Don A. Vroblesky | Search USGS

USGS2014

Dendrochemical patterns of calcium, zinc, and potassium related to internal factors detected by energy dispersive X-ray fluorescence (EDXRF)

Energy dispersive X-ray fluorescence (EDXRF) provides highly sensitive and precise spatial resolution of cation content in individual annual growth rings in trees. The sensitivity and precision have prompted successful applications to forensic dendrochemistry and the timing of environmental releases of contaminants. These applications have highlighted the need to distinguish dendrochemical effects of internal processes from environmental contamination. Calcium, potassium, and zinc are three marker cations that illustrate the influence of these processes. We found changes in cation chemistry in tree rings potentially due to biomineralization, development of cracks or checks, heartwood/sapwood differentiation, intra-annual processes, and compartmentalization of infection. Distinguishing internal from external processes that affect dendrochemistry will enhance the value of EDXRF for both physiological and forensic investigations.

Chemosphere↗

USGS2011

Investigation of the potential source area, contamination pathway, and probable release history of chlorinated-solvent-contaminated groundwater at the Capital City Plume Site, Montgomery, Alabama, 2008-2010

Detection of the organic solvent perchloroethylene (PCE) in a shallow public-supply well in 1991 and exposure of workers in 1993 to solvent vapors during excavation activities to depths near the water table provided evidence that the shallow aquifer beneath the capital city of Montgomery, Alabama, was contaminated. Investigations conducted from 1993 to 1999 by State and Federal agencies confirmed the detection of PCE in the shallow aquifer, as well as the detection of the organic solvent trichloroethylene (TCE) and various inorganic compounds, but the source of the groundwater contamination was not determined. In May 2000 the U.S. Environmental Protection Agency proposed that the site, called the Capital City Plume (CCP) Site, be a candidate for the National Priorities List. Between 2000 and 2007, numerous site-investigation activities also did not determine the source of the groundwater contamination. In 2008, additional assessments were conducted at the CCP Site to investigate the potential source area, contamination pathway, and the probable release history of the chlorinated-solvent-contaminated groundwater. The assessments included the collection of (1) pore water in 2008 from the hyporheic zone of a creek using passive-diffusion bag samplers; (2) tissue samples in 2008 and 2009 from trees growing in areas of downtown Montgomery characterized by groundwater contamination and from trees growing in riparian zones along the Alabama River and Cypress Creek; and (3) groundwater samples in 2009 and 2010. The data collected were used to investigate the potential source area of contaminants detected in groundwater, the pathway of groundwater contamination, and constraints on the probable contaminant-release history. The data collected between 2008 and 2010 indicate that the PCE and TCE contamination of the shallow aquifer beneath the CCP Site most likely resulted from the past use and disposal of industrial wastewater from printing operations containing chlorinated solvents into the sanitary sewer and (or) stormwater systems of Montgomery. Moreover, chlorinated-solvent use and disposal occurred at least between the 1940s and 1970s at several locations occupied by printing operations. The data also indicate that PCE and TCE contamination continues to occur in the shallow subsurface near potential release areas and that PCE and TCE have been transported to the intermediate part of the shallow aquifer.

Alabama↗

USGS2010

Relation of nickel concentrations in tree rings to groundwater contamination

Increment cores were collected from trees growing at two sites where groundwater is contaminated by nickel. Proton-induced X ray emission spectroscopy was used to determine the nickel concentrations in selected individual rings and in parts of individual rings. Ring nickel concentrations were interpreted on the basis of recent concentrations of nickel in aquifers, historical information about site use activities, and model simulations of groundwater flow. Nickel concentrations in rings increased during years of site use but not in trees outside the contaminated aquifers. Consequently, it was concluded that trees may preserve in their rings an annual record of nickel contamination in groundwater. Tulip trees and oaks contained higher concentrations of nickel than did sassafras, sweet gum, or black cherry. No evidence was found that nickel accumulates consistently within parts of individual rings or that nickel is translocated across ring boundaries.

