Document ID: s3://data.kl3m.ai/documents/govinfo/USCOURTS/USCOURTS-caDC-93-01555/USCOURTS-caDC-93-01555-0/pdf.json

Parties Involved:
City of Pueblo, Colorado
Petitioner
Environmental Protection Agency
Respondent

Document Text:

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United States Court of Appeals

FOR THE DISTRICT OF COLUMBIA CIRCUIT

Argued October 3, 1994 Decided November 15, 1994

No. 93-1187

LEATHER INDUSTRIES OF AMERICA, INC.,

PETITIONER

V.

ENVIRONMENTAL PROTECTION AGENCY;

CAROL M. BROWNER, ADMINISTRATOR,

UNITED STATES ENVIRONMENTAL PROTECTION AGENCY,

RESPONDENTS

No. 93-1376

ASSOCIATION OF METROPOLITAN SEWERAGE AGENCIES,

PETITIONER

v.

ENVIRONMENTAL PROTECTION AGENCY;

CAROL M. BROWNER, ADMINISTRATOR,

UNITED STATES ENVIRONMENTAL PROTECTION AGENCY,

RESPONDENTS

No. 93-1404

MILWAUKEE METROPOLITAN SEWERAGE DISTRICT,

A SPECIAL PURPOSE WISCONSIN MUNICIPAL CORPORATION,

PETITIONER

v.

ENVIRONMENTAL PROTECTION AGENCY;

CAROL M. BROWNER, ADMINISTRATOR,

UNITED STATES ENVIRONMENTAL PROTECTION AGENCY,

RESPONDENTS

No. 93-1555

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CITY OF PUEBLO, COLORADO,

PETITIONER

v.

ENVIRONMENTAL PROTECTION AGENCY,

RESPONDENT

Appeal from an Order of the

Environmental Protection Agency

Thomas J. Crawford argued the cause for petitioners Association

of Metropolitan Sewerage Agencies and Milwaukee Metropolitan

Sewerage District. With him on the briefs were Lee C. White and

Michael J. McCabe.

Ronald L. Raider argued the cause for petitioner City of Pueblo,

Colorado. With him on the briefs were Thomas K. Bick and Thomas

J. Florczak.

John L. Wittenborn argued the cause and filed the briefs for

petitioner Leather Industries of America, Inc. William M.

Guerry, Jr. entered an appearance.

Daniel S. Goodman and Mark A. Nitczynski, Attorneys, United

States Department of Justice, argued the cause for respondents. 

With them on the briefs were Lois J. Schiffer, Acting Assistant

Attorney General, United States Department of Justice, Caroline

H. Wehling, Assistant General Counsel, and Richard T. Witt,

Attorney, United States Environmental Protection Agency.

Before WALD, WILLIAMS and ROGERS, Circuit Judges.

Opinion for the Court filed by Circuit Judge WALD.

WALD, Circuit Judge: In these consolidated cases,

petitioners seek review of several aspects of the Standards for

the Use or Disposal of Sewage Sludge, 58 Fed. Reg. 9387 (1993)

(to be codified at 40 C.F.R. parts 257 and 403) ("Regulations"),

issued on February 10, 1992 by the Environmental Protection

Agency ("EPA" or "agency"). Because petitioners have raised

valid challenges to (1) the use of the 99th percentile figures

from the National Sewage Sludge Survey ("NSSS") for the Table 3

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"clean sludge" caps, (2) the assumed rate and duration of

application underlying the risk-based data in Table 3 as applied

to heat-dried sludge, (3) the assumed exposure possibilities

underlying the risk-based cap on selenium as applied to public

contact sites with low potential for occupancy, and (4) the lack

of data to support the risk-based cap on chromium, we remand

those parts of the regulations to the EPA for modification or

additional justification. We reject the challenges to the

classification of "dedicated uses" as "land disposal" and to the

EPA's refusal to provide for site-specific variances from the

pollutant limitations for land-applied sewage sludge.

I. BACKGROUND

A. Statutory Framework

The Clean Water Act of 1972 ("CWA" or "Act") was enacted to

"restore and maintain the chemical, physical, and biological

integrity of the Nation's waters." 33 U.S.C. § 1251(a). The Act

prohibits "the discharge of any pollutant by any person" into the

navigable waters of the United States, except in compliance with

various provisions of the Act, 33 U.S.C. § 1311(a), and directs

the EPA to regulate the discharge of wastewater into the

navigable waters by various industrial, commercial, and public

sources. See 33 U.S.C. § 1311(b). As amended by the Federal

Water Pollution Control Act of 1977, Pub. L. No. 95-217, 91 Stat.

1566 (codified at 33 U.S.C. § 1251 et seq.), and the Water

Quality Act of 1987, Pub. L. No. 100-4, 101 Stat. 7 (1987), the

CWA also requires the EPA to promulgate comprehensive regulations

for the management of sewage sludgethe by-product of

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pre-discharge sewage and wastewater treatment by publicly and

privately owned treatment works ("POTWs").

POTWs receive sewage and liquid industrial wastes. POTW

treatment of these waste streams produces a liquid effluent that

meets CWA discharge standards and may be expelled into surface

water and a residual material, sewage sludge, which may not be

discharged into the waters. POTWs dispose of sewage sludge

through incineration or landfill deposits; they also apply it to

land or sell it to the public for use as a fertilizer. 

Implementation of the Clean Water Act of 1972's restrictions on

effluent discharge has led to more pre-discharge treatment of

sewage wastes and, consequently, more sewage sludge is generated

as a by-product of treatment. The production of sewage sludge

each year has nearly doubled since the original enactment of the

Clean Water Act. See 58 Fed. Reg. 9249.

The Federal Water Pollution Control Act of 1977, an

amendment to the Clean Water Act, directed the EPA in general

terms to develop a regulatory program to ensure the safe use and

disposal of sewage sludge. See 33 U.S.C. § 1345(d) (1982). In

1987, Congress enacted another amendment to the CWA, the Water

Quality Act, to require the EPA to issue specific regulations for

the use and disposal of sewage sludge. Under the amended Act,

the EPA must identify and set numeric limits for toxic pollutants

that "may be present in sewage sludge in concentrations which may

adversely affect public health or the environment," and establish

management practices for the use and disposal of sludge

containing these toxic pollutants. 33 U.S.C. § 1345(d)(2). Its

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regulations are to be issued in two phasesthe first round to be

promulgated "on the basis of available information," the second

to encompass pollutants unaddressed by the first round. Id. It

is the Round One regulations that are now at issue.

B. Regulatory Development

At the start of the rulemaking process, the EPA made an

initial assessment in the aggregate that "current use and

disposal practices for sewage sludge pose little risk to public

health." 58 Fed. Reg. 9320. Sewage sludge that meets safety

requirements is a "valuable resource" as "fertilizer and a soil

conditioner," 58 Fed. Reg. 9249, and the EPA "strongly support[s]

the beneficial reuse of sewage sludge." 58 Fed. Reg. 9251. The

EPA identifies "land application" as one type of beneficial reuse

and defines it as "the spraying or spreading of sewage sludge

onto the land surface; the injection of sewage sludge below the

land surface; or the incorporation of sewage sludge into the

soil so that the sewage sludge can either condition the soil or

fertilize crops or vegetation grown in the soil." § 503.11(h),

58 Fed. Reg. 9391. The Round One regulationsStandards for the

Use or Disposal of Sewage Sludgeregulate land application of

sewage sludge as well as surface disposal and incineration.

