"ENA of heterocyclic hydrocarbons using hydrogen peroxide and groundwater circulation wells - pilot application in the plume of a former gasworks -
"Based on the hydro-geological and contaminant situation along the plume (800 m long, 70 m wide) downstream of a former gasworks (Testfeld Süd, TFS) in Stuttgart, Germany, the most applicable technology to enhance the natural degradation of PAH and NSO-HET was selected and tested under controlled conditions in a large physical model (Large Flume of VEGAS). The promising results of the Large Flume experiment lead to a field trial of the ENA-technology of about 12 months duration.
This technology uses a groundwater circulation well system (GCW) to mix hydrogen peroxide (H2O2) into the contaminant plume. A three dimensional numerical flow and transport model based on MODFLOW 2000 and GSM 6.0© was validated during the Large Flume experiment and then used to design the GCW field trial.
Before starting the field trial the concentration of each contaminant group, PAH and NSO-HET were approximately 100 µg/L entering 80 µg/L leaving the test field. The initial addition of air (oxygen) on the circulation flow resulted in an O2-concentration of 4 mg/L in the near vicinity of the GCW and lead to a significant reduction of both PAH and NSO-HET. After 14 days of air infiltration the unexpected high iron contents (up to
15 mg/L) caused a clogging of the wells. The mixing had to be stopped, the GCW was regenerated and additional filtration units were installed to separate generated Fe(III) from the infiltrated groundwater. After two months of H2O2-mixing the hydraulic system of the GCW had to be changed due to clogging in the vicinity of the well. A "satellite well" (RP6) was installed downstream the GCW in the range of the circulation flow field (distance of 5 m to the GCW) and 50% of the GCW discharge (1.5 m³/h) was infiltrated at RP6. This system maintained a capture zone of 12 m width and a downstream spreading of the electron acceptors until the end of the field trial (5 months).
The O2-concentration ranged between 1.5 and 16 mg/L at a distance of 10 m up to 25 m, respectively, downstream the GCW. The induced aerobic biological degradation of PAH and NSO-HET reduced the concentration between 55 % and 80%.
Based on the pilot trial, the costs for a long-term ENA measure for the pilot site are estimated at 40,000 EUR per year.
The investigations were funded by BMBF, Funding Priority KORA, FKZ: 02WN0363.