Question:  How much biomass could be available on a sustainable basis–that is, without causing unwanted negative impacts?  

Short answer:  Obtaining the woody biomass needed to scale up to 1.0 GtCO2eq/yr would be feasible in the coming decade using U.S. resources, and it could occur earlier if international sources of wood are used.  A variety of other carbon-bearing materials are a nuisance at the ground surface, but they could be useful ingredient for Carbon SIRGE.   

Questions:  How rapidly would wood, or other forms of biomass, be released from storage in the shallow subsurface?  How does the degradation process affect the permanence of storing carbon at shallow depths?  

Short answer:  Wood seems to be remarkably durable under anoxic conditions typical of saturated conditions in the subsurface.  There are many old wooden boats and logs that have been preserved for hundreds to 1000s of years in shallow sediments.  Scientific studies have used laboratory experiments to evaluate wood degradation in landfills.  The results indicate that degradation would likely be less than 10 percent of the injected material under saturated, anoxic conditions.    

Questions:  Is there enough land available to store carbon at the GtCO2eq/yr rate?  How much land is negatively affected by flooding, or flood risk? 

Short answer:   There are several to many 1000 km2 of land in the U.S. with important built structures, like houses, roads, airports, that are threatened by flooding.  There are many times more farmland, or coastal wetlands that are also threatened by flooding and that could benefit from increased elevations.  

Questions:   How rapidly could land be raised?  How can the effects of uneven uplift on built structures be managed? 

Short answer:   Raising elevations at the rate of the field demo would result in 0.5 m in one year, and 5 m of uplift in one decade.  An increase of 0.5 m of elevation can significantly reduce the effects of nuisance flooding, and 5 m puts land at or above the elevation created by the Galveston grade-raising, which has protected Galveston from severe storm surges for more than a century.  Increasing the depth of injection and using deformation monitoring will improve the uniformity of the uplift and lessen the risks to infrastructure.  

Question:    What would a potential Carbon SIRGE project look like?  

Short answer:  There would be an array of casings in the ground that are connected by a pipe network to equipment used to mix and inject slurry.  Dewatering wells in the vicinity would be used to recycle injected water.    

Question:      What is the total carbon balance for Carbon SIRGE, and how does this compare to other carbon removal methods?  What are other impacts from Carbon SIRGE?  

Short answer:  The LCA indicates less than 10 percent of the stored carbon would be emitted during the process.  The LCA for Carbon SIRGE is much better than for Direct Air Capture.  

Question:    Will Carbon SIRGE affect the groundwater quality?  

Short answer:  Yes, but it will be manageable.  Wood will release organic compounds that are common in nature, but that are undesirable in drinking water.  Dewatering wells can be used to recycle water, close the water balance, and limit the migration of compounds derived from wood.  Carbon SIRGE projects would avoid drinking water aquifers and their design would include an analysis of the local groundwater flow system.   

Question:  Will injecting wood slurry create earthquakes?  

Short answer:  No.  Carbon SIRGE will be done at depths that are too shallow to create seismicity that can be felt by humans.