[Federal Register Volume 66, Number 246 (Friday, December 21, 2001)]
[Notices]
[Pages 66228-66235]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 01-31342]



[[Page 66227]]

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Part IV





Environmental Protection Agency





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Standards for the Use or Disposal of Sewage Sludge; Notice

  Federal Register / Vol. 66, No. 246 / Friday, December 21, 2001 / 
Notices  

[[Page 66228]]


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ENVIRONMENTAL PROTECTION AGENCY

[FRL-7120-5]


Standards for the Use or Disposal of Sewage Sludge

AGENCY: Environmental Protection Agency.

ACTION: Notice.

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SUMMARY: The Environmental Protection Agency (EPA) is giving final 
notice of its determination that numeric standards or management 
practices are not warranted for dioxin and dioxin-like compounds in 
sewage sludge that is disposed of at a surface disposal site or 
incinerated in a sewage sludge incinerator. In December 1999, EPA 
proposed to amend the Standards for the Use or Disposal of Sewage 
Sludge to limit dioxin and dioxin-like compounds in sewage sludge that 
is applied to the land. In that proposal, EPA also stated that the 
Agency was not proposing amendments to add numeric standards or 
management practice requirements for dioxins in sewage sludge that is 
placed in a surface disposal unit or incinerated in a sewage sludge 
incinerator. Final action on the proposal to amend the Standards for 
the Use or Disposal of Sewage Sludge for sewage sludge which is applied 
to the land will be published separately at a later date.

FOR FURTHER INFORMATION CONTACT: Arleen Plunkett, U.S. Environmental 
Protection Agency, Office of Water, Health and Ecological Criteria 
Division (4304), 1200 Pennsylvania Avenue, N.W., Washington, DC 20460. 
(202) 260-3418. [email protected].

SUPPLEMENTARY INFORMATION:

I. Affected Entities
II. Docket Information
III. Historical and Legal Background
IV. What Did EPA Propose for Dioxins in Sewage Sludge?
V. What Final Action is EPA Taking Today?
VI. Risk Assessment Methodologies and Results
    A. Approach and Assumptions in EPA's Risk Assessments for 
Exposure to Dioxins Resulting from Surface Disposal and Incineration
    B. Description of Surface Disposal Risk Assessment
    1. Overview of Risk Assessment Methodology for Surface Disposal
    2. Key Assumptions for the Surface Disposal Risk Assessment
    3. Surface Disposal Risk Characterization
    C. Description of Incineration Risk Assessment
    1. Overview of Risk Assessment Methodology for Incineration
    2. Key Assumptions for the Incineration Risk Assessment
    3. Incineration Risk Characterization
VII. Summary of Public Comments and EPA Responses
    A. Major Comments Applicable to Both Surface Disposal and 
Incineration
    B. Major Comments on Surface Disposal
    C. Major Comments on Incineration
VIII. List of References

I. Affected Entities

    Entities typically regulated by Standards for the Use or Disposal 
of Sewage Sludge are those that prepare sewage sludge and/or use or 
dispose of the sewage sludge through application to the land, placement 
in a surface disposal unit, or incineration in a sewage sludge 
incinerator. Categories and entities affected by today's action 
include:

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              Category                  Examples of affected entities
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State/Local/Tribal Government......  Publicly-owned treatment works and
                                      other treatment works that treat
                                      domestic sewage, that prepare
                                      sewage sludge and/or dispose of
                                      sewage sludge by placement in a
                                      surface disposal unit or
                                      incineration in a sewage sludge
                                      incinerator.
Federal Government.................  Federal Agencies with treatment
                                      works that treat domestic sewage,
                                      that prepare sewage sludge and/or
                                      dispose of sewage sludge by
                                      placement in a surface disposal
                                      unit or incineration in a sewage
                                      sludge incinerator.
Industry...........................  Privately-owned treatment works
                                      that treat domestic sewage, and
                                      persons who receive sewage sludge
                                      and change the quality of the
                                      sewage sludge before it is
                                      disposed in a surface disposal
                                      unit or incinerated in a sewage
                                      sludge incinerator.
------------------------------------------------------------------------
This table is not intended to be exhaustive, but rather provides a guide
  for readers regarding entities affected by today's Notice pertaining
  to Standards for the Use or Disposal of Sewage Sludge.

II. Docket Information

    The record for this Notice has been established under docket number 
W-99-18 and includes supporting documentation as well as the printed 
paper versions of electronic materials. The record is available for 
inspection from 9 a.m. to 4 p.m. Eastern Standard or Daylight time, 
Monday through Friday, excluding legal holidays, at the Water Docket, 
Room EB 57, USEPA Headquarters, 401 M Street, SW., Washington, DC 
20460. For access to the docket materials, please call 202-260-3027 to 
schedule an appointment.
    For information on the existing rule in 40 CFR part 503, you may 
obtain a copy of A Plain English Guide to the EPA Part 503 Biosolids 
Rule on the Internet at http://www.epa.gov/owm/bio.htm or request the 
document (EPA publication number EPA/832/R-93/003) from: Municipal 
Technology Branch, Office of Wastewater Management (4204), Office of 
Water, U.S. Environmental Protection Agency, 1200 Pennsylvania Avenue, 
NW., Washington, DC 20460-0001.

III. Historical and Legal Background

    EPA promulgated Standards for the Use or Disposal of Sewage Sludge 
(40 CFR part 503) under section 405(d) and (e) of the Clean Water Act 
(CWA), 33 U.S.C. 1345(d), (e), as amended by the Water Quality Act of 
1987. In these amendments to section 405 of the CWA, Congress, for the 
first time, set forth a comprehensive program for reducing the 
potential environmental risks and maximizing the beneficial use of 
sewage sludge. As amended, section 405(d) of the CWA requires EPA to 
establish numeric limits and management practices that protect public 
health and the environment from the reasonably anticipated adverse 
effects of toxic pollutants in sewage sludge. Section 405(e) prohibits 
any person from disposing of sewage sludge from a publicly owned 
treatment works (POTW) or other treatment works treating domestic 
sewage through any use or disposal practice for which regulations have 
been established pursuant to section 405 except in compliance with the 
section 405 regulations.
    Amended section 405(d) also established a timetable for the 
development of the sewage sludge use or disposal regulations. H. Rep. 
No. 1004, 99th Cong. 2d. Sess. 158 (1986). Section 405(d) calls for two 
rounds of sewage sludge regulations. In the first

