Senior Design in Biosystems Engineering at UT

Hydraulic Fracking Sub-Soil for Stormwater Infiltration Enhancement
Matthew Johnsen, Christian Patterson, James Lewis and Ryan Watson

– First Place at ASABE Gunlogson Design Competition
– Second Place at EUReCA UT Engineering Design Competition

Rain gardens are common stormwater control measures that are essentially shallow depressions in the landscape created to capture impervious runoff and infiltrate it into the ground. Rain gardens installed above heavily compacted soil tend to become inundated with ponded stormwater that will not infiltrate due to low permeability. The ponded stormwater converts to runoff and carries with it the pollutants that would have been sequestered in the rain garden. The design team’s approach to mitigate rain garden failure is to emulate hydraulic fracking done by the oil and gas industry to induce fractures in compacted soil layers. These fractures offer multiple connected pathways for the infiltrated stormwater to enter the subsoil, greatly increasing the rate at which water can flow through a rain garden. Biochar was selected as a proppant for its ability to adsorb contaminants and its strength to resist compression. During testing of control and fracked plots, the designed system greatly increased infiltration from an average of 2 mm/hr to 88 mm/hr which is well above the Knoxville Stormwater Standard of 12.7 mm/hr for a functioning rain garden (City of Knoxville Stormwater Engineering, 2018). The results showed that a hydraulic fracking method is an effective means of increasing infiltration within heavily compacted clay soils that can often exist beneath rain gardens. Remediation of these stormwater control measures by hydraulic fracking represents an immense savings of cost and time as compared to demolishing and re-installing the infrastructure.