Water Resources Research↗

USGS2010

Deducing the distribution of terminal electron-accepting processes in hydrologically diverse groundwater systems

The distribution of microbially mediated terminal electron-accepting processes (TEAPs( was investigated in four hydrologically diverse groundwater systems by considering patterns of electron acceptor (nitrate, sulfate) consumption, intermediate product (hydrogen (H 2 )) concentrations, and final product (ferrous iron, sulfide, and methane) production. In each hydrologic system a determination of predominant TEAPs could be arrived at, but the level of confidence appropriate for each determination differed. In a portion of the lacustrine aquifer of the San Joaquin Valley, for example, all three indicators (sulfate concentrations decreasing, H 2 concentrations in the 1–2 nmol range, and sulfide concentrations increasing along flow paths identified sulfate reduction as the predominant TEAP, leading to a high degree of confidence in the determination. In portions of the Floridan aquifer and a petroleum hydrocarbon-contaminated aquifer, sulfate reduction and methanogenesis are indicated by production of sulfide and methane, and hydrogen oncentrations in the 1–4 nmol and 5–14 nmol range, respectively. However, because electron acceptor consumption could not be documented in these systems, less confidence is warranted in the TEAP determination. In the Black Creek aquifer, no pattern of sulfate consumption and sulfide production were observed, but H2 concentrations indicated sulfate reduction as the predominant TEAP. In this case, where just a single line of evidence is available, the least confidence in the TEAP diagnosis is justified. Because this methodology is based on measurable water chemistry parameters and upon the physiology of microbial electron transfer processes, it provides a better description of predominant redox processes in groundwater systems than more traditional Eh-based methods.

Water Resources Research↗

USGS2010

Groundwater Hydrology and Chemistry in and near an Emulsified Vegetable-Oil Injection Zone, Solid Waste Management Unit 17, Naval Weapons Station Charleston, North Charleston, South Carolina, 2004-2009

The U.S. Geological Survey and the Naval Facilities Engineering Command Southeast investigated the hydrology and groundwater chemistry in the vicinity of an emulsified vegetable-oil injection zone at Solid Waste Management Unit (SWMU) 17, Naval Weapons Station Charleston, North Charleston, South Carolina. In May 2004, Solutions-IES initiated a Phase-I pilot-scale treatability study at SWMU17 involving the injection of an edible oil emulsion into the aquifer near wells 17PS-01, 17PS-02, and 17PS-03 to treat chlorinated solvents. The Phase-I injection of emulsified vegetable oil resulted in dechlorination of trichloroethene (TCE) to cis-1,2-dichloroethene (cDCE), but the dechlorination activity appeared to stall at cDCE, with little further dechlorination of cDCE to vinyl chloride (VC) or to ethene. The purpose of the present investigation was to examine the groundwater hydrology and chemistry in and near the injection zone to gain a better understanding of the apparent remediation stall. It is unlikely that the remediation stall was due to the lack of an appropriate microbial community because groundwater samples showed the presence of Dehalococcoides species (sp.) and suitable enyzmes. The probable causes of the stall were heterogeneous distribution of the injectate and development of low-pH conditions in the injection area. Because groundwater pH values in the injection area were below the range considered optimum for dechlorination activity, a series of tests was done to examine the effect on dechlorination of increasing the pH within well 17PS-02. During and following the in-well pH-adjustment tests, VC concentrations gradually increased in some wells in the injection zone that were not part of the in-well pH-adjustment tests. These data possibly reflect a gradual microbial acclimation to the low-pH conditions produced by the injection. In contrast, a distinct increase in VC concentration was observed in well 17PS-02 following the in-well pH increase. Adjustment of the pH to near-neutral values in well 17PS-02 may have made that well relatively favorable to VC production compared with much of the rest of the injection zone, possibly accounting for acceleration of VC production at that well. Following a Phase-II injection in which Solutions-IES, Inc., injected pH-buffered emulsified vegetable oil with an improved efficiency injection approach, 1,1-dichloroethene, TCE, and cDCE rapidly decreased in concentration and are now (2009) undetectable in the injection zone, with the exception of a low concentration (43 micrograms per liter, August 2009) of cDCE in well 17PS-01. In August 2009, VC was still present in groundwater at the test wells in concentrations ranging from 150 to 640 micrograms per liter. The Phase-II injection, however, appears to have locally decreased aquifer permeability, possibly resulting in movement of contamination around, rather than through, the treatment area.