[[Page 66229]]

round, EPA was to establish numeric limits and management practices for 
those toxic pollutants which, based on ``available information on their 
toxicity, persistence, concentration, mobility, or potential for 
exposure may be present in sewage sludge in concentrations which may 
adversely affect public health or the environment.'' CWA section 
405(d)(2)(A). The second round was to address toxic pollutants not 
regulated in the first round ``which may adversely affect public health 
or the environment.'' CWA section 405(d)(2)(B).
    EPA did not meet the timetable in section 405(d) for promulgating 
the first round of regulations, and a citizen's suit was filed to 
require EPA to fulfill this mandate. (Gearhart v. Whitman, Civ. No. 89-
6266-HO (D. Ore.)). In accordance with the consent decree entered by 
the court in this case, EPA promulgated the first round of sewage 
sludge regulations in 1993, 40 CFR part 503. 58 FR 9248 (Feb. 19, 1993) 
(``Round One''). The consent decree also established a schedule for EPA 
to identify additional toxic pollutants in sewage sludge and completing 
the second round of regulation under section 405(d)(2)(B) (``Round 
Two''). In May 1993, EPA identified 31 pollutants not regulated in 
Round One that EPA was considering for regulation. In November 1995, 
EPA notified the court that it was revising the original list of 31 
pollutants and considering two pollutant groups for the second round 
rulemaking: polychlorinated dibenzo-p-dioxins/dibenzofurans (PCDDs/Fs) 
and dioxin-like coplanar polychlorinated biphenyls (PCBs) (USEPA, 
1996a). The consent decree required the Administrator to sign a notice 
for publication proposing Round Two regulations no later than December 
15, 1999, and to sign a notice taking final action on the proposal no 
later than December 15, 2001.
    On December 15, 1999, the Administrator signed a proposal to 
establish numerical limits for dioxins in sewage sludge that is applied 
to the land and proposed not to regulate dioxins in sewage sludge that 
is disposed of in a surface disposal unit or fired in a sewage sludge 
incinerator. 64 FR 72045 (Dec. 23, 1999).

IV. What Did EPA Propose for Dioxins in Sewage Sludge?

    EPA proposed a numeric standard for ``dioxins'' in sewage sludge 
that is land applied, measured as toxic equivalents (TEQs), and related 
monitoring, recordkeeping and reporting requirements. EPA proposed a 
definition of ``dioxins'' to mean 29 specific congeners of 
polychlorinated dibenzo-p-dioxins, polychlorinated dibenzofurans, and 
coplanar PCBs that have been found in sewage sludge. The proposed 
definition of ``dioxins'' specifies seven 2,3,7,8,-substituted 
congeners of polychlorinated dibenzo-p-dioxins (PCDDs), ten 2,3,7,8-
substituted congeners of polychlorinated dibenzofurans (PCDFs), and 
twelve coplanar PCB congeners. See 64 FR 72048-72051 for a full 
discussion of proposed requirements for land application.
    EPA also assessed the risk of exposure to dioxins in sewage sludge 
that is disposed of by placement in a surface disposal unit or 
incinerated in a sewage sludge incinerator. EPA concluded that no 
numerical limits on dioxins or additional management practices are 
needed for sludge disposed of in either of these manners; i.e., that 
existing regulation of surface disposal and sewage sludge incinerators 
is adequate to protect public health and the environment from any 
reasonably anticipated adverse effects of dioxins. Therefore EPA did 
not propose any regulatory changes to 40 CFR part 503, subparts C and 
E.

V. What Final Action Is EPA Taking Today?

    EPA is providing final notice of its decision not to regulate 
dioxins in sewage sludge that is placed in a surface disposal unit or 
fired in a sewage sludge incinerator. As explained below in sections 
VI.B. and C., EPA has determined that no further regulation of sewage 
sludge that is placed in a surface disposal unit or incinerated in a 
sewage sludge incinerator is needed to protect public health and the 
environment from any reasonably anticipated adverse effects of dioxins. 
Therefore, no additional numeric limit, operational standard, or 
monitoring requirements are currently being established.
    EPA will address at a later time the proposed provisions related to 
dioxin and dioxin-like compounds in sewage sludge that is land applied.

VI. Risk Assessment Methodologies and Results

A. Approach and Assumptions in EPA's Risk Assessments for Exposure to 
Dioxins Resulting From Surface Disposal and Incineration

    As we explained in the proposal, EPA conducted separate risk 
assessments for surface disposal of sewage sludge and incineration of 
sewage sludge in a sewage sludge incinerator. (64 FR 72051-72055). The 
four steps of the risk assessment process include hazard 
identification, dose-response assessment, exposure assessment, and risk 
characterization. Both risk assessments used similar hazard 
identification and dose-response data and assumptions. However, the 
risk assessments examined different exposure pathways and have 
different risk characterizations. The following presents an overview of 
the approaches used for these risk analyses.
    Today's final action is based on assessments of the risks to human 
health posed by dioxins that are in surface-disposed sewage sludge or 
sewage sludge incinerator emissions.\1\ The hazard identified for these 
risk assessments is cancer as a human health endpoint from the 
compounds assessed. We took into account the impacts on human cancer 
risk nationwide. We examined the cancer risk of 2,3,7,8-TCDD and 
estimated several dose-response relationships for this congener (USEPA, 
1994). The cancer risk of the other congeners included in the risk 
assessment are expressed in relation to the cancer risk of 2,3,7,8-TCDD 
(USEPA, 1994).
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    \1\ Of the approximately 6.9 million dry metric tons produced 
annually in the United States, we estimate that less than two 
percent is placed in sewage sludge-only surface disposal units, and 
19 percent is fired in sewage sludge incinerators (Bastian, 1997).
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    The risk assessments for the proposal evaluated cancer as the human 
health risk using the 1985 cancer slope factor for dioxin (USEPA, 
1994). Because the Agency's Dioxin Reassessment has not yet been 
finalized, the final determination for surface disposal and 
incineration continues to be based on evaluation of cancer risk 
applying the 1985 cancer slope factor. Our conclusions on the 
protection of human health that support this no action decision would 
be the same even if we considered the 2000 Draft Dioxin Reassessment 
(USEPA, 2000a), since use of the pertinent information from the Draft 
Reassessment would increase the risks only slightly.
    Regarding exposure pathways, our evaluation of surface disposal of 
sewage sludge considered the human health risks associated with 
drinking ground water contaminated by dioxins and breathing air 
containing volatilized dioxins. For incineration in a sewage sludge 
incinerator, we evaluated human exposure to dioxins directly through 
inhalation of gases and particles in the emissions from sewage sludge 
incinerators, and indirectly by consumption of crops and animal 
products produced on agricultural lands and home gardens affected by 
the

[[Page 66230]]

deposition of particles from sewage sludge incinerator emissions.
    You will find below descriptions of routes of exposure (called the 
exposure pathways) through surface disposal and incineration of sewage 
sludge that we assessed. We then calculated risks associated with these 
pathways by comparing exposures with dose-response information for the 
pollutants.

