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TMDL Assessment

TMDL Assessment. ERS 482/682 Small Watershed Hydrology. 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

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TMDL Assessment

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  1. TMDL Assessment ERS 482/682 Small Watershed Hydrology

  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

  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 qualityin the waterbody

  4. effluentwater quality Point source controls EASY ambientwaterquality Point and nonpoint source controls NOT SO EASY

  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!

  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

  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

  8. Determinedesignated use/standard Every two years Listing Planning Implementation TMDL process NRC (2002) Figure 1-1 All waters

  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

  10. NPDES permits(effluent stds) TMDL standard Instreamflows; TMDLplans 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

  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.

  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)

  13. 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…

  14. Biological integrity Figure 3: Karr and Chu (1999)

  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

  16. 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.

  17. TMDL process NRC (1999) • Identify designated uses • Identify impaired water bodies • Establish priority • Allocate maximum total loadings of contaminants among sources

  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 HERE

  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

  20. Adaptive implementation 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

  21. Figure 5-2: NRC (2001)

  22. NRC (2001)

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