Maryland Department of the Environment v. County Commissioners of Carroll County, 

Maryland

No. 5, September Term 2018

Frederick County, Maryland v. Maryland Department of the Environment

No. 7, September Term 2018

Environmental Law – Administrative Law – Clean Water Act – Stormwater 

Discharge Permits – Impervious Surface Restoration. The Maryland Department of the 

Environment may lawfully include an impervious surface restoration requirement in a 

municipal separate storm sewer system (MS4) discharge permit without reference to the 

“maximum extent practicable” standard in the federal Clean Water Act for certain pollution 

controls. The Department was not arbitrary or capricious in deciding to include such a 

provision in Frederick County’s most recent MS4 permit. 33 U.S.C. §1342(p)(3)(B)(iii); 

Maryland Code, Environment Article, §9-322 et seq. 

Environmental Law – Administrative Law – Clean Water Act – Stormwater 

Discharge Permits – Scope of MS4 Permit. The Maryland Department of the 

Environment may lawfully include an impervious surface restoration requirement in a 

municipal separate storm sewer system (MS4) discharge permit when that requirement is 

derived from commitments in the State Watershed Implementation Plan that were accepted 

by the federal Environmental Protection Agency (EPA) when it adopted the Chesapeake 

Bay TMDL, which in turn allocated pollutant reductions among various sources of 

pollution for the purpose of achieving water quality standards in the Chesapeake Bay, in 

compliance with the federal Clean Water Act. To the extent that other restoration 

requirements in a permit are based on pollutant reduction allocation decisions made in other 

EPA-approved TMDLs, any challenge to those decisions should have been made in 

connection with the EPA’s approval of the TMDLs themselves and cannot be made as part 

of judicial review in State court of a permit issued by the Department. 33 U.S.C. §1342(p); 

Maryland Code, Environment Article, §§1-606, 9-322 et seq. 

Environmental Law – Administrative Law – Clean Water Act – Stormwater 

Discharge Permits – Classification of Phase I Jurisdictions. The Maryland Department 

of the Environment had authority to treat Frederick County and Carroll County as Phase I 

jurisdictions for purposes of their municipal separate storm sewer system (MS4) discharge 

permits. It was not arbitrary or capricious for the Department to classify Carroll County 

as a Phase I jurisdiction without also including Washington County in that category. 33 

U.S.C. §1342(p)(1)-(2); Maryland Code, Environment Article, §9-322 et seq.
Environmental Law – Administrative Law – Clean Water Act – Stormwater 

Discharge Permits – Water Quality Trading. A potential compliance method in a 

municipal separate storm sewer system (MS4) discharge permit could authorize the 

permittee to engage in water quality trading. Water quality trading occurs when a permittee 

takes credit for a pollution reduction accomplished by another entity that the permittee 

compensates. It was not arbitrary or capricious for the Maryland Department of the 

Environment to omit water quality trading from an MS4 permit until it had finally adopted 

regulations that it had proposed concerning that compliance method. 33 U.S.C. §1342(p); 

Maryland Code, Environment Article, §9-322 et seq.

Environmental Law – Administrative Law – Clean Water Act – Stormwater 

Discharge Permits – Permit Provision Related to Comprehensive Plan. The Maryland 

Department of the Environment included a provision in municipal separate storm sewer

system (MS4) discharge permits requiring the permittees to cooperate with other agencies 

during completion of the water resources element of the local comprehensive plan required 

by a Maryland statute. The permit provision stated that such cooperation “shall not be 

restricted by the responsibilities attributed to other entities by separate State statute, 

including but not limited to reviewing and approving plans and appropriating funds.” 

While the language of this provision is ambiguous, it does not, and could not, transfer the 

responsibilities of other agencies to the permittee. 33 U.S.C. §1342(p); Maryland Code, 

Environment Article, §9-322 et seq.; Land Use Article, §3-101 et seq. 
IN THE COURT OF APPEALS

OF MARYLAND

Nos. 5 & 7

September Term, 2018

MARYLAND DEPARTMENT OF THE ENVIRONMENT

V.

COUNTY COMMISSIONERS OF CARROLL COUNTY,

MARYLAND

FREDERICK COUNTY, MARYLAND

V.

MARYLAND DEPARTMENT OF THE ENVIRONMENT

Barbera, C.J.,

*Greene

*Adkins

McDonald

Watts

Hotten

Getty,

JJ.

Opinion by McDonald, J.

Watts, Hotten, and Getty, JJ., dissent.

Filed: August 6, 2019

 

*Greene and Adkins, JJ., now retired, 

participated in the hearing and conference of this 

case while active members of this Court; after 

being recalled pursuant to the Maryland

Constitution, Article IV, Section 3A, they also 

participated in the decision and adoption of this 

opinion.

Circuit Court for Carroll County

Case No. 06-C-15-068141

Circuit Court for Frederick County

Case No. 10-C-15-000293

Argued: September 13, 2018
In the quest to conserve a vital resource – the nation’s waters – Congress has enlisted 

the federal, state, and local governments under the Clean Water Act (“the Act”)1in a 

regulatory approach sometimes called “cooperative federalism.” This effort involves a

type of regulation that takes the form of a “permit” issued by a federal agency (or a state 

agency with federal oversight) at specified intervals to the regulated entity. Such permits 

authorize discharges of pollution into waterways, which the Act otherwise prohibits. When 

the targeted pollution is in stormwater, the permittee – i.e., the regulated entity – is often a

local government. Inevitably, as in any assignment of responsibility for solving a serious 

problem, there is disagreement as to the solution and the allocation of that responsibility. 

One way to resolve such disputes is through judicial review of the permit.

This consolidated appeal concerns judicial review of the most recent permits issued

to Carroll County and Frederick County (“the Counties”) under the Act and a parallel 

Maryland regulatory scheme. The permits regulate the discharge of polluted stormwater 

into waterways in the Chesapeake Bay watershed. The permits were developed and issued 

by the Maryland Department of the Environment (“Department”) under the supervision of

the United States Environmental Protection Agency (“EPA”), as part of an EPA-led, multistate effort to restore the Chesapeake Bay in compliance with the Act.

 

1 33 U.S.C. §1251 through §1388.
2

Both Counties raise serious issues concerning the scope of the permits, the level of 

effort required of each County, the classification of the Counties (which affects certain 

conditions in the permits), and the absence or inclusion of certain terms in the permits. 

Ultimately, we hold that the Department did not exceed its authority under State and federal 

law when it issued the permits, nor did it act arbitrarily or capriciously in including the 

challenged terms in the permits. 

I

Background

A. The Clean Water Act and Stormwater Controls for the Chesapeake Bay

The Chesapeake Bay lies between the western and eastern shores of Maryland and 

Virginia. As a recent federal court opinion has noted, its name derives from the Algonquin 

word for “great shellfish bay.” Norfolk Southern Railway Co. v. City of Roanoke, 916 F.3d 

315, 323 (4th Cir. 2019) (Wilkinson, J., concurring). While the Bay once hosted a quantity 

of fish and shellfish described as “unbelievable, ... indescribable, and ...

incomprehensible,” that is no longer the case and “[i]nstead of fish, we quantify 

phosphorus, nitrogen, sediment, and other pollutants” that threaten the health of the Bay’s

marine life. Id.

The watershed of the Chesapeake Bay – the land from which water drains into it –

covers about 64,000 square miles in six states and the District of Columbia (“the Bay 

States”), and extends from Cooperstown, New York, to Norfolk, Virginia. Pollution from 

that region contaminates the waters that feed the Bay and ultimately the Bay itself. 

“Restoring damaged waters like the Chesapeake Bay requires sustained effort, entailing 
3

cooperation and coordination among the federal government, state and local governments, 

the enterprise of the private sector, and all the people who make this region their home.” 

Norfolk Southern, 916 F.3d at 323 (internal quotation marks and citation omitted).

Federal, state, and local governments have spent decades devising programs to 

reduce the pollution that enters the Bay. This appeal concerns one such program. In any 

effort to describe a complex regulatory regime, overseen by various government agencies, 

one inevitably must become familiar with the concepts, jargon, and acronyms that define 

that effort. We begin with an overview of the key elements pertinent to this appeal.

Where Pollutants Come From – Point and Nonpoint Sources

An important distinction for purposes of the Clean Water Act is the difference

between “point sources” and “nonpoint sources” of water pollution. Point sources are 

discrete and localized, like a pipe carrying discharges from a factory or wastewater 

treatment plant.2 Nonpoint source pollution, by contrast, comes from dispersed areas like 

farms or fields where water runs off the land without being collected or channeled into a 

point source.

3

 This distinction matters for purposes of the Act because the federal statute

regulates point sources of water pollution but does not directly regulate nonpoint sources.

 

2

 A “point source” is defined as “any discernible, confined and discrete conveyance, 

including but not limited to any pipe, ditch, channel, [or other types of conveyance], from 

which pollutants are or may be discharged.” 33 U.S.C. §1362(14). 

3

“Nonpoint source” is not defined in the Act. The EPA regards a “nonpoint source” 

as “any source of water pollution that does not meet the legal definition of ‘point source’

in [the Act].” See EPA, Basic Information about Nonpoint Source (NPS) Pollution, 

https://perma.cc/QPW5-LADC.
4

Discharge Permits

The Act generally prohibits “any person”

4

from discharging pollutants from a point 

source into a waterway.

5 33 U.S.C. §1311(a). Accordingly, the statute requires a permit 

for the discharge of pollutants into a water body from a point source under specified 

conditions. The Act establishes the National Pollution Discharge Elimination System 

(“NPDES”) to govern such permits. 33 U.S.C. §1342. The EPA is authorized to issue and 

enforce these permits. 33 U.S.C. §§1319, 1342(a)(1). The EPA may also delegate that

authority to a state so long as the state’s law establishes a parallel permitting program 

consistent with the Act. 33 U.S.C. §1342(b). The EPA has delegated such authority to 

most states, including Maryland.

6

Each discharge permit in Maryland is issued under the Act and under a parallel State 

program. See Maryland Code, Environment Article (“EN”), §9-322 et seq.; COMAR 

26.08.04.07. Under Maryland law, the Department is the agency designated to issue and 

enforce these permits. EN §9-253; COMAR 26.08.04.01. Permits are generally issued for 

fixed terms of five years or less, subject to renewal. See 33 U.S.C. §1342(b)(1)(B); EN

 

4 Under the Act, “person” includes “an individual, corporation, partnership, 

association, State, municipality, commission, or political subdivision of a State, or any 

interstate body.” 33 U.S.C. §1362(5).

5

“Discharge of a pollutant” means “any addition of any pollutant to navigable 

waters from any point source [or] any addition of any pollutant to the waters of the 

contiguous zone or the ocean from any point source other than a vessel or other floating 

craft.” 33 U.S.C. §1362(12).

6 See EPA, NPDES Permits Around the Nation, https://perma.cc/2VF2-C7MK.
5

§9-328(b). As a general rule, the Act prohibits subsequent permits from containing “less 

stringent” conditions than the conditions in the previous permit – sometimes referred to as 

the “anti-backsliding prohibition” in the Act. 33 U.S.C. §1342(o).

The Act does not require permits for nonpoint sources or otherwise directly regulate 

them. Accordingly, the EPA does not regulate those sources of water pollution. States 

may do so through their own regulatory programs, as Maryland has done.

7

 The Act 

authorizes federal grants to assist the states in such efforts. 33 U.S.C. §1288.

Pollution Controls in Permits – Water Quality Standards and Effluent Limitations

Under the Act, “water quality standards” are the benchmark for clean water. For 

each water body covered by the Act, states submit water quality standards to the EPA for 

review and approval.8 The standards are to be based on the water body’s “designated use” 

(e.g., public water supply, fishing, recreational use) and include criteria necessary to 

support that use (e.g., specific limits on certain pollutant concentrations). See 33 U.S.C. 

§1313(c)(2)(A); 40 CFR §§130.3, 131.6; COMAR 26.08.02.01-.03.

 

7 The State relies on a “wide array of nonpoint source pollution control programs 

[to combat] these varied pollution sources.” Maryland Department of the Environment, 

Nonpoint Source Program (319) Management and Financial Assistance,

https://perma.cc/X6ZV-6T5E. Such programs include septic system upgrades, erosion and 

sediment control on farms, fertilizer application management, and many others. See

Maryland Department of the Environment, Maryland’s 2015-2019 Nonpoint Source 

Management Plan (updated August 4, 2016), available at https://perma.cc/RR5K-6EMB.

8

If the EPA does not approve a state-authored water quality standard, the EPA must 

establish the standard itself. 33 U.S.C. §1313(c)(4).
6

To achieve water quality standards, the Act requires that discharge permits include 

pollution controls for point sources. 33 U.S.C. §1311(b). The Act calls these controls 

“effluent limitations” – “effluent” being the material discharged by a point source.9 

Effluent limitations may be “technology based” or “water quality based.” See EPA, 

NPDES Permit Limits, https://perma.cc/L4G6-24K9; Natural Resources Defense Council 

v. EPA, 808 F.3d 556, 563 (2d Cir. 2015). 

Technology based effluent limitations are generally the first round of controls in the 

effort to achieve water quality standards. See 33 U.S.C. §1311(b)(1)(A). They “represent 

the minimum level of control that must be imposed in a permit[.]” 40 CFR §125.3(a). But 

even the most stringent technology based effluent limitations have not achieved water 

quality standards in thousands of the nation’s waterways.10 Congress anticipated this 

possibility in 1972 by retaining water quality standards “as a supplementary basis for 

effluent limitations ... so that numerous point sources, despite individual compliance with 

effluent limitations, may be further regulated to prevent water quality from falling below 

acceptable levels.” EPA v. California ex rel. State Water Resources Control Board, 426 

U.S. 200, 205 n.12 (1976). If technology based limitations do not achieve the water quality 

 

9 The term “effluent” is not defined in the Act. However, the Act defines “effluent 

limitation” as “any restriction established by a State or the [EPA] on quantities, rates, and 

concentrations of chemical, physical, biological, and other constituents which are 

discharged from point sources into navigable waters, the waters of the contiguous zone, or 

the ocean, including schedules of compliance.” 33 U.S.C. §1362(11).

10 See American Farm Bureau Federation v. EPA, 792 F.3d 281, 289-91 (3d Cir. 

2015).
7

standards, permits may include “any more stringent limitation ... necessary to meet water 

quality standards” – i.e., “water quality based effluent limitations.” 33 U.S.C. 

§1311(b)(1)(C); 40 CFR §130.7(c).11 Thus, regardless of whether a waterway is overpolluted due to point sources, nonpoint sources, or some mixture of both, the Act authorizes 

the imposition of water quality based controls on point sources, in addition to the most 

stringent technology based controls.12 

These two types of effluent limitations differ in their reference point and in their 

strategies for reducing pollution.13 For technology based limitations, the reference point is 

the source, and the strategy is to deploy pollutant-reducing technology at that source 

regardless of its contribution of pollutants to the waterway. By contrast, for water quality 

based effluent limitations, the reference point is the waterway, and the strategy is for the 

 

11 Cf. COMAR 26.08.03.01C(2)(b) (“Best available technology shall be required as 

the minimum for all permitted discharges. If it is determined that compliance with the 

established water quality standards will not be achieved through [best available 

technology], additional treatment shall be [required].”).

12 A core premise of water quality based effluent limitations in general is that 

permitting agencies may require point sources to go beyond their existing capabilities to 

achieve further pollution reductions. See Natural Resources Defense Council v. EPA, 915 

F.2d 1314, 1316-17 (9th Cir. 1990).

13 See Michael P. Healy, Still Dirty After Twenty-Five Years: Water Quality 

Standard Enforcement and the Availability of Citizen Suits, 24 Ecology L.Q. 393, 399 

(1997) (“Technology-based standards are based on the source’s technological capacity to 

control pollution, while water quality-based standards are based on the environmental 

effect of the discharged pollution.”).
8

point source to implement any additional actions (beyond the already required 

technologies) necessary to achieve the applicable water quality standard.14

The Point Sources Here – Municipal Separate Storm Sewer Systems (MS4s)

This appeal concerns permits for a type of point source known as a “municipal 

separate storm sewer system” (“MS4”).

15

 An MS4 is a network of conveyances (including

storm drains, gutters, and other drainage systems) designed to carry only stormwater (as 

opposed to a “combined sewer system” that conveys both sanitary sewage and stormwater). 

40 CFR §122.26(b)(8).

MS4s differ from typical “end-of-pipe” point sources in certain respects. A 

common point source, such as a pipe that discharges waste from a factory, usually 

discharges a known and finite set of pollutants from a specific location. By contrast, 

stormwater picks up various pollutants as it flows across widely dispersed areas, including

paved (or “impervious”) surfaces, on its way to one of the many conveyances that make up 

an MS4, and then into a waterway. The quantity of stormwater that flows through these 

 

14 See EPA, NPDES Permit Writer’s Manual (September 2010) (“EPA Permit 

Writer’s Manual”), available at https://perma.cc/P8BX-MNUY, at 5-1 (Technology based 

effluent limitations “are developed independently of the potential impact of a discharge on 

the receiving water, which is addressed through water quality standards and water qualitybased effluent limitations[.]”).

15 Shortly after the passage of the Clean Water Act in the 1970s, the question of 

whether – and if so, how – to treat MS4s as point sources under the Act generated 

regulations and litigation. The EPA initially adopted regulations exempting MS4s from 

the Act’s permit requirement. That exemption was challenged and held invalid in Natural 

Resources Defense Council v. Costle, 568 F.2d 1369, 1372-73 (D.C. Cir. 1977). 

Ultimately, Congress enacted the Water Quality Act of 1987, which explicitly established 

a discharge permit requirement for MS4s. See 33 U.S.C. §1342(p).
9

conveyances into a waterway can vary unpredictably depending on the weather, any 

development of the land (e.g., whether the land is paved), and other activities on the land

(e.g., litter, use of lawn fertilizers). 

Given these differences between an MS4 and a typical point source like a factory, a 

discharge permit for an MS4 differs from that for a typical point source. A discharge permit 

for a typical end-of-pipe point source usually sets numeric limits as effluent limitations for 

the known set of pollutants discharged from that pipe.16 Using that same approach for an 

MS4 would entail setting effluent limitations for each conveyance within the stormwater 

drainage system, which would be administratively, technically, and financially 

burdensome.17 Instead, an MS4 permit generally requires the permittee to implement

flexible management programs designed to reduce the pollution introduced into 

 

16 EPA Permit Writer’s Manual, supra note 14, Ch. 5 (explaining in detail a 

permitting agency’s process for developing technology based effluent limitations); Natural 

Resources Defense Council v. EPA, 808 F.3d 556, 567 (2d Cir. 2015) (A discharge permit 

imposes effluent limitations on a point source “based on how much technology is able to 

reduce the amount of a pollutant at issue”). 

17 See EPA, National Pollutant Discharge Elimination System Permit Application 

Regulations for Storm Water Discharges, 55 Fed. Reg. 47990, 48037-38 (November 16, 

1990) (“EPA Preamble to 1990 Phase I MS4 Rule”). The discussion of the background of 

the regulations that appears together with the notice announcing the EPA’s final adoption 

of the regulations is sometimes informally referred to as a “preamble” to the regulations.

However, it is not itself part of the regulations and does not appear in the Code of Federal 

Regulations. See James T. O’Reilly, Administrative Rulemaking §10:1 (2019 ed.).
10

stormwater, thereby limiting the amount of pollution discharged into the waterway.

18 In 

the language of the Act, an MS4 permit is to include “controls to reduce the discharge of 

pollutants to the maximum extent practicable, including management practices, control 

techniques and system, design and engineering methods, and such other provisions as the 

[EPA] or the State determines appropriate for the control of such pollutants.” 33 U.S.C.

§1342(p)(3)(B)(iii). 

Implementation of the MS4 Permit Requirement – Phase I and Phase II

The Act and related EPA regulations have applied the permit requirement to MS4s 

in two phases. The first phase (“Phase I”) took effect during the period 1987-94 and 

included stormwater systems that were serving more heavily populated areas – dubbed 

“large” and “medium” MS4s – and those that were contributing to the failure of a water 

body to meet water quality standards, irrespective of the size of the population served. See

33 U.S.C. §1342(p)(2); 40 CFR §122.26(b). Subsequently, a second phase (“Phase II”) 

covered “small” MS4s. See 33 U.S.C. §1342(p)(5)-(6); 40 CFR §122.34. As a general 

rule, permits for MS4s included in Phase I have been subject to an earlier timetable and 

more stringent conditions than permits for MS4s included in Phase II. 

 

18 See EPA Preamble to 1990 Phase I MS4 Rule, 55 Fed. Reg. at 48037-38; Natural 

Resources Defense Council v. New York State Dep’t of Envtl. Conservation, 34 N.E.3d 

782, 787 (N.Y. 2015).
11

Total Maximum Daily Load (TMDL)

An important element in determining the conditions that appear in a discharge 

permit is what is known as the “total maximum daily load” – or “TMDL.” The Clean 

Water Act does not define this phrase, but describes it as the “level” of a pollutant that a 

water body can tolerate without violating applicable water quality standards. 33 U.S.C. 

§1313(d)(1)(C). In practice, the acronym “TMDL” has come to refer to more than just a 

numeric measure of a pollutant. It has also come to refer to the process and calculations 

used to determine that level of a pollutant and its allocation among sources of the pollutant. 

The document in which an agency calculates the TMDL, in the sense of a numeric measure 

of a pollutant, and allocates that level among various sources of pollution is also sometimes 

referred to as a “TMDL.” A singularly complex example pertinent to this case is what is 

referred to as the Chesapeake Bay TMDL (“Bay TMDL”),

19 which is discussed in greater 

detail below.

The EPA has elaborated on the meaning of TMDL as a numeric measure of pollution 

in its regulations. The term “load” refers to a measure of water pollution. See 40 CFR 

§130.2(e) (defining “load” as “[a]n amount of matter or thermal energy that is introduced 

into a receiving water”). The phrase “total maximum daily load” or “TMDL” is defined in 

regulation as “the sum of” amounts of the relevant pollutant emanating from various point 

and nonpoint sources together with a “natural background” amount of the pollutant and a 

 

19 EPA, Chesapeake Bay Total Maximum Daily Load for Nitrogen, Phosphorus and 

Sediment (December 29, 2010), available at https://perma.cc/RWM2-Y22N.
12

“margin of safety.” 40 CFR §§130.2(i), 130.7(c)(1). A TMDL, in this sense, “can be 

expressed in terms of either mass per time, toxicity, or other appropriate measure....” 40 

CFR §130.2(i). To understand this definition of TMDL as a numeric measure requires an 

understanding of the TMDL process.

The TMDL process is based on the direction in the Act that each state identify

waterways for which technology based effluent limitations are not achieving water quality 

standards.20 33 U.S.C. §1313(d)(1)(A). If water quality standards are not being met in a 

waterway due to excess levels of a particular pollutant, the state is to determine the 

maximum amount of that pollutant that the waterway can receive without violating water 

quality standards – i.e., the TMDL for that pollutant as to that waterway. 33 U.S.C. 

§1313(d)(1)(C). The resulting TMDL – as a cap on the pollutant – is sometimes referred 

to as a “pollution budget” or “pollution diet.” E.g., Norfolk Southern, 916 F.3d at 324; 

Conservation Law Foundation v. EPA, 964 F. Supp. 2d 175, 179 (D. Mass. 2013). 

The EPA’s regulations recognize that, in order for a state to calculate the maximum 

level of a pollutant that a waterway can tolerate without violating water quality standards, 

a state agency must conduct a complex scientific analysis. The state agency must consider, 

among other things, the relationship between the water quality standards and the level of 

the pollutant in the waterway, the various sources of the pollutant, and the extent to which 

 

20 As indicated above, when technology based effluent limitations are inadequate to 

achieve water quality standards, discharge permits may include water quality based 

effluent limitations. 
13

each source contributes to the violation of water quality standards. See 40 CFR §130.7(c). 

As indicated earlier, in developing the TMDL for that pollutant, the agency must also factor 

in “seasonal variations and a margin of safety which takes into account any lack of 

knowledge concerning the relationship between effluent limitations and water quality.” 33 

U.S.C. §1313(d)(1)(C).

Once the agency produces its best estimate of the maximum pollutant level 

consistent with water quality standards – i.e., the TMDL in the sense of a numeric measure 

of pollution – it must then apportion that amount to the relevant sources of that pollution 

while allowing for the margin of safety required by the Act. See 40 CFR §§130.2(i), 

130.7(c). The portion assigned to each relevant point source is called a “wasteload 

allocation.” 40 CFR §130.2(h). The portion assigned to each nonpoint source is called a 

“load allocation.” 40 CFR §130.2(g). In all, therefore, the TMDL – in the sense of a 

numeric amount – for a given pollutant for a particular waterway is the sum of the 

wasteload allocations, the load allocations, the natural background, and the margin of 

safety. 40 CFR §§130.2(i), 130.7(c)(1). After a state has determined a TMDL for a 

particular pollutant with respect to a particular waterway, it is to be submitted to the EPA 

for approval. 33 U.S.C. §1313(d)(2).

When a state submits a TMDL to the EPA, the state provides not only the maximum 

pollutant amount, but also the various wasteload allocations and load allocations, together 

with an explanation of the calculations that resulted in that maximum amount and the 

allocations. EPA, Water Quality Planning and Management, 50 Fed. Reg. 1774, 1775 

(January 11, 1985) (“it is impossible to evaluate whether a TMDL is technically sound and 
14

whether it will be able to achieve [water quality] standards without evaluating component 

[wasteload and load allocations] and how these loads were calculated”). As indicated 

earlier, an example of a document that contains the separate TMDLs (in the sense of 

numeric amounts) for relevant pollutants, explains the reasoning and calculations 

underlying those caps, and allocates those totals among the relevant sources of pollution is 

the Bay TMDL.

A TMDL such as the Bay TMDL is neither self-implementing nor directly 

enforceable. Rather, it serves as an informational tool that the EPA and the states use in 

seeking to achieve the specified pollutant levels – and the applicable water quality 

standards – by means of discharge permits and other regulatory tools. See American Farm 

Bureau Federation v. EPA, 984 F. Supp. 2d 289, 297-98 (M.D. Pa. 2013), aff’d, 792 F.3d 

281 (3d Cir. 2015). To enforce the TMDL limits and corresponding water quality 

standards, agencies that issue discharge permits seek to ensure that the total pollution 

discharged by point sources does not exceed the wasteload allocations in the relevant 

TMDLs. The combined pollution allotted to all of the point sources should equal the sum 

of the wasteload allocations in a TMDL. Therefore, the discharge permit for each point 

source is to contain water quality based effluent limitations consistent with the 

“assumptions and requirements” of the wasteload allocation for that source in any

applicable TMDL. 40 CFR §122.44(d)(1)(vii)(B). 

