SAWPA Waste Load Allocation Model Update

Customer Profile

The Santa Ana River Watershed drains a 2,650 square-mile area that is home to more than 6 million people. The Santa Ana Watershed Project Authority (SAWPA) focuses on a broad range of water resource issues including water supply reliability, water quality improvement, recycled water, wastewater treatment, groundwater management, brine disposal, and integrated regional planning.

The SAWPA Basin Monitoring Program Task Force is a group of 20 stakeholders representing public agencies that serve areas in the Santa Ana River Watershed.

Waste load is the maximum load of pollutants a body of water can receive and still meet water quality standards. The Waste Load Allocation Model (WLAM) supports regional permitting to determine the portion of the total load that each entity is authorized to discharge.


SAWPA developed a waste load allocation model (WLAM) to gain insight into the potential impacts on the basin from surface water discharge and to forecast Total Dissolved Solids (TDS) and Total Inorganic Nitrogen (TIN) concentrations in surface water and groundwater recharge. 

To support ongoing salt management and to assist the permitting process for wastewater discharge, the task force needed to update and recalibrate previous models to project surface water concentrations for each reach of the Upper Santa Ana River, including discharge at Prado Dam. Unfortunately, the existing model was developed using proprietary software that constrained their alternatives when updates were required.

SAWPA needed a partner with extensive understanding of, and experience with, projects of this scope, with a proven track record of navigating not only the science, but also the permitting process and the challenge of balancing the demands of multiple stakeholders.

Geoscience Solution

The task force engaged Geoscience to update the model. To provide SAWPA with maximum flexibility and the peace of mind that the modeling program was well tested, Geoscience migrated the previous WLAM from proprietary code to an industry-standard open-source platform (HSPF) that is widely used and federally supported by the Environmental Protection Agency and the U.S. Geological Survey.

Geoscience expanded the new model domain to capture Orange County Water District recharge operations south of Prado Dam, incorporated new hydrologic data, and recalibrated against observed streamflow and TDS and TIN concentrations.

Contact Lauren Wicks to learn more about this case study.

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