Formatted Title:

Remedy Optimization Analysis at a Shoreline Landfill Impacted by Climate Change

Background/Objectives:

The Site 10 North End Landfill, located on the northernmost point of NAVMAG Indian Island in Washington State, provides a case study of climate change impacts to a remedy in place. The case study illustrates the lengthy timeframes and large-scale remedy optimization efforts that must be evaluated for these sites.

Site 10 is approximately 3.7 acres and contains an inactive shoreline landfill, with a remedy implemented in 1997 that includes an engineered cap and shoreline erosion protection. The shoreline protection was positioned based on predicted wave energies along the shoreline. It included sections of armor rock and soft bank consisting of native vegetation and anchored drift logs. Actual conditions, including storm events during king tides, caused erosion of the shoreline protection concentrated at the transition from armor rock to soft bank protection. The erosion caused by wave energy during the storms required repair and extension of the armor rock area six times between 2003 and 2019.

Portions of the landfill waste (positioned along the shoreline) are submerged below current sea level and, therefore, predictions regarding rising sea levels over the next 80 years (through 2100) were a fundamental factor in the development and evaluation of optimized remedial alternatives. Predicted sea level rise in response to climate change over these timeframes is expected to negatively impact the remedy’s ability to isolate the waste and maintain landfill integrity.

Approach/Activities:

The optimized remedial alternatives developed and evaluated include: 1) no action (used as a baseline to compare other alternatives); 2) continued long-term operation and maintenance (O&M), long-term monitoring (LTM), and instituional controls (ICs) under the current remedy over 30-, 60-, and 80-year timeframes; 3) landfill removal (implemented over the short term); and 4) Rat Island sand spit restoration as a barrier to wave impacts on the landfill over 30-, 60-, and 80-year time periods. Where optimized remedial alternatives involved long-term O&M or LTM, the alternatives were evaluated based on timeframes of 30, 60, and 80 years to account for how these alternatives would respond to predicted sea level rise.

Results/Lessons Learned:

This case study illustrates the long timeframes and large-scale remedy optimization efforts that must be evaluated for these sites. Although FS evaluations typically focus on a 30-year timeframe per EPA guidance, this timeframe is not long enough to account for climate change effects. Addressing climate change effects can necessitate considering large-scale remedy changes -- in this case, moving a landfill or rebuilding a barrier island.

Remedy designs must now attempt to account for the long-term effects of climate change, even as climate science rapidly evolves and the scale and pace of environmental change continues to be difficult to predict accurately. Designs that do not stand up to actual conditions induced by climate change risk radical rework of remedies in place.

Josh Sacker

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Remedy Optimization Analysis at a Shoreline Landfill Impacted by Climate Change