Deborah S. Sklarew

The influence of microbial activity and sedimentary organic carbon on the isotope geochemistry of the Middendorf Aquifer

Microorganisms present in deep Atlantic coastal plain sediments affect the geochemical evolution of groundwater and its chemical and isotopic composition, yet the factors controlling their origin, distribution, and diversity are poorly understood. The evolution of the groundwater chemistry, the fractionation of stable carbon isotopes, and the groundwater age are all indicators of the inorganic and microbial reactions occurring along a given flow path from groundwater recharge to groundwater discharge. In this study, tritium, 14C, and groundwater chemistry along three flow paths of the Middendorf aquifer in South Carolina were analyzed. The 14C ranged from 89 percent modern carbon (pmC) in the recharge zone to 9.9 pmC in the distal borehole; the δ13C remained relatively constant at ∼−22‰, suggesting microbial oxidation of organic carbon. Carbon isotope analyses of particulate organic carbon from core sediments and groundwater chemistry were used to model the carbon chemistry; the groundwater ages obtained from 14C ranged from modern to 11,500 years B.P. The highest frequencies of occurrence, numbers, and diversity of aerobic and anaerobic bacteria were found in boreholes near the recharge zone where the calculated ages were <1000 years B.P. The transport of microorganisms from the recharge zone may be responsible for this distribution as well as the electron acceptors necessary to support this diverse community of bacteria. The presence of both aerobic heterotrophs and anaerobic sulfate- and iron-reducing bacteria in the core sediments suggested the occurrence of anaerobic microsites throughout this otherwise aerobic aquifer. The highest in situ microbial respiration rate, as determined by modeling, was found along a flow path near the recharge area. It is likely that the electron acceptors necessary for supporting a diverse microbial community are depleted by the time the groundwater residence time in the Middendorf aquifer exceeds several hundred years.

Detection of organomercury, selenium and arsenic compounds by a capillary column gas chromatography-microwave plasma detector system

Abstract Low-pressure and atmospheric-pressure microwave-induced helium plasma detectors were interfaced with a capillary column gas chromatograph. A number of dialkyl mercury, diaryl mercury and monoalkyl mercury chlorides have been separated on both systems. The capillary column is well suited for the separation of organomercury compounds, but the selection of the appropriate scavenge gas is critical to achieve good peak shapes for these mercury compounds. The atmospheric pressure system exhibited better sensitivity and selectivity for organomercury compounds than the low-pressure system. In addition to the organomercury compounds, satisfactory separation has been achieved for trimethyl, triethyl and triphenylarsine on the gas chromatograph lowpressure microwave plasma detector system. Preliminary work using the atmospheric-pressure system for arsenic and selenium line selection is also presented.

A low-pressure Beenakker-type microwave-induced helium plasma source as a simultaneous multi-element gas chromatographic detector

Abstract A low-pressure version of a Beenakker-type microwave-induced helium plasma optical emission spectroscopy detector for gas chromatographic effluents is described. The plasma is sustained in a 1.3-rum i.d. quartz tube and is viewed axially through a quartz window. Operating characteristics of the source were studied for power levels of 15–115 W, for carrier-gas flows of 20–1000 mi min−1, and for pressures of 2–700 torr. A gas chromatographic system involving a fused-silica capillary column is used as the sample introduction system for compounds containing carbon, hydrogen, nitrogen, sulfur, and chlorine. Elemental response factors and the precision of elemental response ratios were studied. The use of this detector in evaluating empirical formulae is also discussed. Empirical formulae for a number of hydrocarbons and sulfur-containing aliphatic and heterocyclic compounds are presented, together with a discussion of the factors that affect accuracy and precision. It is concluded that this type of detector combines some of the best fearutes of the atmospheric-pressure Beenakker and the Evenson-type sources.

In Situ Redox Manipulation of Subsurface Sediments from Fort Lewis, Washington: Iron Reduction and TCE Dechlorination Mechanisms

The feasibility of chemically treating sediments from the Ft. Lewis, Washington, Logistics Center to develop a permeable barrier for dechlorination of TCE was investigated in a series of laboratory experiments.

