bluuebunny/crossref_metadata_2025_split huggingface dataset:
Agricultural Chemicals and Ground Water Quality ‐ Issues and Challenges
Authors: Bouwer Herman 
Published: February 2007

AbstractAnthropogenic agricultural chemicals of concern in ground water include nitrate and pesticides. Increased legislation and regulation of contaminant levels in ground water can be expected. Ground water contamination should be prevented from getting worse, but more research is necessary so as to base regulations on sound criteria. Health effects and acceptable risks must be better formulated. More research on chemical movement in the vadose zone is necessary for accurate predictive modeling of pesticide transport to ground water. Best management practices need to be developed so that farmers will be able to farm profitably while complying with regulations for maximum contaminant levels in underlying ground water. People from all concerned disciplines, citizens’groups, and policy‐makers need to work together to develop realistic regulatory policies and management practices that will effectively protect public health while ensuring a viable and sustainable agriculture.
Small‐Scale Retrospective Ground Water Monitoring Study for Simazine in Different Hydrogeological Settings
Authors: Roux Paul H. , Hall Robert L. , Ross Richard H. 
Published: February 2007

AbstractA ground water monitoring study was conducted for the triazine herbicide simazine at 11 sites in the United States. The study used carefully selected, small‐scale sites (average size: about 33 acres) with documented product use and sensitive hydrogeological settings. The sites selected were Tulare County, California (two sites); Fresno County, California; Sussex County, Delaware; Hardee and Palm Beach counties, Florida; Winnebago County, Illinois; Jackson County, Indiana; Van Buren and Berrien counties, Michigan; and Jefferson County, West Virginia. These sites satisfied the following criteria: a history of simazine use, including the year prior to the start of the study; permeable soil and vadose zone; shallow depth to water; no restrictive soil layers above the water table; and gentle slopes not exceeding 2 percent. A variety of crop types, climates, and irrigation practices were included. Monitoring well clusters (shallow and deep) were installed at each site except in California and West Virginia, where only shallow wells were installed. Simazine was monitored at these sites at quarterly intervals for a two‐year period during 1986–1988.The results of the study showed that out of 153 samples analyzed, 45 samples showed simazine detections. A substantial majority of the detections (32 out of 45) occurred in Tulare, Fresno, and Jefferson counties. The detections in these areas were attributed to mechanisms other than leaching, such as drainage wells, karst areas, surface water recharge, or point source problems. An additional 11 detections in Van Buren County were apparently due to an unknown upgradient source. Only one detection (in Palm Beach County, Florida) near the screening level of 0.1 ppb was attributed to possible leaching. The results of this investigation support the hypothesis that simazine does not leach significantly under field use conditions.
A Gas Chromatographic/Chemical Indicator Approach to Assessing Ground Water Contamination by Petroleum Products
Authors: Thomas Debra H. , Delfino Joseph J. 
Published: February 2007

AbstractThe water‐soluble fractions of unleaded gasoline, kerosene and diesel fuel were evaluated by U.S. EPA Methods 602, 610, and 625.Several chemical indicator compounds useful in assessing petroleum contamination of ground water, including benzene, substituted benzenes, n‐alkanes, and polynuclear aromatic hydrocarbons, were identified. These were applied to the interpretation of data collected from monitoring wells at gasoline service stations that were undergoing ground water remediation. The chemical indicators are used to identify the likely type(s) of petroleum contamination. Certain hydrocarbons may be unique to specific fuel types.Gas chromatograms of field sample extracts were compared with chromatograms of laboratory water‐soluble fractions (WSFs) and neat fuels (unleaded gasoline, kerosene, and diesel). In some situations, field samples represented water‐soluble fractions of the contaminating fuel. In others, a fuel‐water agglomeration was indicated, with the chromatograms showing peaks that represented components of both the WSFs and the neat fuels.The use of both gas chromatography pattern identification and chemical indicators appears to be a viable approach to assessing ground water contamination caused by petroleum products.
Ground Water Modeling for Risk Assessment Purposes: Use of a Gaussian‐Distributed Transport Model and a Batch Flush Model
Authors: Cushman David J. , Ball Stephen D. 
Published: February 2007

