ALBERT

Notizen: Site selection for ground-water production wells was made easier using a microgravity survey technique. The ground-water regime beneath the Carleton University campus is dominated by fracture flow associated with major faults. These faults are located within buried bedrock valleys where preferential erosion of the bedrock has occurred. A series of faults is inferred from bedrock topography and hydrogeological testing; however, the precise orientation of the faults is to a large extent uncertain. The bedrock surface is masked by fluvial, glacial, and glaciomarine overburden of variable thickness.High precision, small-scale microgravity profiling was carried out to identify the bedrock valleys. Gravity anomalies of up to 0.05 mgal correspond to valley depths ranging from 5 to 15 meters. The density contrast between overburden and limestone bedrock is estimated as 0.3 g/cm3. Forward modeling using a polygon technique suggests that the observed, corrected gravity profile is a smoothed reflection of the bedrock surface at depth.Based on the locations of the bedrock valleys, several faults were identified and four test wells were drilled as part of the development of Phase 2 of the Carleton Groundwater Energy Project. Three of these wells produced high yields, exceeding 60 I/sec, when converted to 12 inch diameter production wells. The fourth well also encountered a bedrock valley but with a slightly lower yield of water.The favorable drilling results have shown that small-scale microgravity profiling, in an area that is largely unsuitable for the detection of subsurface features using other geophysical techniques, is an effective method for imaging the bedrock surface. The positions of the faults, which are known to exist on the basis of stratigraphy, geophysical well log correlations, bedrock topography, and calcite-filled fractures exposed in outcrop or core, have been more accurately defined.

Notizen: Di-n-butyl phthalate (DBP) was found to be transformed by microorganisms under aerobic and anaerobic conditions at 10° C in microcosms simulating the Canadian Forces Base (CFB) Borden subsurface environment. Biotransformation of DBP was observed under aerobic, nitrate-reducing, Fe(III)-reducing, and sulfate-reducing conditions. The biotransformation of DBP in the microcosms was significantly decreased as the redox potential was lowered, especially under sulfate-reducing conditions. However, other factors such as nutrient depletion and buildup of toxic intermediates could have affected the biotransformation rates. The highest DBP biotransformation rate (0.57 μg DBP.g sediment−1.day−1) was observed under aerobic conditions whereas the lowest rate (0.05 μg DBP.g sediment−1.day−1) was under sulfate-reducing conditions. Biotransformation of DBP at 10° C was significantly enhanced by the addition of 10 mM NaNO3 suggesting that both the addition of nitrate and high redox conditions favor its biotransformation in subsurface environments.

Notizen: Lake Chad, a closed basin lake, is the only large surface-water body in the African Sahel. Future water resource development in the Chad Basin requires an understanding of the hydrogeology of the basin. In this paper we examine the hydraulic relationship between the lake and the phreatic aquifer of the Chad Formation. Electrical resistivity data from 30 surveys were combined with over 60 open well measurements to construct a water-table map of the southwestern quadrant of the lake. The map indicates that the Lake Chad water level is at a higher hydraulic level than the phreatic aquifer and that the ground-water flow is southwest, away from the lake. The average measured seepage rate into the phreatic aquifer in the southwestern and southern parts of the lake was 7.1 × 10−3 m/d (median = 1.3 × 10−3 m/d) which is about 21% of the annual water input to the lake. This measured seepage flux (9.96 × 109 m3/yr) can account for about 107% of the annual solute input to the lake. Solute transport model simulations indicate about 32% (15.3 × 109 m3/yr) of the input water and 152% (2.87 × 1012 g/yr) of the total solute input can be removed by ground-water recharge (seepage) from the lake. These results provide an explanation to account for the freshness of Lake Chad's water despite its surficial closed basin geologic setting: solutes delivered to the lake via surface-water inflow leave the lake via ground-water recharge. These results also indicate recharge from the lake (∼ 1010 m3/yr) represents an enormous amount of water available as a ground-water resource in the African Sahel.

Notizen: Aqueous geochemical data from unconfined sand aquifers beneath two operating domestic septic systems are used to illustrate and evaluate a conceptual model of septic-system geochemistry. This model emphasizes the changing redox and alkalinity conditions in the septic system and the subsurface. The septic-tank effluents flow as distinct plumes downward through the unsaturated zones and then primarily laterally in the ground-water zones. The composition of the effluent was measured at several points in each system. At each site, the septic-tank effluent underwent aerobic oxidation in the unsaturated zone, which caused conversion of NH4+ to NO3−, organic C to CO2 and organic S to SCh42-. At the first site, calcium carbonate dissolution in the unsaturated zone buffered the acidity released by the redox reactions. In contrast, the second system was poorly buffered and the pH dropped from 6.7 to 4.9 as aerobic oxidation occurred. Below the water table a small amount of aerobic oxidation occurred at each site. Nitrate-N concentrations in the cores of both plumes were above 25 mg/1 as the plumes traveled from the septic systems. At the second site, the ground-water plume discharges to a river at the edge of the property. As the effluent flowed through the organic C-rich sediments of the river bed, NO3− disappeared and alkalinity increased, presumably due to denitrification. Differences in sediment composition at the two sites also led to different behaviors of Fe, Al, and possibly PO43-. The conceptual model offers an organized approach to interpreting the major geochemical trends observed in the two systems, which are determined mostly by the well-aerated unsaturated zones below the drain fields and the amount of buffering material present in the sediments.

Notizen: Characterizing the extent and severity of ground-water contamination at waste sites is expensive and time-consuming. A probabilistic approach, based on the acceptance of uncertainty and a finite probability of making classification errors (contaminated relative to a regulatory threshold vs. uncontaminated), is presented as an alternative to traditional site characterization methodology. The approach utilizes geostatistical techniques to identify and model the spatial continuity of contamination at a site (variography) and to develop alternate plausible simulations of contamination fields (conditional simulation). Probabilistic summaries of many simulations provide tools for (a) estimating the range of plausible contaminant concentrations at unsampled locations, (b) identifying the locations of boundaries between contaminated and uncontaminated portions of the site and the degree of certainty in those locations, and (c) estimating the range of plausible values for total contaminant mass. The first paper in the series presents the geostatistical framework and illustrates the approach using synthetic data for a hypothetical site. The second paper presents an application of the proposed methodology to the probabilistic assessment of ground-water contamination at a site involving ground-water contamination by nitrate and herbicide in a shallow, unconfined alluvial aquifer in an agricultural area in eastern Oregon.

Notizen: An analysis of the deformation of a homogeneous electrical field caused by a long, thin inclined bed, which is of considerable importance in the exploration of ground water and minerals, is presented using the Hilbert transform. The thickness of the bed and the inclination are expressed as a function of the abscissae of the points of intersection of the horizontal and vertical derivatives of the field. The procedure is illustrated with a theoretical example and substantiated with field examples from the fractured Crystalline Basement Complex in Burkina Faso, Africa, and Pre-Cambrian limestones of the Cuddappah Basin in Andhra Pradesh, India. The results derived from the analytical method are shown to agree well with the ground truth.

Notizen: Eight Schlumberger soundings and four Wenner anisotropy measurements were conducted in the northwestern section of the Yucatan Peninsula for hydrogeological investigations of a karst aquifer. This system is influenced by a circular high permeability zone (Ring of Cenotes) probably related to the Chicxulub Impact Crater. Schlumberger soundings and Wenner anisotropy measurements show that the karst aquifer can be modeled as an electrically anisotropic medium. Anisotropy is related to preferential permeability directions channeling ground-water flow within the aquifer. Directions of maximum permeability were determined using Wenner anisotropy measurements. Electrical soundings were conducted at different sites near the Ring of Cenotes. Resistivity values decrease toward the Ring of Cenotes supporting the hypothesis that selected segments of the Ring have high permeability. Several soundings were conducted in order to study lateral permeability variations along the Ring. A high permeability section can be identified by low resistivity models and is related to a zone of high cenote density. A low permeability section of the Ring was found showing high resistivity models. This zone overlaps with an area of low cenote density. Electrical soundings were used to determine the depth of the fresh-water lens; the interface was detected along two profiles perpendicular and parallel to the Ring of Cenotes resulting in a depth that ranged from 18 m near the coast up to 110 m in the southeastern part of the study area. The predicted depths of the interface using electrical methods showed a good correlation with Ghyben-Herzberg and measured interface depths at some sites. Discrepancies between calculated and interpreted interface depths at two sites may be explained by horizontal-to-vertical permeability anisotropy.

Notizen: The “pore tree” model of pore structure was originally developed for catalyst and sorbent grains to allow coupled reactions and diffusion into and out of nonpermeable porous media in the absence of convection through the media. The pore tree model is extended herein to describe the permeable pore structure which characterizes the subsurface transport of gas and water in soil, the dispersion of contaminants, and in situ remediation. The interconnectivity of the pore structure is obtained via a statistical determination of the “branches” that are common to several trees to allow convection and diffusion through the large scale (permeable) structure in addition to diffusion and reactions in the smaller scale (nonpermeable) structure. The extended pore tree model has successfully explained measurement errors in the permeability of soil due to the measurement scale size and has successfully predicted the bulk gaseous diffusivity in partially saturated soil as a function of a saturation scale size. The extended pore tree model provides an analytic description of the pore structure of soil upon which bulk transport, small scale diffusion, and coupled chemical reactions may be added to accurately describe contaminant transport and in situ remediation.

Notizen: Two-dimensional, finite-difference, saturated, ground-water flow models such as MODFLOW can be useful in simulating “mise-a-la-masse” electrical flow through conductive porous media. A new technique for using an existing numerical code to develop an approximate solution for point source electrical flow is presented. Incorporating a change in variables from ground-water flow to electrical flow within the MODFLOW input file allows the ground-water flow code to model the effects of resistivity contrasts directly. By adjusting the input data as presented herein, spherical electrical flow through contaminated porous media can be approximated in two dimensions.

Notizen: Soil gas pump tests are commonly performed to identify important unsaturated zone parameters such as the effective gas permeability tensor and the influence of tight or leaky confining units. An interactive FORTRAN computer program called GASSOLVE has been developed for analyzing these tests under both transient and steady-state conditions. The code uses one of two general analytical solutions for radially symmetric gas flow to a well: the solution for transient compressible gas flow to a partially penetrating well in which the ground surface is open to the atmosphere; and the solution for transient compressible gas flow to a partially penetrating well bounded above by a leaky confining layer. Pump tests involving steady-state conditions, fully penetrating wells, or tight confining layers are considered as special cases of these solutions. The field gas pressure data from multiple observation wells are inverted using a multidimensional nonlinear optimization routine to provide a best fit of the data with the selected analytical solution.

