Formatted Title:

Adaptive Modeling Approach to Inform Source Identification and Management Decisions in San Leandro Bay

Background/Objectives:

Assessment of the fate and transport of contaminants in San Francisco Bay is needed to address priority sediment and contaminant management questions for local stakeholders. In particular, polychlorinated biphenyl (PCB) contamination in sediment in San Leandro Bay (SLB) has resulted in its designation as a high-priority area for further study in San Francisco Bay. Contaminated sediment enters SLB through multiple local tributaries associated with industrial activity. The incoming upland material mixes with sediment within the SLB and more widely in San Francisco Bay and deposits on intertidal mudflats where it poses an ecological risk to local biota. The exposure risk of PCBs within the environment is governed, in part, by the contribution of contaminated material from source areas and the rate of relatively clean material depositing on the older contaminated sediment. In conjunction with available sediment and contaminant data, numerical modeling has been used to evaluate the relative contribution from a range of potential sources and project recovery time scales in the system to inform watershed management decisions.

Approach/Activities:

The San Francisco Estuary Institute (SFEI) and Integral Consulting Inc. have completed a study to evaluate the sediment transport patterns within SLB by utilizing a combination of measured data and numerical models to assess recovery rates and sediment bed response over multiple time scales. The team developed and applied sediment loading from a Watershed Dynamic Model (WDM) to introduce sediment to a hydrodynamic and sediment transport model of SLB to evaluate sediment and contaminant transport patterns over various conditions. The transport model was used to understand contaminant transport patterns in SLB by individually tracking sediment from multiple sources to the system to determine their impact on bedded sediment in SLB.

Results/Lessons Learned:

The hydrodynamic and sediment transport model in SLB demonstrated deposition patterns consistent with historic sedimentation rate estimates. Model results provide the distribution of sediment from each of the potential sources of contamination throughout SLB. This approach provides useful management information despite data gaps in source concentrations of contaminated material. For example, the composition of sediment from sources at specific hot spot locations with SLB can be used to determine which sources are key contributors to ongoing bedded sediment contamination as well as evaluate the impact of PCB management and mitigation strategies on site conditions. The model results can readily be updated with source concentration data, as they become available. This study, as well as future data collection and model evaluations, will support sediment management decisions within SLB and the greater San Francisco Bay.

Allie King

Affiliation

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Adaptive Modeling Approach to Inform Source Identification and Management Decisions in San Leandro Bay