AbstractSeveral state regulatory agencies require that risk assessments be performed at contaminated sites to quantify the contaminant levels that may reach the nearest receptors and to evaluate the health risks associated with exposure to such contaminant levels. Petroleum retail facilities with leaking underground storage tanks are prime examples of sites where risk assessments may be required. Ground water modeling is often necessary when evaluating future completed exposure pathways associated with dissolved contaminants. If the aquifer conditions are relatively homogeneous, analytical contaminant transport models may be used in place of complex numerical models. A two‐dimensional, Gaussian‐distributed boundary condition transport model and a batch flush model may be combined to simulate contaminant transport with linear equilibrium adsorption/desorption and biodegradation effects, This enables a relatively rapid and cost‐effective prediction of contaminant levels at sensitive downgradient receptors. The predicted contaminant levels may then be evaluated through an exposure assessment, toxicity assessment, and risk characterization in accordance with U.S. EPA risk assessment protocols.A case study was presented for a gasoline station with a leaking underground storage tank system. The two‐dimensional, Gaussian‐distributed transport model and batch flush model were used to predict dissolved phase contaminant concentration profiles at a downgradient drinking water well. The predicted contaminant concentrations were subsequently converted to chronic daily intakes which were evaluated in terms of toxicity. Reasonable maximum exposures were developed for both carcinogens and non‐carcinogens. The results of the risk assessment indicated that there were no unacceptable risks posed by the residual ground water contamination at the site. This led to the recommendation that the project be closed out in the absence of a demonstrated need for active ground water remediation. The State Water Control Board concurred with the recommendation.
Comparison Between Pump and Treat, Biorestoration, and Biorestoration/ Pump and Treat Combined: Lessons from Computer Modeling
Authors: Marquis Samuel A. , Dineen Dennis 
Published: February 2007

AbstractThis study compares pump and treat, bioremediation. and bioremediation/pump and treat for cleanup of a chemical plume using BIOPLUME II, a numerical solute transport code which simulates the transport of dissolved hydrocarbons under oxygen‐limited biodegradation. Nineteen remediation scenarios were evaluated under one set of hydrogeologic and chemical conditions using different injection and extraction well configurations and injected dissolved oxygen (D.O.) concentrations of 8 or 50 parts per million (ppm). The cleanup objective was to reduce the concentration of naphthalene in the plums by the greatest percentage without increasing the volume of contaminated ground water in the aquifer. Each scenario was ranked in terms of plume control and contaminant concentration reduction for a one‐year remediation period.Based on the performance criteria, scenarios that included pump and treat were superior in containing the migration of the plume and in restricting the plume from separating into smaller, localized plumes or “hot spots.” Bioremediation and bioremediation/pump‐and‐treat scenarios in which 50 ppm D.O. was injected throughout the plume (areal injection) or in the most concentrated portion of the plume (interior injection) achieved the greatest plume control and concentration reductions. Bioremediation cases with 8 ppm D.O. did not successfully control the plume or achieve major reductions in concentrations. The important conclusions drawn from the results were the following: (1) minimize the distance that the plume needs to be pulled toward extraction wells or that the D.O. needs to be circulated through to reach the contaminant zone; (2) inject water containing as high a level of D.O. as possible while meeting microbial and oxygen demand requirements: and (3) design the wellfield to produce convergent flow toward a central location and to minimize divergent flow and upgradient and intraplume stagnation areas.The study results suggest that bioremediation and bioremediation/ pump and treat should perform better than pump and treat for sand and gravel aquifers contaminated with biodegradable hydrocarbons. In particular, four remediation scenarios should be seriously considered in the design phase of biorestoration projects: areal injection/downgradient extraction, interior injection, interior extraction/exterior (i.e., outside of the plume) injection, and areal injection. Although the actual number of wells, injection and extraction rates, and D.O. concentrations will vary for each site, it is expected that areal injection: downgradient extraction and interior injection should perform well under high natural flow velocities, whereas interior extraction/exterior injection and areal injection should be more amenable to sites with lower natural flow velocities.
The Effects of Ground Water Sampling Devices on Water Quality: A Literature Review
Authors: Parker Louise V. 
Published: February 2007