Notizen: The Yuma area has experienced agricultural development since the late 1890s and ground-water levels have risen over 70 feet due to recharge from heavy application of irrigation water, unlined canals and flooding along the Colorado and Gila Rivers. The resulting shallow water levels have seriously impacted residential areas and prime agricultural land.The Arizona Department of Water Resources in conjunction with Yuma County Flood Control District developed a regional three-dimensional ground-water flow model of the Yuma area. The purpose of the model is to assist local agencies in evaluating remedial water management alternatives to mitigate the shallow ground-water level problems.The model domain incorporates over 900 mi2 of Arizona, California, and Mexico and simulates ground-water pumpage, deep percolation from agricultural irrigation, evapotranspiration from phreatophytes and flow in 12 canals, 16 drains, and the Colorado and Gila Rivers. The model contains four layers with over 30,000 model cells ranging in size from 40 acres to 640 acres.Different model scenario simulations were conducted to evaluate the effectiveness of proposed water management alternatives on lowering ground-water levels within the northern portion of Yuma Valley. These scenarios include lining a portion of the East Main canal and pumping two drainage wells, lining the All-American canal, and simulating a decrease in deep percolation from agricultural irrigation on the Yuma Mesa and northern portion of Yuma Valley.

Notizen: The first paper in this series (Rautman and Istok, 1996) presented a geostatistical framework for obtaining a probabilistic assessment of ground-water contamination. This paper presents the results of a case study that applies this framework to define the spatial extent and severity of nitrate and Dacthal (dimethyl tetrachloroterephthalate or DCPA, a herbicide) contamination in the unsaturated and saturated zones for a 150 km2 site near Ontario, Oregon. Sediment samples collected from 35 boreholes were used to compute vertical accumulations of nitrate and DCPA in the unsaturated zone. Measured nitrate and DCPA concentrations in ground-water samples collected from 42 wells were used to compute vertical accumulations of nitrate and DCPA in the saturated zone. Sample variograms were fit with nugget and spherical models to describe the pattern of spatial continuity of nitrate and DCPA concentrations and accumulations. Conditional, sequential Gaussian simulation was used to generate 100 simulations for each variable on a 0.5 × 0.5 km grid. Probabilistic summaries of these simulations were used to develop (a) maps showing the probability of contamination exceeding specified theshold values, (b) probability distributions for contaminant accumulation and concentration at unsampled locations, (c) probabilistic descriptions for the location of contaminant-plume boundaries, and (d) probability distributions for the total contaminated area and total contaminant mass. The results demonstrate that interpretations of site characterization data to determine the extent and magnitude of contamination at a site will vary depending upon the level of uncertainty that will be tolerated by the decision maker. This case study also illustrates the potential applicability and utility of the probabilistic approach for the interpretation of site characterization data and the design of future data collection activities.

Notizen: The results of an extended analysis of the chloride breakthrough curves (BTCs) obtained from transport experiments on undisturbed soil monoliths previously reported by Sassner et al. (1994) are discussed. Parameter values for different forms of the advection-dispersion equation (ADE) were obtained by curve-fitting using the nonlinear least-squares optimization code CXTFIT developed by Parker and van Genuchten (1984). Good fits to the experimental BTCs from the individual soil monoliths were obtained for three different forms of the ADE, allowing for anion exclusion, immobile water, and both of these processes, respectively. Although the more complex forms of the ADE possess more flexibility to provide a slightly more refined fit to the individual breakthrough curves, larger uncertainty is associated with the fitted parameter values. Due to the limited amount of information manifested in the BTCs it is not possible on the basis of this information to distinguish which of the models is physically more meaningful. Furthermore, when more parameters are included in the optimization procedure, the resulting values are more uncertain. The same ADE models were also fitted with equally good results to a hypothetical large-scale BTC derived by flux-averaging the responses from the individual monoliths. However, regardless of the form of the ADE used, the resulting parameter values for the large-scale transport (i.e., not only the dispersivity value that is expected to increase) were inconsistent with the corresponding parameter values obtained for the individual BTCs. This supports previous indications that ADE models may not be accurate for predicting large-scale transport in heterogeneous soil systems corresponding to e.g. the scale of an agricultural field or a grid element in a numerical catchment model because model parameters are not determinable from independent measurements on a scale corresponding to a practical manageable core size or to standard intrumentation.

Notizen: By employing the principle of superposition, we offer a semianalytical solution for a one-dimensional advective-dispersive solute transport equation under an arbitrary concentration boundary condition. The technique is applicable to many other existing analytical solutions of solute transport problems.

Notizen: An experimental study was conducted to assess how ion exchange processes, which occur during subsurface transport of oilfield brines, manifest themselves on graphical water quality diagrams. Concentrated brine soil column studies indicated sodium in the brine solution is able to exchange for calcium and magnesium on the soil, thereby retarding transport of sodium relative to the average ground-water velocity and resulting in the development of a “hardness halo” at the leading edge of the brine plume. In this zone, calcium and magnesium concentrations exceed the values for both the brine and the fresh ground water. The hardness halo manifests itself as a characteristic deviation away from the mixing lines on the Piper diagram. Initially, the hardness halo causes concentrations to plot left of the fresh-water end member in the cationic triangle. Chloride domination in oilfield brine causes concentrations to plot in the lower right corner of the anionic triangle almost immediately. After the hardness halo passes through the column, the sampling results show a characteristic pattern of movement parallel to the mixing line in the cation triangle or along the (decreasing) hardness axis of the upper diamond of the Piper diagram. The laboratory results were similar to those exhibited by monitoring well samples taken at a field site involving oilfield brine contamination. The results of this study show the Piper diagram to be potentially useful for early detection of brine contamination episodes.

Notizen: This note shows how to construct and perform a graphical type-curve analysis using a computer spreadsheet. Formulas are provided to generate the axis shifting behavior that is required for the graphical fit. Arbitrary match points are obtained by trial-and-error (or by closed form solution) for use in the calculation of aquifer hydraulic parameters. The analysis is illustrated using a leaky aquifer type curve and a confined aquifer type curve. Macro programming is not required, only data entry and the ability to use plotting features of a computer spreadsheet. The approach can be adapted for parameter estimation using any tabulated type curve.

Notizen: Chlorinated organic solvents introduced to unlined lagoons at an industrial waste-water treatment plant in the Inner Piedmont of South Carolina resulted in ground-water contamination of a fractured-rock aquifer. Part of the ground-water contamination discharges to Little Rocky Creek, downgradient from the waste-water treatment plant. Passive vapor collectors were buried in the bottom sediment of the creek to locate areas where ground water contaminated with volatile organic compounds was discharging to the creek. High concentrations of volatile organic compounds (VOCs) were found in passive vapor collectors in an area where VOCs were known to be discharging from ground water to surface water. This area was also a site where very low frequency electromagnetic anomalies (interpreted as fracture zones) intersected the creek or converged near the creek. The data show that passive vapor collectors in bottom sediment of Little Rocky Creek provided information on the location of fractures that were discharging contaminated ground water to surface water.

Notizen: Analytical equations are developed to model changes in porosity, specific surface area, and permeability caused by biomass accumulation in porous media. The proposed equations do not assume any specific pattern for microbial growth but instead are based on macroscopic estimates of average biomass concentrations. For porous media with a pore-size distribution index value (λ) equal to 3, the macroscopic model predictions of porosity, specific surface area, and permeability changes are in exact agreement with biofilm-model predictions. At other values of λ between 2 and 5, simulated porosity profiles are identical and relative specific surface area and permeability profiles show minor deviations. In comparison to biofilm-based models, the macroscopic models are relatively simple to implement and are computationally more efficient. Simulations of biologically reactive flow in a one-dimensional column show that the macroscopic and biofilm approach based transport codes predict almost identical porosity and permeability profiles. The macroscopic models are simple and useful tools for estimating changes in various porous media properties during bioremediation of contaminated aquifers.

Notizen: A method is presented for determining steady-state capture zones in three dimensions around horizontal drains and vertical wells in homogeneous, anisotropic aquifers in a uniform flow field. Equations are presented for determining drawdown and velocity vector components in three dimensions around drains and wells. Using these equations, a second-order Runge-Kutta particle tracking algorithm is applied to trace streamlines in three dimensions. By tracking a large number of particles, it is possible to determine areas where capture occurs and areas where particles escape capture. The resulting 3D capture zones are diagrammed as both 2D (section view) plots and 3D plots.

Notizen: A nonparametric statistical methodology based on kernel function estimation is developed for assessing the probability that a particular location in the aquifer has high or low conductivity using borehole information. The approach presented is an alternative to Indicator Kriging. Soils are classified through a binary indicator function defined as 0 for low and as 1 for a high conductivity soil. Estimates of the probability of occurrence of a high or low conductivity soil are made on a three-dimensional grid. Each such estimate is formed as a local weighted average of the indicator function values that lie within an averaging interval or bandwidth of the point of estimate. A different vertical bandwidth is chosen at each borehole log. Horizontal bandwidths are selected independently at each horizontal level. These bandwidths are chosen by cross validation. Observations closer to the point of estimate are weighted higher using a kernel or weight function. Unlike Kriging, the underlying stochastic process is not assumed to be stationary. An application using data from Lake Bonneville deposits in Davis County, Utah is presented.

Notizen: Vertical profiles of tritium and nitrate pore-water concentrations were determined to ∼8 m depth across two loess hillslopes. Mean recharge fluxes, estimated from chloride mass balance, are 5–10 times larger at the mid- and toe-slope positions than at the top-slope; the magnitudes of the values compare reasonably with results from other methods. The tritium and nitrate profiles exhibit multiple peaks which indicate that piston flow is not the sole flow process in this system. Results of a simple 1-D mixing model suggest that infiltration-exfiltration cycles in zones of plant root activity explain the shallow tritium peaks. Deeper peaks result from preferential vertical and/or lateral flow. The importance of these dispersive processes is underlined by great dilution of observed tritium concentrations, relative to expected concentrations assuming piston flow. In this setting, chloride is useful as a recharge estimator while tritium and nitrate serve as tracers of landscape-scale water movement.

