bluuebunny/crossref_metadata_2025 huggingface dataset:
An Analysis of Low‐Flow Ground Water Sampling Methodology
Authors: Sevee John E. , White Carol A. , Maher David J.
Published: February 2007

Low‐flow ground water sampling methodology can minimize well disturbance and aggravated colloid transport into samples obtained from monitoring wells. However, in low hydraulic conductivity formations, low‐flow sampling methodology can cause excessive drawdown that can result in screen desaturation and high ground water velocities in the vicinity of the well, causing unwanted colloid and soil transport into ground water samples taken from the well. Ground water velocities may increase several fold above that of the natural setting. To examine the drawdown behavior of a monitoring well, mathematical relationships can be developed that allow prediction of the steady‐state drawdown for constant low‐flow pumping rates based on well geometry and aquifer properties. The equations also estimate the time necessary to reach drawdown equilibrium. These same equations can be used to estimate the relative contribution of water entering a sampling device from either the well standpipe or the aquifer. Such equations can be useful in planning a low‐flow sampling program and may suggest when to collect a water sample. In low hydraulic conductivity formations, the equations suggest that drawdown may not stabilize for well depths, violating the minimal drawdown requirement of the low‐flow technique. In such cases, it may be more appropriate to collect a slug or passive sample from the well screen, under the assumption that the water in the well screen is in equilibrium with the surrounding aquifer.
An Evaluation of Physicochemical Treatment Technologies for Water Contaminated with MTBE
Authors: Keller Arturo A. , Sandall Orville C. , Rinker Robert G. , Mitani Marie M. , Bierwagen Britta , Snodgrass Michael J.
Published: February 2007

Treatment of methyl tertiary‐butyl ether (MTBE) from contaminated surface and ground water supplies presents specific challenges due to the physicochemical properties of MTBE that depend strongly on its hydrophilic nature, and translate into a high solubility in water, and low Henry's constant and low affinity for common adsorbents. We evaluate four treatment technologies‐air stripping, granular activated carbon (GAC), hydrophobic hollow fiber membranes, and advanced oxidation processes (AOP)‐using ozone or ozone/hydrogen peroxide. Experimental work was carried out to generate parameter values necessary for the design of these processes. Ten different flow rates/concentration combinations were evaluated in our designs to cover the range from high flow rate/low concentration typical of surface water and ground water drinking water supplies to low flow rate/high concentration typical of ground water remediation sites. For all cases, the processes were designed to produce effluent water of 5 μg/L or less. Capital costs and operation and maintenance costs were determined at the feasibility level by using standard engineering estimating practices.

Air stripping is the lowest cost technology for high flow rales (100 to 1000 gpm) if no air treatment is required. Hollow fiber membranes are the lowest cost technology for flow rates of 10 to 100 gpm if no air treatment is required, which is typical at these low flow rates. GAC will be most costeffective at all flow rates if air treatment is required and the influent water has low levels of other organic compounds. AOP using ozone or ozone/hydrogen peroxide is in all cases more expensive than the alternative technologies, and there are sufficient uncertainties at this point with respect to byproducts of AOP to warrant further study of this technology. The cost of treating MTBE‐contaminated water for conventional technologies such as air stripping and GAC is 40% to 80% higher than treating water contaminated only with other hydrocarbons such as benzene.
DNAPL Removal from a Heterogeneous Alluvial Aquifer by Surfactant‐Enhanced Aquifer Remediation
Authors: Londergan John T. , Meinardus Hans W. , Mariner Paul E. , Jackson Richard E. , Brown Chris L. , Dwarakanath Varadarajan , Pope Gary A. , Ginn Jon S. , Taffinder Sam
Published: February 2007

A demonstration of surfactant‐enhanced aquifer remediation (SEAR) was conducted at Hill Air Force Base (AFB), Utah. Two surfactant floods were undertaken in a test section of a heterogeneous alluvial aquifer with a hydraulic conductivity range of 2.8 to 8.6 ft/day (10‐5 to 10‐4 m/sec) and a pore volume of approximately 15,000 gallons (57 m3). The wellfield installed for the demonstration consisted of lines of three injection and three extraction wells, a central monitoring well, and a single hydraulic control well. No physical barriers to flow, such as sheet‐pile walls, were employed; surfactant flooding was controlled entirely by hydraulic manipulation of the flow field. The inter‐well distance between injectors and extractors was 20 feet (6 m); the distance between individual injectors and extractors in line was 10 feet (3 m). The water table was 25 feet (7.6 m) below ground surface with a saturated zone approximately 19‐feet thick (5.8 m). Residual dense nonaqueous phase liquids (DNAPL) remained in a zone of alluvium 42 to 46 feet (13 to 14 m) below ground surface following extraction of free‐phase DNAPL. The injectors and extractors were screened in this DNAPL zone. Three partitioning interwell tracer tests (PITTs) and two surfactant floods were conducted over four months during 1996. The surfactant floods removed 341 out of 346 gallons of residual DNAPL (1290 of 1310 L), according to the PITTs. This represents a total recovery of about 98.5% of the DNAPL volume present in the zone of residual DNAPL as determined by comparing the initial and final PITTs. There was no reduction in hydraulic conductivity due to colloid mobilization during the surfactant floods; in fact, the hydraulic gradient across the test zone decreased as the floods progressed. Concentrations of dissolved total chlorinated hydrocarbons in the test section decreased from 1000 mg/L before the floods to less than 10 mg/L following the floods. This demonstration is evidence of the technical practicability of DNAPL removal from alluvium.
Experimental and Economic Assessment of Two Surfactant Formulations for Source Zone Remediation at a Former Dry Cleaning Facility
Authors: Ramsburg C. Andrew , Pennell Kurt D.
Published: February 2007