B. Description of Surface Disposal Risk Assessment

    We performed an exposure assessment in order to estimate the risk 
to humans from surface disposal of sewage sludge containing dioxins. In 
this exposure assessment we identified the population that may be 
exposed, determined the routes through which exposure to dioxins may 
occur, and estimated the magnitude, duration, and timing of dioxin 
doses that people may receive. This procedure resulted in a 
distribution of predicted individual exposures. We used this 
distribution of individual exposures to determine the types of 
individuals who may be at highest risk as well as those with average 
(``central tendency'') risks. High-end assumptions are intended to 
estimate risks that are expected to occur in small but definable ``high 
end'' portions of the subject population. This means that exposure is 
above the 90th percentile exposure in a population, but not higher than 
the individual in the population who has the highest exposure. To 
estimate high-end risk, we used some high-end parameters and some 
central tendency parameters. The central estimate of individual 
exposure was based on either the arithmetic mean or the median 
exposure. In addition to individual descriptors, we also estimated 
population risk to obtain an estimate of the number of health effects 
that might be expected in the population over a specific time period.
1. Overview of Risk Assessment Methodology for Surface Disposal
    This risk assessment methodology focused on the last two steps of 
the risk assessment process, exposure assessment and risk 
characterization. The hazard identification and dose-response 
assessment portions of the risk assessment were taken from the External 
Review Draft Dioxin Reassessment Document (USEPA, 1994).
    The purpose of this analysis was to estimate the total 
concentration of dioxins, furans, and coplanar PCBs that can be present 
in sewage sludge and still be protective of human health when sewage 
sludge is managed by surface disposal in monofills (i.e., sludge-only 
landfills) or surface impoundments. In order to assess the potential 
exposures from dioxins in sewage sludge placed in a surface disposal 
unit, we characterized the management practices associated with surface 
disposal facilities. This included ascertaining the environmental 
settings where surface disposal of sewage sludge may occur and 
identifying scenarios under which contaminants in sewage sludge may be 
transported through the environment to a human receptor.
    We considered two possible exposure pathways: volatilization of 
dioxins from the surface disposal facility with subsequent inhalation 
of these pollutants and the leaching of dioxins to groundwater with 
subsequent consumption of this groundwater. Based on the general 
requirements and management practices for surface disposal under 
subpart C of the 40 CFR part 503 standards and the fact that dioxin 
congeners have an extremely low water solubility, we concluded that 
there is an insignificant chance that dioxins would be released to 
groundwater or surface water even during extreme wet weather 
conditions. Part 503, subpart C includes management practices designed 
to prevent groundwater and surface water contamination. For example, 40 
CFR 503.24(d) prohibits the siting of an active sewage sludge surface 
disposal unit within 60 meters of an active seismic fault to prevent or 
significantly mitigate contamination of groundwater as a result of 
seismic events. These management practices also include requirements 
that prevent or significantly mitigate contamination of surface water. 
40 CFR 503.24(b), (g). These requirements specify that an active sewage 
sludge surface disposal unit shall not restrict the flow of a base 
flood; runoff from an active sewage sludge unit shall be collected and 
disposed under applicable requirements; and the runoff collection 
system employed for the active sewage sludge unit shall have the 
capacity to handle runoff from a 24 hour, 25 year storm event. These 
requirements in part 503, subpart C for surface disposal units, 
therefore, serve to either prevent or significantly mitigate dioxin 
transport to and subsequent contamination of groundwater and surface 
waters.
2. Key Assumptions for the Surface Disposal Risk Assessment
    There are two principal configurations used for surface disposal 
today (USEPA, 1990). We considered each to determine which had the 
highest potential for dioxin exposure to the modeled population. We 
then modeled the worse case (USEPA, 1999a).
    The first surface disposal configuration that we considered is a 
monofill that is an unlined, sewage sludge-only trench fill receiving 
dewatered sludge with a solids content greater than 20%. Operating 
procedures for monofills established in 40 CFR 503.25 require vector 
control, which may include application of daily cover, and Sec. 503.22 
requires a written closure and post closure plan, including final cover 
provisions.
    The second surface disposal configuration that we considered is a 
surface impoundment for which we assumed a continuous inflow of sewage 
sludge with a solids content of between 2% and 5%. For surface 
impoundments, a vertical outflow pipe maintained the surface liquid 
level at a constant height, and liquid was assumed to leave the 
impoundment both in the outflow (possibly for return to the treatment 
works) and in seepage through the floor of the impoundment. Over time, 
particulate settling would occur and a denser layer of solids 
accumulated on the floor of the impoundment. Eventually, this layer of 
solids reached the top of the impoundment and no further inflow was 
possible.
    In order to assess the maximum level of risk for the surface 
disposal, surface impoundments were the modeled configuration. Surface 
impoundments are considered to be the worse of the two cases for dioxin 
transport and subsequent human exposure for the following reasons. With 
respect to exposure from volatilized dioxins, we assumed that, unlike 
monofills, there was no daily cover applied to the surface impoundment 
to reduce volatilization of dioxins to the ambient air. However, upon 
closure, we assumed that the surface impoundment was covered under the 
applicable requirements of part 503, subpart C. Pollutants, including 
dioxins, also can more readily leach to groundwater from surface 
impoundments than from monofills. This results from a greater hydraulic 
head in surface impoundments to transfer pollutants through the bottom 
of the unit.
    Our exposure evaluation and risk assessment for surface 
impoundments (USEPA, 1999a) concluded that there is an insufficient 
flux of dioxins to ambient air from volatilization and to groundwater 
from leaching to result in a significant risk to exposed individuals. 
Therefore, placement of sewage sludge in a monofill also was determined 
not to result in a significant risk from dioxins to exposed 
individuals.

