San Diego Region - Chollas Creek TMDL for Diazinon


The San Diego Water Board developed the Chollas Creek Total Maximum Daily Load (TMDL) to address water quality impairment due to the pesticide diazinon. Diazinon is causing acute and chronic toxicity to aquatic life in Chollas Creek, an urban creek draining to San Diego Bay. Diazinon is an organophosphate insecticide common in indoor, residential, landscape and agricultural applications. Urban storm water flows are the primary source of diazinon to Chollas Creek.

Toxicity in Chollas Creek due to diazinon during storm events was the basis for placement of Chollas Creek onto the List of Water Quality Limited Segments in 1996 (commonly referred to the 303(d) List). Federal law required the San Diego Water Board to develop a TMDL for waters on this list.

A diazinon TMDL was developed to the meet the toxicity water quality objective in Chollas Creek, ensuring that water quality with respect to diazinon supports the aquatic life beneficial uses of the creek. The San Diego Water Board adopted the TMDL on August 14, 2002, the State Water Resources Control Board subsequently approved the TMDL on July 16, 2003. The Office of Administrative Law and the USEPA approved the TMDL on September 11, 2003, and November 3, 2003 respectively.

Public Documents

Documents associated with the adoption of this TMDL 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 Documents available for public review include, but are not limited to:

  • Resolution No. R9-2002-01213
    • Attachment A (Basin Plan Amendment)
  • Technical Report (Dated August 14, 2002)

The Chollas Creek TMDL for Diazinon is being implemented through Order No. R9-2004-0277, and through other requirements incorporated into the San Diego County storm water discharge requirements contained in Order No. R9-2013-0001.

For Additional Information

Please contact Ms. Cynthia Gorham at 619-521-3921, or by email at