North Carolina↗

USGS2010

Contamination movement around a permeable reactive barrier at Solid Waste Management Unit 12, Naval Weapons Station Charleston, North Charleston, South Carolina, 2009

The U.S. Geological Survey and the Naval Facilities Engineering Command Southeast investigated natural and engineered remediation of chlorinated volatile organic compound groundwater contamination at Solid Waste Management Unit 12 at the Naval Weapons Station Charleston, North Charleston, South Carolina, beginning in 2000. In early 2004, groundwater contaminants began moving around the southern end of a permeable reactive barrier (PRB) installed by a consultant in December 2002. The PRB is a 130-foot-long and 3-foot-wide barrier consisting of varying amounts of zero-valent iron with or without sand mixture. Contamination moving around the PRB probably has been transported at least 75 feet downgradient from the PRB at a rate of about 15 to 29 feet per year. The diversion of contamination around the southern end of the PRB may be due to construction difficulties associated with the PRB installation or to reduced permeability in the PRB. An event that took place during installation of the PRB, which may have caused permeability loss, was the collapse and subsequent abandonment of a 110-foot-long trench originally designed to be the PRB on November 11, 2002, approximately 25 feet upgradient (west) from the final PRB. Guar gum with antimicrobial preservative in a polymer slurry had been used to stabilize the abandoned trench prior to collapse and was only partially recovered. Residual guar gum can cause permeability reduction in a PRB. It also is possible that permeability reduction took place within the PRB by slow degradation of the guar gum slurry or mineral precipitation. Despite the likely permeability reduction in and near the PRB immediately following installation, there is evidence that contaminants moved through the PRB and were degraded, consistent with the planned purpose of the PRB. Volatile organic compound contamination in groundwater downgradient from the PRB is subject to attenuation by phytovolatilization, sorption, and biodegradation. Pulses of contamination increases have been observed in some monitoring wells downgradient from the PRB. The pulses may reflect downgradient transport of contaminant pulses; however, lateral shifting of the plume is a more likely explanation for the concentration changes at well 12MW-12S. The ability to monitor the fate and behavior of the plume in the forest is severely limited because the present axis of maximum contamination in that area bypasses all but one of the existing monitoring wells (12MW-12S). Moreover, the 2009 data indicate that there are no optimally placed sentinel wells in the probable path of contaminant transport. Thus the monitoring network is no longer adequate to monitor the groundwater contamination downgradient from the PRB.

South Carolina↗

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↗

USGS2009

Investigation of Contaminated Groundwater at Solid Waste Management Unit 12, Naval Weapons Station Charleston, North Charleston, South Carolina, 2008

The U.S. Geological Survey and the Naval Facilities Engineering Command Southeast investigated natural and engineered remediation of chlorinated volatile organic compound (VOC) groundwater contamination at Solid Waste Management Unit 12 at the Naval Weapons Station Charleston, North Charleston, South Carolina, beginning in 2000. The primary contaminants of interest in the study are tetrachloroethene, 1,1,1-trichloroethane, trichloroethene, cis-1,2-dichloroethene, vinyl chloride, 1,1-dichloroethane, and 1,1-dichloroethene. Engineered remediation aspects at the site consist of a zero-valent-iron permeable reactive barrier (PRB) installed in December 2002 intercepting the contamination plume and a phytoremediation test stand of loblolly pine trees planted in the source area in May 2003. The U.S. Geological Survey planted an additional phytoremediation test stand of loblolly pine trees on the upgradient side of the southern end of the PRB in February 2008. At least once during the summer, however, the trees were inadvertently mowed during lawn cutting activity. The PRB along the main axis of the contaminant plume appears to be actively removing contamination. In contrast to the central area of the PRB, the data from the southern end of the PRB indicate that contaminants are moving around the PRB. Concentrations in wells upgradient from the PRB showed a general decrease in VOC concentrations. VOC concentrations in some wells in the forest downgradient from the PRB showed a sharp increase in 2005, followed by a decrease in 2006. Farther downgradient in the forest, the VOC concentrations began to increase in 2007 and continued to increase into 2008. The VOC-concentration changes in groundwater beneath the forest appear to indicate movement of a groundwater-contaminant pulse through the forest. It also is possible that the data may represent lateral shifting of the plume in response to changes in groundwater-flow direction.

