Rate limited diffusion and dissolution of multi-component non-aqueous phase liquids (NAPLs) in groundwater

Contamination of soil and groundwater by nonaqueous phase liquids (NAPLs) poses serious risks to human health and the environment and presents major challenges for cleanup. The presence of complex NAPL mixtures in the subsurface further complicates remediation efforts, transport predictions, and the development of accurate risk assessments. A comprehensive laboratory-scale study was conducted to elucidate the factors affecting dissolution and removal of NAPL including 1) the distribution of NAPL (uniform vs. non-uniform), 2) NAPL-water interfacial area (constant vs. changing), 3) multi-component NAPL systems (composition dependence), and 4) intra-NAPL diffusion. A series of column and time sequential batch experiments were conducted to assess the factors controlling dissolution processes under dynamic flow and equilibrium conditions. For comparison purposes, two independent NAPL systems were established for the series of experiments including single-component trichloroethene (TCE) whereby the NAPL interfacial area decreases as dissolution proceeds, and two-component TCE-hexadecane (HEX) in which the bulk NAPL (comprised primarily of insoluble HEX) interfacial remains constant. The results of this study show that significant dissolution rate and removal limitations during water-flushing exist for systems containing non-uniform NAPL (TCE) distributions, due to less available NAPL-water interfacial area. Effective TCE removal was 2 times longer for the non-uniform NAPL distribution experiment. TCE dissolution in the two-component NAPL systems (TCE and HEX) experienced significantly less rate limitation (absence of concentration tailing) than the single-component TCE systems due to the presence of a constant interfacial area for mass-transfer to occur during flushing. Each column experiment resulted in differing effectiveness with respect to mass removal. The multi-component TCE:HEX system experienced the fastest mass removal time, but was not considered the most efficient. The batch experiments demonstrated that as mole fraction of a particular component of a NAPL (TCE) mixture decreases, greater dissolution nonideality occurs, resulting in greater observed concentrations than those predicted by equilibrium dissolution (i.e. Raoult's Law). Dissolution nonideality, quantified by the NAPL-activity coefficient, increased for the lower TCE mole fraction systems from 1.7 to 6.1 for TCE:HEX mole fractions of 0.2:0.8 to 0.003:0.997, respectively. The results of the batch experiments also indicate that dissolution mass-transfer rates were nearly identical for both the single-component TCE systems and the TCE:HEX systems. This suggests that intra-NAPL diffusion is not a rate-limited process under the conditions of these experiments. Mass flux reduction analyses showed that the two-component (TCE:HEX) NAPL experiment resulted in less efficient removal behavior than the single-component TCE flushing experiments, likely due to the significantly lower TCE mass within the mixed NAPL system. The results from this study improved the understanding of NAPL dissolution and removal processes; most notably for NAPL mixture systems where NAPL-water interfacial area may be maintained during flushing and where significant dissolution nonideality may result from decreasing mole fractions of target contaminants in NAPL. (Published By University of Alabama Libraries

Sedimentological and geochemical records of depositional environments of the Late Devonian Chattanooga shale

The Late Devonian is characterized by substantial changes in both land and marine biodiversity. The organic matter-rich Chattanooga Shale was deposited in shelfal waters, thereby serving as an invaluable archive recording changes in land and marine biota as well as terrestrial-marine biogeochemical linkages in the Late Devonian. In the present study, we identified carbon sources and reconstructed depositional environments of the Chattanooga Shale using two outcrops in northeastern Alabama, combining sedimentological and geochemical approaches. The two outcrops share similar sedimentological features (i.e., thinly laminated, fissile, grayish shale strata in the lower part of the outcrop and nearly homogeneous, black, blocky shale in the upper part). The lower part may be assigned to the low to middle units of the Gassaway Member and contains the top of the Dowelltown Member deposited around the Frasnian-Famennian boundary. The upper part is likely equivalent to the upper Gassaway Member. Rock-Eval parameters and the carbon number distribution of normal alkanes show that the organic matter in the Chattanooga Shale is in thermogenic gas window and contains Type II to III kerogen. Low Pristane/Phytane values show that the depositional environment was reducing with interruptions of oxic periods. In the upper part, the values of (Pristane/nC17) / (Phytane/nC18) increase, showing that water may become more oxic. Furthermore, terrestrial organic matter input increased toward the top of the outcrops, as evidenced by increased proportions of long-chain n-alkanes, higher terrigenous/aquatic ratios, lower nC17/nC27 values, and elevated concentration of polycyclic aromatic hydrocarbons derived from terrestrial plants. These data indicate that terrestrial plants became an increasingly important carbon source during the deposition. The presence of pyrosynthetic polycyclic aromatic hydrocarbon compounds can be attributed to prevalent forest fire, in accompanying with the diversification of early land plants in the Eastern Laurasia. These data demonstrate that enhanced inputs of terrestrial organic matter to shelfal waters may have played a vital role in the formation of black shales in the Late Devonian. (Published By University of Alabama Libraries

