Browsing by Subject "NAPL"
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Item The evaluation of sorbent containing geotextiles for the remediation of PAH and NAPL contaminated sediment(2009-08) Trejo, Gabriel; Reible, Danny D.; Liljestrand, Howard M.As more sites containing contaminated sediments are remedied with sediment caps, so grows the interest among site managers and engineers in the benefits afforded by active capping. While traditional sediment caps can effectively manage strongly solid-associated contaminants in many situations, under certain conditions active caps or amendments may be needed to effectively reduce risk to an acceptable level. This research assessed the predicted and observed breakthrough of dissolved organic contaminants in two newly developed geotextiles; one designed to sorb non-aqueous–phase liquids (NAPLs), the other dissolved-phase contaminants. The performance of the geotextiles was then compared to that of another remediation technology that has been deployed in the field for two years. All active materials were then evaluated based on their sorption capacity and their predicted life under field conditions. The sorbent containing geotextiles designed for active capping applications were tested in columns to simulate field conditions, where upwelling groundwater would be contaminated by impacted sediments, thereby transporting contaminants to the water column. The contaminants of interest in these studies were three polycyclic aromatic hydrocarbons (PAHs) of varying hydrophobicity. Breakthrough curves for the materials vii of interest were constructed for the three PAHs and were fit to an advection-dispersion model to predict the mass of contaminants sorbed onto them. This mass was then compared and verified to be similar to values found in literature. The performance of the geotextiles was compared to that of organoclay deployed in Portland, OR, at the McCormick & Baxter Creosoting Company Superfund Site. In 2004, over 22 acres of sediment at the site were remedied with both passive and active caps to mitigate the effects of decades worth of contamination. In certain portions of the site, a 12 inch thick layer of organoclay was employed, while at other portions of the site, conventional sand or a thin reactive core mat with the equivalent of approximately 1 cm of organoclay were employed. The continued effectiveness of these sediment caps was evaluated using a variety of laboratory techniques, including measuring samples’ hexane extractable material, which is a proxy for NAPL contamination, as well as their PAH bulk concentrations. These analyses performed on core samples allowed for the generation of vertical profiles critical to cap evaluation. Despite possessing a significantly greater specific sorption capacity, the geotextiles could not offer the same protection for the extended period of time that the bulk organoclay could. The greater mass of organoclay deployed in bulk at the McCormick & Baxter site allowed a much greater sorption capacity to be placed. It would take over sixty stacked layers of the one of the geotextiles evaluated in these studies to achieve the same capacity for dissolved-phase contaminants as the 1 ft organoclay cap. However, no significant penetration of NAPL into the bulk organoclay has been noted, and thus even the thin layer within a geotextile might have been sufficient at the site, despite its significantly lower overall capacity. The data generated provides information as to the expected capacity of the various sorbent placement approaches and can help guide decisions at other sites.Item Geotechnical containment of non aqueous phase liquid contaminated sediments(2012-05) Erten, Mustafa Bahadir; Gilbert, Robert B. (Robert Bruce), 1965-; El Mohtar, Chadi Said; Charbeneau, Randall J.; Reible, Danny D.; Lake, Larry L.In situ capping is a remediation alternative for contaminated sediments which has been implemented to contain contaminants in sediments in rivers, lakes and ponds. One concern with in situ capping is that the additional load due to the in situ cap may cause consolidation-induced mobilization of non aqueous phase liquids (NAPL). Therefore, it is important to understand the consolidation behavior of NAPL contaminated soils. The difficulties of testing river-bed sediments are that these sediments usually are very soft, have very high porosities, and are very compressible. In addition, the contaminants in these sediments should be contained during testing. The primary objective of this research is to investigate the behavior of NAPL contaminated sediments under anisotropic consolidation. A modified triaxial testing system was developed to simulate the consolidation of very soft sediment specimens along with a reconstituted NAPL contaminated specimen preparation procedure. Kaolinite and Anacostia River sediments were used for the sediments’ solids phase. A low viscosity mineral oil, Soltrol 130, was used to represent the NAPL phase. Tap water was used as the water phase. PM199TM, a type of