Notizen: Enthalpy and entropy of volatilization from dilute aqueous solutions for 26 volatile organic compounds (VOCs) have been determined using Henry's Law values reported in published literature. Based on the linearity of van't Hoff plots, for the temperature ranges common in soils, the differences in heat capacities of volatilization for reactants and products are very small for the VOCs studied.When volatile solutes such as VOCs are present in soil water, soil-gas concentration often nearly is in equilibrium with the dissolved solute. Setchinow salting coefficients are linearly related to dissolved partial molar volumes for halogenated aliphatic compounds. Based in part on approximations from this linear relationship, equilibrium deviations from Henry's Law behavior for dilute VOC concentrations due to capillary tension or the presence of ionic solutes are small for common soil conditions.Since gas/water partitioning of VOCs if temperature-sensitive and since annual soil moisture and temperature patterns vary geographically in documented fashion, geographically specific temporal patterns in soil-gas VOC concentrations are predictable in vadose zones containing dissolved VOCs. A U.S. map depicting these general soil-moisture and temperature patterns is provided. Gas concentrations in vadose zones containing dissolved VOCs tend to increase with increasing temperature and decreasing moisture content due to equilibrium partitioning effects.Diagrams useful for understanding the results of soil-gas surveys and the efficacy of various remediation options are provided. The effect of bubbles in VOC water-sample vials on aqueous concentrations is shown to be very small. The effect of head-space volume of soil samples on estimated soil-gas concentrations can be large.

Notizen: Samana Cay, Bahamas, is a leading candidate among the sites proposed as the first landfall of Columbus in the New World. One main point of contention against this identification is that Samana lacks a feature matching the laguna observed by Columbus in the middle of his landfall island. However, this argument has failed to consider the paleogeographic aspects of the problem. A hydrogeologic computer model suggests the existence of a sizable surface-water feature in the medial interior of Samana Cay under conditions theorized to have been present when Columbus arrived in the Bahamas. This feature may correspond to the laguna described by Columbus.

Notizen: Case histories of LNAPL contaminated sites indicate that LNAPL thicknesses in monitoring wells exhibit certain characteristic behaviors when related to water-table fluctuations. This paper investigates these behaviors using established theories for fluid saturataions in three-phase (air-LNAPL-water) porous media systems. A semianalytical model is developed to predict the LNAPL thickness in a monitoring well considering the effects of saturation hysteresis and air/LNAPL entrapment. Given the total LNAPL volume in the soil profile and the historical sequence of water-table elevations, the model predicts LNAPL thicknesses, based on the assumption of a succession of hydrostatic pressure distributions. For example simulations, the model indicates that the LNAPL thickness in a monitoring well can exhibit complex behaviors that are strongly dependent on the previous saturation history. While many of these predicted behaviors are consistent with field observations, some are not. This suggests that certain aspects of current theories pertaining to three-phase fluid saturations warrant further technical evaluation.

Notizen: Combined optimization-simulation models for designing ground-water remediation systems generally focus on design strategies that use only one remedial technology, typically pumping. In practice, many field remediation programs use pumping along with one or more additional ground-water control technologies, such as drains, trenches, slurry walls, and low permeability caps. Simulated annealing provides a flexible optimization framework that can incorporate a number of different remedial technologies into the design process. Using simulated annealing, additional remedial technologies can be added to or subtracted from the optimization at any time. This flexibility can provide for remedial design evaluations that are more consistent with current field implementations. The use of simulated annealing is demonstrated by a series of hypothetical remediation design problems that incorporate four different remedial technologies. The computed optimal design solution depends on the relative costs of the remedial tools as specified by the cost function and on the effects that each tool has on the system behavior. A sensitivity analysis can reveal which costs are critical to the outcome of the optimization.

Notizen: Surfactant mobility in unsaturated soil will impact the effectiveness and efficiency of using these compounds for in situ environmental remediation above the water table. For this reason, transient unsaturated column tests were used to study the influence of boundary conditions and soil attributes on anionic surfactant transport. In these tests, aqueous surfactant solutions were injected into the inlet of horizontally mounted soil columns. Two commercial anionic surfactants were used, an alkyl ether sulfate (AES) and a linear alkylbenzene sulfonate (LAS).The overall study was divided into two parts. First, boundary condition effects including injected surfactant solution concentration, initial moisture content, and surfactant application rate were investigated. Increasing the injection solution concentration increased anionic surfactant mobility in the column while changes in the initial soil moisture content and surfactant application rate had no significant impact. Second, the impacts of soil attributes such as texture, dominant exchangeable cation, and resident organic matter were measured. With respect to texture, mobility was found to be greater in a sandy soil as compared with two loamy soils. Both surfactants, especially LAS, were found to be more mobile in a Na+ dominated soil rather than one dominated by Ca−2.The absence of soil organic matter increased LAS mobility.

Notizen: In volcanic areas, when two conditions are satisfied, there is a linear correlation between the range of negative self-potential (SP) anomalies and the thickness of the unsaturated zone measured in borings. The first condition is a high ratio between the resistivity of the unsaturated zone, and the resistivities of the substratum and the water-saturated zone. The second condition is the homogeneity of the unsaturated zone. From this relation, we develop the concept of a geophysical surface (SPS surface) calculated from SP and topographic data. Under these conditions, the SPS surface is both an equipotential SP surface and the interface between the unsaturated zone and the saturated medium below. Borehole logs for three field sites show that drainage courses and watersheds are located exactly on respectively the valleys and the ridge lines of the SPS surface.

Notizen: This paper presents an approach to regional hydrological balance where the number and integrated discharge of springs are used to estimate recharge. This technique is applied to Spain, where approximately two-thirds of the country has an inventory of spring lithology and discharge (17,000 springs). The data are used to extrapolate results to the entire region and are compared to independent methods of estimating recharge. This is an informative use of commonly available information and it could be applied to other regions with a similar data base.From this sample, a distribution of the spring flow volume contribution in Spain is estimated (a) according to flow spring discharge, (b) as a limit of a lognormal distribution, which in our sample is simplified in a potential formula a(x) = 24,101.x −0.91. In this way it is calculated that the total flow volume of the springs is 14,877 hm3/yr. The study does not take into account seepage (diffuse discharge) draining to seas, rivers, or lakes but only water at the spring source. The most permeable lithological groups considered are the source of 94.2% of the total flow supplied by the springs. Limestone is especially significant, contributing 66.2%. The net recharge of precipitation to ground water varies widely according to lithologies. It reaches to 20.3% in limestones and drops to less than 1% for quartzites, slates, and plutonic rocks.

Notizen: A series of ground-water flow and tracer experiments were performed on an undisturbed column of fractured clay-rich till, 0.5 m diameter by 0.5 m long, in a pressure-controlled cell. The measured hydraulic conductivity of the sample was 1.0 to 1.2 × 10–6 m/sec and the average hydraulic gradient during the tracer experiments ranged from 0.45 to 0.49. The experiments clearly show that ground-water flow and contaminant migration through the sample is primarily controlled by fractures and root holes. Tracer experiments using a solute (chloride), colloid-sized bacteriophage (PRD-1 and MS-2) and uncharged latex microspheres, indicated very fast transport rates of 4 to 360 m/day. These rates are similar to fracture flow velocities calculated on the basis of the measured bulk hydraulic conductivity of the column, and measured fracture spacing, using the cubic law for flow through parallel-walled fractures. Fracture aperture values calculated from the ground-water flow data (35 to 56 μxm) are of the same magnitude as values calculated from the breakthrough of tracers (13 to 120 μm). Aperture values calculated for fractures (1 to 94 μm) and root holes (2 to 188 μm), on the basis of measured immiscible creosote entry pressures, are also comparable with these values. The injected creosote, a DNAPL, penetrated most of the visible and a few invisible fractures and root holes, indicating that, for this till, fractures and root holes are important conduits for the transport of DNAPL's.

Notizen: Detailed vertical sampling is useful in aquifers where vertical mixing is limited and steep vertical gradients in chemical concentrations are expected. Samples can be collected at closely spaced vertical intervals from nested wells with short screened intervals. However, this approach may not be appropriate in all situations. An easy-to-construct and easy-to-install multiport sampling well to collect ground-water samples from closely spaced vertical intervals was developed and tested. The multiport sampling well was designed to sample ground water from surficial sand-and-gravel aquifers. The device consists of multiple stainless-steel tubes within a polyvinyl chloride (PVC) protective casing. The tubes protrude through the wall of the PVC casing at the desired sampling depths. A peristaltic pump is used to collect ground-water samples from the sampling ports. The difference in hydraulic head between any two sampling ports can be measured with a vacuum pump and a modified manometer. The usefulness and versatility of this multiport well design was demonstrated at an agricultural research site near Princeton, Minnesota where sampling ports were installed to a maximum depth of about 12 m below land surface. Tracer experiments were conducted using potassium bromide to document the degree to which short-circuiting occurred between sampling ports. Samples were successfully collected for analysis of major cations and anions, nutrients, selected herbicides, isotopes, dissolved gases, and chlorofluorcarbon concentrations.

Notizen: At the Fernald Environmental Management Project (FEMP) site in southwestern Ohio, sand and gravel lenses within till provide potential pathways for the flow of contamination into the underlying aquifer. These high-permeability lenses account for 22% of the volume of the till, have a complex arrangement, and are smaller in scale than the site. Even the relatively dense subsurface sampling program at the FEMP site is not adequate to determine facies interconnections with certainty. To delineate probable facies boundaries, a binary indicator random variable was used to represent the presence of high or low-permeability sediment. The 800 available lithologic logs that penetrate the till were coded with the binary system at 2 ft (0.6 m) intervals yielding 15,829 observations. These data were used to compute the declustered mean of indicator values in horizontal intervals, giving an estimate of the proportion of high-permeability sediment in each vertical zone. The areal correlation in specific zones was examined through indicator variograms, which had pronounced anisotropy. Three-dimensional indicator point kriging was used to produce maps of the probability of existence of high-permeability sediment. These maps were used in a preliminary analysis of sand body interconnectedness. Results indicate that portions of sand bodies are interconnected through the entire interval studied and that the areal extent of vertical interconnection is up to 1000 ft.

Notizen: A new method is presented to determine the transmissivity and the storage coefficient from recovery data measured after a pumping period of an aquifer test. Previously available methods can determine the storage coefficient during the pumping period only or under restrictive conditions. This method requires observations from a minimum of two points (e.g., the pumping well and an observation well). For each time during recovery, the drawdowns observed in the two wells are first plotted with regard to the distance from the pumping well centrum, giving an intercept A and a slope B for each pair of data. The plot of A values with regard to time allows to calculate the transmissivity value, while the plot of B values versus time gives the storage coefficient value. The method is applied to two sets of field data, and the results obtained are close to those obtained using the classical methods (Theis or Jacob) applied to the drawdown data obtained during the pumping period. This method well determines transmissivity and storativity from recovery data obtained at short times after the completion of pumping, i.e., for times shorter than those which can be used by the Cooper-Jacob approximation.

