Measurement of Carbon Dioxide in Soil Gases for Indication of Subsurface Hydrocarbon Contamination

A preliminary field evaluation of a new application of soil-gas measurement for delineation of subsurface organic contamination is described. The method measures carbon dioxide concentrations in soil gases and is based on the hypothesis that carbon dioxide concentrations from subsurface oxidation of organic compounds will be porportional to the extent of organic contamination. A correlation coefficient (r) of 0.81 (n=6) was observed between ground water dissolved organic carbon ground water concentrations and carbon dioxide concentrations in the overlying soil gases at one site. Soil-gas carbon dioxide concentrations measured ranged from 0.09 percent to 0.45 percent.     

Organic Contamination of Ground Water at Gas Works Park, Seattle, Washington

Gas Works Park, in Seattle, Washington, is located on the site of a coal and oil gasification plant that ceased operation in 1956. During operation, many types of wastes, including coal, tar, and oil, accumulated on-site. The park soil is currently (1986) contaminated with compounds such as polynuclear aromatic hydrocarbons, volatile organic compounds, trace metals, and cyanide. Analyses of water samples from a network of observation wells in the park indicate that these compounds are also present in the ground water.
Polynuclear aromatic hydrocarbons and volatile organic compounds were identified in ground water samples in concentrations as large as 200 mg/L. Concentrations of organic compounds were largest where ground water was in contact with a non-aqueous phase liquid in the soil. Where no non-aqueous phase liquid was present, concentrations were much smaller, even if the ground water was in contact with contaminated soils. This condition is attributed to weathering processes in which soluble, low-molecular-weight organic compounds are preferentially dissolved from the non-aqueous phase liquid into the ground water. Where no non-aqueous phase liquid is present, only stained soils containing relatively insoluble, high-molecular-weight compounds remain. Concentrations of organic contaminants in the soils may still remain large.     

In Situ Remediation of Jet A in Soil and Ground Water by High Vacuum, Dual Phase Extraction

This report summarizes the initial results of subsurface remediation at Terminal 1, Kenneth International Airport, to remediate soil and ground water contaminated with Jet A fuel. The project was driven and constrained In the const ruction schedule of a major new terminal at the facility. The remediation system used a combination of ground water pumping, air injection, and soil vapor extraction. In the first five months of operation, the combined processes of dewatering, volatilization, and biodegradation removed a total of 36,689 pounds of total volatile and semivolatile organic jet fuel hydrocarbons from subsurface soil and ground water. The. results of this case study have shown that 62 percent of the removal resulted from biodegradation, 21 percent occurred as a result of liquid removal, and 11 percent resulted from the extraction of volatile organic compounds (VOC's).     

Screening of Ground Water Samples for Volatile Organic Compounds Using a Portable Gas Chromatograph

A portable gas chromatograph was used to screen 32 ground water samples for volatile organic compounds. Seven screened samples were positive; four of the seven samples had volatile organic substances identified by second-column confirmation. Four of the seven positive, screened samples also tested positive in laboratory analyses of duplicate samples. No volatile organic compounds were detected in laboratory analyses of samples that headspace screening indicated to be negative. Samples that contained volatile organic compounds, as identified by laboratory analysis, and that contained a volatile organic compound present in a standard of selected compounds were correctly identified by using the portable gas chromatograph. Comparisons of screened-sample data with laboratory data indicate the ability to detect selected volatile organic compounds at concentrations of about 1 microgram per liter in the headspace of water samples by use of a portable gas chromatograph.     

Monitoring Dissolved Oxygen in Ground Water: Some Basic Considerations

Dissolved oxygen (D.O.) concentration has a significant effect upon ground water quality by regulating the valence state of trace metals and by constraining the bacterial metabolism of dissolved organic species. For these reasons, the measurement of dissolved oxygen concentration should be considered essential in most water quality investigations. D.O. measurements have been frequently neglected in ground water monitoring. This is because O₂ has often been assumed absent below the water table; measurement of O₂, concentrations is not mandated by drinking water standards; and the redox potential has previously been considered an adequate and encompassing electrochemical measurement. Redox potentials, however, cannot adequately predict dissolved oxygen concentrations nor can D.O. concentrations be used to calculate redox potentials.
D.O. concentrations can be measured precisely in the field by titration or electrode methods. The best methods of sample recovery are those that use positive pressure displacement devices. A fully adequate sampling procedure will isolate ground water from the atmosphere and will collect samples at restricted depth intervals at ambient temperature and pressure.     

