ERS 482/682 (Fall 2002) Lecture 21 - 1

TMDL Assessment

ERS 482/682Small Watershed Hydrology

ERS 482/682 (Fall 2002) Lecture 21 - 2

Definitions

• TMDL: total maximum daily load of a pollutant that achieves compliance with a water quality standard

• TMDL process: plan to develop and implement a TMDL

• pollutant: substance added by humans or human activities; also habitat destruction, hydrologic modification, etc.

• pollution: man-made or man-induced alteration of chemical, physical, biological, and radiological integrity of water

ERS 482/682 (Fall 2002) Lecture 21 - 3

TMDL program

• Originates from Section 303d of the Clean Water Act:– Makes it the responsibility of the states to

assess whether or not ambient water quality standards are being met for individual waterbodies

– If the ambient water quality standards are not being met, a water quality management program must be implemented to achieve the standards water quality

in the waterbody

ERS 482/682 (Fall 2002) Lecture 21 - 4

ambientambientwaterwaterqualityquality

effluenteffluentwater qualitywater quality

Point source controls

Point and nonpoint source controls

EASEASYY

NOT SO EASYNOT SO EASY

ERS 482/682 (Fall 2002) Lecture 21 - 5

Nonpoint sources

• Examples:– Runoff from urban areas,

construction sites, golf courses, etc.

– Atmospheric deposition– Groundwater seepage– Snowmelt

• We need to know about watershed hydrology!

ERS 482/682 (Fall 2002) Lecture 21 - 6

TMDL program

• States must identify waters not meeting ambient water quality standards– Define pollutants– Define sources– Establish TMDLs necessary to secure the standards– Allocate responsibility for reducing pollutant releases

• 1992 amendment to TMDL regulations– States must submit lists of impaired water bodies

every two years

ERS 482/682 (Fall 2002) Lecture 21 - 7

TMDL program

• Reports are at: http://www.epa.gov/owow/tmdl/

• Nevada’s TMDL report is at http://oaspub.epa.gov/waters/state_rept.control?p_state=NV

ERS 482/682 (Fall 2002) Lecture 21 - 8

TMDL process

All waters

Determinedesignated use/

standard

Listing

Planning

Implementation

NRC (2002) Figure 1-1

Every two years

ERS 482/682 (Fall 2002) Lecture 21 - 9

Ambient water quality standards

• Designated use: Describes the goal of the water quality standard– Examples:

• Swimming• Boating• Drinking water• Wildlife

• Criterion: represents the condition of the waterbody that supports the designated use

ERS 482/682 (Fall 2002) Lecture 21 - 10

Types of water quality criteria

• Pollutant load(s) from source(s)• Ambient pollutant concentration in

waterbody• Human health and biological condition• Controls on sources of pollution other

than pollutants:– Land use– Characteristics of the channel/riparian zone– Flow regime– Species harvest condition

NPDES permits(effluent stds)

TMDLstandard

Instreamflows; TMDL

plans

ERS 482/682 (Fall 2002) Lecture 21 - 11

Desirable criteria

• Measurable– Specify duration, frequency, and magnitude

for chemical criteria

• Derived from the designated use– Biocriteria such as numeric measures of

fish, benthic invertebrates, algae, etc.

ERS 482/682 (Fall 2002) Lecture 21 - 12

Some problems with standards

• Standards that are not measurable– Problem: What do you do if you can’t

measure as specified?

• Non-exceedence standard– Problem: Under what circumstances do you

define exceedence?

• Flow restriction standards– Problem: Wet weather flows (storm runoff)

ERS 482/682 (Fall 2002) Lecture 21 - 13

Integrity standards

• Integrity: biological condition of waterbodies that have not been altered by human activity

BUT…No integrity does not

necessarily mean the waterbody is impaired!!!

ERS 482/682 (Fall 2002) Lecture 21 - 14

Biological integrityFigure 3: Karr and Chu (1999)

ERS 482/682 (Fall 2002) Lecture 21 - 15

Integrity standards

• Indices (Box 3-5)– Index of Biological Integrity (IBI)

• Multimetric approach to assess biological condition• Combines measures of condition in

– Individuals– Populations– Assemblages– Landscapes

• Sites are scored according to metrics• Overall score indicates the biological condition of

the waterbody

ERS 482/682 (Fall 2002) Lecture 21 - 16

Common pitfalls

• Expectation of simple correlations• Inappropriate application of reference

condition• Inadequate sampling design• Inappropriate consideration of sources

of variability• Incompatible data sets• Inappropriate tests of metrics• Etc.

Karr and Chu (1999)

ERS 482/682 (Fall 2002) Lecture 21 - 17

TMDL process

• Identify designated uses

NRC (1999)

• Identify impaired water bodies• Establish priority• Allocate maximum total loadings of

contaminants among sources

ERS 482/682 (Fall 2002) Lecture 21 - 18

Allocation of maximum loads

• Determine relative contributions of different stressors

• Assess possible management options– Changes in hydrology– Changes in biology– Pollutant load limits

MODELS CAN BE USEFUL HEREMODELS CAN BE USEFUL HERE

ERS 482/682 (Fall 2002) Lecture 21 - 19

Model selection

• Focus on standard/criteria• Based on scientific theory• Prediction uncertainty is reported• Appropriately complex• Appropriate for available data• Credible to stakeholders• Cost is feasible and sustainable• Flexibility

ERS 482/682 (Fall 2002) Lecture 21 - 20

TMDL process

• Identify designated uses

NRC (1999)

• Identify impaired water bodies• Establish priority• Allocate maximum total loadings of

contaminants among sources• Implement controls• Assess results

Adaptive implementation

ERS 482/682 (Fall 2002) Lecture 21 - 21

Figure 5-2: NRC (2001)

ERS 482/682 (Fall 2002) Lecture 21 - 22

NRC (2001)