Theme: 03. Green and Sustainable Remediation

Topic Area: 3c. Climate Resilience and Site Remediation

Formatted Title:

Cleanup Sites Transition to Carbon Farms: Potential Application of Soil Carbon Sequestration Practices for Sustainable Site Remedies

Background/Objectives:

Background/Objectives. Nature-based carbon sequestration (NBCS), such as regenerative management of croplands, grazing land, and grasslands, holds great potential for carbon capture and storage within the soils. These same methods can be incorporated in soil covers installed at remediation sites to enhance resiliency, biodiversity, and overall economy. While NBCS practices are commonly associated with agricultural lands, application of these practices at environmental restoration sites, such as atop earthen covers at closed mines, may provide significant climate benefits, as well as a potential revenue stream to support site monitoring and maintenance programs. In the US, soil carbon sequestration has been reported to be capable of accruing from 144 to 432 million tonnes (Tg) of carbon on an annual basis (for comparison, total annual emissions of the US agriculture sector averaged 178 Tg between 2017 and 2021), with variability stemming from different site characteristics and sequestration approaches. Limited information has been systematically compiled on rates of carbon accrual within different soil types and climates or from various management practices. This data gap hampers the ability to evaluate the potential effectiveness and benefits of soil carbon sequestration efforts at a given remediation site. Further, the large number of waste sites, including brownfields, closed mining sites, and sites under Monitored Natural Attenuation (MNA), could collectively present significant carbon sinks, but to our knowledge the overall potential of adapting NBCS land management practices at these sites as a climate change mitigation strategy is unexplored to date.

Approach/Activities:

Approach/Activities. To address the knowledge gaps described above, we have compiled information from over 130 sites where soil carbon has been measured and accrual quantified for five general categories of regenerative management practices: grassland management, Conservation Reserve Program (farmlands are reserved from active cultivation), cropland management, grazing management, and combined crop-livestock systems. We have compared soil carbon accrual rates based on soil types, climate, and land management practices. Publicly available data on locations and areas of remediation sites are also presented. Through geospatial analysis and the compilation of accrual rates, we estimate the overall potential for sequestering carbon in soils at remediation sites situated in favorable soil/climate settings.

Results/Lessons Learned:

Results/Lessons Learned. We present statistical distributions of carbon sequestration rates (metric tonnes [Mg] CO₂ ha^-1 year^-1) achieved by each category of management practice. These data show differences among the various factors examined. These results can be used to support integration of EPA green remediation principles (e.g., land management and ecosystems protection) and optimization of remedial design toward climate benefits. Grassland restoration is evaluated further as a potential approach for remediation site transition or redevelopment, as it requires less intensive management activities compared to other practices. The overall potential for sequestering carbon is estimated for closed mining sites, brownfields, and sites under MNA suitable for grassland restoration. Preliminary analysis is performed on the economics of this approach in terms of capital costs, long-term operation and maintenance costs, and benefits in the context of voluntary carbon credits and carbon offsets. These costs are then compared to typical cost ranges for active remedies such as excavation and incineration. While the evaluation of NBCS potential at remediation sites and its associated benefits is ongoing, the data compiled and analyses performed in this study provide a scientific basis for adapting NBCS practices for sustainable resilient remediation. Carbon storage potential and erosion control could become important considerations in assessing soil covers as a remedial approach or mitigation measure for extreme weather and changing climatic conditions.

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Letitia Smith