Development of TDS & Nitrogen Water Quality Objectives Based On Maximum Beneficial Use

Groundwater Runoff
in the Chino Basin

Chino Basin Watermaster /
Inland Empire Utilities Agency

The Chino Basin Watermaster (CBWM) and the Inland Empire Utilities Agency (IEUA) participated in the Santa Ana Watershed-wide Total Dissolved Solids (TDS) and Nitrogen Investigation. The purpose of this investigation was to develop TDS and nitrogen objectives based on the State Water Resources Control Board (SWRCB) Executive Order 68-16. The Executive Order 68-16 requires that Regional Boards develop water quality objectives based on the ambient water quality conditions that were present at the time when the first Basin Plan was developed.

WEI developed a scientifically-based method to compute ambient TDS and nitrogen concentrations. The method was developed in 1973 (corresponding to the objectives) and in 1997 (corresponding to the then current ambient concentration). The proposed objectives for the northern Chino Basin Management Zones ranged from 260 to 290 mg/L for TDS and 4 to 5 mg/L for nitrogen. The then current ambient TDS and nitrogen concentrations were 300 mg/L and 7.4 mg/L, respectively; thus, implying that there was no assimilative capacity for TDS or nitrogen. The implication of no assimilative capacity is that the TDS and nitrogen mass added to groundwater from the recharge of recycled water would have to be mitigated at great cost.

WEI was successful in raising the TDS and nitrogen objectives to 420 mg/L and 5 mg/L for TDS and nitrogen, respectively. Through technical, financial, and institutional analyses, WEI was able to demonstrate that raising the objectives would promote the maximum beneficial use of the waters of the State and be protective of beneficial uses.

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