The Round One regulations establish limits on ten pollutants

in sludge destined for land application. To set these land

application pollutant limits, the EPA sought first to identify

"those [pollutants] most likely to pose a hazard to human health

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1Office of Water Regulations and Standards, U.S. EPA,

Summary of Environmental Profiles and Hazard Indices for

Constituents of Municipal Sludge 1 (1985), reprinted in J.A. at

889. 

or the environment."1 It enlisted federal, state, academic, and

private sector experts to screen a list of 200 pollutants to

determine which, if any, posed a potential risk to human health

or the environment if contained in sewage sludge that was applied

to or disposed of on land or incinerated. These experts selected

forty-eight pollutants, for which the EPA compiled environmental

profiles. Based on data and information from published

scientific reports, the profiles assessed the pollutants' general

toxicity and persistence, as well as the particular pathways by

which they might cause harm to human health or the environment. 

See 58 Fed. Reg. 9263-64 (Table III-1). Using these profiles and

preliminary data about the concentration and frequency of these

pollutants in sewage sludge, the EPA exempted from regulation

those pollutants that presented no risk to human health or the

environment at the highest observed concentration and deferred

consideration of those for which it had insufficient data to make

this risk determination. See 58 Fed. Reg. 9264. It initially

proposed limits for 25 pollutants in sludge to be applied to

land, see 54 Fed. Reg. 5761 (Table III-4), and concluded by

regulating ten heavy metals in sludge applied to land in the

final Round One sewage sludge regulations, see 58 Fed. Reg. 9392. 

These portions of the regulations establish numeric limits on

pollutants in sludge that is applied to agricultural land,

forests, public contact sites, or reclamation sites.

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2Elsewhere in the record, the EPA uses the figure of 180 for

the number of POTWs at which it performed sampling and analysis. 

58 Fed. Reg. 9268. We are not certain which, in fact, is

correct. 

II. THE LAND APPLICATION REGULATIONS

In establishing the limits for the ten regulated heavy

metals pollutantsarsenic, cadmium, chromium, copper, lead,

mercury, molybdenum, nickel, selenium, and zincthe EPA generated

two sets of data.

A. The Underlying Data

The first data set on the ten pollutants describes their

current concentration in sewage sludge. The data is culled from

the EPA's National Sewage Sludge Survey ("NSSS"), in which the

EPA sent questionnaires to 479 POTWsout of a national total of

11,407and performed sampling and analysis at 208 of the 479. 

See 58 Fed. Reg. 9269.2 Based on this sampling and analysis, the

EPA identified the pollutant concentrations in current sludge

output, and calculated 99th-percentile concentration numbers: 

the pollutant concentration not exceeded by 997 of the sludge

samples in the NSSS ("99th percentile caps").

The second data set on the ten pollutants is risk-based. 

Under its risk-based analysis, the EPA modelled 14 pathways by

which pollutants in land-applied sludge could affect human health

or the environment and then identified a hypothetical "highly

exposed individual" ("HEI") for each pathway and calculated a

pollutant limit that would protect the HEI. The pathway model

analyzes the exposure potential from the total quantity of metal

in a given area of soil. The EPA proceeded on the uncontested

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31 U.S. EPA Technical Support Document for Land Application

of Sewage Sludge 6-17 (1992), reprinted in J.A. at 728

("Technical Support Document"). 

premise that "metals persist in the soil and accumulate over

time,"3 and the pathway model assesses the risk posed by the

total accumulation of pollutants in a given hectare of land. The

resulting pollutant limit, accordingly, "represent[s] the total

quantity of metals that could be added to [a given area] of soil. 

So long as the total quantity ... for the metal is not exceeded,

the exposure assessment models predict that there will be no

injury to the HEI. The model is unconcerned whether the total

quantity of the pollutant is received in a single load or over

time." 58 Fed. Reg. 9282 (emphasis added). The risk-based

exposure model, then, is indifferent as to the concentration of a

pollutant in any given load of sludge.

The EPA chose also to regulate concentration limits. "[B]y

applying certain conservative assumptions" about the amount of

sludge that would be applied to a given area of land, the EPA

"backcalculated" from the total pollutant limits in a given area

of land to a permissible sludge pollutant concentration per load. 

58 Fed. Reg. 9317. The "backcalculation" provides the EPA a

means of converting the cumulative pollutant limit into a

concentration cap for the pollutant in any given load of sludge. 

The model assumes a total amount of sludge that will be applied

to a given hectare of land based on an assumed yearly application

rate and assumed duration of application. The EPA assumed that

ten metric tons of sludge would be applied annually to a hectare

of land for 100 years. This converts into an assumption that, in

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total, 1000 metric tons of sludge will be applied to a given

hectare of land. Based on (1) this total amount of sludge that

the EPA assumed would accumulate on an area of land, and (2) the

total amount of pollutant that the EPA had determined could

safely accumulate on an area of land, the EPA calculated

pollutant/sludge, the permissible concentration of pollutant in

any application of sludge. For instance, assuming that 1000

metric tons of sludge would be applied to a hectare of land over

its lifetime, and having determined that 41 kilograms of arsenic

could safely accumulate in that hectare, the EPA determined that

it could allow 41 kgs of arsenic in 1000 metric tons of sludge,

or 41 mgs of arsenic per kilogram of sludge. This numberin

mg/kgis the EPA's risk-based concentration cap, and derives from

the "backcalculation" from the EPA's risk analysis, which is

based on the EPA's application rate and duration assumptions.

B. The Regulatory Design

The EPA designed its final regulations of pollutants in

land-applied sewage sludge on the basis of its risk-based and

empirical data sets. These regulations use the following four

tables in a manner described in the text below:

Pollutant limits, § 503.13(b), 58 Fed. Reg. 9392.

1. Ceiling Concentrations

Table 1Ceiling Concentrationscontains the less stringent

of the two concentration limits, the risk-based concentration cap

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4Bulk, not packaged, sewage sludge applied to a lawn or home

garden must comply with the Table 3 "clean sludge" regulations.

See § 503.13(a)(3), 58 Fed. Reg. 9391-92. This provision is not

at issue. 

and the 99th percentile concentration cap, for each of the ten

pollutants. See § 503.13(b)(1), 58 Fed. Reg. 9392. No sewage

sludge may be applied to the land unless the concentration of

each of the pollutants is under the Table 1 limits. Once it

complies with the Table 1 limits, it must comply either with the

Table 3 limitsqualifying as "clean" sludgeor with the

cumulative limits in Tables 2 and 4. Each option is discussed

below.4

2. "Clean" or "High Quality" Sludge

Table 3Pollutant Concentrations ("clean sludge

caps")contains the more stringent of the two concentration

limits, the risk-based concentration cap and the 99th percentile

concentration cap, for each of the ten pollutants. See §

503.13(b)(3), 58 Fed. Reg. 9392. If sludge meets Table 3i.e.,

the concentration of each of the pollutants in sludge is under

the Table 3 caps, as well as the Table 1 capsit is considered

"clean" sludge, and may be applied to land with no further

regulation.