A discharge permit may incorporate provisions related to several TMDLs. The 

permits at issue in this case incorporate provisions not only from the Bay TMDL, but also 

from TMDLs, developed by the Department and approved by the EPA, for certain
15

waterways.

21

 Appendices to the Counties’ MS4 permits list the approved TMDLs

applicable to each County. One example, which will be discussed later in this opinion, is 

the TMDL for fecal bacteria in Double Pipe Creek, whose watershed spans both Counties. 

Chesapeake Bay TMDL and Maryland Watershed Implementation Plan (WIP)

In 2009, after decades of multilateral efforts aimed at restoring the Chesapeake 

Bay,22 the EPA began the development of a Chesapeake Bay-wide TMDL.23 After 

publishing a draft for a period of public review, the EPA adopted the Bay TMDL in late 

2010.

24 The Bay TMDL establishes limits for three pollutants – nitrogen, phosphorus, and 

sediment – that threaten marine life by feeding large algae blooms that block sunlight and

 

21 See Maryland Department of the Environment, Approved TMDLs, 

https://perma.cc/99S9-C7Q3.

22 For a summary of Bay clean-up efforts over the past several decades, see Farm 

Bureau, 984 F. Supp. 2d at 298-303.

23 The EPA “established the Chesapeake Bay TMDL pursuant to a number of 

existing authorities, including the [Clean Water Act] and its implementing regulations, 

judicial consent decrees requiring EPA to address certain [waters in the Chesapeake Bay 

watershed that were failing to meet water quality standards], a settlement agreement 

resolving litigation brought by the Chesapeake Bay Foundation, the 2000 Chesapeake 

Agreement [between certain Bay states], and Executive Order 13508.” See Bay TMDL at 

1-16. That Executive Order directed the EPA to “mak[e] full use of its [Clean Water Act] 

authorities to lead a collaborative and effective federal and state effort to meet the Bay’s 

nutrient and sediment goals.” Id. at 1-17. 

24 See EPA, Clean Water Act Section 303(d): Preliminary Notice of Total Maximum 

Daily Load (TMDL) Development for the Chesapeake Bay, 74 Fed. Reg. 47792 (September 

17, 2009); EPA, Clean Water Act Section 303(d): Notice for the Establishment of the Total 

Maximum Daily Load (TMDL) for the Chesapeake Bay, 76 Fed. Reg. 549 (January 5, 2011) 

(stating that the EPA established the Bay TMDL on December 29, 2010).
16

reduce oxygen levels in the water.25 Bay TMDL at 2-6, 2-7. Specifically, the Bay TMDL 

pollutant caps are designed to satisfy water quality standards involving “aquatic life uses” 

and criteria such as water clarity and dissolved oxygen levels. Id. at 3-1, 3-2.

Given the breadth and complexity of the Bay TMDL, the EPA established a unique

accountability framework to achieve its goals. Bay TMDL at ES-8. Although the Act 

generally does not require an implementation plan for a TMDL, the EPA directed each Bay 

State to create a “Watershed Implementation Plan” (“WIP”) to reduce pollution to the 

levels set by the Bay TMDL. Each Bay State’s WIP serves two basic purposes – to break 

down the EPA’s statewide Bay TMDL pollutant allocations among geographic areas and 

among point and nonpoint sources within the state, and to identify the programs and 

policies that the state will use to achieve those pollutant reductions. The Maryland WIP 

was developed by the Department together with the Departments of Planning, Agriculture, 

and Natural Resources. Maryland’s Final Phase I Watershed Implementation Plan (Dec. 

3, 2010), available at https://perma.cc/8CMV-ENCB (“Maryland WIP”).

26 Like the other 

 

25 More precisely, the Bay TMDL divides waterways in the Chesapeake Bay 

watershed into 92 “segments,” and establishes individual TMDLs – in the sense of numeric 

amounts – for each segment for each of the three pollutants. Thus, the Bay TMDL is “an 

assemblage of 276 TMDLs: individual TMDLs for each of the 3 pollutants – nitrogen, 

phosphorus, and sediment – for each of the 92 segments (3 x 92 = 276).” Bay TMDL, at 

xiii & 2-7.

26 The EPA anticipated that each state would write its WIP in three phases. The 

State has published the first two iterations of its WIP and a draft version of the third 

iteration. See Maryland Department of the Environment, Watershed Implementation 

Plans, https://perma.cc/J985-WQ65. Citations in the text are to the first iteration of the 

WIP, often referred to as the Phase I WIP. The “phases” of the WIP should not be confused 
17

Bay State WIPs, the Maryland WIP functions as a “roadmap” for how and when the State 

will reach the pollution reduction goals set forth in the Bay TMDL. Maryland Department 

of the Environment v. Anacostia Riverkeeper, 447 Md. 88, 109 (2016). 

Implementing the Maryland WIP in MS4 Permits

The Maryland WIP listed several requirements to be included in the then-upcoming 

round of Phase I MS4 permits in Maryland. Two of these requirements correspond to terms 

in the Counties’ permits that are part of the dispute in this litigation.

First, a commitment in the Maryland WIP involves restoration of impervious 

surfaces – i.e., areas that have been paved or otherwise developed, as opposed to natural, 

undeveloped areas. Natural areas allow stormwater to soak into the ground, where 

pollutants are filtered to some extent. Impervious surfaces prevent that filtration process. 

Instead, stormwater that encounters an impervious surface rushes over it, collecting

pollutants along the way. To “restore” an impervious surface is to make it function more 

like a natural terrain that absorbs and filters rain water. Doing so accomplishes the same 

end as a direct pollutant control, like a filter or other cleansing mechanism attached to a 

conveyance. The less impervious surface that exists, the less polluted stormwater will run 

across it and into the conveyances of the MS4. Thus, as is true in general for stormwater 

management programs in MS4 permits, an impervious surface restoration requirement 

serves as a surrogate for direct pollution controls. See Anacostia Riverkeeper, 447 Md. at 

 

with the two phases of the MS4 permitting program, which will be discussed in some detail 

in Part II.D. of this Opinion. 
18

122-23. The Maryland WIP called for “[c]ompletion of restoration efforts for twenty 

percent of the [Phase I MS4] counties’ impervious surface area that is not already restored 

to the maximum extent practicable.” Maryland WIP at 5-30.

Second, another provision of the Maryland WIP refers to many applicable local 

TMDLs with stormwater wasteload allocations. For example, for the Counties, the relevant 

local TMDLs are compiled, as mentioned above, in appendices to their MS4 permits. The 

Maryland WIP requires the creation of “[s]tormwater watershed implementation plans for 

each EPA approved stormwater wasteload allocation” in the relevant local TMDLs.

Maryland WIP at 5-30. Such local watershed implementation plans are distinct from the 

overall Maryland WIP.

Maryland Stormwater Management Act

In addition to the permitting program, the State Stormwater Management Act has, 

since the mid-1980s, required local jurisdictions to implement stormwater management 

programs “to reduce as nearly as possible the adverse effects of stormwater runoff.” EN 

§4-201. Each county and municipality is to adopt ordinances necessary to implement such 

a program consistent with State law. EN §4-202. The Legislature directed the Department 

to adopt regulations governing such programs that would, among other things, indicate that 

the primary goal is “to maintain after development, as nearly as possible, the 

predevelopment runoff characteristics.” EN §4-203(b)(1); see also Anacostia Riverkeeper,

447 Md. at 110-13. The statute authorizes jurisdictions to impose and collect stormwater 

remediation fees and other charges to carry out such programs. EN §§4-202.1, 4-204; see 

also 96 Opinions of the Attorney General 61 (2011). Such fees provide “important revenue
19

needed to offset the costs of building and maintaining municipal gutters and drains, 

monitoring pollution levels, policing illegal discharges of polluted water, and educating the 

public on proper environmental practices.” Norfolk Southern, 916 F.3d at 325 (referring 

to similar local stormwater fee in Virginia).

The Carroll County and Frederick County MS4 Permits 

The Department first issued MS4 permits to Carroll County and Frederick County 

during the 1990s as part of Phase I of the MS4 permitting process, and has renewed those 

permits several times since then. The permits that are the subject of this case are Carroll 

County’s fourth and Frederick County’s third round of MS4 permits, which were both 

issued in December 2014. In accordance with State law, the Department first issued draft 

permits for public comment. See EN §1-604(a). In each case, the Department held a public 

hearing and accepted comments on the draft permit. After considering those comments, 

the Department made a Final Determination to issue each permit together with a document 

entitled “Basis for Final Determination” that provided an explanation for its action. EN 

§1-604(b). 

Pertinent to this case, the Maryland WIP commitment involving impervious surface 

restoration is incorporated into Part IV.E.2.a of each permit. This provision has two 

components. First, it requires each County to submit to the Department an “impervious 

surface area assessment” consistent with guidelines provided by the Department. That 

assessment, if approved by the Department, “shall serve as the baseline for the restoration 

efforts” required by the permit. Second, by the end of the permit term, each County “shall 

commence and complete the implementation of restoration efforts for twenty percent of 
20

the County’s impervious surface area consistent with the methodology described in [a 

Department guidance document] that has not already been restored to the” maximum extent 

practicable. 

Part IV.E.2.b of each permit includes a provision based on the commitment in the

Maryland WIP concerning local TMDLs. This provision requires each County to submit 

to the Department for approval a plan to implement each stormwater wasteload allocation 

in each relevant, EPA-approved local TMDL. Each plan must include a final date for 

“meeting applicable [wasteload allocations] and a detailed schedule for implementing all

[necessary] structural and nonstructural water quality improvement projects, enhanced 

stormwater management programs, and alternative stormwater control initiatives.” Upon 

approval by the Department, the plans become enforceable conditions of the permits. 

Two other aspects of the permits are at issue here. The first is Part VI.B of each 

permit, which requires the Counties to cooperate with other State agencies in the 

development of elements of the Counties’ comprehensive growth plans that involve 

stormwater management. The second contested aspect of the permits is the absence of an 

authorization for “water quality trading.”27 As relevant here, such trading would allow the 

Counties to earn credit for pollution reduction by paying others (whether point or nonpoint 

sources) to take pollution-reducing actions. A County might consider water quality trading

 

27 “Water quality trading” is sometimes referred to as “nutrient trading.” 
21

in situations where paying another party to achieve a pollution reduction costs less than the 

County’s own efforts to achieve a similar reduction. 

B. Procedural History

In January 2015, Carroll County sought judicial review of its 2014 MS4 permit in 

the Circuit Court for Carroll County. At the request of the parties, the matter was stayed 

for more than a year while the parties pursued settlement and while challenges to similar 

permits by environmental advocates were being litigated.28 After the stay expired, the 

Circuit Court issued an opinion dated June 26, 2017, agreeing with the County on some of 

its claims and with the Department on others. The court remanded the County’s permit to 

the Department. The Department appealed that ruling and the County filed a cross-appeal. 

In January 2015, Frederick County sought judicial review of its 2014 permit in the 

Circuit Court for Frederick County. As in the Carroll County case, the matter was stayed 

pending settlement discussions and other litigation. After the stay expired, the Circuit 

Court issued an opinion dated July 14, 2017, that largely rejected the County’s arguments, 

but remanded the permit to the Department to address what the court believed were 

ambiguities and inconsistencies in the permit’s wording. Frederick County appealed that 

ruling. 

The Court of Special Appeals consolidated the two appeals for argument. Prior to 

argument and decision in the Court of Special Appeals, the Counties asked this Court to 

 

28 This Court resolved that litigation in Maryland Department of the Environment 

v. Anacostia Riverkeeper, 447 Md. 88 (2016). 
22

grant a writ of certiorari in their respective cases. The Department agreed that the 

Counties’ petitions should be granted. This Court granted the two petitions and 

consolidated the cases for argument. 

II

Discussion

Both Counties challenge conditions set forth in their most recent MS4 permits,

although some of the bases for their challenges differ. 

Two of the alleged flaws in the permits concern the impervious surface restoration 

requirement. First, Frederick County argues that the Department exceeded its authority 

under the Clean Water Act by failing to consider “practicability” when it included the 

impervious surface restoration requirement in its permit. Frederick County bases this 

argument on a provision of the Act that requires MS4 permits to include controls to reduce 

pollution discharges “to the maximum extent practicable” – what is sometimes called the 

MEP standard. Frederick County further argues that, even if the Act allows the Department

to set the restoration requirement without regard to the MEP standard, the Department 

arbitrarily and capriciously failed to consider the County’s contention that compliance with 

the degree of restoration required by the permit is impossible. 

Second, both Counties assert that the Department exceeded its authority under the 

Act by including in the permit an impervious surface restoration requirement in which the 

baseline for measuring compliance with the requirement relates to the unrestored 

impervious surface throughout the entire County, rather than only the area served by the 

County’s MS4.
23

Both Counties argue that the Department has unlawfully treated them as Phase I 

jurisdictions for purposes of their MS4 permits – thereby subjecting them to more stringent 

permit terms required of Phase I jurisdictions than those later required of Phase II 

jurisdictions – because it incorrectly classified them in the early 1990s as “medium” 

jurisdictions based on population. Carroll County also argues that its inclusion in Phase I 

of the MS4 permitting program was arbitrary and capricious. 

Both Counties argue that the Department arbitrarily and capriciously failed to 

include water quality trading as a compliance mechanism in their permits. 

Finally, Carroll County argues that a provision in its permit that requires the County 

to cooperate with other State agencies in the development of stormwater-related aspects of 

the County’s comprehensive growth plan unlawfully imposes new obligations on the 

County.

We first discuss the standards that govern our consideration of these arguments. We 

then consider the substantive issues raised by the Counties.

A. What and How We Review

The General Assembly has provided for judicial review of permits issued by the 

Department, such as the MS4 permits issued to the Counties. EN §1-601(a)(3), (c). Such 

review is based on an administrative record that includes the various items set forth in EN 

§1-606(c).29 Judicial review begins in the circuit court pursuant to the Maryland Rules. 

 

29 Among other things, the record may include the permit application and any 

accompanying data, documents contained in the supporting file for the draft permit, 

comments submitted to the Department from the public, responses to those comments, the 
24

See Maryland Rule 7-201 et seq. (governing judicial review of administrative actions when 

a statute provides for judicial review).

In an appeal of the circuit court’s review of an agency action, an appellate court

reviews the agency’s action itself rather than the decision of the circuit court. 

Hollingsworth v. Severstal Sparrows Point, LLC, 448 Md. 648, 654 (2016). Thus, while 

the circuit court decisions here set the stage for our review and determined who would be 

appellant and appellee in our Court, we are not assessing the merits of those court decisions. 

Rather, we directly review the permits in light of the issues raised by the Counties.

1. Standards for Review of Discharge Permits

a. General Standards for Review of Agency Action

The standards for judicial review of a discharge permit – and their corresponding

levels of deference to the agency – vary depending on whether the court is reviewing an 

agency’s fact findings, discretionary decisions, or legal conclusions. See Anacostia 

Riverkeeper, 447 Md. at 118-21.

Review of Fact Findings

For fact findings, a reviewing court applies the “substantial evidence” standard, 

under which the court defers to the facts found and inferences drawn by the agency when 

the record supports those findings and inferences. Anacostia Riverkeeper, 447 Md. at 120. 

 

tape or transcript of any public hearings, and the Department’s statement of the basis for 

its determinations with respect to the permit. 
25

In particular, with respect to factual issues that involve scientific matters within an 

agency’s area of technical expertise, the agency is entitled to “great deference.” Id.

Review of Matters Committed to the Agency’s Discretion

With respect to matters committed to agency discretion, a reviewing court applies 

the “arbitrary and capricious” standard of review, which is “extremely deferential” to the 

agency. Harvey v. Marshall, 389 Md. 243, 296-99 (2005); Spencer v. Md. State Bd. of 

Pharmacy, 380 Md. 515, 529 (2004). This standard is highly contextual, but generally the 

question is whether the agency exercised its discretion “unreasonably or without a rational 

basis.” Harvey, 389 Md. at 297; Arnold Rochvarg, Maryland Administrative Law, §4.38 

at 128 (2011).

For guidance, a reviewing court may look to case law applying the similar standard

in federal administrative law. See Anacostia Riverkeeper, 447 Md. at 120-21; Office of 

People’s Counsel v. Public Service Commission, 461 Md. 380, 399 (2018).

30

 Under this 

standard, a reviewing court is not to substitute its own judgment for that of the agency and 

should affirm decisions of “less than ideal clarity” so long as the court can reasonably 

 

30 Under the federal standard, the reviewing court may consider whether: (1) the 

agency’s choice was rationally connected to the facts found; (2) the agency considered the 

relevant factors; (3) the agency made a clear error of judgment; (4) the agency relied on 

factors the legislature did not intend for it to consider; (5) the agency failed to consider an 

important aspect of the problem; (6) an explanation for the decision runs counter to the 

evidence; and (7) the decision is so implausible that it could not be ascribed to a difference 

in view or the product of agency expertise. Office of People’s Counsel, 461 Md. at 399 

n.16. 
26

discern the agency’s reasoning. Bowman Transp., Inc. v. Arkansas-Best Freight System, 

Inc., 419 U.S. 281, 285-86 (1974).

Review of the Agency’s Legal Conclusions

With respect to an agency’s legal conclusions, a reviewing court accords the agency 

less deference than with respect to fact findings or discretionary decisions. Anacostia 

Riverkeeper, 447 Md. at 122. In particular, a court will not uphold an agency action that 

is based on an erroneous legal conclusion. Id. However, in construing a law that the agency 

has been charged to administer, the reviewing court is to give careful consideration to the 

agency’s interpretation.

In construing a statute, a reviewing court applies the oft-stated approach to statutory 

construction. That is, the court seeks to ascertain legislative intent – whether that of the 

General Assembly or of Congress. That endeavor begins with the plain meaning of the 

text, keeping in mind that the plainest language is controlled by the context in which it 

appears. Kaczorowski v. Mayor & City Council of Baltimore, 309 Md. 505, 514 (1987). 

The legislative history of the statute may then be reviewed to understand the purpose of 

the legislation, resolve ambiguities, and confirm the apparent meaning of the text. Past 

case law construing a provision is, of course, also helpful. Throughout, the court must be 

mindful that the purpose is not to discern “purely judicial notions of public policy,” but 

rather legislative intent. BAA, PLC v. Acacia Mutual Life Ins. Co., 400 Md. 136, 157 

(2007). 

When a party challenges the agency’s interpretation of the statute the agency

administers, the court must assess how much weight to accord that interpretation, keeping 
27

in mind that it is “always within [the court’s] prerogative to determine whether an agency’s 

conclusions of law are correct.” Schwartz v. Md. Dep’t of Nat. Res., 385 Md. 534, 554 

(2005). The weight given an agency’s interpretation of a statute it administers depends on 

several factors. Baltimore Gas & Electric Co. v. Public Service Commission, 305 Md. 145, 

161 (1986). More weight is appropriate when the interpretation resulted from a process of 

“reasoned elaboration” by the agency, when the agency has applied that interpretation 

consistently over time, or when the interpretation is the product of contested adversarial 

proceedings or formal rule making. Id. at 161-62.

b. Effect of the Clean Water Act’s Scheme of Cooperative Federalism

In our consideration of the Department’s interpretation and application of the Clean 

Water Act, we must take into account the extent to which the EPA’s administrative 

interpretation and federal case law set parameters for the Department’s actions. The shared 

implementation of a federal policy or program by federal and state agencies is sometimes 

referred to as “cooperative federalism.” See Anacostia Riverkeeper, 447 Md. at 101. It 

can affect how a state court reviews that implementation when the state agency’s actions 

are limited by federal policies. In general, a state agency that is delegated the 

administration of the discharge permitting program under the Act is “bound to follow 

EPA’s interpretation of the [Act].” Natural Resources Defense Council v. New York State 

Dep’t of Envtl. Conservation, 34 N.E.3d 782, 794 n.16 (N.Y. 2015) (declining to entertain 
28

a challenge to an EPA regulation interpreting the Act and state agency’s compliance with 

that interpretation).31

Under the Act’s cooperative federalism scheme, the EPA has delegated the 

administration of the Act’s discharge permitting program in Maryland to the Department. 

Nonetheless, the EPA reviews and has the right to object to the Department’s draft 

discharge permits. 40 CFR §123.44 (“EPA review of and objections to State permits”); 

see also Memorandum of Agreement between EPA and Department (May 18, 1989),

available at https://perma.cc/3UNE-4CLN (explaining that the EPA will review all Stateprepared permits and may object to them). In addition, the EPA has overseen Maryland’s 

efforts (as well as those of the other Bay States) to achieve the goals of the Bay TMDL –

i.e., efforts to develop and carry out the WIPs. See Farm Bureau, 984 F. Supp. 2d at 323-

24.

 

31 See also BellSouth Telecommunications, Inc. v. Sanford, 494 F.3d 439, 449 (4th 

Cir. 2007) (state’s authority over telecommunications issue is part of deliberately 

constructed model of “cooperative federalism” under which state agency applies expertise 

and experience “subject to the boundaries set by Congress and federal regulators”); Perry 

v. Dowling, 95 F.3d 231, 236-37 (2d Cir. 1996) (a state agency’s interpretation of the 

federal Medicaid statute “warrants deference” when “the state has received prior federalagency approval to implement its plan, the federal agency expressly concurs in the state’s 

interpretation of the statute, and the interpretation is a permissible construction of the 

statute”); Aaron Saiger, Chevron and Deference in State Administrative Law, 83 Fordham 

L. Rev. 555, 581 (2014) (“State officials who deal with the environment, education, or 

antiterrorism are enmeshed in a system of regulatory federalism that often very 

substantially deprives them of freedom of action.”). 
29

c. Deference Owed to the EPA’s Construction of the Clean Water Act

In assessing the weight to be accorded the EPA’s construction of the Act, we look 

to the deference that would be accorded such interpretations under federal case law. In 

general, when an agency exercises authority to “make rules carrying the force of law” –

i.e., rulemaking, adjudications, or other actions involving similarly extensive 

administrative procedures – the agency’s interpretation warrants deference under Chevron 

U.S.A. v. Natural Resources Defense Council, 467 U.S. 837 (1984). Less formal agency 

action may also merit Chevron deference depending on “the interstitial nature of the legal 

question, the related expertise of the Agency, the importance of the question to 

administration of the statute, the complexity of that administration, and the careful 

consideration the Agency has given the question over a long period of time.” Barnhart v. 

Walton, 535 U.S. 212, 222 (2002). 

Under Chevron, a federal court first determines “whether Congress has directly 

spoken to the precise question at issue” in the pertinent statute – in this case, the Clean

Water Act. 467 U.S. at 842. If the Congressional intent is clear, the court “must give effect 

to [that] unambiguously expressed intent.” Id. at 842-43. But “if the statute is silent or 

ambiguous with respect to the specific issue,” the court must decide “whether the [EPA’s] 

answer is based on a permissible [or reasonable] construction of the statute.” Id. at 843-

44.

Even if the particular agency interpretation does not meet the criteria for Chevron

deference, a reviewing court may defer to that interpretation based on the persuasiveness 

of the agency interpretation, considering factors such as “the thoroughness evident in its 
30

consideration, the validity of its reasoning, its consistency with earlier and later 

pronouncements, and all those factors which give it power to persuade, if lacking power to 

control.” Skidmore v. Swift & Co., 323 U.S. 134, 140 (1944) (Jackson, J.).

32

 

This Court has assessed the validity of State agency actions consistent with a federal 

agency’s regulations or interpretations of a federal statute in light of these principles. See 

Anacostia Riverkeeper, 447 Md. at 142 & n.61 (citing federal administrative deference case 

law and finding an EPA policy memorandum “instructive” on interpretation of federal 

regulation under the Clean Water Act); Sugarloaf Citizens’ Ass’n v. Department of the 

Environment, 344 Md. 271, 313 (1996) (affirming Department action based in part on EPA 

interpretation of the federal Clean Air Act, which was entitled to deference under 

Chevron); Koons Ford of Baltimore, Inc. v. Lobach, 398 Md. 38, 54 (2007) (applying 

Chevron and adopting the FTC’s interpretation of a federal statute that the FTC 

administers); Montgomery Cty. v. Glenmont Hills Associates Privacy World at Glenmont 

Metro Ctr., 402 Md. 250, 271-72 (2007) (citing Chevron in adopting HUD’s interpretation 

that a federal statute did not preempt local agency action that the Court affirmed). 

 

32 If those factors sound familiar, perhaps it is because Skidmore is a direct ancestor 

of the leading case of this Court concerning the degree of judicial deference accorded to 

state agency actions. See Baltimore Gas & Electric Co. v. Public Service Commission, 305 

Md. 145, 161-62 (1986), citing and relying on Comptroller v. John C. Louis Co., 285 Md. 

527, 544 (1978), which cites and relies upon Skidmore.
31

2. Reviewability of Permit Terms Derived from TMDLs and WIP

Incorporation of TMDLs and the Maryland WIP in the Counties’ MS4 Permits

The MS4 permits at issue in this appeal incorporate or reference elements of the Bay 

TMDL, the Maryland WIP, and certain local TMDLs. That raises the question whether 

this litigation is the appropriate forum for what amounts to a challenge to those prior 

administrative actions.

The Appropriate Forum for Challenging Permit Provisions Derived from a TMDL

Carroll County argues that provisions of a TMDL that are implemented in a permit 

must be reviewable in the context of judicial review of that permit – i.e., in an action like

this one. The County reasons that, because Maryland statutory law does not provide for 

judicial review of State-authored TMDLs and because the TMDLs themselves are not selfexecuting, the only viable mode of judicial review is a challenge to a permit.

The County is correct that the Maryland Code does not provide for judicial review 

of a TMDL. The County is also correct that a TMDL is not self-executing. Farm Bureau, 

792 F.3d at 291 n.4. However, the absence of a statutory mechanism for review of a TMDL

in State court does not mean it is not reviewable in any court. The EPA’s approval of a 

state-submitted TMDL “is an act taken pursuant to the [Clean Water Act] and thus is 

subject to challenge [in federal court] under the [federal Administrative Procedure Act.]” 

Anacostia Riverkeeper, Inc. v. Jackson, 798 F. Supp. 2d 210, 222 (D.D.C. 2011). For 

example, the major case challenging the validity of the Bay TMDL was held to be ripe for 

judicial review in federal court because the “parties present[ed] a purely legal dispute on a 

well-developed record about the EPA’s process of promulgating a TMDL.” Farm Bureau, 
32

792 F.3d at 293-94. Similarly, parties challenging other state-prepared, EPA-approved 

TMDLs have obtained judicial review of the EPA’s approval of those TMDLs in federal 

court. See, e.g., Friends of Earth, Inc. v. EPA, 446 F.3d 140 (D.C. Cir. 2006); Natural

Resources Defense Council v. Muszynski, 268 F.3d 91 (2d Cir. 2001); City of Kennett v. 