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    The following were the major assumptions used in the surface 
disposal risk assessment:

--Pollutant mass was assumed to enter the surface impoundment through 
continuous inflow of sewage sludge and leave through four loss 
processes: degradation within the impoundment; seepage through the 
floor; liquid overflow to a treatment facility; and volatilization.
--Rates of pollutant loss (including volatilization) were assumed to be 
``first-order'' (i.e., the higher the concentration of the pollutant, 
the greater the rate of loss).
--Pollutants were assumed to be either attached to the surface of the 
sludge particles or dissolved in the surrounding water and to be at 
equilibrium (i.e., in a state of balance between the liquid and solid 
phases).
--Rates of pollutant transfer and loss when the impoundment is half-
filled with solids were assumed to be typical of the surface 
impoundment both before and after it fills with sewage sludge.
3. Surface Disposal Risk Characterization
    We found that the risks to human health from the surface disposal 
of sewage sludge to be extremely small. The incremental cancer risk to 
a highly exposed individual (i.e., ``high end'' risk) did not exceed 
3.5 in ten million (3.5  x  10-7) for either exposure 
pathway (USEPA, 1999a). Dioxins have extremely low volatility and would 
not be expected to offer significant exposure through inhalation. Also, 
dioxins do not dissolve readily in water. Even in the absence of a 
liner, combined with high porosity soil and a short distance to ground 
waters, only insignificant amounts of dioxins could ever reach the 
groundwater. For these reasons, we conclude that no action to regulate 
dioxins for sewage sludge surface disposal is necessary.
    The surface disposal risk assessment supporting the proposal for no 
action did not explicitly consider cancer risks based on infant or 
childhood exposures. Based on the overall low cancer risk estimated for 
surface disposal of sewage sludge in that risk assessment which 
supports this final action, EPA has concluded that the cancer risk to 
infants and children due to exposure to dioxins from surface-disposed 
sewage sludge is not expected to be significant.
    The surface disposal risk assessment also did not explicitly 
consider ecological risks. Surface disposal units are sited, designed, 
operated, and maintained to contain and isolate sewage sludge in order 
to minimize or eliminate exposure to humans and other organisms. The 
human health risk assessment that was performed for surface disposal 
units identified only two relevant exposure pathways for receptor 
populations: volatilization of dioxins to the atmosphere and leaching 
to groundwater. The summed exposures and subsequent incremental cancer 
risk estimated for dioxins from these two pathways to the modeled 
highly exposed human populations were very low (i.e., 3.5  x  
10-7). As already noted, dioxins have low volatility which 
results in insignificant volatilization. Dioxins also are extremely 
hydrophobic (i.e., do not readily dissolve in water), which likewise 
results in minimal leaching to groundwater and subsequent transport to 
surface waters to impact aquatic organisms. Based on the properties of 
dioxins and the design and operational characteristics of the disposal 
units, only an insignificant quantity of dioxins could move to the 
surrounding media to expose humans and other species. In addition 
dioxins exhibit similar mechanisms of toxicity across vertebrate 
species, including humans (USEPA 2000a). Therefore, while ecological 
impacts could not be predicted, we assumed that the results of the 
sewage sludge risk assessments that protect humans are also generally 
protective for ecological species.
    In sum, EPA concluded that existing regulations are adequate to 
protect public health and the environment from the reasonably 
anticipated adverse effects of dioxins in sewage sludge that is 
surface-disposed.

C. Description of Incineration Risk Assessment

    We used four steps to estimate risks from firing sewage sludge in 
sewage sludge incinerators (USEPA, 2000b). First, we estimated the rate 
at which pollutants are emitted from incinerator stacks. Next, we 
estimated the movement of pollutants in air near incinerators, 
including estimates of how much pollutant plumes overlap. We then 
overlaid maps of expected ground-level concentrations of pollutants and 
human populations. Finally, we determined the extent and nature of 
resulting health risks of human exposure to emitted dioxins.
    The last step was accomplished by performing a multi-pathway risk 
assessment for exposure to dioxins that result from the firing of 
sewage sludge in a sewage sludge incinerator. The risk assessment 
estimated hypothetical average and high end risks to the highly-exposed 
sub-populations of farmers and home gardeners. We evaluated the risk to 
the hypothetical highly-exposed individual who is exposed by both a 
direct route (e.g., inhalation) and indirect routes (e.g., eating 
contaminated food). In addition, we conducted a probabilistic analysis 
to estimate the range of risks for home gardeners and farmers impacted 
by the modeled facilities and to quantify the uncertainty associated 
with these estimates.
    In response to peer review comments, EPA corrected an emission rate 
for one sewage sludge incinerator and recalculated risks. We also 
combined the risk assessment and the risk characterization into a 
single document (USEPA, 2000b). Finally, we clarified the discussion 
and explanation of the multi-pathway exposure and risk model that was 
used in this risk assessment.
    We considered multiple hearth units without afterburners to be the 
worst case technology for sewage sludge incineration and likely the 
highest emitters of dioxins and coplanar PCBs. The analysis focused on 
the six highest emitting incinerators for dioxins/dibenzofurans and 
coplanar PCBs from an initial screening of 135 incinerators so as to 
provide a high end to a bounding estimate of the risk from sewage 
sludge incineration.
1. Overview of Risk Assessment Methodology for Incineration
    The assessment considered 15 exposure pathways. We evaluated those 
pathways expected to result in the highest risk estimates for which 
data were available. We selected two exposure scenarios to represent 
highly-exposed sub-populations that reside near sewage sludge 
incinerators: (1) Beef and dairy farmers consuming home produced meat, 
dairy and crops and, at recreational fisher levels, fish caught near 
sewage sludge incinerators; and (2) home gardeners consuming home-grown 
produce grown near a sewage sludge incinerator as a portion of their 
diet. For both scenarios, we estimated average and high end exposures 
for children and adults at locations where they are expected to reside. 
We used a geographical information system to identify land uses and 
terrain around facilities, to identify watershed and water body 
parameters for estimating fish and drinking water ingestion risks, and 
to provide census information about farmers and residents exposed to 
incinerator emissions. We estimated the numbers of individuals exposed 
and the associated risks for six population age groups.

