1 / 21

Introduction to TMDLs

West Metro Water Alliance A Path to Clean Water – Understanding TMDLs and Watershed Planning September 21, 2011. Introduction to TMDLs. Diane Spector Wenck Associates, Inc. Outline. What is a TMDL? What are the most common impairments? How are TMDLs calculated?

dyani
Download Presentation

Introduction to TMDLs

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. West Metro Water Alliance A Path to Clean Water – Understanding TMDLs and Watershed Planning September 21, 2011 Introduction to TMDLs Diane Spector Wenck Associates, Inc.

  2. Outline • What is a TMDL? • What are the most common impairments? • How are TMDLs calculated? • What is the difference between a wasteload and load and why should I care? • Biotic impairments: fish and bugs matter

  3. 1972 Clean Water Act • 1972 Federal Water Pollution Control Act was intended: • “… to restore and maintain the chemical, physical, and biological integrity of the Nation’s waters.”

  4. Minnesota Impaired Waters As of 2008 • 2,575 total impairments • Restored 14 impairments (2 lakes and 12 river segments) • 680 TMDLs in development (excl toxics) • 220 approved TMDLs in implementation In the Upper Mississippi River Basin • 69 rivers and 263 lakes are impaired • 468 TMDL studies needed

  5. Common Impairments-2010 list • 1,774 impairments on 388 rivers and 647 lakes. • 3,049 total impaired waters

  6. What is a TMDL? • A Total Maximum Daily Load is a calculation of the maximum amount of a pollutant that a water body can receive and still meet water quality standards, and an allocation of that amount to the pollutant sources.

  7. TMDL – A Number • WLA = Wasteload Allocation (attributed to existing or future permitted sources) • LA – Load Allocation (attributed to existing or future non-permitted sources) • MOS – Margin of Safety • RC – Reserve Capacity (Future Capacity)

  8. How are TMDLs calculated? Identify and measure or quantify sources of pollutant load • Watershed runoff • Point sources • Septic systems • Lake bottom sediments • Stream sediment oxygen demand • Atmospheric deposition

  9. How are TMDLs calculated? Model watershed hydrology and pollutant loading • Hydrologic and water quality model: P8, XP-SWMM, SWAT, HSPF • Predicted runoff volume based on actual precip • Pollutant load

  10. Modeled Sediment Load by Land Cover

  11. Total Phosphorus Budget Bald Eagle Lake

  12. How are TMDLs calculated? Model lake or stream response • Lake response model: BATHTUB, MNLEAP • Streams: QUAL2K • Inputs: annual runoff volume, load, lake volume, depth, stream morphometry, fitting factors • Adjust factors until model predictions match actual observed data

  13. How are TMDLs calculated? Using calibrated model, reverse calculate maximum load

  14. TMDL: Bald Eagle Lake

  15. What is the difference between Load and Wasteload? • A Wasteload is a permitted source • Industrial point source • Construction permit • MS4s: stormwater • Wasteload allocations are regulated in your NPDES Phase I and II permits • Load allocations are not regulated by permit: internal load, natural processes, atmospheric deposition, rural runoff

  16. Wasteload Allocations • Individual allocations • One or more permitted sources are allocated their own wasteload and reduction • Categorical allocations • Groups of permittees are allocated wasteloads and reductions

  17. Biotic Impairments • Measure with an Index of Biotic Integrity • IBI reflects composition and health of the biotic community in comparison to a reference • Summary of metrics, e.g.: • # target species • % community composition by target species • % or # pollution intolerant or tolerant species • # individuals or species

  18. Biotic Impairments • First step is Stressor Identification study • Often identify stressors other than conventional pollutants • May be a numeric TMDL or surrogate such as flow or impervious cover • May also include non-numeric targets

  19. Shingle Creek Biota TMDL Numeric: • Sediment oxygen demand load allocations, channel reshaping standards • Chloride wasteload allocations Non-numeric: • Specific habitat enhancements • Removal of fish barriers • Desirable flow duration curve

  20. A note on process • The purpose of a TMDL is to identify the load reductions necessary to restore water quality and biotic integrity • Also includes general implementation actions that will likely help meet those targets • Not expected to “solve the problem” • Implementation Plan contains more detailed actions

  21. Thank you!

More Related