EPA, 887 F.3d 424 (8th Cir. 2018).

To the extent that the Counties are challenging decisions previously made or actions 

taken in adopting an EPA-approved TMDL, judicial review of those decisions or actions

was available in federal court. Unsurprisingly, as this Court has previously indicated, an 

action for judicial review of a discharge permit in State court is not the forum for raising 

belated challenges to a TMDL that the challenger could have raised elsewhere. See

Anacostia Riverkeeper, 447 Md. at 129 n.46.33 Thus, in an action by a permittee under EN 

 

33 In Anacostia Riverkeeper, this Court cited In re City of Moscow, Idaho, 10 E.A.D. 

135, 2001 WL 988721 (EAB July 27, 2001) to illustrate this principle. Moscow was an 

opinion of the Environmental Appeals Board (“Board”), the EPA’s final decisionmaker of 

administrative appeals under the statutes that the EPA administers. In Moscow, a 

municipality pursued an administrative appeal of a discharge permit for its sewage 

treatment plant issued by the EPA. The municipality challenged, among other things, a 

term in the permit that was derived from a state-prepared TMDL for the water body into 

which the plant discharged pollutants. 2001 WL 988721 at *1, *16. The permit term 

established a “seasonal constraint” on phosphorus discharges (between May and October, 

the “normal growing season months” of algae blooms, which are fed in part by 

phosphorus). Id. at *16 n.53. 

The municipality argued, among other things, that the EPA’s decision to adopt the 

TMDL’s seasonal growth period as part of the permit was arbitrary and capricious, but the 

Board disagreed. The Board observed that the TMDL clearly specified the growth period 

and that federal regulations required that the municipality’s permit be consistent with the 

“assumptions and requirements” of the treatment plant’s wasteload allocation established 

by the TMDL. 2001 WL 988721 at *16.
33

§1-601 challenging a permit term derived from a TMDL, the permittee may not base that 

challenge on a decision that was previously made in the development of the TMDL.34

Consistent with the principle recognized in Anacostia Riverkeeper, we conclude that 

claims concerning a discharge permit that are essentially challenges to a governing TMDL

and that could have been raised in an action for judicial review of the EPA’s approval of 

 

The municipality also claimed that the TMDL’s seasonal growth period was 

inaccurate. The Board also rejected that argument, holding that the administrative appeal 

of the permit terms was not the appropriate forum for raising that claim. 2001 WL 988721 

at *17. The Board reasoned that it was authorized to review “contested permit conditions” 

but not the validity of “prior, predicate regulatory decisions that are reviewable in other 

fora,” and that the TMDL was a prior predicate regulatory decision reviewable in a federal 

district court under the federal Administrative Procedure Act. Id. at *18. The Board 

concluded that the municipality’s claim was essentially a belated challenge to 

determinations previously made in the TMDL and the EPA’s earlier decision to approve 

the TMDL – which were reviewable elsewhere. 

As this Court indicated in Anacostia Riverkeeper, that reasoning applies in actions 

to review discharge permits in Maryland courts. In Maryland, State courts are authorized 

to review a discharge permit issued by the Department, but not a TMDL on which parts of 

the permit may be predicated. Specifically, although the General Assembly has provided 

for judicial review of discharge permits in EN §1-601(c), it has not authorized judicial 

review of State-prepared TMDLs (which are not final until they receive EPA approval).

Instead, as noted in the text, the EPA’s approval of such a TMDL – necessary for it to be 

effective – may be challenged in federal court. 

34 Of course, just because something is mentioned in a TMDL does not mean that it 

would be ripe for a challenge in federal court. For example, when an environmental group 

challenged an alleged “authorization” of water quality trading in the Bay TMDL in federal 

court, the court held that the claim was not ripe because the Bay TMDL only “expected” 

or “encouraged” trading without making a final decision about it – let alone “authorizing”

it in a permit. See Food & Water Watch v. EPA, 5 F. Supp. 3d 62, 73-86 (D.D.C. 2013). 

In other words, the challenger failed to identify a final, concrete decision in the TMDL that 

was suitable for judicial review. That case illustrates that the principle identified in 

Anacostia Riverkeeper applies only to provisions of a TMDL that reflect a reviewable final 

action taken in the TMDL.
34

that TMDL cannot be raised in a judicial review action under EN §1-601.

35

 Accordingly, 

as explained further below, we will not entertain some of the Counties’ arguments that are

essentially challenges to provisions in EPA-approved TMDLs.36

B. Whether the Impervious Surface Restoration Permit Term Unlawfully Exceeds 

the MEP Standard or is Arbitrary and Capricious

The Clean Water Act, in describing provisions to be included in an MS4 permit,

refers to a standard of “maximum extent practicable” – often denominated by the acronym 

“MEP.” 33 U.S.C. §1342(p)(3)(B)(iii). Whether the MEP standard governs all provisions 

in an MS4 permit, or only certain provisions, is a matter of debate – a debate that we shall 

wade into presently. Frederick County’s flagship argument in its appeal is that the 

Department unlawfully disregarded the MEP standard and therefore exceeded its authority 

when it included the impervious surface restoration requirement in the County’s permit. 

 

35 We need not, and do not, address whether a State court would have authority to 

directly review a TMDL prepared by the Department pursuant to an administrative 

mandamus action, Maryland Rule 7-401 et seq., or otherwise.

36 Carroll County argues that the Department is “estopped” from arguing that the 

County may not challenge a provision of a TMDL incorporated in its permit. The County’s 

basis for this argument is that, in a 2003 case, the Department successfully argued that a

discharger cannot claim to have been aggrieved by a TMDL until the Department proposes 

to issue a discharge permit that includes effluent limitations based on the TMDL. See In 

re Wicomico River TMDL, No. 22-C-01-000623 (Wicomico Cty. Cir. Ct. June 13, 2003). 

The County’s argument is not without some force as the Department’s position here 

appears to contradict its argument in Wicomico River. However, the reviewability of a 

permit term is a legal question, not subject to an estoppel argument. For the reasons set 

forth in the text, it is our view that permit terms that directly implement a decision made in 

an EPA-approved TMDL are not subject to review in an action in State court challenging 

the permit.
35

The County further argues that, even if the Act allows the Department to include provisions 

in the permit without reference to the MEP standard, the impervious surface restoration 

requirement is impossible to achieve and that the Department acted arbitrarily and 

capriciously in including it in the permit. Carroll County does not join either of these 

arguments, although its permit includes an identical impervious surface restoration 

requirement.

1. The MEP Standard

Congress did not define the MEP standard in the Act and the EPA has explicitly 

declined to define it as well.37 The phrase “maximum extent practicable” suggests a 

standard that is, or is close to, the most stringent standard in a hierarchy of possible 

standards under the Act. However, in the context of the Act’s standards for pollution 

controls, that is not the case.38 To understand why, it is helpful to review the dichotomy 

between technology based and water quality based effluent limitations for point sources 

and then consider how the MEP standard relates to those limitations.

 

37 The EPA has explained that it “intentionally [has] not provided a precise 

[regulatory] definition of MEP to allow maximum flexibility in MS4 permitting.” EPA, 

National Pollutant Discharge Elimination System – Regulations for Revision of Water 

Pollution Control Program Addressing Storm Water Discharges, 64 Fed. Reg. 68722, 

68754 (December 8, 1999).

38 See Jones Creek Investors, LLC v. Columbia County, Ga., 98 F. Supp.3d 1279, 

1300 n.4 (S.D. Ga. 2015) (In the MS4 context, “[t]he phrase ‘maximum extent practicable’

is a term of art, and should not be attributed the ordinary meaning usually applied to those 

words.”); National Research Council, Urban Stormwater Management in the United States 

(The National Academies Press 2009) at 60 (“[T]he [MEP] standard for MS4s ... [is] a 

floor, not a ceiling, for permit requirements when receiving waters are impaired.”).
36

The Clean Water Act’s Hierarchy of Pollution Controls

In principle, the most that a regulatory agency can require of a point source is to do 

what is necessary to reduce pollutants to a level such that the waterway satisfies water 

quality standards. Thus, the most stringent level of control – for any point source – is strict 

compliance with water quality standards for the pertinent waterway. Given the difficulty 

of calculating and enforcing such standards, Congress in the Act chose not to “make the 

perfect the enemy of the good” and authorized the use of technology based effluent 

limitations for typical, end-of-pipe point sources. 33 U.S.C. §1311(b)(1)(A). Such 

controls achieve some pollution reduction, although often not enough to achieve water 

quality standards for the pertinent waterway. As explained above, technology based 

effluent limitations are designed from the perspective of the discharger while controls 

based on water quality standards – water quality based effluent limitations – are designed 

from the perspective of the waterway.

MEP Standard versus Water Quality Based Standard

The MEP standard is analogous to a technology based effluent limitation in that its 

reference point is the MS4 operator rather than the waterway.

39

 A water quality based 

effluent limitation is more stringent than an MEP-level control just as such a limitation is 

 

39 National Research Council, supra note 38, at 60 (grouping the MEP standard with 

“other technology-based requirements” for stormwater permittees); see also Jones Creek 

Investors, 98 F. Supp.3d at 1300 n.4 (MEP standard defined in the pertinent MS4 permits 

as “the technology-based discharge standards and controls necessary for the reduction of 

pollutants discharged from [an MS4]”).
37

more stringent than a technology based control. Despite this analogy, water quality based 

effluent limitations operate differently in end-of-pipe point source permits than they do in

MS4 permits. With an end-of-pipe point source, a technology based effluent limitation is 

typically a numeric level of pollution and the point source must install technology to ensure 

that the amount of pollution emitted from the pipe is below the specified level. A water 

quality based effluent limitation may simply ratchet down that numeric level, requiring the 

point source to come up with ways to reduce pollution further. 

With MS4s, however, there generally is no corresponding numeric cap on the 

amount of pollution discharged by each conveyance within an MS4.40 Instead, the MS4 

operator must implement the various MEP-level management programs required by its 

permit. In that context, a water quality based control is a program in addition to the MEPlevel programs. To say that water quality based controls are “more stringent” than or 

“beyond” MEP-level controls simply means that the MS4 operator must comply with the 

water quality based control in addition to the MEP-level controls. For example, Frederick 

County’s permit lists six management programs under the MEP standard. See Frederick 

County Phase I MS4 Permit MD0068357, Part IV.D.1-6. In addition to those programs, 

and under a separate section of the permit, the County is to comply with the impervious 

surface restoration requirement. Id., Part IV.E.2.a.

 

40 See Upper Missouri Waterkeeper v. Montana Dep’t of Envtl. Quality, 438 P.3d 

792, 799 (Mont. 2019) (noting that MS4 permits generally have included best management 

practices rather than numeric limits).
38

The County and the Department appear to agree that the impervious surface 

restoration requirement in the County’s permit is a water quality based control that is in 

addition to those provisions included under the MEP standard. However, the County 

asserts that the Department may not include such a term in the permit if it “goes beyond”

the MEP standard.

2. Whether an MS4 Permit Term May “Go Beyond” the MEP Standard

At first blush, this Court’s decision in Anacostia Riverkeeper seems to resolve this 

issue in the Department’s favor.

41

 In a background section of that opinion, the Court stated:

MS4s are subject to the MEP standard[.] [They] are not, however, 

required to [achieve] effluent limitations necessary to meet water 

quality standards. [But the Act] still requires Maryland to set water 

quality standards and TMDLs – subject to the EPA’s approval. 

Flowing from this obligation is the requirement that MS4s are subject 

to effluent limitations that are consistent with [wasteload allocations] 

of EPA-approved TMDLs.

 

41 The Dissenting Opinion of Judge Watts contends that the Court’s holding in 

Anacostia Riverkeeper is an “obstacle” to the Department’s position in this case and that 

the permit term in question is “incompatible” with Anacostia Riverkeeper. Watts 

Dissenting slip op. at 4-5. The Dissenting Opinion appears to have the mistaken belief that 

Anacostia Riverkeeper somehow supports Frederick County’s challenge to this permit 

term. In fact, in that case, the Court considered a permit term that appears in Phase I MS4 

permits of five other jurisdictions and that is identical to the permit term that Frederick 

County challenges here. The Court held that the term was valid and authorized by the 

Clean Water Act. 447 Md. at 122-26. If we were simply to recite the holding of Anacostia 

Riverkeeper and stop, Frederick County loses. But, in fairness to Frederick County and as 

indicated in the text, the holding in Anacostia Riverkeeper was in response to a challenge 

from a different perspective. Environmental groups argued that the permit term was 

inadequate to comply with the MEP standard. Here, Frederick County argues, from the 

opposite perspective, that the permit term unlawfully exceeds that standard. However, for 

the reasons explicated in the text, we disagree and reach the same outcome that Anacostia 

Riverkeeper did – that the permit term is valid and authorized by the Act.
39

447 Md. at 104. In other words, an MS4 permit may include, as needed, effluent limitations 

consistent with TMDL wasteload allocations, in compliance with the EPA regulation that 

requires a discharge permit for a point source to contain such effluent limitations. See 40 

CFR §122.44(d)(1)(vii)(B). Given that the impervious surface restoration requirement is 

such an effluent limitation, Anacostia Riverkeeper seems to answer the question raised by 

Frederick County – i.e., that the 20 percent impervious surface restoration requirement in 

the permit is valid and authorized by the Clean Water Act. However, in Anacostia 

Riverkeeper, the Court was addressing a question somewhat distinct from the one posed in 

this case. In that case, the question was whether the impervious surface restoration 

requirement satisfied the MEP standard whereas in this case the question is whether it 

unlawfully exceeds it. The resolution of this question requires statutory construction of the

provision in which the MEP standard appears – 33 U.S.C. §1342(p)(3)(B)(iii) – which we 

shall refer to as clause (B)(iii) for ease of reference.

Construing Clause (B)(iii) – Statutory Language

The Clean Water Act specifically addresses municipal and industrial stormwater 

discharges in 33 U.S.C. §1342(p), which consists of six paragraphs. Paragraph 3 of that 

subsection sets forth “permit requirements.”42 That paragraph reads as follows:

 

42 Paragraphs 1 and 2 concern the timing of the requirement to obtain certain 

stormwater discharge permits. Paragraph 4 concerns the application requirements for those 

permits. Paragraph 5 authorizes the EPA to conduct a study on other stormwater discharges 

not covered by those permits. Paragraph 6 authorizes the EPA to adopt regulations based 

on the study required by paragraph 5. 33 U.S.C. §1342(p)(1)-(2), (4)-(6). 
40

 (3) Permit requirements

(A) Industrial discharges

Permits for discharges associated with industrial activity shall meet 

all applicable provisions of [section 1342] and section 1311 of this 

title.

(B) Municipal discharge

Permits for discharges from municipal storm sewers—

(i) may be issued on a system- or jurisdiction-wide basis;

(ii) shall include a requirement to effectively prohibit nonstormwater discharges into the storm sewers; and

 (iii) shall require controls to reduce the discharge of pollutants 

to the maximum extent practicable, including management practices, 

control techniques and system, design and engineering methods, and 

such other provisions as the [EPA] Administrator or the State 

determines appropriate for the control of such pollutants.

33 U.S.C. §1342(p)(3). Subparagraph (A) relates to permit requirements for discharges by 

industrial sources such as factories, landfills, construction sites, and power plants that have 

operations exposed to rain water or snow melt. Subparagraph A does not directly relate to 

the requirements in MS4 discharge permits.43 

Our focus is on Subparagraph (B) concerning the requirements for MS4 permits. 

The first two clauses concern the geographic scope of an MS4 permit (clause (B)(i)) and 

 

43 See 40 CFR §122.26(b)(14) (“Storm water discharge associated with industrial 

activity means the discharge from any conveyance that is used for collecting and conveying 

storm water and that is directly related to manufacturing, processing or raw materials 

storage areas at an industrial plant.”).
41

the separation of stormwater discharges from other discharges (clause (B)(ii)), but do not 

include a reference to the MEP standard. 

Clause (B)(iii) concerns the controls and provisions required to reduce the discharge 

of pollutants from MS4s. As is evident, the MEP standard appears in this clause. The 

Department and the County disagree as to the role that the MEP standard plays in clause 

(B)(iii). 

To construe clause (B)(iii) we begin, of course, with the plain language of the 

statute. As this case illustrates, however, statutory language is not always “plain” in the 

sense that it may take on different meanings, depending on how one parses a series of 

words or clauses. The Department and Frederick County tabulate clause (B)(iii) in slightly 

different ways to support their contrary interpretations. We apply an editorial pen below 

to illustrate these different interpretations.

Frederick County’s favored construction of clause (B)(iii) can be illustrated as 

follows:

Permits for discharges from municipal storm sewers –

(iii) shall require controls to reduce the discharge of pollutants to the

maximum extent practicable, including (1) management practices, (2)

control techniques and systems, (3) design and engineering methods, 

and (4) such other provisions as the [EPA] Administrator or the State 

determines appropriate for the control of such pollutants.

Under the County’s construction, the “controls” subject to the MEP standard are listed in 

a series following the word “including” – a series of four categories that includes (1) 

management practices, (2) control techniques and systems, (3) design and engineering 

methods, and (4) such other provisions as the permitting agency deems appropriate. In that 
42

view, there are four categories of pollution controls that might be required by an MS4 

permit, including a final catchall category, and all four fall under the MEP umbrella. As 

indicated above, to support its preferred tabulation and avoid a phrase in the middle of the 

series of clauses (“system methods”) that the County claims is nonsensical, the County 

asserts that the word “system” is the result of a “typographical error” in the statute that 

needs to be corrected to “systems.”44

In contrast, the Department’s construction opts for a different tabulation, but does 

not require revision of the language of the statute. That interpretation can be illustrated as 

follows:

Permits for discharges from municipal storm sewers –

(iii) shall require (1) controls to reduce the discharge of pollutants to 

the maximum extent practicable, including (a) management practices, 

(b) control techniques and (c) system, design and engineering methods, 

and (2) such other provisions as the [EPA] Administrator or the State 

determines appropriate for the control of such pollutants.

Under this construction of the statute, the three categories of controls enumerated in the 

initial series – i.e., certain “practices,” “techniques,” and “methods” – are subject to the 

MEP standard while “other provisions” that the permitting agency deems appropriate under 

the final clause are not limited by the MEP standard. The Department’s construction does 

not require revision of the text itself, and groups items that could comfortably fit within the 

 

44 In support of its contention that the statute contains a typographical error, the 

County notes that the word “systems” appears in various documents related to stormwater 

discharge permits, including two statements made while the legislation was debated in 

Congress.
43

category of “controls” separately from the final clause’s vaguer and seemingly broader 

reference to “appropriate ... provisions.”

Confronted with similar competing grammatical arguments concerning the 

application of the MEP standard in clause (B)(iii), a state appellate court in California 

concluded that “[a]lthough it is not the clearest way of articulating the concept, the 

language of [clause (B)(iii)] does communicate the basic principle that the EPA [or an 

authorized state] retains the discretion to impose ‘appropriate’ water pollution controls in 

addition to those that come within the definition of [MEP].” Bldg. Indus. Assn. of San 

Diego Cty. v. State Water Res. Control Bd., 124 Cal. App. 4th 866, 882-83 (2004) (“BIA

case”).45 That court upheld requirements in an MS4 permit based on water quality 

standards in the face of a contention, similar to that of Frederick County in this case, that 

those provisions unlawfully exceeded the MEP standard.

Thus, the statement in Anacostia Riverkeeper in a somewhat different context and 

the assessment of the BIA court in a similar context both favor the Department’s 

construction of clause (B)(iii). We also consider what legislative history exists and the 

administrative construction of this federal statute by the federal agency charged with 

administering it – the EPA. 

 

45 See also John H. Minan, Municipal Separate Storm Sewer System (MS4) 

Regulation Under the Federal Clean Water Act: The Role of Water Quality Standards?, 42 

San Diego L. Rev. 1215, 1241-42 (2005) (discussion of grammatical argument in BIA case 

by law professor who served on the permitting agency in that case).
44

Legislative History of Clause (B)(iii)

When Congress was considering the legislation that added the MS4 permit 

requirements to the Act, legislators often spoke in general terms about achieving water 

quality standards without elaborating on the MEP standard or addressing whether that 

standard should apply to every pollutant control in an MS4 permit. Some statements 

suggested that water quality based standards – i.e., standards other than MEP – would be 

part of MS4 permits. For example, one senator stated that MS4 permit pollution control 

“requirements are to contain control technology or other techniques to control these 

discharges and should conform to water quality requirements.” 133 Cong. Rec. S733-02,

1987 WL 928615 (January 14, 1987) (statement of Senator Chafee). On the other hand, 

another senator paraphrased clause (B)(iii) in language that mirrors the County’s 

interpretation, including substituting the plural “systems” for “system.” Id. (statement of 

Senator Durenberger). Yet another member of Congress both alluded to the goal of 

controlling stormwater discharges “to protect the quality of the Nation’s waters” and in 

paraphrasing the legislation, used the word “systems.” 133 Cong. Rec. H168-03, 1987 WL 

928356 (January 8, 1987) (statement of Representative Roe). In the end, what legislative 

history exists is “not especially illuminating” on the role of the MEP standard.46 

 

46 Minan, supra, note 45, at 1243-44.
45

EPA’s Administrative Construction of Clause (B)(iii)

The EPA’s position for many years was that an MS4 permit, like any discharge 

permit, must achieve compliance with water quality standards.47 Indeed, when it adopted 

regulations for Phase I MS4 permits, the agency described the controls that would be 

required by such permits as follows: “[MS4] permits are to establish controls to the 

maximum extent practicable[,] effectively prohibit non-storm water discharges to the 

[MS4] and, where necessary, contain applicable water quality-based controls.” EPA, 

National Pollutant Discharge Elimination System Permit Application Regulations for 

Storm Water Discharges – Final Rule, 55 Fed. Reg. 47990, 47995 (November 16, 1990) 

(“EPA Preamble to 1990 Phase I MS4 Rule”) (emphasis added).

The EPA partially backed away from this view after the United States Court of 

Appeals for the Ninth Circuit held that MS4 permits need not include water quality based 

effluent limitations. See EPA, National Pollutant Discharge Elimination System –

Regulations for the Water Pollution Control Program Addressing Storm Water Discharges

- Final Rule, 64 Fed. Reg. 68722, 68753 (December 8, 1999) (“EPA Preamble to 1999 

 

47 EPA, Interim Permitting Approach for Water Quality-Based Effluent Limitations 

in Storm Water Permits, 61 Fed. Reg. 43761 (August 26, 1996); EPA, Questions and 

Answers Regarding Implementation of an Interim Permitting Approach for Water QualityBased Effluent Limitations in Storm Water Permits, 61 Fed. Reg. 57425 (November 6, 

1996); EPA, Memorandum from E. Donald Elliott, Assistant Administrator and General 

Counsel, EPA, re: Compliance with Water Quality Standards in NPDES Permits Issued to 

Municipal Separate Storm Sewer Systems (January 9, 1991) at 1; see also Oliver A. Houck, 

TMDLs III: A New Framework for the Clean Water Act’s Ambient Standards Program, 28 

Envtl. L. Rep. 10415, 10428 (1998) (discussing the EPA’s interpretation); Minan, supra,

note 45, at 1245-46 (same). 
46

Phase II MS4 Rule”) (recognizing that a Ninth Circuit decision “disagree[d] with EPA’s 

interpretation of the relationship between” §1311 and §1342(p)). Specifically, in 

Defenders of Wildlife v. Browner, 191 F.3d 1159, 1164 (9th Cir. 1999), the Ninth Circuit 

held that §1342(p)(3) “unambiguously demonstrates that Congress did not require [MS4s] 

to comply strictly with” §1311(b)(1)(C), which requires that discharge permits contain 

water quality based effluent limitations as needed.48 On the other hand, the court also stated 

that the final provision of clause (B)(iii) gives the EPA (and thus a state permitting agency)

the discretion to “determine that ensuring strict compliance with state water-quality 

standards is necessary to control pollutants [or] to require less than strict compliance with 

state water quality standards.” 191 F.3d at 1166.49 Thus, while the Ninth Circuit did not 

 

48 As noted earlier, while clause (A) of §1342(p)(3) requires industrial stormwater 

dischargers to comply with all of §1311 (i.e., with both technology based and water quality 

based effluent limitations), clause (B) lays out different requirements for MS4s without 

mentioning §1311. The Ninth Circuit reasoned that, for MS4 permits, clause (B)(iii) 

“replaces” both the technology and water quality based effluent limitation requirements in 

§1311. 191 F.3d at 1165.

49 A related question – which is not raised here and which, therefore, we do not 

address – is whether MS4 permits may require strict compliance with water quality 

standards. That question is at issue in two cases in the United States Court of Appeals for 

the District of Columbia Circuit that are currently in settlement proceedings. Center for 

Regulatory Reasonableness v. EPA, Case Nos. 17-1060 & 16-1246 (D.C. Cir.). The 

challengers in those cases argue that certain Phase II MS4 general permits issued by the 

EPA violate clause (B)(iii) by requiring compliance with water quality standards. The 

situation here is different in that no party claims that the Counties’ permits expressly

require compliance with water quality standards.
47

agree with the EPA’s existing construction, it nevertheless recognized that a permitting 

agency had discretion to include permit terms based on water quality standards.

50

In any event, after the Defenders of Wildlife decision, the EPA modified its 

administrative interpretation of clause (B)(iii). Whereas the agency had taken the view that 

MS4 permits, like all discharge permits, must contain water quality based effluent 

limitations as needed, after the Ninth Circuit decision the EPA viewed such limitations as 

permissible, but not mandatory, in MS4 permits. It cited Defenders of Wildlife as support 

for the proposition that clause (B)(iii) “specifically preserves the authority for EPA or 

[authorized states] to include other provisions determined appropriate to reduce pollutants 

in order to protect water quality.” EPA Preamble to 1999 Phase II MS4 Rule, 64 Fed. Reg. 

at 68788. Accordingly, the Phase II regulation provides that “[a]s appropriate, the permit

[for a small MS4] will include [m]ore stringent terms and conditions, including permit 

requirements ... based on an approved [TMDL] or equivalent analysis, or where the [EPA 

or state] determines such terms and conditions are needed to protect water quality.” 40 

CFR §122.34(c)(1). Although the 1999 preamble and rule concern Phase II MS4 permits, 

the EPA’s views on water quality based limitations generally apply to all MS4 permits. 