Pyroclastic evidence of syn-eruptive degassing at the explosive/effusive transition

The 2010 eruption of Merapi (Java, Indonesia) initiated with an uncharacteristic explosion, followed by rapid lava dome growth and collapse, all of which generated deadly pyroclastic density currents (PDCs). PDC samples from the initial explosion on October 26th were collected from several locations surrounding the edifice. Plagioclase phenocrysts represent the primary component of the dominant ash mode due to the elutriation of the finer ash fraction during PDC transport. Secondary electron images of 45 phenocrysts were taken using the scanning electron microscope (SEM) to examine preserved glass coatings on phenocrysts, which represent the interstitial melt within the magma at the point of fragmentation. Using these images, the bubble number densities (BNDs) were determined, and the decompression rate meter of Toramaru (2006) was used to calculate the decompression rate during the initial explosion of the 2010 Merapi eruption. Calculated decompression rates range from 6.08x10^7 Pa/s to 1.4x10^8 Pa/s. Decompression rates have shown to correlate with eruption column height; therefore Merapi’s rates should be similar to those of other Vulcanian explosions, because the eruption column was 8-9 km in height. Sakurajima volcano (Japan) experienced decompression rates from 7.0 × 10^3 to 7.8 × 10^4 Pa/s during the later phase of the fall 2011 Vulcanian explosions. Plinian explosions, such as at the 1991 eruption of Mt. Pinatubo and the 1980 eruption of St. Helens had much higher column heights compared to the initial 2010 Merapi explosion; 35 km, 19 km, and 8-9 km, respectively, but decompression rates in a comparative range (10^8 Pa/s). Higher decompression rates during the 2010 initial explosion at Merapi likely resulted from increased overpressure in the shallow conduit, as revealed through previous geochemical analyses of the erupted crystals Results indicate that decompression rates may be underestimated for Vulcanian explosions. (Published By University of Alabama Libraries

Subsurface fracture analysis using FMI logs: implications for regional state of stress prediction in the Black Warrior Basin, Alabama

The Black Warrior Basin is a Paleozoic foreland basin located at the southern tip of the exposed northeast-trending Alleghanian fold-thrust belt. It is bounded by the northwest-trending Ouachita fold-thrust belt to the southwest. The eastern Black Warrior Basin is broken by a multitude of thin-skinned normal faults that generally strike northwest, parallel to the Ouachita trend and perpendicular to the Alleghanian trend. However, little is known about the regional state of stress in the Black Warrior Basin. This study uses FMI (Fullbore Formation MicroImager) and other conventional open hole logs to define the orientation of subsurface natural fractures. Using well log data from the Gorgas #1, the present-day stress orientation was interpreted from induced fractures (borehole breakouts and drilling-induced tensile fractures), indicating a maximum horizontal stress orientation (SHmax) of N 65°E. The image log interpretation revealed three sets of conductive and resistive fractures with strikes of (i) 45°-75°, (ii) 300°-320°, and (iii) 0°-10°. Fracture sets (i) and (ii) were interpreted as a part of the previously identified and documented regional east-northeast (ENE) joint system and the cross-fold joint system, respectively. Fracture set (iii) consists of only resistive (healed) fractures detected in the Lower Pottsville and older strata. It is postulated that the origin of these NNE oriented fractures, on the basis of the subsidence pattern of the Pennsylvanian strata in the basin and the similarity with the regional joint system observed in the Arkoma basin, is the Ouachita orogeny. The interpreted NNE Ouachita convergence direction indicates that thin-skinned normal faults in the Pottsville Formation are not related to the Ouachita thrust belt system, but are instead related to the NE-SW oriented extensional stress field created at a right angle to the northwest-converging Alleghanian orogeny. (Published By University of Alabama Libraries

Influence of flow regime on U(VI) sorption kinetics in fine sediments at the Hanford site, Washington, USA

The effect of flow rate on U(VI) sorption kinetics was investigated by a series of column tests using the reactive mass fraction (<2mm) of sediments from the 300 Area in Hanford, WA. Three sets of constant flow rates subject to multiple stop flow events were employed to obtain U(VI) breakthrough curves at the column outlet. A lognormal distributed multi-rate surface complexation model was used to match the experimental breakthrough curves and calibrate the parameters of the multi-rate distribution. The results from the column tests clearly show that the mean of the lognormal distributed sorption rate constants increase with the flow rate, while the standard deviation of the lognormal distributions decreases with the flow rate. This finding is the first empirical evidence for the flow rate dependence of the multi-rate sorption kinetics and is thus of fundamental importance for future efforts to further improve the predictive modeling and remediation of U contamination. (Published By University of Alabama Libraries