3. Cumulative Pollutant Limits for Bulk Sewage Sludge

If bulk sewage sludge does not meet the Table 3 caps, it

must comply with Table 2the Cumulative Pollutant Loading Rates

("CPLRs"). While Tables 1 and 3 regulate pollutant concentration

in sludge, Table 2 regulates pollutant concentration in land. It

contains the cumulative risk-based limit derived from the EPA's

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5From our reading of the regulations, it appears that if

both "clean" and non-"clean" sludge are applied to land, only the

pollutant contribution from the non-"clean" sludge must be

recorded and controlled. 

pathway exposure model. The CPLRs represent the total amount of

pollutant that can ever permissibly concentrate in a given area

of land. Compliance with the cumulative option in Table 2

requires the maintenance of centralized land application records

to ensure that the total pollutant limit is not exceeded. Each

time non-"clean" sludge is applied to land, the amount of sludge

applied and the concentration of the pollutants in that sludge

must be recorded, so that the agency can keep track of the

pollutants accumulating in that piece of land. See §

503.12(e)(2), 58 Fed. Reg. 9391 (person who applies sewage sludge

in accordance with Table 2 must first contact permitting

authority for prior Table 2 application records and ensure that

Table 2 limits are not exceeded); § 503.12(j), 58 Fed. Reg. 9391

(must notify permitting authority of application); §

503.17(a)(5)(ii), 58 Fed. Reg. 9394 (recordkeeping requirements

for person who applies sewage sludge in accordance with Table

2).5

4. Annual Pollutant Limits for Packaged Sewage Sludge

Packaged sewage sludge that does not meet the Table 3 caps

must comply with Table 4the Annual Pollutant Loading Rates

("APLRs"). Table 4 also regulates the pollutant concentration in

land. It contains the cumulative limit in "annualized

form"imposing a limit on how much pollutant can accumulate in a

given area of land each year. Because packaged sludge is

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6See 1 Technical Support Document at 6-18, reprinted in J.A.

at 729. 

7Id. at 6-7, reprinted in J.A. at 718. 

generally applied to home gardens, the EPA did not think it would

be feasible to maintain centralized records and control of

packaged sludge applications.6 Accordingly, it converted the

Table 2 cumulative limits into annual limits: the total amount

of pollutant that could be allowed to accumulate in one year.

Assuming that packaged sewage sludge would "probably not be

applied longer than 20 years,"7 the EPA determined that

one-twentieth of the cumulative limit for each pollutant could be

applied each year. The Table 4 APLRs are thus the Table 2 CPLRs

divided by 20. Each year, non-"clean" packaged sewage sludge can

only be applied in quantities such that none of the pollutant

limits in Table 4 is exceeded. See § 503.13(a)(4)(ii), 58 Fed.

Reg. 9392. For packaged sludge, the EPA enforces this

application limit through labelling: non-"clean" packaged sewage

sludge must be labeled with the maximum yearly application so as

to ensure that none of the Table 4 APLRs will be exceeded. See §

503.14(e), 58 Fed. Reg. 9392 (label shall be affixed on bag or

other container with: name and address of person who prepared

the sludge, statement that application is prohibited expect in

accordance with instructions, and the annual application rate

that does not cause any of the ceilings in Table 4 to be

exceeded). For instance, the Table 4 APLR for arsenic is 2 kgs

of arsenic per hectare. See § 503.13(b)(4), 58 Fed. Reg. 9392. 

If packaged sewage sludge contained 50 mgs of arsenic per

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8For nickel, the risk-based and 99th percentile caps are

identical. 

kilogram of sludge, then 40 kgs of that sludge could be applied

to a hectare of land before reaching the APLR. (If there are 50

mgs of arsenic in each kilogram of sludge, then 40 kilograms of

sludge contain 2 kgs of arsenic.) Such sludge must be labelled

so that no more than 40 kgs may be applied to a hectare per year.

5. Summary

In brief, all sludge must meet the Table 1 caps as a

threshold requirement to land application. Then, there is a

choice between meeting the Table 3 "clean sludge" capsin which

case there is no further regulatory control of land

applicationor the cumulative limits of Tables 2 and 4, in which

case there are continuing recordkeeping obligations in the case

of bulk sewage sludge (Table 2) or labeling requirements in the

case of packaged sewage sludge (Table 4).

III. CHALLENGES TO THE TABLE 3 "CLEAN SLUDGE" CAPS

Petitioners challenge various aspects of the Table 3 "clean

sludge" caps. As explained above, Table 3 contains the more

stringent of the risk-based and 99th percentile concentration

caps for each of the ten pollutants. For chromium and selenium,

this more stringent cap is the 99th percentile number; for the

other regulated pollutants, it is the risk-based cap.8 Sludge

that meets both the Table 1 caps and the Table 3 caps is

considered "high quality" sludge, and may be applied to the land

without further regulation. Sludge that does not meet the Table

3 caps must meet the cumulative limits in Table 2 or Table 4,

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which involve more complicated regulatory oversight.

All of the petitionersthe Leather Industries of America

("Leather Industries"), the City of Pueblo ("Pueblo"), and,

jointly, the Association of Metropolitan Sewerage Agencies and

the Milwaukee Metropolitan Sewerage District (collectively

"AMSA")challenge the EPA's use of the 99th-percentile caps in

Table 3 on the grounds that they are unrelated to risk. The AMSA

also challenges the application rate and duration assumptions

that underlie the risk-based caps in Table 3 on the grounds that

these assumptions cannot rationally be applied to heat-dried

sludge, which is applied at lower rates and for shorter

durations.

A. Safe Harbor Defense

In defending the Table 3 caps, the EPA suggests that because

the Table 3 caps do no more than offer land appliers an

additional option, rather than impose a mandatory requirement,

they should withstand review. Land appliers need not comply with

Table 3if sludge does not meet Table 3, it can nonetheless be

applied to land under the recordkeeping or labelling schemes of

Tables 2 and 4. Table 3 only offers a safe harbor from the more

involved regulatory controls of Tables 2 and 4. Although

"[c]omplying with the "clean sludge' pollutant concentrations in

Table 3 may be advantageous" because it relieves the land applier

from the recordkeeping and management practice requirements

controlling non-"clean" sludge, Table 3 is not a prerequisite to

land application. EPA Brief at 24.

Because it is not requiring compliance with Table 3, the EPA

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9The AMSA also argues that the 99th percentile caps are in

conflict with the section of the statute authorizing removal

credits. We find this particular tack meritless. Under the

removal credit system, POTWs may issue removal credits to

indirect dischargersthe industrial facilities that discharge

waste to the POTWsin those cases where the POTWs perform

treatment that would otherwise be the responsibility of the

indirect dischargers. These removal credits prevent double

treatment by the POTWs and the indirect dischargers. Under the

statute, removal credits are only available if they do not

prevent the ultimate sewage sludge from complying with the

regulations at issue, the sludge use and disposal regulations. 

