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At least 163 records · Page 9Linked to original sources
USGS2005

Microbial H2 cycling does not affect δ2H values of ground water

Stable hydrogen-isotope values of ground water (δ 2 H) and dissolved hydrogen concentrations (H (2(aq) ) were quantified in a petroleum-hydrocarbon contaminated aquifer to determine whether the production/consumption of H 2 by subsurface microorganisms affects ground water &delta 2 H values. The range of &delta 2 H observed in monitoring wells sampled (-27.8 ‰ c to -15.5 ‰ c ) was best explained, however, by seasonal differences in recharge temperature as indicated using ground water δ 18 O values, rather than isotopic exchange reactions involving the microbial cycling of H 2 during anaerobic petroleum-hydrocarbon biodegradation. The absence of a measurable hydrogen-isotope exchange between microbially cycled H 2 and ground water reflects the fact that the amount of H 2 available from the anaerobic decomposition of petroleum hydrocarbons is small relative to the amount of hydrogen present in water, even though milligram per liter concentrations of readily biodegradable contaminants are present at the study site. Additionally, isotopic fractionation calculations indicate that in order for H 2 cycling processes to affect δ 2 H values of ground water, relatively high concentrations of H 2 (>0.080 M) would have to be maintained, considerably higher than the 0.2 to 26 nM present at this site and characteristic of anaerobic conditions in general. These observations suggest that the conventional approach of using δ 2 H and δ 18 O values to determine recharge history is appropriate even for those ground water systems characterized by anaerobic conditions and extensive microbial H 2 cycling.

Ground Water↗
USGS2005

A simple method for calculating growth rates of petroleum hydrocarbon plumes

Consumption of aquifer Fe(III) during biodegradation of ground water contaminants may result in expansion of a contaminant plume, changing the outlook for monitored natural attenuation. Data from two research sites contaminated with petroleum hydrocarbons show that toluene and xylenes degrade under methanogenic conditions, but the benzene and ethylbenzene plumes grow as aquifer Fe(III) supplies are depleted. By considering a one‐dimensional reaction front in a constant unidirectional flow field, it is possible to derive a simple expression for the growth rate of a benzene plume. The method balances the mass flux of benzene with the Fe(III) content of the aquifer, assuming that the biodegradation reaction is instantaneous. The resulting expression shows that the benzene front migration is retarded relative to the ground water velocity by a factor that depends on the concentrations of hydrocarbon and bioavailable Fe(III). The method provides good agreement with benzene plumes at a crude oil study site in Minnesota and a gasoline site in South Carolina. Compared to the South Carolina site, the Minnesota site has 25% higher benzene flux but eight times the Fe(III), leading to about one‐sixth the expansion rate. Although it was developed for benzene, toluene, ethylbenzene, and xylenes, the growth‐rate estimation method may have applications to contaminant plumes from other persistent contaminant sources.

Ground Water↗
USGS2009

MTBE, TBA, and TAME attenuation in diverse hyporheic zones

Groundwater contamination by fuel-related compounds such as the fuel oxygenates methyl tert-butyl ether (MTBE), tert-butyl alcohol (TBA), and tert-amyl methyl ether (TAME) presents a significant issue to managers and consumers of groundwater and surface water that receives groundwater discharge. Four sites were investigated on Long Island, New York, characterized by groundwater contaminated with gasoline and fuel oxygenates that ultimately discharge to fresh, brackish, or saline surface water. For each site, contaminated groundwater discharge zones were delineated using pore water geochemistry data from 15 feet (4.5 m) beneath the bottom of the surface water body in the hyporheic zone and seepage-meter tests were conducted to measure discharge rates. These data when combined indicate that MTBE, TBA, and TAME concentrations in groundwater discharge in a 5-foot (1.5-m) thick section of the hyporheic zone were attenuated between 34% and 95%, in contrast to immeasurable attenuation in the shallow aquifer during contaminant transport between 0.1 and 1.5 miles (0.1 to 2.4 km). The attenuation observed in the hyporheic zone occurred primarily by physical processes such as mixing of groundwater and surface water. Biodegradation also occurred as confirmed in laboratory microcosms by the mineralization of U- 14 C-MTBE and U- 14 C-TBA to 14 CO 2 and the novel biodegradation of U- 14 C-TAME to 14 CO 2 under oxic and anoxic conditions. The implication of fuel oxygenate attenuation observed in diverse hyporheic zones suggests an assessment of the hyporheic zone attenuation potential (HZAP) merits inclusion as part of site assessment strategies associated with monitored or engineered attenuation.