 

50 Other courts have pointed to Defenders of Wildlife as setting forth the discretion 

that the EPA (and state permitting agencies) have in drafting MS4 permit terms to require 

pollution controls that satisfy the MEP standard or a more demanding water quality based 

standard. See Natural Resources Defense Council v. New York State Dep’t Envtl 

Conservation, 994 N.Y.S. 2d 125, 135 (N.Y. App. 2014), aff’d, 34 N.E.3d 782 (N.Y. 2015); 

Conservation Law Foundation, Inc. v. Boston Water and Sewer Commission, 2010 WL 

5349854 at *5-6 (D. Mass. 2010); Tualatin Riverkeepers v. Oregon Dep’t Envtl Quality, 

230 P.3d 559, 563-64 & n.10 (Ore. App. 2010); City of Arcadia v. State Water Resources 

Control Board, 135 Cal.App. 4th 1392, 1429 (2006).
48

For example, the Defenders of Wildlife decision upheld Phase I MS4 permits issued by the 

EPA that included water quality based limitations.51

The EPA has maintained that position through at least the time period relevant for 

this litigation. In other words, since 1990, the EPA has held the view that the Act at least 

authorizes water quality based effluent limitations in MS4 permits.52 For example, in a 

letter to the Department concerning Frederick County’s permit that appears in the 

administrative record, the EPA made clear that permitting agencies may include water 

quality based effluent limitations in MS4 permits: “Where the [permitting] authority 

determines that MS4 discharges have the reasonable potential to cause or contribute to a 

water quality standard excursion as [the Department] has done in this case, EPA 

recommends that the ... permitting authority exercise its discretion to include appropriate 

narrative and/or numeric water quality-based effluent limitations ... as necessary to meet 

water quality standards.” EPA Letter to Maryland Department of the Environment re 

 

51 See In re: Arizona Municipal Storm Water NPDES Permits for City of Tucson, 

Pima County, City of Phoenix, City of Mesa, and City of Tempe, 1998 WL 284966, at *2 

n.1 (EAB May 21, 1998) (stating, in the administrative decision that was reviewed in 

Defenders of Wildlife, that the permittees were properly classified as operators of MS4s 

requiring Phase I permits).

52 In its critique of the impervious surface restoration term of the Frederick County 

MS4 permit, the Dissenting Opinion of Judge Watts discounts the EPA’s interpretation of 

the Clean Water Act which, as indicated in the text, follows the interpretation of the Act 

by the Ninth Circuit in Defenders of Wildlife. See Watts Dissenting slip op. at 11-12 & 

n.7. Given the ambiguity in clause (B)(iii), the EPA’s interpretation – which is consistent 

with the construction of the statute by the federal courts – is entitled to deference under 

Chevron (and even if the Chevron did not apply, under Skidmore). 
49

Supplemental Comments on Frederick County Phase I MS4 Permit (September 23, 2014). 

The EPA also stated that the requirement of consistency between TMDLs and permits 

applies to MS4s as it does to all point sources: “Pursuant to 40 CFR 122.44(d)(1)(vii)(B), 

where there is an applicable [TMDL] approved or established by EPA, a [discharge] permit 

must include effluent limitations that are consistent with the wasteload allocation . . . in the 

TMDL. This includes MS4 permits.” Id.

Harmonizing MS4 Permit Terms with the TMDL Process

Clause (B)(iii) is to be read harmoniously with the Act as a whole, including the 

TMDL process. See King v. St. Vincent’s Hospital, 502 U.S. 215, 221 n.10 (1991) (when 

construing statute, court should read statute as a whole and harmonize its provisions); 

Condon v. State of Maryland-Univ. of Maryland, 332 Md. 481, 491 (1993) (same). In our 

view, the EPA’s and Department’s interpretation of clause (B)(iii) is more consistent with 

the Act as a whole than the alternative proposed by Frederick County.

The EPA’s regulations require that a water quality based effluent limitation be 

derived from the applicable water quality standard, without referring to a practicability test. 

Permitting agencies “shall ensure that [t]he level of water quality to be achieved by [water 

quality based effluent limitations] on point sources ... is derived from, and complies with, 

all applicable water quality standards.” 40 CFR §122.44(d)(1)(vii)(A). The EPA’s 

rationale is that “[d]eriving water quality-based effluent limits from water quality standards 

is the only reliable method for developing water quality-based effluent limits that protect

aquatic life and human health.” EPA, National Pollutant Discharge Elimination System; 

Surface Water Toxics Control Program – Final Rule, 54 Fed. Reg. 23868, 23879 (June 2, 
50

1989) (preamble to publication of the EPA’s rule that, in part, adopted 40 CFR 

§122.44(d)(1)(vii)). Importantly, this rationale does not distinguish between types of point 

sources, i.e., whether the discharger is a factory, a wastewater treatment plant, an MS4, or 

any other kind of point source. The process of implementing TMDLs via discharge permits 

“results in effluent limits that protect aquatic life and human health because the limits are 

derived from water quality standards.” Id. In other words, when translating TMDL 

wasteload allocations to effluent limitations in a permit, the pertinent water quality standard 

remains the touchstone. Thus, when an entity discharges to a waterway subject to a TMDL, 

its permit must contain effluent limitations consistent with the “assumptions and 

requirements” of the corresponding wasteload allocation in the TMDL. 40 CFR 

§122.44(d)(1)(vii)(B).

When the final provision of clause (B)(iii) is read to encompass water quality based 

effluent limitations, MS4 permits are treated like any other discharge permit for purposes 

of implementing TMDLs. This interpretation harmonizes clause (B)(iii) with the TMDL 

provisions insofar as the latter likewise do not distinguish between types of point sources. 

By contrast, if permitting agencies must constrain all TMDL based effluent limitations in 

MS4 permits by some sort of practicability analysis, there would be tension with the basic 

tenet that water quality based effluent limitations must derive from water quality standards. 

Summary

In including the impervious surface restoration requirement in Frederick County’s 

permit, the Department acted consistently with the EPA’s interpretation of clause (B)(iii) 

– that is, that the Act authorizes permitting agencies to include water quality based effluent 
51

limitations in MS4 permits without reference to the MEP standard. As explained earlier, 

clause (B)(iii) is ambiguous. A federal court reviewing the EPA’s interpretation of an 

ambiguous federal statutory provision under Chevron would defer to the agency’s 

reasonable construction of that language. In our view, the EPA’s interpretation of clause 

(B)(iii) is a reasonable construction that is consistent with the rest of the Act and accords 

with the Ninth Circuit decision in Defenders of Wildlife and other applicable court 

decisions. Even under the less deferential Skidmore standard of review, a federal court 

would likely defer to the agency’s interpretation in light of its consistent view that MS4 

permits are subject to standards emanating from TMDLs. Moreover, the Department was 

“bound to follow EPA’s interpretation” in light of the Clean Water Act’s scheme of 

cooperative federalism. Natural Resources Defense Council v. New York State Dep’t of 

Envtl Conservation, supra. Accordingly, we hold that the Department did not act 

unlawfully in including a water quality based effluent limitation (the impervious surface 

restoration requirement) not subject to the MEP standard in the County’s permit.53

3. Whether the Inclusion of the Impervious Surface Restoration Requirement 

in Frederick County’s Permit was Arbitrary and Capricious

Frederick County also argues that, regardless of whether the Act authorizes the 

Department to include an impervious surface restoration requirement in MS4 permits

 

53 Because we hold that the Act authorizes the impervious surface restoration 

requirement in the County’s permit, we need not address the Department’s alternative 

argument that Maryland law allows such a condition as consistent with the federal Act’s 

provision allowing for more stringent state-set permit conditions. See 33 U.S.C. §1370. 
52

without reference to the MEP standard, the Department acted arbitrarily and capriciously 

when it included such a provision in the County’s permit. The County notes that, during 

the comment period on the draft permit, it submitted to the Department a report that 

purportedly demonstrated that compliance with the permit’s requirements within five years 

was financially and logistically impossible.54

As noted earlier, when agency action is challenged as arbitrary and capricious, the 

question is whether there was a rational basis for that action. See Part II.A. of this Opinion. 

In answering that question, a reviewing court is to be “extremely deferential” to the agency 

and not to substitute its own judgment for that of the agency. To assess whether the 

Department acted arbitrarily and capriciously in its consideration of Frederick County’s 

objection to the permit term, we review both the procedure that the Department followed 

and the substance of its action.

Procedure 

Consistent with EN §1-604(a), the Department first issued a “tentative 

determination” together with the draft permit on June 28, 2014. A public comment period

followed, during which the Department received many comments on the draft permit. 

After consideration of those comments, the Department published a “final determination” 

 

54 As described above, the General Assembly authorized counties to charge a 

stormwater remediation fee to help finance stormwater management and restoration 

required by MS4 permits. See EN §4-202.1. Frederick County adopted a fee of 1¢; at oral 

argument before this Court, the County explained that it had elected to use general funds 

to finance its obligations under the Clean Water Act. 
53

on December 10, 2014, along with the final permit, consistent with EN §1-604(b). See

Basis for Final Determination to Issue Frederick County’s NPDES MS4 Permit

MD0068357 (December 2014) (“Basis for Final Determination – Frederick County”). 

In general, the Environment Article gives the Department broad discretion in

replying to comments when the agency takes final action on a proposed permit. The 

Department is not obliged to respond to all public comments, but rather may “pick and 

choose” the comments it addresses. Kor-Ko Ltd. v. Maryland Dep’t of the Env’t, 451 Md. 

401, 422 n.18 (2017). The fact that an agency does not change a proposed action or 

regulation in light of comments requesting a change does not mean that the process lacked 

a meaningful opportunity for comment or that the agency failed to consider those 

comments. See Fogle v. H & G Rest., Inc., 337 Md. 441, 463 (1995). 

Substance

In its comments on the draft permit, Frederick County voiced its concerns about the 

feasibility of compliance with the impervious surface restoration requirement. The 

Department addressed Frederick County’s concerns about cost and feasibility, as well as a 

number of other issues in the Basis for Final Determination that the Department published 

with the final version of the permit.55 Basis for Final Determination – Frederick County at 

18. The Department noted that the County believed that the 20 percent restoration 

 

55 In the same document, the Department also addressed similar cost and feasibility 

“estimates” submitted by Charles County and Harford County. Basis for Final 

Determination – Frederick County at 18.
54

requirement “exceeds an MEP level of effort and that compliance would be financially and 

operationally infeasible.” Id. at 22. The Department responded to those concerns by 

explaining that the restoration requirement was necessary for consistency with the Bay 

TMDL and the Maryland WIP. Id. The Department also stated that the EPA had reviewed 

the permit for such consistency and was “satisfied” that the permit achieved it based, in 

part, on the impervious surface restoration requirement. Id. Although the Department’s 

response may not have amounted to a point-by-point refutation of every detail of the 

County’s comments, it did address the significant issues raised by the County. We cannot 

say that the Department failed to respond in a reasoned manner.

In particular, the Department had a rational basis for saying that the restoration 

requirement is necessary for consistency with the Bay TMDL and the Maryland WIP. As 

this Court recognized in Anacostia Riverkeeper, the EPA relied on the Maryland WIP, 

which included the impervious surface restoration requirement, when developing the Bay 

TMDL and the restoration requirement was a “key element” in securing EPA’s 

endorsement of the Maryland WIP. 447 Md. at 128. 

It was reasonable for the Department to respond to the County’s claim of 

impossibility by explaining that the restoration requirement derives from the Bay TMDL 

and the Maryland WIP. The Bay TMDL and Maryland WIP were the result of significant 

deliberation among various stakeholders together with the EPA and the Department. For 

example, the record shows that Frederick County and the Department had been discussing 

practicability and feasibility since at least 2012. 
55

In our view, the Department was not arbitrary or capricious in including the 

impervious surface restoration requirement in Frederick County’s MS4 permit.

C. Whether the Permits Exceed the Appropriate Geographic Scope of an MS4 Permit

Both Counties assert that their permits exceed the appropriate scope of an MS4 

permit. The Counties focus on Part IV.E. of their permits. That section of the permit 

requires the County to (1) conduct a detailed watershed assessment for the entire County; 

(2) complete restoration of 20 percent of the impervious surface area in the County; (3) 

develop and implement restoration plans for meeting applicable stormwater wasteload 

allocations in EPA-approved TMDLs; (4) conduct public outreach and encourage public 

participation in the watershed assessments, restoration plans, and achievement of the 

TMDL limits and water quality standards; and (5) evaluate and document its progress in 

meeting stormwater wasteload allocations in EPA-approved TMDLs.

The Counties argue that the Department exceeded its authority under the Clean 

Water Act in its specification of the impervious surface restoration condition and in 

requiring compliance with stormwater wasteload allocations in applicable EPA-approved 

TMDLs. To some extent, these arguments are based on making a distinction between the 

permittee – in these cases, Frederick and Carroll Counties – and the activity that is 

authorized by the permits – the discharge of pollutants by the MS4s operated in each 

County.

1. Jurisdiction-Wide versus System-Wide Permits

The Clean Water Act provides that “[p]ermits for discharges from municipal storm 

sewers may be issued on a system- or jurisdiction-wide basis.” 33 U.S.C. 
56

§1342(p)(3)(B)(i). The EPA’s regulations reiterate that a permitting authority such as the 

EPA or the Department may issue permits for Phase I MS4s on a system-wide or 

jurisdiction-wide basis. See 40 CFR §122.26(a)(1)(v) (in exercising residual designation 

authority to require Phase I permit, state or EPA may make designation on system-wide or 

jurisdiction-wide basis), 40 CFR §122.26(a)(3)(ii) (permit for a large or medium MS4 may 

be issued on system-wide basis or on a number of other bases, including with reference to 

the “jurisdiction”). Neither the statute nor the regulations elaborate on what it means for 

an MS4 permit to be issued on a “jurisdiction-wide” basis – as opposed to a “system-wide” 

basis.56 The explanation offered by the EPA at the time it adopted these regulations 

indicates that it was concerned with ensuring that permitting authorities had the necessary 

flexibility to adapt permits to local conditions such as existing administrative systems, 

police powers, and land use authority. EPA Preamble to 1990 Phase I MS4 Rule, 55 Fed. 

Reg. at 48043. 

 

56 The EPA regulations suggest that – at least with respect to a Phase I MS4 that is 

classified as “large” or “medium” – a “jurisdiction-wide” permit may cover only a portion 

of the corresponding system. See 40 CFR §122.26(a)(3)(ii) (authorizing the issuance of 

either a system-wide permit “covering all discharges from [the MS4]” or “distinct permits 

for appropriate categories of discharges within [the MS4] including, but not limited to ... 

discharges located within the same jurisdiction...”) (emphasis added). This provision does 

not concern residually designated Phase I MS4s.
57

The permits that are the subject of this appeal are each issued to a County – a 

jurisdiction – in its capacity as the operator of an MS4 – a system.57 But the challenges 

raised by the Counties cannot be resolved by the descriptive label attached to their MS4 

permits. The Counties contend that, regardless of whether a permit is issued on a systemwide or jurisdiction-wide basis, the scope of the regulatory conditions in the permit must 

relate to the discharges authorized by the permit. They argue that the baseline calculation 

for the impervious surface restoration requirement effectively makes the Counties 

responsible for pollutants carried by stormwater that does not flow into their MS4s. The 

Counties further argue that permit provisions related to stormwater wasteload allocations 

in local TMDLs also do so.

2. The Impervious Surface Restoration Requirement

Impervious surface restoration requirements have been part of MS4 permits issued 

by the Department since at least 1999. Maryland WIP at 2-26. The previous generation

of each County’s permit included an impervious surface restoration requirement of 10 

percent of each County’s unrestored impervious surface.58 

 

57 The Carroll County permit also includes, as co-permittees, all of the incorporated 

municipalities in the County and thus pertains to several jurisdictions and several systems. 

See 40 CFR §122.26(a)(3), (b)(1).

58 The general permit applicable to Phase II small MS4s also includes an impervious 

surface restoration term, although it differs from the one included in the permits of Phase 

I MS4s like the Counties. The current Phase II general permit requires restoration of 20 

percent of the unrestored impervious surface in each permittee’s urbanized area by 2025. 
58

The Impervious Surface Restoration Condition in the Current Permit

With respect to impervious surface restoration, the current permit provides:

Within one year of permit issuance, [the] County shall submit an 

impervious surface area assessment consistent with the methods 

described in the [Department] document “Accounting for Stormwater 

Wasteload Allocations and Impervious Acres Treated, Guidance for 

National Pollutant Discharge Elimination System Stormwater Permits” 

(MDE, June 2011 or subsequent versions). Upon approval by [the 

Department], this impervious surface area assessment shall serve as the 

baseline for the restoration efforts required in this permit.

By the end of this permit term, [the] County shall commence and 

complete the implementation of restoration efforts for twenty percent 

of the County’s impervious surface area consistent with the 

methodology described in the [Department] document cited in [this 

section] that has not already been restored to the MEP. Equivalent 

acres restored of impervious surfaces, through new retrofits or the 

retrofit of pre-2002 structural [best management practices], shall be 

based upon the treatment of the WQv criteria and associated list of 

practices defined in the 2000 Maryland Stormwater Design Manual. 

For alternate [best management practices], the basis for calculation of 

equivalent impervious acres restored is based upon the pollutant loads 

from forested cover.

Carroll County Phase I MS4 Permit MD0068331, Part IV.E.2.a; Frederick County Phase I 

MS4 Permit MD0068357, Part IV.E.2.a. 

On its face, this provision does not require the County to undertake impervious 

surface restoration outside the geographic area that drains to the MS4, as it does not dictate 

where such restoration must take place.

59

 But the permit provision uses unrestored 

 

59 Some permit terms specify actions within the MS4 service area. For example, 

Part IV.D. of the permit requires the County to implement certain management programs 

in “areas served by [the] County’s MS4.” Some required programs involve actions that 

are necessarily conducted on a county-wide basis, including outside the service area of the 

MS4 – e.g., an “acceptable stormwater management program” under EN §4-201 et seq., an 
59

impervious surface throughout the entire County – not just within the MS4 service area –

as a starting point, or baseline, for calculating the required restoration.60 (In the case of 

both Counties, the County’s MS4 serves only a portion of the County’s geographic area).

The Counties do not contend that the inclusion of an impervious surface restoration 

requirement itself is beyond the scope of an MS4 permit. Rather, they argue that the 

reference to a county-wide measure of impervious surface as the baseline for the 

requirement in the permit exceeds the Department’s authority. They assert that the 

reference to that baseline in a permit has the effect of making the County responsible for 

pollutants that never enter the County’s MS4. 

Anacostia Riverkeeper

This Court considered the validity of an impervious surface restoration requirement 

in Anacostia Riverkeeper. In that case, the Phase I MS4 permits in question included an 

identical term requiring the permittee counties to restore 20 percent of the unrestored 

 

“acceptable erosion and sediment control program” under EN §4-101 et seq. and a “public 

education and outreach program to reduce stormwater pollutants.” MS4 Permits, Part 

IV.D. 1, 2, 6. If the permits are modified (as sought by the Counties) to allow water quality 

trading as a compliance method, the pollution reductions for which a County would receive 

credit would not necessarily occur within the County, much less within its MS4 service 

area. See Part II.E. of this Opinion.

60 In particular, the permit term refers to restoration of 20 percent of the County’s 

impervious surface area consistent with the methodology in the Department’s guidance 

document. That methodology involves a calculation of the impervious surface area 

throughout the entire County (after excluding certain areas that are not directly at issue 

here). See Accounting for Stormwater Wasteload Allocations and Impervious Acres 

Treated (August 2014) at 1, 6-10.
60

impervious surface over the five-year period covered by their permits. The requirement 

was challenged by environmental advocacy groups as “too opaque” to satisfy the Act’s 

direction that MS4 permits include provisions to reduce pollutants that satisfy the MEP 

standard.

61

 They also argued that the Department had failed to adequately explain its use 

of the 20 percent restoration condition or how that level of restoration would achieve the 

Bay TMDL. 

This Court concluded that impervious surface restoration, as carried out in 

accordance with the Department’s Stormwater Design Manual (incorporated by reference 

in the permit term), is a stormwater management practice that functions as a “surrogate” 

for direct reduction of pollutants in stormwater and that satisfies the MEP standard. 447 

Md. at 122-23. Noting that the 20 percent restoration requirement was consistent with the 

Maryland WIP, the Court further held that the Department’s decision to include that 

requirement in the permits under review was supported by substantial evidence and was 

not arbitrary and capricious. Id. at 128-29. The Court also upheld the temporal baseline 

selected by the Department for measuring compliance with the 20 percent requirement. In 

particular, it held that the Department had not erred in using the measure of unrestored 

impervious surface in the counties in 2002 as the baseline. Id. at 132. 

In this case, the Counties also challenge the baseline used for the impervious surface 

restoration requirement. However, in contrast to Anacostia Riverkeeper, the basis of that 

 

61 The MEP standard is discussed in Part II.B. of this Opinion.
61

challenge is geographic rather than temporal.62 It is rooted in the notion that MS4 permits 

under the Act regulate discharges of pollutants only from an MS4 itself. See 33 U.S.C. 

§1342(p)(3) (setting forth permit requirements for “permits for discharges from [MS4s]”).

In the Counties’ view, use of a county-wide baseline violates that principle because some 

of the impervious surface included in that baseline is associated with pollution that never 

enters the MS4.63 According to the Counties, to be consistent with the Clean Water Act, 

an impervious surface restoration requirement must reference a baseline that includes only 

the MS4 service area.64

 

62 The Counties point out that the use of 2002 as the baseline year for assessment of 

the County’s impervious surface – instead of 1985, the baseline year in the Maryland WIP 

– would effectively increase the target amount of restoration. Use of 2002 as the baseline 

year would increase the baseline amount of impervious surface by including development 

between 1985 and 2002. (In Anacostia Riverkeeper, environmental groups had argued that 

a baseline year later than 2002 should have been used – i.e., that use of the 2002 baseline 

was too lenient). However, in arguing that they are being held responsible for pollutant 

discharges that do not emanate from their MS4s, the Counties focus on the geographical 

element of the baseline calculation.

63 This is based on the following reasoning. Obviously, rain can fall anywhere in a 

jurisdiction, such as a county, that operates an MS4. The rain will carry some pollutants 

into conveyances within the county’s MS4 and, from there, into waterways. Other 

pollutants, however, may never encounter the MS4. Instead, they will run into waterways 

directly from fields, farms, parking lots, or other land uses in the county that are out of 

reach of the MS4. Under the Act, the pollutants carried through the MS4 constitute a form 

of point source pollution, and the pollutants not carried through the system are a form of 

nonpoint source pollution (often called “stormwater runoff”). Since MS4 permits under 

the Act authorize only discharges from point sources, such a permit may only include 

conditions related to stormwater and the accompanying pollutants that enter (and are 

discharged from) the MS4, not stormwater that never encounters the MS4. See Envtl Def. 

Ctr., Inc. v. EPA, 344 F.3d 832, 841 n.8 (9th Cir. 2003). 

64 Carroll County also invokes the doctrine of offensive non-mutual collateral 

estoppel to argue that the Department is barred from using a county-wide baseline for 
62

Origin of the 20 Percent Restoration Requirement

There is no question that the pollutant discharges that the permit authorizes are those 

from each County’s MS4. As this Court noted in Anacostia Riverkeeper and as discussed 

in the previous section of this Opinion, the impervious surface restoration term is a water 

quality based effluent limitation authorized by 33 U.S.C. §1342(p)(3)(B)(iii). In particular, 

such a permit term is a numeric water quality based effluent limitation, as recognized by 

the EPA.65

 

impervious surface. In particular, the County cites a 2003 administrative decision by the 

Department’s final decisionmaker, which struck certain provisions of wastewater discharge 

permits issued to three poultry processors. Tyson Foods, Inc., et al. v. MDE, OAH Case 

No. MDE-WMA-063-200200001 (June 12, 2003). The final decisionmaker concluded 

that, under State law, the permits could not include conditions that required the processors

to undertake certain activities relating to chicken manure at the farms of those who raised 

chickens that were sold or otherwise provided to the processors, particularly when the 

growers were not co-permittees.

The Tyson Foods administrative decision did not involve an MS4 permit, much less 

an issue identical to the one in this case, and did not discuss the Clean Water Act, EPA 

regulations, or any other federal law, for that matter. Under those circumstances, the 

doctrine of offensive non-mutual collateral estoppel does not apply to determine the 

outcome of this case. See Garrity v. Maryland State Board of Plumbing, 447 Md. 359, 369 

(2016) (among other things, issue decided in prior adjudication must be identical for 

collateral estoppel to apply). The reasoning of the administrative decision in Tyson Foods

may be analogous in some respects to the argument advanced by the Counties in this case, 

but it is not dispositive.

65 See EPA, Post-Construction Performance Standards & Water Quality-Based 

Requirements: A Compendium of Permitting Approaches (June 2014) at 19 (including 

impervious surface restoration terms in Maryland MS4 permits in a list of examples of 

numeric water quality based effluent limitations); EPA, Revisions to the November 22, 

2002 Memorandum “Establishing Total Maximum Daily Load (TMDL) Wasteload 

Allocations (WLAs) for Storm Water Sources and NPDES Permit Requirements Based on 

WLAs” (November 26, 2014) at 10 (identifying an identical 20% restoration term in the 

Prince George’s County MS4 permit as a numeric water quality based effluent limitation).
63

Importantly, the amount of impervious surface to be restored is simply a surrogate 

or proxy for an amount of pollution to be reduced. The Department’s guidance document 

incorporated in the permit term explains how to calculate loads of pollution reduced, given 

a certain kind and quantity of impervious surface restoration activity. Thus, when the 

Department is determining how a county should calculate the number of impervious 

surface acres to be restored, the Department is effectively determining a measure of 

pollution reduction.

As explained earlier, the EPA’s regulations require that a water quality based 

effluent limitation be derived from applicable water quality standards, without reference to 

a practicability test. See 40 CFR §122.44(d)(1)(vii)(A). This is because “[d]eriving water 

quality-based effluent limits from water quality standards is the only reliable method for 

developing water quality-based effluent limits that protect aquatic life and human health.” 

EPA, National Pollution Discharge Elimination System: Surface Water Toxics Control 

Program – Final Rule, 54 Fed. Reg. 23868, 23879 (June 2, 1989); see also Natural 

Resources Defense Council v. Fox, 909 F. Supp. 153, 156 (S.D.N.Y. 1995).

With respect to the baseline for the impervious surface restoration requirement, 

those regulations require a permitting agency to craft the numeric component of a water 

quality based effluent limitation by reference to “all applicable water quality standards.”