Using electrical resistivity tomography to calibrate seawater intrusion models along the Alabama Gulf Coast

Numerical models (e.g., MODFLOW/SEAWAT) are commonly used to quantify the extent and magnitude of seawater intrusion (SI). Since coastal communities must account for SI into local aquifers, numerical models can be an effective planning and management tool as coastal populations increase. While these models tend to be limited by the availability of hydrological data, uncertainty in these results can be substantially reduced through the integration of field geophysical measurements. Field measurements employing electrical resistivity tomography (ERT) were utilized to calibrate a density-dependent groundwater flow model for Gulf Shores, Alabama. Specifically, six independent ERT profiles were produced within a modeled area adjacent to a shallow lake and along the near-shore boundary. The ERT methods were employed to a depth of 95 meters, encapsulating two aquifer systems with previously identified SI concerns (Chandler et al, 1986; Murgulet and Tick, 2008). Results from the ERT deployments were compared to previously developed models' near shore density boundary constructed from local borehole data, then utilized to calibrate the model freshwater/saltwater mixing zone. Other geophysical investigations employing similar methodology (e.g. Time-Domain Electromagnetics) have been used to calibrate SI models and to explore the extent of SI in a number of coastal regions. This study expands upon previous research through the integration of a 3-D groundwater flow model with greater resolution ERT measurements to more accurately determine the extent of SI, and delineate the near shore freshwater/seawater boundary zone. (Published By University of Alabama Libraries

Using 3-D seismic inversion data as a tool for predicting porosity in the Wilburton gas field, Arkoma Basin, southeastern Oklahoma

Understanding and identifying changes in rock properties over an area is critical in characterizing a reservoir. In order to identify porosity changes, a 3-D seismic inversion volume was inverted for acoustic impedance in the Red Oak and Brazil Sandstones in the Wilburton gas field located in the Arkoma Basin, southeastern Oklahoma. The tops and bases of these two sandstones were identified to be analyzed based on acoustic impedance and porosity. Establishing a relationship between acoustic impedance and porosity allows porosity to be predicted away from the wellbore using the seismic acoustic impedance data. Interpretation of the seismic inversion data suggests that a) there is a linear correlation between acoustic impedance and porosity in the sandstone portions of the Red Oak and Brazil Sandstones; b) seismic thickness cannot be used to predict actual thickness of these sandstone units due to variations in velocity; and c) prediction of porosity using seismic inversion data inverted for acoustic impedance in sandstone containing interbeds of shale is not reliable, and the method should be limited to homogeneous sandstone. (Published By University of Alabama Libraries

Kinematic analysis of the southern Funeral Mountains: implications for Cenozoic extensional tectonics

Map-view area balance of extensional strain in the west-central Basin and Range indicates that the area has undergone 250-300 km of upper crustal extension. Consistent 25-30 km moho depth across the area suggests that the ductile lower crust has uniformly thinned in response to the extension. These strain estimates are based on the palinspastic realignment of various compressional structures developed within the Late Proterozoic to Mesozoic passive margin and foreland basin rocks of the North American Cordillera. The type example of correlations used to reconstruct the west-central Basin and Range lay in Death Valley. The magnitude, order, spacing, and vergence pattern of compressional structures in the Cottonwood and Funeral Mountains indicates that the two range blocks, now separated by ~70 km along the Death Valley-Furnace Creek fault zone, were once adjoined. However, the original structural architecture in the Funeral Mountains has been aliased by extensional faulting. Thus, the correlation of the Cottonwood and Funeral Mountains is contingent on determining the true pre-extensional spacing between the compressional structures. I reconstruct one NW-SE cross section through the Funeral Mountains to determine the pre-extensional geometry of the fold-thrust belt and compare the geometry to the Cottonwood Mountains. The reconstruction indicates that the interior of the Funeral Mountains has been extended by 8 km (40%) of its pre-Miocene length. The derived pre-extensional spacing between compressional structures within the range matches that previously determined for structures in the Cottonwood Mountains. Thus, these results support reconstructions that indicate ~ 70 km across the Death Valley-Furnace Creek fault zone. Finally, the Funeral and Cottonwood Mountains are interpreted to be correlative range blocks. (Published By University of Alabama Libraries

High resolution molecular characterization of photochemical and microbial transformation of dissolved organic matter in temperate streams of different watershed land use

