to over-estimate the bioaccumulation of
constituents with very large Kows such as PAHs. In an effort to make this estimate agree more
closely to real world values for very hydrophobic compounds without measured BCFV values the
BCFV estimated using the Bacci equation was reduced by a factor of 40. This approach was
presented in the Addendum to Methodology for Assessing Health Risks Associated with Indirect
Exposure to Combustor Emissions (EPA/600/AP-93/003, page 5-9). No additional data are
available for reducing the uncertainty associated with these factors.
Comment 11 : EPA over estimated the risk due to the consumption of root vegetables because
Briggs et al.'s experiments used to derive the empirical equation used to estimate the
concentration of organic compounds in root vegetables used barley plants. The concentrations
measured for hydrophobic compounds in barley roots will be higher than concentrations
expected for bulkier root vegetables such as carrots or potatoes. EPA (1993, Addendum, p. 5-3)
suggested an empirical reduction factor to account for the lower surface area to volume ratio for
edible root vegetables compared with barley. A factor of 0.01 was recommended based on the
ratio for carrots. This factor should be incorporated into the calculation of Br for the PAHs,
which are also highly lipophilic. Estimates of risk from consumption of root vegetables will, by
including this factor, be reduced 100-fold. (API, 00046)
105Bioconcentration Of Organic Chemical Vapors In Plant Leaves: Experimental
Measurements And Correlation, Environ. Sci. Technol. 24(6):885-889. 1990.
106Simonich and Hites, 1994, "Vegetation-Atmosphere Partitioning Of Polycyclic
Aromatic Hydrocarbons." Environ. Sci. Technol. 28:939-943.
June 29, 1998 111-58
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N. INFILTRATION RATES
Comment 1: EPA's EPACMTP -simulated groundwater exposure concentrations for the onsite
landfill hydrorefining and hydrotreating catalyst scenarios are too high because an overly
conservative infiltration rate was employed.
EPA uses a 50th percentile value of 5.3xlO"7 cm/s (0.168 m/yr.) for the infiltration rate in the two
parameter high-end analysis. In simple terms, the Agency is assuming the median Subtitle D
landfill is built on a typical clay soil and the clay is always 100% water saturated (i.e., a unit
gradient assumption). This is similar to saying that the median landfill has the same performance
characteristics as an operating surface impoundment with a liner that has a saturated hydraulic
conductivity 5.3xlO"7 cm/s. However, in reality, the median value used by EPA resembles the
worst case that could be expected at a landfill. Assuming saturated conditions is overly
conservative and ignores the fact that most landfills by design have covers to divert precipitation.
EPA provides no justification for the assumptions it used to calculate the infiltration rate used in
this rule. In the EPACMTP model, infiltration rate is the net rate of downward water flow
through the unsaturated zone to the water table. EPA developed infiltration rates for EPACMTP
using its HELP model (Hydrologic Evaluation model for Landfill Performance). EPA's
conceptual model for applying HELP to the refinery residual listing rule is (1) Subtitle D
industrial landfills are located on soils that can be described as either sandy loam, silty loam and
silty clay loam, to represent coarse, medium and fine textured soil and (2) coarse, medium and
fine grained soil represent 15.4 percent, 56.6 percent and 28.0 percent, respectively, of the soils
that have mapped around the country (based on the Soil Conservation Service database). EPA
provides no technical basis for the assumption that the distribution of soil types used by HELP to
generate infiltration rates for the EPACMTP model is representative of Subtitle D industrial
landfills in operation today. The conceptual model also assumes that the vegetative cover
resembles a 'fair' grass and the cover has a 2 percent top slope. However, none of the
background documents provide any justification for these assumptions as they relate to the
landfills used to manage refinery residuals.
EPA also should provide justification as to why RCRA §3007 survey data was not considered in
determining the infiltration rate. The §3007 survey requested information about landfill cover
design and composition, vegetation growing on the unit, landfill liners and their design and
composition (including hydraulic conductivity) and unsaturated zone soil type. This information
could be used to develop an infiltration rate appropriate for current refineries and the offsite
landfills that they use, as opposed to the HELP-generated nationwide mean rate that the Agency
chose to use.
To understand the effect of using more reasonable infiltration rates on groundwater exposure
concentrations, API modeled EPA's two parameter, high-end analysis (no biodegradation) with
infiltration/recharge rates of 10-8 and 10-9 cm/s. The results are presented in Table 21,
"Comparison of impact of infiltration rates on refinery residual results" in Attachment 27 of the
June 29, 1998 111-60
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benzene, those equations are readily available in EPA's own CERCLA risk assessment guidance
and in the published literature. (EOF, 00036)
Response: EPA has considered non-ingestion risks from exposure to groundwater in response to
this comment, as described in the April 8, 1997 NODA's direct and indirect risk assessment
background documents
Comment 3: As a legal matter, the failure to consider important and documented groundwater
risks violates the RCRA mandate to protect human health, and the mandate in Section 3-30 l(b)
of Executive Order 12898 to identify multiple and cumulative exposures. (EDF, 00036)
Response: EPA has considered non-ingestion risks from exposure to groundwater in response to
this comment, as described in the April 8, 1997 NODA's direct and indirect risk assessment
background documents.
June 29, 1998 111-62
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been an oversight. Regardless, EPA believes that the 90th percentile value is more appropriate to
use in the type of high end sensitivity analysis performed for this rulemaking, and that the 95th%
value would be unreasonably conservative.