Notizen: Approaches to investigate possible recharge during a pumping test period are demonstrated by analyzing the pumping test data from the Nottingham aquifer, UK. The pumping lasted more than 200 days and the data for different observed periods are used to obtain aquifer parameters. If recharge is ignored, estimated transmissivities and storativities change progressively with the observation time. This indicates that a gradually added new source may be involved. Then the observed data in both pumping and recovery periods at one of the pumping sites are matched by the data calculated from the Theis equation. The match is very good except near the end of the recovery period. It shows that the real drawdown recovered more quickly than predicted by the model, indicating that the aquifer obtained extra recharge from other sources. The match between the observation and the model is improved by including a fixed-head boundary or leakage in the model. The recharge to the aquifer is estimated to be 19% and 34% of the pumpage at the end of pumping, depending on the method used. The real source of the additional recharge is not clear; it could be from the surface water in the unconfined area, the storage of the aquitard, the compaction of the aquitard, or a combination of the three. This requires further hydrogeological investigation.

Notizen: The Clarendon Basin of south-central Jamaica has been recognized for its productive sugar cane industry since the late 1800s. Much of its success is attributed to rich alluvial soils, a year-round tropical climate and copious supplies of good quality irrigation water from a karstic limestone aquifer of Tertiary age. This aquifer extends throughout the northern part of the basin, but ends abruptly at the South Coast Fault, an east west feature that forms the northern boundary of a deep graben filled with alluvial sediments. These alluvial sediments are the only source of water for the area south of the fault (the Vere Plain). However, the sediments also lap onto the limestone to the north of the fault (the Clarendon Plain) and provide a supplementary ground-water source. By the early 1970s nearly 200 wells supplied irrigation water for over 20,000 hectares of land. As development increased, the salinity of the ground water increased. Consequently, many wells were closed down and several sugar plantations were abandoned. In the study presented here, major ion (Ca, Mg, Na, K, HCO3, Cl, SO4, and NO3), minor ion (F, Br, and I), and environmental isotope (δ18O,δD) hydrochemistry is used to resolve the hydrodynamics of ground-water flow in the basin and identify the source and mode of emplacement of the saline water.Oxygen and hydrogen isotope data confirm that while the major well production areas are located in lowland coastal areas, recharge originates almost exclusively as rainfall in the cooler elevated parts of the basin above 750 m (asl). Subsurface conduit flow brings this water to the limestone well fields, and any excess water is able to cross the South Coast Fault to feed the alluvial aquifer of the Vere Plain. The thin alluvial aquifer of the Clarendon Plain also receives limestone water but this water does not enter entirely by subsurface means. Instead data suggest that while some of the water can be attributed to natural upward vertical leakage in the northwest of the Clarendon Plain, the remainder can be attributed to the seepage of irrigation water drawn, at least in part, from wells developed in the underlying limestone.Saline ground waters affect all the aquifers of the basin and several potential sources have been proposed. Major and minor ion data point to a sea-water source, and a sea-water wedge extending beneath the thick alluvial aquifer of the Vere Plain is an obvious candidate for the source of salinity observed in wells from this aquifer. Closer examination of the chemical data reveals, however, that wells in the limestone and alluvial aquifers to the north of the South Coast Fault do not derive their salinity from this source location, and instead draw sea water from the east and west along the relatively permeable South Coast Fault zone. This water can move to limestone wells directly; wells in the alluvium of the Clarendon Plain, however, receive most of the saline water indirectly via leakage of irrigation water pumped initially from the limestone. Sea water drawn along the fault may also be the primary source of salinity in the aquifer of the Vere Plain but this cannot be confirmed on the basis of hydrochemical evidence alone.

Notizen: The presence of dense nonaqueous phase liquids is one of the principal problems associated with current ground-water remediation efforts. Standard pump-and-treat methods are ineffective largely because of the low aqueous solubilities of DNAPL components. Surfactants can increase DNAPL solubility and hence have the potential for increasing the rate of DNAPL dissolution in pump-and-treat systems. To test the effectiveness of surfactants under field conditions, a controlled field test at Canadian Forces Base Borden was undertaken. Results indicate surfactant-enhanced aquifer remediation can rapidly remove the majority of DNAPL using simple modifications of a pump-and-treat system. As in all pump-and-treat systems, the efficiency is a function of the hydraulic conductivity. The persistence of high DNAPL concentrations at specific elevations within the aquifer throughout the test indicates that little vertical movement of DNAPL occurred as a result of the introduction of the surfactant. Since the test was stopped when small amounts of DNAPL still remained, the limit of removal was not investigated.

Notizen: A numerical code which utilizes the boundary element method (BEM) for solving steady-state ground-water flow problems is illustrated. The paper concentrates on accuracy in studying the situations which are generally considered to involve some mathematical difficulty, such as zoned domains and flux discontinuities. A numerical BEM code is proposed, the main feature of which involves accurately calculating flux discontinuities using a structure particularly flexible in multizoned domains. Two examples are reported, the results of which are comparable with those available in the literature.

Notizen: Ground-water chemistry data from wells are cokriged with ground conductivity measurements to quantitatively describe ground-water chemical quality at a site. The cokriged estimates are shown to be superior to both simple rescaling of ground conductivity by a linear regression model and to interpolation of ground-water chemistry data from wells using ordinary kriging. By extending the use of geophysical measurements in this way, significant cost savings in site assessment can be realized and the geophysics will have more data “worth.”

Notizen: For compound mixtures or compounds with two or more differently sorbing isomers which are not analytically distinguished, combined sorption parameters determined in the laboratory are dependent upon the ratio of different compounds or isomers and upon experimental methods and conditions. The purpose of this paper is to mathematically examine the effects of these factors on sorption parameters calculated from batch (shake-flask) and continuous flow column sorption studies of compound or isomer mixtures. The analysis in this paper helps explain the apparent anomalies between batch and column sorption results in previously published studies of Rhodamine WT (RWT). In batch reactors, the solid: liquid ratio, Rs, has a major effect on batch sorption results. As Rs decreases, partitioning coefficients determined from batch results approach those determined from column results, which is contrary to the trend that may be anticipated for single component analytes. A single column sorption coefficient or retardation factor for multiple constituents does not accurately describe the transport of the individual compounds. The implications of the effects of experimental methods suggest that sorption parameters determined from batch studies for compound or isomer mixtures (e.g., BTEX, combined xylenes, and others) should be interpreted with care. Significant errors in prediction and description of contaminant transport can result if the presence of multiple compounds or isomers is not recognized or if batch or column data for compound or isomer mixtures are misinterpreted.

Notizen: An analysis was conducted of multidimensional subsurface moisture flow in a hypothetical low-level radioactive waste disposal facility. The key design feature examined in the analysis was a sloping sand/gravel capillary barrier designed to route natural infiltration around a concrete vault. Three barrier slopes (1:25, 1:10, and 1:5) and three sand/gravel property combinations were considered. The slopes and material property combinations were selected to represent a range in barrier effectiveness. The porous media flow code used for this analysis was VAM3DCG, a three-dimensional, finite-element code which was able to use nonorthogonal grid discretizations and employed robust, efficient numerical techniques. Three-dimensional modeling demonstrated that flow in the hypothetical design exhibited cross-slope flow because of the pressure gradient produced in the third, cross-slope dimension. Barrier effectiveness was shown to be highly sensitive to the sand/ gravel material properties. Barrier slope was less important, especially for the effective material combinations. The presence of three-dimensional flow could be important in a performance assessment if the quantity of water predicted to breach the capillary barrier by a two-dimensional model were different from that predicted by a three-dimensional model. Comparative modeling demonstrated that a two-dimensional analysis resulted in underestimation of barrier effectiveness. For the considered design, two-dimensional modeling is a conservative, yet reasonable, approach in a performance assessment application.

Notizen: Laguna Asososca, a large ground-water-fed volcanic crater, is an important source of municipal water supply for the city of Managua. In 1990, after 65 years of pumping at increasing rates from the crater, the gradient between the Laguna and the highly contaminated Lake Managua had potentially reversed, leading to a scenario where the Laguna was possibly drawing in contaminated ground water from Lake Managua and/or a highly contaminated aquifer below an industrial area located between the Laguna and Lake Managua. A drilling and sampling program undertaken between 1990 and 1992 found: (1) four synthetic organic chemicals in the Laguna (methylene chloride, chloroform, 1,3-dichlorobenzene and 1,4-dichlorobenzene), (2) numerous other synthetic organic chemicals near Laguna Asososca in the ground water below the industrial area, and (3) no evidence of Laguna Asososca drawing water from Lake Managua. It appears that the Laguna Asososca capture zone extended into the industrial area but not as far as Lake Managua. Ground-water flow modeling of the regional ground-water flow system was consistent with the field interpretation. Estimates of the relative mobilities of the synthetic organic chemicals indicated that the chemicals found in the water of Laguna Asososca likely represented the mobile leading edge of a contaminant plume emanating from the industrial area. The simplest and most effective solution to mitigate contamination of Laguna Asososca is to maintain its water level above that of Lake Managua by reducing its pumpage to about 50% of the 1990 rate.

Notizen: Cutoff walls are becoming increasingly attractive options for the control of solute migration from long-term sources of contamination. The main advantage of low permeability enclosures is that they restrict advective transport of solutes away from the source. However, with high concentration source zones surrounded by cutoff walls, there exists the potential for notable mass fluxes outward due to diffusive transport. This paper shows, through the use of the steady-state flux equations, that there is an optimal range of hydraulic conductivities for barrier materials which permit the outward diffusive flux to be counter balanced by an inward advective and dispersive flux. This concept of designing optimum contaminant containment using an inward advective flux to counter the outward diffusive flux is valid for sealable joint sheet pile walls, bentonite-slurry walls and clay liners, but not synthetic membrane materials with extremely low hydraulic conductivities. The effective diffusion coefficient for the common chlorinated organic solvents such as TCE in water-saturated clayey materials is approximately 1 × 10−6 cm2/sec, resulting in an optimum hydraulic conductivity ranging from 1 × 10−6 to 1 × 10−8 cm/sec. This range in hydraulic conductivity is within the range of common barrier materials but not the lowest achievable. The steady-state concentration profile in a slurry cutoff wall can result in a substantial amount of contaminant mass stored within the wall which will need to be considered over the long term or dealt with during site remediation. Large inward advective fluxes reduce the total chemical mass stored within the low permeability barrier material.

