CL-Out Completes Remediation After Stalled Natural Attenuation
CL-Out Completes Remediation After Stalled Natural Attenuation
CL-Out bioremediation can complete remediation stalled by a lack of oxygen. Investigation of an industrial dry cleaners near Philadelphia, Pennsylvania found concentrations of breakdown products of PCE in the soil and ground water. The parent PCE presumably was reductively dechlorinated to TCE, DCE and vinyl chloride. However, since the daughter products DCE and vinyl chloride are more readily degraded under aerobic conditions, the breakdown was incomplete and natural attenuation stalled. CL-Out was applied with an oxygen supplement to complete the remediation under aerobic conditions favorable for DCE and vinyl chloride bioremediation.
Geology
The geology of the property is interbedded sandy silt, silt and clay layers. The contamination was found in a shallow silty sand formation that is underlain by a dense clay layer. A sand layer directly beneath the clay layer was unaffected by the contamination in the upper sand.
Hydrogeology
The perched ground water was within a fill layer, so the hydraulic conductivity was expected to be variable. Slug testing results showed the hydraulic conductivity in the upper sand ranged from 1.1 to 3.9 ft/day. The ground water flow direction was consistently toward a local surface stream. The extent of the contamination plume was approximately 10,000 square feet.
Ground Water Contamination
The contaminants found at the site were mainly TCE and DCE with trace levels of vinyl chloride. This suite of contaminants indicated that there was natural degradation of the PCE to lesser halogenated compounds. The maximum concentrations prior to bioaugmentation were 220 ug/L of DCE, 9.2 ug/L of TCE and 31 ug/L of vinyl chloride.
Remediation
CL-Out was introduced into the ground water through one-inch diameter tubing installed using a direct push sampler. The use of small diameter injection points made the remediation possible without disruption the dry cleaner operations. Three injection points were installed in the high concentration area. Additional injection was made in places where shallow soil had been excavated.
The CL-Out injection was a dosing of four drums in December 2005.
Results
Three months after the injection of CL-Out, the DCE concentration dropped from 200 to 54 ug/L. The vinyl chloride concentration decreased from 31 to 11 ug/L. After seven months the TCE and vinyl chloride concentrations were below detection limits and the DCE concentration decreased to 2.9 ug/L.
Due to the relatively anoxic conditions, an oxygen supplement was added to support the aerobic cometabolism. During the active treatment the dissolved oxygen levels increased from 1.9 to 8.5 mg/L. The CL-Out microbial population was maintained at 200,000 cells per milliliter.
The monitoring results suggest that by supplementing the dissolved oxygen levels, the CL-Out population was maintained for an extended period. The extended peak of CL-Out population made possible a greater level of contaminant removal.