Comment 2: The 102 meter value is inconsistent with the comparable value used for the non-
groundwater risk assessment. EPA assumed the distance to the nearest residence is 75 meters at
the high-end and 305 meters at the 50 percent value in the non-groundwater risk assessment.
This discrepancy between the distance values in the two risk assessments is never addressed or
justified. (EOF, 00036)
Response: EPA disagrees that the distances must be equivalent, because different pathways are
represented in each assessment. Exposure from groundwater pathways occurs through drinking
water wells, and exposure from nongroundwater pathways occurs through multiple mechanisms,
such as runoff and air releases. Therefore, EPA used different data sets to estimate receptor
distances for these pathways to account for well locations for groundwater and residences for the
nongroundwater pathways. For distances to residences in the nongroundwater pathways EPA
used information compiled for Treatment Storage and Disposal Facilities (National Survey of
Hazardous Waste Generators and Treatment, Storage, Disposal, and Recycling Facilities in 1986:
Hazardous Waste Management in RCRA TSDR Units, July 1991).
The commenter correctly states, that different receptor distance values are used for each of the
ground water and non-ground water pathways; EPA believes that such use is appropriate.
Specifically, the non-groundwater assessment used a high end (10th percentile) receptor distance
of 75 meters and a central tendency (50th percentile) distance of 305 meters. See U.S. EPA,
Assessment of Risks from the Management of Petroleum Refining Wastes: Background
Document, August 1995. In contrast, the groundwater assessment used a high end (90th
percentile) distance of 102 meters and a central tendency (50th percentile) distance of 430
meters. See U.S. EPA, Petroleum Refining Waste Listing Determination: Background Document
for Ground-water Pathway Analysis, August 1995.
EPA justifies this difference based on the type of pathways used in each assessment. Exposure
from groundwater pathways occurs, for almost all waste streams evaluated, through the
consumption of groundwater downgradient of a landfill (other assessments included surface
impoundments and land treatment units). To estimate receptor distances, EPA used data
characterizing the distances of wells from landfills based on a previous OSW survey. See the
March 1997 Supplemental Background Document for Groundwater Pathway Analysis.
(Additional discussion concerning the distance to wells is found in Section I. A.6 of the NODA
response to comments). Conversely, exposure from non-groundwater pathways occurs through
multiple mechanisms (e.g., runoff, air releases) originating from a land treatment unit.
Therefore, EPA used a different data set to estimate receptor distances for these pathways. EPA
used data characterizing the distance from land treatment unit to surface water bodies, and also
used these same values as the distances from the land treatment unit to gardens and other
receptor locations. See U.S. EPA, Assessment of Risks from the Management of Petroleum
June 29, 1998 111-64
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to overestimate risks in all affected wells by not considering other well locations. Therefore,
EPA does not agree with the commenter, and believes that the approaches used by the Agency in
the revised risk analysis fully considered well placement.
Comment 5: The distance of 75 meters to a receptor well in the groundwater pathway may be
unreasonably conservative. Landfills that accept industrial wastes are generally larger landfills
that have large buffer zones around them. (EEI, 00026)
Response: The commenter incorrectly states that 75 meters was used as the receptor distance for
the ground water pathway (instead, 75 meters was the high end distance for non-ground water
pathways). EPA calculated the 90th percentile distance of receptor well locations from landfills
to be 102 meters, based on the results of an OSW survey of the distances of wells to municipal
waste landfills. See U.S. EPA, Health Risk Assessment: Background Document for the Dyes and
Pigments Manufacturing Industry, November 28, 1994. EPA acknowledges that it has no data
characterizing receptor well distances from industrial landfills. In the absence of such
information, EPA is using the data cited.
Comment 6 There is ample evidence in the RCRA §3007 Petroleum Refinery database that
land treatment units average more than one mile from the nearest residence. (See submitted data)
(Exxon, 00035)
Response: Because of the lack of completeness of the reported well distances in the
Questionnaire, the Agency decided to use well distances from the Subtitle D Survey Database
The Questionnaire response was incomplete and inadequate Of the 172 RCRA §3007
questionnaires returned, 27 facilities reported the presence of nonhazardous on-site landfills used
for the disposal of any waste in the survey in any year. Of these 27, EPA found that only 15
reported the distance to the nearest drinking water well with any reliable documentation (e.g.,
well location maps, groundwater flow gradients, company survey of nearby wells) (Additional
Listing Support Analyses for the Petroleum Refining Listing Determination, 1998). This limited
data set is not surprising given the problems associated with seeking information from the
refineries that is not related to on-site operations. Furthermore, wells may be placed closer to the
on-site landfills in the future. Therefore EPA relied on distances obtained from the OSW
database as more representative of potential well locations. EPA notes that the Questionnaire
only provides well location information for evaluating on-site landfills, and even if used, would
not have impacted the modeling results for off-site landfills. Because the risks from off-site
landfills were higher or comparable to risks calculated for on-site landfills, any change in the
results for on-site landfills is unlikely to alter any decisions to list wastes.
R. ADDITIVE RISKS ACROSS PATHWAYS
Comment 1: Despite clear Agency listing policy that the risks posed through different pathways
should be summed when the potential for simultaneous exposure exists, the Agency did not
follow that policy in this rulemaking. EPA did not sum these risks because it was assumed the
June 29, 1998 111-66
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for arsenic is orders of magnitude less protective than the comparable cancer risks from other
HBNs. (EOF, 00036)
Response: MCLs were not used in the groundwater pathway risk assessment.
June 29, 1998 HI-68
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