40 CFR §122.44(d)(1)(vii)(A). Thus, when establishing how each County is to calculate 

the number of impervious surface acres to be restored – i.e., the proxy for an amount of 

pollution to be reduced – the Act and EPA regulations direct the Department to focus on 

what is necessary to achieve water quality standards in the Bay and the waters that feed it. 
64

In our view, the Department’s use of a county-wide baseline as a reference point for 

calculating the impervious surface restoration condition does not exceed the Department’s

authority under the Act because the impervious surface restoration condition implements a 

stormwater wasteload allocation in a TMDL (specifically, the Bay TMDL) designed to 

achieve water quality standards. Since at least 1991 the EPA has determined in various 

contexts, including regulation, that permitting authorities may make trade-offs between 

pollutant allocations for point and nonpoint sources. The EPA’s definition of TMDL 

contemplates such trade-offs. See 40 CFR §130.2(i) (“If ... nonpoint source pollution 

controls make more stringent load allocations practicable, then wasteload allocations can 

be made less stringent. Thus, the TMDL process provides for nonpoint source control 

tradeoffs.”). 

Given that the possibility of such trade-offs is inherent in the definition of TMDL, 

it is perhaps not surprising that the EPA has reiterated that concept when discussing how 

states are to develop TMDLs. See EPA, Surface Water Toxics Control Program and Water 

Quality Planning and Management Program, 57 Fed. Reg. 33040, 33048 (July 24, 1992) 

(“States have the flexibility to consider the relative costs of point and nonpoint source 

controls when preparing TMDLs, along with such other factors as reliability, relative 

effectiveness, and degree of assurance that nonpoint source controls will actually be 

implemented and maintained.”); EPA, Guidance for Water Quality-based Decisions: The 

TMDL Process (1991) at 15 (“Under the [Act], the only federally enforceable controls are 

those for point sources through the NPDES permitting process. In order to allocate loads 

among both nonpoint and point sources, there must be reasonable assurances that nonpoint 
65

source reduction will in fact be achieved. Where there are not reasonable assurances, under 

the [Act], the entire load reduction must be assigned to point sources.”). 

This long-established EPA policy is a reasonable interpretation of the Act and is 

entitled to deference under Chevron. Even if the EPA policy were not entitled to Chevron

deference under federal law, we would defer to the agency under Skidmore and our own 

standards of review. As explained at the outset of this opinion, the Act requires the 

establishment of TMDLs when an existing regime of point source pollution controls is 

inadequate to achieve water quality standards. TMDLs reflect pollutant levels necessary 

to achieve those standards in compliance with the Act. The EPA has reasonably concluded 

that permitting authorities must have the discretion to allocate pollutant loads between 

point and nonpoint sources as needed to achieve the TMDL limits, including potentially 

ratcheting up the requirements on point sources when necessary. See Farm Bureau, 984 

F. Supp.2d at 326 (in a case concerning the Bay TMDL, describing how a permit writer 

may apportion pollutant amounts – “loads” – among point and nonpoint sources in 

accordance with EPA guidance).66

 

66 In practice, the broad discretion to allocate TMDL-established pollutant amounts 

between point and nonpoint sources means that permitting agencies may impose a level of 

pollution reduction on point sources in part to help offset nonpoint source pollution. See

Michael M. Wenig, How “Total” Are “Total Maximum Daily Loads”? – Legal Issues 

Regarding the Scope of Watershed-Based Pollution Control Under the Clean Water Act, 

12 Tul. Envtl. L.J. 87, 117 & n.131 (1998) (recognizing that TMDL allocations can require 

point sources to “bear the brunt of pollution reductions necessary to achieve” TMDLs); 

Oliver A. Houck, TMDLs III: A New Framework for the Clean Water Act’s Ambient 

Standards Program, 28 ELR 10415, 10420 (August 1998) (recognizing permitting 

agencies’ option of “ratcheting down further on point sources” when setting wasteload 

allocations).
66

Thus, nonpoint source pollution reduction may be assigned to point sources – i.e., 

through wasteload allocations in the development of TMDLs. At bottom, it is this 

assignment of pollutant reductions to their wasteload allocations that is the essence of the 

Counties’ objection to the impervious surface restoration requirement in their permits.67

The Department’s use of a county-wide baseline for the impervious surface restoration

condition is thus related to the broad discretion of the states and the EPA, in drafting a 

TMDL, to assign an amount of nonpoint source pollution reduction to point sources. 

Moreover, federal regulations require that point source permits contain effluent 

limitations consistent with the “assumptions and requirements” in wasteload allocations in 

applicable TMDLs. See 40 CFR §122.44(d)(1)(vii)(B). As this Court noted in Anacostia 

Riverkeeper, this standard is flexible. 447 Md. at 135. In this case, the impervious surface 

restoration term in the Counties’ permits is consistent with the underlying premise of the 

Bay TMDL (by way of the Maryland WIP) that Maryland’s Phase I MS4 permits will 

include a corresponding impervious surface restoration requirement.

That provision underwent significant development before reaching its final form in 

the permits. For example, in accordance with the EPA regulations governing discharge 

permits and a related memorandum of understanding with the Department, the EPA 

 

67 The Maryland WIP states that the impervious surface restoration “strategy” (i.e., 

30% cumulative restoration for Phase I MS4s) is associated with a particular “load 

reduction,” i.e., a certain quantity of pollution reduction. Maryland WIP at 5-30.
67

formally objected to the Counties’ draft permits because, among other things, the 

impervious surface restoration requirement was “not adequately expressed” and did not 

achieve compliance with the Bay TMDL. See EPA, Specific Objection to Carroll County 

Phase I MS4 Permit MD0068331 (September 20, 2012); EPA, Specific Objection to 

Frederick County Phase I MS4 Permit MD0068357 (September 20, 2012). In response to 

such objections and to comply with the requirement of consistency between TMDLs and 

discharge permits, the Department adjusted the impervious surface term in the Counties’ 

permits to a form acceptable to the EPA. The EPA found the consistency requirement to 

be satisfied in the final version of the permits and withdrew its objection. EPA,

Supplemental Comments on Carroll County Phase I MS4 Permit (September 23, 2014); 

EPA, Supplemental Comments on Frederick County Phase I MS4 Permit (September 23, 

2014). 

Summary

The impervious surface restoration term in the Counties’ MS4 permits is a numeric 

water quality based effluent limitation corresponding to Maryland’s stormwater wasteload 

allocation within the Bay TMDL. As such, when crafting that limitation, the Department 

was authorized to focus on what would be necessary to achieve water quality standards, 

and the Department determined that the baseline calculation method it chose was necessary 

to achieve applicable water quality standards for the Bay. The Department did not exceed 
68

its authority under the Clean Water Act when it directed calculation of the impervious 

surface using a county-wide baseline.68

3. Restoration Requirement Related to Local TMDLs

Both Counties point to certain permit conditions that require the Counties to adopt 

restoration plans and provide reports concerning compliance with stormwater wasteload 

allocations set forth in EPA-approved TMDLs for waterways in the Counties. They argue 

that these provisions unlawfully make the Counties responsible for discharges of third 

parties. These provisions appear in Part IV.E. of each County’s permit and read as follows: 

2. Restoration Plans

* * *

b. Within one year of permit issuance, [the] County shall submit to [the 

Department] for approval a restoration plan for each stormwater 

[wasteload allocation] approved by EPA prior to the effective date of 

the permit. The County shall submit restoration plans for subsequent 

TMDL [wasteload allocations] within one year of EPA approval. Upon 

approval by [the Department], these restoration plans shall be 

enforceable under this permit. As part of the restoration plans, [the] 

County shall: 

i. Include the final date for meeting applicable [wasteload allocations] 

and a detailed schedule for implementing all structural and 

nonstructural water quality improvement projects, enhanced 

stormwater management programs, and alternative stormwater control 

initiatives necessary for meeting applicable [wasteload allocations];

ii. Provide detailed cost estimates for individual projects, programs, 

controls, and plan implementation;

 

68 Given this conclusion, we need not address whether the impervious surface 

restoration requirement is permissible as a State-determined effluent limitation that is 

“more stringent” than what the Act requires. 
69

iii. Evaluate and track the implementation of restoration plans through 

monitoring or modeling to document the progress toward meeting 

established benchmarks, deadlines, and stormwater [wasteload 

allocations]; and 

iv. Develop an ongoing, iterative process that continuously implements 

structural and nonstructural restoration projects, program 

enhancements, new and additional programs, and alternative [best 

management practices] where EPA approved TMDL stormwater 

[wasteload allocations] are not being met according to the benchmarks 

and deadlines established as part of the County’s watershed 

assessments.

* * *

4. TMDL Compliance

[The] County shall evaluate and document its progress toward meeting 

all applicable stormwater [wasteload allocations] included in EPA 

approved TMDLs. An annual TMDL assessment report with tables 

shall be submitted to [the Department]. This assessment shall include 

complete descriptions of the analytical methodology used to evaluate 

the effectiveness of the County’s restoration plans and how these plans 

are working toward achieving compliance with EPA approved TMDLs. 

[The] County shall further provide:

a. Estimated net change in pollutant load reductions from all completed 

structural and nonstructural water quality improvement projects, 

enhanced stormwater management programs, and alternative 

stormwater control initiatives;

b. A comparison of the net change in pollutant load reductions detailed 

above with the established benchmarks, deadlines, and applicable 

stormwater [wasteload allocations];

c. Itemized costs for completed projects, programs, and initiatives to meet 

established pollutant reduction benchmarks and deadlines;

d. Cost estimates for completing all projects, programs, and alternatives 

necessary for meeting applicable stormwater [wasteload allocations]; 

and
70

e. A description of a plan for implementing additional watershed 

restoration actions that can be enforced when benchmarks, deadlines, 

and applicable stormwater [wasteload allocations] are not being met or 

when projected funding is inadequate.

Carroll County Phase I MS4 Permit MD0068331, Part IV.E.2.b, IV.E.4; Frederick County 

Phase I MS4 Permit MD0068357, Part IV.E.2.b, IV.E.4.

The Counties assert that these permit terms are overbroad because some EPAapproved local TMDLs assign nonpoint source pollution to the Counties’ MS4s, which are 

point sources. Carroll County specifically cites the fecal bacteria TMDL for Double Pipe 

Creek – one of the EPA-approved local TMDLs incorporated by reference in Attachment 

B to the Carroll County permit.

69

 

The Double Pipe Creek TMDL assigns certain nonpoint source pollution – namely, 

“contributions [of fecal bacteria] from domestic animal and [septic system] sources” – to a

stormwater wasteload allocation, which includes pollution budgeted to Carroll County’s 

MS4.70 Because the permit requires the County to develop “restoration plans” to achieve 

the stormwater wasteload allocations of relevant local TMDLs, the County argues that the

permit makes the County responsible for addressing nonpoint pollution from third parties 

that never enters the County’s MS4. The County uses the Double Pipe Creek TMDL as an 

 

69 The Double Pipe Creek watershed includes parts of both Counties and is also 

incorporated in Frederick County’s permit.

70 The Double Pipe Creek TMDL distributes this nonpoint source pollution between 

Carroll County’s and Frederick County’s MS4s. 
71

example, but this argument would apply to any EPA-approved local TMDL that assigns

nonpoint source pollution to stormwater wasteload allocations.

71

This dispute concerns not so much the incorporation of EPA-approved local TMDLs 

in the permit, as the decisions that were made in the development of those TMDLs. In the 

case of the Double Pipe Creek TMDL, Carroll County is questioning a decision made when 

the EPA approved the Double Pipe Creek TMDL – namely, the decision to allocate 

pollution from nonpoint sources to the Counties’ MS4s by way of a stormwater wasteload 

allocation in the TMDL.

Frederick County argues that, like the impervious surface restoration term, the 

restoration planning requirement “unlawfully regulates stormwater beyond the scope” of 

the Department’s authority. The County bases this argument on the assertion that the local 

TMDLs “cover[] areas that do not drain to the County’s MS4.” The County provides little 

explanation for this argument, but as far as we can tell, it derives from the same concern 

raised by Carroll County – i.e., the decision made by the Department at the local TMDL 

development stage to include nonpoint source pollution within the stormwater wasteload 

allocation.

 

71 This issue is somewhat distinct from the issue discussed in the previous section 

of this Opinion concerning impervious surface restoration in that the allocations at issue 

there derived from the EPA’s reliance on the Maryland WIP in devising the Bay TMDL, 

rather than directly from the EPA-approved TMDL itself.
72

For the reasons outlined earlier in this Opinion,72 the Counties should have raised 

these arguments in a challenge to the EPA’s approval of the Double Pipe Creek TMDL and 

other, similar local TMDLs. See, e.g., City of Kennett v. EPA, 887 F.3d 424 (8th Cir. 2018) 

(municipal challenge to EPA-approved TMDL that would affect municipality’s wastewater 

permit). Therefore, we will not entertain these arguments here. See Anacostia Riverkeeper, 

447 Md. at 129 n.46.

D. Whether the Counties are Appropriately Classified as Phase I Jurisdictions

Frederick County first received an MS4 permit as a Phase I jurisdiction in 1994. It 

subsequently applied for and received a Phase I permit in 2002. In 2006, it applied for the 

Phase I permit at issue in this appeal. It first contested its status as a Phase I jurisdiction 

during the public comment period following the Department’s publication of its draft 

permit in 2014 and reiterated those arguments when it sought judicial review of the final 

2014 permit. 

Carroll County first received an MS4 permit as a Phase I jurisdiction in 1995. It 

subsequently applied for and received Phase I permits in 2000 and 2005. Unlike Frederick 

County, it did not question its status as a Phase I jurisdiction during the administrative 

process for its most recent permit, which was issued in 2014, but first contested its status 

as a Phase I jurisdiction when it sought judicial review of that permit.73

 

72 See Part II.A.2 of this Opinion.

73 The Department argues that Carroll County may not now challenge its Phase I 

classification because, unlike Frederick County, it failed to raise the issue during the public 

comment period on its draft 2014 permit. However, given that Frederick County did 
73

Both Counties argue that the Department has unlawfully treated them as Phase I 

jurisdictions because it has incorrectly classified them as “medium” (and therefore Phase 

I) – as opposed to “small” (and therefore Phase II) – MS4 jurisdictions since the time when 

they first applied for and received their first MS4 permits in the early 1990s. This 

distinction matters because, as indicated earlier, Phase I jurisdictions have generally been 

subject to earlier and more stringent permit requirements than Phase II jurisdictions. In 

particular, the Counties point to the impervious surface restoration requirement in their 

Phase I permits.

74

 As relief, both Counties seek to be re-classified as Phase II jurisdictions 

with their permit terms conformed to those that apply to Phase II MS4s.

1. Application of the MS4 Permit Requirement in Phases

Phase I MS4 Permits

In 1987, when Congress added the permit requirement for MS4s to the Clean Water 

Act, it did not require permits for all MS4 discharges immediately. Instead, it adopted a

staggered approach.

75

 This approach started with applying the permit requirement first to 

 

challenge the classification during the administrative process for its permit and that the 

issue is essentially the same for both Counties, we will not avoid the issue on the basis of 

lack of preservation.

74 The impervious surface restoration requirement is more stringent in Phase I MS4 

permits than a similar term in Phase II MS4 permits, in three ways: larger baseline (county 

wide vs. urbanized areas), earlier deadline (2019 vs. 2025), and higher percentage of area 

to be restored (30% vs. 20%).

75 Congress created this staggered approach in the Water Quality Act of 1987 by 

explicitly recognizing that all MS4 discharges were subject to the Act’s permit 

requirement, establishing a moratorium on that requirement until 1994, and then exempting 
74

discharges from systems with the greatest potential to pollute waterways, which was

referred to as Phase I. These MS4s included those serving larger populations, because 

areas with larger and denser populations tend to have more developed land with impervious 

surface and, as a result, generate more stormwater pollution.76 Also included in the first 

round were MS4s determined by the EPA or a state to be significant contributors of 

pollutants, regardless of the size of the population served by those MS4s. This statutory 

authority to issue permits based on water quality impact (as opposed to the proxy of 

population served) is often referred to as the “residual designation authority” of the EPA 

and the states. 

For our purposes, the relevant Phase I categories77 are the following:

(1) Large MS4. A discharge from an MS4 serving a population of 

250,000 or more, referred to in the statute as a “large MS4.” 33 

U.S.C. §1342(p)(2)(C), (p)(4)(A).

(2) Medium MS4. A discharge from an MS4 serving a population of 

100,000 or more but less than 250,000, referred to in the EPA’s 

 

certain discharges from that moratorium at various intervals. See 33 U.S.C. §1342(p)(1)-

(2). As a result, the permit requirement was imposed on MS4s in stages. 

76 Population served as a proxy for the amount of pollution in stormwater because 

“discharges from [MS4s] serving larger populations are thought to present a higher 

potential for contributing to adverse water quality impacts.... [P]ollutant loads from urban 

runoff strongly depend on the total area and imperviousness of developed land, which in 

turn is related to population.” EPA Preamble to 1990 Phase I MS4 Rule, 55 Fed. Reg. at

48038.

77 In all, Phase I covered five categories of MS4 stormwater discharges. See 33 

U.S.C. §1342(p)(1)-(2). The other two Phase I categories are discharges for which a permit 

had been issued before 1987 and discharges associated with industrial activity – neither of 

which is at issue in this appeal. 33 U.S.C. §1342(p)(2)(A)-(B).
75

regulations as a “medium MS4.” 33 U.S.C. §1342(p)(2)(D); 40 

CFR §122.26(a)(1)(iv).

(3) Residually Designated MS4. A discharge for which the EPA or a

state “determines that the stormwater discharge contributes to a 

violation of a water quality standard or is a significant contributor 

of pollutants to waters of the United States.” 33 U.S.C. 

§1342(p)(2)(E).

The EPA adopted regulations in 1990 setting forth the permit requirements for Phase I 

jurisdictions. EPA, National Pollutant Discharge Elimination System Permit Application 

Regulations for Storm Water Discharges – Final Rule, 55 Fed. Reg. 47990 (November 16, 

1990), codified in 40 CFR §122. Other than establishing different deadlines for the 

submission of permit applications by large and medium jurisdictions, the regulations 

generally did not distinguish among these three categories of Phase I MS4s. See 40 CFR

§122.26(d).

Thus, in the early 1990s, an MS4 operated by a local government, like those of the 

Counties, would be required to obtain a Phase I permit if: (1) the MS4 served 100,000 or 

more people based on census figures, or (2) the EPA or the state had classified the MS4 as 

a Phase I jurisdiction under the residual designation authority. 

Phase II MS4 Permits

The Phase II round of MS4 permits covered stormwater discharges other than the

Phase I categories. 33 U.S.C. §1342(p)(6). Included in Phase II are MS4s serving fewer 

than 100,000 people, referred to as “small” MS4s. In 1999, the EPA adopted regulations

setting forth permit requirements for small MS4s. See EPA Preamble to 1999 Phase II 
76

MS4 Rule; see also 40 CFR §122.34.78 Those regulations provided deadlines for initial 

Phase II permit applications at various intervals during the early 2000s.

2. Population Classification for Purposes of Phase I

As noted above, the Clean Water Act classifies MS4s according to the population 

served by the MS4. The statute does not define what it means for an MS4 to “serve” a 

population of a given size. In carrying out its statutory charge to adopt regulations on MS4 

permit requirements,79 the EPA defined “medium” MS4s as falling into one of four 

subcategories. The most relevant here included systems comprising storm sewers that are:

(i) Located in an incorporated place with a population of 100,000 or 

more but less than 250,000, as determined by the latest Decennial 

Census by the Bureau of the Census (appendix G); or

(ii) Located in the counties listed in appendix I, except municipal 

separate storm sewers that are located in the incorporated places, 

townships or towns within such counties;

40 CFR §122.26(b)(7)(i)-(ii) (as adopted in 1990). Like the statute, the regulations on their 

face appear to use as a reference point the total population of the particular jurisdiction 

without attempting to refine that number according to the portion of the population that 

lives or works within the area “served” by the MS4.

 

78 For reasons not relevant here, the 1999 small MS4 regulations were remanded 

and reissued in 2016. See Envtl. Def. Ctr., Inc. v. EPA, 344 F.3d 832 (9th Cir. 2003)

(remanding the 1999 regulations); EPA, National Pollutant Discharge Elimination System 

(NPDES) Municipal Separate Storm Sewer System General Permit Remand Rule, 81 Fed. 

Reg. 89320 (December 9, 2016).

79 33 U.S.C. §1342(p)(4).
77

Appendix I, referenced in the second subcategory of the regulation, listed 32

counties and was entitled “Counties With Unincorporated Urbanized Areas Greater Than 

100,000, But Less Than 250,000 According to the Latest Decennial Census by the Bureau 

of the Census” (emphasis added). As is evident, the title of Appendix I refers not only to 

“unincorporated” areas, but also to “urbanized” areas – a term that does not appear in the 

statute or otherwise in the EPA’s regulations. 

In explanatory material that accompanied the 1990 publication of the Phase I 

regulations – what is sometimes referred to informally as a “preamble” to such a 

publication80 – the agency elaborated on its conception of the second subcategory. It stated 

that the second subcategory was meant to capture MS4s in “counties having areas that are 

designated as urbanized areas by the latest decennial Bureau of Census estimates and where 

the population of such areas exceeds 100,000 [but is less than 250,000], after the population 

in the incorporated places, townships or towns within such counties is excluded.” EPA 

Preamble to 1990 Phase I MS4 Rule, 55 Fed. Reg. at 48039.

81

 As defined by the Census 

Bureau, the term “urbanized” generally refers to “high density development.” Id. at 48041 

n.5. 

 

80 See note 17 above.

81 An EPA guidance document issued shortly after adoption of the Phase I 

regulations similarly stated the “medium” MS4 category included “Counties with census 

designated urbanized areas that have a population greater than [or] equal to 100,000 but 

less than 250,000 after incorporated areas, towns, and townships within such counties are 

excluded.” EPA, Guidance Manual for the Preparation of Part 1 of MS4 Permit 

Applications (April 1991) at 9 (emphasis added).
78

In its initial iteration in connection with the regulations adopted in 1990, Appendix

I listed jurisdictions in the second subcategory based on figures from the 1980 census – at 

that time “the latest decennial census” – as did Appendix G with respect to jurisdictions in 

the first subcategory. In 1999, at the same time that the EPA adopted regulations governing 

Phase II MS4 permits, the agency also updated Appendix I (as well as Appendix G) based 

on the 1990 census – which was then “the latest decennial census.” But the EPA also

amended the regulation concerning “medium” population jurisdictions to refer specifically 

to the 1990 census and deleted the reference to the “latest” census. The agency stated that 

it would not continue to update those appendices based on later decennial censuses. In the 

preamble to the publication of those regulations and amendments, the EPA explained that 

it was “freezing” the regulatory definition and listing based on the 1990 census because all 

the covered MS4s had already applied for permits and “the deadlines from the existing 

regulations have lapsed.”82 EPA Preamble to 1999 Phase II MS4 Rule, 64 Fed. Reg. at

68838, 68848-49. The EPA further explained that MS4s that later met the definition of a 

“medium” jurisdiction could be made subject to the Phase I requirements by the permitting 

agency, alluding to the agency’s residual designation authority under the Act. Id. at 68749 

(“the permitting authority can always require more from operators of MS4s serving ‘newly 

over 100,000’ populations”); see also EPA, National Pollutant Discharge Elimination 

 

82 As noted earlier, at that time, Carroll and Frederick Counties were among those 

operators of MS4s that, at the behest of the Department, had already applied for, and 

received, Phase I permits, although they were not listed in Appendix I.
79

System – Proposed Regulations for Revision of the Water Pollution Control Program 

Addressing Storm Water Discharges, 63 Fed. Reg. 1536-01, 1567 (January 9, 1998). 

3. Residual Designation Authority

Factors for Designation and Procedural Requirements

As indicated above, the Act authorizes the EPA, or the pertinent state agency, to 

require that an MS4 obtain a Phase I permit if the agency “determines that the [MS4]

contributes to a violation of a water quality standard or is a significant contributor of 

pollutants....” 33 U.S.C. §1342(p)(2)(E). In its Phase I permit regulations, the EPA 

identified the following factors that could affect such a determination: the location of the 

discharge, the size of the discharge, the nature and quality of the pollutants, and “other 

relevant factors.” 40 CFR §122.26(a)(1)(v). Those regulations also specified certain 

procedures that would be followed by the EPA when the EPA itself made such a 

determination (as well as other types of case-by-case determinations). See 40 CFR 

§124.52.83 No particular procedure was required of a state agency that made such a 

determination.84 The parties have not presented – and we have not been able to identify –

 

83 In the context of a citizen petition to the EPA to exercise its residual designation 

authority, the EPA may issue a formal document concerning the water quality impacts by 

a stormwater discharger. See Conservation Law Foundation, Inc. v. Pruitt, 881 F.3d 24, 

32 (1st Cir. 2018). However, the EPA’s practice in that context does not establish any 

particular requirement for state agencies.

84 The regulation requires the EPA Regional Administrator to send written notice of 

a designation by the Regional Administrator to the MS4, accompanied by an application 

form for a Phase I permit. The regulations further provide that the propriety of the 
80

any further procedural or other requirements that a state must follow when designating an 

MS4 as a Phase I permittee.85

Use of Residual Designation Authority to Expand the Phase I Universe

The vast majority of the MS4s subject to the Phase I permit requirements have been 

brought into Phase I under the residual designation authority, rather than on the basis of

population. In a 2000 report to Congress, the EPA stated that, of the 1,017 MS4s that were 

part of the Phase I program at that time (including Carroll and Frederick Counties), only 

216 had been listed in the appendices to the 1990 and 1999 regulations, while 670 were copermittees with a larger MS4 or had been designated separately for inclusion in the 

program. See EPA, Report to Congress on the Phase I Stormwater Regulations (2000), at 

3-5, available at https://perma.cc/BJG3-TPWP. Thus, despite the fact that the listing of 

large and medium MS4s required to obtain Phase I permits in the appendices to the Phase 

 

designation remains open for consideration during the notice and comment period relating 

to the permit.

Prior to adoption of those regulations, a memorandum of the EPA’s Office of Water 

Enforcement and Permits had appeared to indicate that state agencies would be expected 

to follow the same procedure. Memorandum of the Director of the EPA Office of Water 

Enforcement and Permits to Water Management Division Directors, et al. concerning 

Designation of Storm Water Discharges for Immediate Permitting (August 8, 1990), 

available at https://perma.cc/4NFA-NCXL, at 11. (Of note, that memorandum also 

suggested that discharges from the area around Chesapeake Bay would be appropriate for 

such a designation. Id. at 8-9). However, the regulations as adopted by the EPA set forth 

procedures solely for a designation by the EPA itself.

