LNAPL Removal with Petrox
Site Summary
Petrox® bioaugmentation was implemented to remediate fuel spilled at a railway in at Central, Ohio. The impacted soil in the source area was excavated for off-site disposal. The fuel, however, percolated through the fill into underlying soil. The fuel migrated through the soil, seeped to the surface and formed a sheen on the water of an adjacent pond. The LNAPL was removed and no longer visible in the pond and ground water monitoring seeps in less than 90 days after one application of Petrox®.
Geology and Hydrogeology
The spill occurred on a railroad embankment that is adjacent to a pond. The fill of the embankment is 2 to 3 feet thick. The fill is on top of sandy clay deposits. The slope of the embankment is very steep and slopes down to the pond. After the fuel began to appear on the surface water, sumps were installed near the base of the slope and perched ground water was encountered at a few feet deep in the sumps. The remediation was based on a conceptual model for the fuel seepage and migration. Under the conceptual model, the fuel percolated through the fill to the native silty clay soil. Once in the native soil, the fuel migrated through fractures as an LNAPL and seeped from weeps in the hillside.
Contamination
In immediate response to the fuel spill, the impacted ballast and fill were excavated and disposed off site. Residual fuel remained in the soil below the excavation. A hydrocarbon sheen was observed on the surface of the adjoining surface water approximately one month after the spill. Containment booms were placed on the surface water and sumps were installed in the adjoining slope. The LNAPL on ground water was as much as 0.2 feet thick in the sumps. The assumed area of the LNAPL was approximately 1,500 square feet.
Remediation
Petrox® was applied by injecting one drum (55-gallons) of a concentrated solution into the fill in the excavation area. The Petrox® was allowed to flush through the impacted soil and follow the migration path of the fuel. As the weather became seasonally dry, additional water was added to the excavation to support the microbial growth and to flush the microbes into the soil fractures. During remediation the LNAPL thicknesses were measured in the sumps. After each measurement the LNAPL was bailed from the sumps.
Results
Following Petrox® bioaugmentation the LNAPL thickness appeared to increase in some locations. However, in 90 days the LNAPL was no longer present in the sumps and a sheen was no longer observed on the surface water. The following table shows representative LNAPL thickness measurements (in feet).
| Sump Number | Pre-Treatment | 30 Days Post Treatment | 60 Days Post Treatment | 90 Days Post Treatment |
| 1 | 0.04 | 0.06 | No LNAPL | No LNAPL |
| 10 | 0.15 | 0.12 | 0.08 | No LNAPL |
| 11 | 0.13 | 0.08 | 0.07 | No LNAPL |
| 15 | 0.12 | 0.10 | 0.18 | No LNAPL |
The treatment was successful in reducing the residual environmental impact of the fuel spill. The treatment also verified the effectiveness of Petrox® bioaugmentation for petroleum LNAPL situations.