Ground Water↗
USGS2007

Fate of MTBE relative to benzene in a gasoline-contaminated aquifer (1993-98):

Methyl tert -butyl ether (MTBE) and benzene have been measured since 1993 in a shallow, sandy aquifer contaminated by a mid-1980s release of gasoline containing fuel oxygenates. In wells downgradient of the release area, MTBK was detected before benzene, reflecting a chromatographic-like separation of these compounds in the direction of ground water flow. Higher concentrations of MTBE and benzene were measured in the deeper sampling ports of multilevel sampling wells located near the release area, and also up to 10 feet (3 m) below the water table surface in nested wells located farther from the release area. This distribution of higher concentrations at depth is caused by recharge events that deflect originally horizontal ground water flowlines. In the laboratory, microcosms containing aquifer material incubated with uniformly labeled 14 C-MTBE under aerobic and anaerobic. Fe(III)-reducing conditions indicated a low but measurable biodegradation potential (<3% 14 C-MTBW as 14 CO 2 ) after a seven-month incubation period, Tert -butyl alcohol (TBA), a proposed microbial-MTBE transformation intermediate, was detected in MTBE-contaminated wells, but TBA was also measured in unsaturated release area sediments. This suggests that TBA may have been present in the original fuel spilled and does not necessarily reflect microbial degradation of MTBE. Combined, these data suggest that milligram per liter to microgram per liter decreases in MTBE concentrations relative to benzene are caused by the natural attenuation processes of dilution and dispersion with less-contaminated ground water in the direction of flow rather than biodegradation at this point source gasoline release site.

Groundwater Monitoring & Remediation↗
USGS2006

Use of plume mapping data to estimate chlorinated solvent mass loss

Results from a plume mapping study from November 2000 through February 2001 in the sand-and-gravel surficial aquifer at Dover Air Force Base, Delaware, were used to assess the occurrence and extent of chlorinated solvent mass loss by calculating mass fluxes across two transverse cross sections and by observing changes in concentration ratios and mole fractions along a longitudinal cross section through the core of the plume. The plume mapping investigation was conducted to determine the spatial distribution of chlorinated solvents migrating from former waste disposal sites. Vertical contaminant concentration profiles were obtained with a direct-push drill rig and multilevel piezometers. These samples were supplemented with additional ground water samples collected with a minipiezometer from the bed of a perennial stream downgradient of the source areas. Results from the field program show that the plume, consisting mainly of tetrachloroethylene (PCE), trichloroethene (TCE), and cis-1,2-dichloroethene (cis-1,2-DCE), was approximately 670 m in length and 120 m in width, extended across much of the 9- to 18-m thickness of the surficial aquifer, and discharged to the stream in some areas. The analyses of the plume mapping data show that losses of the parent compounds, PCE and TCE, were negligible downgradient of the source. In contrast, losses of cis-1,2-DCE, a daughter compound, were observed in this plume. These losses very likely resulted from biodegradation, but the specific reaction mechanism could not be identified. This study demonstrates that plume mapping data can be used to estimate the occurrence and extent of chlorinated solvent mass loss from biodegradation and assess the effectiveness of natural attenuation as a remedial measure.

Ground Water Monitoring and Remediation↗
USGS2024

Krumholzibacteriota and Deltaproteobacteria contain rare genetic potential to liberate carbon from monoaromatic compounds in subsurface coal seams

Biogenic methane in subsurface coal seam environments is produced by diverse consortia of microbes. Although this methane is useful for global energy security, it remains unclear which microbes can liberate carbon from the coal. Most of this carbon is relatively resistant to biodegradation, as it is contained within aromatic rings. Thus, to explore for coal-degrading taxa in the subsurface, this study reconstructed relevant metagenome-assembled genomes (MAGs) from coal seams by using a key genomic marker for the anaerobic degradation of monoaromatic compounds as a guide: the benzoyl-CoA reductase gene ( bcrABCD ). Three MAGs were identified with this genetic potential. The first represented a novel taxon from the Krumholzibacteriota phylum, which this study is the first to describe. This Krumholzibacteriota MAG contained a full set of genes for benzoyl-CoA dearomatization, in addition to other genes for anaerobic catabolism of monoaromatics. Analysis of Krumholzibacteriota MAGs from other environments revealed that this genetic potential may be common, and thus, Krumholzibacteriota may be important organisms for the liberation of recalcitrant carbon in a broad range of environments. Moreover, the assembly and characterization of two Syntrophorhabdus aromaticivorans MAGs from different continents and a Syntrophaceae sp. MAG implicate the Deltaproteobacteria class in coal seam monoaromatic degradation. Each of these taxa are potential rate-limiting organisms for subsurface coal-to-methane biodegradation. Their description here provides some understanding of their function within the coal seam microbiome and will help inform future efforts in coal bed methane stimulation, anoxic bioremediation of organic pollutants, and assessments of anoxic, subsurface carbon cycling and emissions.

