Browsing by Subject "Vadose zone"
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Item Bioremediation of explosives in vadose zone soil using vapor phase carbon source additions(Texas Tech University, 2005-05) Radtke, Corey W.; Cobb, George P.; Anderson, Todd; Dickerson, Richard L.; Roberto, Francisco F.Explosives contamination in vadose zone soil presents difficulties in remediation. Because vadose zone contamination can extend deep into the subsurface and underneath existing buildings and utilities, excavation is often infeasible. In response, this dissertation focuses on the development and testing of a practical system to enhance the remediation of vadose zone explosives contamination. Soil at the DOE Idaho National Engineering and Environmental Laboratory field area was characterized for explosives contamination. Of the soil tested, the particulate TNT retained on a 3 mm screen contributed approximately 2000 ppm (96.4%) of the overall soil contamination, compared to the soil that passed through the sieve, which averaged 75 ppm TNT. Contributing significantly to the contamination profile, heterogeneously dispersed, and likely point sources of contamination, the particulates thereby present difficulties in estimating the extent, risk, and treatability of explosives contamination in the soil. For monitoring soil gases, a method was developed and validated using solid phase microextraction coupled with gas chromatography and mass selective detection (SPME-GCMS). The within-run precision (repeatability) was 3.5X tighter than the between-run precision (reproducibility) in the 4 days. The esters gave the best repeatability from 50 to 80 ppmv while the corresponding alcohols gave the best results at 10 to 20 ppmv. The method was applied to monitor gases in laboratory and field studies testing explosives remediation in vadose zone soil. Anaerobic and microaerobic batch and column studies using soil from the DOE Pantex Facility contaminated with hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX), octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX), and 1,3,5-trinitrobenzene (TNB) were performed using gaseous carbon source additions. In the anaerobic batch study, over 99 days, flasks periodically receiving headspace pulses of 330 to 570 ppmv n-propyl acetate yielded 97.5±0.3% TNB and 66.7±43.2% RDX removal. Using ethanol in place of n-propyl acetate yielded similar results. Two column studies were performed using throughputs of oxygen, nitrogen gas, and organic carbon combinations. The columns supported less robust HE degradation than the batch systems. This difference in HE degradation between batch and column work may indicate that a key factor accumulated in the headspace of batch flasks, but was continually removed in the columns.Item Experimental analysis and modeling of perfluorocarbon transport in the vadose zone : implications for monitoring CO₂ leakage at CCS sites(2013-05) Gawey, Marlo Rose; Breecker, Dan O.; Romanak, Katherine Duncker; Larson, Toti ErikPerfluorocarbon tracers (PFTs) are commonly proposed tracers for use in carbon capture and sequestration (CCS) leak detection and vadose zone monitoring programs. Tracers are co-injected with supercritical CO₂ and monitored in the vadose zone to identify leakage and calculate leakage rates. These calculations assume PFTs exhibit “ideal” tracer behavior (i.e. do not sorb onto or react with porous media, partition into liquid phases or undergo decay). This assumption has been brought into question by lab and field evaluations showing PFT partitioning into soil contaminants and sorbing onto clay. The objective of this study is to identify substrates in which PFTs behave conservatively and quantify non-conservative behavior. PFT breakthrough curves are compared to those of a second, conservative tracer, sulfur hexafluoride (SF₆). Breakthrough curves are generated in 1D flow-through columns packed with 5 different substrates: silica beads, quartz sand, illite, organic-rich soil, and organic-poor soil. Constant flow rate of carrier gas, N₂, is maintained. A known mass of tracer is injected at the head of the columns and the effluent analyzed at regular intervals for tracers at picogram levels by gas chromatography. PFT is expected to behave conservatively with respect to SF₆ in silica beads or quartz sand and non-conservatively in columns with clay or organics. However, results demonstrate PFT retardation with respect to SF₆ in all media (retardation factor is 1.1 in silica beads and quartz sand, 2.5 in organic-rich soil, >20 in organic-poor soil, and >100 in illite). Retardation is most likely due to sorption onto clays and soil organic matter or condensation to the liquid phase. Sorption onto clays appears to be the most significant factor. Experimental data are consistent with an analytical advection/diffusion model. These results show that PFT retardation in the vadose zone has not been adequately considered for interpretation of PFT data for CCS monitoring. These results