Treatability tests and cost analyses were conducted to provide objective criteria for selection of a surfactant formulation to be used for surfactant enhanced aquifer remediation (SEAR) of a tetrachloroethene (PCE)‐contaminated site in Oscoda, Michigan. Two surfactant formulations, 4% Tween 80 + 500 mg/L CaCl2 and 8% Aerosol MA/IPA +15,000 mg/L NaCl + 1000 mg/L CaCl2, were considered based on their capacity to solubilize PCE and prior use in SEAR applications. Results of a two‐dimensional aquifer cell experiment indicated that 53% of the released PCE was recovered after flushing with approximately 8 pore volumes of 4% Tween 80. In contrast, only 3 pore volumes of 8% Aerosol MA/IPA solution were required to recover 78% of the PCE from the two‐dimensional aquifer cell, although the greater recovery of PCE was attributed, in large part, to the higher concentration of Aerosol MA. However, mobilization of PCE as free product was observed during the 8% Aerosol MA/IPA flood, which was consistent with total trapping number (NT) calculations. At the pilot‐scale, SEAR treatment costs were estimated to be $222,000 and $244,000 for 4% Tween 80 and 8% Aerosol MA/IPA, respectively, which compared favorably to the estimated pump‐and‐treat cost of $316,000. Projected full‐scale costs, based on a line‐drive flushing system, were $382,000 for 4% Tween 80 and $443,000 for 8% Aerosol MA/IPA. In contrast, full‐scale pump‐and‐treat costs were estimated to be $1,167,000. Surfactant recycling was shown to be logistically and economically infeasible at the pilot scale, and provided only a minimal cost benefit for 4% Tween 80 at the full scale. Based on the similarities in solubilization capacity and treatment cost, but substantially lower risk of PCE displacement, Tween 80 was recommended over Aerosol MA/IPA for pilot‐scale testing of SEAR.
Application Procedures for the Electromagnetic Borehole Flowmeter in Shallow Unconfined Aquifers
Authors: Crisman Stefanie A. , Molz Fred. J. , Dunn David L. , Sappington Frank C.
Published: February 2007

It is increasingly common for the electromagnetic borehole flowmeter (EBF) to he used to measure hydraulic conductivity (K) distributions in subsurface flow systems. Past applications involving the EBF have been made mostly in confined aquifers (Kabala 1994; Boman et al. 1997; Podgorney and Ritzi 1997; Ruud and Kabala 1997a, 1997b; Flach et al. 2000), and it has been common to set up a flow field around a test well using a small pump that is located near the top of the well screen (Mob, and Young 1993). In thin, unconfined aquifers that exhibit ground water tables near the ground surface and that undergo drawdown during pumping, such a configuration can be problematical because pumping and associated drawdown may effectively isolate the upper portion of the aquifer from the flowmeter. In these instances, a steady‐state flow field in the vicinity of the test well may be created using injection rather than pumping, allowing for testing in the otherwise isolated upper portion of the aquifer located near the initial water table position. Using procedures developed by Molz and Young (1993), which were modified for an injection mode application, testing was conducted to determine whether or not the injection mode would provide useful information in a shallow, unconfined aquifer that required the collection of data near the initial water table position. Results indicated that the injection mode for the EBF was well suited for this objective.
In Situ Measurement of Electro‐Osmotic Fluxes and Conductivity Using Single Wellbore Tracer Tests
Authors: McNab Walt W. , Ruiz Roberto
Published: February 2007

Electro‐osmosis (EO), the movement of water through porous media in response to an electric field, offers a means for extracting contaminated ground water from fine‐grained sediments, such as clays, that are not easily amenable to conventional pump‐and‐treat approaches. The EO‐induced water flux is proportional to the voltage gradient in a manner analogous to the flux dependence on the hydraulic gradient under Darcy's law. The proportionality constant, the soil electro‐osmotic conductivity or keo, is most easily measured in soil cores using bench‐top tests, where flow is one‐dimensional and interfering effects attributable to Darcy's law can be directly accounted for. In contrast, quantification of EO fluxes and keo in the field under deployment conditions can be difficult because electrodes are placed in ground water wells that may be screened across a heterogeneous mixture of lithologies. As a result, EO‐induced water fluxes constitute an approximate radial flow system that is superimposed upon a Darcy flow regime through permeable pathways that may or may not be coupled with hydraulic head differences created by the EO‐induced water fluxes. A single well comparative tracer test, which indirectly measures EO fluxes by comparing wellbore tracer dilution rates between background and EO‐induced water fluxes, may provide a means for routinely quantifying the efficacy of EO systems in such settings. EO fluxes measured in field tests through this technique at a ground water contamination site were used to estimate a mean keo value through a semianalytic line source model of the electric field. The resulting estimate agrees well with values reported in the literature and with values obtained with bench‐top tests conducted on a soil core collected in the test area.
Remediation of Sea Water Intrusion: A Case Study
Authors: Tsanis Ioannis K. , Song Li‐Fan
Published: February 2007