mBio↗
USGS2007

A framework for assessing the sustainability of monitored natural attenuation

The sustainability of monitored natural attenuation (MNA) over time depends upon (1) the presence of chemical/biochemical processes that transform wastes to innocuous byproducts, and (2) the availability of energy to drive these processes to completion. The presence or absence of contaminant-transforming chemical/biochemical processes can be determined by observing contaminant mass loss over time and space (mass balance). The energy available to drive these processes to completion can be assessed by measuring the pool of metabolizable organic carbon available in a system, and by tracing the flow of this energy to available electron acceptors (energy balance). For the special case of chlorinated ethenes in ground-water systems, for which a variety of contaminant-transforming biochemical processes exist, natural attenuation is sustainable when the pool of bioavailable organic carbon is large relative to the carbon flux needed to drive biodegradation to completion. These principles are illustrated by assessing the sustainability of MNA at a chlorinated ethene-contaminated site in Kings Bay, Georgia. Approximately 1,000 kilograms of perchloroethene (PCE) was released to a municipal landfill in the 1978-1980 timeframe, and the resulting plume of chlorinated ethenes migrated toward a nearby housing development. A numerical model, built using the sequential electron acceptor model code (SEAM3D), was used to quantify mass and energy balance in this system. The model considered the dissolution of non-aqueous phase liquid (NAPL) as the source of the PCE, and was designed to trace energy flow from dissolved organic carbon to available electron acceptors in the sequence oxygen > chlorinated ethenes > ferric iron > sulfate > carbon dioxide. The model was constrained by (1) comparing simulated and measured rates of ground-water flow, (2) reproducing the observed distribution of electron-accepting processes in the aquifer, (3) comparing observed and measured concentrations of chlorinated ethenes, and (4) reproducing the observed production and subsequent dilution of dissolved chloride, a final degradation product of chloroethene biodegradation. Simulations using the constrained model indicated that an average flux of 5 milligrams per liter per day of organic carbon (CH2O) per model cell (25 square meters) is required to support the short-term sustainability of MNA. Because this flux is small relative to the pool of renewable organic carbon (about 4.7 x 107 milligrams [mg] per model cell) present in the soil zone and non-renewable carbon (about 6.9 x 108 mg per model cell) in an organic-rich sediment layer overlying the aquifer, the long-term sustainability of MNA is similarly large. This study illustrates that the short- and long-term sustainability of MNA can be assessed by: 1. Estimating the time required for contaminants to dissolve/disperse/degrade under ambient hydrologic conditions (time of remediation). 2. Quantifying the organic carbon flux to the system needed to consume competing electron acceptors (oxygen) and direct electron flow toward chloroethene degradation (short-term sustainability). 3. Comparing the required flux of organic carbon to the pool of renewable and non-renewable organic carbon given the estimated time of remediation (long-term sustainability). These are general principles that can be used to assess the sustainability of MNA in any hydrologic system.

Circular↗
USGS2011

Groundwater geochemical and selected volatile organic compound data, Operable Unit 1, Naval Undersea Warfare Center, Division Keyport, Washington, June 2009