Notizen: Flow-through microcosms were constructed to conduct ecological experiments on aquifer organisms. The two 5-channel microcosms were simple to construct, were fed by an artesian spring, and maintained close to in situ temperature and O2 concentrations. They were used to test relative microbial colonization of three substrate sizes: silt (0.063 mm), sand (0.9 mm), and gravel (3 mm). After 96 days of incubation, O2 microelectrode measurements revealed the lowest O2 tension in the silt, the highest in the gravel, and intermediate values in the sand. Microbial activity (3[H]-thymidine incorporation) was greatest in the gravel, followed by sand and then silt. Denitrification was greatest in the silt, followed by sand and then gravel. Microbial activity may be greatest with the largest particle size because of increased water exchange through pores, and denitrification may be greatest with the smallest particle sizes because of the occurrence of anaerobic microzones.

Notizen: On March 8 and 9, 1992, a thermal-infrared-multispectral scanner (TIMS) was flown over two military ordnance disposal facilities at the Edgewood Area of Aberdeen Proving Ground, Maryland. The data, collected by the National Aeronautics and Space Administration, in cooperation with the U.S. Army and the U.S. Geological Survey, were used to locate ground-water discharge zones in surface water. The images from the flight show areas where ground-water discharge is concentrated, as well as areas of diffuse discharge. Concentrated discharge is predominant in isolated or nearly isolated ponds and creeks in the study area. Diffuse discharge is found near parts of the shoreline where the study area meets the surrounding estuaries of the Chesapeake Bay and the Gunpowder River. The average temperature for surface water, measured directly in the field, and the average temperature, calculated from atmospherically corrected TIMS images, was 10.6° C (Celsius) at the first of two sites.Potentiometric surface maps of both field sites show discharge toward the nontidal marshes, the estuaries which surround the field sites, and creeks which drain into the estuaries. The average measured temperature of ground water at both sites was 10.7° C. The calculated temperature from the TIMS imagery at both sites where ground-water discharge is concentrated within a surface-water body is 10.4° C. In the estuaries which surround the field sites, field measurements of temperature were made resulting in an average temperature of 9.0° C. The average calculated TIMS temperature from the estuaries was 9.3° C. Along the shoreline at the first site and within 40 to 80 meters of the western and southern shores of the second site, water was 1° to 2° C warmer than water more than 80 meters away. This pattern of warmer water grading to cooler water in an offshore direction could result from diffuse ground-water discharge. Tonal differences in the TIMS imagery could indicate changes in surface-water temperatures. These tonal differences can be interpreted to delineate the location and extent of ground-water discharge to bodies of surface water.

Notizen: The slug test is one of the most commonly used field methods for obtaining in situ estimates of hydraulic conductivity. Despite its prevalence, this method has received criticism from many quarters in the ground-water community. This criticism emphasizes the poor quality of the estimated parameters, a condition that is primarily a product of the somewhat casual approach that is often employed in slug tests. Recently, the Kansas Geological Survey (KGS) has pursued research directed at improving methods for the performance and analysis of slug tests. Based on extensive theoretical and field research, a series of guidelines have been proposed that should enable the quality of parameter estimates to be improved. The most significant of these guidelines are: (1) three or more slug tests should be performed at each well during a given test period; (2) two or more different initial displacements (H0) should be used at each well during a test period; (3) the method used to initiate a test should enable the slug to be introduced in a near-instantaneous manner and should allow a good estimate of Ho to be obtained; (4) data-acquisition equipment that enables a large quantity of high quality data to be collected should be employed; (5) if an estimate of the storage parameter is needed, an observation well other than the test well should be employed; (6) the method chosen for analysis of the slug-test data should be appropriate for site conditions; (7) use of pre-and post-analysis plots should be an integral component of the analysis procedure, and (8) appropriate well construction parameters should be employed. Data from slug tests performed at a number of KGS field sites demonstrate the importance of these guidelines.

Notizen: It is a general belief that useful estimates of total dissolved solids concentrations of ground water cannot be made from borehole geophysical logs. A case study of estimating total dissolved solids concentration of ground water in the local area using the ratio method yielded estimates with an average error of less than 25 percent. The results do not support the hypothesis that useful estimates of total dissolved solids concentration cannot be made from borehole geophysical logs.The case study included a comparison of estimates of total dissolved solids concentration utilizing a resistivity of the mud input versus using resistivity of the mud filtrate input. Estimates made using resistivity of mud had a correlation coefficient of 0.97 whereas estimates using resistivity of mud filtrate had a correlation coefficient of only 0.27. The results from the case study suggest that at least in some cases the resistivity of the mud (Rm) may produce a better estimate of the resistivity of water (Rw) in the fully flushed zone than an estimate using the resistivity of the mud filtrate Rmf.The ratio method can be easily used to estimate ground-water resistivity and total dissolved solids concentration of the formation water based only on data from resistivity logs. The advantage of the method is that data on porosity, cementation exponent, temperature, and volume of clay are not required. The method, which has been used by the oil industry to crudely estimate water resistivity, is based in part on the ratio of the resistivity of a fully water-saturated formation to the resistivity of the fully flushed zone adjacent to the annulus in a mud-filled borehole. The method, which is very robust, requires only an estimate of the resistivity of a fully water-saturated formation from a deep looking induction or resistivity log, an estimate of the resistivity of the fully flushed zone from a microresistivity or short normal log, and a measurement of resistivity of the mud or mud filtrate and its temperature.

Notizen: Surface application offers an inexpensive, noninvasive alternative to injection wells and infiltration galleries for in situ ground-water bioreniediation applications. The technology employs artificial recharge to create favorable hydraulic conditions for mixing and vertical transport of supplemental electron acceptor and nutrients. A test plot infdtration test and a conservative tracer test at Eglin Air Force Base, FL confirmed the potential for transporting solutes to the subsurface via recharging water. These experiments demonstrated both the mounding hydraulics and vertical solute transport that occurs in response to surface application. Modeling provided quantitative estimates of site-specific hydrogeologic and transport parameters. Experimental results also indicated that dilution may be a dominant attenuation mechanism associated with high surface application rates. The tests also served as the basis for the design of a pilot scale surface application system for delivery of nitrate to bioremediate a JP-4 contaminated aquifer at the Eglin site. Models calibrated to data from the infiltration experiment were scaled up for design of the pilot scale surface application system. Preliminary tracer results from the pilot scale experiment confirm that surface application can adequately deliver chemicals to the subsurface.

Notizen: The results of a field experiment comparing water-quality constituents, specific conductance, geophysical measurements, and well-bore hydraulics in two long-screen wells and adjacent vertical clusters of short-screen wells show bias in ground-water data caused by well-bore flow in long-screen wells. The well screen acts as a conduit for vertical flow because it connects zones of different head and transmissivity, even in a relatively homogeneous, unconfined, sand and gravel aquifer where such zones are almost indistinguishable. Flow in the well bore redistributes water and solutes in the aquifer adjacent to the well, increasing the risk of bias in water-quality samples, failure of plume detection, and cross-contamination of the aquifer. At one site, downward flow from a contaminated zone redistributes solutes over the entire length of the long-screen well. At another site, upward flow from an uncontaminated zone masks the presence of a road salt plume.Borehole induction logs, conducted in a fully penetrating short-screen well, can provide a profile of solutes in the aquifer that is not attainable in long-screen wells. In this study, the induction-log profiles show close correlation with data from analyses of water-quality samples from the short-screen wells; however, both of these data sets differ markedly from the biased water-quality samples from the long-screen wells. Therefore, use of induction logs in fully cased wells for plume detection and accurate placement of short-screen wells is a viable alternative to use of long screen wells for water-quality sampling.

Notizen: Efficient allocation of remediation resources is a critical need throughout the nation. Economic risk-cost-benefit analysis is an important tool for meeting this need. This paper provides site engineers, geologists, and managers with a conceptual understanding of economic risk-cost-benefit analysis and shows how it can be applied, even in situations where existing data are sparse or poor in quality. An example analysis is applied to the remediation of radioactive waste at Oak Ridge National Laboratory, in which the cost-effectiveness is compared for two remediation alternatives: containment of the waste or monitoring only. A data-worth analysis is also carried out to estimate the maximum justifiable exploration budget and the cost-effectiveness of two proposed data collection programs. Results indicate that the methodology has potential in making robust remediation decisions regarding certain types of questions.

Notizen: In situ air sparging is used to remediate petroleum fuels and chlorinated solvents present as submerged contaminant source /ones and dissolved contaminant plumes, or to provide barriers to dissolved contaminant plume migration. Contaminant removal occurs through a combination of volatilization and aerobic biodegradation: thus, the performance at any given site depends on the contaminant and oxygen mass transfer rates induced by the air injection. It has been hypothesized that these rates are sensitive to changes in process flow conditions and site lithology, but no data is available to identify trends or the magnitude of the changes. In this work, oxygenation rates were measured for a range of air injection rates, ground water flow rates, and pulsing frequencies using a laboratory-scale two-dimensional physical model constructed to simulate a homogeneous hydrogeologic setting. Experiments were conducted with water having low chemical and biochemical oxygen demand. Results suggest the following: that there is an optimum air injection rate: advective How of ground water can be a significant factor when ground water velocities are 〉 0.3 m/d: and pulsing the air injection had little effect on the oxygenation rate relative lo the continuous air injection case.

Notizen: Cryogenic drilling is a technique developed at the University of California (UC), Berkeley, for drilling in unstable sediments of environmental monitoring, for characterizing, and for remediation wells, The method uses standard air rotary drilling techniques, but with cold nitrogen rather than ambient air as the circulating fluid in order to freeze and stabilize the borehole wall. Several laboratory and full-scale field tests have been performed. A.52-foot-deep (16 m) soil boring and 24 foot (7 m) monitoring well have been drilled as part of the Lawrence Berkeley Laboratory Site Characterization Project. Continued testing and refinement of the equipment and operational method are in progress. The method has been proposed for use as part of the Department of Energy (DOE) weapons site cleanup at locations with unstable sediments such as Hanford, Sandia, and Idaho National Engineering Laboratory (INEL).

Notizen: Laboratory 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.