See 33 U.S.C. § 1317(b). The AMSA argues that "removal credits

are consistent with the national policy that the discharge of

toxic pollutants in toxic amounts be prohibited." AMSA Brief at

23 (emphasis in original). This argument adds nothing to its

position: to the extent that the sludge regulations are valid,

the removal credits can be conditioned on those sludge

regulations. The important question is whether the sludge

regulations are valid on their own terms. 

suggests, it should have greater leeway in designing Table 3. As

the EPA acknowledges, however, the Table 3 safe harbor "provides

significant relief from the [otherwise controlling] regulatory

safeguards." EPA Brief at 24. Failure to meet the Table 3 caps

subjects the would-be applier of sludge to not insignificant

burdens, and undoubtedly makes non-"clean" sludge less attractive

to the applier. Because the Table 3 clean sludge safe harbor

provides "significant relief" to complying sludge, the design of

that safe harbor is subject to the same rational basis review as

the rest of the regulatory scheme.

B. NSSS 99th Percentile Caps

Petitioners argue that the 99th percentile caps are not

risk-based and therefore exceed the EPA's statutory authority

under the enabling legislation.9 The statute directing the EPA

to issue the Round One pollutant limits for sewage sludge

provides:

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[T]he Administrator shall identify those toxic

pollutants which, on the basis of 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, and propose

regulations specifying acceptable management practices

for sewage sludge containing each such toxic pollutant

and establishing numerical pollutant for each use

identified under paragraph (1)(A).

33 U.S.C. § 1345(d)(2)(A)(i) (emphasis added). It further

instructs that the management practices and numerical criteria so

established "shall be adequate to protect public health and the

environment from any reasonably anticipated adverse effects of

each pollutant." 33 U.S.C. § 1345(d)(2)(D) (emphasis added).

In determining whether the 99th percentile limits in Table 3

are a permissible interpretation of the statute, we turn to

Chevron U.S.A. Inc. v. Natural Resources Defense Council, Inc.,

467 U.S. 837 (1984), and its progeny. We must first determine

whether Congress' intent is clear as to the permissibility of the

agency's interpretation. If it is not, "the question for the

court is whether the agency's answer is based on a permissible

construction of the statute." Chevron, 467 U.S. at 843.

The EPA does not contest that its statutory authority is

limited to promulgating regulations "adequate to protect public

health and the environment from any reasonably anticipated

adverse effects." 33 U.S.C. § 1345(d)(2)(D). As a matter of

Chevron's first step, then, there is no dispute that the statute

clearly mandates regulations based on "reasonably anticipated

adverse effects," and, thus, bearing some relation to risk. The

EPA argues, however, that the 99th percentile caps fulfill this

mandate of adequate protection from reasonably anticipated

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adverse effects and bear a relation to risk because they provide

"an additional safety mechanism." EPA Brief at 26. The EPA

suggests two ways in which the 99th percentile caps function as a

safety mechanism: (1) they provide a "margin-of-safety"

"necessary to ensure "adequate' protection from these

pollutants," EPA Brief at 28; and (2) they prevent current

sewage sludge practicesfound to be safe in the aggregatefrom

deteriorating. EPA Brief at 27. We conclude, however, that the

EPA has failed to show that the 99th percentile caps are

risk-related, and thus that they accord with the express mandate

of the statute.

First, the EPA states that the 99th percentile caps are

based on "a margin-of-safety analysis [that] is consistent with

the legislative intent underlying section 405 of the Act." EPA

Brief at 28. Whatever the underlying legislative intent, we do

not view the 99th percentile caps as merely a "margin-of-safety"

device. The fact that one cap is more restrictive than another

does not automatically make it a "margin of safety." Rather, a

margin of safety must be rooted in an analysis of risk. "[T]he

Administrator [must] base[ ] his conclusion as to an adequate

margin of safety on a reasoned analysis and evidence of risk." 

American Petroleum Institute v. Costle, 665 F.2d 1176, 1187 (D.C.

Cir. 1981) (emphasis added), cert. denied, 455 U.S. 1034 (1982).

The 99th percentile caps are not related to risk. In its

initial version of the regulations, the EPA proposed to cap all

pollutants at the higher of the pathway-generated numbers and the

98th percentile level. This proposal came under heavy attack

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10There is no indication in the record of the regulatory or

statutory basis for this peer review committee. 

11Memorandum of July 24, 1989, reprinted in J.A. at 30. 

12Coop. State Research Serv. Technical Comm. W-170, Peer

Review: Standards for the Disposal of Sewage Sludge 86-87

(1989), reprinted in J.A. at 60-61 ("Peer Review Report"). 

13Id. at 86, reprinted in J.A. at 60. 

14Clearly, the EPA's mandate to establish standards

"adequate to protect public health and the environment from any

reasonably anticipated adverse effects of each pollutant," 33

U.S.C. § 1345(d)(2)(D), does not give the EPA blanket one-way

ratchet authority to tighten standards. Cf. Contract Courier v.

Research & Special Programs Admin., 924 F.2d 112, 115 (7th Cir.

1991) ("Statutes do more than point in a direction, such as "more

safety.' They achieve a particular amount of that objective, at

a particular cost in other interests. An agency cannot treat a

statute as authorizing an indefinite march in a single

from "a specially convened group of sewage sludge experts," the

Land Practices Peer Review Committee ("PRC"). 58 Fed. Reg.

9267.10 The PRC, composed of "experts from EPA, academia,

environmental groups, and units of state and local government

agencies,"11 concluded that the 98th percentile approach was

"arbitrary," would "either over- or under-regulate," and "ha[d]

no technical merit."12 It pointed to the absence of any relation

between the percentile numbers and risk, noting that, because the

percentile concentrations are purely descriptive, they "may be

insignificant from a risk standpoint" just as easily as they "may

pose significant risks."13 We can discern no reasonand the EPA

has provided nonewhy the 99th percentile numbers are less

"arbitrary" or have more "technical merit" than the 98th

percentile figures. We find no support for the 99th percentile

caps as a risk-based margin of safety for chromium and selenium,

the two pollutants capped by the 99th percentile in Table 3.14

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direction."). 

15Leather Industries challenges the 99th percentile cap for

chromium on the grounds that the underlying data did not include

any POTW that accepts significant amounts of wastewater from a

leather tannery. Leather Industries Brief at 18 n.10. 

Specifically, Leather Industries states that while the highest

Second, the EPA argues that the 99th percentile caps reflect

a legitimate "antibacksliding" approach. EPA Brief at 27. The

EPA notes that its risk assessment suggests that current

practices pose little risk to human health, and concludes that it

should ensure that there is no deterioration from current

practices. See 58 Fed. Reg. 9283. The antibacksliding rubric,

however, cannot evade the requirement that the numeric limits on

land application be risk-relatedbased on reasonably anticipated

adverse effects. The conclusion that current sludge composition

is safe absent a showing that alterative sludge composition would

not be safe does not justify a mandate to freeze current sludge

quality. In Natural Resources Defense Council v. EPA, 859 F.2d

156 (D.C. Cir. 1988), we upheld an antibacksliding system that

prevented a retreat by industrial facilities from standards

regulating pollutant discharge that had been established in

individual permits once the individual permitting process was

replaced by national standards. In that case, the EPA had been

authorized in the first place to issue the standards from which

backsliding was prohibited, and those standards were based on the

same statutory factors as the subsequent national standards. See

859 F.2d at 201. In sum, when the statute mandates risk-based

regulation, standards from which facilities may not retreat must

also be risk-based.15

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reported level of chromium concentration from the NSSS is 3,750

mg/kg, sludges from the POTWs receiving significant amounts of

wastewater from tanneries have chromium concentrations in excess

of 30,000 mg/kg. Leather Industries Brief at 18 n.10. The EPA

has not contested this claim.