Previous investigations indicate that natural attenuation and biodegradation of chlorinated volatile organic compounds (VOCs) are substantial in groundwater beneath the 9-acre former landfill at Operable Unit 1 (OU 1), Naval Undersea Warfare Center, Division Keyport, Washington. Phytoremediation combined with ongoing natural attenuation processes was the preferred remedy selected by the U.S. Navy, as specified in the Record of Decision for the site. The U.S. Navy planted two hybrid poplar plantations on the landfill in spring 1999 to remove and to control the migration of chlorinated VOCs in shallow groundwater. The U.S. Geological Survey (USGS) has continued to monitor groundwater geochemistry to ensure that conditions remain favorable for contaminant biodegradation as specified in the Record of Decision. This report presents groundwater geochemical and selected VOC data collected at OU 1 by the USGS during June 15-17, 2009, in support of long-term monitoring for natural attenuation. For 2009, groundwater samples were collected from 13 wells and 9 piezometers. Samples from all wells and piezometers were analyzed for redox sensitive constituents, and samples from 10 of 18 upper-aquifer wells and piezometers and 3 of 4 intermediate-aquifer wells also were analyzed for chlorinated VOCs. Concentrations of redox sensitive constituents measured in 2009 were consistent with previous years, with dissolved hydrogen (H2) concentrations ranging from less than 0.1 to 1.8 nanomolar (nM), dissolved oxygen concentrations all at 0.6 milligram per liter or less; little to no detectable nitrate; abundant dissolved manganese, iron, and methane; and commonly detected sulfide. The reductive declorination byproducts-methane, ethane, and ethene-were not detected in samples collected from the upgradient wells in the landfill or the upper aquifer beneath the northern phytoremediation plantation. Chlorinated VOC concentrations in 2009 at most piezometers were similar to or slightly less than chlorinated VOC concentrations measured in previous years. In 2009, concentrations of reductive dechlorination byproducts ethane and ethene were less than those measured in 2008 at most northern plantation wells and piezometers. For the upper aquifer beneath the southern phytoremediation plantation, chlorinated VOC concentrations in 2009 at the piezometers were extremely high and continued to vary considerably over space and between years. At piezometer P1-9, the total chlorinated VOC concentration increased from 25,000 micrograms per liter in 2008 to more than 172,000 micrograms per liter in 2009. At piezometer P1-7 in 2009, the concentrations of trichloroethene and cis-1,2-dichloroethene (cis-DCE) were the highest to date. The reductive dechlorination byproducts ethane and ethene were detected at all wells and piezometers in the southern plantation with the exception of piezometer P1-8, although the measured concentrations were not consistently high. For the intermediate aquifer, concentrations of redox sensitive constituents and VOCs in 2009 at wells MW1-25, MW1-28, and MW1-39 were consistent with concentrations measured in previous years. Concentrations of the reductive dechlorination byproducts ethane and ethene at wells MW1-25 and MW1-28 were equal to or greater than previously measured concentrations.

Washington↗
USGS1998

Simulating transport of volatile organic compounds in the unsaturated zone using the computer model R-UNSAT

Subsurface spills of gasoline and other petroleum products are a common environmental problem throughout the industrialized world. The U.S. Environmental Protection Agency has estimated that 40 percent of the more than 200,000 retail service stations in the United States have had accidental releases of petroleum hydrocarbons to the subsurface (U.S. Environmental Protection Agency, 1991). Restoration of a contaminated aquifer to regulatory standards is a technically difficult problem even when best engineering strategies are applied. Natural attenuation, a remediation strategy that relies on intrinsic physical, chemical, and biological processes to decrease contaminant concentrations, is gaining widespread acceptance in aquifer restoration efforts (Tremblay and others, 1995). The potential for successful remediation by natural attenuation depends on the fate of the organic constituents of the spilled product, which may include additives such as methyl tert-butyl ether (MTBE). These compounds can dissolve in ground water, adsorb to subsurface sediments, volatilize and diffuse through the unsaturated zone, or undergo chemical and biological reactions (fig. 1). Volatilization and biodegradation near the water table are two processes that can contribute significantly to the natural attenuation of volatile organic compounds (VOCs) in shallow ground water (McAllister and Chiang, 1994). To date, quantitative information on the rates at which these processes occur has been limited. R-UNSAT, a computer model designed for quantifying rates of volatilization and biodegradation of organic compounds near the water table, was developed and documented by the U.S. Geological Survey (USGS) and is now available to the public. R-UNSAT also can be applied, however, to other unsaturated-zone transport problems that involve gas diffusion, such as radon migration, and the deposition of compounds from the atmosphere to shallow ground water. This fact sheet describes the transport model and demonstrates its capabilities through applications to point- and nonpoint-source contamination.

Fact Sheet↗
USGS1999

Simulating contaminant attenuation, double-porosity exchange, and water age in aquifers using MOC3D