[[Page 66232]]

2. Key Assumptions for the Incineration Risk Assessment
    Many important factors in estimating exposure vary from facility to 
facility. As a result, the highest emitting facility will not always 
produce the highest risk. We therefore selected the six highest 
emitting incinerators that also resulted in the highest potential 
inhalation exposures from the initial screening assessment of 135 
incinerators. The variables that are important for exposure assessment 
and considered in the screen include, for example, distance to exposed 
population, activities of the exposed population, effective release 
height of pollutants, and meteorological conditions. We also considered 
emission rates, emission release characteristics, and actual 
populations near the facilities in the initial screening assessment.
    To address high end risk, plausible ranges of values for key 
exposure and model variables were modeled using Monte Carlo procedures. 
This analysis estimated the range of possible risk values and their 
probability of occurring. The variables considered for the Monte Carlo 
modeling were identified by sensitivity analyses. The variables were 
exposure duration, beef and dairy consumption, beef and dairy 
biotransfer factors, air to plant transfer, dry sludge throughput, 
adult inhalation rate, and fraction of time an adult is indoors and 
outdoors.
    The large number of exposure values used in the risk assessment are 
shown in appendix B of the Technical Support Document for incineration 
(USEPA, 2000b). Unless otherwise noted in the Technical Support 
Document, the source of the exposure values used in the incineration 
risk assessment is the EPA Exposure Factors Handbook (USEPA, 1997). The 
following is a summary of a few key values:
     Adult body weight is 71.8 kilograms (kg).
     Body weight of a 3-5 year old is 17.5 kg.
     Exposure duration for the farmer is 17.3 years.
     Exposure duration for the home gardener is 12 years.
     Adult inhalation rate is 13.3 cubic meters each day.
     Child 3-5 years old inhalation rate is 8.3 cubic meters 
each day.
     Child daily soil ingestion rate is 0.1 grams each day.
     Adult daily soil ingestion rate is 0.05 grams each day.
     Adult daily fish ingestion rate is 0.162 grams per kg. 
body weight per day.
    For the farmer exposure pathway, we evaluated the inhalation of 
vapor and particle-bound pollutants released from the incinerator 
stack(s), soil ingestion, ingestion of homegrown fruits and vegetables, 
ingestion of home-produced beef and dairy products, ingestion of 
drinking water from nearby surface water bodies, and ingestion of fish 
at recreational fisher levels from those water bodies. The home 
gardener pathway included inhalation of vapor and particle-bound 
pollutants, soil ingestion, ingestion of homegrown fruits and 
vegetables, and ingestion of drinking water from surface water bodies. 
For infants in both home gardener and farm families, breast milk 
ingestion from an exposed mother also is included. Dermal exposure to 
soil and water, and consumption of other animal products were not 
quantified since exposures from these pathways are expected to be 
significantly less than the pathways evaluated.
    Cancer risks due to infant and childhood exposures were calculated 
as a part of the multi-pathway sewage sludge incineration risk 
assessment. Risks were estimated for infants and children aged: less 
than one year, 1-2 years, 3-5 years, 6-11 years, and 12-17 years for 
both the home gardener and the farmer/recreational fisher exposure 
scenarios. The infant age group also included exposure via breast milk 
ingestion. In all scenarios modeled for infants and children, the 
estimated lifetime cancer risks were similar to those modeled for 
adults, and were less than or equal to 1 x 10-6.
3. Incineration Risk Characterization
    We found that average and high-end risks were about the same for 
farmers and home gardeners. However, estimated risks were higher for 
receptors closer to the facility than farther away in both groups. The 
most significant pathway for the farmer was ingestion of home-grown 
beef and dairy products and was ingestion of home-grown produce for the 
home gardener. At locations where farmers and home gardeners are likely 
to reside near the six assessed facilities, potential risks ranged from 
1 x 10-8 to 1 x 10-6 for farmers, and from 
4 x 10-8 to 1 x 10-6 for gardeners. For infants 
of farmers, the highest estimated risks for the breast milk ingestion 
pathway were 2 x 10-8, and were 5 x 10-8 for 
infants of home gardeners. These risks are at or below the Agency's 
acceptable risk range of 1 x 10-6 to 1 x 10-4. 
Furthermore, based on census data, an extremely small numbers of 
farmers are predicted to be exposed to risk levels near the upper end 
of the predicted range. The risk assessment estimates that the average 
and high-end risks for highly exposed sub-populations in the proximity 
of the six largest dioxin emitters are at or below the range of 
acceptable risks.
    Additionally, the concentration of dioxins in sewage sludge fed 
into sewage sludge incinerators does not influence the amounts of 
dioxins being emitted from the incinerator. The key factors influencing 
the amount of dioxins being emitted are the combustion conditions in 
the incinerator, incinerator design, and the efficiency and operational 
conditions of any air pollution control devices used on the 
incinerator. The Agency's Dioxin Source Inventory (USEPA, 2001a) 
estimated that total dioxins (chlorinated dioxins and chlorinated 
dibenzofurans only) being emitted from all of the Nation's sewage 
sludge incinerators was approximately 14.8 g. TEQ per year in 1995, a 
very minor fraction of the total North American dioxin inventory, which 
was 3255 g. TEQ per year as of 1995. The amount of dioxins emitted from 
sewage sludge incinerators is expected to be further reduced as the 
self-implementing means to meet the requirement for all sewage sludge 
incinerators to comply with either 100 parts per million (ppm) total 
hydrocarbons (THC) or 100 ppm carbon dioxide (CO) in their emissions 
are implemented. 40 CFR 503.45, 64 FR 42552, 42560 (Aug. 4, 1999).
    We reviewed plans for any future changes for the six multiple 
hearth incinerators used in our risk assessment to determine if any 
significant reductions in emissions of dioxin and dioxin-like compounds 
might be expected in the future. The operators of three of the six 
incineration facilities indicated that no changes that might reduce 
emissions were planned in the foreseeable future. These facilities are 
currently meeting the total hydrocarbon emission limitation of 100 ppm.
    One facility started up a new fluidized bed incinerator in June 
2000, replacing two existing multiple hearth incinerators. One of the 
two existing multiple hearth incinerators will remain as a backup 
incinerator, with only occasional use. Testing of fluidized bed 
incinerators has demonstrated more complete destruction of organic 
compounds than in multiple hearth incinerators (USEPA, 1992). Another 
facility has shut down its incineration operation completely and is 
drying their sewage sludge instead.
    The operator of the largest and highest emitting of the 
incineration facilities plans to start eliminating incineration of 
sewage sludge in their multiple hearth incinerators over the next three 
to four