Sea water intrusion and remediation in the Upper Floridan Aquifer in South Carolina is simulated using the finite‐element model SUTRA developed by the U.S. Geological Survey. A sensitivity analysis of the effect of the hydrogeologic parameters on the sea water recharge and seepage velocities is performed. An increase in confining unit and/or in aquifer conductivity results in an increase of the sea water recharge. An increase in aquifer porosity results in a decrease of the sea water recharge. Among the three remedial techniques simulated—reduced aquifer withdrawals, an injection well, and a combined injection and capture well—the reduced aquifer withdrawals and injection well are the best methods for preventing sea water intrusion.
Analytical Model for Removal of a Uniformly Distributed Single‐Component NAPL Under Nonequilibrium Conditions
Authors: Brouwers H.J.H. , Augustijn D.C.M.
Published: February 2007

In this paper a simple analytical model is presented for the one‐dimensional transport equation describing the removal of a uniformly distributed, single‐component NAPL under nonequilibrium conditions. Both advective and dispersive transport are included in the model. The model describes two distinct stages: a solution for the time the amount of NAPL declines but the length of the NAPL‐containing region remains constant, and a solution from the moment the front, behind which all NAPL is depleted, starts to move. The model is valid for both dissolution (i.e., by water) or volatilization (i.e., by air). Dissolution (or volatilization) is considered a firstorder rate process with a constant mass‐transfer rate coefficient. As expected, the model approaches the solution for equilibrium conditions if the mass‐transfer coefficient tends to infinity. Even though the model is based on some rigorous assumptions, the simplicity of the model makes it useful for obtaining an initial mass‐transfer rate coefficient from experimental data, which can be used to estimate the time required to dissolve all NAPL, as shown for two data sets taken from the literature.
Tracer Tests and Image Analysis of Biological Clogging in a Two‐Dimensional Sandbox Experiment
Authors: Kildsgaard Jesper , Engesgaard Peter
Published: February 2007

A two‐dimensional flow experiment on biological clogging was carried out by biostimulating a sandbox packed with sand inoculated with bacteria. Biostimulation consisted of continuously injecting nutrients (acetate and nitrate). Clogging was visualized by frequently carrying out colored tracer experiments using Brilliant Blue. The tracer experiments were recorded with a digital camera and converted to concentration maps using an image‐analysis method that revealed in detail the complex spreading pattern surrounding clogged areas. Clogging resulted in a finger‐like spreading of the tracer around the main clogged area. Fingers were asymmetric and their dominant direction changed over time. Although the flow field was complex around the main clogged area, the effect on the bulk hydraulic conductivity at the scale of the sandbox was very small.
Nitrate Source Identification Using δ15N in a Ground Water Plume Near an Intensive Swine Operation
Authors: Karr Jonathan D. , Showers William J. , Hinson Thomas H.
Published: February 2007

Nitrate‐contaminated ground water beneath and adjacent to an intensive swine (Sus scrofa domesticus) production facility in the Middle Coastal Plain of North Carolina was analyzed for δ15N of nitrate (δ15N‐NO3). Results show that the isotopic signal of animal waste nitrogen is readily identifiable and traceable in nitrate in this ground water. The widespread land application of animal wastes from intensive livestock operations constitutes a potential source of nitrogen contamination to natural water throughout large regions of the United States and other countries. The site of the present study has been suspected as a nitrate contamination source to nearby domestic supply wells and has been monitored for several years by government and private water quality investigators through sampling of observation wells, ditches, and streams. δ15N of nitrate allowed direct identification of animal waste‐produced nitrate in 11 of 14 wells sampled in this study, as well as recognition of nitrate contributions from non‐animal waste agricultural sources in remaining wells.
Laboratory Column Experiments Using Polymer Mats to Remove Selected VOCs, PAHs, and Pesticides from Ground Water
Authors: Patterson Bradley Mark , Davis Gregory Bruce , McKinley Allan James
Published: February 2007

Large‐scale column experiments were undertaken to evaluate the potential of polymer mats to remove selected volatile organic compounds, polycyclic aromatic hydrocarbons, and pesticides (atrazine and fenamiphos) from ground water and potentially to act as permeable reactive barriers in contaminated ground water environments. The polymer mats, composed of interwoven silicone (dimethylsiloxane) tubes and purged with air, were installed in 2 m long flow‐through columns. The polymer mats proved efficient in physically removing (stripping) benzene and naphthalene from contaminated water. Removal efficiencies for both these compounds from an aqueous phase flowing past a polymer mat were 75% or greater. However, for atrazine and fenamiphos, removal efficiencies were 5% or less, probably as a result of their lower Henry's law constants and possibly lower polymer diffusion coefficients.