Evaluation of a Carbon Adsorption Method for Sampling Gasoline Vapors in the Subsurface

Monitoring of the vapor phase has emerged as a very convenient method for detecting volatile organic contaminants in the subsurface. It can provide a reliable way of placing ground water monitoring and recovery wells. The most common method uses a driveable ground probe (DGP) to extract a vapor-phase sample followed by direct injection of the vapor into a portable gas chromatograph (GC). However, many regional offices of regulatory agencies and consultants do not have ready access to such equipment. This research explores an alternative–the carbon adsorption method—in which the vapor is withdrawn by the DGP but concentrated on a small activated carbon trap (150mg). The carbon traps can be returned to a central laboratory for solvent extraction and GC analysis. This provides the advantages of increased sensitivity, reduction in field equipment and convenience of in-lab analyses (multiple GC injections are possible). A simple DGP and carbon trap system was constructed and tested at a field site. Vapor-phase concentrations of target compounds present in gasoline were mapped quite conveniently, ranging from 10,000μg/liter (vapor phase) to less than 10μg/L. These concentrations were also shown to decrease in the direction of the ground surface, as expected. Measurements of target compounds in soil showed that the vapor phase contributed a large fraction of the total contaminant burden where a non-aqueous-phase layer (NAPL) had been identified; as important, however, is the rather uniform contamination of the soil outside the NAPL region. Finally, the concentrations of target compounds in the vapor phase and ground water could be related in a manner roughly described by a simple equilibrium model, although exceptions were noted.     

Application of VLEACH to Vadose Zone Transport of VOCs at an Arizona Superfund Site

Cleanup standards for volatile organic compounds in thick vadose zones can be based on indirect risk (transport to ground water) when contamination is below depths of significant direct risk. At one Arizona Superfund site, a one-dimensional vadose zone transport model (VLE-ACH) was used to estimate the continued transport of VOCs from the vadose zone to ground water. VLEACH is a relatively simple and readily available model that proved useful for estimating indirect risk from VOCs in the vadose zone at this site. The estimates of total soil concentrations used as initial conditions for VLF.ACH incorporated a variety of data from the site. Soil gas concentrations were found to be more useful than soil matrix data for estimating total soil concentrations at this arid-zone site. A simple mixing cell model was used with the VLEACH-derived mass loading estimates from the vadose zone over time to estimate the resulting changes in ground water concentrations. For this site, the results of the linked VLEACH/mixing cell simulations indicate it is likely that the federal MCI. for TCE will be exceeded in underlying ground water if remedial action on I he vadose zone is not pursued.     

Field Studies on the Fate and Transport of Pharmaceutical Residues in Bank Filtration

Bank filtration and artificial ground water recharge are important, effective, and cheap techniques for surface water treatment and removal of microbes, as well as inorganic, and some organic, contaminants. Nevertheless, physical, chemical, and biological processes of the removal of impurities are not understood sufficiently. A research project titled Natural and Artificial Systems for Recharge and Infiltration attempts to provide more clarity in the processes affecting the removal of these contaminants. The project focuses on the fate and transport of selected emerging contaminants during bank filtration at two transects in Berlin, Germany. Several detections of pharmaceutically active compounds (PhACs) in ground water samples from bank filtration sites in Germany led to furthering research on the removal of these compounds during bank filtration. In this study, six PhACs including the analgesic drugs diclofenac and propyphenazone, the antiepileptic drugs carbamazepine and primidone, and the drug metabolites clofibric acid and 1-acetyl-1-methyl-2-dimethyl-oxamoyl-2-phenylhydrazide were found to leach from the contaminated streams and lakes into the ground water. These compounds were also detected at low concentrations in receiving public supply wells. Bank filtration either decreased the concentrations by dilution (e.g., for carbamazepine and primidone) and partial removal (e.g., for diclofenac), or totally removed PhACs (e.g., bezafibrate, indomethacine, antibiotics, and estrogens). Several PhACs, such as carbamazepine and especially primidone, were readily transported during bank filtration. They are thought to be good indicators for evaluating whether surface water is impacted by contamination from municipal sewage effluent or whether contamination associated with sewage effluent can be transported into ground water at ground water recharge sites.     