Notizen: Two methods were used to approximate site-specific biodegradation rates of monoaromatic hydrocarbons (benzene, toluene, ethylbenzene, and xylenes [BTEX]) dissolved in ground water. Both use data from monitoring wells and the hydrologic properties of the quifer to estimate a biodegradation rate constant that can be used in ground water solute fate and transport models. The first method uses a biologically recalcitrant tracer in the ground water associated with the hydrocarbon plume to normalize changes in concentration of BTEX under anaerobic conditions; attenuation of the tracer is attributed to dilution, sorption, and/or volatilization. Attenuation of BTEX in excess of the attenuation of the tracer is attributed to biodegradation, although other processes may affect the observed rate. The second method assumes that the plume has evolved to a dynamic steady-state equilibrium. A one-dimensional analytical solution to the advection-dispersion equation is used to extract the rate of attenuation that would be necessary to produce a steady-state plume of the configuration found at the site. Attention is attributed largely to biodegradation bacause the analytical solution removes the effects of sorption and dispersion and volatilization is assumed to be minimal.Neither method fully accounts for the effects of continuing dissolution of BTEX in the source area or nonlinear sorption. Therefore, the rats cannot be attributed fully to biodegradation, but still are useful for ground water contaminant fate and transport modeling. The methods were applied to a data set from a JP-4 jet fuel spill at Hill Air Force Base, Utah. In estimats along two seprate flow paths, natural attenuation rates for BTEX ranged form 0.006 to 0.038 day−1, with most rates near 0.02 day−1. The rate for benzene ranged from 0.025 to 0.038 day−1. The rates of attenuation of individual BTEX compounds as estimated by the two methods were in close aggrement. For an individual compound, the rate estimated using the second method was at most 36 percent greater than, but usually within 20 percent of, the rate estimated using the first method, suggesting that intrinsic bioremediation was the dominant process that attenuated BTEX.

Notizen: The goal of this study was the cleanup of residual solvents in the saturated zone using an in situ biochemical treatment. Perchloroethylene (PCE) was chosen as a model compound because it is the most commonly found organic ground water contaminant. A mixture of vitamin B12 with titanium citrate was pumped as the remedial solution through a column containing 100 μL of PCE residual. The rate of reaction was found to be first order with respect 10 the concentration of PCE and to the concentration of vitamin B2. At 10 ppm B12, more than 85 percent PCM was degraded to trichloroelhylene (TCE) and dichloroelhylene (DCE) in two hours. The presence of low to moderate concentrations of organic carbon had no significant effect on the reaction. Vitamin B12 reduced by titanium citrate was found lo be compatible with the survival of anaerobic bacteria. The four major advantages of the biochemical system over the use of anaerobic bacteria are that (1) the rate is faster: (2) there is no need for the careful balance of nutrients or the addition of an extraneous carbon source: (3) there is no restriction in the concentration range of the compound to be treated; and (4) the remedial solution is mobile, even in the presence of organic carbon.

Notizen: Hydrologic investigations typically involve the collection of water level measurements at discrete points in space and time. The high cost of commercial electronic recorders can be a burden. We have developed an inexpensive (∼$200) electronic water level recorder consisting of a Motorola microcontroller, a clock, memory, pressure transducers, and associated circuitry. The instrument is powered by a 6-V battery. These devices, each capable of monitoring up to eight channels of analog input, are presently providing continuous monitoring of nested piezometers, tide gauges, and rain gauges in hydrologic studies at the Savannah River site and the North Inlet (South Carolina) Long-Term Ecological Research (LTER) site. The instruments can be custom tailored to record water levels at any specified time interval, or whenever the water level changes by a specified amount, and can store up to 32,000 water level observations. These instruments have been used to conduct slug tests and can be configured to monitor observation wells for pumping tests. Simplicity of construction and availability of components offer hydrologists an inexpensive but reliable method of water level recording. Several examples of the use of this instrumentation in diverse hydrologic settings are described.

Notizen: Based on aquifer performance tests, 13 out of 15 wells situated at the Mixed Waste Disposal (MWD) area located at the Savannah River site. South Carolina, exhibited high skin factors and low well efficiencies indicative of severely damaged wells. The use of damaged wells in aquifer testing can lead to inaccurate determinations of aquifer properties, and such wells are unusable in future remediation programs. Moreover, damaged wells can go dry during purging, thus compromising sample collection. Pump tests, chemical analyses, and biological investigations revealed that the poor well performance at MWD was attributable to calcite precipitation on the well screen and drilling mud in the filter pack. The calcite problem resulted from improper well installation, and the drilling mud in the filter pack was due to inadequate well development.Experimental rehabilitation procedures employed on two wells, MWD 5A and 1A, included acidification, swabbing, introduction of surfactants, and surging. Treatment of the wells substantially improved well yields, skin factors, and well efficiencies. Moreover, well rehabilitation was determined to be a reasonable alternative to drilling new wells at the MWD wellfield.

Notizen: Depth-discrete aquifer in formal ion was obtained using recently developed adaptations and improvements to conventional characterization techniques. These improvements included running neutron porosity and hulk density geophysical logging tools through a cased hole, performing an enhanced point-dilution tracer test for monitoring tracer concentration as a function of Lime and depth, and using pressure derivatives for diagnostic and quantitative analysis of constant rate discharge lest data. Data results from the use of these techniques were used to develop a conceptual model of a heterogeneous aquifer. Depth-discrete aquifer information was required to effectively design field-scale deployment and monitoring of an in situ bioremediation technology.Geophysical logging and point-dilution tracer test results provided the relative distribution of porosity and horizontal hydraulic conductivity, respectively, with depth and correlated well. Hydraulic pumping tests were conducted to estimate mean values for transmissivity and effective hydraulic conductivity, Tracer lest and geophysical logging results indicated that ground water flow was predominant in the upper approximate 10 feet of the aquifer investigated. These results were used to delineate a more representative interval thickness for estimating effective hydraulic conductivity. Hydraulic conductivity, calculated using this representative interval, was estimated lo be 73 ft/d, approximately three limes higher than that calculated using the full length of the screened test interval.

Notizen: A preliminary field performance evaluation of in situ bioremediation of a contaminated aquifer at the Libby, Montana, Superfund site, a former wood preserving site, was conducted for the Bioremediation Field Initiative sponsored by the U.S. Environmental Protection Agency (U.S. EPA). The current approach for site remediation involves injecting oxygen and nutrients into the aquifer to stimulate microbial degradation of target compounds that include polycyclic aromatic hydrocarbons and pentachlorophenol. The preliminary field evaluation determined that, in addition to the oxygen demand associated with the microbial oxidation of the organic contamination, uncontaminated aquifer sediments at the site are naturally reduced and also exert a significant oxygen demand. This conclusion is supported by three types of information: (1) analyses of ground water samples; (2) results from a field-scale tracer test; and (3) results of laboratory evaluations of oxygen use by reduced aquifer sediment samples. An estimate of the cost of supplying hydrogen peroxide to satisfy the oxygen demand of the uncontaminated reduced sediments is provided to demonstrate that the additional cost of oxidizing the reduced sediments could be significant. The presence of naturally occurring reduced sediments at a contamination site should be considered in the design of subsurface oxidant delivery systems.

Notizen: An in situ microcosm (ISM) consists of a stainless steel cylinder isolating about 2 L of the aquifer and is equipped with valves allowing for loading and sampling from the ground surface. During the last five years, this technique has been used frequently to study the degradation of organic chemicals in polluted and pristine aquifers representing different redox environments. The ISM technique has great potential for providing field-relevant degradation potentials and rate constants, but care must be taken in using the equipment and interpreting the results. This paper provides details concerning the installation and operation of an ISM and presents experiences concerning data interpretation and monitoring of redox conditions.

Notizen: Three methods (multiplicative, additive, and allometric) were developed to extrapolate physiological model parameter distributions across species, specifically from rats to humans. In the multiplicative approach, the rat model parameters are multiplied by the ratio of the mean values between humans and rats. Additive scaling of the distributions is denned by adding the difference between the average human value and the average rat value to each rat value. Finally, allometric scaling relies on established extrapolation relationships using power functions of body weight. A physiologically-based pharmacokinetic model was fitted independently to rat and human benzene disposition data. Human model parameters obtained by extrapolation and by fitting were used to predict the total bone marrow exposure to benzene and the quantity of metabolites produced in bone marrow. We found that extrapolations poorly predict the human data relative to the human model. In addition, the prediction performance depends largely on the quantity of interest. The extrapolated models underpredict bone marrow exposure to benzene relative to the human model. Yet, predictions of the quantity of metabolite produced in bone marrow are closer to the human model predictions. These results indicate that the multiplicative and allometric techniques were able to extrapolate the model parameter distributions, but also that rats do not provide a good kinetic model of benzene disposition in humans.

Notizen: Road traffic accident involvement rates show clear age and gender differences which may in part be accounted for by differences in risk perception and perceptions of driving competence. The present study extends and replicates that of Matthews and Moran (1986). Young (18–30 years) and older (45–60 years) male and female drivers responded to a questionnaire on perceived accident risk and driving competence (judgment and skill) with respect to themselves and four target groups, and also rated a series of videotaped driving sequences with respect to likelihood of accident occurrence and perceived driving competence. Results showed that effects of rater characteristics were generally confined to the questionnaire. Younger males were perceived as most likely to experience an accident and were judged to be lower than other groups in driving competence. Younger groups showed little bias against older groups and vice versa, but gender-related bias was apparent. The findings of Matthews and Moran were generally confirmed. The results are discussed with reference to four main issues: (1) demographic bias effects—which are generally weak; (2) stereotyping on the basis of gender and/or age of driver; (3) group-specific bias; (4) self-appraisal bias.

Notizen: Public reaction to chemical technologies has included a perception that chemical exposure is a contributor to human health problems. Though these perceptions sometimes correspond with technical assessments of chemical risks, at other times they do not. This paper presents a descriptive model of the relationship between perception of one's health status and a set of factors that are used by individuals as part of causal reasoning about the meaning of somatic change. The model incorporates both personal events and experiences associated with somatic change (e.g., stress, sensory cues), as well as aspects of an individual's social context in which perceptions of chemical risks serve as a powerful framework for attributing meaning to chemical exposure. Within this model, the causal inferences that people make about the effects of chemical exposure on symptomatology are viewed as part of a natural, psychological adaptation in which the individual seeks to decrease their uncertainty about the factors or conditions that cause them to feel as they do.

