Sharing the Burden – Cost-Benefit Analysis from the First Reasonable Assurance Analysis Performed in the San Francisco Region
The recently adopted Municipal Regional Permit (MRP) for the San Francisco Region MS4 permittees includes new requirements for the development of Green Infrastructure Plans (GI Plans) and implementation of Total Maximum Daily Loads (TMDL) for PCBs and mercury in San Francisco Bay. Those efforts include a Reasonable Assurance Analysis (RAA) to quantitatively demonstrate how management actions result in the attainment of TMDL wasteload allocations and interim milestones defined by the MRP. The San Mateo Countywide Water Pollution Prevention Program (SMCWPPP) embarked on the first RAA performed in the San Francisco Bay Region. The baseline model used to establish the target pollutant loads for this analysis was a calibrated continuous simulation of runoff volume, sediment load, Mercury load, and PCB load for the critical condition year from the San Francisco Bay PCB Total Maximum Daily Load (TMDL), water year 2002 (10/1/2001 – 9/30/2002). Per MRP guidelines, GI implementation was responsible for 17.6% load reduction, which was 20.8% of the overall required load reduction for the TMDL (84.6%). This regional RAA provided a unique opportunity for the 20 municipal co-permittees to collaborate and identify a range of potential management scenarios to achieve those GI implementation targets. This collaboration provided opportunities for cost-sharing, adding efficiency and flexibility to the implementation of the permit. Four scenarios were developed to highlight bookends of projected implementation strategies, outcomes, and cost-savings. Each was derived using cost-benefit optimization analysis, as summarized below:
Scenarios 1 and 2: Uses cohesive sediment load as the reduction objective (most conservative approach). Given the uncertainties about PCB source locations, targeting an overall 17.6% load reduction of cohesive sediment (i.e., silts and clays) achieves the PCB load reduction objective for GI.
Scenarios 3 and 4: Assume that PCB sources are spatially distributed according the some of the best available spatial distribution estimates. The cost-benefit optimization process targets the modeled subwatersheds with the highest likelihood of having PCBs. Those scenarios highlight the potential cost savings (relative to Scenarios 1 and 2) that could be realized if PCB sources are identified and managed.
There are many possible ways to achieve a 17.6% load reduction for San Mateo County; however, the stakeholders’ collective interests are best served if the management responsibility is equitably allocated. There were two two different spatial constraints applied in formulating the optimization scenarios. The “Proportional” approach stipulates that each jurisdiction must individually achieve at least a 17.6% load reduction. On the other hand, the “Targeted” approach achieves the 17.6% load reduction countywide by allowing the management burden to vary freely across jurisdictional boundaries. Results showed that the targeted scenarios (2 and 4) provided significant cost savings over the proportional scenarios (1 and 3), especially in places where pollutant sources were spatially concentrated.
The speakers will provide an overview of the modeling approach and scenario results and engage the audience by inviting questions regarding other planning and management decisions that the modeling could support. This presentation demonstrates that where there is cooperation among jurisdictions, results from these types of scenarios can provide a useful analytical framework for cost-sharing implementation of the most cost-effective management scenarios.