South Carolina↗

USGS2009

Tritium concentrations in environmental samples and transpiration rates from the vicinity of Mary's Branch Creek and background areas, Barnwell, South Carolina, 2007-2009

Tritium in groundwater from a low-level radioactive waste disposal facility near Barnwell, South Carolina, is discharging to Mary's Branch Creek. The U.S. Geological Survey conducted an investigation from 2007 to 2009 to examine the tritium concentration in trees and air samples near the creek and in background areas, in groundwater near the creek, and in surface water from the creek. Tritium was found in trees near the creek, but not in trees from background areas or from sites unlikely to be in direct root contact with tritium-contaminated groundwater. Tritium was found in groundwater near the creek and in the surface water of the creek. Analysis of tree material has the potential to be a useful tool in locating shallow tritium-contaminated groundwater. A tritium concentration of 1.4 million picocuries per liter was measured in shallow groundwater collected near a tulip poplar located in an area of tritium-contaminated groundwater discharge. Evapotranspiration rates from the tree and tritium concentrations in water extracted from tree cores indicate that during the summer, this tulip poplar may remove more than 17.1 million picocuries of tritium per day from the groundwater that otherwise would discharge to Mary's Branch Creek. Analysis of air samples near the tree showed no evidence that the transpirative release of tritium to the air created a vapor hazard in the forest.

South Carolina↗

USGS2008

Real-Time and Delayed Analysis of Tree and Shrub Cores as Indicators of Subsurface Volatile Organic Compound Contamination, Durham Meadows Superfund Site, Durham, Connecticut, August 29, 2006

This study examined volatile organic compound concentrations in cores from trees and shrubs for use as indicators of vadose-zone contamination or potential vapor intrusion by volatile organic compounds into buildings at the Durham Meadows Superfund Site, Durham, Connecticut. The study used both (1) real-time tree- and shrub-core analysis, which involved field heating the core samples for 5 to 10 minutes prior to field analysis, and (2) delayed analysis, which involved allowing the gases in the cores to equilibrate with the headspace gas in the sample vials unheated for 1 to 2 days prior to analysis. General correspondence was found between the two approaches, indicating that preheating and field analysis of vegetation cores is a viable approach to real-time monitoring of subsurface volatile organic compounds. In most cases, volatile organic compounds in cores from trees and shrubs at the Merriam Manufacturing Company property showed a general correspondence to the distribution of volatile organic compounds detected in a soil-gas survey, despite the fact that most of the soil-gas survey data in close proximity to the relevant trees were collected about 3 years prior to the tree-core collection. Most of the trees cored at the Durham Meadows Superfund Site, outside of the Merriam Manufacturing Company property, contained no volatile organic compounds and were in areas where indoor air sampling and soil-gas sampling showed little or no volatile organic compound concentrations. An exception was tree DM11, which contained barely detectable concentrations of trichloroethene near a house where previous investigations found low concentrations of trichloroethene (0.13 to 1.2 parts per billion by volume) in indoor air and 7.7 micrograms per liter of trichloroethene in the ground water. The barely detectable concentration of trichloroethene in tree DM11 and the lack of volatile organic compound detection in nearby tree DM10 (adjacent to the well having 7.7 micrograms of trichloroethene) may be attributable to the relatively large depth to water (17.6 feet), the relatively low soil-vapor trichloroethene concentration, and the large amount of rainfall during and preceding the tree-coring event. The data indicate that real-time and delayed analyses of tree cores are viable approaches to examining subsurface volatile organic compound soil-gas or vadose-zone contamination at the Durham Meadows Superfund Site and other similar sites. Thus, the methods may have application for determining the potential for vapor intrusion into buildings.