MOC3D is a general-purpose computer model developed by the U.S. Geological Survey (USGS) for simulation of three-dimensional solute transport in ground water (Konikow and others, 1996). The model is an update to the widely used USGS two-dimensional solute-transport model (MOC) and is implemented as an optional “package” for the ground-water flow model MODFLOW (Harbaugh and McDonald, 1996). Directly coupling the time-tested MOC transport algorithms with the widely used MODFLOW program makes MOC3D a powerful tool for simulation of solute transport in ground water in many hydrogeologic settings. The model simulates transport processes that include: Advection - Transport of dissolved solutes at the same rate as the average ground-water flow velocity. Diffusion - Spreading of solute from areas of high concentration to areas of low concentration, caused by “random” molecular motion Dispersion - Diffusion-like spreading of solute that is caused primarily by spatial variability in aquifer properties, which results in spatial variability in transport velocity. Retardation - Reduction in the apparent solute velocity, compared to the ground-water velocity, caused by linear equilibrium sorption on aquifer materials. Decay - Disappearance of solute caused by reactions such as radioactive decay or biodegradation that are proportional to concentration. Growth - Creation (or disappearance) of solute mass caused by reactions that proceed independent of the solute concentration, such as some cases of biodegradation Double-porosity exchange - rate-limited exchange of solute mass between mobile and immobile zones; for example, between fractures and the rock matrix.

Fact Sheet↗
USGS2003

Selected natural attenuation monitoring data, Operable Unit 1, Naval Undersea Warfare Center, Division Keyport, Washington, June 2001

Previous investigations have shown that natural attenuation and biodegradation of chlorinated volatile organic compounds (CVOCs) are substantial in shallow ground water beneath the 9-acre former landfill at Operable Unit 1 (OU 1), Naval Undersea Warfare Center (NUWC), Division Keyport, Washington. The U.S. Geological Survey (USGS) has continued to monitor ground-water geochemistry to assure that conditions remain favorable for contaminant biodegradation. This report presents the ground-water geochemical and selected CVOC data collected at OU 1 by the USGS during June 11-14, 2001 in support of the long-term monitoring for natural attenuation. Overall, the June 2001 data indicate that redox conditions in the upper aquifer remain favorable for reductive dechlorination of CVOCs because strongly reducing conditions persisted beneath much of the former landfill. Redox conditions in the intermediate aquifer down gradient of the landfill appear to have become more favorable for reductive dechlorination because June 2001 dissolved hydrogen concentrations indicated strongly reducing conditions there for the first time. Although changes in redox conditions were observed at certain wells during 2001, a longer monitoring period is needed to ascertain if phytoremediation activities are affecting the ground-water chemistry. A minor change to future monitoring is proposed. Filtered organic carbon (previously referred to as dissolved, and defined as that which passes through a 0.45-micrometer membrane filter) should be analyzed in the future rather than unfiltered (previously referred to as total) organic carbon because the filtered analysis may be a better measure of bioavailable organic carbon. Unfiltered and filtered organic carbon data were collected during June 2001 for comparison. Filtered organic carbon data collected in the future could be reasonably compared with historical unfiltered organic carbon data by multiplying the historical data by a factor of about 0.9.

Open-File Report↗
USGS2000

Simple Techniques For Assessing Impacts Of Oil And Gas Operations On Federal Lands - A Field Evaluation At Big South Fork National River And Recreation Area, Scott County, Tennessee

Simple, cost-effective techniques are needed for land managers to assess the environmental impacts of oil and gas production activities on public lands so that sites may be prioritized for further, more formal assessment or remediation. These techniques should allow the field investigator to extend the assessment beyond the surface disturbances documented by simple observation and mapping using field-portable instruments and expendable materials that provide real-time data. The principal contaminants of current concern are hydrocarbons, produced water, and naturally occurring radioactive materials (NORM). Field investigators can examine sites for the impacts of hydrocarbon releases using a photoionization detector (PID) and a soil auger. Volatile organic carbon (VOC) in soil gases in an open auger hole or in the head space of a bagged and gently warmed auger soil sample can be measured by the PID. This allows detection of hydrocarbon movement in the shallow subsurface away from areas of obvious oil-stained soils or oil in pits at a production site. Similarly, a field conductivity meter and chloride titration strips can be used to measure salts in water and soil samples at distances well beyond areas of surface salt scarring. Use of a soil auger allows detection of saline subsoils in areas where salts may be flushed from the surface soil layers. Finally, a microRmeter detects the presence of naturally occurring radioactive materials (NORM) in equipment and soils. NORM often goes undetected at many sites although regulations limiting NORM in equipment and soils are being promulgated in several States and are being considered by the USEPA. With each technique, background sampling should be done for comparison with impacted areas. The authors examined sites in the Big South Fork National River and Recreation Area in November of 1999. A pit at one site at the edge of the flood plain of a small stream had received crude oil releases from a nearby tank. Auger holes down gradient from the pit showed the presence of anomalous concentrations of VOCs at depths of 3 feet for a distance of about 50 feet. PID readings at other sites showed 1) one reclaimed site where hydrocarbon biodegradation was incomplete; 2) one reclaimed site where biodegradation had left no traces of VOCS; and 3) two sites where traces of substantial offsite migration of hydrocarbons occurred. Produced water salts at one site have migrated many 100s of feet downvalley from the area of salt scarring and tree death adjacent to the pits. Naturally occurring radioactivity (NORM) at most sites was at background. One site showed anomalous radioactivity related to NORM in a small brine pit. Some of this NORM has moved downslope from the outlet pipe to the pit.

