Maintaining water quality in groundwater resources will be a high priority when implementing Shallow GCS. The anaerobic degradation of wood can release sugars and a variety of compounds from depolymerization of lignin and carbohydrates 62,63. These compounds would occur naturally in surface water, but there could be health risks or nuisance concerns if groundwater containing these compounds was used for drinking water. Many of the locations that would be ideal for Shallow GCS-Carbon SIRGE are underlain by fine-grained formations, or formations with water containing high dissolved solids and would therefore be poorly suited to hosting drinking water aquifers. Nevertheless, risks to groundwater associated with wood exposure would need to be evaluated for each site.
A possible Shallow GCS-Carbon SIRGE design Example Design includes dewatering wells that are operated at a rate equal to the injection rate. The produced water could be reused during subsequent injections. This closes the water balance for the process and it will drop the hydraulic head and limit migration of compounds released from the injected biomass.
Several investigators64,65 have used wood chips as the basis for bioreactors that sorb or degrade contaminants like nitrate. This suggests that Shallow GCS could improve water quality in some locations.