Title
Recommendation to Accept the September 2020 Report Titled, “City of Alameda, The Response of the Shallow Groundwater Layer and Contaminants to Sea Level Rise.” (Public Works 310)
Body
To: Honorable Mayor and Members of the City Council
EXECUTIVE SUMMARY
The 2019 Climate Action & Resiliency Plan (CARP) identified emergent groundwater as a potential future hazard and recommended additional analysis to characterize the shallow groundwater layer in Alameda and its response to sea level rise. Staff collaborated with Silvestrum Climate Associates to prepare, “The Response of the Shallow Groundwater Layer and Contaminants to Sea Level Rise” (September 2020, “Groundwater Report”). The Groundwater Report finds that the areas at risk of future flooding increase by up to 25% when considering emergent groundwater, and in certain areas this flooding occurs before coastal floodwaters overtop the shoreline. The Groundwater Report also identifies areas with projected emergent groundwater and existing contaminant concentrations above human health benchmarks as areas of potential concern. The Groundwater Report recommends adaptation solutions for the next update to Alameda’s CARP, including amendments to local building codes. Staff recommends the City Council accept the Groundwater Report and further the City of Alameda’s (City) integrated adaptation planning efforts.
BACKGROUND
Researchers at Silvestrum Climate Associates and the University of California, Berkeley collaborated on the development of a high-level, regional shallow groundwater layer in the San Francisco Bay Area using groundwater monitoring well data. The results of the analysis, released in 2018, revealed widespread shallow groundwater conditions along most of the shore of San Francisco Bay. As sea levels rise, the groundwater surface will also rise, and these areas are at highest risk of experiencing impacts to buried infrastructure, soil behavior, human health, and nearshore ecosystems. These areas are also at risk for flooding due to emergent groundwater. The findings of this high-level assessment highlighted the need to understand the full range of sea level rise impacts for prioritizing adaptation investments, and selecting appropriate strategies in coastal communities.
CARP recognized that many homes in Alameda are already affected by groundwater and given the findings in the newly published research, recommended further characterizing of rising groundwater as a potential future hazard in Alameda’s climate change vulnerability assessment.
DISCUSSION
The 2018 research revealed that Alameda is at risk for rising groundwater in the face of climate change. However, due to sparse well data within city limits, and a strong tidal and precipitation influence within the Alameda soils, enhancements to the regional mapping were needed to characterize the shallow groundwater layer in Alameda. Staff engaged Silvestrum Climate Associates to develop a more refined model using geotechnical soil boring data collected throughout the city and the Oakland International Airport. This local groundwater model was then used to assess the groundwater surface response to various sea level rise scenarios. As the groundwater table rises, contaminants with the shallow groundwater will rise closer to the ground. The potential for contaminants to become emergent was also examined.
The Groundwater Report finds that the areas at risk of future flooding increase by up to 25% when considering emergent groundwater, and in certain areas this flooding occurs well before coastal floodwaters overtop the shoreline. Rising groundwater, even before it is emergent, will affect below grade infrastructure such as building foundations, basements and utilities.
Although many of the contaminated lands in the city have been cleaned up or are in the process of being cleaned up; residual contamination often remains with institutional controls intended to protect human health and/or the environment. Institutional controls are developed based on existing conditions, and historically have not considered changing environmental conditions with climate change. As the groundwater table rises; however, underground contaminants could be brought to the surface, which could have health implications for humans, pets, wildlife, and the Bay. The Groundwater Report includes an assessment of where contaminants could be mobilized over time and presents a suite of strategies to mitigate harmful impacts. Most importantly, the report highlights an emerging issue for the State and Regional Water Quality Control Boards and the Department of Toxic Substance Control. The City can advocate with the regulating community for contaminated lands to consider climate change in remediation efforts.
The Groundwater Report recommends adaptation solutions to include in the next update to CARP, such as amendments to local building codes to address flood proofing and guidance for homeowners regarding sump pumps. Other follow-ups to the Groundwater Report include, among other items, integrating the study’s results into relevant chapters of the General Plan, further analyzing potential landfill risks, and updating the digital elevation model used in the groundwater mapping given recent changes in-grade at Corica Park and other areas of recent land development.
As a first study of its kind in the Bay Area, the Groundwater Report puts Alameda at the leading edge of climate adaptation planning and represents an early implementation success for CARP. Alameda’s Groundwater Report was instrumental in the San Francisco Estuary Institute’s win of a California Resilience Grant extending this important work to four Bay Area counties. More research will help Alameda and other Bay Area communities better understand, plan and implement adaptation solutions for the effect of sea level rise on groundwater tables and critical infrastructure. The full Groundwater Report, including an Executive Summary, is attached as Exhibit 1.
ALTERNATIVES
• Accept the Groundwater Report in its current form.
• Direct staff to amend the Groundwater Report and re-submit for acceptance.
• Do not accept the Groundwater Report.
FINANCIAL IMPACT
There is no financial impact from accepting the Groundwater Report.
MUNICIPAL CODE/POLICY DOCUMENT CROSS REFERENCE
This action does not affect the Alameda Municipal Code.
ENVIRONMENTAL REVIEW
The City, as the lead agency under the California Environmental Quality Act, prepared a Mitigated Negative Declaration (MND) for CARP. A preliminary public hearing was held July 16, 2019, and final public hearing held September 3, 2019, when the City Council adopted a resolution adopting the MND, Mitigation Monitoring and Reporting Program. The MND considered the potential environmental impacts of CARP, including additional studies like the Groundwater Report, and potential impacts of future actions by the City to make physical changes to existing structures and facilities to reduce greenhouse gas emissions or address sea level rise. The MND found that some construction activities may result in some potentially significant impacts, but that all of the potential impacts can be mitigated to a level of less than significant through standard construction mitigations.
CLIMATE IMPACTS
By adopting this plan, there will be little to no impact on climate change. By implementing this plan, the City and its residents will be better prepared and protected from inevitable climate change hazards such as sea and groundwater levels.
RECOMMENDATION
Accept the September 2020 report titled, “City of Alameda, The Response of the Shallow Groundwater Layer and Contaminants to Sea Level Rise.”
CITY MANAGER RECOMMENDATION
The City Manager recommends approval of the September 2020 report “City of Alameda, The Response of the Shallow Groundwater Layer and Contaminants to Sea Level Rise”.
Respectfully submitted,
Erin Smith, Public Works Director
Financial Impact section reviewed,
Annie To, Finance Director
Exhibit:
1. Sea Level Rise Report
cc: Eric Levitt, City Manager