85 As was the case with clause (B)(iii) concerning the application of the MEP 

standard, see Part II.B. of this Opinion above, the legislative history of §1342(p)(2)(E), 

which established the residual designation authority, is not particularly illuminating. 
81

I regulations was “frozen” based on the 1990 census, that universe has been significantly 

expanded under the statutory designation authority. See id. at 3-2 n.7.

86

4. Classification of Frederick County and Carroll County in the 1990s

Neither Frederick County nor Carroll County was included in the listing of 

jurisdictions deemed “medium” based on population in Appendix I to the EPA regulations

– either in the initial version of that listing based on the 1980 census or in the amended 

version based on the 1990 census. Rather, the Department asked the Counties to apply for 

Phase I MS4 permits in the early 1990s, and the Counties did so. It is inevitably difficult 

to reconstruct events from the vantage point of 30 years later, but the parties have provided 

some correspondence from that era that suggests how the Department and the Counties 

came to accept the Counties’ status as Phase I jurisdictions.87

After Congress added the MS4 permit requirement to the Act and the EPA first 

adopted the Phase I regulations in 1990, the Department began corresponding with the 

 

86 See also EPA, Stormwater Phase II Final Rule: Who’s Covered? Designation and 

Waivers of Regulated Small MS4s (revised June 2012), at 2, available at

https://perma.cc/7WFA-VTYG (“Phase I MS4s were automatically designated nationwide 

as medium MS4s ... or as large MS4s [based on population.] Many MS4s in areas below 

100,000 in population, however, have been individually brought into the Phase I program 

[by] permitting authorities.”) (emphasis added).

87 This correspondence appears in appendices to the parties’ briefs. There is no 

documentation in the administrative record of these permits as to how either County came 

to be treated as a Phase I jurisdiction in the 1990s. In the explanatory document that the 

Department issued with the final version of the most recent Frederick County permit, it 

indicated that it had not needed to exercise its residual designation authority to classify the 

County as a Phase I jurisdiction in the 1990s because the County had agreed to apply for a 

Phase I MS4 permit.
82

Counties about whether they had to apply for a permit. At first, the Department told the 

Counties it was “unclear” whether they would need to do so. Each County responded that

its unincorporated population was below the statutory threshold of 100,000. Carroll 

County also emphasized its “primarily rural character.”88 Both Counties apparently asked 

the Department to refrain from including them in Phase I, or at least to delay the application 

of the Phase I requirements. The Department acceded to the latter request and postponed 

the deadlines for both Counties to submit a Phase I permit application. Both Counties 

eventually submitted applications for Phase I permits, apparently without further protest.

As best we can tell from the available correspondence, neither the Department nor 

the Counties focused on urbanized population in their correspondence when they discussed 

the relevant population in the early 1990s. This is perhaps unsurprising because neither 

the federal statutory nor regulatory text refers to “urbanized” areas.

89

 Instead, in their 

correspondence, both the Counties and the Department discussed only total population and

the population in unincorporated areas with respect to whether the Counties were 

“medium” MS4 jurisdictions that should apply for a Phase I permit. 

 

88 The fact that a county may have a large rural area does not necessarily affect 

whether it should be classified as a Phase I MS4 jurisdiction. See EPA Preamble to 1990 

Phase I MS4 Rule, 55 Fed. Reg. at 48041 (“some of the counties addressed by [the Phase 

I regulations] have, in addition to areas with high unincorporated urbanized populations, 

areas that are essentially rural or uninhabited and may not be the subject of planned 

development”). 

89 As explained above, that criterion was explained in the preamble to the 

publication of the 1990 Phase I regulations, but did not appear in the actual text of the 

regulations.
83

In the correspondence available to us, the Department did not explicitly invoke the 

statutory residual designation authority with respect to either County. However, the EPA 

has at least twice included Carroll County and Frederick County in lists of permittees as 

residually designated jurisdictions. EPA, Final National Pollutant Discharge Elimination 

System Storm Water Multi-Sector General Permit for Industrial Activities, 60 Fed. Reg.

50804, 51272 (September 29, 1995); EPA, Storm Water Discharges Potentially Addressed 

By Phase II of National Pollutant Discharge Elimination System Storm Water Program: 

Report to Congress (March 1995) at A-14; see also EPA, Report to Congress on the Phase 

I Storm Water Regulations (February 2000), at Apx. A (including Carroll County and 

Frederick County in Table A-2 listing “Additional MS4s Participating in Phase I MS4 

Program” – i.e., “additional” to Table A-1 listing the Phase I MS4 permittees named in the 

population-based appendices to the regulations).90 There are also other indications, 

outlined below, that the Counties were regarded as residually designated Phase I 

jurisdictions in the 1990s.

 

90 Similarly, the version of the Maryland WIP issued in 2010 stated that Carroll 

County had been designated by the Department as a Phase I MS4 under the residual 

designation authority in the early 1990s. See Maryland WIP at 2-30.
84

5. Analysis

The Counties assert that they are not properly classified as Phase I MS4s because 

they are not “medium” jurisdictions and were not otherwise designated as Phase I 

jurisdictions by the Department in the early 1990s. They contend that they should not be 

considered “medium” jurisdictions. In their view, the list of jurisdictions in Appendix I to 

the Phase I regulations is the exclusive list of medium MS4 counties and neither County

appears on that list. Moreover, the Counties assert that their unincorporated, urbanized

populations never reached 100,000, either in the 1990s or recently.91 They argue the 

Department did not exercise its residual designation authority in the 1990s, and Carroll 

County argues it is unlikely the Department even could have done so. In addition, Carroll 

County argues that the decision to include it as a Phase I jurisdiction was arbitrary and 

capricious.

So far as we can tell, the Counties’ challenge to their MS4 classification as Phase I 

jurisdictions raises novel issues for this or any court. We have not found – nor have the 

parties cited – any case that involves a county’s challenge to its classification as a Phase I 

MS4.

 

91 Carroll County also claims that the Clean Water Act did not authorize the 

Department’s use of population projections in the 1990s. We do not consider this argument 

separately because we do not see it as materially distinct from the County’s other 

population-based arguments.
85

Whether it is Unlawful for the Department to Treat the Counties as Phase I MS4s

If the Counties had raised the question of their classification as Phase I jurisdictions 

in the early 1990s, we might well have agreed that they should not have been brought into 

Phase I as “medium” jurisdictions. However, the argument that Appendix I to the Phase I 

regulations is the exclusive list of “medium” Phase I jurisdictions is without merit, as the 

EPA itself has recognized that jurisdictions not listed could later qualify.92 However, given 

the EPA’s interpretation of its own regulations expressed in the preamble to the publication 

of the Phase I regulations in 1990, neither County likely met the EPA’s contemporaneous 

interpretation of the medium category. In retrospect, it appears that neither County had a 

population at that time above 100,000 in unincorporated, urbanized areas.93

But we are not addressing this question in 1991.94 We decline to hold that today, 

after nearly three decades as part of the Phase I permitting program, the Counties should 

 

92 As discussed above, the EPA “froze” the list in Appendix I in 1999 based on the 

1990 census because the deadlines set for Phase I permit applications had expired and the 

pertinent jurisdictions had already applied (as had Carroll and Frederick Counties). The 

agency recognized that jurisdictions that later qualified as medium jurisdictions could be 

brought into the Phase I program through the residual designation authority. In any event, 

the agency could not, by regulation, negate a legislative determination that MS4s serving 

populations of a certain size were subject to the permit requirement.

93 In 1990, Frederick County’s “urbanized area” population was 58,393, and its total 

“urban” population was 86,686; for Carroll County, the numbers were 0 and 38,418, 

respectively. There is no need not explore the difference between “total urban” and 

“urbanized area,” at least for 1990, since both figures were under 100,000 with respect to 

each County.

94 Even if we could purport to be examining this issue from the perspective of the 

early 1990s, it is not entirely clear that we have a complete record from that period.
86

instead be relegated to a Phase II general permit with less stringent pollutant controls. We 

reach this conclusion for several reasons:

● The approach taken by the Department in calculating the relevant 

population of the Counties in the early 1990s was arguably consistent 

with the statutory text and the text of the regulations, although it

deviated from the EPA’s interpretation of those regulations, as 

articulated in the preamble to the publication of the regulations.

95

 

● When the Counties were originally treated as Phase I jurisdictions in 

1991, neither County (nor apparently anyone else) questioned the 

method that the Department used to assess the relevant population. 

● Both Counties stipulated, as recently as 2014, that they satisfy the 

statutory definition of a medium Phase I MS4 in consent orders that 

they entered into with the EPA concerning violations of earlier MS4 

permits.96

● In the case of the Carroll County permit, all of the incorporated 

municipalities in the County are included as co-permittees on the 

County’s Phase I permit, which thus regulates discharges of MS4s 

 

95 The Dissenting Opinion of Judge Getty suggests that we have deferred 

excessively to the EPA’s and the Department’s application of the Phase I classification, in 

contravention of the “plain language” of the Clean Water Act and the EPA’s regulations 

concerning the classification of MS4s. Getty Dissenting slip op. at 8. However, neither 

the statutory nor regulatory text concerning Phase I jurisdictions refers to “urbanized” 

populations – the key language on which the Dissenting Opinion relies. See 33 U.S.C. 

§1342(p)(2); 40 CFR §122.26(a)(1)(iv). As explained in the text, that language appears 

solely in the title of an appendix and in explanatory material prepared by the agency (the 

preamble to the 1990 publication of the regulations).

96 In the Matter of Carroll County, Maryland, Consent Agreement and Final Order

(United States Environmental Protection Agency June 6, 2014) at ¶¶ 7, 14, 15; In the Matter 

of the Board of County Commissioners of Frederick County, Maryland, Consent 

Agreement and Final Order (United States Environmental Protection Agency November 

25, 2014) at ¶¶ 8, 15, 16. Both orders recite that the pertinent County’s “MS4 serves a 

population of at least 100,000,” which is verbatim the language of the Clean Water Act 

defining medium Phase I jurisdictions. See 33 U.S.C. §1342(p)(2)(D).
87

serving those populations. See Carroll County Phase I MS4 Permit 

MD0068331, Part I.B.; see also 40 CFR §122.26(a)(3).

● The record before us does not include any document in which the 

Department explicitly exercised its residual designation authority to 

designate the Counties as Phase I jurisdictions independent of their 

status as medium jurisdictions. However, this is presumably because 

the Counties agreed to, or at least acquiesced in, their treatment as 

medium MS4s which may have foreclosed any need to invoke the 

Department’s residual designation authority.

● There are noteworthy indications that the Department and EPA believed 

that the Counties were appropriately designated as Phase I 

jurisdictions:97

o The Maryland WIP refers to Carroll County as a residually 

designated Phase I jurisdiction. Maryland WIP at 2-30.

o The fact that the Department agreed to delay the Counties’ 

designation as Phase I jurisdictions suggests that it was acting, 

at least in part, under the residual designation authority, as the 

Phase I regulations refer to an agency authorizing a delay in the 

submission of an application only in the case of a residually 

designated Phase I jurisdiction.98

o Given that TMDLs exist for waterways in both Counties – which 

indicates that water quality standards are being violated – there 

is a sound basis for concluding that discharges from each 

County’s MS4 contribute to violations of water quality 

 

97 Carroll County asserts that, if the Department had acted under its residual 

designation authority, it was required to notify the County of its determination in writing 

and send an application form with that notice under 40 CFR §124.52. However, as 

discussed above, the cited regulation applies only to a Regional Administrator of the EPA, 

not a state agency. Even if the notification requirement applied to the Department, Carroll 

County does not explain why the Department’s correspondence with the County in 1991 

would not satisfy the requirement. The regulation only requires that the permitting 

authority shall notify the permittee of the decision to require a permit and “the reasons for 

it.”

98 See 40 CFR §122.26(e)(5).
88

standards, thus triggering the exercise of the residual designation 

authority to include them as Phase I MS4 jurisdictions. 

o As indicated above, the EPA referred to the Counties as 

residually designated Phase I jurisdictions in publications in 

1995 and 2000. A contemporaneous guidance document issued 

by the EPA identified jurisdictions in the Chesapeake Bay 

watershed as examples of appropriate exercise of residual

designation authority. See note 84 above. 

● Relegating the Counties from a Phase I permit to a Phase II permit 

with less stringent requirements at this juncture risks a violation of 

the anti-backsliding prohibition in the Clean Water Act.99 See 33 

U.S.C. §1342(o).

The limited evidence of the Department’s decision-making process in classifying 

these Counties as Phase I jurisdictions in 1991 may reflect the difficulty of responding to 

challenges raised more than 20 years after the fact. The delay by the Counties in raising 

this issue has also posed difficulties for this Court in evaluating the parties’ arguments and 

the EPA’s views of the issue. There is not a clear picture of how the Department’s 

population-based reasoning in 1991 translated into the EPA’s stated view in 1995 that the 

Department had used its residual designation authority.

What is clear, however, is that the Department had authority to classify the Counties 

as Phase I jurisdictions and, at least in the EPA’s view, it did so. The Counties, in turn, 

 

99 The EPA had objected to earlier drafts of both permits on the basis that simply 

keeping the same terms of the Counties’ prior Phase I permits “would constitute 

impermissible backsliding” in violation of the Act. See EPA, Specific Objection to Carroll 

County Phase I MS4 Permit MD0068331 (September 20, 2012) at 3; EPA, Specific 

Objection to Frederick County Phase I MS4 Permit MD0068357 (September 20, 2012) at 

3.
89

have at the very least acquiesced in that classification since the 1990s. There is thus no 

question that the agencies charged with administering the Clean Water Act have 

consistently regarded the Counties as Phase I MS4s and that there is a reasonable basis for 

doing so. The Counties’ delay in challenging their Phase I designation perhaps means that 

the Department did not exercise its designation authority more formally in the past, but that 

does not require that we direct that they now be treated as Phase II jurisdictions. 

Whether Carroll County’s Classification is Arbitrary and Capricious

As indicated in Part II.A. of this Opinion, the Department’s exercise of discretion 

in crafting permit terms is subject to the “arbitrary and capricious” standard of review. The 

Department’s decisions survive challenge under this standard so long as the Department 

had a rational basis for its actions.

Carroll County asserts that the Department acted arbitrarily and capriciously in 

classifying it as a Phase I MS4 jurisdiction. Its argument is largely based on comparing 

itself to other jurisdictions in Maryland that have been designated as Phase I and Phase II 

MS4s. Carroll County claims its treatment as a Phase I MS4 subjects it to the same effluent 

limitations as larger urban jurisdictions in Maryland, while other counties similar to it in 

population size and land use are subject to less stringent regulation as Phase II jurisdictions. 

In particular, it draws a comparison to Washington County, which has been designated as

a small (Phase II) MS4 jurisdiction. Carroll County asserts that it is not challenging the 
90

population categories in the Clean Water Act, but rather the different treatment of two 

similarly situated counties.

100

In our view, the Department had a rational basis for making the impervious surface 

restoration terms more stringent for Phase I MS4s than for Phase II MS4s, even accounting 

for similarities between the smallest medium MS4s and the largest small MS4s. The 

Department notes that the population of Carroll County exceeded that of Washington 

County by a significant amount (when incorporated areas were excluded) at the time that 

the Department began to treat the counties as Phase I or Phase II jurisdictions. In addition, 

the Department’s discretion in crafting MS4 permit terms is bounded by the Bay TMDL, 

the Maryland WIP, and the EPA. 

In the Maryland WIP, the Department committed to including impervious surface 

restoration terms in MS4 permits similar to the ones the Department in fact included in the 

permits it issued after the EPA incorporated the Maryland WIP into the Bay TMDL. 

Moreover, the 30 percent restoration requirement for Phase I permittees inherently takes 

account of differences in the population size of those permittees. As the Department 

explained when it issued the Carroll County permit, “larger, more densely developed 

jurisdictions will have more impervious area and medium jurisdictions will have less 

impervious area that will require restoration.” Basis for Final Determination to Issue 

 

100 In terms of the impervious surface restoration requirement, the Department 

designed the Phase I MS4 permits to be more stringent than Phase II MS4 permits in three 

ways: larger baseline (county-wide vs. urbanized areas), earlier deadline (2019 vs. 2025), 

and higher percentage of area to be restored (30% vs. 20%).
91

Carroll County’s NPDES MS4 Permit MD0068331 (December 2014) at 29. Finally, in an 

objection to an earlier draft of the Carroll County permit, the EPA advised the Department 

that the impervious surface restoration term in the Carroll County permit should align with 

that in Prince George’s County’s permit, in order to comply with the Bay TMDL. EPA,

Specific Objection to Carroll County Phase I MS4 Permit MD0068331 (September 20, 

2012) at 3. Thus, the Department had a rational basis for the differences in permit terms 

between the Phase I and Phase II counties, even if some of them are close in population

size and share some similar characteristics.

E. Whether the Permits Should Have Provided for Water Quality Trading

“Water quality trading” is a method for complying with discharge permits that uses 

market forces to reduce overall pollution at lower cost by shifting pollution reduction 

activities from one entity to another. In particular, an entity subject to a pollution limit 

may take credit for a pollution reduction accomplished by another entity that it 

compensates for that privilege.101 Such trading presumably happens only if the other entity 

is able to accomplish the pollution reduction at less cost than the entity subject to the 

pollution limit. Thus, if water quality trading is available as a compliance method in a 

permit, a permittee might satisfy part of its obligations under the permit by purchasing 

pollutant reduction credits from other entities that take certain pollutant-reducing actions. 

 

101 See EPA, Water Quality Trading Evaluation (October 2008), available at

https://perma.cc/KT3P-WXRS, at 1-1; EPA, Water Quality Trading Toolkit for Permit 

Writers (updated June 2009), available at https://perma.cc/866S-M4V4, at 4.
92

The permits that are the subject of this appeal do not include water quality trading 

as a compliance method. The Counties wanted their permits to include water quality 

trading as a compliance option and contend that the Department’s decision not to allow for 

water quality trading in the permits when they were issued in 2014 was arbitrary and 

capricious. 

As the Counties point out, both the Department and the EPA support water quality

trading as an option in discharge permits. Over the past several years, the Department has 

been developing a water quality trading program in Maryland. In December 2017, the 

Department proposed regulations to establish such a program. See 44:25 Md. Reg. 1189-

95 (December 8, 2017). Following the requisite notice and comment period, the 

Department adopted those regulations, which became effective July 16, 2018. See 45:14 

Md. Reg. 698-702 (July 6, 1018), codified at COMAR 26.08.11. In addition, on April 27, 

2018, the Department issued a Phase II MS4 general permit,

102 effective October 31, 2018, 

which includes a term that conditionally allows water quality trading.

103

 The Department 

 

102 While permits applicable to Phase I MS4s are usually customized for each 

jurisdiction, the Department has developed a less rigorous general permit for Phase II 

MS4s. See Maryland Department of the Environment, Maryland’s NPDES Municipal 

Separate Storm Sewer System (MS4) Phase II General Permits, https://perma.cc/MLX2-

5NDU; EPA, Stormwater Discharges from Municipal Sources, https://perma.cc/UBS6-

NDK3.

103 In pertinent part, the Maryland Phase II MS4 general permit provides: “[The 

Department] supports trading as a cost-effective means for achieving pollutant load 

reductions[, and t]herefore, trading with other source sectors may be an option after formal 

regulatory procedures are satisfied.” National Pollutant Discharge Elimination System 
93

did so because it anticipated that the final water quality trading regulations would be 

adopted in 2018, as indeed they were. See Basis for Final Determination to Issue the 

General Permit for Discharges from Small Municipal Separate Storm Sewer Systems

(April 27, 2018) at 25.

The Counties argue that the Department also should have conditionally approved 

water quality trading in their permits, and that the failure to do so was arbitrary and 

capricious. We disagree. The Department issued these permits to the Counties in 2014,

just a year after it had convened a stakeholder group charged with examining several 

fundamental issues about trading and making recommendations for a draft trading policy. 

The Department explicitly mentioned that ongoing review when it explained in the Basis 

for Determination as to each permit why the permit did not include water quality trading 

as a compliance mechanism. By 2018, however, when the Department was completing the 

Phase II MS4 general permit, it had already proposed trading regulations and reasonably 

anticipated that those regulations would be adopted by the time that permit was effective. 

The Department therefore had a rational basis for conditionally approving water quality

trading in the Phase II MS4 general permit but not in the permits issued four years earlier 

to the Counties. See Harvey v. Marshall, 389 Md. at 297-99 (a “reasonable or rationally 

motivated” administrative decision is not “arbitrary or capricious.”). 

 

General Permit for Discharges from Small Municipal Separate Storm Sewer Systems (No. 

13-IM-5500), at B-10.
94

Carroll County points out that, in order to add water quality trading to its permit 

now, it must pursue a permit modification and undergo what it characterizes as “a lengthy 

public participation process.” But the County has not shown that any burden associated 

with the permit modification process would warrant a finding that the Department’s 

decision in 2014 not to include water quality trading was arbitrary and capricious.104

F. Effect of Permit Reference to Statutory Responsibilities of Other Entities

One provision of the permits contains language that, in the view of Carroll County, 

impermissibly transfers statutory obligations of other governmental entities to the 

Counties. In particular, Part VI.B of each County’s permit provides as follows:

[The] County shall cooperate with other agencies during the completion 

of the Water Resources Element (WRE) as required by the Maryland 

Economic Growth, Resource Protection and Planning Act of 1992 

(Article 66B, Annotated Code of Maryland). Such cooperation shall 

entail all reasonable actions authorized by law and shall not be 

restricted by the responsibilities attributed to other entities by separate 

State statute, including but not limited to reviewing and approving 

plans and appropriating funds.

(emphasis added). 

 

104 At least six other counties – including Frederick County – have requested that 

the Department modify their Phase I MS4 permits to incorporate the new water quality 

trading program as an option for complying with an impervious surface restoration 

requirement. We take judicial notice that the Department accepted those proposals and 

issued final determinations in December 2018 modifying the permits for Anne Arundel, 

Prince George’s, and Baltimore counties; in July, the Department issued tentative 

modification determinations for Charles, Harford, and Frederick counties. See Maryland 

Department of the Environment, Maryland’s NPDES Municipal Separate Storm Sewer 

System (MS4) Permits, https://perma.cc/KFY9-VBDU.
95

The law referenced in this part of the permits concerns how counties plan their future 

development. Now codified in Title 3 of the Land Use Article (“LU”) of the Maryland 

Code, the pertinent provisions of the Economic Growth, Resource Protection and Planning 

Act, as amended, direct each county to develop a comprehensive plan that includes, among 

other things, “a water resources element.” See LU §§3-101(a), 3-102(a)(1)(viii).105 As 

part of the water resources element, a county must identify “suitable receiving waters and 

land areas to meet stormwater management and wastewater treatment and disposal needs 

of existing and future development.” LU §3-106(a)(2). 

Only Carroll County raises an issue on appeal concerning this provision of the 

permits.

106

 In doing so, Carroll County contests only the language italicized in the 

quotation above. The County concedes that the EPA allows states to coordinate federal 

and state permitting requirements, as the Department attempts to do in requiring 

 

105 The Economic Growth, Resource Protection and Planning Act of 1992 was 

originally codified in Article 66B. Chapter 437, Laws of Maryland 1992. In 2006, the 

General Assembly enacted the “water resources element” requirement in Article 66B, 

§1.03(iii). Chapter 381, Laws of Maryland 2006. In 2012, the Legislature re-codified 

various provisions of Article 66B, including those concerning the water resources element 

requirement, as part of the new Land Use Article. Chapter 426, Laws of Maryland 2012.

106 Frederick County challenged the same provision in its permit in the Circuit Court. 

The Circuit Court ruled that the Department could lawfully incorporate the cooperation 

requirement of the Land Use Article into the permit. It also held that the language italicized 

above seemed to require the County to disregard other State statutes, which would 

impermissibly amend the Land Use Article. The Department did not contest that ruling. 

For the reasons set forth in text, we agree that the permit term may not amend the Land 

Use Article and may not be construed to do so or to require the Counties to disregard any 

other laws.
96

cooperation with other agencies in this permit term.107 The County argues, however, that 

the italicized language “seems to purport that the comprehensive planning provision 

overrides all other State statutes and relieves other entities of responsibilities attributed to 

them by State statute, instead imposing those responsibilities on the County.” 

Although the Department admits that the language is opaque, it asserts that the 

purpose of the final clause of this permit term “is to make clear that the County, when 

formulating the water resources element of its comprehensive plan, may not decline to 

cooperate with another agency because that agency, and not the County, has statutory 

responsibility for a specific governmental activity, whether it be reviewing and approving 

plans or appropriating funds.” In that view, this provision only precludes the County from 

relying on other agencies’ specific responsibilities as a reason not to coordinate with those 

agencies. 

In our view, the County’s interpretation is not a reasonable reading of the permit 

provision. Some ambiguity arguably exists in the closing phrase of the permit provision: 

“including but not limited to reviewing and approving plans and appropriating funds.” At 

least in terms of grammar, what “including” modifies is not obvious. It could modify the 

County’s “cooperation,” its “reasonable actions,” or the other entities’ “responsibilities.” 

By the last antecedent rule, however, “including” would ordinarily be understood to modify

 

107 See EPA Preamble to 1999 Phase II MS4 Rule, 64 Fed. Reg. at 68739 (discharge 

“permits may incorporate the requirements of existing State ... programs, thereby 

accommodating State[s] ... seeking to coordinate the storm water program with other 

programs”).
97

“responsibilities.” See McCree v. State, 441 Md. 4, 21 (2014) (“Under the last antecedent 

rule, a qualifying clause ordinarily is confined to the immediately preceding word or 

phrase”) (internal quotations omitted). That reading makes the most sense here.

The provision says only that other entities’ statutory requirements “shall not ... 

restrict” the County’s obligation under State law to cooperate with those entities. This 

permit term has no effect on statutory requirements pertaining to other entities, nor does it 

transfer those obligations to the County. In other words, the permit term provides that the

responsibilities of other entities under State law to take such actions as “reviewing and 

approving plans [or] appropriating funds” do not restrict the County’s obligation to 

cooperate with those entities. Reasonably read, the permit term incorporates existing State 

law without imposing new requirements on the County or relieving other entities of their 

obligations under State law.

III

Conclusion

For the reasons set forth above, we hold:

(1) The Department may lawfully include an impervious surface restoration 

requirement in an MS4 permit without reference to the MEP standard. The Department’s 

decision to do so in Frederick County’s most recent permit was not arbitrary or capricious.