The objective of the present study was to provide better understanding of the effects of watershed land use on molecular composition of streamwater DOM and molecular transformations associated with photochemical and microbial processing of DOM. We compared DOM from headwater streams draining forest-dominated watersheds (FW) and pasture-dominated watersheds (PW) in the lower Chesapeake Bay region (Virginia, USA). Electrospray Ionization Fourier Transform Ion Cyclotron Resonance Mass Spectrometry analysis was conducted on streamwater DOM prior to and after laboratory incubations: 1) bacteria-only incubations; 2) light-only incubations; and 3) combined light+bacterial incubations. Results showed that DOM in FW streams and PW streams differed in molecular characteristics--the former was characterized by greater structural complexity and aromaticity, higher proportions of condensed aromatic molecules and black carbon-like components, while the latter was higher in the proportions of lipid-like components, protein-like components and aliphatic compounds. Relative to DOM from FW streams, DOM from PW streams was more reactive to bacterial transformation. Protein-like components, lipid-like components and unsaturated hydrocarbon-like components are primarily responsible for the changes associated with bacterial transformation of DOM. However, similar behavior was also observed for DOM in FW streams and PW streams under the influence of bacterial and photochemical processes. Bacterial transformation reduced the proportions of lipid-like components but increased the proportions of lignin-like components and carboxyl-rich alicyclic molecule-like components, indicating that lipid-like components was a bioreactive class while lignin-like components and carboxyl-rich alicyclic were resistant to bacterial processing. Photochemical processes, alone or combined with microbial alterations, increased the proportions of protein-like components, which may be due to the light stimulation of autochthonous production of protein-like components, and increased the relative abundance of carboxyl-rich alicyclic molecule-like components, which indicates the refractory nature of these molecules. Photochemical processes also significantly reduced the amount of dissolved black carbon-like components, which suggests dissolved black carbon was a photoreactive class, countering the conventional view that black carbon was an inter group in carbon cycle. Collectively, these findings suggest that human land use in upstream watersheds may lead to alterations to the molecular composition of streamwater DOM as well as to its behavior to photochemical and microbial processing. (Published By University of Alabama Libraries

Detrital zircon U-Pb age constraints on the provenance of the late Jurassic Norphlet Formation, eastern Gulf of Mexico: implications for paleogeography

Detrital zircon U-Pb geochronology and thin-section petrology of core samples taken from onshore Alabama and offshore federal lease blocks, including Destin Dome, Pensacola, and Mobile, constrain sediment provenance for the Upper Jurassic Norphlet Formation in the eastern Gulf of Mexico. Previous research of the Norphlet Fm. in onshore Alabama suggests that sediments near onshore areas of Alabama originated from metamorphic rocks of the Talladega slate belt and Piedmont. This study provides evidence that the Gondwanan Suwannee terrane is another potential source for the Norphlet Fm. in the EGOM. This study determined U-Pb ages for 1111 detrital zircons from 13 Norphlet Fm. core and cutting samples were determined using LA-ICPMS. The Norphlet Fm. yields four major U-Pb age ranges: 197.9 - 350 Ma, 350 - 770 Ma, 800 - 1650 Ma, and 1650 - 3390 Ma. These ages correspond with known U-Pb ages of source terranes common to Laurentia, including the Grenville (950 - 1300 Ma), (Granite-Rhyolite (1350 - 1550 Ma), Yavapai-Matzatzal (1650 - 1750 Ma), Penokean (1800 - 1900 Ma), and Superior Provinces (>2500 Ma). U-Pb ages also reveal sourcing from the Gondwanan Suwannee Terrane (540 - 580 Ma and 2000 - 2200 Ma). This study establishes four geochronologic source terranes: the ancient Appalachian Mountains, the Appalachian foreland basin, Mesozoic rift basins, and the Suwannee Terrane. Ten samples from onshore Alabama yield detrital zircon U-Pb ages characteristic of Laurentian sources (Appalachian mountains and Appalachian foreland basin), whereas two offshore samples yield characteristic Gondwanan (Suwannee Terrane) ages. Four samples located adjacent to the Mesozoic rift basin reveal ages characteristic of both Laurentia and Gondwana - indicating an area of sediment mixing during the late Jurassic. Twelve thin-sections taken from 9 cores in the onshore and state waters areas were point counted for 400 grains each for compositional analysis. Petrolographic analyses reveal plagioclase and potassium feldspars, polycrystalline quartz, metamorphic and volcanic lithic fragments as dominant grain types. Petrologic data corroborate that onshore Alabama samples were sourced by recycled orogenic and cratonic rocks of Laurentia and southern samples were sourced by less mature sources characteristic of a rift basin (Mesozoic rift basins). A paleogeographic reconstruction illustrates sediment being distributed from Laurentian and Gondwanan sources via alluvial, fluvial, eolian, and marine depositional environments. (Published By University of Alabama Libraries