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At least 199 records · Page 11Linked to original sources
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↗
USGS2021

Groundwater hydrology and chemistry of Jamestown Island, Virginia—Potential effects of tides, storm surges, and sea-level rise on archaeological, cultural, and ecological resources

As the site of the first permanent English settlement in North America in 1607, Jamestown Island, Colonial National Historical Park (COLO), Virginia, contains a rich archaeological record that extends from the Paleoindian period (15,000 to 8,000 years ago) through the 20th century. The island is located on the lower James River near the mouth of Chesapeake Bay. Jamestown Island vegetation is dominated by upland forests surrounded by tidal, freshwater-to-oligohaline marshes. Along the Virginia coast, relative sea-level rise was more than 2.5 times the global average during the 20th century. Consequently, the National Park Service (NPS) has identified COLO as one of the 25 national parks most threatened by climate change. Surface waters across the island are hydraulically connected to the laterally continuous Surficial aquifer. The land-surface altitude of the island is low, with two-thirds of the island less than 5 feet (ft) above the North American Vertical Datum of 1988 (NAVD 88). Consequently, sea-level rise, combined with tides and storm surges, threatens the island and its resources as surface-water and groundwater levels rise, saltwater enters the Surficial aquifer, and groundwater chemistry changes. The impact of sea-level rise on the island’s surface-water resources has been well studied, but groundwater effects have been largely ignored. Quantifying the effects of tides, storm surges, and sea-level rise on groundwater levels and chemistry is essential to developing an effective strategy for managing climate-induced changes. The first step in developing a response strategy includes a parkwide general risk assessment for archaeological sites on the island, so that sites can be prioritized for management actions. The U.S. Geological Survey and the NPS began a study in 2015 to develop a long-term groundwater-monitoring program to evaluate this risk and to develop an updated management strategy. The groundwater-monitoring program consists of 45 wells and piezometers in two individual clusters and three transects across the island in different hydrologic and chemical settings. Samples for water quality were collected from the wells and piezometers from October 2015 through September 2018 at variable time intervals. Results of the monitoring identified disparate hydrologic and chemical responses to saltwater intrusion across the island. Specific conductance (an indicator of salinity) of groundwater beneath several marshes responded differently to changes in James River salinity. Groundwater response to changes in James River specific conductance appeared to be controlled by land-surface altitude and slope, differences in lateral and vertical sediment characteristics, distance from surface waters, and the degree of surface water/groundwater connectivity between channels and the aquifer. Groundwater chemistry data from monitoring wells at Black Point, a low-altitude, upland setting, are in contrast with conditions observed in Island House observation wells, a high-altitude, upland setting. Specific conductance (less than 200 microsiemens per centimeter [μS/cm]) and pH (greater than 5.0) of groundwater beneath much of the uplands that characterize the Island House observation wells are typical of groundwater in noncarbonate sedimentary aquifers recharged by precipitation. At Black Point, specific conductance ranged from 2,490 to 15,200 μS/cm, and pH ranged from 3.1 to 6.6 standard units. At the Black Point observation wells, the most saline and dense water was at the water table rather than deeper in the aquifer, causing a density inversion that persisted throughout the study. The density inversion likely resulted from differences in permeability between the shallow clay and fine-grained sands and the deeper coarse-grained sand and gravel. Groundwater with the lowest pH was at the water table. As saline groundwater flows through organic sediment beneath the marshes, bacterial biodegradation of organic matter creates anoxic conditions. Continued biodegradation concomitantly reduces iron-oxide minerals in the sediment and sulfate in saline water. When oxygen is reintroduced into groundwater, iron and sulfur can reoxidize to form sulfuric acid, locally lowering the pH of the water. This report describes the groundwater monitoring network design, rationale for site selection, monitoring approach, and results of monitoring from October 2015 through September 2018. Maps of inundation at selected water-level altitudes are included to identify the risk to archaeological, cultural, and ecological resources. The monitoring results of the hydrology and chemistry data are interpreted, and the different hydrologic and chemical settings are described. The implications of the study results for management decisions are presented, and suggestions for improving the monitoring network are included.