Subsurface Transport of Inorganic and Organic Solutes from Experimental Road Spreading of Oil-Field Brine

A study designed to evaluate ground water quality changes resulting from spreading oil-field brine on roads for ice and dust control was conducted using a gravel roadbed that received weekly applications of brine eight times during the winter phase and 11 times during the summer phase of the study. A network of 11 monitoring wells and five pressure-vacuum lysimeters was installed to obtain ground water and soil water samples. Thirteen sets of water- quality samples were collected and analyzed for major ions, trace metals, and volatile organic compounds. Two sets of samples were taken prior to brine spreading, four sets during winter-phase spreading, five sets during summer- phase spreading, and two sets during the interim between the winter and summer phases. A brine plume delineated by elevated specific-conductance values and elevated chloride concentrations developed downgradient of the roadbed during both the winter and summer phases. The brine plume caused chloride concentrations in ground water samples to exceed U.S. EPA public drinking-water standards by two-fold during the winter phase and five-fold during the summer phase. No other major ions, trace metals, or volatile organic compounds exceeded the standards during the winter or summer phases. More than 99 percent dilution of the solutes in the brine occurred between the roadbed surface and the local ground water flow system. Further attenuation of calcium, sodium, potassium, and strontium resulted from adsorption, whereas further attenuation of benzene resulted from volatilization and adsorption.     

In Situ Measurement and Numerical Simulation of Oxygen Limited Biotransformation

Enhanced subsurface biorestoration is rapidly becoming recognized as a valuable tool for the restoration of hydrocarbon-contaminated aquifers and sediments. Previous field and laboratory studies at a former wood creosoting facility near Conroe, Texas, have indicated that insufficient oxygen is the primary factor limiting the biotransformation of polynuclear aromatics (PNAs) in sediments and ground water at this site. A series of laboratory experiments and field push-pull injection tests were performed as part of this project to: (1) study the effect of low oxygen concentrations on the biotransformation of PNAs; (2) identify the minimum concentration of PNAs that could be achieved through the addition of oxygen alone; (3) confirm that enhanced subsurface biorestoration is feasible at this site; and (4) test an existing numerical model of the biotransformation process (BIOPLUME). The laboratory studies demonstrated that biotransformation of the PNAs was not inhibited at dissolved oxygen concentrations as low as 0.7 mg/L although this work did suggest that there may be a minimum PNA concentration of 30 to 70 μg/L total PNAs below which biotransformation was inhibited. The field push-pull tests confirmed that addition of oxygen was effective in enhancing the subsurface biodegradation of the PNAs. The minimum concentration achieved using oxygen alone was approximately 60 μg/L total PNAs. Minimal biotransformation of these compounds was observed without oxygen addition. The numerical model BIOPLUME was tested against monitoring data from the field experiments and appears to provide a good approximation of the biodegradation process.     

Observed Spatial and Temporal Distributions of CVOCs at Colorado and New York Vapor Intrusion Sites

The vapor intrusion impacts associated with the presence of chlorinated volatile organic contaminant plumes in the ground water beneath residential areas in Colorado and New York have been the subject of extensive site investigations and structure sampling efforts. Large data sets of ground water and indoor air monitoring data collected over a decade-long monitoring program at the Redfield, Colorado, site and monthly ground water and structure monitoring data collected over a 19-month period from structures in New York State are analyzed to illustrate the temporal and spatial distributions in the concentration of volatile organic compounds that one may encounter when evaluating the potential for exposures due to vapor intrusion. The analysis of these data demonstrates that although the areal extent of structures impacted by vapor intrusion mirrors the areal extent of chlorinated volatile organic compounds in the ground water, not all structures above the plume will be impacted. It also highlights the fact that measured concentrations of volatile organic compounds in the indoor air and subslab vapor can vary considerably from month to month and season to season. Sampling results from any one location at any given point in time cannot be expected to represent the range of conditions that may exist at neighboring locations or at other times. Recognition of this variability is important when designing sampling plans and risk management programs to address the vapor intrusion pathway.     