These experiments indicate that, at least for relatively volatile compounds, polymer mats can provide a remediation technique for the removal of organic compounds from contaminated water. Application of this technique may be well suited as a longer‐term, semipassive strategy to remediate contaminated ground water, using natural ground water flow to deliver contaminated ground water to polymer mats engineered as sorption‐stripping barriers.

Additional benefits of this technique may include targeted delivery of gaseous chemical amendments, such as oxygen, to enhance aerobic biodegradation and to further reduce any residual concentrations of contaminants.
DNAPL Characterization Methods and Approaches, Part 2: Cost Comparisons
Authors: Kram Mark L. , Keller Arturo A. , Rossabi Joseph , Everett Lome G.
Published: February 2007

Contamination from the use of chlorinated solvents, often classified as dense nonaqueous phase liquids (DNAPLs) when in an undissolved state, pose environmental threats to ground water resources worldwide. DNAPL site characterization method performance comparisons are presented in a companion paper (Kram et al. 2001). This study compares the costs for implementing various characterization approaches using synthetic unit model scenarios (UMSs), each with particular physical characteristics. Unit costs and assumptions related to labor, equipment, and consumables are applied to determine costs associated with each approach for various UMSs. In general, the direct‐push sensor systems provide cost‐effective characterization information in soils that are penetrable with relatively shallow (less than 10 to 15 m) water tables. For sites with impenetrable lithology using direct‐push techniques, the Ribbon NAPL Sampler Flexible Liner Underground Technologies Everting (FLUTe) membrane appears to be the most cost‐effective approach. For all scenarios studied, partitioning interwell tracer tests (PITTs) are the most expensive approach due to the extensive pre‐and post‐PITT requirements. However, the PITT is capable of providing useful additional information, such as approximate DNAPL saturation, which is not generally available from any of the other approaches included in this comparison.
Experimental Evaluation of Fouling Processes in Porous Polyethylene Well Screens Used for Horizontal Wells
Authors: Logan Andrew J. , Siegrist Robert L. , Munakata‐Mars Junko
Published: February 2007

The hydraulic performance of porous polyethylene well screens was examined in laboratory columns to understand the processes that affect well performance in many field applications. Conditions studied included (1) well‐screen pore size; (2) the presence of biodegradable drilling fluid, biological electron acceptors, and biofouling organisms; and (3) chlorine development. Custom‐fabricated, segmentable acrylic columns (8.9 cm diameter. 64 cm length) were employed using a factorial design statistical approach to mimic a variety of representative field conditions experienced during field applications. After circular well‐screen coupons (circular sections of the well screen cut to match the diameter of the columns) were cut and secured horizontally in the columns, sand media, and, in some cases, biodegradable drilling fluid were packed on top of the well screens. Those columns receiving chlorine development were allowed to sit overnight after a 1000 ppm chlorine solution was introduced beneath the well screen following upflow saturation. The columns were upflow saturated and then operated with simulated ground water in a down flow mode under constant hydraulic head for up to 75 days. Residual head with depth was measured and flux density values were recorded over time. Effluent samples were collected and analyzed for dissolved oxygen (D.O.), electrical conductance, pH, and total solids. After achieving pseudo‐steady‐state throughput condition as indicated by relatively constant effluent flux densities, the columns were dismantled and the well‐screen coupons were examined under a scanning electron microscope to observe causes of any loss in flow observed. The hydraulic conductivities of the well screens were also measured before and after operation in the columns. Results show that these porous polyethylene well screens resist fouling due to microbial colonization or chemical precipitation. Scanning electron microscopy revealed little or no colonization of the surfaces by microbes or blockage of pores by particle entrapment. Hydraulic head measurements revealed that the cause of headloss in the columns was a result of processes that occurred in the overlying sand media and not within the well screens themselves.
Field Evaluation of In Situ Chemical Oxidation Through Vertical Well‐to‐Well Recirculation of NaMnO4
Authors: Lowe K.S. , Gardner EG. , Siegrist R.L.
Published: February 2007