Virginia↗
USGS2003

Anaerobic degradation of 1,1,2,2-tetrachloroethane and association with microbial communities in a freshwater tidal wetland, Aberdeen Proving Ground, Maryland: Laboratory experiments and comparisons to field data

Defining biodegradation rates and processes is a critical part of assessing the feasibility of monitored natural attenuation as a remediation method for ground water containing organic contaminants. During 1998–2001, the U.S. Geological Survey conducted a microbial study at a freshwater tidal wetland along the West Branch Canal Creek, Aberdeen Proving Ground, Maryland, as part of an investigation of natural attenuation of chlorinated volatile organic compounds (VOCs) in the wetland sediments. Geochemical analyses and molecular biology techniques were used to investigate factors controlling anaerobic degradation of 1,1,2,2-tetrachloroethane (TeCA), and to characterize the microbial communities that potentially are important in its degradation. Rapid TeCA and daughter product degradation observed in laboratory experiments and estimated with field data confirm that natural attenuation is a feasible remediation method at this site. The diverse microbial community that seems to be involved in TeCA degradation in the wetland sediments varies with changing spatial and seasonal conditions, allowing continued effective natural attenuation throughout the year. Rates of TeCA degradation in anaerobic microcosm experiments conducted with wetland sediment collected from two different sites (WB23 and WB30) and during three different seasons (March–April 1999, July–August 1999, and October–November 2000) showed little spatial variability but high seasonal variability. Initial first-order degradation rate constants for TeCA ranged from 0.10±0.01 to 0.16±0.05 per day (halflives of 4.3 to 6.9 days) for March–April 1999 and October–November 2000 microcosms incubated at 19 degrees Celsius, whereas lower rate constants of 0±0.03 and 0.06±0.03 per day were obtained in July–August 1999 microcosms incubated at 19 degrees Celsius. Microbial community profiles showed that low microbial biomass and microbial diversity in the summer, possibly due to competition for nutrients by the wetland vegetation, could account for these unexpectedly low degradation rates. In microcosms incubated at 5 degrees Celsius, about 50 percent of the initial TeCA in solution was converted to daughter products within a 35-day incubation period, indicating that biodegradation in the wetland sediments can continue during cold winter temperatures. Initial pathways of TeCA degradation were the same in the wetland sediment microcosms regardless of the season or sediment collection site, the reduction-oxidation conditions, and the previous exposure of the sediment to contamination. Immediate and simultaneous dichloroelimination and hydrogenolysis, producing 1,2-dichloroethene (12DCE) and 1,1,2-trichloroethane (112TCA), respectively, were the initial TeCA degradation pathways in all live microcosm experiments. The production and degradation of vinyl chloride (VC), which is the most toxic of the TeCA daughter compounds, was affected by spatial and seasonal variability, reduction-oxidation condition, and pre-exposure of the wetland sediment. TeCA-amended microcosms constructed with WB30 sediment showed approximately twice as much VC production as those constructed with WB23 sediment. Results of 112TCA-amended microcosms indicated that the greater production of VC in the WB30 sediment resulted from a greater predominance of the 112TCA dichloro elimination pathway in these sediments. VC degradation also was substantially higher in microcosms constructed with WB30 sediment than those constructed with WB23 sediment, resulting in lower VC concentrations at the end of WB30 microcosms. Enrichment experiments in which microcosm slurry was amended with high initial VC concentrations showed that the spatial difference in VC degradation was negligible after prolonged incubation under methanogenic conditions. Inhibition of methanogenic activity in microcosms by addition of sulfate or of 2-bromoethanesulfonic acid inhibited production and degradation of VC. Inhibition of methanogenesis by addition of ferric iron or of 2-bromoethanesulfonic acid also completely inhibited VC degradation in VC-amended enrichment experiments. Pre-exposure to VC substantially increased degradation in VC-amended enrichment experiments. A microbial consortium, rather than one microbial species or group, likely is involved in the degradation of TeCA, as indicated by the occurrence of multiple degradation pathways and the variability in VC production and degradation. A bacterial peak at 90 base pair (bp) fragment length in terminal- restriction fragment length polymorphism (TRFLP) profiles was associated with TeCA hydrogenolysis to 112TCA, and bacterial species represented by 198 and 170 bp fragment lengths were associated with TeCA dichloroelimination to 12DCE. Dichloroelimination of 112TCA to VC was associated with increasing dominance of the 198 bp bacterial peak in March–April 1999 and October–November 2000 microcosms, whereas an 86 bp or the 170 bp bacterial peak was associated with 112TCA dichloroelimination in the summer experiment. Hydrogenolysis of 12DCE to VC was associated with a carbon dioxide-utilizing methanogen at 307 bp in the March–April 1999 and October–November 2000 microcosm experiments, whereas production of VC occurred despite low methanogen biomass and methane production in the July–August 1999 experiments. Production of VC in the absence of methane production also occurred in 12DCE-amended enrichment cultures. The exponential production of VC in the 12DCE-amended enrichment cultures after an initial lag indicated growth of a microbial species or group, possibly one of the known dehalorespiring bacteria. Molecular analyses using specific primers targeting dehalorespiring bacteria of the Dehalococcoides group (Dehalococcoides ethenogenes and Dehalococcoides sp. strain FL2) and of the acetate-oxidizing Desulfuromonas group (Desulfuromonas sp. strain BB1 and Desulfuromonas chloroethenica) showed the presence of these bacteria in microcosm slurry from site WB30 but not from site WB23. Addition of hydrogen, which is the favored substrate of Dehalococcoides, tripled VC production in 12DCE-amended enrichment cultures. VC degradation showed a marked association with an increase in the relative proportion of Methanosarcinaceae, a family of methanogens that includes all those capable of utilizing acetate as a substrate, in the total methanogen community. Half-lives for TeCA and TCE estimated from field data were in the range of 60 to 100 days, which agrees well with laboratory estimates of degradation rates considering the inherent differences in the laboratory and field systems. Both laboratory microcosm experiments and field data showed that 12DCE and VC are the predominant, persistent daughter compounds from TeCA degradation. In addition, porewater chemistry showed higher accumulation of VC in the wetland sediment at site WB30 than at site WB23, as was observed in the microcosm experiments. Molecular analyses of grab samples of surficial wetland sediment showed that all the microbial species or groups linked to TeCA degradation in the microcosm experiments were present in all sediment samples. Microbial biomass and diversity were lowest in an area of the wetland (transect C-C') where porewater VOC concentrations are highest, indicating that the higher VOC concentrations could result from lower degradation rates. The lower microbial biomass and diversity in this area could be caused by toxic effects of the contaminants, or possibly from differences in frequency and duration of tidal inundation.