Removal of Volatile Organic Compounds from Surfactant Solutions by Flash Vacuum Stripping in a Packed Column

Volatile organic compounds (VOCs) am be removed from contaminated ground water and subsurface media by surfaclant-enhanced remediation processes. For the process to be economically competitive it is necessary to recover and reuse the surfactant from this concentrated solution. The VOC can be removed from this concentrated solution by flash vacuum stripping, leaving the surfactant solution for reuse. In this study, the flash vacuum stripping of trichloroethylene (TCE) from an anionic surfactant solution in a co-current packed column was studied under rough vacuum conditions. The presence of surfactants lead to a reduction in the overall liquid phase volumetric mass transfer coefficient (MTC) of 40 to 95%. depending on flow rate and surfactant concentration at 50°C and 16 kPa. At liquid loading rates of less than 13 cm³/cm²min, the MTC of TCE decreases rapidly with an increase in liquid loading rate, and at liquid loading rates above that, the MTC decreases slightly with an increase in the liquid loading rate. This trend may have been due to foaming. At surfactant concentrations above the critical micelle concentration, the effect of surfactant concentration was not significant at liquid loading rates less than 13 cm³/cm²min. However, beyond that rate, the MTC of TCE decreased drastically with an increase in surfactant concentration. The MTC of TCE increased with an increase in temperature. A large pressure drop (3 to 4 kPa/m) was observed across the packed bed due to foaming.     

Biological and Physical Attenuation of Endocrine Disruptors and Pharmaceuticals: Implications for Water Reuse

A select group of endocrine disrupters, pharmaceuticals, and personal care products was studied to determine the degree of biological attenuation in water reuse applications. Laboratory investigations involved both batch reactors using biologically active sand and continuous flow simulated aquifer storage and recovery experiments. All laboratory experiments were conducted using Colorado River water spiked with various target compounds at concentrations between 10 and 100 ng/L. Field studies were also conducted to determine the occurrence and attenuation of target compounds in water reuse applications. Two golf courses irrigated with reuse water were studied to determine if turf applications led to contamination of nearby ground water. A waste water treatment facility that uses rapid infiltration basins seasonally was also tested to determine the degree of attenuation of detectable target compounds along a subsurface flowpath. A qualitative structural activity relationship model was applied to the target compounds to predict the general rate of aerobic biological degradation. Significant attenuation of many target compounds was observed in both laboratory and field experiments. Conversely, several compounds displayed limited removal during these studies. Field experiments were limited to detectable compounds and various nonbiological removal or concentration effects that may impact data interpretations, which are discussed in this paper. The predictive model was found to be moderately accurate within the confines of the project scope.     

Diffusion Samplers as an Inexpensive Approach to Monitoring VOCs in Ground Water

Diffusion samplers installed in observation wells were found to be capable of yielding polyethylene to transmit other volatile compounds, such as benzene and toluene, indicates that the samplers can be used for a variety of volatile organic compounds. In wells at the study area, the volatile organic compound concentrations in water samples obtained using the samplers without prior purging were similar to concentrations in water samples obtained from the respective wells using traditional purging and sampling approaches. The low cost associated with this approach makes it a viable option for monitoring large observation-well networks for volatile organic compounds.     

Biodegradation of Creosote Compounds: Comparison of Experiments at Different Scales

This paper compares the results of biodegradation experiments with creosote compounds performed at different scales. The experiments include field observations, field experiments, large-scale intact laboratory column experiments, model fracture experiments, and batch experiments. Most of the experiments were conducted with till or ground water from the field site at Ringe on the island of Funen. Although the experiments were conducted on different scales, they revealed that some phenomena—e.g., an extensive biodegradation potential of several of the creosote compounds, the inhibitory influence of the pyrroles on the biodegradation of benzene, and the biodegradation of benzothiophene occurs only in the presence of a primary substrate. The experiments show that some biodegradation processes of organic compounds may be common to different microorganisms.     

Utilization of decadal tritium variation for assessing the residence time of base flow

An iterative algorithm is presented that allows the user to model the subsurface residence time of shallow ground water comprising stream base flow based on decadal scale variation of tritium concentrations. The algorithm accounts for the effects of radioactive decay, the shallow subsurface mixing of ground water with precipitation, and ground water flux. The inverse of the best-fitting modeled flux through the saturated zone is equivalent to the residence time. The data required for this model include at least two measurements of tritium in base flow for a given stream location made at least a decade apart and the long-term tritium input in precipitation for the region of interest. The model is sensitive to relatively small changes in tritium concentrations and is limited by analytic uncertainties to an accuracy of approximately +/-5 years. The algorithm was applied to stream base flow for several basins in the Piedmont Province of Georgia in which tritium concentrations were measured during the early 1990s and again in the 2000s. The model results produced highly concordant residence times for three hydrogeologically similar basins in the Upper Ocmulgee Basin in North Central Georgia. The best estimate of the average residence time for ground water comprising base flow in this Piedmont basin using this new method is between approximately 14 and 18 years. These results are generally consistent with calculations made in previous studies, and these relatively long residence times can be attributed to the storage of water in the clay soils that dominate Piedmont Province watersheds.     