[[Page 66233]]

years. This facility plans to use a new high temperature process to 
convert sludge to a glass-like aggregate. An initial evaluation 
indicates that the aggregate process is cost-effective. The facility 
operator expects to submit a permit application within the next year to 
build the first aggregate unit. If this initial unit is successful, the 
operator will submit another permit application to build additional 
units to replace the entire multiple hearth incineration facility. 
However, if the new aggregate process does not prove feasible, then 
this facility will continue to use the existing multiple hearth 
incinerators. The facility operator also may consider building 
fluidized bed incinerators to start replacing the aging multiple hearth 
incinerators.
    EPA promulgated amendments to the incineration subpart of the Part 
503 standards on August 4, 1999 (64 FR 42551-42573). These amendments 
included a provision making all sewage sludge incineration requirements 
self-implementing. All incinerator owners/operators must now 
continuously monitor for either THC or CO emissions and operate their 
incinerators to limit either THC or CO emissions to 100 ppm or less (40 
CFR 503.40, 503.44, 503.45 (a)). We will continue to inspect the 
operations and records of these incinerators to assure attainment of 
the THC or CO limits.
    The exposure and risk assessments performed for dioxins from sewage 
sludge incinerators estimated very low exposure and subsequent 
incremental cancer risk (i.e., 1 x 10-6) to the modeled 
highly exposed human population. This small incremental dioxin exposure 
from incineration of sewage sludge predicts that contamination of 
surrounding environmental media such as soils, surface water, and 
sediments is also small. On this basis, we concluded that sewage sludge 
incineration also would not appreciably increase dioxin concentrations 
in surrounding environmental media. In addition, dioxins exhibit 
similar mechanisms of toxicity across vertebrate species, including 
humans (USEPA 2000a). For these reasons, we would not expect ecological 
species to suffer adverse effects due to dioxins from sewage sludge 
incineration.
    In making our final decision, we considered the results of the 
completed risk assessment for dioxins emissions from sewage sludge 
incinerators, the comments to our proposal not to set national 
standards for dioxin and dioxin-like compounds for sewage sludge 
incinerators, and the projected reductions of dioxin and dioxin-like 
compounds in emissions from sewage sludge incinerators. Based on the 
results summarized above, we conclude that no further regulatory action 
is needed to protect public health and the environment from adverse 
effects from dioxins in sewage sludge fired in a sewage sludge 
incinerator.

VII. Summary of Public Comments and EPA Responses

    EPA received over 200 comments on the proposed amendments to the 
Standards for the Use and Disposal of Sewage Sludge. The majority of 
these comments concerned the proposed amendments to 40 CFR part 503, 
subpart B, land application of sewage sludge. EPA will address those 
comments when the Agency takes final action on the proposed amendments 
to subpart B of part 503. Today's final action concerns only the 
surface disposal and sewage sludge incinerator portions of part 503, 
found in subparts C and E. EPA's decision not to regulate dioxins in 
sewage sludge that is placed in a surface disposal unit is based in 
part on discrete portions of the risk assessment for land application. 
Regarding comments on the risk assessment, EPA is responding to those 
comments that relate directly to surface disposal as part of today's 
final action.

A. Major Comments Applicable to Both Surface Disposal and Incineration

    We received relatively few comments on our proposal not to directly 
regulate dioxin and dioxin-like compounds in sewage sludge disposed in 
surface disposal and sewage sludge incineration facilities. The most 
prevalent comment that we received was overall support for the Agency's 
proposal not to further regulate dioxins for sewage sludge-only surface 
disposal units and incinerators. This group of commenters included a 
number of municipalities and treatment works associations, a sewage 
sludge processing company and a trade association. These commenters 
agreed that the risk to human health from dioxins in sewage sludge 
disposed in these types of facilities was very small and did not 
warrant setting limits. One municipality which supported the proposal 
not to further regulate surface disposal and incineration suggested 
that this decision be supported with a risk assessment similar to the 
risk assessment conducted for land application. This commenter 
apparently was unaware that comparable risk assessments which evaluated 
the appropriate exposure pathways for these management practices were 
conducted to support the Agency's proposal not to further regulate 
surface disposal and incineration.
    A comment from a public policy institute stated that the decision 
not to regulate dioxins in sewage sludge disposed of by surface 
disposal and incineration is unacceptable because dioxin has been 
linked to health effects other than cancer. The commenter suggested 
that we evaluate other health effects, particularly reproductive and 
developmental toxicity. A comment from an environmental advocacy 
organization expressed a similar concern specifically about the 
incineration decision. We agree that other significant health effects 
may be associated with dioxin and dioxin-like compounds, but existing 
methodologies are not available to develop probabilistic estimates of 
human health non-cancer risks or to determine levels that would be 
without risk. Because the predicted cancer risk for dioxin is so low 
(i.e., 10-6 or less), we believe that existing regulations 
for surface disposal and sewage sludge incineration are adequate to 
protect public health from both cancer and non-cancer effects.
    One State commenter asked if there is a connection between these 
actions not to regulate sewage sludge surface disposal and 
incinerators, and the effluent guidelines and standards for landfills 
at 40 CFR part 445. There is no connection intended or implied by the 
Agency.