(2) The Department may lawfully include an impervious surface restoration 

requirement in an MS4 permit in which the required amount of restoration is based on the 

amount of unrestored surface throughout the county that operates the MS4 when the 

amount of restoration derives from commitments made in the Maryland WIP as part of the 
98

development of the Chesapeake Bay TMDL. To the extent that the Counties challenge 

restoration provisions in their permits that derive from EPA-approved local TMDLs, such 

challenges should have been made when the local TMDL was approved by the EPA and 

are not appropriately part of judicial review of an MS4 permit in State court.

(3) The Department had authority to treat Frederick County and Carroll County 

as Phase I jurisdictions for purposes of their MS4 permits. It was not arbitrary or capricious 

for the Department to classify Carroll County as a Phase I jurisdiction without also 

including Washington County in that category.

(4) Although the Department later elected to include “water quality trading” as 

a compliance method for MS4 permittees, it was not arbitrary or capricious for the 

Department to refrain from doing so in the Counties’ 2014 permits because it had not yet

finally adopted regulations it had proposed concerning that compliance method.

(5) A somewhat ambiguous provision in the Carroll County MS4 permit that 

requires it to cooperate with other agencies in the development of the water resources 

element of the County’s comprehensive plan under LU §3-101 et seq. did not – and could 

not – transfer the responsibilities of those agencies to the County.

After all the jargon, technical analysis, and regulatory provisions have been digested 

and applied, it seems fitting to conclude with the words of Judge Wilkinson in a recent case 

concerning the operation and financing of an MS4 in the Chesapeake Bay region:

“No one is so naïve as to believe that the Chesapeake Bay [and its tributaries] can 

be restored to the pristine condition ... in which this country’s earliest inhabitants found 

them. We would be fortunate to preserve a wholesome fraction of what once there was. 
99

This case is but a tiny chapter in the story of our nation’s effort to reconcile the just 

demands of development with the imperative of preserving an environment that can help 

make productive enterprise worth having.... We happily accepted the abundance that came 

down from our forebears. How then can we impoverish the environment for those who 

come after?”108

IN NO. 5, JUDGMENT OF THE CIRCUIT COURT FOR CARROLL 

COUNTY AFFIRMED IN PART AND REVERSED IN PART. 

COSTS TO BE SPLIT EVENLY BETWEEN THE PARTIES.

IN NO. 7, JUDGMENT OF THE CIRCUIT COURT FOR 

FREDERICK COUNTY AFFIRMED IN PART AND REVERSED IN 

PART. COSTS TO BE SPLIT EVENLY BETWEEN THE PARTIES.

 

108 Norfolk Southern, 916 F.3d at 325 (Wilkinson, J., concurring).
IN THE COURT OF APPEALS

OF MARYLAND

Nos. 5 & 7

September Term, 2018

______________________________________

MARYLAND DEPARTMENT OF THE 

ENVIRONMENT

v.

COUNTY COMMISSIONERS OF CARROLL 

COUNTY, MARYLAND

______________________________________

FREDERICK COUNTY, MARYLAND

v.

MARYLAND DEPARTMENT OF THE 

ENVIRONMENT

______________________________________

Barbera, C.J.

*Greene

*Adkins

McDonald

Watts

Hotten

Getty,

JJ.

______________________________________

Dissenting Opinion by Watts, J., which Hotten and 

Getty, JJ., joins.

______________________________________

Filed: August 6, 2019

*Greene and Adkins, JJ., now retired, participated in 

the hearing and conference of this case while active 

members of this Court; after being recalled pursuant 

to the Maryland Constitution, Article IV, Section 3A, 

they also participated in the decision and adoption of 

this opinion.

Circuit Court for Carroll County

Case No. 06-C-15-068141 

Circuit Court for Frederick County

Case No. 10-C-15-000293 

Argued: September 13, 2018 
Respectfully, I dissent. Although I agree with the Majority that it was not arbitrary 

and capricious for the Maryland Department of the Environment (“the MDE”) not to 

include water quality trading as a compliance method in the municipal separate storm sewer 

system (“MS4”) permits of Carroll County and Frederick County, I disagree with the 

Majority as to the other issues. See Maj. Slip Op. at 97-98. I would hold that the MDE 

was not authorized to set forth in Frederick County’s MS4 permit requirements that exceed 

the “maximum extent practicable” standard, that the MDE lacked the authority to require 

the Counties to restore 20% of the impervious surfaces1throughout the entirety of each 

county, and that the MDE misclassified the Counties’ MS4s as medium rather than small.

2

Under 33 U.S.C. § 1311(a)—part of the Clean Water Act, 33 U.S.C. §§ 1251-

1388—generally, it is illegal to discharge pollutants into navigable waters. That said, the 

Environmental Protection Agency (“the EPA”)—or, under certain circumstances, a State 

environmental agency, such as the MDE—may issue a permit for the discharge of 

pollutants into navigable waters. See 33 U.S.C. § 1342(a)(1), (b). For example, the MDE 

may issue to a county a permit for an MS4. See 33 U.S.C. § 1342(p)(3)(B). 33 U.S.C. § 

1342(p)(3)(B) states:

 

1

“‘Impervious surface’ means a surface that does not allow stormwater to infiltrate 

into the ground.” Md. Code Ann., Env’t (1987, 2013 Repl. Vol.) (“EN”) § 4-201.1(d)(1). 

“‘Impervious surface’ includes rooftops, driveways, sidewalks, or pavement.” EN § 4-

201.1(d)(2).

2Because I agree with Frederick County that the MDE was not authorized to set 

forth in Frederick County’s MS4 permit requirements that exceed the “maximum extent 

practicable” standard, there is no need to address Frederick County’s alternative argument 

that its MS4 permit’s requirements are impossible to fulfill. Similarly, although I disagree 

with the Majority as to the issue regarding Carroll County’s cooperation with other State 

agencies, it is not necessary to go into detail in light of my positions on the other issues.
- 2 -

Permits for discharges from municipal storm sewers--

(i) may be issued on a system- or jurisdiction-wide basis;

(ii) shall include a requirement to effectively prohibit non-stormwater 

discharges into the storm sewers; and

(iii) shall require controls to reduce the discharge of pollutants to the 

maximum extent practicable, including management practices, control 

techniques and system, design and engineering methods, and such other 

provisions as the [EPA] or the State determines appropriate for the control of 

such pollutants.[3] 

On brief, the MDE does not deny that it set forth in Frederick County’s MS4 permit 

requirements that exceed the “maximum extent practicable” standard. To the contrary, the 

MDE contends that it was authorized to impose on Frederick County requirements that go 

beyond the “maximum extent practicable” standard. 

I disagree, and would conclude that 33 U.S.C. § 1342(p)(3)(B)(iii)’s plain language 

establishes that the MDE is authorized only to require Frederick County “to reduce the 

discharge of pollutants to the maximum extent practicable[.]” In other words, in 33 U.S.C. 

§ 1342(p)(3)(B)(iii), the “such other provisions” language does not authorize the MDE to 

impose on Frederick County requirements that exceed the “maximum extent practicable” 

standard. In 33 U.S.C. § 1342(p)(3)(B)(iii), every single item in question—namely, 

“management practices, control techniques and system, design and engineering methods, 

 

3Consistent with 33 U.S.C. § 1342(p)(3)(B)(iii), 40 C.F.R. § 122.26(d)(2)(iv) states 

that “[a] proposed management program” to control pollutants from an MS4 “shall include 

a comprehensive planning process which involves public participation and where 

necessary intergovernmental coordination, to reduce the discharge of pollutants to the 

maximum extent practicable using management practices, control techniques and system, 

design and engineering methods, and such other provisions which are appropriate.”
- 3 -

and such other provisions as the [EPA] or the State determines appropriate for the control 

of such pollutants”—is part of a list of “controls to reduce the discharge of pollutants to 

the maximum extent practicable[.]” In short, in 33 U.S.C. § 1342(p)(3)(B)(iii), the “such 

other provisions” language is subject to the “maximum extent practicable” standard. 

Nothing in 33 U.S.C. § 1342(p)(3)(B)(iii) indicates that the “such other provisions” 

language grants the MDE freewheeling authority to impose on the Counties whatever 

requirements that it deems “appropriate[,]” no matter how onerous or costly.4

This interpretation of 33 U.S.C. § 1342(p)(3)(B)(iii) is warranted not only by its 

plain language, but also by our case law. Just three years ago, in Md. Dep’t of Env’t v. 

Anacostia Riverkeeper, 447 Md. 88, 126, 134 A.3d 892, 915 (2016), this Court 

unanimously held that the requirement to restore 20% of impervious surfaces in multiple 

counties’ MS4 “[p]ermits complies with the [maximum extent practicable] standard” under 

33 U.S.C. § 1342(p)(3)(B)(iii). In so holding, this Court rejected environmental groups’ 

contention “that the 20% restoration requirement is too opaque to comply with 33 U.S.C. 

§ 1342(p)(3)(B)(iii), the [maximum extent practicable] standard.” Id. at 123, 134 A.3d at 

913. This Court pointed out “that MS4s are subject to the [maximum extent 

practicable] standard under 33 U.S.C. § 1342[(p)(3)(B)(iii)].” Id. at 104, 134 A.3d at 

901 (emphasis added). Similarly, this Court noted that 33 U.S.C. § 1342(p)(3)(B)(iii) 

 

4After an examination of a statute’s language, it is permissible to consider the 

statute’s “legislative history as a confirmatory process.” Gomez v. Jackson Hewitt, Inc., 

427 Md. 128, 160, 46 A.3d 443, 462 (2012) (citation omitted). But, as the Majority notes, 

“what legislative history exists is not especially illuminating on the role of the [maximum 

extent practicable] standard.” Maj. Slip Op. at 44 (cleaned up).
- 4 -

“requires ‘controls to reduce the discharge of pollutants’ to the [maximum extent 

practicable.]” Id. at 177, 134 A.3d at 945 (emphasis added). And, this Court stated that 

“stormwater management programs that are designed by regulated parties must, in every 

instance, be subject to meaningful review by an appropriate regulating entity to ensure that 

each such program reduces the discharge of pollutants to the maximum extent 

practicable.” Id. at 157, 134 A.3d at 933 (cleaned up) (emphasis added).

This Court’s holding in Anacostia Riverkeeper, id. at 126, 134 A.3d at 915, was 

premised on the principle—expressed multiple times throughout the opinion—that MS4 

permits are subject to the “maximum extent practicable” standard under 33 U.S.C. § 

1342(p)(3)(B)(iii). Accordingly, Anacostia Riverkeeper forecloses the MDE’s contention 

that 33 U.S.C. § 1342(p)(3)(B)(iii) allows it to impose on Frederick County requirements 

that exceed the “maximum extent practicable” standard. If the MDE’s position were valid, 

then this Court’s holding in Anacostia Riverkeeper, id. at 126, 134 A.3d at 915, would have 

been completely meaningless; after all, if the MDE were free to ignore the “maximum 

extent practicable” standard when issuing MS4 permits, why would this Court have 

bothered to determine whether the MS4 permits complied with the “maximum extent 

practicable” standard?

Seeking to get around the obstacle that Anacostia Riverkeeper poses to its position, 

the MDE sets forth a novel theory—namely, that the “maximum extent practicable” 

standard is a “floor” rather than a “ceiling,” and that Anacostia Riverkeeper does not 

indicate that the MDE may not impose requirements that go beyond the “maximum extent 

practicable” standard. The Majority essentially goes along with the MDE’s interpretation 
- 5 -

of Anacostia Riverkeeper, reasoning that, in Anacostia Riverkeeper, “the question was 

whether the impervious surface restoration requirement satisfied the [maximum extent 

practicable] standard whereas in this case the question is whether it unlawfully exceeds it.” 

Maj. Slip Op. at 39 (emphasis in original). The view of the Majority and the MDE is simply 

incompatible with this Court’s holding in Anacostia Riverkeeper, 447 Md. at 126, 134 A.3d 

at 915, which, to reiterate, was squarely based on the principle that MS4 permits must 

comply with the “maximum extent practicable” standard. If MS4 permits did not need to 

comply with the “maximum extent practicable” standard, this Court would have had no 

reason to determine that the requirement to restore 20% of impervious surfaces in multiple 

counties’ MS4 “[p]ermits complies with the [maximum extent practicable] standard” under 

33 U.S.C. § 1342(p)(3)(B)(iii). Anacostia Riverkeeper, 447 Md. at 126, 134 A.3d at 915.5

 

5Perplexingly, the majority opinion states that, in Anacostia Riverkeeper, 447 Md. 

at 122-26, 134 A.3d at 912-15: 

[T]he Court considered a permit term that appears in Phase I MS4 permits of 

five other jurisdictions and that is identical to the permit term that Frederick 

County challenges here. The Court held that the term was valid and 

authorized by the Clean Water Act. If we were simply to recite the holding 

of Anacostia Riverkeeper and stop, Frederick County loses.

Maj. Slip Op. at 38 n.41 (cleaned up) (emphasis in original). Essentially, after asserting 

that, in Anacostia Riverkeeper, this Court answered a question that is not at issue in this 

case, oddly, the majority opinion asserts that, under the holding of Anacostia Riverkeeper, 

Frederick County would “lose[.]” Maj. Slip Op. at 38 n.41. In actuality, the circumstance 

that, in Anacostia Riverkeeper, this Court considered a permit term that is identical to a 

term in the permit that Frederick County challenges informs the outcome of this case. In 

Anacostia Riverkeeper, 447 Md. at 126, 134 A.3d at 914-15, this Court concluded that the 

challenged permit term complied with the “maximum extent practicable” standard. In 

Anacostia Riverkeeper, id. at 123-26, A.3d at 913-15, there was no allegation that the 

permit term exceeded the “maximum extent practicable” standard. Frederick County 
- 6 -

To be sure, as Frederick County acknowledges, its interpretation of 33 U.S.C. § 

1342(p)(3)(B)(iii) indicates that the statute contains a typographical error—namely, the 

word “system” should be “systems” so that it, like the immediately preceding noun 

“techniques,” is plural. It is not unheard of for a statute to contain a typographical error. 

Indeed, another sentence within 33 U.S.C. § 1342 contains three such errors; 33 U.S.C. § 

1342(l)(3)(C) erroneously refers to “Section 1365(a) of this title” (in which “Section” 

should be lowercase), and, in two instances, erroneously omits the word “section” before 

referring to a certain provision “of this title[.]”

Helpfully, the Majority sets forth illustrations of how each party parses the sentence 

within 33 U.S.C. § 1342(p)(3)(B)(iii). See Maj. Slip Op. at 41-43. As the Majority notes, 

Frederick County parses that sentence, in pertinent part, as follows: “shall require controls 

to reduce the discharge of pollutants to the maximum extent practicable, including (1)

management practices, (2) control techniques and systems, (3) design and engineering 

methods, and (4) such other provisions as the [EPA] Administrator or the State determines 

appropriate for the control of such pollutants.” Id. at 41 (alterations in original). 

Meanwhile, the MDE parses the sentence, in pertinent part, as follows: “shall require (1)

controls to reduce the discharge of pollutants to the maximum extent practicable, including 

(a) management practices, (b) control techniques and (c) system, design and engineering 

methods, and (2) such other provisions as the [EPA] Administrator or the State determines 

 

would not “lose[]” under this Court’s holding in Anacostia Riverkeeper, Maj. Slip Op. at 

38 n.41; rather, this Court’s holding in that case clearly demonstrates that MDE has 

exceeded its authority.
- 7 -

appropriate for the control of such pollutants.” Id. at 42 (alterations in original). The 

Majority adopts the MDE’s interpretation of 33 U.S.C. § 1342(p)(3)(B)(iii), reasoning that 

it “does not require revision of the text itself, and groups items that could comfortably fit 

within the category of ‘controls’ separately from the final clause’s vaguer and seemingly 

broader reference to ‘appropriate ... provisions.’” Maj. Slip Op. at 42-43 (ellipsis in 

original).

The Majority fails to address three matters that demonstrate that the MDE’s 

interpretation of 33 U.S.C. § 1342(p)(3)(B)(iii) is incorrect. Specifically, the MDE’s 

interpretation renders most of the sentence at issue nugatory, leads to an illogical result, 

and indicates that the sentence has not one, but two glaring errors. These circumstances 

violate the rules of statutory interpretation, under which a court must read a statute “as a 

whole so that no word, clause, sentence or phrase is rendered surplusage, superfluous, 

meaningless[,] or nugatory[,]” and must read the statute “to avoid an illogical result.” 

Gomez v. Jackson Hewitt, Inc., 427 Md. 128, 143, 156, 46 A.3d 443, 452, 460 (2012) 

(cleaned up).

If, as the MDE asserts, 33 U.S.C. § 1342(p)(3)(B)(iii) directs it to “require . . . such 

other provisions as [it] determines appropriate for the control of such pollutants[,]” then 

the rest of the provision is nugatory. Under the MDE’s interpretation, the “such other 

provisions” language allows it to impose on the Counties whatever provisions it 

“determines appropriate[,]” without reference to the “maximum extent practicable” 

standard. That begs the question: If the MDE may freely ignore it, what is the point of the 

“maximum extent practicable” standard? In fact, what is the point of the list of items that 
- 8 -

begins with “management practices”? Simply put, there would be no reason for either the 

“maximum extent practicable” standard or the list of items if 33 U.S.C. § 1342(p)(3)(B)(iii) 

directs the MDE to impose whatever requirements it deems fit, whether “practicable” or 

not.

The MDE volunteers a possible reason for the “maximum extent practicable” 

standard—but that reason reveals an internal inconsistency in the MDE’s contentions. The 

MDE reasons that the “maximum extent practicable” standard is a “floor” rather than a 

“ceiling.” In other words, according to the MDE, the “maximum extent practicable” 

standard sets forth the minimum that the MDE must require of Frederick County, not the 

maximum that it may require of Frederick County. That argument, however, is inconsistent 

with the MDE’s assertion that the “such other provisions” language is not subject to the 

“maximum extent practicable” standard. If, as the MDE maintains, the “such other 

provisions” language is independent of the “maximum extent practicable” standard, then 

the “maximum extent practicable” standard is neither a floor nor a ceiling—it is 

meaningless, as the MDE is free to impose whatever requirements it deems fit, whether 

practicable or not.

The Majority refers to the “such other provisions” language as the “final clause[.]” 

Maj. Slip Op. at 43. I agree with the Majority that the “such other provisions” language is

the final clause—and, moreover, it is clear that the final clause is a catchall clause that

supports Frederick County’s interpretation of 33 U.S.C. § 1342(p)(3)(B)(iii), not the 

MDE’s. Under Frederick County’s position, there are four groups of controls that may be 

included in an MS4 permit, including a final catchall category—the “such other provisions” 
- 9 -

clause—that are all governed by the “maximum extent practicable” standard. Under the 

MDE’s position, the “such other provisions” language is an all-encompassing blank check 

that sidesteps the “maximum extent practicable” standard and allows the MDE to impose 

any requirement that it “determines appropriate[.]” Because the MDE’s interpretation of 

33 U.S.C. § 1342(p)(3)(B)(iii) renders most of the statutory provision nugatory, I cannot 

endorse it.

Additionally, the MDE’s interpretation of 33 U.S.C. § 1342(p)(3)(B)(iii) leads to an 

illogical result. As the Majority notes, under Frederick County’s interpretation of 33 

U.S.C. § 1342(p)(3)(B)(iii), the list of items includes “control techniques and systems” and 

“design and engineering methods[.]” Maj. Slip Op. at 41 (alteration in original). This 

explanation is logical, as the term “control systems” makes as much sense as the term 

“control techniques[.]” By contrast, under the MDE’s interpretation, the list of items 

includes “control techniques” and “system, design and engineering methods[.]” Id. at 42. 

I am unable to fathom what exactly “system methods” are. The Majority acknowledges 

that Frederick County refers to the term “system methods” as “nonsensical[,]” id. at 42, yet 

the Majority makes no effort to explain what the term means. Simply put, the term “system 

methods” is indeed nonsensical, in sharp contrast to the terms “design methods” and 

“engineering methods[.]” Adopting Frederick County’s interpretation of 33 U.S.C. § 

1342(p)(3)(B)(iii) avoids the illogical result of construing the statute to refer to “system 

methods”—an incomprehensible term.

Finally, the MDE’s interpretation of 33 U.S.C. § 1342(p)(3)(B)(iii) indicates that 

the sentence has not one, but two glaring errors. Specifically, under the MDE’s position, 
- 10 -

the sentence would be missing two serial commas:6 one after the word “techniques[,]” and 

one after the word “design[.]” To be sure, as noted above, it is not unheard of for a statute 

to contain a typographical error; and, the inclusion of serial commas is a matter of style 

rather than a grammatical necessity. Even so, independent of 33 U.S.C. § 

1342(p)(3)(B)(iii), the rest of the statute includes fourteen serial commas in all. See 33 

U.S.C. § 1342(a)(1), (a)(2), (b)(1)(A), (b)(2)(B), (b)(9), (f), (g) (twice, counting the title), 

(k), (l)(2) (twice, counting the title), (q)(1) (title), (q)(3), (s)(3)(A)(ii). And, unlike the 

practice of including the lowercase word “section” when drafting a statute that refers to 

other statutes, see 33 U.S.C. § 1342(l)(3)(C), the practice of including a serial comma is 

not unique to legal writing, and is often a habit that becomes ingrained as a result of years 

of day-to-day writing. Accordingly, it is difficult to believe that 33 U.S.C. § 

1342(p)(3)(B)(iii)’s drafters simply forgot to include a serial comma in not one, but two 

instances.

Without meaningfully addressing the fatal flaws in the MDE’s interpretation of 33 

U.S.C. § 1342(p)(3)(B)(iii) and its conflict with this Court’s holding in Anacostia 

Riverkeeper, 447 Md. at 126, 134 A.3d at 915, the Majority quotes an opinion by one of 

California’s six intermediate appellate courts. See Maj. Slip Op. at 43. In Bldg. Indus. 

Ass’n of San Diego Cty. v. State Water Res. Control Bd., 124 Cal. App. 4th 866, 882-83 

 

6Also known as a Harvard comma or an Oxford comma, a serial comma is “a comma 

[that is] used to separate the second-to-last item in a list from a final item [that is] 

introduced by the conjunction and or or[.]” Serial Comma, Merriam-Webster, https://

www.merriam-webster.com/dictionary/serial%20comma [https://perma.cc/3KGX-2LJC]

(italics in original). For example, the phrase “red, white, and blue” includes a serial 

comma. Id.
- 11 -

(2004), the Fourth District Court of Appeal of California reasoned that the “such other 

provisions” language in 33 U.S.C. § 1342(p)(3)(B)(iii) directs State environmental 

agencies to impose whatever requirements they determine appropriate, without reference 

to the “maximum extent practicable” standard. The California Court agreed with the 

contention of State water boards and environmental organizations that, “given the absence 

of a comma after the word ‘techniques,’” and “because the word ‘system’ [] is singular, it 

necessarily follows from parallel-construction grammar principles that the word ‘system’ 

is part of the phrase ‘system, design and engineering methods’ rather than the phrase 

‘control techniques and system.’” Id.

The California Court’s logic is unpersuasive for several reasons. First and foremost, 

the California Court treated the lack of a comma after the word “techniques” as an 

indication that the words “techniques” and “system” do not go together—when, in fact, the 

exact opposite is true; i.e., the lack of a comma between the words “techniques” and 

“system” indicates that, indeed, the words go together. On a related note, for all its concern 

about the lack of a comma after the word “techniques[,]” the California Court failed to 

acknowledge that its interpretation of 33 U.S.C. § 1342(p)(3)(B)(iii) meant that there 

should have been a serial comma after the word “techniques”—as well as a serial comma 

after the word “design[.]” Also, the California Court did not mention the possibility that 

the word “system” is singular due to a typographical error. Nor did the California Court 

acknowledge that its interpretation of 33 U.S.C. § 1342(p)(3)(B)(iii) renders most of the 

sentence, including the “maximum extent practicable” standard, nugatory. Nor did the 

California Court mention that its interpretation of 33 U.S.C. § 1342(p)(3)(B)(iii) indicates 
- 12 -

that the statute includes the nonsensical term “system methods”—much less attempt to 

explain what that term means.

In addition to quoting Bldg. Indus. Ass’n of San Diego Cty., the Majority gives 

deference to the EPA’s interpretation of 33 U.S.C. § 1342(p)(3)(B)(iii), under which the 

MDE may impose on Frederick County requirements that exceed the “maximum extent 

practicable” standard. See Maj. Slip Op. at 50-51. Although a court should give some 

deference to an administrative agency’s interpretation of a statute that it administers, the 

court is not obligated to adopt a statutory construction that renders most of the statute 

meaningless and leads to an illogical result. In a nutshell, even after giving some deference, 

I would decline to adopt the EPA’s strained interpretation of 33 U.S.C. § 

1342(p)(3)(B)(iii).7

 

7

In a futile attempt to bootstrap deference to the EPA’s interpretation of the Clean 

Water Act, the Majority relies on case law that does not apply—Chevron, U.S.A., Inc. v. 

Nat. Res. Defense Council, Inc., 467 U.S. 837 (1984)—and an opinion from the United 

States Court of Appeals for the Ninth Circuit—Defs. of Wildlife v. Browner, 191 F.3d 

1159 (9th Cir. 1999)—that does not address the issue that is before this Court. See Maj. 

Slip Op. at 48 n.52. As to Defs. of Wildlife, the Majority states: “[W]hile the Ninth Circuit 

did not agree with the EPA’s existing construction, it nevertheless recognized that a 

permitting agency had discretion to include permit terms based on water quality 

standards.” Maj. Slip Op. at 46-47. As the Majority appears to recognize, the relevant 

question before the Ninth Circuit was whether the Clean Water Act authorized the EPA to 

“require strict compliance with [S]tate water-quality standards[.]” Defs. of Wildlife, 191 

F.3d at 1166. The Ninth Circuit answered that question in the affirmative, explaining that 

33 U.S.C. § 1342(p)(3)(B)(iii) “gives the EPA discretion to determine what pollution 

controls are appropriate.” Id. Significantly, nowhere in Defs. of Wildlife did the Ninth 

Circuit indicate that 33 U.S.C. § 1342(p)(3)(B)(iii) authorizes the EPA—or a State 

environmental agency—to impose whatever requirements it determines appropriate, 

without reference to the “maximum extent practicable” standard. Indeed, in two instances, 

the Ninth Circuit recognized that, under 33 U.S.C. § 1342(p)(3)(B)(iii), local governments 
- 13 -

In addition to wrongfully setting forth in Frederick County’s MS4 permit 

requirements that exceed the “maximum extent practicable” standard, the MDE improperly 

required the Counties to restore 20% of the impervious surfaces throughout the entirety of 

each county, as opposed to 20% of the impervious surfaces in the Counties’ urbanized 

 

that manage MS4s must “reduce the discharge of pollutants to the maximum extent 

practicable[.]” Id. at 1165 (internal quotation marks omitted).