A field pilot test was conducted at a U. S. Department of Energy site to evaluate in situ chemical oxidation of trichloroethene (TCE) in a silty‐sandy gravel aquifer located at 26 to 30 feet (8 to 9 m) below ground surface. A vertical well‐to‐well recirculation system was designed and implemented by placing four corner extraction wells in a square grid, with each well 45 feet (13.7 m) from a center injection well. Ground water was extracted from the four perimeter wells, combined aboveground in a piping network, and then amended inline with sodium permanganate (NaMnO4) before reinjection into the aquifer through a center injection well. During the pilot test, oxidant amended ground water (250 mg/L NaMnO4) was injected at 18 gpm (68.1 L/m) for 10 days, during which time‐354 pounds (160.6 kg) of NaMnO4 were delivered and approximately 240,660 gallons (911 kL) of ground water were recirculated and treated. NaMnO4 injection using vertical wells in a five‐spot pattern was capable of providing sufficient hydraulic control to deliver oxidant throughout the permeable zones of the 4100 ft2 (380 m2) test area within three days. TCE concentrations were reduced, from 2,000 μg/L to <10 μg/L, throughout all but the lower permeable eastern edge of the test region, indicating an apparent reduction in contaminant levels of 92% within three days and 97% within 10 days (two hours after the end of active recirculation). One month after system shut down, residual oxidant concentrations in the ground water had declined to <1 mg/L, while a gradual increase in TCE concentrations was observed. Oxidant consumption over time is expected due to a combination of factors, including oxidation of the natural organic material present, oxidation of TCE that diffused out from the finer‐grained and less permeable zones, and advection of TCE into the test area from the upgradient plume. No adverse effects to system toxicity, generation of reaction intermediates and products (e.g., chlorinated organic acids or partially degraded chlorocarbons), or reduction in formation permeability were observed.
Urban Ground Water Pollution: A Case Study in Cuttack City, India
Authors: Das Jyotirmaya , Sahoo Rama Krishna , Sinha B.K.
Published: February 2007

A large number of ground water samples (360) was collected from 60 stations over six consecutive seasons to study the influence of the main sewerage drain on shallow ground water table beneath the municipal area of Cuttack, India. A majority of the samples collected from stations close to the drain exceeded the maximum permissible limits set by the World Health Organization (WHO). Almost all the samples near the drain exceeded the WHO limit for NO3‐ and Na+. However, the concentrations decreased as the distance from the drain increased. The winter season registered the maximum concentrations of NH4+, NO3‐, and SO42‐ ions whereas the minimum values always coincided with the rainy season. R‐mode factor analysis was conducted to find relationships amongst the 16 chemical parameters studied. Fluoride showed a negative correlation with Cl‐, Na+, NO3‐, SO42‐, and PO43‐. The concentration of F‐ may be lower in raw waste water than naturally occurs in the ground water. Therefore, a decrease in the concentration of F‐ near the drain may be attributed to dilution by contributions of waste water to the ground water. The rest of the parameters were found to be directly related to the distance of collection points to the sewerage. The distribution of nutrients is strongly affected by leaching of waste water into the ground water.
Biocurtain Design Using Reactive Transport Models
Authors: Phanikumar M.S. , Hyndman David W. , Criddle Craig S.
Published: February 2007

Bioremediation is an attractive alternative to traditional remediation methods for a variety of ground water contaminants. However, widespread implementation of bioremediation is currently limited by the complexity of the dynamic chemical and biological processes that need to be understood and incorporated into the design approach. Reactive transport models provide a powerful tool to simulate these complex interactions and, thus, can be used to improve and guide the design of bioremediation systems. We present a remediation design approach for intermittently stimulated biodegradation using multicomponent reactive transport models, parameterized using a series of nondimensional Damkohler numbers. Designs were based on either (1) a target aqueous phase concentration at the exit of the treatment system, or (2) the total contaminant mass fraction removed from a region of interest. The equation set used to develop this design approach is specific to the case of intermittent electron donor addition to drive cometabolic transformations. We illustrate the design procedure for a biocurtain that removes carbon tetrachloride. Our results for this case indicate that intermittent injection is significantly more efficient than strategies based on continuous pumping. Example design parameters include the length of the biologically active zone (i.e., biocurtain), the effective rate of degradation in this zone, and the interval between electron donor injection cycles. The presented dimensionless parametric approach can be used to design bench‐scale column studies and should be helpful for scale‐up to field‐scale remediation systems.
Designing Monitoring Programs to Effectively Evaluate the Performance of Natural Attenuation
Authors: Wiedemeier Todd H. , Haas Patrick E.
Published: February 2007

Natural attenuation processes affect the fate and transport of organic compounds in many hydrologic systems. Over the last several years, regulatory agencies and environmental professionals have come to recognize the importance of these natural processes in effecting contaminant attenuation. When they are shown to be protective of human health and the environment, and when a well‐designed monitoring program is in place to document the efficiency of these processes, they can be a valuable component of site remediation strategies.
Cautions and Suggestions for Geochemical Sampling in Fractured Rock
Authors: Shapiro Allen M.
Published: February 2007

