Formatted Title
Sea Level Rise Impacts on Coastal Site Remediation: Conducting Vulnerability Assessments to Ensure Remedy Resilience
Background/Objectives
Sea level rise (SLR) affects coastal areas in two ways: (1) surface inundation of near-shoreline areas by rising seawater, and (2) an increase in groundwater level due to the rising head imposed by surface water. Both processes have the potential to affect existing remedies and remedial planning for near-shore properties. Although surface water inundation can be controlled by engineered structures and nature-based solutions, the impact of SLR on rising groundwater levels presents greater challenges.
Regulatory agencies in California have developed guidance for conducting SLR Vulnerability Assessments (SLRVAs) and developing adaptation plans to ensure existing and future remedies are resilient in the face of climate change. In addition, coastal landfills in the San Francisco Bay Area are now required to prepare Long-Term Flood Protection Plans (LTFPPs) that include an evaluation of landfill resilience (containment and stability) from SLR-induced surface water inundation and groundwater rise/emergence. The new guidance and order now serve as the basis for potential changes to approved and completed site remedies and containment systems.
Screening tools for predicting groundwater rise under multiple SLR scenarios for the San Francisco Bay Area are available to the public, and some regulatory agencies direct responsible parties to use them. However, some of the modeled results are in reference to inappropriate datums and the predictions do not consider important site-specific data and information. We performed multiple site-specific SLRVAs along the California coast using conservative methods to evaluate potential future impacts to site remedies and develop LTFPPs. This presentation focuses on the technical approach and methodology to evaluate potential SLR-induced groundwater impacts at coastal contaminated sites and landfills.
Approach/Activities
Case studies will be presented to demonstrate the technical approach to conducting SLRVAs. The approach includes site-specific analysis of historical water level trends, tidal influence, groundwater flow conditions, and future development plans. The response of the groundwater system to the changing SLR discharge boundary is evaluated with a flux-controlled approach (i.e., linear superposition of SLR magnitudes) and modeling that considers the dissipation of the groundwater response with distance from the shore under various climatic conditions (recharge). We will describe methods for generating maps of predicted groundwater rise and emergence, and how to use the results to quantify remedy vulnerability and identify adaptations.
Results/Lessons Learned
Site-specific evaluation of SLR-induced groundwater rise is necessary to evaluate remedy resilience and ensure proper contingencies are in place for adaptation. Quantifying groundwater occurrence and historical trends while incorporating uncertainty analysis of future climatic conditions need to be continuously evaluated over a project’s lifespan. Overly conservative approaches by California regulatory agencies and use of outdated SLR projections has the potential to delay development at sites with low threat and low risk to human health and the environment. Regional adaptation planning is also an important factor when considering site resilience to SLR.