Geologic perspective for carbon sequestration by woody biomass burial

Abstract

Carbon sequestration by Woody Biomass Burial (WBB) leverages carbon capture through natural photosynthesis, followed by the isolation of dead or fallen wood in a relatively shallow Underground Wood Vault (UWV). Long-term geologic containment, including any greenhouse gas decomposition products, depends on the careful selection of UWV location and depth. To achieve carbon sequestration durability of 100 y, an initially low-moisture UWV should be built as follows: (a) low-permeability, high-plasticity clays with a hydraulic conductivity of ≤10−9 m/s, and with vertical/lateral separation distance of ≥1 m from the nearest aquifer; (b) residual compaction voids at least partially filled, with loose, smectite-rich clay; (c) capped with ≥2 m of clay compacted to achieve hydraulic conductivity <5 × 10−9 m/s; (d) restricted to locations where the 50-y seismic Peak Ground Acceleration (PGA) is ≤9% g (8.8 × 10−1 m/s2). A UWV built in a low-PGA location, with larger cap and confinement thicknesses and/or lower hydraulic conductivity, should be capable of sequestration durability approaching 500–1000 y or more.