Collecting water samples for geochemical analyses in open bedrock boreholes or in discrete intervals of boreholes intersected by multiple fractures is likely to yield ambiguous results for ground water chemistry because of the variability in the transmissivity, storativity, and hydraulic head of fractures intersecting the borehole. Interpreting chemical analyses of water samples collected in bedrock boreholes requires an understanding of the hydraulic conditions in the borehole under the ambient flow regime in the aquifer as well as during sampling. Pumping in open boreholes, regardless of the pumping rate and the location of the pump intake, first draws water from the borehole and then from fractures intersecting the borehole. The time at which the volumetric rate of water entering the borehole from fractures is approximately equal to the pumping rate can be identified by monitoring the logarithm of drawdown in the borehole as a function of the logarithm of time. Mixing of water entering the borehole from fractures with water in the borehole must be considered in estimating the time at which the pump discharge is representative of aquifer water. In boreholes intersected by multiple fractures, after the contribution from the borehole volume has diminished, the contribution of fractures to the pump discharge will be weighted according to their transmissivity, regardless of the location of the pump intake. This results in a flux‐averaged concentration in the pump discharge that is biased by the chemical signature of those fractures with the highest transmissivity. Under conditions where the hydraulic head of fractures varies over the length of the borehole, open boreholes will be subject to ambient flow in the water column in the borehole. In some instances, the magnitude of the ambient flow may be similar to the designated pumping rate for collecting water samples for geochemical analyses. Under such conditions, the contributions to the pump discharge from individual fractures will be a function not only of the transmissivity of the fractures, but also of the distribution of hydraulic head in fractures intersecting the borehole. To reduce or eliminate the deleterious effects of conducting geochemical sampling in open boreholes, a straddle‐packer apparatus that isolates a single fracture or a series of closely spaced fractures is recommended. It is also recommended that open boreholes be permanently outfitted with borehole packers or borehole liners in instances where maintaining the hydraulic and chemical stratification in the aquifer is of importance. In a field example, a comparison of results from sampling in an open borehole and in discrete intervals of the same borehole showed dramatic differences in the concentrations of chemical constituents in the water samples, even though chemical field parameters stabilized prior to both open borehole and discrete interval sampling.
Efficacy of Annual Bacteria Monitoring and Shock Chlorination in Wells Finished in a Floodplain Aquifer
Authors: Oliphant J.A. , Ryan M.C. , Chu A. , Lambert T.W.
Published: February 2007

Public health authorities generally recommend annual water‐quality monitoring of rural water wells and shock chlorination if coliforms are detected. It is implicitly assumed that shock chlorination is effective in ridding most wells of bacteriological pathogens for months to years. Neither annual monitoring nor shock chlorination was effective in addressing coliform contamination of selected water wells in a small town developed on an alluvial aquifer where septic system effluents are impacting well water quality. Considerable temporal variation in total and fecal coliforms was observed in water wells monitored for a six‐month period. Individual wells intermittently met and exceeded the drinking water criteria, indicating annual sampling was insufficient. Shock chlorination of three contaminated wells and their associated distribution systems proved ineffective because colonies apparently originated from outside the wells and reappeared over relatively short time periods (ranging from less than one week up to 21 weeks). The relatively fast and similar rate of recovery of total heterotrophic bacteria suggested they are related to biofilm formation in the wells and not to ground water contamination.
Estimating Aquifer Sensitivity to Nitrate Contamination Using Geochemical Information
Authors: Trojan Michael D. , Campion Moira E. , Maloney Jennifers , Stockinger James M. , Eid Erin P.
Published: February 2007

Methods for predicting aquifer sensitivity to contamination typically ignore geochemical factors that affect the occurrence of contaminants such as nitrate. Use of geochemical information offers a simple and accurate method for estimating aquifer sensitivity to nitrate contamination. We developed a classification method in which nitrate‐sensitive aquifers have dissolved oxygen concentrations > 1.0 mg/L, Eh values >250 mV, and either reduced iron concentrations < 0.1 mg/L or total iron concentrations < 0.7 mg/L. We tested the method in four Minnesota aquifer systems having different geochemical and hydrologic conditions. A surficial sand aquifer in central Minnesota exhibited geochemical zonation, with a rapid shift from aerobic to anaerobic conditions 5 m below the water table. A fractured bedrock aquifer in east‐central Minnesota remained aerobic to depths of 50 m, except in areas where anaerobic ground water discharged upward from an underlying aquifer. A bedrock aquifer in southeast Minnesota exhibited aerobic conditions when overlain by surficial deposits lacking shale, whereas anaerobic conditions occurred under deposits that contained shale. Surficial sand aquifers in northwest Minnesota contained high concentrations of sulfate and were anaerobic throughout their extent. Nitrate‐nitrogen was detected at concentrations exceeding 1 mg/L in 135 of 149 samples classified as sensitive. Nitrate was not detected in any of the 109 samples classified as not sensitive. We observed differences between our estimates of sensitivity and existing sensitivity maps, which are based on methods that do not consider aquifer geochemistry. Because dissolved oxygen, reduced iron, and Eh are readily measured in the field, use of geochemistry provides a quick and accurate way of assessing aquifer sensitivity to nitrate contamination.
An Evaluation of Tertiary‐Butyl Alcohol for the Development of a Drinking Water Action Level in Delaware
Authors: Fischer William “Tripp”
Published: February 2007

For regulators to develop risk‐based screening levels (RBSLs) for a petroleum constituent, a maximum allowable concentration at an exposure point, such as a drinking water action level, must be established. Of particular interest to regulators of leaking underground storage tank (LUST) sites in Delaware is the development of RBSLs for the oxygenated compounds that are added to gasoline to increase octane rating and promote cleaner burning fuel. Whereas methyl‐tertiary butyl ether (MTBE) became the first of the oxygenated compounds to gain regulatory attention in Delaware, tertiary‐butyl alcohol (TBA) is not far behind. TBA has been detected at LUST sites throughout Delaware and in some cases has been detected in private water supplies. However, Delaware does not currently have a drinking water action level, or maximum allowable exposure concentration, on which to base regulatory decisions regarding TBA.