Pueblo argues that the 99th percentile cap for selenium is

arbitrary because it "has penalized communities in Western states

where naturally occurring concentrations [of selenium] are high." 

Pueblo Brief at 17.

Because we have remanded the 99th percentile caps on

chromium and selenium on other grounds, we do not reach these

claims. 

We also note another significant distinction between the

99th percentile caps and the antibacksliding regime approved in

Natural Resources Defense Council v. EPA. The Natural Resources

Defense Council system was site-specific and required only that

each individual facility maintain its existing standards. See

859 F.2d at 201. The 99th percentile caps, by contrast, are not

tailored to individual facilities. There will, by statistical

necessity, be a certain number of POTWs that currently produce

sludge with chromium and selenium concentrations above the 99th

percentile, and these facilities must do more than avoid sliding

back in order to meet the clean sludge caps. Without a finding

or risk, the EPA is without a basis for imposing the

antibacksliding mandate.

C. The Application Rate and Duration Assumptions

For all other pollutants except chromium and selenium, the

risk-based concentration cap is more stringent than the 99th

percentile cap, and is thus the Table 3 "clean" sludge cap. The

AMSA challenges the risk-based caps in Table 3. It argues that

the assumptions about the rate and duration of sludge application

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16These assumptions were used to generate all the risk-based

concentration capsthose in Table 1 as well as those in Table 3. 

The AMSA has only challenged Table 3, so we do not address the

use of these assumptions in Table 1. 

underlying the risk-based concentration caps in Table 3 are

irrational with respect to heat-dried sludge, which is applied at

lower rates for shorter durations. For whatever reason, the EPA

chose not to respond to this particular claim, and the AMSA has

been less than totally clear about what parts of the regulations

are allegedly infected by the use of these assumptions. We are,

accordingly, somewhat handicapped in evaluating the challenge. 

Nonetheless, on the record, we conclude that the EPA has not

adequately justified its use of the assumed rate and duration of

application to apply the risk-based caps in Table 3 to heat-dried

sludge.

The EPA's primary risk-based data is in Table 2. As

explained above, supra pp. 8-9, the EPA used the assumed

application rate of 10 metric tons/hectare and duration of 100

years to convert the Table 2 cumulative risk-based limits into

the risk-based concentration caps used in Tables 1 and 3.16 The

AMSA challenges the use of these assumptions in Table 3. It

argues that these assumptions are irrational as applied to

heat-dried sludge because it "is inconceivable that heat dried

sludge could ever be applied to land at a rate of 1,000 metric

tons/ha." AMSA Brief at 12. The AMSA points to undisputed

evidence in the record that the recommended application for

Milorganitea principal heat-dried sludge productis no more than

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17Comments of Milwaukee Metropolitan Sewerage District at 2

(Aug. 3, 1989), reprinted in J.A. at 160. 

18Comments of Milwaukee Metropolitan Sewerage District at 19

(July 18, 1989), reprinted in J.A. at 151. 

3.5 metric tons/ha per year17; and that heat-dried sludges "are

applied at low annual rates, usually around 2 to 3 metric tons

per hectare, but rarely over 5 metric tons per hectare."18

Under the Administrative Procedure Act, the assumed

application rate and duration must bear some rational

relationship to the actual application rates and durations for

land application of sludge. See Edison Elec. Institute v. EPA, 2

F.3d 438, 446 (D.C. Cir. 1993). The EPA has provided no response

to the AMSA's claim that the assumed rate and duration are

irrational as applied to heat-dried sludge. The EPA's

explanation of the application rate and duration assumptions on

the record is minimal. As explained above, the EPA used these

assumptions to "backcalculate" from the total limit on pollutant

accumulation in land to a concentration cap on pollutant in any

given application of sludge. The agency's only stated basis for

its assumed annual sludge application rate ("AWSAR") of 10 metric

tons per hectare and duration of 100 years is that it "believes

that the pollutant concentrations derived from [these

assumptions] are conservative because it is unlikely that any one

site will receive 10 metric tons of sewage sludge per hectare per

year for 100 consecutive years." 58 Fed. Reg. 9317.

From the NSSS data, the EPA had information on AWSARs. It

reported that typical AWSARs were 7 metric tons per hectare for

agricultural land and 18, 26, and 74 metric tons per hectare,

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respectively, for a public contact site, forest, and a

reclamation site. See 58 Fed. Reg. 9317. The EPA does not

suggest that its assumptions are tailored to this data or to the

information it had about heat-dried sludge; rather it suggests

only that the assumptions are conservative enough to provide

protection under each of these AWSARs. Its reasoning is as

follows. The assumed application rate of ten metric tons for a

duration of 100 years results in a total assumed sludge

application of 1000 metric tons per hectare. This would be

conservative enough to encompass the 74 metric ton rate, the EPA

explained, because the 74 metric ton rate would not likely

continue for more than the 13 years it would take to approach the

assumed total of 1000 metric tons per hectare. (Seventy-four

metric tons of sludge applied yearly for 13 years equals a net

application of 962 metric tons.) Making the same calculation for

the other observed AWSARs of 7, 18 and 26 metric tons per

hectare, the EPA concluded that these types of applications would

not likely continue for longer than the 142, 55, and 38 years it

would take to reach the assumed total of 1000 metric tons per

hectare. See 58 Fed. Reg. 9317. Besides indicating that the

combination of the assumed AWSAR and duration can safely

accommodate much higher actual application rates, the EPA offers

no reason for selecting them. Nor does it offer any reason for

using these assumptions to derive caps for heat-dried sludge

which it knows will be applied at application rates and durations

well below the assumed numbers.

An agency has discretion to design rules that can be broadly

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19We note that for packaged sewage sludge, failure to meet

the Table 3 caps sends the sludge to Table 4. The only

additional burden imposed by Table 4 is that the producer of the

sludge must provide a label with the actual application rate that

will ensure that the annual cumulative limits are not exceeded,

see supra part II.B. Thus, with respect to packaged sewage

sludge, the excessively conservative application assumptions may

be quite easily "cured" with a simple label as to actual safe

application rates.

Where the assumed rates underlying Table 3 are inaccurate

with respect to packaged heat-dried sludge, then, the producer

need only supply its own label with the rates that are accurately

calculated to protect safety. No other burden is imposed on the

producer. Tables 3 and 4 may well be a rational way to

accommodate the actual application rates of packaged heat-dried

sludge. We cannot tell, however, if this is the purpose of the

system. Moreover, to the extent that POTWs produce one type of

sludge product for packaged and bulk use, they would not be

greatly helped by relief only for the packaged use. If they

produced sludge that was not "clean," they could relatively

applied, sacrificing some measure of "fit" for administrability. 

At the same time, however, "[a]n agency must justify its failure

to take account of circumstances that appear to warrant different

treatment for different parties." Petroleum Communications v.