Detection of thiophenes in the offgas condensate of an oil shale retort by a GC-microwave induced helium plasma detector

SummaryA series of alkylthiophenes and dimethyl disulfide were tentatively identified in an oil shale retort gas condensate from a 6-kg bench-scale retort using gas chromatography with a microwave-induced helium plasma detector (GC-MIP). The sulfur species were present in concentrations ranging from 1.5 to 10.7 mol ppm in the undiluted offgas. The GC-MIP technique was successful in selectively detecting the sulfur components in the complex mixture. Quantitation was simplified relative to GC with flame-photometric detection because of the absence of quenching or other interference problems at the concentrations studied. Attempts to determine stoichiometry of the sulfur components by comparison of carbon, hydrogen, and sulfur ratios with those of standards were unsuccessful because of the complexity of the carbon and hydrogen chromatograms.

Partition chromatography-high-performance liquid chromatography facilitates the organic analysis and biotesting of synfuels

Abstract Partition chromatography (Sephadex LH-20 or C 18 -partition) followed by high-performance liquid chromatography facilitated the organic and mutagenic characterization of synfuel samples. The mutagens in oil shale retort waters were polar, whereas those in a shale oil ranged from moderately polar to polar. In contrast, the mutagens in an solvent refined coal-II (SRC-II) distillate blend were primarily moderately polar. The mutagens in an SRC-I process solvent were both less polar and less heterogeneous than those of an SRC-I solid product. Known mutagens (primary aromatic amines and aza-polynuclear aromatic hydrocarbons) were identified in the SRC-I and SRC-II samples but not in the shale oil and retort waters.

Hanford 100-D Area Biostimulation Treatability Test Results

Pacific Northwest National Laboratory conducted a treatability test designed to demonstrate that in situ biostimulation can be applied to help meet cleanup goals in the Hanford Site 100-D Area. In situ biostimulation has been extensively researched and applied for aquifer remediation over the last 20 years for various contaminants. In situ biostimulation, in the context of this project, is the process of amending an aquifer with a substrate that induces growth and/or activity of indigenous bacteria for the purpose of inducing a desired reaction. For application at the 100-D Area, the purpose of biostimulation is to induce reduction of chromate, nitrate, and oxygen to remove these compounds from the groundwater. The in situ biostimulation technology is intended to provide supplemental treatment upgradient of the In Situ Redox Manipulation (ISRM) barrier previously installed in the Hanford 100-D Area and thereby increase the longevity of the ISRM barrier. Substrates for the treatability test were selected to provide information about two general approaches for establishing and maintaining an in situ permeable reactive barrier based on biological reactions, i.e., a biobarrier. These approaches included 1) use of a soluble (miscible) substrate that is relatively easy to distribute over a large areal extent, is inexpensive, and is expected to have moderate longevity; and 2) use of an immiscible substrate that can be distributed over a reasonable areal extent at a moderate cost and is expected to have increased longevity.

Representative Sampling of High-Level Radioactive Waste Tank Headspaces

Headspaces of the underground high-level radioactive waste-storage tanks at the U.S. Department of Energys Hanford Site have been sampled to resolve tank safety and industrial hygiene issues and to estimate regulated air pollutant emissions. Because sampling these tanks is difficult and expensive, samples have been collected from a single location of the headspaces, based on the supposition that this would provide representative samples. In most tanks, mixing of vapors occurs because of thermally driven convection from heat generated by radioactive decay of the waste. However, in some low-temperature tanks, the ground temperature above the tank may be warmer than the waste, minimizing thermally induced convection, and raising the concern that samples from a single location may not be representative. To resolve this issue, six samples at different vertical and horizontal locations were taken from each of three low-temperature tanks and analyzed for ammonia, water, permanent gases, total non-methane organic compound concentration, and selected organic vapors. Statistical analysis of the data indicated that the tanks did not exhibit significant horizontal or vertical concentration gradients.