Scientific Investigations Report↗

USGS2008

User’s guide to the collection and analysis of tree cores to assess the distribution of subsurface volatile organic compounds

Analysis of the volatile organic compound content of tree cores is an inexpensive, rapid, simple approach to examining the distribution of subsurface volatile organic compound contaminants. The method has been shown to detect several volatile petroleum hydrocarbons and chlorinated aliphatic compounds associated with vapor intrusion and ground-water contamination. Tree cores, which are approximately 3 inches long, are obtained by using an increment borer. The cores are placed in vials and sealed. After a period of equilibration, the cores can be analyzed by headspace analysis gas chromatography. Because the roots are exposed to volatile organic compound contamination in the unsaturated zone or shallow ground water, the volatile organic compound concentrations in the tree cores are an indication of the presence of subsurface volatile organic compound contamination. Thus, tree coring can be used to detect and map subsurface volatile organic compound contamination. For comparison of tree-core data at a particular site, it is important to maintain consistent methods for all aspects of tree-core collection, handling, and analysis. Factors affecting the volatile organic compound concentrations in tree cores include the type of volatile organic compound, the tree species, the rooting depth, ground-water chemistry, the depth to the contaminated horizon, concentration differences around the trunk related to variations in the distribution of subsurface volatile organic compounds, concentration differences with depth of coring related to volatilization loss through the bark and possibly other unknown factors, dilution by rain, seasonal influences, sorption, vapor-exchange rates, and within-tree volatile organic compound degradation.

Scientific Investigations Report↗

USGS2008

Investigation of Contaminated Ground Water at Solid Waste Management Unit 12, Naval Weapons Station Charleston, North Charleston, South Carolina, 2006-2007

The U.S. Geological Survey investigated natural and engineered remediation of chlorinated volatile organic compound (VOC) ground-water contamination at Solid Waste Management Unit 12 at the Naval Weapons Station Charleston, North Charleston, South Carolina, beginning in 2000. The primary contaminants of interest in the study are tetrachloroethene, 1,1,1-trichloroethane, trichloroethene, cis-1,2-dichloroethene, vinyl chloride, 1,1-dichloroethane, and 1,1-dichloroethene. The permeable reactive barrier (PRB) along the main axis of the contaminant plume appears to be actively removing contamination. In contrast to the central area of the PRB, the data from the southern end of the PRB indicate that contaminants are moving around the PRB. Concentrations in wells 12MW-10S and 12MW-03S, upgradient from the PRB, showed a general decrease in VOC concentrations. VOC concentrations in some wells in the forest showed a sharp increase, followed by a decrease. In 2007, the VOC concentrations began to increase in well 12MW-12S, downgradient from the PRB and thought to be unaffected by the PRB. The VOC-concentration changes in the forest, such as at well 12MW-12S, may represent lateral shifting of the plume in response to changes in ground-water-flow direction or may represent movement of a contamination pulse through the forest.

South Carolina↗

USGS2008

Comparison of pumped and diffusion sampling methods to monitor concentrations of perchlorate and explosive compounds in ground water, Camp Edwards, Cape Cod, Massachusetts, 2004-05

Laboratory and field tests were conducted at Camp Edwards on the Massachusetts Military Reservation on Cape Cod to examine the utility of passive diffusion sampling for long-term monitoring of concentrations of perchlorate and explosive compounds in ground water. The diffusion samplers were constructed of 1-inch-diameter rigid, porous polyethylene tubing. The results of laboratory tests in which diffusion samplers were submerged in containers filled with ground water containing perchlorate, RDX (hexahydro-1,3,5-trinitro-1,3,5-triazine), and HMX (octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine) indicate that concentrations inside the diffusion samplers equilibrated with concentrations in the containers within the 19-day-long test period. Field tests of the diffusion samplers were conducted in 15 wells constructed of 2- or 2.5-inch-diameter polyvinyl chloride pipe with 10-foot-long slotted screens. Concentrations of perchlorate, RDX, and HMX in the diffusion samplers placed in the wells for 42 to 52 days were compared to concentrations in samples collected by low-flow pumped sampling from 53 days before to 109 days after retrieval of the diffusion samples. The results of the field tests indicate generally good agreement between the pumped and diffusion samples for concentrations of perchlorate, RDX, and HMX. The concentration differences indicate no systematic bias related to contaminant type or concentration levels.

