Introduction to TMDLs with 

Examples from the 

Chesapeake Bay

Rich Batiuk

Associate Director for Science

U.S. EPA Region 3

Chesapeake Bay Program Office
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What is a TMDL?

A calculation of a pollutant load that 

assures that, when implemented, an 

impaired segment will attain and 

maintain all applicable water quality 

standards. T

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What is a TMDL?

TMDL = WLA + LA + MOS

WLA = Sum of all point sources

LA = Sum of all nonpoint sources including natural 

background

MOS = Margin of safety accounting for uncertainty 

about the relationship between loads and water 

quality

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TMDL Allocation

Considerations when making allocation 

decisions:

– Source of the pollutant (point source or runoff)

– Controllability of the pollutant (i.e., atmospheric)

– Regulatory authority to control pollutant

– Cost of each allocation option

– Certainty of water quality impact in receiving water 

– Reasonable assurance that allocation can be met

– Stakeholders objectives

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TMDL Allocation (cont.)

• Each point source with an individual NPDES 

permit receives an individual wasteload allocation 

(WLA)

• Point sources covered under general permits 

may get a gross wasteload allocation (WLA)

• All other sources and background must be 

included in the load allocation (LA), which can be 

one gross number or subdivided among 

individual sources or categories.

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TMDL Allocation

Point Source 1

(WLA)

NPS Source 

Category 2

(LA)

Explicit 

MOS

Reserve

Capacity

Allocation Example

Point Source 3

(WLA)
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Listing of Impaired Waters

1. States identify waters not meeting WQS based 

on “all existing and readily available information”

2. States establish priorities for TMDLs on basis of 

the use and severity of problem 

3. States develop schedule of TMDLs to be 

developed within 2 years 

4. States provide long term plan – complete 

TMDLs 8 to 13 years from first listing

5. EPA has 30 days to approve or disapprove list 

submitted April of each even year

– If EPA disapproves State list, EPA has 30 days to 

develop list for the State

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Adopt Water Quality Standards

Monitor & Assess Waters

List Impaired & Threatened Waters

Develop Total Maximum 

Daily Loads (TMDL) 

CWA Restoration Framework

Implement Point & Nonpoint 

Source Allocations
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TMDL Implementation

• TMDLs are implemented through other 

sections of the Clean Water Act

• Point Sources:

– Permit limits consistent with WLA are 

enforceable under CWA through National 

Pollutant Discharge Elimination System 

(NPDES) 

– Issued by EPA or States w/ delegated authority

• Nonpoint Sources:

– No federal regulatory enforcement program 

– Primarily implemented through State/local NPS 

management programs (limited number 

w/regulatory enforcement)

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Low to no 

dissolved 

oxygen in the 

Bay and tidal 

rivers every 

summer
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Impact of a Pound of Nitrogen/Phosphorus on Bay Water Quality
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Relative effectiveness (Riverine * Estuarine Delivery)

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Major Rivers by Jurisdiction Ranked by Pollution Impact on Bay
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1985 Base 2009 Target Tributary Loading Loading Loading E3 All

Scenario Calibration Scenario Load A Strategy Scenario Scenario Scenario Scenario Forest

342TN 309TN 248TN 200TN 191TN 190TN 179TN 170TN 141TN 58TN

24.1TP 19.5TP 16.6TP 15.0TP 14.4TP 12.7TP 12.0TP 11.3TP 8.5TP 4.4TP

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Open Water Violations

Deep Water Violations

Deep Channel Violations

Dissolved Oxygen Criteria Attainment

Basin-wide load is

190 N and 12.7 P (MPY)
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www.epa.gov/chesapeakebaytmdl

Setting the Pollution Diet
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Setting the Pollution Diet

www.epa.gov/chesapeakebaytmdl
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8 Watershed Implementation Plan Elements

• Nutrient and Sediment Target Loads 

• Current Program Capacity 

• Mechanisms to Account for Growth 

• Gap Analysis

• Commitment to Fill Gaps: Policies, Rules, Dates for 

Key Actions

• Tracking and Reporting Protocols

• Contingencies for Delayed or Incomplete 

Implementation

• Detailed Appendix Supporting Bay TMDL Allocations
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Phase I: 92 Bay Segments Phase II: Counties

2010 2011
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Agriculture and TMDLs

• Ensures all sources get their share of the 

reduction responsibility

• Reasonable assurance puts focus on 

regulated point sources

• Has lead to efforts to fully account for and 

credit non-cost shared conservation practices

• Creates the potential for a large marketplace 

for nutrient trading

• Provides a measure of certainty for producers
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Questions & Comments

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