The San Francisco Bay Area Nutrient Watershed Permit: Challenges Associated with Evaluating 37 Different WRRFs

The San Francisco Regional Water Quality Control Board (Water Board) issued a Regional Watershed Permit for 37 Water Resource Recovery Facilities (WRRFs) discharging into five identified hydrologic sub-embayments in April, 2014 (Order No. R2-2014-0014). The permit requires that Bay dischargers assess their nutrient loads and evaluate strategies for nutrient load reduction, should reductions be required in the future. The permit includes four key elements for evaluating nutrient load reduction opportunities at WRRFs (if supported by sound science):Plant optimizationSidestream treatmentPlant upgradesNutrient reduction by other means (including source control, natural treatment systems, diversion of effluent to water recycling, and others)The 37 WRRFs are working collectively under the joint powers agency, Bay Area Clean Water Agencies (BACWA), to submit one coordinated study. Unit cost metrics were including as part of the Scoping and Evaluation Plan as a means to normalize the data across the WRRFs (HDR and Brown and Caldwell, 2014). The two metrics initially proposed were unit capital cost (/flow capacity) and unit removal cost efficiency (/mass nutrient removed). The challenge has been that the unit costs do not always provide an accurate depiction of the results, in particular the unit removal cost efficiency. This paper will present various approaches, the inherent challenges, and strategies for how to present unit removal cost efficiencies output.