Massachusetts↗

USGS2007

Investigation of Ground-Water Contamination at Solid Waste Management Unit 12, Naval Weapons Station Charleston, North Charleston, South Carolina

The U.S. Geological Survey and the Naval Facilities Engineering Command Southeast investigated natural and engineered remediation of chlorinated volatile organic compound ground-water contamination at Solid Waste Management Unit 12 at the Naval Weapons Station Charleston, North Charleston, South Carolina. The primary contaminants of interest are tetrachloroethene, 1,1,1-trichloroethane, trichloroethene, cis-1,2-dichloroethene, vinyl chloride, 1,1-dichloroethane, and 1,1-dichloroethene. In general, the hydrogeology of Solid Waste Management Unit 12 consists of a surficial aquifer, composed of sand to clayey sand, overlain by dense clay that extends from about land surface to a depth of about 8 to 10 feet and substantially limits local recharge. During some months in the summer, evapotranspiration and limited local recharge result in ground-water level depressions in the forested area near wells 12MW-12S and 12MW-17S, seasonally reflecting the effects of evapotranspiration. Changes in surface-water levels following Hurricane Gaston in 2004 resulted in a substantial change in the ground-water levels at the site that, in turn, may have caused lateral shifting of the contaminant plume. Hydraulic conductivity, determined by slug tests, is higher along the axis of the plume in the downgradient part of the forests than adjacent to the plume, implying that there is some degree of lithologic control on the plume location. Hydraulic conductivity, hydraulic gradient, sulfur-hexafluoride measurements, and historical data indicate that ground-water flow rates are substantially slower in the forested area relative to upgradient areas. The ground-water contamination, consisting of chlorinated volatile organic compounds, extends eastward in the surficial aquifer from the probable source area near a former underground storage tank. Engineered remediation approaches include a permeable reactive barrier and phytoremediation. The central part of the permeable reactive barrier along the main axis of the contaminant plume appears to be actively removing contamination; however, ground-water contamination is moving around the southern end of the permeable reactive barrier. Changes in the contaminant concentrations along the path of ground-water transport reflect a complex variety of influences. Potential influences include dechlorination, sorption and desorption, transpirative removal by trees, lateral shifting of the plume, and the presence of zones of differing concentrations possibly reflecting one or more pulse releases of contamination from the source area. Near the source area at well 12MW-10S, volatile organic compound concentrations of cis-1,2-dichlorothene, vinyl chloride, 1,1-dichloroethane, and 1,1,1-trichloroethane continued an irregular decline, while tetrachloroethene and 1,1-dichloroethene showed marked fluctuations in concentration during 2005 and 2006. Volatile organic compound concentrations at well 12MW-03S continued to show decreasing concentrations with the June 2006 concentrations being the lowest yet recorded at that well for several volatile organic compounds. Concentration and delta carbon 13 data indicate that in the upgradient part of the plume, tetrachloroethene is being degraded to trichloroethene, which is being degraded to cis-1,2-dichloroethene, and cis-1,2-dichloroethene is accumulating faster than it is being depleted. Ground-water volatile organic compound concentrations also changed in some wells in the forested area in the midpart of the plume. Increasing tetrachloroethene and decreasing trichloroethene and 1,1-dichloroethene concentrations were observed at wells 12MW-05S and 12MW-29S, possibly reflecting a lateral shift in the axis of the contamination plume or an advancing contamination pulse. Substantial decreases in contamination occur in the forested area downgradient from well 12MW-05S. Probable major loss mechanisms in this area include evapotranspiration and sorption.

North Carolina, South Carolina↗

USGS2007

Evaluation of pore-water samplers at a drainage ditch, Installation Restoration Site 4, Naval Air Station Corpus Christi, Corpus Christi, Texas, 2005–06

The U.S. Geological Survey, in cooperation with the Naval Facilities Engineering Command Southeast, used innovative sampling methods to investigate ground-water contamination by chlorobenzenes beneath a drainage ditch on the southwestern side of Installation Restoration Site 4, Naval Air Station Corpus Christi, Corpus Christi, Texas, during 2005-06. The drainage ditch, which is a potential receptor for ground-water contaminants from Installation Restoration Site 4, intermittently discharges water to Corpus Christi Bay. This report evaluates a new type of pore-water sampler developed for this investigation to examine the subsurface contamination beneath the drainage ditch. The new type of pore-water sampler appears to be an effective approach for long-term monitoring of ground water in the sand and organic-rich mud beneath the drainage ditch.