Open-File Report↗
USGS2004

Selected natural attenuation monitoring data, Operable Unit 1, Naval Undersea Warfare Center, Division Keyport, Washington, June 2003

Previous investigations have shown that natural attenuation and biodegradation of chlorinated volatile organic compounds (CVOCs) are substantial in shallow ground water beneath the 9-acre former landfill at Operable Unit 1 (OU 1), Naval Undersea Warfare Center (NUWC), Division Keyport, Washington. This report presents the ground-water geochemical and selected CVOC data collected at OU 1 by the U.S. Geological Survey (USGS) during June 17-20, 2003 in support of long-term monitoring for natural attenuation. Strongly reducing conditions favorable for reductive dechlorination of CVOCs were found in fewer upper-aquifer wells during June 2003 than were found during sampling periods in 2001 and 2002. Redox conditions in water from the intermediate aquifer just downgradient from the landfill remained somewhat favorable for reductive dechlorination. As was noted in previous monitoring reports, the changes in redox conditions observed at individual wells have not been consistent or substantial throughout either the upper or the intermediate aquifers. Compared to 2002 data, total CVOC concentrations in June 2003 were nearly unchanged in all northern plantation piezometers sampled, although the concentrations were historically low at two of those sites. Total CVOC concentrations decreased consistently in the southern plantation samples. Historically low total CVOC concentrations were observed in three of the piezometers sampled, and a two order-of-magnitude decrease in total CVOCs was observed at one of those sites. The observed decreases in CVOC concentrations appear to be in contrast with the 2003 redox data that suggested less favorable conditions for reductive dechlorination. The Navy and USGS plan to do more extensive data-collection and interpretation during 2004 to better understand and document possible changes in redox conditions and contaminant biodegradation.

Open-File Report↗
USGS2006

Description, Properties, and Degradation of Selected Volatile Organic Compounds Detected in Ground Water--A Review of Selected Literature

This report provides abridged information describing the most salient properties and biodegradation of 27 chlorinated volatile organic compounds detected during ground-water studies in the United States. This information is condensed from an extensive list of reports, papers, and literature published by the U.S. Government, various State governments, and peer-reviewed journals. The list includes literature reviews, compilations, and summaries describing volatile organic compounds in ground water. This report cross-references common names and synonyms associated with volatile organic compounds with the naming conventions supported by the International Union of Pure and Applied Chemistry. In addition, the report describes basic physical characteristics of those compounds such as Henry's Law constant, water solubility, density, octanol-water partition (log Kow), and organic carbon partition (log Koc) coefficients. Descriptions and illustrations are provided for natural and laboratory biodegradation rates, chemical by-products, and degradation pathways.

Open-File Report↗
USGS2009

Selected Natural Attenuation Monitoring Data, Operable Unit 1, Naval Undersea Warfare Center, Division Keyport, Washington, 2007 and 2008