Maryland↗
USGS2003

Methodology for estimating times of remediation associated with monitored natural attenuation

Natural attenuation processes combine to disperse, immobilize, and biologically transform anthropogenic contaminants, such as petroleum hydrocarbons and chlorinated ethenes, in ground-water systems. The time required for these processes to lower contaminant concentrations to levels protective of human health and the environment, however, varies widely between different hydrologic systems, different chemical contaminants, and varying amounts of contaminants. This report outlines a method for estimating timeframes required for natural attenuation processes, such as dispersion, sorption, and biodegradation, to lower contaminant concentrations and mass to predetermined regulatory goals in groundwater systems. The time-of-remediation (TOR) problem described in this report is formulated as three interactive components: (1) estimating the length of a contaminant plume once it has achieved a steady-state configuration from a source area of constant contaminant concentration, (2) estimating the time required for a plume to shrink to a smaller, regulatoryacceptable configuration when source-area contaminant concentrations are lowered by engineered methods, and (3) estimating the time needed for nonaqueous phase liquid (NAPL) contaminants to dissolve, disperse, and biodegrade below predetermined levels in contaminant source areas. This conceptualization was used to develop Natural Attenuation Software (NAS), an interactive computer aquifers. NAS was designed as a screening tool and requires the input of detailed site information about hydrogeology, redox conditions, and the distribution of contaminants. Because NAS is based on numerous simplifications of hydrologic, microbial, and geochemical processes, the program may introduce unacceptable errors for highly heterogeneous hydrologic systems. In such cases, application of the TOR framework outlined in this report may require more detailed, site-specific digital modeling. The NAS software may be downloaded from the Web site http://www.cee.vt.edu/NAS/ Application of NAS illustrates several general characteristics shared by all TOR problems. First, the distance of stabilization of a contaminant plume is strongly dependent on the natural attenuation capacity of particular ground-water systems. The time that it takes a plume to reach a steady-state configuration, however, is independent of natural attenuation capacity. Rather, the time of stabilization is most strongly affected by the sorptive capacity of the aquifer, which is dependent on the organic matter content of the aquifer sediments, as well as the sorptive properties of individual contaminants. As a general rule, a high sorptive capacity retards a plume.s growth or shrinkage, and increases the time of stabilization. Finally, the time of NAPL dissolution depends largely on NAPL mass, composition, geometry, and hydrologic factors, such as ground-water flow rates. An example TOR analysis for petroleum hydrocarbon NAPL was performed for the Laurel Bay site in South Carolina. About 500 to 1,000 pounds of gasoline leaked into the aquifer at this site in 1991, and the NAS simulations suggested that TOR would be on the order of 10 years for soluble and poorly sorbed compounds, such as benzene and methyl tertiary-butyl ether (MTBE). Conversely, TOR would be on the order of 40 years for less soluble, more strongly sorbed compounds, such as toluene, ethylbenzene, and xylenes (TEX). These TOR estimates are roughly consistent with contaminant concentrations observed over 10 years of monitoring at this site where benzene and MTBE concentrations were observed to decrease rapidly and are approaching regulatory maximum concentration limits, whereas toluene, ethylbenzene, and xylene concentrations decreased at a slower rate and have remained relatively high. An example TOR analysis for petroleum hydrocarbon NAPL was performed for the Laurel Bay site in South Carolina.