B. Major Comments on Surface Disposal

    One treatment authority stated that dioxin limits should be set for 
surface disposal sites which are operated similarly to land application 
sites (i.e., for cattle grazing and food crop production). We are aware 
of only two surface disposal sites which are operated in this manner. 
The current part 503 regulation addresses this situation: 
Sec. 503.24(k) and (l) prohibit growing crops or grazing animals on 
active surface disposal sites ``unless the owner/operator * * * 
demonstrates to the permitting authority that through management 
practices public health and the environment are protected from any 
reasonably anticipated adverse effects of pollutants in sewage sludge * 
* *.''
    A comment from an environmental advocacy group expressed concern 
that dioxins may become soluble and contaminate ground water when in 
the presence of solvents and surfactants, also found in sewage sludge. 
Data from the National Sewage Sludge Survey, which analyzed for more 
than 400 chemicals, indicate that the concentrations of solvents and 
surfactants in sewage sludge are relatively small (USEPA 1990). On this 
basis, we assumed that solubilization of dioxin and dioxin-like 
compounds by

[[Page 66234]]

solvents and surfactants in sewage sludge would not be significant.

C. Major Comments on Incineration

    A comment from a public policy institute noted that we gave no 
explanation for our use of different assumptions for soil ingestion by 
children in risk assessments for incineration and land application to 
support our proposals (0.1 grams/day and 0.4 grams/day, respectively.) 
The apparent difference in the two values is attributable to the 
different approaches incorporated in the risk assessments for the land 
application and incineration proposals. The land application proposal 
was supported by a deterministic risk assessment for which single point 
values are assumed for various input parameters. The commenter is 
correct that the land application risk assessment for the proposal 
assumed 0.4 grams/day for soil ingestion by children. For incinerator 
risk assessment, we conducted a probabilistic analysis that uses 
distributions of values for exposure variables where a range of data is 
available, including soil ingestion by children. This distribution 
included low end values, mid-range values, and high end values. Soil 
ingestion by children at a rate 0.1 grams/day is the mean value and 0.4 
grams/day is a high end value.
    This commenter also stated that no additional dioxin exposure to 
humans should be allowed as a result of sewage sludge incineration. A 
comment from an environmental advocacy organization expressed a similar 
concern. We agree with the principle that additional exposure to dioxin 
should be minimized and are concentrating our resources on reducing the 
emissions from the sources which have the highest dioxin emissions in 
order to achieve this reduction. The total annual dioxins emitted from 
sewage sludge incinerators are very small in comparison to other 
sources (USEPA, 2001). Furthermore, based on the very low predicted 
risk, we are confident that no further regulatory action is necessary.
    Another comment from the same public policy institute questioned 
EPA's finding that the estimated risks were higher for individuals 
close to a sewage sludge incinerator than those farther away since 
dioxins can travel more than 100 miles from their source. We agree that 
dioxins can travel for extended distances from the source, but disagree 
that the risks would be the same or higher for individuals farther away 
from the source. Our assessment estimated close-in risks as well as 
risks out to 30 miles. The assessment estimated risks at locations 
where individuals are likely to be found and calculated risks at sites 
of maximum exposure whether or not people are at these sites. The 
assessment looked at risk from inhalation as well as ingestion of food 
and water. In all cases the estimated risks were not significant 
(USEPA, 2000b).
    Finally, this commenter expressed concern that if sewage sludge 
incinerators are upgraded as EPA is predicting, the ash from these 
incinerators will become even more toxic and hazardous to land apply. 
This concern appears to be based on the assumption that dioxins that 
are removed from the air emissions will be recycled in the fly and 
bottom ash from the incinerator. The upgrades for multiple hearth 
incinerators are designed to destroy dioxin-like compounds by 
increasing the temperature and time of exposure of emissions exiting 
from the multiple hearth incinerators. Fly ash collected by particulate 
collection systems have been exposed to the increased temperature and 
time conditions before their collection. Thus not only are the stack 
emissions of dioxin-like compounds greatly reduced, but any dioxin-like 
compounds contained in the fly ash is greatly reduced. In addition, the 
bottom ash from multiple hearth incinerators is not affected by the 
installation of air pollution equipment on the exit gas stream. In the 
situation where a multiple hearth incinerator is replaced with a 
fluidized bed incinerator, the net production of dioxin-like compounds 
in a fluidized bed combustion chamber has been demonstrated to be an 
order of magnitude less than that occurring in a multiple hearth 
incinerator. Thus the replacement of a multiple hearth incinerators 
with a fluidized bed incinerator will reduce the dioxin-like compounds 
in both the stack emissions and in the ash removed from the fluidized 
bed incinerator.
    A public interest group contended that the incinerator risk 
assessment looks only at inhalation exposures. The commenter stated 
that the major issue with dioxin emissions from incinerators is not 
inhalation but deposition to the soil, crops, and water in the 
neighboring area. The commenter believes that without including data on 
increased generation and/or deposition of particulates due to sludge 
burning, the incineration risk analysis fails to adequately address the 
dangers posed to nearby residents from the combination of dietary 
impacts and inhalation factors. In response, the Agency notes that, as 
described above, the incineration risk assessment estimated risks from 
both direct inhalation and ingestion of substances impacted by 
deposition of incinerator emissions. The ingestion scenarios included 
ingestion of beef and dairy products, fish, and vegetables by children 
and adults, and soil ingestion by children.
    A comment from an environmental advocacy group raised a number of 
concerns about deficiencies in the risk model EPA used in developing 
the proposal for incineration, including: protection of children and 
fetuses; use of deterministic methods instead of probabilistic methods; 
consideration of synergistic effects of pollutant exposures; 
consideration of ecological impacts; and background levels of human 
exposure to dioxins.
    Cancer risks due to infant and childhood exposures were calculated 
as a part of the multi-pathway sewage sludge incineration risk 
assessment. Risks were estimated for infants and children aged: Less 
than one year, 1-2 years, 3-5 years, 6-11 years, and 12-17 years for 
both the home gardener and the farmer/recreational fisher exposure 
scenarios. The infant age group also included exposure via breast milk 
ingestion. In all scenarios modeled for infants and children, the 
estimated lifetime cancer risks were similar to those modeled for 
adults, and were less than or equal to 1 x 10-6.
    The incineration risk assessment was deterministic in approach. 
However, probabilistic methods and data distributions formed the second 
part of the risk assessment. This probabilistic component served as a 
sensitivity instrument and was used to select the most appropriate 
input values for the deterministic model runs. Finally, this risk 
assessment was subjected to external peer review. This review found 
that the risk assessment was scientifically sound.
    At the present time, there is no method for evaluating synergistic 
health effects from exposure to pollutants with different mechanisms or 
modes of toxicity.
    The exposure and risk assessments performed for dioxins from sewage 
sludge incinerators estimated very low exposure and subsequent 
incremental cancer risk (i.e., 1 x 10-6) to the modeled 
highly exposed human population. This small incremental dioxin exposure 
from incineration of sewage sludge predicts that contamination of 
surrounding environmental media such as soils, surface water, and 
sediments is also small. On this basis, we concluded that sewage sludge 
incineration also would not appreciably increase dioxin concentrations 
in surrounding environmental media. In addition, dioxins exhibit 
similar mechanisms of toxicity across vertebrate species,

