Engineering topics

Denham, Miles

Publications and source records attributed to Denham, Miles.

21 records · Page 2

DOE OSTI2016

Waste Disposition Methodology at the Portsmouth Gaseous Diffusion Plant - 16469

Cost-effective and sustainable remedial design is a prudent and required approach for dealing with legacy wastes at the U.S. Department of Energy (DOE) sites. The concept of using contaminated soils as engineered fill for waste disposal facilities is a sustainable remediation process that warrants investigation. Options for cost-effective site-wide remediation were evaluated by DOE and its site contractor, including completion of evaluations for excavation of certain closed landfills and the excavation of contaminated soil in areas of known groundwater plumes to be used as engineered fill for the operation of an On-Site Waste Disposal Facility (OSWDF) at Portsmouth. The evaluations concluded that excavating select landfills and significant volumes of soil associated with the groundwater plumes considering Portsmouth site specific geology would mitigate the project lifecycle risk. As a result of this evaluation, the excavation of the landfills and soils associated with the groundwater plumes is being incorporated into the project's lifecycle baseline. On-site independent Headquarters review of this sustainable design approach and evaluation was performed in 2013 by the U.S. Army Corps of Engineers. Extensive presentations, background information, and data were provided to the independent review team along with tours of the affected areas. The review team agreed with the approach, and the Final Waste Disposition Record of Decision (ROD) for the OSWDF at the Portsmouth Site issued in June 2015, provides for the use of contaminated fill as an option provided that additional regulatory authorization/approval is obtained to use contaminated fill. Stakeholder and regulatory support is evidenced by the issuance of resolutions advocating this sustainable approach. The Commissioners of each of the four surrounding counties and the Portsmouth Site Specific Advisory Board have issued resolutions advocating this approach. They, along with other local leaders and Ohio's congressional delegation, are continuing to pursue implementation of this approach that they believe will enhance the attractiveness of the site for future re-industrialization. This approach at the Portsmouth Gaseous Diffusion Plant (PORTS) in Piketon, Ohio, is estimated to save more than $200 million over the lifecycle of the decontamination and decommissioning (D and D) project. This strategy has merit not only at Portsmouth, but perhaps other sites within the U.S. Department of Energy's Office of Environmental (EM) Management - and beyond. (authors)

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DOE OSTI2016

Migration and Distribution of Natural Organic Matter Injected into Subsurface Systems - 16523

The Savannah River Site (SRS) was one of the major U.S. Department of Energy facilities that produced large amounts of radioactive and hazardous waste during the Cold War era, a legacy of material production for defense purposes. The unlined F-Area seepage basins received approximately 1.8 billion gallons of acidic waste solutions containing low-level radioactivity from numerous isotopes generated by uranium slug and irradiated fuel processing. Sufficient quantities of uranium isotopes, I-129, Tc-99, and tritium migrated into the groundwater, creating an acidic plume with a pH between 3 and 5.5. Humic substances (HS) are complex heterogeneous mixtures of poly-dispersed materials formed by biochemical and chemical reactions during the decay and transformation of plant and microbial remains. They are known for their excellent binding capacity for metals, making them a strong candidate for remediation efforts to reduce the mobility of uranium (VI) in the subsurface. Studies showed that HS are an important ion exchange and metal-complexing ligand, carrying a large number of functional groups with high complexing capacity that can greatly affect the mobility behavior of actinides in natural systems. Hence, it is a potential in situ amendment for treating groundwater contaminated with these constituents. Column experiments were conducted to address the complexities of HS in flow-through porous media representative of the acidic aquifer at the SRS F-Area Seepage Basins. The humate source used, Huma-K, is high in humic and fulvic compounds. The column studies were done using the soil obtained from SRS's FAW-1 core-hole at a depth interval of 60'-70'. A bromide tracer test was performed to obtain the pore volume (PV), variance and Peclet number. The columns were saturated with an artificial groundwater solution prepared to mimic the groundwater at SRS that was pH adjusted to 3.5 and 5 until the effluent pH reached equilibrium. Approximately one (1) PV of 5000 ppm of Huma-K was injected into the columns at 2 ml/min to study the sorption of Huma-K on the sediment. Desorption of Huma-K was studied by injecting approximately four (4) PVs of the pH adjusted artificial groundwater solution. A faster increase in pH was observed in column 1 (saturated with pH 3.5 AGW) compared to column 2 (saturated with pH 5 AGW). After injection of 2 PV of AGW, the pH of the columns reached 6.5 and 7, respectively, for columns 1 and 2. After injecting an additional PV of AGW, the pH remained relatively stable. With an increase in pH from 3.5 to 5.0, the overall retention of HA increased from 461 mg/kg for the column with pH 3.5 to 642 mg/kg for the column with pH 5. This suggests that retention is not due to adsorption alone, but adsorption coupled with precipitation and re-dissolution of Huma-K as it flows through the columns is a possible explanation for greater retention at pH 5. This negates the use of a simple Langmuir isotherm to explain humate behavior in the acidic environment of column 1. (authors)

