Nitrogen / Total Dissolved Solids (N/TDS) Task Force

The Santa Ana River
in the Chino Basin

Chino Basin Watermaster /
Inland Empire Utilities Agency

The Santa Ana Watershed Project Authority (SAWPA) is a Joint Powers Authority located in Riverside, California. The Porter-Cologne Water Quality Control Act and the Federal Clean Water Act both mandate periodic review of water quality control plans. A N/TDS Task Force was formed to conduct studies regarding the TDS and nitrate objectives and other components of the N/TDS management plan. SAWPA, acting as administrator for the Task Force, retained WEI to conduct scientific investigations to support the Task Force.

A work plan and stakeholder process was developed to address all of the TDS and nitrogen related issues in the Basin Plan. WEI developed and implemented methodologies to re-define groundwater quality objectives based on the best data and technology available. WEI updated the groundwater sub-basin boundaries — now termed management zones — based on the most current hydrogeologic understanding. WEI developed a comprehensive relational database for groundwater and surface water for the entire Santa Ana River Watershed and developed conceptual models for all of the groundwater basins in the watershed. In addition, WEI developed a new methodology to estimate ambient water quality in groundwater basins based on sound scientific and statistical methods. Computed historical ambient groundwater quality was then used to establish groundwater quality objectives in the entire watershed.

WEI was able to demonstrate that the TDS and nitrogen objectives could be raised above antidegradation levels for the Beaumont, Chino, Cucamonga, and Yucaipa Basins. These are the only groundwater basins in the State of California with maximum benefit-based objectives.

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