[[Page 66235]]

including humans. For these reasons, we would not expect ecological 
species to suffer adverse effects due to dioxins from sewage sludge 
incineration.
    Our decision was based on the incremental exposure to dioxins from 
incineration of sewage sludge, in line with Agency procedures for 
assessing cancer risks. However, EPA did consider background levels of 
exposure to dioxins in making this decision. We compared the 
incremental dioxin exposure from sewage sludge incineration to 
background dioxin exposure and concluded that no further regulatory 
action is needed to protect public health.
    A treatment works association commenter agreed with the proposed 
decision not to regulate dioxin emissions from sewage sludge 
incinerators, but expressed concerns that the complex modeling used in 
the incineration risk assessments had not been adequately peer-
reviewed, has largely not been verified, and has not been subjected to 
rigorous quality control measures. This commenter stated that most of 
the references for the modeling performed in the risk assessment have 
not themselves been peer-reviewed, and that adequate evaluation of such 
complex modeling requires a longer period than the 90 days allotted for 
public comments. We agree that the complex models were not individually 
peer-reviewed prior to proposal. However the entire incineration risk 
assessment using these models was peer-reviewed and appropriately 
revised prior to making our final determination. Furthermore, the 
verification to date shows that the models perform reasonably well for 
dioxins and furans (Lorber, et. al., 2000). We are currently conducting 
a lengthy peer review and extensive model verification for an updated 
multi-pathway model (the Total Risk Integrated Methodology--TRIM) that 
will eventually replace the multi-pathway model used in the incinerator 
risk assessment. The models used in the risk assessment for sewage 
sludge incinerators are the best available at this time and adequate 
for purposes of this action. We also note that the comment period was 
originally 60 days, and EPA was requested to extend the comment period 
to allow for more time to review the technical support documents. EPA 
agreed and reopened the comment for an additional 30 days. 65 FR 1278 
(March 2, 2000). Consistent with similar Agency actions, we believe 
that a 90 day comment period was reasonable for this action.
    A State environmental agency commented that dioxin emissions from 
medical waste combustors and solid waste combustors should be further 
reduced since these are the main sources of air deposition compared to 
wastewater treatment plants. EPA has issued guidance and regulations 
for reduction of dioxin emissions from both municipal waste combustors 
and medical waste incinerators that have already resulted in drastic 
reductions of dioxin-like compounds. For municipal waste combustors, 
national emissions of dioxin-like compounds have been reduced from 
4,170 g. TEQ per year in 1990 to 40.6 g. TEQ per year in 2000. 
Continued compliance with current regulations is expected to further 
reduce emissions to 12 g. TEQ per year by 2005 (USEPA, 1999b). For 
medical waste incinerators, emissions of dioxin-like compounds have 
been reduced from 600 g. TEQ per year in 1990 to 150 g. TEQ per year in 
2000 and further reductions are expected to drop to 5-7 g. TEQ per year 
by 2002 (USEPA, 1996b).

VIII. List of References

Bastian, R.K. 1997. Biosloids (Sludge) Treatment, Beneficial Use, 
and Disposal Situation in the USA. European Water Pollution Control, 
Vol. 7, No. 2: 62-80.
Lorber, M., Eschenroder, A. and R. Robinson. 2000. Testing the 
USEPA's ISCST-Version 3 Model on Dioxin: a Comparison of Predicted 
and Observed Air and Soil Concentrations. Atmospheric Environment 
34: 3995-4010.
USEPA, 1990. National Sewage Sludge Survey; Availability of 
Information and Data, and Anticipated Impacts on Proposed 
Regulations; Proposed Rule. Federal Register 55 (218): 47210-47283.
USEPA, 1992. Technical Support Document for Sewage Sludge 
Incineration. Office of Water. Washington, DC. EPA/822-R-93-003.
USEPA, 1994. Health Assessment for 2,3,7,8-TCDD and Related 
Compounds. External Review Draft. EPA/600/BP-92/001a-c.
USEPA, 1996a. Technical Support Document for the Round Two Sewage 
Sludge Pollutants. Office of Science and Technology. Washington, DC. 
EPA-822-R-96-003.
USEPA, 1996b. National Dioxin Emissions from Medical Waste 
Incinerators. Office of Air Quality Planning and Standards. Research 
Triangle Park, NC.
USEPA, 1997. Exposure Factors Handbook: Volumes I, II, and III. 
National Center for Environmental Assessment. Office of Research and 
Development. Washington, DC. EPA/600/P-95/002 Fa.
USEPA, 1999a. Risk Analysis for the Round Two Biosolids Pollutants. 
Office of Science and Technology. Washington, DC.
USEPA, 1999b. Summary of the National Emission Estimates for 
Municipal Waste Combustion Units. Office Air Quality Planning and 
Standards. Research Triangle Park, NC.
USEPA, 2000a. Exposure and Human Health Reassessment of 2,3,7,8-
Tetrachlorodibenzo-p-Dioxin (TCDD) and Related Compounds. Science 
Advisory Board External Review Draft. National Center for 
Environmental Assessment, Office of Research and Development 
Washington, DC.
USEPA, 2000b. Sewage Sludge Incineration Dioxin-Like Compound Risk 
Analysis. Revised Technical Support Document. Office of Air Quality 
Planning and Standards. Research Triangle Park, NC.
USEPA, 2001. Database of Sources of Environmental Releases of 
Dioxin-Like Compounds in the United States: Reference Years 1987 and 
1995. National Center for Environmental Assessment, Office of 
Research and Development. March, 2001. EPA/600/C-01/012.

    Dated: December 14, 2001.
Christine Todd Whitman,
Administrator.
[FR Doc. 01-31342 Filed 12-20-01; 8:45 am]
BILLING CODE 6560-50-P