AbstractThis paper reviews both field and laboratory studies that tested or compared the ability of various types of sampling devices to deliver representative ground water samples. Several types of grab samplers, positive displacement devices, and suction‐lift devices were evaluated, Gas‐lift and inertial‐lift pumps were also evaluated. This study found that most of these devices can. under certain circumstances, alter the chemistry of ground water samples, das‐lift pumps, older types of submersible centrifugal pumps, and suction‐lift devices are not recommended when sampling for sensitive constituents such as volatile organics and inorganics, or inorganics that are subject to oxidation/precipitation reactions. In general, of the devices reviewed in this paper, bladder pumps gave the best recovery of sensitive constituents. However, better performance could be achieved for several devices if improved operational guidelines were developed by additional testing, especially at lower flow rates. Clearly, further research is warranted. Future studies should focus on pumping rate, flow control mechanisms, and dedication or decontamination of sampling devices.
Pump‐and‐Treat Accomplishments: A Review of the Effectiveness of Ground Water Remediation in Santa Clara Valley, California
Authors: Bartow Gregory , Davenport Clifton 
Published: February 2007

AbstractPump and treat has been successful in significantly reducing the volatile organic contaminant concentrations in ground water in Santa Clara Valley. California. The California Regional Water Quality Control Board. San Francisco Bay Region, currently oversees 61 sites in Santa Clara Valley with operating pump‐and‐treat systems, of which 42 sites have been extracting ground water since at least 1987. This review‐ evaluates the effects of ground water extraction on contaminant concentrations at 37 of those 42 sites. The evaluation focuses on trichloroethane, trichloroethene, and dichloroethane, as these were the most prevalent contaminants encountered at the sites. The majority of sites obtained greater than 90 percent reduction in maximum concentrations for one or more of the three contaminants. While only one of the 37 sites obtained maximum contaminant levels (MCL) for all contaminants, six of the sites included in the analyses reached MCLs for one or more of the sampled contaminants, and an additional seven of the sites are near MCLs for al least one contaminant. Our findings indicate that, while pump and treat successfully reduced maximum concentrations al most of the sites reviewed, successful attempts to reduce maximum contaminant concentrations to below MCLs are limited.
Radionuclide Sorption on Well Construction Materials
Authors: Thompson Joseph L. 
Published: February 2007

AbstractLaboratory experiments were conducted to measure the extent to which trace concentrations of radioactive materials would sorb on well construction materials and to assess the rapidity with which sorption would occur. The radionuclides employed in these studies were tritium, Cs‐137, and Co‐57, Solutions with trace concentrations of these radionuclides were contracted with casings of PVC, fiberglass‐epoxy, stainless steel, carbon steel, and steel rods coated wtih expoy. The PVC showed no interaction with the tritium or Cs‐137 during contact times of two hours to these weeks; however, it did sorb Co‐57. The fiberglass‐epoxy also interacted only with the cobalt. The stainless steel sorbed cesium and cobalt. The carbon steel (or the ferric hydroxide forming on its surface) also sorbed both cesium and cobalt. The epoxy‐coated steel rods did not interact measurably with day of the radio‐nuclides so long as the coating was intact. The sorption reactions generally were apparent after a few days of contact: in the case of carbon steel, they were detectable in a few hours.
A Method to Assess Analytical Uncertainties Over Large Concentration Ranges With Reference to Volatile Organics in Water
Authors: Devlin J. F. 
Published: February 2007