are preliminary and do not take into account more realistic vadose zone conditions such as the presence of water, in which PFTs are insoluble. Increased moisture content will likely decrease sorption onto porous media and retardation in the vadose zone may be less than determined in these experiments.Item Laboratory investigation of explosives degradation in vadose zone soil using carbon source additions(2005-05) Radtke, Corey William; Cobb, George P.; Anderson, Todd A.; Dickerson, Richard L.; Roberto, Francisco F.Explosives contamination in vadose zone soil presents difficulties in remediation. Because vadose zone contamination can extend deep into the subsurface and underneath existing buildings and utilities, excavation is often infeasible. In response, this dissertation focuses on the development and testing of a practical system to enhance the remediation of vadose zone explosives contamination. Soil at the DOE Idaho National Engineering and Environmental Laboratory field area was characterized for explosives contamination. Of the soil tested, the particulate TNT retained on a 3 mm screen contributed approximately 2000 ppm (96.4%) of the overall soil contamination, compared to the soil that passed through the sieve, which averaged 75 ppm TNT. Contributing significantly to the contamination profile, heterogeneously dispersed, and likely point sources of contamination, the particulates thereby present difficulties in estimating the extent, risk, and treatability of explosives contamination in the soil. For monitoring soil gases, a method was developed and validated using solid phase microextraction coupled with gas chromatography and mass selective detection (SPME-GCMS). The within-run precision (repeatability) was 3.5X tighter than the between-run precision (reproducibility) in the 4 days. The esters gave the best repeatability from 50 to 80 ppmv while the corresponding alcohols gave the best results at 10 to 20 ppmv. The method was applied to monitor gases in laboratory and field studies testing explosives remediation in vadose zone soil. Anaerobic and microaerobic batch and column studies using soil from the DOE Pantex Facility contaminated with hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX), octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX), and 1,3,5-trinitrobenzene (TNB) were performed using gaseous carbon source additions. In the anaerobic batch study, over 99 days, flasks periodically receiving headspace pulses of 330 to 570 ppmv n-propyl acetate yielded 97.5±0.3% TNB and 66.7±43.2% RDX removal. Using ethanol in place of n-propyl acetate yielded similar results. Two column studies were performed using throughputs of oxygen, nitrogen gas, and organic carbon combinations. The columns supported less robust HE degradation than the batch systems. This difference in HE degradation between batch and column work may indicate that a key factor accumulated in the headspace of batch flasks, but was continually removed in the columns.Item Understanding the effects of wildfire on soil moisture dynamics(2013-08) Kanarek, Michael Richard; Cardenas, Meinhard Bayani, 1977-Moisture dynamics in the critical zone have significant implications for a variety of hydrologic processes, from water availability to plants, to infiltration and groundwater recharge rates. These processes are perturbed by events such as wildfires, which may have long-lasting impacts. In September 2011, the most destructive wildfire in Texas history occurred in and around Bastrop State Park, which was significantly affected; thus this is a rare opportunity to study soil moisture under such burned conditions. A 165 m long transect, bridging burned and unburned areas, was established within the “Lost Pines” of the park. Soil moisture was monitored using a variety of methods, including 2D electrical resistivity imaging (using dipole-dipole and Schlumberger configurations), handheld measurements using a ThetaProbe, and readings at depth using PR2 profile probes. Field measurements were collected at approximately one-month intervals to study temporal and seasonal effects on soil moisture. Greater soil moisture was found near the ground surface at the heavily burned end of the transect, where the majority of trees were killed by the fire and grasses now dominate, and lower near-surface soil moisture and higher resistivity at the opposite end of the transect, which is still populated by pine trees. These variations can likely be attributed to the vegetative variations between the two ends of the transect, with trees consuming more water at one end and the ground cover of grasses and mosses consuming less water and helping reduce evaporation at the burned end. Soil texture differences could also be a factor in greater soil moisture retention at the burned end of the transect. Given the higher moisture throughout the soil profile at the burned end of the transect, this could be an indication of greater infiltration, and could increase recharge, at least in the short term.