Transcript TMDL Assessment ERS 482/682 Small Watershed Hydrology Lecture 21 - 1

TMDL Assessment
ERS 482/682
Small Watershed Hydrology
ERS 482/682 (Fall 2002)
Lecture 21 - 1
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
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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
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water quality
in the waterbody
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effluent
water quality
Point source controls
EASY
ambient
water
quality
Point and nonpoint source controls
NOT SO EASY
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Nonpoint sources
• Examples:
– Runoff from urban areas,
construction sites, golf
courses, etc.
– Atmospheric deposition
– Groundwater seepage
– Snowmelt
• We need to know about
watershed hydrology!
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TMDL program
• States must identify waters not meeting ambient
water quality standards
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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
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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
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TMDL process
NRC (2002) Figure 1-1
All waters
Determine
designated use/
standard
Every two years
Listing
Planning
Implementation
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Ambient water quality standards
• Designated use: Describes
the goal of the water quality
standard
– Examples:
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Swimming
Boating
Drinking water
Wildlife
• Criterion: represents the
condition of the waterbody
that supports the designated
use
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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:
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Land use
Characteristics of the channel/riparian zone
Flow regime
Species harvest condition
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NPDES permits
(effluent stds)
TMDL
standard
Instream
flows; TMDL
plans
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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.
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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)
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Integrity standards
• Integrity: biological condition of
waterbodies that have not been altered by
human activity
BUT…
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No integrity does not
necessarily mean the
waterbody is impaired!!!
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Biological integrity
Figure 3: Karr and Chu (1999)
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Integrity standards
• Indices (Box 3-5)
– Index of Biological Integrity (IBI)
• Multimetric approach to assess biological condition
• Combines measures of condition in
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Individuals
Populations
Assemblages
Landscapes
• Sites are scored according to metrics
• Overall score indicates the biological condition of the
waterbody
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Common pitfalls
Karr and Chu (1999)
• 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.
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TMDL process
NRC (1999)
• Identify designated uses
• Identify impaired water bodies
• Establish priority
• Allocate maximum total loadings of
contaminants among sources
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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 HERE
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Model selection
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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
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TMDL process
NRC (1999)
• Identify designated uses
• Identify impaired water bodies
• Establish priority
• Allocate maximum total loadings of
contaminants among sources
• Implement controls
Adaptive implementation
• Assess results
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Figure 5-2: NRC (2001)
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NRC (2001)
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