AbstractThe uncertainty associated with a volatile organic concentration measurement is a function of variability and bias introduced at the various levels of sample handling: collection, storage, and analysis. During the past decade, sampling materials and the development and/or improvement of sampling protocols have been the subject of considerable research activity. As a result, in cases of samples properly handled, the analytical variability can be the dominant source of uncertainty in a given concentration value. Here analytical variability refers to any error that might arise during analysis, including the detector response error and any sample handling errors common to both standards and samples. This can be a particular concern for field analyses by gas chromatography (GC), Well‐established statistical methods are available to estimate analytical uncertainty from linear calibration curves, but these methods are poorly suited for the analysis of volatile organics because organic samples frequently require instrument calibration (usually GC) over several orders of magnitude in concentration. If a single linear calibration curve is used to determine sample concentrations and uncertainties, then unrealistically large uncertainties may be assigned to low concentration samples. However, the methods can be adopted for extended concentration range calibration curves by breaking the overall calibration line down into smaller sub‐calibration lines that span smaller ranges. These can then be examined and used selectively to determine concentrations with more appropriate uncertainties attached. The method of multiple callbration line analysis described here is suitable for programming with any high level computer language. It can be used to calculate meaningful analytical uncertainty values for any substance analyzed over a wide range in concentrations (i.e., an order of magnitude or more).
Petroleum Hydrocarbon Bioventing Kinetics Determined in Soil Core, Microcosm, and Tubing Cluster Studies
Authors: Moyer Ellen E. , Ostendorf David W. , Richards Robin J. , Goodwin Steve 
Published: February 2007

AbstractAerobic biodegradation of vapor‐phase petroleum hydrocarbons was evaluated in an intact soil core from the site of an aviation gasoline release. An unsaturated zone soil core was subjected to a flow of nitrogen gas, oxygen, water vapor, and vapor‐phase hydrocarbons in a configuration analogous to a biofilter or an in situ bioventing or sparging situation. The vertical profiles of vapor‐phase hydrocarbon concentration in the soil core were determined by gas chromatography of vapor samples. Biodegradation reduced low influent hydrocarbon concentrations by 45 to 92 percent over a 0.6‐m interval of an intact soil core. The estimated total hydrocarbon concentration was reduced by 75 percent from 26 to 7 parts per million. Steady‐state concentrations were input to a simple analytical model balancing advection and first‐order biodegradation of hydrocarbons. First‐order rate constants for the major hydrocarbon compounds were used to calibrate the model to the concentration profiles. Rate constants for the seven individual hydrocarbon compounds varied by a factor of 4. Compounds with lower molecular weights, fewer methyl groups, and no quaternary carbons tended to have higher rate constants. The first‐order rate constants were consistent with kinetic parameters determined from both microcosm and tubing cluster studies at the field site.
Evaluating Natural Attentuation with Spreadsheet Analytical Fate and Transport Models
Authors: Ollila Paul W. 
Published: February 2007

AbstractSuperposition techniques can extend the capabilities of relatively simple analytical fate and transport models. Complex source geometries, simple aquifer boundaries, and electron acceptor limited biodegradation can be simulated by using superposition techniques in computer spreadsheets. Spreadsheet models are an easily used tool for interpreting sampling results and for estimating attenuation and degradation rates in relatively homogeneous aquifers. Analytical spreadsheet models are based on the Domenico analytical model and can provide results that are in close agreement with the numerical model UIOPLUMH II.
Neutron Moisture Probe Measurements of Fluid Displacement During In Situ Air Sparging
Authors: McKay Daniel J. , Acomb Lawrence J. 
Published: February 2007

AbstractStrawberry Point, located on Hinchinbrook Island, Alaska, is the site of a Federal Aviation Administration air navigation facility that is contaminated with gasoline‐ and diesel‐range hydrocarbons in soil and ground water. An air sparging system was installed to promote bioremediation in the zone of seasonal ground water fluctuation where the contaminant is concentrated. The sparge wells were placed in a homogeneous formation, consisting of fine‐grain beach and eolian sands. The system was then evaluated to determine the ground water region of influence and optimum frequency of operation. Neutron probe borehole measurements of percentage; of fluid displacement during sparging at two wells revealed dynamic air distributions defined by an initial and relatively rapid expansion phase followed by a consolidation phase. Air distribution was stable within 12 hours after startup, reaching a peak air saturation of greater than 50 percent. The radius of peak expansion varied with time and depth, with measurable fluid displacement occurring beyond 12 feel from the sparge well near the water table. The percentage of air saturation stabilized within one hour following cutoff of the air flow, leaving pockets of entrapped air near the water table. When air injection was resumed, air saturation levels were found to be repeatable. The observations at this site indicated that the effective region of influence is relatively small and that frequent pulsing is needed to optimize oxygen distribution.
Patterns of Chemical Changes During Environmental Alteration of Hydrocarbon Fuels
Authors: Kaplan Isaac R. , Galperin Yakov , Alimi Hossein , Lee Ru‐Po , Lu Shan‐Tan 
Published: February 2007