As a matter of fact, contrary to the Majority’s assertion that “[o]ther courts have 

pointed to Defenders of Wildlife as setting forth the discretion that the EPA (and state 

permitting agencies) have in drafting MS4 permit terms to require pollution controls that 

satisfy the [‘maximum extent practicable’] standard or a more demanding water quality 

based standard[,]” that is not the case. See Maj. Slip Op. at 47 n.50. Although the Ninth 

Circuit’s opinion in Defs. of Wildlife was mentioned in each of the cases that the Majority 

identifies, none of those cases relied on Defs. of Wildlife as a basis for concluding that the 

EPA or State environmental agencies have the discretion to issue MS4 permits that contain 

requirements that exceed the “maximum extent practicable” standard. In actuality, in each 

of those cases, the courts relied on Defs. of Wildlife for other propositions. See Nat. Res. 

Def. Council v. New York State Dep’t of Envtl. Conservation, 994 N.Y.S. 2d 125, 135 

(N.Y. App. 2014) (The New York Supreme Court relied on Defs. of Wildlife for the 

specific proposition that permits issued for “industrial dischargers” must comply with the 

effluent limitations set forth in 33 U.S.C. § 1311.); Conservation Law Found., Inc. v. 

Boston Water and Sewer Comm’n, 2010 WL 5349854, at *5-6 (D. Mass. 2010)

(unreported) (The U.S. District Court for the District of Massachusetts relied on Defs. of 

Wildlife for the proposition that the EPA has the authority to “determine that ensuring strict 

compliance with state water-quality standards is necessary to control pollutants” and the 

proposition that the EPA has the authority to “require less than strict compliance with state 

water-quality standards.”); Tualatin Riverkeepers v. Oregon Dep’t of Envtl. Quality, 230 

P.3d 559, 562 n.8 (Ore. App. 2010) (The Court of Appeals of Oregon relied on Defs. of 

Wildlife for the proposition that permits providing for discharges of municipal storm water 

“need not require strict compliance with state water quality standards.”); City of Arcadia 

v. State Water Res. Control Bd., 135 Cal. App. 4th 1392, 1429 (2006) (The Court of Appeal 

for the Fourth District of California relied on Defs. of Wildlife for the proposition that the 

EPA has the discretion to “‘determine that ensuring strict compliance with state waterquality standards is necessary to control pollutants’” and that the EPA also has the authority 

to “‘require less than strict compliance with state water-quality standards[.’]” (Quoting 

Defs. of Wildlife, 191 F.3d at 1166-67)). Nowhere in any of these cases did the various 

courts conclude that Defs. of Wildlife established the EPA’s—or State environmental 

agencies’—authority to issue MS4 permits that contain requirements exceeding the 

“maximum extent practicable” standard.
- 14 -

areas—i.e., the areas that the Counties’ MS4s serve. As noted above, 33 U.S.C. § 

1342(p)(3)(B)(iii) provides that MS4 permits “shall require controls to reduce the discharge 

of pollutants to the maximum extent practicable, including management practices, control 

techniques and system, design and engineering methods, and such other provisions as the 

[EPA] or the State determines appropriate for the control of such pollutants.” Pursuant to 

33 U.S.C. § 1342(p)(3)(B)(iii), see Anacostia Riverkeeper, 447 Md. at 151 n.71, 134 A.3d 

at 930 n.71, on December 3, 2010, multiple State agencies, including the MDE, submitted 

to the EPA “Maryland’s Phase I Watershed Implementation Plan for the Chesapeake Bay 

Total Maximum Daily Load[.]” University of Maryland et al., Maryland’s Phase I 

Watershed Implementation Plan for the Chesapeake Bay Total Maximum Daily Load at 1 

(Dec. 3, 2010), available at https://mde.maryland.gov/programs/Water/TMDL/

Documents/www.mde.state.md.us/assets/document/MD_Phase_I_Plan_12_03_2010_Sub

mitted_Final.pdf [https://perma.cc/XV7P-P3VT] (“the WIP”). In the WIP, under the 

heading “Additional Program, Practices and Policies to Meet the 2017 Goal for Non-Point 

Source Urban Stormwater[,]” and under the subheading “Increase [National Pollutant 

Discharge Elimination System (‘NPDES’)] Watershed Restoration Requirements for MS4 

Phase I County permits, including [State Highway Administration,]” the State agencies 

stated:

The following key elements of the strategy support reasonable assurance of 

the implementation of this element of the [WIP]: [] Establish impervious 

acreage treatment requirements in NPDES []MS4[] permits to achieve 

specific reductions in sediment, phosphorus and nitrogen consistent with this 

[WIP]. These permits will require the development of a detailed watershed 

restoration strategy that contains the following elements: . . . Completion of 

restoration efforts for twenty percent of the counties’ impervious surface area 
- 15 -

that is not already restored to the maximum extent practicable[].

WIP at 5-30 (paragraph breaks omitted).

Consistent with the WIP, in 2014, the MDE issued to the Counties MS4 permits 

“requiring compliance with the Chesapeake Bay [total maximum daily load] through the 

use of a strategy that calls for the restoration of twenty percent of previously developed 

impervious land with little or no controls within this five[-]year permit term as described 

in” the WIP. MDE, National Pollutant Discharge Elimination System Municipal Separate 

Storm Sewer System Discharge Permit [for Carroll County] at 15, available at https://mde.

maryland.gov/programs/Water/StormwaterManagementProgram/Documents/Carroll%20

Final%20Permit%20with%20attachments.pdf [https://perma.cc/FL5D-6UPU]; MDE, 

National Pollutant Discharge Elimination System Municipal Separate Storm Sewer System 

Discharge Permit [for Frederick County] at 15, available at https://mde.maryland.gov

/programs/Water/StormwaterManagementProgram/Documents/Signed%20Frederick%20

Permit%20with%20Attachments.pdf [https://perma.cc/XC4Y-8EMY].

From my perspective, the MDE lacked the authority to require the Counties to 

restore 20% of the impervious surfaces throughout the entirety of each county; in other 

words, the Counties’ MS4 permits simply require the Counties to restore 20% of the 

impervious surfaces in urbanized areas—i.e., the areas that the Counties’ MS4s serve. Just 

as the urbanized areas of each county determined whether the county’s MS4 was small, 

medium, or large, see 40 C.F.R. § 122.26(b)(4)(i), (b)(7)(i); 40 C.F.R. Pt. 122, App. I, so, 

too, do the urbanized areas of each county determine the extent of the county’s 

responsibility to restore 20% of impervious surfaces. It makes sense that each county 
- 16 -

should be responsible only for restoring 20% of impervious surfaces in urbanized areas; in 

other words, the areas that each county’s MS4 serves should be the same as the areas in 

which the county’s MS4 permit makes the county responsible for restoring 20% of 

impervious surfaces.

In addition to improperly requiring the Counties to restore 20% of the impervious 

surfaces throughout the entirety of each county, the MDE misclassified the Counties’ MS4s 

as medium rather than small. Generally, before October 1, 1994, the EPA and the MDE 

could “not require a permit . . . for discharges [that were] composed entirely of 

stormwater.” 33 U.S.C. § 1342(p)(1). But, this exception to the permit requirement did

not apply to “[a] discharge from a[n MS4] serving a population of 250,000 or more[,]” 33 

U.S.C. § 1342(p)(2)(C), or “[a] discharge from a[n MS4] serving a population of 100,000 

or more but [fewer] than 250,000[,]” 33 U.S.C. § 1342(p)(2)(D). An MS4 that serves a 

population of at least 250,000 is known as a “large” MS4, 40 C.F.R. § 122.26(b)(4)(i); an 

MS4 that serves a population of at least 100,000, but fewer than 250,000, is known as a 

“medium” MS4, 40 C.F.R. § 122.26(b)(7)(i); and, generally, an MS4 that is neither large 

nor medium is known as a “small” MS4, 40 C.F.R. § 122.26(b)(16)(ii). In short, “[p]ermits 

must be obtained for all discharges from large and medium [MS4]s.” 40 C.F.R. § 

122.26(a)(3)(i).

Whether an MS4 is large, medium, or small depends on the population of the 

incorporated place that the MS4 served according to the 1990 Decennial Census. See 40 

C.F.R. § 122.26(b)(4)(i), (b)(7)(i). The EPA promulgated an appendix that listed the 

counties that, according to the 1990 Decennial Census, had “[u]nincorporated urbanized 
- 17 -

population[s]” of at least 100,000, but less than 250,000. See 40 C.F.R. Pt. 122, App. I. 

The only Maryland county that the appendix listed was Howard County. See id. In other 

words, according to the EPA, Howard County’s MS4 was Maryland’s only medium MS4. 

See id.

The Majority correctly observes that, in 1990, neither Carroll County nor Frederick 

County had a population of at least “100,000 in unincorporated, urbanized areas[,]” and 

that, accordingly, neither Carroll County nor Frederick County “likely met the EPA’s 

contemporaneous interpretation of the medium [MS4] category[.]” Maj. Slip Op. at 85

(cleaned up). Yet, the Majority “decline[s] to hold that[,] today, . . . the Counties should 

instead be” considered to have had small MS4s. Id. at 85-86. I am unpersuaded by the 

reasons that the Majority gives for declining to right the wrong that has evidently 

occurred—namely, the misclassification of the Counties’ MS4s as medium rather than 

small. See id. at 85-89. Nor would I find merit in the MDE’s contentions, such as its 

argument that the Counties are equitably estopped from challenging the misclassification. 

In my view, the Counties’ mere “acquiesce[nce]” to the misclassification, id. at 89, is 

neither a reason to refrain from addressing the merits of their contention, nor a basis for 

concluding that the MDE properly exercised its authority to classify the Counties’ MS4s 

as medium. The MDE, not the Counties, has been in the driver’s seat when it comes to 

classification and permitting. If there is any question as to whether a misclassification has

occurred, the fault lies with the MDE, not the Counties.

Without a doubt, government protection of the environment has a sustaining and 

welcome purpose. Indeed, protecting and fostering the health of the environment is an 
- 18 -

important goal in today’s society, now more than ever. But, the government must follow 

the statutes and regulations that it establishes. Misapplication of environmental statutes 

and regulations serves no purpose and will result in diminishment of regard for the law.

For the above reasons, respectfully, I dissent.

Judge Hotten and Judge Getty have authorized me to state that they join in this 

opinion.
IN THE COURT OF APPEALS

OF MARYLAND

Nos. 5 & 7

September Term, 2018

______________________________________

MARYLAND DEPARTMENT OF THE 

ENVIRONMENT

v.

COUNTY COMMISSIONERS OF CARROLL 

COUNTY, MARYLAND

______________________________________

FREDERICK COUNTY, MARYLAND

v.

MARYLAND DEPARTMENT OF THE 

ENVIRONMENT

______________________________________

Barbera, C.J.

*Greene

*Adkins

McDonald

Watts

Hotten

Getty,

JJ.

______________________________________

Dissenting Opinion by Getty, J.

______________________________________

Filed: August 6, 2019

*Greene and Adkins, JJ., now retired, participated in 

the hearing and conference of this case while active 

members of this Court; after being recalled pursuant 

to the Maryland Constitution, Article IV, Section 3A, 

they also participated in the decision and adoption of 

this opinion.

Circuit Court for Carroll County

Case No. 06-C-15-068141 

Circuit Court for Frederick County

Case No. 10-C-15-000293 

Argued: September 13, 2018 
I join the dissent written by Judge Watts and agree with her analysis that the 

Maryland Department of the Environment (“the Department”) exceeded its authority by 

(1) issuing permit requirements that exceed the “maximum extent practicable” standard;

(2) requiring the Counties to restore 20% of all impervious surfaces county-wide; and (3) 

classifying each County’s municipal separate storm sewer system (MS4) as medium rather 

than small. Dis. Slip Op. at 1. 

I write separately to express my concern with this Court’s tradition of granting broad 

deference to an agency’s interpretation of statutes and regulations. Under the facts of this 

case, I would scale back the agency deference doctrine as recognized in Maryland. 

The Majority cites to Chevron U.S.A. v. Nat. Res. Def. Council, 467 U.S. 837 (1984), 

for the broad principle that this Court must defer to an agency’s interpretation of its 

controlling statutes. However, in Auer v. Robbins, 519 U.S. 452 (1997), the Supreme Court 

held that deference is only owed to an agency’s reasonable interpretations of its ambiguous

regulations. At a minimum, I would adopt the constraints of Auer deference – that the 

agency’s regulation be ambiguous and its interpretation reasonable to merit judicial 

deference. Absent such determinations, this Court has a duty to exercise its best judgment 

and resolve the issues at hand, else we “deny the people who come before us the neutral 

forum for their disputes that they rightly expect and deserve.” Kisor v. Wilkie, 139 S. Ct. 

2400, 2448 (2019) (Gorsuch, J., concurring).1 

 

1

In Kisor v. Wilkie, the Supreme Court clarified that Auer deference requires that (1) the 

regulation is “genuinely ambiguous”; (2) the agency’s reading is “reasonable,” or within 

the zone of ambiguity; and (3) the “character and context of the agency interpretation 
- 2 -

The pressing need for such constraints is best illustrated by the Majority’s deference

to the Department’s improper classification of each County’s MS4 as medium rather than 

small. The Clean Water Act and its corresponding regulations are not ambiguous—in fact, 

the Majority has already acknowledged that “neither County likely met the EPA’s 

contemporaneous interpretation of the medium category,” under “the EPA’s interpretation 

of its own regulations.” Maj. Slip Op. at 85. Rather than correct this error, the Majority

upholds a flawed agency decision that has subjected two rural counties to a burdensome 

regulatory scheme intended for densely populated jurisdictions such as Montgomery 

County and Baltimore City.

2

 

As described by the Majority, the Water Quality Act of 1987 extended the Clean 

Water Act’s effluent permit requirements to encapsulate point-source pollution contained 

in municipal stormwater. Nat’l Res. Def. Council, Inc. v. EPA, 966 F.2d 1292, 1296 (9th 

Cir. 1992). The Act proscribed a timetable for the implementation of these requirements, 

proceeding in two phases based on the size and perceived impact of each stormwater 

system. 33 U.S.C. § 1342(p)(2)-(4). As relevant, between 1987 and 1994 (“Phase I” of 

 

entitles it to controlling weight.” Id. at 2414-16 (2019). As Kisor was decided on July 26, 

2019, it was not briefed or argued by either party. I include it in this dissent not as 

controlling precedent, but to further illustrate the contours of Auer deference, and to 

highlight the persuasive concurrence calling for a more constrained, moderated view of 

agency deference. 

2 The EPA promulgated its Phase I implementing regulations in 1990 with the intent of 

regulating MS4s servicing “urbanized” areas, characterized by the Census Bureau as “highdensity development . . . a central city (or cities) with a surrounding closely settled area.”

See EPA, National Pollutant Discharge Elimination System Permit Application 

Regulations for Storm Water Discharges, Final Rule, 55 Fed. Reg. 47990, 48041, 48050 

n.5 (Nov. 16, 1990).
- 3 -

the permitting program) state agencies could only require permits for MS4s that (1) serve 

a population of 250,000 or more (a “large MS4”); (2) serve a population of more than 

100,000 but less than 250,000 (a “medium MS4”); or (3) are designated “a significant 

contributor of pollutants to waters of the United States.” § 1342(p)(2)(C)-(E). The 

substantive requirements contained in MS4 permits were left entirely to the discretion of 

the EPA and state regulatory bodies. See § 1342(p)(3)(B) (“Permits for discharges from 

municipal storm sewers . . . shall require controls to reduce the discharge of pollutants . . . 

as the Administrator or the State determines appropriate”).

The EPA has issued implementing regulations to further define its Phase I 

classifications. Rules promulgated in 1990 governing Phase I permits establish that the

“medium” category encompasses (i) MS4s serving between 100,000 and 250,000 people 

in an incorporated municipality; and (ii) a list of jurisdictions enumerated in Appendix I of 

the regulatory text.

3 40 CFR § 122.26(b)(7)(i)-(ii). In 1999, once all permitting deadlines 

had passed, the EPA elected to freeze these classifications based on each jurisdiction’s

population as reported in the 1990 census. EPA, National Pollutant Discharge Elimination 

System – Regulations for Revision of Water Pollution Control Program Addressing Storm 

 

3 Appendix I listed counties with at least 100,000 people in urbanized unincorporated 

areas, a threshold satisfied by neither County. As of the 1990 census, Frederick County 

had a total population of 150,208 with only 58,393 residing in urbanized areas – while 

Carroll County was home to 123,372 people, with no urbanized population. See Maryland 

Department of Planning, Urban and Rural Population in Maryland: 2000 and 1990 (May 

2002), available at: 

http://planning.maryland.gov/MSDC/Documents/Census/Cen2000/urban_rural/ua_rural2

k_cnty.pdf
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Water Discharges, Final Rule, 64 Fed. Reg. 68772, 68748-49 (Dec. 8, 1999).

4 These 

regulations contain “no minimum criteria or performance standards,” instead encouraging

the permitting agency to develop pollution controls for each permit on a case by case basis. 

Nat’l Res. Def. Council, 966 F.2d at 1308. 

Under this statutory and regulatory framework, neither County satisfied the 

requirements for a “medium MS4” during the Phase I permit period. As acknowledged by 

the Majority, “neither County likely met the EPA’s contemporaneous definition of the 

medium category,” as neither County had a population of 100,000 in an incorporated area, 

and neither County was enumerated in Appendix I. Maj. Slip Op. at 85; See Nat. Res. Def.

Council, Inc. v. New York State Dep’t of Envtl. Conservation, 34 N.E.3d 782, 794 n.16 

(N.Y. 2015) (holding that state agencies administering programs under the Clean Water 

Act are “bound to follow [the] EPA’s interpretation”). Although the Department may, 

notwithstanding population, designate jurisdictions as “significant contributor[s] of 

pollutants to the waters of the United States,” contemporaneous reports and 

correspondence by the Department demonstrate that the Counties were classified based 

solely on their projected population growth.

5 Therefore, by nonetheless requiring permits 

 

4 As the EPA suggested in the preamble to its 1999 regulations, state agencies may use 

their residual designation authority to “require more from operators of MS4s serving 

‘newly over 100,000’ populations.” Id. at 68749. This commentary does not expand the 

scope of the residual authority, which remains predicated on the determination that “storm 

water discharge from the source contributes to a violation of a water quality standard or is 

a significant contributor of pollutants to the waters of the United States.” Id. at 68781.

5 These reports and correspondence are detailed in appendices to the parties’ briefs. See, 

e.g., MDE, Basis for Final Determination to Issue Frederick County’s NPDES MS4 Permit
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of both Counties during Phase I, the Department contravened the unambiguous

requirements of the Clean Water Act. 

No statutory, regulatory, or judicial authority requires we adhere to this result. 

Contrary to the assertions of the Department and the conclusion of the Majority, 

reclassification would not implicate the anti-backsliding provision of the Clean Water Act. 

See 33 U.S.C. §1342(o)(1) (“[A] permit may not be renewed, reissued, or modified . . . to 

contain effluent limitations which are less stringent than the comparable effluent 

limitations in the previous permit”). This provision is inapplicable, as the Act contains an 

explicit exception for permits issued on the basis of “technical mistakes or mistaken 

interpretations of law.” 33 U.S.C. §1342(o)(2)(b)(ii). Absent the legally inaccurate 

designation of Carroll and Frederick County stormwater systems as “medium MS4s,” the 

Department would not have been authorized to require a permit of either County during 

the Phase 1 period. See 33 U.S.C. §1342(p)(1) (providing that, beyond the MS4 categories 

enumerated in §1342(p)(2), “the Administrator or the State . . . shall not require a permit 

under this section for discharges composed entirely of stormwater”). 

Similarly, the Counties’ “acquiescence” to their MS4 classification is entirely 

irrelevant to the question of reclassification. The Majority relies heavily on the notion that 

the Counties have operated within the Phase I permitting program for three decades without 

 

at 30 (Dec. 2014) (“MDE did not make a claim under its RDA [residual designation 

authority] that Frederick County must apply as a Phase I. . . . MDE had no need to . . . make 

a determination based on water quality violations or impairments”); MDE, Maryland’s 

NPDES Municipal Stormwater Monitoring at 1 (1997) (“MDE used projections from the 

Maryland Office of Planning (MOP) to designate Carroll, Charles, Washington, and 

Frederick counties when their populations surpassed 100,000”). 
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protest. See Maj. Slip Op. at 88-9 (reasoning that the Counties “have at the very least 

acquiesced [to Phase I] classification since the 1990s;” that “neither County (nor apparently 

anyone else) questioned the method that the Department used to assess the relevant 

population;” and that their acquiescence “may have foreclosed any need to invoke the 

Department’s residual designation authority”). In the 1990s, the Counties dipped their toes 

in the water, so to speak, with the altruistic goal of doing their fair and proportionate share 

to achieve Maryland’s clean water objectives. Their agreement and voluntary participation 

in the permitting program has no bearing on whether their classification was ever correct, 

as the Clean Water Act outright prohibited states from requiring a Phase I permit of

jurisdictions that do not meet the requirements of §1342(p)(2). Moreover, no established 

precedent suggests that historical acquiescence or administrative reliance have foreclosed

the Counties’ right to challenge their designation.

6

Lacking any legal justification for refusing the Counties’ request for reclassification, 

the Majority nonetheless defers to the post hoc judgment of the EPA, concluding that “the 

agencies charged with administering the Clean Water Act have consistently regarded the 

 

6 This argument appears to implicitly evoke the Department’s claim of equitable estoppel. 

MDE insists that Maryland’s Watershed Improvement Plan (WIP) relies on the Counties’ 

Phase I commitments. Equitable estoppel results from (1) a party’s voluntary action, (2) 

inducing good faith reliance, (3) resulting in a detrimental change in position. Permanent 

Fin. Corp. v. Montgomery Cty., 308 Md. 239, 247 (1986). At a very minimum, the 

Department has not suffered a detrimental change in position, as the Counties are on track 

to meet their Phase I commitments during the current permit cycle. E.g. Carroll County, 

2017 NPDES MS4 Permit Annual Report at 10 (Dec. 15, 2017), available at

http://ccgovernment.carr.org/ccg/npdes/2017_NPDES_Annual_Report.pdf. Moreover, 

any reliance was arguably in bad faith, as the Department, not the Counties, is responsible 

for interpreting its governing regulations.
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Counties as Phase I MS4s and that there is a reasonable basis for doing so.” Maj. Slip Op.

at 89. Granting an agency controlling authority over the interpretation of its own governing 

regulations amounts to an abdication of this Court’s essential duty to interpret and apply 

the law. See Kisor, 139 S. Ct. at 2425 (Gorsuch, J., concurring) (arguing deference 

“requires judges to accept an executive agency’s interpretation of its own regulations even 

when that interpretation doesn’t represent the best and fairest reading”).

Such absolute deference is improper even under the Majority’s stated standard of 

review. Although an agency’s factual findings are entitled to deference when supported 

by “substantial evidence,” Md. Dep’t of the Env’t v. Anacostia Riverkeeper, 447 Md. 88, 

120 (2016), the Majority openly acknowledges that the record contains “limited evidence 

of the Department’s decision-making process in classifying these Counties as Phase I 

jurisdictions in 1991.” Moreover, “it is always within our prerogative to determine whether 

an agency’s conclusions of law are correct.” Schwartz v. Md. Dep’t of Nat. Res., 385 Md. 

534, 554 (2005); See also Auer, 519 U.S. at 461 (deference not warranted where agency 

interpretation is “plainly erroneous or inconsistent with the regulation.”). The legal 

sufficiency of the Counties’ Phase I permits, governed entirely by the Clean Water Act and 

its corresponding regulations, falls squarely within the purview of this Court.7

 

7 The substantive terms of an MS4 permit are at the discretion of the Department, and 

therefore subject to an “arbitrary and capricious” standard of review. See Harvey v. 

Marshall, 389 Md. 243, 296-99 (2005). The Majority fails to identify any rational basis 

for tying pollution controls categorically to the scheduling requirements of the Clean Water 

Act—for example, requiring all Phase I counties to restore 30% of their total surface area 

by 2019, while requiring Phase II counties to restore 20% of their urbanized area by 2025. 

Rather, as discussed supra, the Clean Water Act and EPA regulations encourage states to 
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Applying Auer deference, an agency’s interpretation of its own regulations is only 

entitled to deference “if [the] regulation is genuinely ambiguous . . . even after a court has 

resorted to all the standard tools of interpretation.” Kisor, 139 S. Ct. at 2414. “[I]f the law 

gives an answer—if there is only one reasonable construction of a regulation—then a court 

has no business deferring to any other reading, no matter how much the agency insists it 

would make more sense.” Id. at 2415. Nowhere does the Majority identify any ambiguity 

in the plain language of the Clean Water Act or the implementing regulations promulgated 

in 1990 and 1999. Rather, as the Majority acknowledges, the law provides a clear answer: 

Neither County’s population, as reported in the 1990 Census, authorized their classification 

as “medium” MS4s under established law.

Allowing the Department to issue Phase I permits notwithstanding would “permit 

the agency, under the guise of interpreting a regulation, to create de facto a new 

regulation.” Id. (quoting Christensen v. Harris County, 529 U.S. 576, 588 (2000)). 

Moreover,

[w]hen we defer to an agency interpretation that differs from what we believe to be 

the best interpretation of the law, we compromise our judicial independence and 

deny the people who come before us the impartial judgment that the Constitution 

guarantees them. And we mislead those whom we serve by placing a judicial 

imprimatur on what is, in fact, no more than an exercise of raw political executive 

power.

Kisor, 139 S. Ct. at 2439 (Gorsuch, J. concurring). 

In the simplest terms, the Majority acknowledgesthat the Department’s construction

 

develop substantive permit terms on a case by case basis. See 33 U.S.C. § 1342(p)(3)(B); 

Nat’l Res. Def. Council, 966 F.2d at 1308.
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of its unambiguous regulatory mandate was incorrect, finds little evidence on record to 

support this interpretation, identifies no legal authority that bars judicial review, and yet 

defers regardless. By nonetheless “affording ‘controlling weight’ to [the Department’s] 

post-promulgation views” of its governing regulations, our ruling today perpetuates a 

longstanding inequity, and risks foreclosing judicial review to litigants seeking to challenge 

administrative overreach. Id. at 2446 (Gorsuch, J. concurring).

For the foregoing reasons, I respectfully dissent.