Toxicological data is inconclusive in classifying TBA as a carcinogen. However, carcinogenic responses are reported in rat and mice studies at extremely high doses. To address TBA in Delaware's Risk‐Based Corrective Action Program, the Delaware Division of Public Health must calculate drinking water action levels based on the results of the toxicological data. However, the establishment of TBA action levels could have a tremendous impact on the costs associated with investigating and remediating a LUST site. TBA may add $2000 to $5000 per year in analytical costs alone for an average LUST site in Delaware.
Simulation of a Ground Water Recirculation Well with a Dual‐Column Laboratory Setup
Authors: Lesage Suzanne , Brown Susan , Millar Kelly , Steer Helena
Published: February 2007

This paper describes a dual‐column laboratory setup consisting of a glass column and a stainless‐steel column filled with aquifer material. The setup was used to replicate a ground water recirculation well that serves as an in situ reactor and a combined injection/withdrawal well. The treatment solution consisted of a buffered titanium (III) citrate/vitamin B12 mixture. The first column, representing the well, was made of glass, allowing for visual inspection of the mixing. The stainless‐steel column was instrumented with redox (Eh) probes to monitor the changes in redox conditions. The redox measurement showed that, although the sand contained large quantities of iron oxides, the oxidation rate was relatively slow and the titanium solution would remain reduced for some time in the aquifer, continuing to react with the contaminants. This laboratory setup was used to optimize the reagent concentrations and rate of delivery for field implementation. It was found that 4 mM titanium citrate and 3 mg/L vitamin B12 were sufficient to degrade 1,1,2,2‐tetrachloroethane and carbon tetrachloride within one day, but not trichloroethylene, which required five days with 10 mM titanium citrate and 5 mg/L vitamin B12.
Optimizing Landfill Ground Water Analytes—New South Wales, Australia
Authors: Hart Barbara F. , Chaseling Janet
Published: February 2007

A study of analytes for ground water monitoring was conducted at 10 municipal solid waste landfills in northern New South Wales (NSW), Australia. From literature review, analytes were proposed and then approved by the NSW Environment Protection Authority (EPA) for initial ground water and leachate monitoring. Eight rounds of initial baseline monitoring using traditional geochemical analytes were conducted in uncontaminated ground water at a new, lined landfill. Four rounds of initial assessment monitoring were conducted at nine unlined or only partially lined old landfills. Analytes for the old landfills were selected with a health risk emphasis because ground water may already be contaminated.

At the old landfill sites, analytes with values indicating contamination were often limited to one particular analytical group, although the analytical group represented differed from site to site. As a result, the most environmentally responsible suite of analytes for baseline monitoring is the traditional geochemical approach; free carbon dioxide for landfill gas; and organics in the form of volatile organic compounds for old landfills, but benzene, toluene, ethylbenzene, and xylene when wells are close to a new landfill. The current Subtitle D (U.S. EPA 1991) analytes proved inadequate. They would not have detected the majority of contaminants or contaminant indicators at the old landfills, i.e., organic nitrogen, ammonia, nitrate, iron, and manganese.

After completion of initial monitoring at each site, reduced lists of analytes for ongoing monitoring were proposed and approved by the NSW EPA. The lists were based on literature evidence, contaminants, and contaminant indicators found in ground water at the old landfills, and in some cases leachate versus ground water concentrations. For the new landfill, the principle of limited analytes representing a broad range of analytical groups was used to assure precautionary environmental outcomes. At present‐day costs, cost savings for analyses alone at the new landfill are ÄD251, 160 over the 70‐year life of the landfill.
Application of Natural Attenuation to Ground Water Contaminated by Phenoxy Acid Herbicides at an Old Landfill in Sjoelund, Denmark
Authors: Tuxen Nina , Ejlskov Palle , Albrechtsen Hans‐Jørgen , Reitzel Lotte A. , Pedersen Jørn K. , Bjerg Paul L.
Published: February 2007

Investigations of geology, hydrogeology, and ground water chemistry in the aquifer downgradient from Sjoelund Landfill, Denmark, formed the basis for an evaluation of natural attenuation as a remediation technology for phenoxy acid herbicides at the site. Concentrations of phenoxy acids were up to 65 μg/L in the ground water, primarily 4‐chlor‐2‐methylphenoxypropionic acid (MCPP) and 2,4‐dichlorophenoxypropionic acid (dichlorprop). Mass removal of the phenoxy acids was shown within 50 to 100 m of the landfill by calculation of contaminant fluxes passing transects at three distances. There was accordance between increasing oxygen concentrations and decreasing phenoxy acid concentrations with distance from the landfill, indicating that aerobic degradation was a major mass removal process. Presence of high concentrations of putative anaerobic phenoxy acid metabolites suggested that anaerobic degradation was also occurring. Laboratory degradation experiments using sediment and ground water from the aquifer supported aerobic and anaerobic degradability of MCPP at the site. It was concluded that natural attenuation may be applicable as a remedy for the phenoxy acids at the Sjoelund Landfill site, although uncertainties related to calculations of chloride and phenoxy acid fluxes at a complex site and identification of specific in situ indicators were encountered. Thus, there is a pronounced need for development and broader experience with evaluation tools for natural attenuation of phenoxy acids, such as specific metabolites, changes in enantiomeric fractions, compound‐specific stable carbon isotope ratios, or microbial fingerprints.
In Situ Monitoring of Vapor Phase TCE Using a Chemiresistor Microchemical Sensor
Authors: Ho Clifford K. , Lohrstorfer Charles F.
Published: February 2007

