The South San Francisco Bay Shorelands, July 2024 (photo by S. D. Warner)
Sea level-induced groundwater rise must now be assessed for environmental remediation sites in California. On October 10, 2024, the California Environmental Protection Agency, Department of Toxic Substances Control (CalEPA-DTSC) published the “Sea Level Rise Guidance to DTSC Project Managers for Cleanup Activities,”[1] (SLR Guidance)– a document that was several years in the making and which was finally published after the Agency reviewed and considered hundreds of public comments on the draft guidance released one year earlier.
As described in its introductory paragraphs, the new SLR Guidance document is intended to assist Agency managers with overseeing a variety of environmental sites within zones of coastal influence including active sites where waste is left in place, and historical sites where regulatory determinations have already been made. The impetus for creating this guidance came from California Senate Bill 1, the Sea Level Rise Mitigation and Adaptation Action of 2021[2] which directed California state agencies to evaluate to the extent feasible, and within their statutory authorities, the actions necessary to “avoid, minimize, and mitigate” the impacts, current and projected of climate change including sea level rise on contaminated sites.
This new guidance includes a strong recommendation for performing a “sea level rise (SLR)” vulnerability assessment (SLRVA) for contaminant and waste sites that lie within the zone of coastal influence such that any SLR could promote negative conditions including, but not limited to:
The SLRVA should determine if sea level rise conditions are occurring or may occur in a reasonable (though not quantitatively defined) time frame such that stability of environmental conditions at a site would be compromised – possibly increasing the risk of contaminant exposure on human and/or ecological receptors. If such assessment does identify a current or potential increase in risk profile (e.g. due to potential exposure, water quality degradation and/or infrastructure damage, etc.), development of an adaptation plan to increase remedy reliance and sustainability could become necessary depending on the severity of the projection.
This new guidance includes a pragmatic flow chart that leads the user through a decision matrix intent on identifying firstly, if there is a sea level rise/groundwater problem to be addressed, and secondly, if so, what is the best available approach (administratively and/or scientifically) to safeguard the environmental site and/or nearby receptors from adverse conditions brought on by sea surface (and thus groundwater) changes. The DTSC guidance recommends that any groundwater contamination mitigation remedy should be protective under both current and future conditions and importantly that the agency “cannot sign off on any remedial decision unless SLR is accounted for.” A further calculation in this process is that the Agency also expects any proposed remedy be developed with financial assurance in mind (consistent with State law) and for a period no less than 30 years following implementation of the remedy. What the guidance does not include, however, are the quantitative methods by which to conduct such analysis, how to stem the effects of sea level rise induced problems, and how the regulatory process will remain engaged over time. Although the guidance provides several external references to the reader, there does not appear to be easily found remedies for mitigating effects of sea level rise for site contamination projects that a site or project manager may rely on due to the nascency of the issue. This conclusion acknowledges, however, that hydraulic barriers using deep water injection, for example, have been applied for many years (such as in Southern California) to reduce the influence of sea water intrusion in affecting fresh groundwater resources. However, this approach may not be a first choice for the conventional shoreline-located contamination project site being discussed by the newly developed guidance.
Why is this new guidance timely and of such importance? The UC Berkeley, Utah State University, and University of Newcastle/BBJ Group research team of Hill, et al. (2023)[3], relying in part on various technical analyses, including the numerical modelling by Befus, et al (2020)[4], found that nationally, some 326 Superfund sites may be exposed to inundation from sea level induced groundwater rise. Furthermore, the team also identified more than 5,000 sites (including both regulatory-closed and active environmental sites) in the San Francisco Bay region that may be exposed to rising groundwater as sea level rises and exceeds 1 meter higher than today’s baseline. Many of these sites are in areas where the residential population is of lower-income or otherwise economically disadvantaged. As discussed in Hill, et al. (2023), comparable studies performed in other coastal regions of the United States may find similar results. We will continue to watch for updated and new guidance from different jurisdictions – Local, State, and Federal – where both direct and indirect influence from climate change may affect site characterization and mitigation approaches.[5]
For California sites, DTSC has made available a “Sea Level Rise Web Application” [6] which integrates data from DTSC, the United States Geological Survey, and the National Oceanic and Atmospheric Administration (NOAA) in an ArcGIS Platform to help users and stakeholders develop a survey level analysis of their location of interest with respect to SLR and groundwater rise conditions. The primary data sets of environmental contamination sites managed within the EnviroStor[7] web portal managed by DTSC, are assessed using the USGS’s Coastal Storm Modelling System (CoSMOS)[8] to project whether any part of a site of interest falls within the approximate boundaries where a SLRVA may be considered. Other web-based tools also exist, including that developed by “Our Coast, Our Future” (OCOF) which is a collaboration between the Point Blue Conservation Science organization and the USGS Pacific Coastal and Marine Science Center.[9] The OCOF Hazard Mapping tool is quite user friendly and provides a survey level assessment of numerous scenarios related to different SLR heights, storm frequency, and subsurface hydrogeological characteristics. An example for the south San Francisco Bay region is shown in the corresponding figure where a 200- centimetre (cm) SLR scenario is used to assess potential groundwater rise conditions and the extent of impact inward away from the shoreline.