FCC, 22 F.3d 1164, 1172 (D.C. Cir. 1994). In this case, the EPA

did not provide any justification for its assumptions of 10

metric tons/hectare for 100 years in the case of heat-dried

sludge use, when it had information in the record (1) regarding

the actual rate and duration of use of heat-dried sludge, and (2)

data showing that heat-dried sludge was not an anomalous type of

land application. Given that the EPA had at hand the information

necessary accurately to prevent the known risks, it must provide

some explanation for ignoring it in favor of blanket, highly

conservative assumptions. Absent any further justification, the

EPA has not supplied a rational basis for its assumed application

duration and rate in the case of heat-dried sludge.19

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easily label it for packaged sale, but bulk use would still be

considerably more burdensome. We invite the agency to elaborate

on these issues as it justifies or reconsiders the risk-based

caps in Table 3. 

20Pathway 1, for instance, is "Sewage Sludge -> Soil ->

Plant -> Human." The EPA describes all the pathways at 58 Fed.

Reg. 9284-88. 

We therefore require that the EPA reconsider the Table 3

risk-based caps with regard to heat-dried sludge in order either

to justify its general assumptions on rate and duration or to

provide more tailored caps that fit the data on heat-dried

sludge.

IV. CITY OF PUEBLO'S ADDITIONAL CHALLENGES

In addition to its challenge to the 99th percentile caps,

Pueblo challenges the risk assessment that underlies the

pollutant limits for selenium, found in Tables 1 and 2. It

challenges both the EPA's decision to regulate selenium at all

and the exposure assumptions used to derive the risk-based

limits. It also challenges the EPA's refusal to provide a

variance procedure. We agree that the EPA has not justified the

use of high-occupancy exposure assumptions to regulate the

selenium content of sludge applied to low-occupancy sites. In

declining to provide variances, however, the EPA acted within its

discretion.

A. Risk-Based Cap on Selenium

The EPA's method of risk assessment for each identified

pollutant was to model 14 possible exposure pathways through

which sewage sludge applied to the land could pose a threat to

human health or the environment,20 and a prototype "Highly

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21The HEI for Pathway 1 on nonagricultural land, for

instance, is "a person who regularly harvests edible wild plants

... from forests or range lands that have been amended with

sewage sludge." 1 Technical Support Document at 5-4, reprinted

in J.A. at 613. 

22See Office of Water Regulations and Standards, U.S. EPA,

Environmental Profiles and Hazard Indices for Constituents of

Municipal Sludge: Selenium (1985), partially reprinted in J.A.

at 258-267. 

Exposed Individual" ("HEI") for each pathway.21 The EPA analyzed

each pathway for each pollutant, and the pathway producing the

most restrictive limit on the pollutant became the basis for the

cumulative pollutant loading rates (CPLRs) in Table 2, and then

the risked-based caps in Tables 1 and 3.

For selenium, the pathway leading to the most stringent cap

was Pathway 3, "Sewage Sludge -> Human," which "assesses the

hazard to a child of ingesting undiluted sewage sludge." 1

Technical Support Document at 5-104, reprinted in J.A. at 632. 

The highly exposed individual for this path is a 1-to-6-year-old

child who ingests sewage sludge daily for a maximum of 5 years. 

See id. Accordingly, the final risk-based concentration cap for

selenium, which governs all land application of sewage sludge, is

based on the Pathway 3 scenario.

Pueblo first challenges the inclusion of selenium in the

regulations at all, on the grounds that it conflicts with an

earlier EPA profile of selenium. In 1985, the EPA issued a

preliminary analysis of selenium as part of a series assessing a

total of 32 chemicals of potential concern in sewage sludge.22

It concluded then that "[n]o human health hazard due to

Se[lenium] is expected when either sludge-amended soil or pure

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23Id. at 2-2, reprinted in J.A. at 264. 

24See id. at 2-1 to 2-2, reprinted in J.A. at 263-64. 

25Id. at i, reprinted in J.A. at 259. 

sludge is ingested."23 For some of the other pathways, it did

identify risks when sludge containing typical amounts of selenium

was applied at high rates or when sludge containing high amounts

of selenium was applied at lower rates.24 The profile explained

that it was a "rapid screening tool" and if a significant hazard

was indicated, a more detailed assessment would be undertaken.25

The final regulations cap selenium for precisely the pathway that

the profile found to present no threat: human digestion of

sewage sludge. As the EPA explained, however, the 1985 profile

was a preliminary assessment. Our task today is to evaluate the

final rule based on its underlying, more detailed, assessment. 

If the final regulation of selenium is adequately supported on

its own terms, any conflict with the earlier, preliminary

assessment is not significant. Accordingly, we now turn to

whether that conditionadequate support for the regulationis

satisfied.

With respect to the final regulation, Pueblo challenges the

risk-assessment underlying the risk-based limits on selenium in

Tables 1 and 2 as applied to Pueblo's land application practices. 

As explained above, the risk-based limit for selenium is derived

from Pathway 3human ingestion of sludge. Pueblo objects to the

use of the Pathway 3 HEIa child who ingests sewage sludge daily

for up to 5 yearsto regulate the application of sewage sludge to

"public contact sites" to which children will not have

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access"including all of the various land application sites

utilized by Pueblo," such as highway medians, roadside

cemeteries, golf courses, and industrial parks. Pueblo Brief at

14.

The EPA recognizes that public contact sites "include both

those with "a high potential for occupancy,' such as parks, and

those with "a low potential for occupancy,' including highway

medians and roadside cemeteries." EPA Brief at 48-49. 

Nevertheless, it chose "to be conservative" and define the HEI

based on sites with a high potential for occupancy. Id at 49. 

See also 1 Technical Support Document at 5-360, reprinted in J.A.

at 686.

The EPA has failed to demonstrate a rational relationship

between its highly conservative exposure assumptions and the

actual usage regulated by those assumptions. See Edison Elec.

Institute v. EPA, 2 F.3d at 446. Indeed, the EPA has

acknowledged the mis-fit, but argues that in a "rulemaking of

staggering complexity, the Agency was not required to refine its

analysis so precisely as to devise a separate exposure analysis

for children who ingest sludge on highway medians or in

cemeteries." EPA Brief at 49. Although the EPA is not held to a

standard of precise refinement, it is held to one of rationality

and it must supply a reasoned basis for its regulatory choices. 

If, as Pueblo's practices suggest, a significant proportion of

sewage sludge application involves sites with low potential for

public and child contact, then it is irrational, at least without

further explanation, to sweep these applications willy-nilly into

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26The Table 2 CPLR is the basis for the risk-based

concentration limit as well, which is used in Table 1. 

a category based on a high-child-exposure model. Accordingly, we

remand the selenium limits in Tables 1 and 2 for further

justification or modification.

B. Site-Specific Variances

Pueblo also argues that the EPA's decision not to allow

site-specific variances "effectively negated Pueblo's right

[under the Administrative Procedure Act] to petition the Agency

to amend or repeal the land application limitations for

selenium." Pueblo Brief at 19. The absence of a variance

procedure by which Pueblo could request an exemption from the

requirements, however, has no bearing on Pueblo's right to

petition the agency to amend or repeal its caps. The EPA was

within its discretion in rejecting a variance procedure because

"site-specific pollutant limits would have to be developed on a

site-by-site basis for possibly thousands of land application

sites." 58 Fed. Reg. 9309. Cf. Edison Elec. Institute v. EPA, 2

F.3d at 446 (upholding EPA's rejection of a variance mechanism). 

