TMDL Assessment

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TMDL Assessment

• ERS 482/682
• Small Watershed Hydrology

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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

water qualityin the waterbody
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EASY
ambientwaterquality
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
• 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/
• Nevadas TMDL report is at http//oaspub.epa.gov/w
  aters/state_rept.control?p_stateNV

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TMDL process
NRC (2002) Figure 1-1
All waters
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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

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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
• Land use
• Characteristics of the channel/riparian zone
• Flow regime
• Species harvest condition

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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 cant 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

No Integrity
No integrity does not necessarily mean the
waterbody is impaired!!!
BUT
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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
• 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

• 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
• Assess results

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Figure 5-2 NRC (2001)
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NRC (2001)