Site-Specific Water Effect Ratios (WERs) for Chollas Creek Copper and Zinc Total Maximum Daily Loads (TMDLs)

The San Diego Water Board is responsible for the regulation, protection and administration of water quality. The Water Quality Control Plan for the San Diego Basin (Basin Plan) designates beneficial uses for water bodies in the San Diego Region and establishes water quality objectives and implementation plans to protect those beneficial uses.

Any change to the Basin Plan requires a Basin Plan amendment. All Basin Plan amendments are subject to a full public participation and hearing process prior to adoption by the San Diego Water Board. Basin Plan amendments also must be approved by the State Water Resources Control Board (State Water Board), Office of Administrative Law (OAL) and, in many cases, the US Environmental Protection Agency (USEPA).

To receive information and announcements on Basin Plan amendments for the San Diego Region, including the Basin Plan amendment related to site-specific WERs for Chollas Creek copper and zinc TMDLs, please subscribe to the "Basin Planning Issues" email list at

The current Basin Plan includes TMDLs for dissolved metals in Chollas Creek. These TMDLs went into effect on October 22, 2008. In accordance with the California Environmental Quality Act (CEQA), the San Diego Water Board prepared substitute environmental documents for the establishment of the TMDLs. Those documents contained significant environmental analysis and numerous findings related to the reasonably foreseeable methods of compliance, the impacts of the methods of compliance, feasible mitigation measures, and alternative means of compliance. Due to limited site-specific data during Chollas Creek Metals TMDL development, a default WER value of 1 was used to calculate numeric targets for metals. Since that time, data have been collected to update numeric target equations with site-specific WERs, which take into account the physical and chemical characteristics of the water in Chollas Creek.

This approach is consistent with USEPA's water quality criteria for toxic pollutants in inland surface waters, enclosed bays, and estuaries (California Toxics Rule; 40 CFR 131.38). The update requires a Basin Plan amendment.

CEQA Analysis

On September 24, 2015, the San Diego Water Board held a CEQA scoping meeting to provide information on the Basin Plan amendment and to receive public input on any new potential impacts to the environment from reasonably foreseeable methods of compliance for the Chollas Creek Metals TMDLs.

The San Diego Water Board accepted written comments through October 23, 2015 on the CEQA Environmental Checklist and any environmental impacts that should be considered. The following memo addresses comments submitted regarding the potential for downstream impacts to beneficial uses:

The investigative order for the mouth of Chollas Creek (referenced in the memo) was adopted on October 26, 2015. To review monitoring and assessment results of this investigative order, please visit the Geotracker website at (GeoTracker Site ID T10000006999).

Peer Review

The San Diego Water Board requested an external scientific peer review for the Basin Plan amendment pursuant to pursuant to California Health and Safety Code Section 57004.

San Diego Water Board Adoption

The Board considered adoption of the Basin Plan amendment at its December 14, 2016 meeting. Several issues were raised during the meeting. The Board asked staff to look into these issues and to bring the item back on the February 2017 Board meeting agenda. On February 8, 2017, the Board adopted Resolution No. R9-2017-0015.

State Water Board Adoption

The State Water Board accepted written comments on the Basin Plan amendment from August 23, 2017 to October 18, 2017.

On October 19, 2018, the San Diego Water Board sent a memo to the State Water Board regarding the protectiveness of site-specific water quality objectives for Chollas Creek. The purpose of the memo is, in part, to request that the State Water Board include additional data analyses to the record and release them for public review and comment.

The following data was analyzed in the memo:

The data set includes 1) 2010 and 2014 data collected by the City of San Diego for a study to develop site-specific WERs and 2) 2007-2017 data collected by municipal separate storm sewer system (MS4) dischargers in response to TMDL requirements and requirements in the San Diego Region National Pollutant Discharge Elimination System (NPDES) permit for MS4s. The additional data and associated analyses were incorporated into the Basin Plan amendment's administrative record.

The State Water Board accepted written comments on the memo from November 28, 2018 to January 18, 2019.

The State Water Board approved the Basin Plan amendment at its September 17, 2019 public hearing.

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