Notizen: There are a number of sources of variability in food consumption patterns and residue levels of a particular chemical (e.g., pesticide, food additive) in commodities that lead to an expected high level of variability in dietary exposures across a population. This paper focuses on examples of consumption pattern survey data for specific commodities, namely that for wine and grape juice, and demonstrates how such data might be analyzed in preparation for performing stochastic analyses of dietary exposure. Data from the NIAAA/NHIS wine consumption survey were subset for gender and age group and, with matched body weight data from the survey database, were used to define empirically-based percentile estimates for wine intake (μl wine/kg body weight) for the strata of interest. The data for these two subpopulations were analyzed to estimate 14-day consumption distributional statistics and distributions for only those days on which wine was consumed. Data subsets for all wine-consuming adults and wine-consuming females ages 18 through 45, were determined to fit a lognormal distribution (R2= 0.99 for both datasets). Market share data were incorporated into estimation of chronic exposures to hypothetical chemical residues in imported table wine. As a separate example, treatment of grape juice consumption data for females, ages 18–40, as a simple lognormal distribution resulted in a significant underestimation of intake, and thus exposure, because the actual distribution is a mixture (i.e., multiple subpopulations of grape juice consumers exist in the parent distribution). Thus, deriving dietary intake statistics from food consumption survey data requires careful analysis of the underlying empirical distributions.

Notizen: Book review in this article Our Stolen Future: Are We Threatening Our Fertility, Intelligence, and Survival? A Scientific Detective Story By Theo Colborn, Dianne Dumanoski, and John Myers

Notizen: Biologic data on benzene metabolite doses, cytotoxicity, and genotoxicity often show that these effects do not vary directly with cumulative benzene exposure (i.e., concentration times time, or c×t). To examine the effect of an alternate exposure metric, we analyzed cell-type specific leukemia mortality in Pliofilm workers. The work history of each Pliofilm worker was used to define each worker's maximally exposed job/department combination over time and the associated long-term average concentration associated with the maximally exposed job (LTA-MEJ). Using this measure, in conjunction with four job exposure estimates, we calculated SMRs for groups of workers with increasing LTA-MEJs. The analyses suggest that a critical concentration of benzene exposure must be reached in order for the risk of leukemia or, more specifically, AMML to be expressed. The minimum concentration is between 20 and 60 ppm depending on the exposure estimate and endpoint (all leukemias or AMMLs only). We believe these analyses are a useful adjunct to previous analyses of the Pliofilm data. They suggests that (a) AMML risk is shown only above a critical concentration of benzene exposure, measured as a long-term average and experienced for years, (b) the critical concentration is between 50 and 60 ppm when using a median exposure estimate derived from three previous exposure assessments, and is between 20 and 25 ppm using the lowest exposure estimates, and (c) risks for total leukemia are driven by risks for AMML, suggesting that AMML is the cell type related to benzene exposure.

Notizen: The current approach to health risk assessment of toxic waste sites in the U.S. may lead to considerable expenditure of resources without any meaningful reduction in population exposure. Risk assessment methods used generally ignore background exposures and consider only incremental risk estimates for maximally exposed individuals. Such risk estimates do not address true public health risks to which background exposures also contribute. The purpose of this paper is to recommend a new approach to risk assessment and risk management concerning toxic waste sites. Under this new approach, which we have called public health risk assessment, chemical substances would be classified into a level of concern based on the potential health risks associated with typical national and regional background exposures. Site assessment would then be based on the level of concern for the particular pollutants involved and the potential contribution of site contaminants to typical background human exposures. While various problems can be foreseen with this approach, the key advantage is that resources would be allocated to reduce the most important sources of human exposure, and site remediation decisions could be simplified by focussing on exposure assessment rather than questionable risk extrapolations.

Notizen: In several European countries efforts are undertaken, in particular with regard to fixed industrial installations and transport of dangerous substances, to quantify the “societal risk” (SR) of accidents that may cause more than one victim at a time. This article explores the nature of such efforts. SR-models are essentially ways to structure the distribution of potential social costs of decisions about hazardous activities (e.g., costs of risk reduction, of land use forgone). First, the various ways to describe SR quantitatively, and to set limits to SR will be presented in short. Next, using a scheme developed by Fischhoff and colleagues, the various approaches will be placed in broad categories of reaching acceptable risk decisions: bootstrapping, formal analysis, and professional judgment. Each of the three categories offers a particular appreciation of the risks as ‘external costs’. This has important political implications. In the discussion it is argued that local SR-limits, by the very nature of SR, should be set in a way that creates consistency with any potential supra-local interests involved. Second, particular attention is paid to the validity of claims that SR-limits should reflect a strong risk aversion.

Notizen: The exposure of employees of different contracting firms to chemical pollutants was assessed during the five-week biennial maintenance shut-down of an isocyanate (TDI) synthesis plant. This assessment was mainly based on personal sampling, but work-related constraints occasionally required that area samples be used instead. Many tasks were carried out during the shut-down procedure (dismantling of reactors, installation of insulation, refection of kilns, cleaning, painting, electricity, etc.), thereby causing the employees of the contracting firms to be exposed to different kinds of pollutants, including products used or manufactured in the process (solvents, TDI and its synthesis intermediates), and products specific to the contractors’ activity (welding fumes, crystalline silica, mineral fibers of heat insulation). The highest level of exposure (mainly to TDI) was found for the mechanical engineering activities undertaken during the dismantling of reactors and for cleaning activities. It was demonstrated that there was much variability in day-to-day exposure levels, and occasionally in the exposure levels encountered during a given shift. Cases of concomitant exposure to TDI (mainly short-term exposures) and other pollutants due to simultaneous activities from different tasks in the same area (co-activity) were also observed. Both the need for, and limitations of personal protective equipment (mainly respiratory) are stressed. Special emphasis is put on the responsibility of the owner of the facilities in helping the contractors in the organization of a health and safety policy.

Notizen: Characterizing the dose-effect relationship and estimating acceptable exposure levels are the primary goals of quantitative risk assessment. A semiparametric approach is proposed for risk assessment with continuously measured or quantitative outcomes which has advantages over existing methods by requiring fewer assumptions. The approach is based on pairwise ranking between the response values in the control group and those in the exposed groups. The work generalizes the rank-based Wilcoxon-Mann-Whitney test, which for the two-group comparison is effectively a test of whether a response from the control group is different from (larger than) a response in an exposed group. We develop a regression framework that naturally extends this metric to model the dose effect in terms of a risk function. Parameters of the regression model can be estimated with standard software. However, inference requires an additional step to estimate the variance structure of the estimated parameters. An effective dose (ED) and associated lower confidence limit (LED) are easily calculated. The method is supported by a simulation study and is illustrated with a study on the effects of aconiazide. The method offers flexible modeling of the dose effect, and since it is rank-based, it is more resistant to outliers, nonconstant variance, and other departures from normality than previously described approaches.

Notizen: The Oregon Department of Environmental Quality has developed a Cross-Media Comparative Risk Assessment model to address certain regulatory concerns. The model generates a Human and Ecological Risk Index for a facility releasing toxins into the environment. The risk indices are based on chemical fate and transport predictions, toxicity, population density, and ecological sensitive areas. The model can be used to rank facilities for inspection or as a tool to assess the progress of pollution prevention programs. Regulatory permitting departments can use the model to address the cross-media transfer of pollutants from one environmental compartment to another. The versatility of the model allows adaptation to each specific users needs.

Notizen: Risk assessment for airborne carcinogens is often limited by a lack of inhalation bioassay data. While extrapolation from oral-based cancer potency factors may be possible for some agents, this is not considered feasible for contact site carcinogens. The change in contact sites (oral: g.i. tract; inhalation: respiratory tract) when switching dose routes leads to possible differences in tissue sensitivity as well as chemical delivery. This research evaluates the feasibility to extrapolate across dose routes for a contact site carcinogen through a case study with epichlorohydrin (EPI). EPI cancer potency at contact sites is compared across three bioassays involving different dose routes (gavage, drinking water, inhalation) through the use of dosimetry models to adjust for EPI delivery to contact sites. Results indicate a large disparity (two orders of magnitude) in potency across the three routes of administration when expressed as the externally applied dose. However, when expressed as peak delivered dose, inhalation and oral potency estimates are similar and overall, the three potency estimates are within a factor of seven. The results suggest that contact site response to EPI is more dependent upon the rate than the route of delivery, with peak concentration the best way to extrapolate across dose routes. These results cannot be projected to other carcinogens without further study.

Notizen: Quantitative knowledge about health damage due to air pollution is an important element in analyses of cost-effective abatement strategies, and is also essential for setting Air Quality Standards. Epidemiological studies, in spite of the numerous problems connected to them, provide a reasonable basis for exposure-response functions in this context. On the basis of a literature review, exposure-response functions that relate ambient air pollutant concentrations to the frequency of various health effects are recommended in this paper. The following end-points were examined: Acute and chronic respiratory symptoms in children and adults, crude mortality, and lung cancer incidence. The effects are attributed to one indicator component, which in most cases is particles. A calculation procedure is suggested which makes it possible to estimate excess annual symptom-days for short-term effects using the annual average concentration.

Notizen: The methods currently used to evaluate the risk of developmental defects in humans from exposure to potential toxic agents do not reflect biological processes in extrapolating estimated risks to low doses and from test species to humans. We develop a mathematical model to describe aspects of the dynamic process of organogenesis, based on branching process models of cell kinetics. The biological information that can be incorporated into the model includes timing and rates of dynamic cell processes such as differentiation, migration, growth, and replication. The dose-response models produced can explain patterns of malformation rates as a function of both dose and time of exposure, resulting in improvements in risk assessment and understanding of the underlying mechanistic processes. To illustrate the use of the model, we apply it to the prediction of the effects of methylmercury on brain development in rats.

Notizen: People make subjective judgments about hazards relying on what they know and feel. These risk perceptions may be based on accurate or inaccurate information and are often optimistically biased. The existence of uncertainties in the evaluation of many environmental hazards effects how risks are perceived. This paper examines fish consumption and risk perception of urban fishermen in the New York/New Jersey estuary, in areas where there were consumption advisories. We interviewed 318 fishermen and crabbers in the Arthur Kill, Raritan Bay, and New Jersey shore. Fish were eaten an average of at least four times per month in all regions, but fishermen in the Arthur Kill fished most frequently, averaging over eight times per month. Although 60% of fishermen and crabbers in the Arthur Kill reported hearing warnings about consuming fish caught in these waters, 70% of fishermen and 76% of crabbers said they ate their catch. Significantly fewer fishermen in the Bay and Shore regions had heard warnings (28% and 30%, respectively), and more reported consuming their catch (88% and 82%, respectively). In all regions, most people thought that the fish were safe to eat, many believing they were “fresher” than store bought fish. Thus, most people ignored the consumption advisories in effect for these waters. Some of these people are consuming high quantities of fish and crabs, and thus are exposed to potentially deleterious levels of contaminants. In general, people failed to consider the possibility of chronic effects and did not perceive that this enjoyable, familiar pastime could be hazardous. Further, fishermen generally had great confidence in their own knowledge, which proved to be inaccurate in many cases, and often expressed distrust in the information source (government). Clearly, simply issuing consumption advisories is insufficient to promote risk-reducing behavior.

