incorporated into remedy selection and design at contaminated sediment sites. These elements should also be considered during ongoing operation.
Challenges and Opportunities for Incorporating Climate Change Adaptation Measures into Sediment Remedies B. Kellems and E. Guyer Integral Consulting Inc.
Background/Objective
EPA’s Guidance
The Intergovernmental Panel on Climate Change released the final part of its Fifth Assessment Report on November 2, 2014, indicating climate change is “unequivocally” caused by human activity and is set to produce “severe, widespread and irreversible impacts” unless emissions are cut dramatically. The impacts of climate change on contaminated sediment sites through extreme weather events, sea level rise, and coastal flooding are challenging issues facing the sediment remediation industry today. These climate change impacts can threaten the long-term effectiveness, permanence, and cost of sediment remediation efforts. It is important and timely that analysis of these impacts and adaptation measures be incorporated into remedy selection and design at contaminated sediment sites. These elements should also be considered during ongoing operation and maintenance and 5-year reviews. Preparation and response to these climate change impacts will determine the viability of many shallow-water and estuarine ecosystems. There is an opportunity to work with various stakeholders to incorporate natural, or green, infrastructure (i.e., healthy ecosystems) and combinations of natural and built infrastructure (‘‘hybrid’’ approaches) into sediment remedies that will ultimately enhance coastal resilience as well as ecosystem protection and restoration.
To address climate change impacts at contaminated sediment sites, EPA released the Climate Change Adaptation Technical Fact Sheet: Contaminated Sediment Remedies in April 2015.
Sea Level Rise and Flooding The future sea level rise scenarios range from 0.66 to 6.6 ft in 2100. Recent work suggests that 4 ft is plausible, and nearly 5 million people in the U.S. live within 4 ft of the local high tide level. Current ME ND
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Source: 2014 National Climate Assessment. U.S. Global Change Research Program
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Encroaching Tides Report, Union of Concerned Scientists (SpangerSiegfried et al. 2014)
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“Other locations that have fewer than five tidal floods per year today—including several on the Gulf Coast—could see a 10-fold or greater increase in the frequency of floods by 2045.” (p. 24)
Frequency of Extreme Storm Events Regional and global models project increases in extreme precipitation for every U.S. region. Heavy downpours are increasing, especially in the Great Plains, Midwest, and Northeast. Regional river flooding trends are consistent with regional climate changes. Overall, there is a strong upward trend in regional extreme precipitation. Extreme precipitation is increasing in the Great Plains, Midwest, and Northeast, where river flooding increases have been observed. Meanwhile in the Southwest, river flooding has decreased. Source: Walsh et al. (2014)
for
Sediment Remediation
Source: USEPA (2015)
Consistent with EPA sediment guidance: “Project managers are encouraged to use an adaptive management approach, especially at complex sediment sites to provide additional certainty of information to support decisions.” *177110* (USEPA 2005) 177110
Sediment Remedy Vulnerabilities • Changes to bathymetry and patterns of erosion and sediment deposition, affecting monitored natural recovery (MNR) or enhanced natural recovery (ENR) • Potential for physical damage to: – In situ cap (habitat, armor, amendment, geotextile or isolation layer) – Clean sediment layer overlaying contaminated sediment, as part of MNR or ENR – Bank stabilization structures and floodplain caps – In-water equipment, confined aquatic disposal, confined disposal facilities, and upland processing facilities • Alteration or loss of wetland or riparian vegetation used for treatment or local buffering
Critique of EPA’s Fact Sheet (USEPA 2015) • Presumption of Dredging/Offsite Disposal “Climate change considerations are particularly important in designs and associated modeling for in situ capping, MNR, and EMNR remedies anticipated to operate for 30 years or longer. If an area is predicted to experience increasingly frequent flooding or storm surge activity or be subject to rising sea levels, disposal of contaminated sediment offsite in an area not subject to these problems may be an option.” • Does Not Allow CostEffective “Tool Box” Approach
Toolkit
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Sediment Remedy Adaptations
• Greater reliance on improved sediment erodibility and deposition assessment • Improved data collection tools for measuring sediment erodibility, such as SEDflume • Confirmation of design storm assumptions (future versus historical 100-year flood differential) • Evaluation of remedial component stability and recontamination potential under design storm • Armor enhancement for in situ caps • Deposition and hydraulic controls (weirs and dams) • Flood controls (barriers, ponds, bioswales) • Appropriate timing of construction activities (weather windows) • Proactive (rather than reactive) strategies • Collaboration with land use agencies • Enhanced bank stabilization – Hard: armor and sheet pile – Soft: bioengineered barriers • Coastal hardening – Hard: seawall or riprap – Soft: replenished sand and/or vegetation • Opportunity to decrease vulnerability of coastal ecosystems through soft approaches
Case Studies
Gowanus Superfund Site, Brooklyn, New York • Despite history of extreme storm event and flooding, there was little treatment of climate change in the remedial investigation and remedy selection • The ROD mentions how climate change impacts will be addressed in remedial design, during sizing of Flooding of the Gowanus Canal from Hurricane combined sewer overflow retention Sandy Storm Surge (October 27, 2012) tanks • Instead, adaptations are outside of CERCLA and are municipal/ community driven; City grant of $1.5 million for pilot study • “Sponge Park” includes softening of edges and green infrastructure: – “Absorbent qualities come from flood-tolerant plantings like asters, Rosa rugosa and sedge grass, as well as a network of sand beds and soils designed to hold water” • Implemented in parallel with sediment cleanup, which includes excavation of turning basin at potential location for Sponge Park, temporary barrier walls/bulkhead upgrades (some implemented by property owners) (NY Times 2015)
Pine Street Canal, Burlington, Vermont • 38-acre former manufactured gas plant site • Output from modeling illustrates the site’s position in a 100-year floodplain • New weir at the canal’s outlet to Lake Champlain maintains minimum water depth, protecting cap from scour and erosion • 2004 remedy: cap emplaced on 8 acres of contaminated sediment with habitat restoration • 2010: reactive cap added to address releases of oil and coal tar seeping through portion of cap, with bank stabilization though reactive cap anchoring and revegetation • 2011: zero NAPL seeps observed and all reactive cap components stable following historic 150-year flooding event (Hurricane Irene)
Conclusions • Serious sediment contamination is concentrated in coastal areas where climate change effects may be most pronounced. • Climate change effects can threaten the long-term effectiveness, permanence, and cost of future remedial efforts, so climate change analysis needs to be incorporated into the remedy selection and design processes. • Because future climate-related design criteria will always be based on modeling and as such have a high degree of uncertainty, the following project elements should be included in all future site remedies where climate change impacts are anticipated: – Risk-based analysis of future climate change impacts – Adaptive management with appropriate long-term monitoring. • Even though the scientific community agrees that climate is changing, there is significant uncertainty about the location, timing, and magnitude of the changes over the planning horizon for sediment remediation projects. Decision making in response to climate change should therefore consider a “risk-based” framework. Risk analysis and management is the primary approach engineers take to deal with future uncertainty. For instance, a comprehensive analysis, based on hydrodynamic and statistical modeling, should evaluate the effects of flooding from sea level rise and storm surges on the proposed remedy using the most accurate climate change data. • Because design criteria based on modeling of climate change scenarios will be uncertain, sediment remedies should include: – Careful consideration of climate change science and modeling – Identification and assessment of vulnerabilities – Risk management of vulnerabilities through engineering toolkit – Adaptive management with long-term monitoring. References available upon request.
Battelle Ninth International Conference on Remediation and Management of Contaminated Sediments, January 9–12, 2017
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