How Can Site Specific Objectives (SSOs) Aid in TMDL Compliance?

Southern California continues to face a multitude of water quality problems. Along with bacteria and trash, ammonia and metals constitute major water quality problem faced by the highly urbanized coast of California. The State has taken steps to address these problems through the development of Metals and Nutrient Total Maximum Daily Loads (TMDLs). Metals TMDLs have been adopted for multiple waterbodies in the region including the Los Angeles River, San Gabriel River, and the Calleguas Creek watershed. TMDLs addressing toxicity related to ammonia have been adopted for the Los Angeles River, San Gabriel River, Santa Clara River, and the Calleguas Creek watershed. These TMDLs outline a path for compliance with numeric targets for the various constituents. However, those numeric targets are based on national water quality criteria that do not necessarily reflect site-specific conditions. In 1994, the USEPA published detailed protocols for adjusting its national metals water quality criteria to reflect site-specific conditions using the “Water-Effect Ratio” (WER) method. The following details how the WER method was used for both copper and ammonia to develop site-specific criteria, which have aided in achieving TMDL compliance.