While a variance procedure might save a marginally overbroad

general rule, the agency was under no general duty to establish

such a procedure, and its reconsideration of the general rule on

remand will presumably remove any need for an escape hatch.

V. LEATHER INDUSTRIES' CHALLENGES TO THE

CHROMIUM CAPS

Leather Industries challenges the Table 2 risk-based

pollutant limit of 3,000 kg/ha for chromium.26 This risk-based

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27The EPA used plant growth as a proxy for crop yield. This

has not been contested. 

figure was derived from Pathway 8Sewage Sludge -> Soil ->

Plantthe most stringent pathway for chromium. Pathway 8

addresses the problem of phytotoxicity: when plants absorb

certain quantities of certain metals their yield can be sharply

reduced. The EPA determined that a pollutant would be capped at

that concentration which evidence showed would create

phytotoxicity effects leading to a more than 507 drop in plant

growth.27 Leather Industries argues that the EPA does not have

authority to regulate on the basis of phytotoxicity, and that,

even assuming it has such authority, the resulting pollutant

limit has insufficient evidentiary support. We conclude that the

EPA has authority to protect against phytotoxicity, but that it

lacks adequate support for its final limit.

A. Phytotoxicity as a Regulatory Criterion

Leather Industries first argues that the EPA does not have

statutory authority to regulate on the basis of phytotoxicity

because reduced crop yield is a purely economic concern, not a

"human health" or "environmental" concern. Leather Industries

Brief at 10-11. Leather Industries did not pursue this claim in

its reply brief or at oral argument, and we find the claim

untenable. The EPA's mandate to establish standards for

pollutants that "may be present in sewage sludge in

concentrations which may adversely affect ... the environment,"

33 U.S.C. § 1345(d)(2)(D), surely encompasses the authority to

protect crop yield, an indisputable aspect of the "environment."

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28See J.J. Morvedt & P.M. Giordano, Response of Corn to Zinc

and Chromium in Municipal Wastes Applied to Soil, 4 J. ENVTL.

QUALITY 170 (1975), reprinted in J.A. at 906. 

B. The Chromium Limit

Leather Industries offers a more compelling challenge to the

quality of the data underlying the final chromium limit. 

Modelling the phytotoxicity pathway involves two steps: (1)

determining the phytotoxicity thresholds"the concentration of

each metal in the tissue of each plant group ... associated with

50 percent reduction in biomass," ("Step 1"), 1 Technical Support

Document 5-200, reprinted in J.A. at 657; and (2) determining

the quantity of pollutant in the soil that would cause the plant

to absorb that amount of pollutant ("Step 2").

1. Step 1: Phytotoxicity Threshold

In the first stepdetermining the phytotoxicity threshold

for chromiumthe EPA relied on short-term laboratory studies to

determine the concentration of pollutant in plant tissue that

would reduce plant growth by 507. As far as we can tell, the EPA

had only one study relating to this step of the analysis for

chromium, a 1975 study of corn grown in pots containing

sludge-amended soil ("Mortvedt & Giordano Study").28 Leather

Industries argues that the EPA improperly relied on this study

because (1) some of its conclusions about the phytotoxic effects

of chromium were based on experiments using hexavalent rather

than trivalent chromium, and (2) the study assessed phytotoxicity

using pot rather than field studies.

a. Trivalent vs. Hexavalent Chromium

Chromium can exist in two states, hexavalent and trivalent. 

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29See R.J. Bartlett, "Chromium," in Penn. Agric. Experiment

Station, Penn. State Univ., Criteria and Recommendations for Land

Application of Sludges in the Northeast 49 (1985), reprinted in

J.A. at 930 ("Bartlett"). 

30Id. at 50, reprinted in J.A. at 931. 

31See id. at 50-51, reprinted in J.A. at 931-32. 

With regard to risk to human health, only hexavalent chromium is

toxic, and the EPA has "delisted" chromium in tanning industry

waste because this chromium is in the trivalent form.29 Chromium

in sewage sludge is also in the trivalent state, and the agency

so assumed in this regulatory process. See 58 Fed. Reg. 9297. 

There are two complications, however, which may nevertheless make

sewage sludge chromium an appropriate target of regulation. 

First, there is some evidence that trivalent chromium can oxidize

to hexavalent chromium. Second, there is some evidencewhich may

be related to the oxidation possibilitythat trivalent chromium

can cause phytotoxicity in plants.

As to the first complication, there are several studies

cited in the record showing that trivalent chromium can oxidize

to hexavalent chromium, though the levels of conversion appear to

be low. A survey of these studies led one scientist to conclude

that a "[trivalent chromium]-containing sludge could release low

levels of [hexavalent chromium] over a long-period of time."30

Because it is not now possible to estimate the extent of

hexavalent chromium formation, that scientist recommended

regulating all chromiumhexavalent and trivalentalike.31 As to

the second complication, the Mortvedt & Giordano study on which

the EPA relied to determine the chromium phytotoxicity threshold

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32See Mortvedt & Giordano at 173, reprinted in J.A. at 909. 

33Mortvedt & Giordano at 173-74, reprinted in J.A. at 909-

10. 

34Peer Review Report at 46, reprinted in J.A. at 56. 

found that trivalent chromium is less toxic to corn, but

nevertheless causes some phytotoxicity.32 There is, then, enough

genuine scientific debate regarding trivalent chromium's

potential harm and its potential conversion to the hexavalent

state to warrant significant discretion on the part of the agency

in its choice to use data on the harm posed by hexavalent

chromium to regulate trivalent chromium.

More important, however, from our reading of the underlying

reports, it appears that to the extent that trivalent chromium is

less toxic to plants than hexavalent chromium, it is not because

plants can absorb trivalent chromium with no harm, but because

trivalent chromium is less available for plant uptake. Thus, the

hexavalent/trivalent distinction appears to be critical to Step

2, discussed below, but not to Step 1. The Mortvedt & Giordano

study, for instance, explains that the lower toxicity of

trivalent chromium "suggests that [trivalent chromium] may have

been fixed by the soil in forms which were less available than

[hexavalent chromium] to plants."33 The Peer Review Committee

likewise explains that "[h]exavalent chromium is more soluble and

more bioavailable for plant uptake than the trivalent chromium

usually found in sludges and field soils."34

The relevant distinction between hexavalent and trivalent

chromium is that trivalent chromium is less available for plant

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uptake. This characteristicavailability for plant uptakeis not

relevant to Step 1. And in Step 2, discussed below, the EPA's

protocol requires that the uptake-based cap be based on field

studies of actual sewage sludge, so any observed uptake would

necessarily be of chromium found in sludge, in whatever form. In

other words, the apparent reason that trivalent chromium is less

toxic to plants is that it cannot get into the plant tissue, not

that it is harmless once it is in plant tissue. Therefore, we

see no problem with using trivalent and hexavalent chromium data

to determine that amount of chromium, once in, that is harmful,

so long as there is data on trivalent or sewage sludge chromium

getting in to the plant. As of now, there appears not to be, as

we discuss below.

b. Pot v. Field Studies

Leather Industries also argues that the EPA's reliance on

the Mortvedt & Giordano study was flawed because that study uses

pot, rather than field, studies. This distinction too, however,

is relevant to uptake, and thus to the second step, not the

first. Pot studies test the growth of plants in pots containing

actual sludge or soil with salt spikes. Many commenters urged to

the agency that salt or pot studies "would drastically

over-estimate plant uptake." 58 Fed. Reg. 9294. This is the

case for salt studies because metal-containing salt spikes "are

not bound to an organic matrix and are, therefore, more freely

taken up by plant roots," and for pot studies because "pots tend

to restrict the area of root growth and the small amount of

contained soil tends to concentrate and retain the sewage sludge

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35See 1 Technical Support Document at 5-200, reprinted in

J.A. at 657. 