Notizen: In this paper, we discuss the conduct and results of a study aimed at eliciting public perceptions of food-related hazards. This study employs the psychometric approach of Paul Slovic and colleagues and aims to extend the recent work of Sparks and Shepherd(1) on defining the primary dimensions of food-related risk perceptions. The study surveyed a nationally representative sample of the general public (respondents = 293; adjusted response rate = 30.1%). Respondents provided ratings on subsets of 22 potential food hazards (e.g., food irradiation and presence of listeria) on a total of 19 risk characteristics (e.g., “perceived severity of risk” and “adequacy of governmental regulations”). In spite of the use of a number of new characteristics and food hazards, Principal Components Analysis revealed a broadly similar factor structure to that obtained by Sparks and Shepherd,(1) suggesting the generalizability of the key dimensions (concerning the severity and awareness of hazards). Interestingly, the positioning in the factor space of potential hazards about which little was generally known (e.g., campylobacter) as being serious and in need of regulation, may suggest a possible “starting position” in the perception of new hazards that have not previously been the subject of risk communications.

Notizen: Trust in risk information about food related-hazards may be an important determinant of public reactions to risk information. One of the central questions addressed by the risk communication literature is why some individuals and organizations are trusted as sources of risk information and others are not. Industry and government often lack public trust, whereas other sources (for example, consumer organizations, the quality media, medical doctors) are highly trusted. Problematically, previous surveys and questionnaire studies have utilized questions generated by the investigators themselves to assess public perceptions of trust in different sources. Furthermore, no account of the hazard domain was made. In the first study reported here, semistructured interviewing was used to elicit underpinning constructs determining trust and distrust in different sources providing food-related risk information (n= 35). In the second study, the repertory grid method was used to elicit the terminology that respondents use to distinguish between different potential food-related information sources (n= 35), the data being submitted to generalised Procrustes analysis. The results of the two studies were combined and validated in survey research (n= 888) where factor analysis indicated that knowledge in itself does not lead to trust, but that trusted sources are seen to be characterised by multiple positive attributes. Contrary to previous research, complete freedom does not lead to trust—rather sources which possess moderate accountability are seen to be the most trusted.

Notizen: Complex engineered systems, such as nuclear reactors and chemical plants, have the potential for catastrophic failure with disastrous consequences. In recent years, human and management factors have been recognized as frequent root causes of major failures in such systems. However, classical probabilistic risk analysis (PRA) techniques do not account for the underlying causes of these errors because they focus on the physical system and do not explicitly address the link between components' performance and organizational factors. This paper describes a general approach for addressing the human and management causes of system failure, called the SAM (System-Action-Management) framework. Beginning with a quantitative risk model of the physical system, SAM expands the scope of analysis to incorporate first the decisions and actions of individuals that affect the physical system. SAM then links management factors (incentives, training, policies and procedures, selection criteria, etc.) to those decisions and actions. The focus of this paper is on four quantitative models of action that describe this last relationship. These models address the formation of intentions for action and their execution as a function of the organizational environment. Intention formation is described by three alternative models: a rational model, a bounded rationality model, and a rule-based model. The execution of intentions is then modeled separately. These four models are designed to assess the probabilities of individual actions from the perspective of management, thus reflecting the uncertainties inherent to human behavior. The SAM framework is illustrated for a hypothetical case of hazardous materials transportation. This framework can be used as a tool to increase the safety and reliability of complex technical systems by modifying the organization, rather than, or in addition to, re-designing the physical system.

Notizen: Utilizing the concept of environmental justice, this paper examines the differential burdens of toxic and hazardous waste facilities locations in low income minority communities. The association between the presence of facilities and socioeconomic characteristics of places are examined for the state of South Carolina at three different spatial scales: counties, census tracts, and census block groups. Three different types of hazardous waste/toxic facilities are also examined: Toxic Release Inventory (TRI) sites, Treatment, Storage, and Disposal sites (TSD), and inactive hazardous waste sites. At the county level, there was some association between the presence of toxic/hazardous waste facilities and race and income. In South Carolina, this translates to a disproportionate burden on White, more affluent communities in metropolitan areas, rather than low income minority communities. At both the census tract and block group levels, there is no association between race and the location of toxic/hazardous waste facilities. There are slight differences in the income levels between tracts and block groups with facilities and those without. This localized ecology of hazard sources must be expanded to include emission/discharge data in order to adequately address environmental justice issues on who bears the burdens of environmental contamination.

Notizen: An adverse health impact is often treated as a binary variable (response vs. no response), in which case the risk of response is defined as a monotonically increasing function R of the dose received D. For a population of size N, specifying the forms of R(D) and of the probability density function (pdf) for D allows determination of the pdf for risk, and computation of the mean and variance of the distribution of incidence, where the latter parameters are denoted E[SN] and Var[SN], respectively. The distribution of SN describes uncertainty in the future incidence value. Given variability in dose (and risk) among population members, the distribution of incidence is Poisson-binomial. However, depending on the value of E[SN], the distribution of incidence is adequately approximated by a Poisson distribution with parameter μ=E[SN], or by a normal distribution with mean and variance equal to E[SN] and Var[SN]. The general analytical framework is applied to occupational infection by Mycobacterium tuberculosis (M. tb). Tuberculosis is transmitted by inhalation of 1–5 μm particles carrying viable M. tb bacilli. Infection risk has traditionally been modeled by the expression: R(D)= 1 – exp(–D), where D is the expected number of bacilli that deposit in the pulmonary region. This model assumes that the infectious dose is one bacillus. The beta pdf and the gamma pdf are shown to be reasonable and especially convenient forms for modeling the distribution of the expected cumulative dose across a large healthcare worker cohort. Use of the the analytical framework is illustrated by estimating the efficacy of different respiratory protective devices in reducing healthcare worker infection risk.

Notizen: The current methods for a reference dose (RfD) determination can be enhanced through the use of biologically-based dose-response analysis. Methods developed here utilizes information from tetrachlorodibenzo-p-dioxin (TCDD) to focus on noncancer endpoints, specifically TCDD mediated immune system alterations and enzyme induction. Dose-response analysis, using the Sigmoid-Emax (EMAX) function, is applied to multiple studies to determine consistency of response. Through the use of multiple studies and statistical comparison of parameter estimates, it was demonstrated that the slope estimates across studies were very consistent. This adds confidence to the subsequent effect dose estimates. This study also compares traditional methods of risk assessment such as the NOAEL/safety factor to a modified benchmark dose approach which is introduced here. Confidence in the estimation of an effect dose (ED10) was improved through the use of multiple datasets. This is key to adding confidence to the benchmark dose estimates. In addition, the Sigmoid-Emax function when applied to dose-response data using nonlinear regression analysis provides a significantly improved fit to data increasing confidence in parameter estimates which subsequently improve effect dose estimates.

Notizen: Recent studies have identified a “hard core” of drinking drivers who do not fit a “social” drinker profile and may require medical intervention. This article builds on these studies by quantifying the role of heavy drinking in motor vehicle fatalities. Data on male alcohol-involved fatally-injured drivers (AIFIDs) were obtained from the U.S. Fatal Accident Reporting System (FARS) for the years 1989–1990 (n = 8876). The AIFIDs were grouped into either a “heavy” or “light” drinking category based on drinking behaviors inferred from prior driving records and blood alcohol concentrations (BAC). The majority of male AIFIDs were between the ages of 20–39 (70%). Sixty-five percent had a BAC of 150 mg/dl or greater, and 41% had a BAC in excess of 200 mg/dl. AIFIDs with high BACs were more likely to have histories of DUI convictions and license suspensions than AIFIDs with low BACs. According to the study's criteria, 73% percent of the AIFIDs could be classified as “heavy” drinkers. There were no driving variables that differentiated the heavy and light drinker groups, indicating that heavy drinking per se is the primary factor that distinguishes the groups. Male alcohol-involved fatally injured drivers are comprised mostly of heavy drinkers who may suffer from serious drinking problems or alcoholism. Successful interventions may require medical treatment as well as punitive criminal justice policies.

Notizen: Traditionally, microbial risk assessors have used point estimates to evaluate the probability that an individual will become infected. We developed a quantitative approach that shifts the risk characterization perspective from point estimate to distributional estimate, and from individual to population. To this end, we first designed and implemented a dynamic model that tracks traditional epidemiological variables such as the number of susceptible, infected, diseased, and immune, and environmental variables such as pathogen density. Second, we used a simulation methodology that explicitly acknowledges the uncertainty and variability associated with the data. Specifically, the approach consists of assigning probability distributions to each parameter, sampling from these distributions for Monte Carlo simulations, and using a binary classification to assess the output of each simulation. A case study is presented that explores the uncertainties in assessing the risk of giardiasis when swimming in a recreational impoundment using reclaimed water. Using literature-based information to assign parameters ranges, our analysis demonstrated that the parameter describing the shedding of pathogens by infected swimmers was the factor that contributed most to the uncertainty in risk. The importance of other parameters was dependent on reducing the a priori range of this shedding parameter. By constraining the shedding parameter to its lower subrange, treatment efficiency was the parameter most important in predicting whether a simulation resulted in prevalences above or below non outbreak levels. Whereas parameters associated with human exposure were important when the shedding parameter was constrained to a higher subrange. This Monte Carlo simulation technique identified conditions in which outbreaks and/or nonoutbreaks are likely and identified the parameters that most contributed to the uncertainty associated with a risk prediction.

Notizen: This paper reports the results of a field test of the hazard warning system used in rock climbing. The system is succinct; it differentiates between magnitudes of hazard; and it establishes a “warnings vocabulary.” The empirical hazard response models include an “individuating factor,” which influences the likelihood of injury, and the severity of injury as independent variables. The models indicate that climbers do assess a “personal” probability of injury and incorporate the hazard warning message when choosing climbing routes. Climbers of greater technical ability are more likely to climb hazardous routes, but they mitigate the likelihood of the hazardous outcome by reducing the technical difficulty of the hazardous route chosen. The response increases with the degree of hazard involved.