The Occurrence of Appendix IX Organic Constituents in Disposal Site Ground Water

Monitoring data from 479 disposal site investigations were used to provide an initial estimate of the occurrence and distribution of 208 Appendix IX organic constituents in ground water. The most prevalent class of contaminants were the volatile organic compounds, which accounted for 84 percent of all the detectable events in the composite data set involving Appendix IX organic constituents. The abundance of the remaining subsets of Appendix IX organic constituents decreased in the following order: base/neutral compounds (8.6 percent), acid extractable compounds (3.5 percent), pesticides (3.0 percent), RCRA pesticides (0.6 percent), and non-priority pollutants (0.25 percent). A total of 66 Appendix IX organic constituents, including one volatile compound, two pesticides, three base/neutral compounds, and 60 non-priority pollutant compounds were not detected in any of the waste disposal site ground water monitoring records that were reviewed.
The current regulatory requirement to monitor for Appendix IX organic constituents is approximately four times more expensive than monitoring for conventional priority pollutants (volatile, base/neutral, acid extractable, and pesticide compounds). Because the non-priority pollutant compounds account for an estimated 76 percent of the Appendix IX analytical costs but only 0.25 percent of the detectable events in disposal site ground water, it has been recommended that this class of compounds be deleted from routine monitoring programs. A scaling back of the current requirement to the conventional priority pollutants would still target more than 99 percent of the Appendix IX organic constituent occurrences in ground water and result in an analytical cost savings of approximately $2750 per sample or an estimated $51 million a year without significantly reducing the volume of useful organic monitoring data that would be generated to assess ground water conditions in the vicinity of waste disposal sites.     

In-Line Measurement of Trichloroethylene Vapors Using Tin Dioxide Sensors

During thermally enhanced in situ remediation of soils and ground water, gas streams are generated with varying temperatures, moisture content, and organic compound concentrations. In this study, we evaluated the performance of tin dioxide sensors for measuring trichloroethylene (TCE) concentrations in gas streams from a thermally enhanced soil vapor extraction system. Temperature, pressure, moisture content, and vapor flow rates affected the resistivity of the sensors, and thus the signal. When fluctuations in these parameters were eliminated by condensing excess water and healing to a constant temperature prior to measurement, the sensors provided reliable in-line measurement of TCE concentrations. Gas tracers such as methane were easily monitored in-line, providing quick and inexpensive data on subsurface vapor flow velocities and direction.     

Use of Total Organic Carbon as an Indicator of Contamination from an Oil Refinery, South-Central Kansas

Water samples collected from 26 sites at an abandoned oil refinery in south-central Kansas were analyzed for total organic carbon (TOC) and specific volatile and semivolatile organic compounds by gas-chromatography/mass-spectrometric methods. Results from a Spearman-rho correlation analysis between TOC concentration and the number of compounds (correlation coefficient = 0.71) and TOC concentration and total concentration of compounds identified (correlation coefficient = 0.83) indicate correlations significant at the 0.01 level.
Although TOC data alone would not be sufficient to evaluate hazards posed by oil-refinery wastes, results of the correlation analysis performed using data collected from the site in Kansas indicate that TOC data can be used effectively to delineate petroleum-related ground water contamination and to help identify sources of ground water contaminants. TOC data collected from a large number of temporary sampling points during the initial phases of an investigation will provide an estimate of the extent of hydrocarbon contamination and allow placement of monitoring wells and more detailed sampling in appropriate areas.     

Sampling for Purgeable Organic Compounds Using Positive-Displacement Piston and Centrifugal Submersible Pumps: A Comparative Study

Positive-displacement piston pumps that minimize sample agitation have no apparent advantage over centrifugal submersible pumps when used to collect ground water samples for analysis of low concentrations of purge-able organic compounds. Analytical uncertainties inherent in laboratory environments appear to influence analytical results of low-concentration purgeable organic compound samples more than either pump type or sampling team. Centrifugal submersible pumps are at least equally efficient as positive-displacement piston pumps in the recovery of carbon tetrachloride, 1,1,1-trichloroethane, trichloroethylene, and chloroform after sampling and analytical influences are made constant.