Total Maximum Daily Load (TMDL)

DEQ manages the Total Maximum Daily Load (TMDL) program for the State of Oklahoma. A TMDL is the process of establishing the sources of impairment in a given waterbody, whether from point sources (discharges) or non-point sources (runoff), determining the amount of reduction necessary to meet water quality standards in that waterbody, and allocating the loads to the various contributors of pollution. A margin of safety is also included in the TMDL calculation process.

Water quality modeling is the linkage between the sources of pollution and the instream water quality of a given waterbody. A model is a representation of the water-quality processes that occur in a given waterbody. Water quality modeling can be resource-intensive. Different levels of complexity may be used depending on the level of confidence required in a given situation.

 

Southeast Oklahoma Draft Bacteria and Turbidity TMDL Report and Public Notice

Please submit comments in writing to: Soojung Lim, Water Quality Division, Oklahoma Department of Environmental Quality, PO Box 1677, Oklahoma City, OK 73101-1677

or by email at Water.Comments@deq.ok.gov

Public Notice for the Southeast Oklahoma Bacteria and Turbidity TMDL – Comment period closes June 27, 2025

Southeast Oklahoma Bacteria and Turbidity Draft TMDL Report

Southeast Oklahoma Bacteria and Turbidity Draft TMDL 208 Fact Sheet

Arkansas – Keystone Basin Study Area Draft Bacterial TMDL Report and Public Notice

Please submit comments in writing to: Soojung Lim, Water Quality Division, Oklahoma Department of Environmental Quality, PO Box 1677, Oklahoma City, OK 73101-1677

or by email at Water.Comments@deq.ok.gov

Public Notice for the Arkansas – Keystone Basin Bacterial TMDL – Comment period closes June 20, 2025

Arkansas – Keystone Basin Draft TMDL Report

Arkansas – Keystone Basin Draft TMDL 208 Fact Sheet

Neosho and Verdigris Basins Bacterial and Turbidity Draft TMDL Report and Public Notice

Please submit comments in writing to: Tamara Scott, Water Quality Division, Oklahoma Department of Environmental Quality, PO Box 1677, Oklahoma City, OK 73101-1677

or by email at Water.Comments@deq.ok.gov

Public Notice for the Neosho and Verdigris Basins TMDL – Comment period closes May 9th, 2025

Neosho and Verdigris Basins Draft TMDL Report

Neosho and Verdigris Basins Draft TMDL 208 Fact Sheet

Lake Oologah TMDL Report  

Public Notice for the Lake Oologah Draft TMDL

Lake Oologah Draft TMDL Report

Appendix A – Data Acquisition and Assessment

Appendix B – Watershed Model Calibration and Validation Report

Appendix C – EFDC Hydrodynamic and Water Quality Model

Appendix D – Oklahoma Antidegradation Policy

Appendix E – Water Withdrawals in Verdigris River Basin

Appendix F – Sanitary Sewer Overflow Bypass Events

Appendix G – Stream Flow Data

Appendix H – NPDES Data

Appendix I – Ambient Monitoring Data at Watershed and Lake Stations

Appendix J – Stormwater Permitting and BMPs

Lake Oologah 208 Factsheet

Fort Gibson Lake TMDL Report

Public Notice for the Fort Gibson Lake Draft TMDL

Fort Gibson Lake TMDL – EPA Approval Letter

Fort Gibson Lake Draft TMDL Report

Appendix A – HSPF Watershed Model

Appendix B – EFDC Model

Appendix C – Antidegradation Policy

Appendix D – Ambient Monitoring Data

Appendix E – Stormwater Permitting and BMPs

Appendix F – SSO Bypass Events

Appendix G – Stream Flow Data

Appendix H – NPDES Data

Appendix I – Distributions for Maximum Daily Loads

Fort Gibson Lake 208 Factsheet

 

Draft TMDLs

Current Draft TMDL Public Notices are posted above.

Completed TMDLs

EPA approved TMDLs for the State of Oklahoma are available for viewing or download at the following web page:

Completed TMDLs by Planning Basin

Lake Thunderbird TMDL Project

Lake Thunderbird TMDLs for Nutrients, Turbidity, and Dissolved Oxygen received EPA approval on November 13, 2013. Documents and information related to development of the Lake Thunderbird TMDL can be found on the Lake Thunderbird TMDL Project Page.

Lake Thunderbird TMDL Report

Lake Thunderbird TMDL Project Page

The TMDL Process

Water Quality Monitoring – Surface water quality data is collected by State, federal, and local agencies.

Waterbody Assessment – Analysis of water quality data to determine if a waterbody is achieving water quality standards

303(d) List of Impaired Waterbodies – Waterbodies in the State of Oklahoma that do not meet water quality standards are compiled in the State’s 303(d) list.

TMDL Prioritization – DEQ prioritizes watersheds containing impaired waterbodies for TMDL development. A rating system is utilized to determine a priority ranking value for each impaired watershed.

TMDL Development – A Total Maximum Daily Load value for each cause of impairment in a waterbody is calculated using appropriate water quality models.

Public Review – TMDL reports are published for public review and comment. DEQ accepts any comments submitted during the specified review period.

Report submittal – DEQ submits the TMDL report to EPA for review and approval.

EPA approval – EPA approves the TMDL report if the TMDL calculations are technically sound and the report satisfies required elements.

Water Quality Modeling

DEQ employs the use of a number of different types of surface water quality modeling software. Model selection is based on the needs and complexity of a given project.

Load Duration Curves – Simple

QUAL2K – Stream and river water quality model developed at Tufts University for EPA

SWAT – Soil & Water Assessment Tool

LOADEST – Load Estimator software developed by USGS

HSPF – Hydrological Simulation Program – FORTRAN

BATHTUB – One-dimensional steady-state lake model

EFDC – Environmental Fluid Dynamics Code

ELCOM-CAEDYM – Estuary, Lake and Coastal Ocean Model – Computational Aquatic Ecostystem DYnamics Model

EPA TMDL Information

EPA Overview of TMDLs

Developing TMDLs

EPA Guidelines for reviewing TMDLs

Contact Watershed Planning

An interactive map of Oklahoma’s waterbodies is available at http://gis.deq.ok.gov/maps/.