Geotextile and Granular Filters for the Remediation of Arctic PCB Contaminated Soils
Kalinovich, Indra K.
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The mobility of contaminants via runoff at sites which require soil excavation as source removal can be controlled through the use of surface permeable reactive barriers. This has been accomplished at a remote military site in the Canadian Arctic for soils contaminated with polychlorinated biphenyls (PCBs). The design of these barriers should incorporate criteria for both granular as well as geotextile filters to maximize particle retention, without hindering hydraulic performance and with the consideration for adsorption/reaction mechanisms. Field observations and laboratory testing in the form of batch and column tests were conducted to evaluate design criteria, filter performance and mechanisms of PCB retention. The initial barrier prototype was constructed on site in July of 2003. Modifications were required to improve hydraulic performance in the barrier and maximize sedimentation processes in the field. These modifications resulted in an increase to funnel area, constructed flow impediments, and more permeable materials in the gate. Two additional barrier systems were constructed in August of 2005. Subsequent field and laboratory work demonstrated that granular materials trapped the majority of PCB-contaminated soil without impeding hydraulic performance; however, fines were escaping. Extensive column testing in the laboratory has shown that a nonwoven geotextile filter can be applied with success with a granular permeable reactive barrier system. Batch and column testing indicated that particle retention was the most important factor in trapping PCBs in the filter system. However, field sample results indicated that up to 62 ± 11% percent of PCB by mass was being partitioned on to the GAC (Granular Activated Carbon), a mechanism that was being inadequately captured by traditional batch and column tests. Cold temperature laboratory tests (2-4oC) demonstrated that the presence of water had no effect on PCB adsorption to GAC and that particle-particle partitioning was affected by temperature. Cold temperature column tests indicated that the primary mechanism of PCB transfer in the barrier system was via particle-particle partitioning. The sequestration of PCBs in a permeable reactive barrier has important implications for both surface and subsurface remediation.