South Carolina↗
USGS2003

Processes affecting the trihalomethane concentrations associated with the third injection, storage, and recovery rest at Lancaster, Antelope Valley, California, March 1998 through April 1999

The formation and fate of trihalomethanes (THM) during the third injection, storage, and recovery test at Lancaster, Antelope Valley, California, were investigated as part of a program to assess the long-term feasibility of using injection, storage, and recovery as a water-supply method and as a way to reduce water-level declines and land-subsidence in the Antelope Valley. The program was conducted by the U.S. Geological Survey in cooperation with the Los Angeles County Department of Public Works and the Antelope Valley-East Kern Water Agency. The water used for injection, storage, and recovery must be disinfected before injection and thus contains THMs and other disinfection by-products. THMs (chloroform, CHCl 3 , bromodichloromethane, CHCl 2 Br, dibromochloromethane, CHClBr 2 , and bromoform, CHBr 3 ) are formed by reaction between natural dissolved organic carbon that is present in water and chlorine that is added during the disinfection step of the drinking water treatment process. THMs are carcinogenic compounds, and their concentrations in drinking water are regulated by the U.S. Environmental Protection Agency. During previous cycles of the Lancaster program, extracted water still contained measurable concentrations of THMs long after continuous pumping had extracted a greater volume of water than had been injected. This raised concerns about the potential long-term effect of injection, storage, and recovery cycles on ground-water quality in Antelope Valley aquifers. The primary objectives of this investigation were to determine (1) what controlled continued THM formation in the aquifer after injection, (2) what caused of the persistence of THMs in the extracted water, even after long periods of pumping, (3) what controlled the decrease of THM concentrations during the extraction period, and (4) the potential for natural attenuation of THMs in the aquifer. Laboratory experiments on biodegradation of THMs in microcosms of aquifer materials indicate that aquifer bacteria did not degrade CHCl 3 or CHBr 3 under aerobic conditions, but did degrade CHBr 3 under anaerobic conditions. However, the aquifer is naturally aerobic and CHCl 3 is the dominant THM species; therefore, biodegradation is not considered an important attenuation mechanism for THMs in this aquifer. The alluvial-fan sediments comprising the aquifer have very low contents of organic matter; therefore, sorption is not considered to be an important attenuation mechanism for THMs in this aquifer. Laboratory experiments on formation of THMs in the injection water indicate that continued THM formation in the injection water after injection into the aquifer was limited by the amount of residual chlorine in the injection water at the time of injection. After accounting for THMs formed by reaction of this residual chlorine, THMs behaved as conservative constituents in the aquifer, and the only process affecting the concentration of THMs was mixing of the injection water and the ground water. The mixing process was quantified using mass balances of injected constituents, the sulfur hexafluoride (SF 6 ) tracer that was added to the injected water, and a simple descriptive mathematical mixing model. Mass balance calculations show that only 67 percent of the injected THMs and chloride were recovered by the time that a volume of water equivalent to 132 percent of the injection water volume was extracted. Pumping 250 percent of the injection water volume only increased recovery of injected THMs to 80 percent. THM and SF 6 concentrations in the extracted water decreased concomitantly during the extraction period, and THM concentrations predicted from SF 6 concentrations closely matched the measured THM concentrations. Because SF 6 is a conservative tracer that was initially only present in the injection water, parallel decreases in SF 6 and THM concentrations in the extracted water must be due to dilution of injection water with ground water. The simple descriptive mixing model mathematically described mixing of injection water and ground water that was displaced by injection using a single-zone mixing model. This simple model adequately predicted the concentrations of conservative constituents (SF 6 , THMs, and chloride) in the extracted water during the extraction period, providing further evidence to support the conclusion that mixing injection water and ground water in the aquifer was the primary process controlling the concentration of the THMs in the extracted water. Water-quality data and modeling results suggest that injection, storage, and recovery cycles will affect aquifer water quality. THM concentrations in water samples from piezometers located 80 horizontal feet from the injection/extraction well remained high and variable throughout the extraction period. This suggests that water entered regions of the aquifer during injection from which it was not efficiently recovered during extraction. In particular, water may have become stranded in the upper parts of the aquifer during injection and therefore could not be efficiently recovered during extraction owing to drawdown around the well. The descriptive mixing model was used to forecast the results of repeated annual cycles of injection, storage, and recovery. For the scenario of equal volumes of injected and extracted water, the model forecasts that the concentration of THMs (or of any conservative constituent in the injection water) in the ground water near the injection/extraction well would increase to nearly 100 percent of the concentration of THMs in the injection water within 10 years. This increase in THM concentration would be less if ground water from outside the region directly affected by injection also mixed with the injected water or if the volume of extracted water greatly exceeded the volume of injected water. Finally, the model results indicate that extraction of all injected constituents is difficult using existing extraction methods because the volume of water that must be extracted increases exponentially as the acceptance criteria for the concentration in the water remaining in the aquifer decreases.