AbstractThis paper discusses major environmental alteration processes and describes a set of chemical tests that have been developed to monitor compositional changes in hydrocarbon fuels released into the environment. The methods examine various homologous series of hydrocarbons including straight chain (paraffins or n‐alkanes), branched chain (isoparaffins or isoprenoids), alicyclic (naphthenes or alkylated cyclohexanes), polycyclic (steranes and terpanes), and aromatic structures (benzene, toluene, ethylbenzene. xylenes, alkylated benzenes, polycyclic aromatic hydrocarbons, and aromatic steranes). Each one of these groups of hydrocarbons has a different tolerance to environmental alteration by evaporation, dissolution (water washing), and biodegradation. When used as an analytical system on environmental samples, the data obtained provide information on fuel type recognition patterns and on degradation levels of the various fuels, allowing for an estimate of residence time.
Hot Methanol Extraction for the Analysis of Volatile Organic Chemicals in Subsurface Core Samples from Dover Air Force Base, Delaware
Authors: Ball W.P. , Xia G. , Durfee D.P. , Wilson R.D. , Brown M.J. , Mackay D.M. 
Published: February 2007

AbstractThe evaluation of contaminant concentrations in ground water and soil is an essential aspect of most hazardous waste remedial investigations. This paper describes methods applied toward obtaining, preserving, and analyzing subsurface samples for the determination of VOC concentrations in the saturated region of an unconfined coastal plain aquifer at Dover Air Force Base (DAFB). Delaware. The described protocol involved headspace‐free subsampling of cores, field preservation of subsamples in methanol, and overnight extraction of the VOCs at elevated temperature (70°C). Methanol‐extracted compounds were subsequently transferred to hexane and analyzed by gas chromatography. The method was found to achieve quantitative extraction from the aquifer sands in a single step, although extraction from fine‐grained and more strongly sorbing aquitard samples required multiple methanol extractions to achieve comparable recovery. An extensive set of DAFB results is presented as an indication of how these methods can be applied toward characterizing field‐scale contamination with a high degree of resolution and accuracy. These data have enabled a quantitative estimate of the contaminant distribution at this site and offer valuable insight into processes of contaminant migration into the underlying aquitard. In these regards, the methods used are believed to have provided much more accurate results than could have been obtained using more commonly applied techniques.
Impact of Turbidity on TCE and Degradation Products in Ground Water
Authors: Paul Cynthia J. , Puls Robert W. 
Published: February 2007

AbstractElevated particulate concentrations in ground water samples can bias contaminant concentration data. This has been particularly problematic for metal analyses where artificially increased turbidity levels can affect metals concentrations and confound interpretation of the data. However, few studies have been conducted to determine the impact of particulates on trichloroethylene (TCE), cis‐dichloroethylene (c‐DCE), and vinyl chloride concentrations.Laboratory batch studies and field investigations were conducted to evaluate the effects of suspended solids on VOC concentrations in ground water samples analyzed by purge‐and‐trap gas chromatography. Three different solids were used to assess the effects of suspended particulates. The solids were aquifer material from a field site in North Carolina and two reference clay minerals (kaolinite and Namontimorillonite). During the laboratory portion of this study, the solids were used to determine effects on TCE concentrations under controlled laboratory conditions.The same solids were used in a field study to compare the laboratory results with field results. Solids were added to the sample vials prior it) sample collection to intentionally increase turbidity levels in the water samples. Results of the study indicate essentially no decrease in TCE, c‐DCH, or vinyl chloride concentrations due to increased turbidity levels.