Previous investigations indicate that natural attenuation and biodegradation of chlorinated volatile organic compounds (VOCs) are substantial in groundwater beneath the 9-acre former landfill at Operable Unit 1 (OU 1), Naval Undersea Warfare Center, Division Keyport, Washington. Phytoremediation combined with on-going natural attenuation processes was the preferred remedy selected by the Navy, as specified in the Record of Decision for the site. The Navy planted two hybrid poplar plantations on the landfill in spring 1999 to remove and to control the migration of chlorinated VOCs in shallow groundwater. The U.S. Geological Survey (USGS) has continued to monitor groundwater geochemistry to ensure that conditions remain favorable for contaminant biodegradation as specified in the Record of Decision. In this report are groundwater geochemical and selected VOC data collected at OU 1 by the USGS during June 18-21, 2007, and June 16-18, 2008, in support of long-term monitoring for natural attenuation. For 2007 and 2008, strongly reducing conditions (sulfate reduction and methanogenesis) most favorable for reductive dechlorination of VOCs were inferred for 9 of 16 upper-aquifer wells and piezometers in the northern and southern phytoremediation plantations. Predominant redox conditions in groundwater from the intermediate aquifer just downgradient from the landfill remained mildly reducing and somewhat favorable for reductive dechlorination of VOCs. Dissolved hydrogen (H2) concentrations measured in the upper aquifer during 2007 and 2008 generally have been lower than H2 concentrations measured before 2002. However, widespread and relatively high methane and sulfide concentrations indicate that the lower H2 concentrations measured do not support a trend from strongly to mildly reducing redox conditions because no widespread changes in groundwater redox conditions were identified that should result in less favorable conditions for the reductive dechlorination of the chlorinated VOCs. For the upper aquifer beneath the northern phytoremediation plantation, chlorinated VOC concentrations in 2007 and 2008 at most piezometers were similar to or slightly less than chlorinated VOC concentrations measured in previous years. The only chlorinated VOC positively detected at piezometers P1-1 and P1-5 was cis-1,2-dichloroethene (cis-DCE); most chlorinated VOC concentrations at piezometer P1-3 were at the lowest levels since monitoring began in 1999. Most VOC concentrations at piezometer P1-4 were similar to VOC concentrations measured in previous years except that vinyl chloride (VC) concentrations inexplicably increased from 280 micrograms per liter (ug/L) in June 2007 to 750 ug/L in June 2008. In 2008, measurement of the sum of concentrations of ethane and ethene, reductive dechlorination byproducts, was at the highest level at most northern plantation wells and piezometers, which is evidence of reductive dechlorination of chlorinated VOCs. For the upper aquifer beneath the southern phytoremediation plantation, chlorinated VOC concentrations in 2007 and 2008 at the piezometers were most often extremely high and they continued to vary considerable over space and between years. At piezometer P1-6, the total chlorinated VOC concentration increased from 380 ug/L in 2007 to more than 20,000 ug/L in 2008. At piezometer P1-7 in 2008, the concentrations of trichloroethene, cis-DCE, and VC were the highest to date, but total chlorinated VOC concentrations at piezometers P1-8, P1-9, and P1-10 in 2008 were relatively low compared to historical levels. The magnitude and persistence of chlorinated VOC concentrations indicate that non-aqueous phase liquid chloroethenes likely are beneath the southern plantation, and the temporal variability in concentrations likely is a result of variations in precipitation and groundwater levels interacting with the non-aqueous phase liquid. The reductive dechlorination byproducts ethane and ethene were detected at

Open-File Report↗
USGS2002

Subsurface and petroleum geology of the southwestern Santa Clara Valley ("Silicon Valley"), California

Gravity anomalies, historical records of exploratory oil wells and oil seeps, new organic-geochemical results, and new stratigraphic and structural data indicate the presence of a concealed, oil-bearing sedimentary basin beneath a highly urbanized part of the Santa Clara Valley, Calif. A conspicuous isostatic-gravity low that extends about 35 km from Palo Alto southeastward to near Los Gatos reflects an asymmetric, northwest-trending sedimentary basin comprising low-density strata, principally of Miocene age, that rest on higher-density rocks of Mesozoic and Paleogene(?) age. Both gravity and well data show that the low-density rocks thin gradually to the northeast over a distance of about 10 km. The thickest (approx 4 km thick) accumulation of low-density material occurs along the basin's steep southwestern margin, which may be controlled by buried, northeast-dipping normal faults that were active during the Miocene. Movement along these hypothetical normal faults may been contemporaneous (approx 17–14 Ma) with sedimentation and local dacitic and basaltic volcanism, possibly in response to crustal extension related to passage of the northwestward-migrating Mendocino triple junction. During the Pliocene and Quaternary, the normal faults and Miocene strata were overridden by Mesozoic rocks, including the Franciscan Complex, along northeastward-vergent reverse and thrust faults of the Berrocal, Shannon, and Monte Vista Fault zones. Movement along these fault zones was accompanied by folding and tilting of strata as young as Quaternary and by uplift of the modern Santa Cruz Mountains; the fault zones remain seismically active. We attribute the Pliocene and Quaternary reverse and thrust faulting, folding, and uplift to compression caused by local San Andreas Fault tectonics and regional transpression along the Pacific-North American Plate boundary. Near the southwestern margin of the Santa Clara Valley, as many as 20 exploratory oil wells were drilled between 1891 and 1929 to total depths as great as 840 m. At least one pump unit is still standing. Although no lithologic or paleontologic samples are available from the wells, driller's logs indicate the presence of thick intervals of brown shale and sandstone resembling nearby outcrops of the Miocene Monterey Formation. Small amounts of oil and gas were observed in several wells, but commercial production was never established. Oil from the Peck well in Los Gatos is highly biodegraded, contains biomarkers commonly found in oils derived from the Monterey Formation, and has a stable-C-isotopic (d13C) composition of –23.32 permil, indicating derivation from a Miocene Monterey Formation source rock. Preliminary calculations suggest that about 1 billion barrels of oil may have been generated from source rocks within the Monterey Formation in the deepest part of the subsurface sedimentary basin between Los Gatos and Cupertino. Most of this oil was probably lost to biodegradation, oxidation, and leakage to the surface, but some oil may have accumulated in as-yet-undiscovered structural and stratigraphic traps along the complex structural boundary between the Santa Clara Valley and the Santa Cruz Mountains. Although some of these undiscovered accumulations of oil may be of commercial size, future petroleum exploration is unlikely because most of the area is currently devoted to residential, recreational, commercial, and industrial uses.