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DOE OSTI2016

Synergetic Interactions between Uranium, Humic Acid, Silica Colloids and SRS Sediments at Variable pH - 16524

The Savannah River Site (SRS) was constructed during the 1950's and became one of the major producers of plutonium for the United States during the Cold War. During its production life, the F/H Area Seepage Basins received approximately 1.8 billion gallons of acidic waste containing radionuclides and dissolved heavy metals. This led to the creation of a highly contaminated groundwater plume with uranium (VI) as a key contaminant of concern within the plume. Now, as a designated hazardous waste management facility, the main activities taking place at the site are nuclear storage and remediation of contaminated soil and groundwater from radionuclides. Humic substances (HS) are major components of soil organic matter having the ability to influence migration behavior and fate of heavy metals and are being investigated for potential use in environmental remediation at SRS. Essentially, HS are polyfunctional organic macromolecules formed by the chemo-microbiological decomposition of biomass or dead organic matter. HS are able to interact with both metal ions and organic compounds based on solubility. Humic acid (HA) represents the fraction of HS soluble at pH greater than 3.5. HA carries a large number of functional groups, provides an important function in ion exchange and is a metal complexing ligand with a high complexation capacity. Silica is the term applied to solid forms with the stoichiometric composition of SiO{sub 2}. The colloidal silica used in this work is amorphous and non-porous in suspension; silica's net surface charge for pH values higher than 3 is negative, due to the isoelectric point being 1.5 - 2.5. Humic acid has been previously used in remediation techniques and silica is found naturally in the soil. This investigation studied the synergistic interactions between four key components: U(VI), humic acid (HA), colloidal silica and SRS sediment under varying pH conditions ranging from 3 to 8. Multi-component batch systems were constructed to effectively analyze the removal of U(VI). The batches were pH adjusted, left to equilibrate for a minimum of 48 hours on a shaker, and then centrifuged. A set of samples, filtered to remove any colloids in suspension, and a set of unfiltered samples were analyzed. For the samples at acidic pH, the uranyl cation is the dominant species; with increasing pH, the mononuclear and polynuclear hydrolyzed uranyl ions become dominant based on speciation modeling. In filtered samples, uranium removal is highest at low pH with the negatively charged moieties of HA readily binding to the uranyl cation. Percent removal of U(VI) steadily decreased with an increase in pH and then remained comparable at a neutral/alkaline pH with the change in uranyl speciation. The percentage of colloidal silica removal was observed to be approximately 80% for both sediment- and non-sediment-bearing samples. As the pH increased, the silica removal in the non-sediment set showed a slight decrease and was in the range of 70% - 75%. Uranium removal in the unfiltered samples showed similar trends as compared to the filtered samples; however, the removal of uranium in the unfiltered samples was slightly lower compared to the filtered samples. Colloidal silica removal in non-sediment-bearing batches showed a decline with increasing pH, from 90% to 50%; conversely, the silica removal remained constant for the sediment-bearing batches at approximately 60%. Colloidal silica does not seem to have a significant effect on the removal of U(VI) before filtration due to U(VI) bound to colloidal silica remaining in suspension. The presence of humic acid, silica colloids, and SRS sediment was shown to synergistically effect the removal of U(VI). (authors)

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