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Watershed Improvement & Protection

TMDL Process, Prioritization & Progress

Revised On: Oct. 30th, 2026 - 10:58 am

The following is an overview of the process for establishing a Total Maximum Daily Load (TMDL) for pollutant parameters in impaired water. Depending on the complexity, watershed size, the number of pollutants contributing to the impairment, etc., this process typically takes three to five years.

TMDL Process

  • Step 1 — Project Prioritization: Arizona’s list of TMDLs on impaired waters is prioritized every two years as part of the Clean Water Act 305(b) & 303(d) Assessment | See Prioritization Criteria >
  • Step 2 — Data Review: Compilation of supporting information and existing data
  • Step 3 — Sampling and Analysis Plan: Includes site selection, sampling design, frequency, project duration, methods, budget, a health and safety plan, and other relevant information
  • Step 4 — Data Collection: Implementation of the sampling and analysis plan
  • Step 5 — Data Analysis: Analysis of all available data to identify sources of pollutants and recommend implementation activities to restore the water quality
  • Step 6 — Draft Report: Draft TMDL report incorporating data analysis findings and conclusions
  • Step 7 — Public Comment: Publish notice to receive public comment on the draft report in the Arizona Administrative Register per Arizona Revised Statutes §49-234(D)
  • Step 8 — Finalize Report: Review and respond to public comments, incorporate input into the report, if appropriate, and publish the final report in the Arizona Administrative Register per Arizona Revised Statutes §49-234(E)
  • Step 9 — TMDL Final Report Approval: Submit to EPA for approval

Arizona TMDL documents can be reviewed with EPA's "How’s My Waterway" portal:

How-to Guide | View > 

EPA's How’s My Waterway Portal | Visit Portal >

  • Oak Creek | Current Step: EPA Review
    Oak Creek and associated tributaries are impaired for E.coli. ADEQ has worked with a contractor to complete data collection and analysis efforts. The TMDL is under review by the EPA and pending their approval. 
  • Statewide Mercury TMDL | Current Step: Public Comment
    31 water bodies in Arizona are impaired for mercury. ADEQ is currently reviewing and responding to comments obtained during the TMDL’s Public Comment period. 
  • Queen Creek TMDL | Current Step: Public Comment
    Queen Creek and associated tributaries are impaired for copper and lead. ADEQ is currently reviewing and responding to comments obtained during the TMDL’s Public Comment period. 
  • Upper Agua Fria TMDL | Current Step: Public Comment
    Reaches of the Upper Agua Fria, Lynx Creek, and Big Bug Creek are impaired by multiple metals — Arsenic, Cadmium, Copper, Lead, Selenium, and Zinc. ADEQ is currently reviewing and responding to comments obtained during the TMDL’s Public Comment period. 
  • Patagonia Mountains Watershed TMDL | Current Step: Informal Public Comment
    Thirteen reaches in the Patagonia Mountains are impaired for heavy metals and pH. These reaches are located in the sub-watersheds of 3R Canyon, Alum Gulch, and Harshaw Creek that all flow into Sonoita Creek. ADEQ has worked with a contractor to update 45 TMDLs developed in 2003 and create TMDLs for six new impairments that were not originally covered. The TMDL draft has been sent to stakeholders for an informal review before undergoing the formal Public Comment process. 
  • Salt River TMDL | Current Step: Data Collection
    Salt River is impaired for Arsenic, E.coli and Phosphorus. ADEQ is sampling the area to account for data gaps.
  • Upper Verde River TMDL | Current Step: Data Collection
    Two reaches of the Upper Verde River are impaired for E. coli. ADEQ is working with a contractor to conduct a Microbial Source Tracking (MST) study to identify the potential sources of this impairment in support of a future TMDL.  
Revised On: Oct. 30th, 2026 - 10:58 am

Opportunities for Public Input

In addition to the required public comment period in Arizona Revised Statutes §49-234, ADEQ will accept informal input throughout the development of a TMDL.

For future ADEQ communications and outreach regarding TMDLs, sign up for email notifications | Subscribe >

TMDL Contact
Ph: 480-202-5039
Email >