A chemiresistor microchemical sensor has been developed to detect and monitor volatile organic compounds in unsaturated and saturated subsurface environments. A controlled study was conducted at the HAZMAT Spill Center at the Nevada Test Site, where the sensor was tested under a range of temperature, moisture, and trichloroethylene (TCE) concentrations. The sensor responded rapidly when exposed to TCE placed in sand, and it also responded to decreases in TCE vapor concentration when clean air was vented through the system. Variations in temperature and water vapor concentration impacted baseline chemiresistor signals, but at high TCE concentrations the sensor response was dominated by the TCE exposure. Test results showed that the detection limit of the chemiresistor to TCE vapor in the presence of fluctuating environmental variables (i.e., temperature and water vapor concentration) was on the order of 1000 parts per million by volume, which is about an order of magnitude higher than values obtained in controlled laboratory environments. Automated temperature control and preconcentration is recommended to improve the stability and sensitivity of the chemiresistor sensor.
CRT‐Hole Closure
Authors: Noce Thomas E. , Holzer Thomas L.
Published: February 2007

The long‐term stability of deep holes 1.75 inches. (4.4 cm) in diameter by 98.4 feet (30 m) created by cone penetration testing (CPT) was monitored at a site in California underlain by Holocene and Pleistocene age alluvial fan deposits. Portions of the holes remained open both below and above the 28.6‐foot (8.7 m)‐deep water table for approximately three years, when the experiment was terminated. Hole closure appears to be a very slow process that may take decades in the stiff soils studied here. Other experience suggests holes in softer soils may also remain open. Thus, despite their small diameter, CPT holes may remain open for years and provide paths for rapid migration of contaminants. The observations confirm the need to grout holes created by CPT soundings as well as other direct‐push techniques in areas where protection of shallow ground water is important.
Modeling Volatile Chemical Transport, Biodecay, and Emission to Indoor Air
Authors: Parker Jack C.
Published: February 2007

A model is presented for estimating vapor concentrations in buildings because of volatilization from soil contaminated by non‐ aqueous phase liquids (NAPL) or from dissolved contaminants in ground water. The model considers source depletion, diffusive‐ dispersive transport of the contaminant of concern (COC) and of oxygen and oxygen‐limited COC biodecay. Diffusive‐advective transport through foundations and vapor losses caused by foundation cross‐flow are considered. Competitive oxygen use by various species is assumed to be proportional to the product of the average dissolved‐phase species concentration and a biopreference factor. Laboratory and field data indicate the biopreference factor to be proportional to the organic carbon partition coefficient for the fuel hydrocarbons studied. Predicted indoor air concentrations were sensitive to soil type and subbase permeability. Lower concentrations were predicted for buildings with shallow foundations caused by flushing of contaminants by cross‐flow. NAPL source depletion had a large impact on average exposure concentration. Barometric pumping had a minor effect on indoor air emissions for the conditions studied. Risk‐based soil cleanup levels were much lower when biodecay was considered because of the existence of a threshold source concentration below which no emissions occur. Computed cleanup levels at NAPL‐contaminated sites were strongly dependent on total petroleum hydrocarbon (TPH) content and COC soil concentration. The model was applied to two field sites with gasoline‐contaminated ground water. Confidence limits of predicted indoor air concentrations spanned approximately two orders of magnitude considering uncertainty in model parameters. Measured contaminant concentrations in indoor air were within model‐predicted confidence limits.
Bentonite as a Natural Adsorbent for the Sorption of Iron from the Ground Water Exploited from Aswan Area, Egypt
Authors: Taha Gharib M. , Elmagd Kamal Abou
Published: February 2007

Sorption of dissolved Fe2+ on bentonite was studied using a batch technique. The distribution coefficient, Kd, was evaluated for a bentonite‐iron system as a function of contact time, pH, sorbent and sorbate concentrations, and temperature. Sorption results were interpreted in terms of Freundlich's and Langmuir's equations. Thermodynamic parameters for the sorption system were determined at three temperatures: 298°, 308°, and 318°K. The values of ΔH°(‐4.0 kjmol−1) and ΔG°(‐2.46 Kjmol−1) at 298°K (25°C) suggest that sorption of iron on bentonite is an exothermic and a spontaneous process. The ΔG° value became less negative at higher temperatures and, therefore, less iron was sorbed at higher temperatures. The desorption studies with 0.01M CaCl2 and deionized water at iron loading on bentonite showed that more than 90 wt% of the iron is irreversibly sorbed, probably due to the fixation of the iron by isomorphous replacement in the crystal lattice of the sorbent.