San Diego Region - Chollas Creek TMDL for Metals

The San Diego Regional Water Quality Control Board (San Diego Water Board) adopted the Chollas Creek Metals TMDLs Basin Plan Amendment (TMDLs) on June 13, 2007. These TMDLs were approved by the State Water Resources Control Board (State Water Board) through Resolution No. 2008-0054 on July 15, 2008. The State Office of Administrative Law (OAL) approved the TMDLs on October 22, 2008 as File No. 2008-0909-01 S. The U.S. Environmental Protection Agency (USEPA) approved the TMDLs on December 18, 2008. Based on the approval date from OAL, the official commencement date for these TMDLs is October 22, 2008. The TMDL documents are available for review at the San Diego Water Board Office. To request a file review please contact the Regional Board receptionist at (619) 516-1990, or email


Chollas Creek is an urban creek with highly variable flows. Much of the Creek has been channelized and concrete lined, but some sections of earthen creek bed remain. The creek originates in the Cities of Lemon Grove and La Mesa. It flows approximately 15 miles downstream, through the City of San Diego, and empties on the eastern shoreline of the central portion of San Diego Bay. Urban runoff enters the Creek throughout its course and is the main cause of the observed conditions as described below.

Since 1994, Chollas Creek storm water samples have frequently exceeded the Basin Plan narrative water quality objective for toxicity. These samples have also exceeded chronic and acute water quality criteria for metals established in the California Toxics Rule. Specifically, during the period 1994 - 2001, concentrations of copper and zinc during storm events have frequently exceeded acute and chronic criteria, while concentrations of cadmium and lead have frequently exceeded chronic and periodically exceeded acute criteria. These conditions resulted in the Creek being placed on the CWA Section 303(d) list in 1996 for toxicity, cadmium, copper, lead and zinc. Cadmium was delisted by the State Water Board in the 2006 list update.

In 1999, Toxicity Identification Evaluations (TIEs) revealed the observed toxicity to be caused primarily by zinc and to a lesser extent by copper. The household pesticide diazinon was also identified as a cause of toxicity and is currently being addressed by a separate TMDL that was adopted by the San Diego Water Board in August 2002. This TMDL was developed to address the toxicity caused by metals to aquatic life in Chollas Creek.

Amendments to the Chollas Creek Metals TMDL

Due to limited site-specific data during the original TMDL development, a default water effect ratio (WER) value of 1 was used to calculate numeric targets. Subsequently, data were collected and evaluated to update the copper and zinc numeric targets with site-specific WERs (for wet weather only), which take into account the physical and chemical characteristics of the water in Chollas Creek. This approach is consistent with USEPA water quality criteria for toxic pollutants in inland surface waters, enclosed bays, and estuaries (California Toxics Rule; 40 CFR 131.38).

On February 8, 2017, the San Diego Water Board adopted Resolution No. R9-2017-0015, amending Chapter 3 and Chapter 7 of the Water Quality Control Plan for the San Diego Basin (Basin Plan) to 1) adopt the site-specific WERs and 2) update the TMDL numeric targets to incorporate the WERs. The State Water Board approved the amendments at its September 17, 2019 public hearing; OAL approved the regulatory action on March 5, 2020 (effective date of updated TMDLs); and USEPA approved the amendments on March 26, 2020.

For more information related specifically to the site-specific WERs for Chollas Creek copper and zinc TMDLs, please visit the following web page:

How to Receive Updates on the Chollas Creek Metals TMDL

The San Diego Water Board would like to keep interested persons fully informed during the final approval process for Chollas Creek Metals TMDLs, including approval by the State Water Board, the OAL, and the USEPA. Updates on the Chollas Creek Metals TMDLs will only be sent to persons that specifically request this information. To receive updates from the San Diego Water Board, you must either: 1) subscribe to our electronic mailing list; or 2) send an email request to the contact person listed below to have information sent to you via U. S. Mail. You can subscribe to our electronic mailing list. You may also obtain information from our Website or by appointment at the San Diego Water Board office.

Public Documents

The following documents are available for review at the San Diego Water Board Office. To request a file review please contact the Regional Board receptionist at (619) 516-1990, or email

Dated Posted Description
State Water Resources Control Board Approval
  • Technical Report
  • Resolution No. R9-2007-0043 and Basin Plan amendment
  • Appendices
    • Appendix A Data
    • Appendix B Cadmium Delisting
    • Appendix C Chollas Creek Sediment Metals
    • Appendix D Wet and Dry Weather Models
    • Appendix E Land Use Loading Analyses
    • Appendix F Statistical Comparison of Measured Values and Modeled Values for Flow and Water Quality
    • Appendix G Metals Concentrations Reduction Percentages
    • Appendix H Site-Specific Objectives
    • Appendix I Environmental Analysis, Checklist, and Economic Factors
    • Appendix J Tentative Resolution No. R9-2007-0043 and Attachment A
    • Appendix K Scientific Peer Review
    • Appendix L Response to Peer Review Comments
    • Appendix M Response to Comments

For documents related specifically to the aforementioned amendments (effective March 5, 2020), please visit the web page for site-specific WERs for Chollas Creek copper and zinc TMDLs:

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