66228 Federal Register / Vol. 66, No. 246 / Friday, December 21, 2001 / Notices

ENVIRONMENTAL PROTECTION

AGENCY

[FRL–7120–5]

Standards for the Use or Disposal of

Sewage Sludge

AGENCY: Environmental Protection

Agency.

ACTION: Notice.

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. plunkett.arleen@epa.gov.

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:

Category Examples of affected entities

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

Federal Register / Vol. 66, No. 246 / Friday, December 21, 2001 / Notices 66229

1Of 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).

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-pdioxins/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-pdioxins (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 doseresponse 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).

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

66230 Federal Register / Vol. 66, No. 246 / Friday, December 21, 2001 / Notices

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 doseresponse 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 doseresponse 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 § 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.

Federal Register / Vol. 66, No. 246 / Friday, December 21, 2001 / Notices 66231

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 × 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 × 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 groundlevel 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 highlyexposed 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 highlyexposed 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.

66232 Federal Register / Vol. 66, No. 246 / Friday, December 21, 2001 / Notices

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 1×10¥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 1×10¥8 to 1×10¥6 for

farmers, and from 4×10¥8 to 1×10¥6 for

gardeners. For infants of farmers, the

highest estimated risks for the breast

milk ingestion pathway were 2×10¥8,

and were 5×10¥8 for infants of home

gardeners. These risks are at or below

the Agency’s acceptable risk range of

1×10¥6 to 1×10¥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

Federal Register / Vol. 66, No. 246 / Friday, December 21, 2001 / Notices 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 selfimplementing. 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., 1×10¥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: § 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

66234 Federal Register / Vol. 66, No. 246 / Friday, December 21, 2001 / Notices

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 1×10¥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., 1×10¥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,

Federal Register / Vol. 66, No. 246 / Friday, December 21, 2001 / Notices 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 multipathway model (the Total Risk

Integrated Methodology—TRIM) that

will eventually replace the multipathway 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