California↗
USGS2003

Fate and Transport Modeling of Selected Chlorinated Organic Compounds at Hangar 1000, U.S. Naval Air Station, Jacksonville, Florida

The Jacksonville Naval Air Station occupies 3,800 acres adjacent to the St. Johns River in Jacksonville, Florida. Two underground storage tanks at Hangar 1000 contained solvents from the late 1960s until they were removed in 1994. Ground-water samples at one of the tank sites had levels of trichloroethene (TCE) and total dichloroethene (DCE) of 8,710 micrograms per liter (mg/L) and 4,280 mg/L, respectively. Vinyl chloride (VC) at the site is the result of the biodegradation of DCE. Ground water beneath Hangar 1000 flows toward a storm sewer. TCE and DCE plumes travel with the ground water and presumably have reached the storm sewer, which discharges to the St. Johns River. Simulation of solute transport indicates that the traveltime from the storage tank site to the storm sewer is 16, 14, and 12 years for TCE, DCE, and VC respectively. TCE has the longest traveltime because it has the highest retardation factor at 2.5, DCE takes less time with a retardation factor of 2.0, and VC has the quickest traveltime because it has the lowest retardation factor of 1.7. Based on modeling results, the release of contaminants in the aquifer occurred more than 16 years ago. Model-derived dispersivity values at Hangar 1000 were: longitudinal 1.5 feet (ft), transverse 0.27 ft, and vertical 0.27 ft. The model-derived first order decay rates for biodegradation of TCE, DCE, and VC were 0.0002 per day (d-1), 0.0002 d-1, and 0.06 d-1, respectively. These rates are equivalent to half-lives of 13.7 years for TCE and DCE and 17 days for VC. Source area reductions in contaminant concentrations of 50 and 100 percent were modeled to simulate remediation. As expected, reducing the source concentration by 50 percent resulted in eventual TCE, DCE, and VC concentrations that were half of the original concentrations. About 16 years were needed for new steady-state TCE concentrations to develop, about 14 years for DCE, and about 12 years for VC. Reducing the source area concentrations by 100 percent in the model eventually resulted in zero concentrations of TCE, DCE, and VC. The modeled period of time for the contaminants to be removed from the aquifer once the source was removed was about 17 years for TCE, 15 years for DCE, and 13 years for VC.

Water-Resources Investigations Report↗