California↗
USGS2009

Source, Transport, and Fate of Groundwater Contamination at Site 45, Marine Corps Recruit Depot, Parris Island, South Carolina

Groundwater contamination by tetrachloroethene and its dechlorination products is present in two partially intermingled plumes in the surficial aquifer near a former dry-cleaning facility at Site 45, Marine Corps Recruit Depot, Parris Island, South Carolina. The northern plume originates from the vicinity of former above-ground storage tanks. Free-phase tetrachloroethene from activities in this area entered the groundwater and the storm sewer. The southern plume originates at a nearby new dry-cleaning facility, but probably was the result of contamination released to the aquifer from a leaking sanitary sewer line from the former dry-cleaning facility. Discharge of dissolved groundwater contamination is primarily to leaking storm sewers below the water table. Extensive biodegradation of the contamination takes place in the surficial aquifer; however, the biodegradation is insufficient to reduce trichloroethene to less than milligram-per-liter concentrations prior to discharging into the storm sewers. The groundwater volatile organic compounds entering the storm sewers are substantially diluted by tidal flushing upon entry and are subject to volatilization as they are transported through the storm sewer to a discharge point in a tributary to Ballast Creek. TCE concentrations of about 2-6 micrograms per liter were present in storm-sewer water near the discharge point (sampled at manhole STS26). On three out of four sampling events at manhole STS14, the storm-sewer water contained no vinyl chloride. During a time of relatively high groundwater levels, however, 20 micrograms per liter of vinyl chloride was present in STS14 storm-sewer water. Because groundwater leaks into that storm sewer and because the storm sewer upgradient from manhole STS14 is adjacent to part of the aquifer where 2,290 micrograms per liter of vinyl chloride have been detected, there is a potential for substantially increased concentrations of vinyl chloride to discharge at the storm-sewer outfall under conditions of high groundwater levels and low tidal flushing. In addition, the observation that free-phase tetrachloroethene may have entered the storm-sewer system during the 1994 discharge means that dense nonaqueous phase liquid tetrachloroethene could have leaked from various parts of the storm sewer or discharged to surface water at the storm-sewer outfall.

South Carolina↗
USGS2012

Microbial mineralization of cis-dichloroethene and vinyl chloride as a component of natural attenuation of chloroethene contaminants under conditions identified in the field as anoxic

Chlororespiration is a key component of remediation at many chloroethene-contaminated sites. In some instances, limited accumulation of reductive dechlorination daughter products may suggest that natural attenuation is not adequate for site remediation. This conclusion is justified when evidence for parent compound (tetrachloroethene, PCE, or trichloroethene, TCE) degradation is lacking. For many chloroethene-contaminated shallow aquifer systems, however, non-conservative losses of the parent compounds are clear but the mass balance between parent compound attenuation and accumulation of reductive dechlorination daughter products is incomplete. Incomplete mass balance indicates a failure to account for important contaminant attenuation mechanisms, and is consistent with contaminant degradation to non-diagnostic mineralization products. An ongoing technical debate over the potential for mineralization of dichloroethene (DCE) and vinyl chloride (VC) to CO 2 in the complete absence of diatomic oxygen has largely obscured the importance of microbial DCE/VC mineralization at dissolved oxygen (DO) concentrations below the current field standard (DO < 0.1-0.5 milligrams per liter) for nominally anoxic conditions. This study demonstrates that oxygen-based microbial mineralization of DCE and VC can be substantial under field conditions that are frequently characterized as "anoxic." Because mischaracterization of operant contaminant biodegradation processes can lead to expensive and ineffective remedial actions, a modified framework for assessing the potential importance of oxygen during chloroethene biodegradation was developed.

Scientific Investigations Report↗