Texas↗

USGS2007

Investigation of ground-water contamination at a drainage ditch, Installation Restoration Site 4, Naval Air Station Corpus Christi, Corpus Christi, Texas, 2005–06

The U.S. Geological Survey, in cooperation with the Naval Facilities Engineering Command Southeast, used newly developed sampling methods to investigate ground-water contamination by chlorobenzenes beneath a drainage ditch on the southwestern side of Installation Restoration Site 4, Naval Air Station Corpus Christi, Corpus Christi, Texas, during 2005-06. The drainage ditch, which is a potential receptor for ground-water contaminants from Installation Restoration Site 4, intermittently discharges water to Corpus Christi Bay. This report uses data from a new type of pore-water sampler developed for this investigation and other methods to examine the subsurface contamination beneath the drainage ditch. Analysis of ground water from the samplers indicated that chlorobenzenes (maximum detected concentration of 160 micrograms per liter) are present in the ground water beneath the ditch. The concentrations of dissolved oxygen in the samples (less than 0.05-0.4 milligram per liter) showed that the ground water beneath and near the ditch is anaerobic, indicating that substantial chlorobenzene biodegradation in the aquifer beneath the ditch is unlikely. Probable alternative mechanisms of chlorobenzene removal in the ground water beneath the drainage ditch include sorption onto the organic-rich sediment and contaminant depletion by cattails through uptake, sorption, and localized soil aeration.

Texas↗

USGS2006

Influence of In-Well Convection on Well Sampling

Convective transport of dissolved oxygen (DO) from shallow to deeper parts of wells was observed as the shallow water in wells in South Carolina became cooler than the deeper water in the wells due to seasonal changes. Wells having a relatively small depth to water were more susceptible to thermally induced convection than wells where the depth to water was greater because the shallower water levels were more influenced by air temperature. The potential for convective transport of DO to maintain oxygenated conditions in a well was diminished as ground-water exchange through the well screen increased and as oxygen demand increased. Convective flow did not transport oxygen to the screened interval when the screened interval was deeper than the range of the convective cell. The convective movement of water in wells has potential implications for passive, or no-purge, and low-flow sampling approaches. Transport of DO to the screened interval can adversely affect the ability of passive samplers to produce accurate concentrations of oxygen-sensitive solutes, such as iron. Other potential consequences include mixing the screened-interval water with casing water and potentially allowing volatilization loss at the water surface. A field test of diffusion samplers in a convecting well during the winter, however, showed good agreement of chlorinated solvent concentrations with pumped samples, indicating that there was no negative impact of the convection on the utility of the samplers to collect volatile organic compound concentrations in that well. In the cases of low-flow sampling, convective circulation can cause the pumped sample to be a mixture of casing water and aquifer water. This can substantially increase the equilibration time of oxygen as an indicator parameter and can give false indications of the redox state. Data from this investigation show that simple in-well devices can effectively mitigate convective transport of oxygen. The devices can range from inflatable packers to simple baffle systems.

Scientific Investigations Report↗

USGS2005

Use of tree-ring chemistry to document historical ground-water contamination events

The annual growth rings of tulip trees ( Liriodendron tulipifera L.) appear to preserve a chemical record of ground-water contamination at a landfill in Maryland. Zones of elevated iron and chlorine concentrations in growth rings from trees immediately downgradient from the landfill are closely correlated temporally with activities in the landfill expected to generate iron and chloride contamination in the ground water. Successively later iron peaks in trees increasingly distant from the landfill along the general direction of ground-water flow imply movement of iron-contaminated ground water away from the landfill. The historical velocity of iron movement (2 to 9 m/yr) and chloride movement (at least 40 m/yr) in ground water at the site was estimated from element-concentration trends of trees at successive distances from the landfill. The tree-ring-derived chloride-transport velocity approximates the known ground-water velocity (30 to 80 m/yr). A minimum horizontal hydraulic conductivity (0.01 to .02 cm/s) calculated from chloride velocity agrees well with values derived from aquifer tests (about 0.07 cm/s) and from ground-water modeling results (0.009 to 0.04 cm/s).

Groundwater↗