For business entities, these changing hydrologic conditions, which may be exacerbated by increasingly significant climatic events including storms and storm surges (often during high tide) may increase the vulnerability of property and other assets. This will require substantial investment in mitigation and management approaches such as that anticipated by developed hazard mitigation guidelines such as that published by the State of New Jersey in 2016[10]. With an evolving standard practice to assess and report on climate-related vulnerabilities, the conditions described herein become of greater interest to owners, users, and residents of all coastal properties and assets, whether developed or not.
Technical management of these issues are in the early stages of development and are thus on a parallel track to the administrative management approaches which will require substantial involvement by qualified professionals at the local, state and federal levels. The technical assessment that will accompany a vulnerability analysis will have to involve not just a detailed evaluation of the local natural conditions – both above ground and below – but will need to integrate knowledge of the surrounding built environment with the controlling geotechnical, geochemical, and hydrogeological conditions of the subsurface to project, predict, and mitigate potentially harmful impacts from the sea water/groundwater inundation phenomenon. As of today, there are few examples where such comprehensive evaluations have been performed. However, the fundamental analysis methods are available and can be integrated with the development of representative conceptual site model (CSM) analyses. The CSM can then be used to develop appropriate numerical simulations of future scenarios, develop monitoring systems to help guard against unwanted problems, and provide basis for mitigation strategies to protect people and assets as sea level continues to rise and inundate shoreline communities.
The US EPA has finally acknowledged that climate change needs to be considered as standard approach to assessing, managing, and remediating contaminated groundwater sites[11] and several recent research studies have begun to identify approaches by which the evaluations can be accomplished (e.g., Warner, et al., 2023)[12]. The State of California is arguably the first State in the nation to acknowledge that climate change is influencing sea surface conditions where the rising sea level has the potential to negatively impact groundwater beyond just degradation by saline water, but also by groundwater inundation and influence on groundwater contamination and remediation strategies. The need to include detailed technical analysis of these conditions is a new development for the environmental consultant – but one that cannot wait until tomorrow as the sea continues to rise, intrude, inundate and change the notion (as false as it has been) of us living on a stable, never-changing coastline where the risk is only from above ground, rather than from an increasing groundwater environment below our feet.
[1] https://dtsc.ca.gov/wp-content/uploads/sites/31/2024/10/SLR_Guidance_2024.pdf
[2] https://leginfo.legislature.ca.gov/faces/billNavClient.xhtml?bill_id=202120220SB1
[3] https://doi.org/10.1029/2023EF003825
[4] https://www.nature.com/articles/s41558-020-0874-1
[5] For example, New Jersey is considering new guidance as found at https://dep.nj.gov/wp-content/uploads/rules/proposals/proposal-20240805b.pdf
[6] https://experience.arcgis.com/experience/e8b8b27b19a54d11b1079b3fbd88c7d6/
[7] https://www.envirostor.dtsc.ca.gov/public/d
[8] https://www.usgs.gov/centers/pcmsc/science/coastal-storm-modeling-system-cosmos
[9] https://ourcoastourfuture.org/about/
[10] https://www.nj.gov/dep/srp/guidance/srra/response_to_catastrophic_events.pdf
[11] https://www.epa.gov/system/files/documents/2024-01/consideration-of-climate-change-at-contaminated-groundwater-sites.pdf
[12] https://doi.org/10.1002/rem.21743