organophilic clay manufactured by CETCO, was used as well to study its effectiveness in containing expelled NAPL. Two sets of consolidation tests were performed: 1) tests on sediment specimens at various NAPL contents and porosities; and 2) tests on specimens contaminated with NAPL with organophilic clays either placed as a layer on top or mixed within the sediment. The results showed that NAPL mobilization was negligible below a threshold NAPL content. Hydraulic conductivities increased with increasing NAPL content up to four orders of magnitude. The tests with organophilic clay showed that when large enough amounts are used, NAPL expulsion can be completely stopped. Organophilic clay reached its full capacity independent of the NAPL content of the underlying sediment.Item Pore-scale analysis of solubilization and mobilization of trapped NAPL blobs in porous media(2009-06-02) Yoon, Sun HeeNAPL (non-aqueous phase liquid) blob mobilization and solubilization models were developed to predict residual NAPL fate and describe flow dynamics of various displacing phases (water and surfactant foam). The models were achieved by pore-scale mass and force balances and were focused on the understanding of the physico-chemical interactions between NAPL blobs and the displacing phases. The pore-level mass balance indicated changes in NAPL saturation instead of mass reduction occurring with blob solubilization. The force balance was used to explain the complex flow configurations among NAPL blobs and the displacing phases. Some factors such as the wettability and the spreading/entering coefficients were useful in determining flow configurations. From the models developed in this study, dimensional analysis was performed to identify NAPL blob motion during water or surfactant foam flooding. In non-dimensionalized forms, a Trapping number employed as an indicator of blob displacement performance was modified to quantify the onset of blob mobilization. Its value for water flooding was nearly 2-3 orders of magnitude greater than that of surfactant foam flooding. Next, to investigate the blob flow regime in porous media, a blob velocity was computed. Regardless of the displacing phases, a blob?s velocity increased with increasing blob sizes after commencement of blob motion, and the velocity of DNAPL (dense non-aqueous phase liquid) blobs was greater than that of LNAPL (light non-aqueous phase liquid) blobs. From this investigation, it is expected that the pore-scale solubilization and mobilization models would provide better understanding leading to a predictive capability for the flow behavior of NAPL blobs removed by various displacing phases in a porous medium. Additionally, the models based on newly approached concepts and modified governing equations would be useful in conceptualization, as well as the model prediction of other immiscible or miscible fluids flowing through a porous medium. Further, the models developed in our study would be a useful contribution to the study of small-scale contaminants or substances such as particle and bacterial transport in porous media.Item Pore-scale analysis of thermal remediation of NAPL-contaminated subsurface environments(2009-05-15) Ahn, MinThe possible benefits of thermal remediation of NAPL-contaminated subsurface were analyzed at pore-scale. Force balance analysis was performed to provide the insight and information on the critical conditions for the blob mobilization. First, the critical blob radius for blob mobilization was calculated in terms of blob radius, temperature, and water velocity. Temperature increase enhanced the blob mobilization along with the decrease of interfacial tension. Water velocity increase also enhanced the blob mobilization. Critical water velocity provided the critical condition for the initiation of blob mobilization to distinguish singlet and doublet in blob size. Second, the terminal (or steady state) blob velocity at the steady state blob motion was determined. Increases of temperature and water velocity raised the terminal blob velocity. When the observation of blob mobilization moved from REV scale (macroscale) to pore-scale, terminal blob velocity showed the different phenomena according to the change of oil saturation. At macro-scale, the terminal blob velocity was smaller than water velocity by an order or two. However, the terminal blob velocity reached to water velocity at pore-scale. This investigation would provide the better understanding on the pore-scale analysis of residual NAPL blob mobilization by thermal remediation. Additionally, the pore-scale analysis developed in this study would be incorporated into a general conservation equation in terms of the accumulation of multiple blobs. It would derive continuumaveraged equations that accurately represent pore-level physics. In conclusion, the study on the critical conditions for the initiation of blob mobilization as a single discrete blob would have some contribution to the transport and fate of NAPL contaminant and the desired subsurface remediation.