Heidi Blischke was accepted to present at the Society of Environmental Toxicologists and Chemistry (SETAC) North America Annual Meeting this November in Orlando, Florida. Her abstract is entitled, “Ongoing Degradation of an Organophilic Clay Amendment in a Sediment Cap 11 Years after Placement.”
Heidi will share her experience with using organophilic clay to sorb oils and prevent them from reaching the river at a former creosoting wood treatment facility on the Willamette River in Portland. This was the first time in the United States that organophilic clay had been used in a riverine setting—up until this point it had only been used in treatment plants.
After the clay had been placed in the river, Heidi and her team noticed a large amount of gas production. This turned out to be methane produced by the clay, which had been degrading to its original hydrophilic bentonite form. Fortunately, the remedy at the river site was robust, with a fully encompassing barrier wall to 88 feet in the upland that prevented the ongoing migration of creosote to the river.
At her presentation, Heidi will discuss the best uses for organophilic clay, as it is still a good method of preventing oil from reaching the river if there is not an ongoing source of oil. In addition, once the clay degrades, it will no longer be permeable and can act more as a hydraulic barrier.
Will you be at SETAC Orlando? Hope to see you there.
Ongoing Degradation of an Organophilic Clay Amendment in a Sediment Cap 11 Years after Placement
Heidi Blischke/GSI Water Solutions, Inc.
A one-foot thick layer of granular organophilic clay (Aqua Technologies ET-1) (OC) was placed within the McCormick & Baxter sediment cap in Portland, Oregon to reduce the potential of creosote seeps from reaching the river. Immediately after its emplacement in summer 2004, ebullition was observed overtop the footprint of the OC placement at significantly higher rates than what was observed in other locations within the sediment cap or elsewhere in the river adjacent to the sediment cap. In order to understand the ebullition, extensive study was conducted on the OC from the sediment cap. No creosote was observed in any of the OC cores from the site, and it was assumed that due to the installation of a barrier wall, the source to potential creosote seeps had been eliminated by the wall. Organic matter and PAHs were analyzed from the ET-1 in 2008, 2009 and 2015. Low level PAHs were detected within the OC that are consistent with low level PAHs present in groundwater passing through the sediment cap. Low-level PAHs were detected at concentrations that typically fell between the method detection limit and reported detection limit. The summation of carcinogenic PAHs range from 0.03 mg/kg to 0.4591 mg/kg.
In a 2008 study, the average organic matter content of several site OC samples was 15.9 percent (+/- 2.6 percent). Fresh OC organic content has an average of 24.1 percent (+/- 0.16 percent). At that time, the OC had been in place within the sediment cap for 4 years, which results in an estimated half-life for the organic matter within the clay of 6.6 years. Since the PAH concentrations within the OC are very low and there are no other significant sources of organic carbon expected to sorb to the OC within the sediment cap, the primary source of organic matter measured in the OC is within the structure of the OC itself. In 2015, the organic content ranged from 7.78 to 9.85 percent with an average of 8.56 percent. These results indicate that the OC is continuing to degrade with a half-life on the order of approximately 6 to 7 years. If the clay continues to degrade at this rate, it will return to its original bentonite form in approximately 40 years after installation of the sediment cap. While the degradation of the OC has not resulted in protectiveness issues at the Site, it has likely caused the limited buckling of the sediment cap observable in areas where the OC was placed due to loss of mass.