36A.C. Chang et al., A Methodology for Establishing

Phytotoxicity Criteria for Chromium, Copper, Nickel, and Zinc in

pollutants around the roots, thus accelerating uptake." Id. The

EPA has acknowledged that salt and pot studies are inadequate to

model plant uptake and has disclaimed their use for uptake

analysis.35 The EPA did rely on pot studies for the first step,

unrelated to uptake. In this context, we see no infirmity with

pot studies, and Leather Industries has identified none.

2. Step 2: Plant Uptake

After arriving at a phytotoxicity threshold of 3.0

micrograms of chromium per gram of plant tissue, the EPA had to

determine the soil concentration of chromium in sewage sludge

that would cause plants to absorb chromium up to the

phytotoxicity threshold. The EPA looked to field studies of corn

grown on sludge-amended soil to make this determination. These

field studies, however, provided no data on plant growth in soil

with chromium levels in excess of 3,000 kg/ha. EPA Brief at 73. 

Moreover, the data the studies did provide indicated no risk of

phytotoxicity in soils with up to 3,000 kg/ha of chromium. 

Indeed, the studies showed an inverse relation between soil

concentration and plant concentration of chromium: the higher

the soil concentration of chromium, the lower the plant

concentration. As one study explains: "the probability of

exceeding the threshold is greater for plants grown in soil not

receiving any sewage sludge than for those grown in

sludge-treated soils."36

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Agricultural Land Application of Municipal Sewage Sludges, 21 J.

ENVTL. QUALITY 521, 529 (1992), reprinted in J.A. at 1039. 

37The EPA also mentions two data points showing a yield

reduction of plants grown in soil with chromium levels of 1,518

kg/ha and 3,036 kg/ha. See 2 Technical Support Document at F-46

to F-47, reprinted in J.A. at 818-19 (data points 285 and 294). 

As far as we can tell, however, this data involves plants grown

in soil containing eight different heavy metals, and does not

isolate the effect of chromium. Indeed, the EPA's cursory

mention of these data points suggests that they could not have

played any prominent role in its final regulatory choice. 

Having no other data available on the connection between

soil concentration and plant uptake, the EPA chose the 3000 kg/ha

threshold. It explained that it chose this limit because it was

"the upper boundary of the range for which EPA had data," and the

EPA "had no data indicating that chromium loading rates in excess

of 3000 kg/ha would be safe for plants." EPA Brief at 72. The

EPA further justifies this decision by explaining that "[w]hile

EPA believes that metals are bound to the sludge and thus

relatively unavailable to be "taken up' by plants, the

understanding of this process is still developing." EPA Brief at

73-74. In the face of this uncertainty, it points to "data

suggesting that chromium may not remain bound to the sludge at

high loading rates." EPA Brief at 74. This data, however, is

the Mortvedt & Giordano study, which, as explained above, used

pot studies, and the EPA has disclaimed reliance on pot studies

to model plant uptake.37 Under the EPA's own protocol, the

Mortvedt & Giordano study cannot support any conclusions about

plant uptake of chromium from sewage sludge amended soils, and

thus cannot justify an otherwise unsupported cap premised on

uptake-potential.

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In sum, the EPA's relevant evidence (1) provided no data for

chromium uptake at soil concentrations greater than 3000 kg/ha,

and (2) showed no uptake danger at a soil concentration of 3000

kg/ha or at any other concentration. Indeed, it indicated a

declining probability of plant uptake with increased soil

concentration. Based on this data, the EPA chose as the ceiling

chromium soil concentration 3000 kg/ha because that was the

highest concentration for which it had data. While the EPA "may

"err' on the side of overprotection," it "may not engage in sheer

guesswork." American Petroleum Institute, 665 F.2d at 1186-87.

VI. ADDITIONAL CLAIMS

The AMSA challenges the EPA's classification of dedicated

beneficial use sites as "surface disposal" rather than "land

application," arguing that this classification is arbitrary and

"promotes a negative public perception of dedicated sites as

"dumping grounds.' " AMSA Brief at 36. Dedicated beneficial use

sites are sites "generally owned, operated, and controlled by, or

are controlled under long-term leases to, the municipal sludge

operator." 58 Fed. Reg. 9259-60. Although dedicated sites may

be used "to produce crops, such as corn, which are sold as animal

feed or for alternative fuel production," 58 Fed. Reg. 9260, the

EPA did not classify dedicated sites as a type of land

application. The EPA explains this decision on the grounds that

dedicated sites involve the application of sludge "at greater

than agronomic rates" and public access is generally strictly

controlled, thus making it appropriate for other aspects of the

regulatory regime to differ. 58 Fed. Reg. 9259. The EPA

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acknowledges that its "distinction is one of degree, since both

land application sites and dedicated sites involve the placement

of sewage sludge on the ground." EPA Brief at 40. Indeed, land

reclamation sites, which also involve application at greater than

agronomic rates, are apparently classified as land application

sites in the final rule. See § 503.11(n), 58 Fed. Reg. 9391. 

The EPA has not explained its reason for distinguishing between

land reclamation sites and beneficial use sites. We note,

however, that while reclamation sites generally receive only one

application at greater than agronomic rates, beneficial use sites

receive repeated applications.

The EPA's reason for distinguishing beneficial use sites

from other land application practices is not entirely clear, but

the fact that these sites receive repeated applications of sludge

at greater than agronomic rates seems a plausible basis for

distinction. Where the agency's line-drawing does not appear

irrational and the AMSA has not shown that the consequences of

the line-drawing are in any respect direthe only harm it has

claimed to identify from the classification involves

unsubstantiated claims of potential public disfavorwe will leave

that line-drawing to the agency's discretion.

VII. CONCLUSION

In sum, we uphold the EPA's refusal to provide site-specific

variances and its decision to classify dedicated sites as a type

of "land disposal." We hold that the EPA has failed to

demonstrate that the 99th percentile caps in Table 3 are based on

risk, as required by the statute, and therefore remand those

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Table 3 caps. We also find that the EPA failed to establish a

rational relationship between the assumed application rate and

site life underlying the risk-based concentration caps in Table 3

and the actual usage of heat-dried sludge, which is regulated by

Table 3. As applied to heat-dried sludge, we remand those caps

as well. We further hold that the EPA failed to provide a

rational basis for applying the risk-based cap on selenium based

on high occupancy exposure assumptions to public contact sites

with low potential for occupancy. Accordingly, we remand the

Table 1 selenium cap as applied to public contact sites with low

potential for occupancy. Finally, we hold that the EPA failed to

provide evidentiary support for its Table 2 cumulative pollutant

limit on chromium, and remand that limit as well.

So ordered.

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