H21E-1048 0800h
Comparison of Modeling Approaches for Simulating Cometabolic Biodegradation in Sorbent-Water Systems
Numerical models are useful for predicting the effectiveness of the bioremediation of organic contaminants in sorbent-water systems. Modeling methods can range from simple approaches (e.g. equilibrium, linear sorption and first-order biodegradation) to much more sophisticated models (nonlinear, multi-domain sorption, Monod biodegradation kinetics, and co-contaminant effects). The relative sensitivity of different modeling methods is investigated for the bio-attenuation of two co-existing contaminants. Eighteen models with different combinations of alternative representations for sorption, mass transfer, and biodegradation are used to simulate the simultaneous biodegradation of toluene (primary substrate) and TCE (cometabolic nongrowth substrate) in completely-mixed batch systems with the various combinations of sorption strength, mass transfer rates, biodegradation rates, and initial contaminant mass loadings. The sensitivity of results to the modeling approach varies with system conditions. For example, the simulations are insensitive to the representation of sorption in systems with low sorption strength and slow biodegradation rates. For such systems, however, predictions can be very sensitive to the model's biodegradation component. Differences among the various modeling results are greater when evaluated in terms of mass removal rather than aqueous concentration reduction. Also, and as expected, the fate of the non-growth cometabolite is more sensitive to the proper consideration of co-contaminant effects than is the fate of the primary growth substrate. These simulations show how the determination of the appropriate level of model complexity can be guided by preliminary assessments of the extent to which the various sorption, mass transfer, and biodegradation processes are expected to control contaminant bioavailability.
H21E-1049 0800h
Direct-Push Cross-Hole Slug Tests: A New Tool for Hydraulic Characterization of Aquifers
Slug tests have traditionally been utilized as a means to determine the hydraulic conductivity (K) of an aquifer at a relatively small scale. When performed in a cross-hole mode, however, slug tests can be used to gain considerably more information. Despite the common perception that a slug test only affects a small volume of the aquifer in the vicinity of the test well, response data with a reasonable signal to noise ratio can be collected at distances of over several hundred times the radius of the screen of the test well. Analysis of such data can yield estimates of specific storage and the horizontal and vertical components of K, as well as providing insight into aquifer heterogeneity. Although cross-hole slug tests have been used in some previous studies, the utility of the approach has been limited by the need for relatively closely spaced wells. That limitation, however, can be readily overcome in unconsolidated formations by exploiting the access to the shallow subsurface provided by direct-push (DP) technology. DP technology can be used to install observation points at positions most advantageous for a particular study and then to reposition points between tests. The potential of DP cross-hole slug tests was investigated in a well-characterized sand and gravel aquifer underlying the Kansas River floodplain. An extensive series of slug tests were performed to assess the dependence of test data on the radius and screen length of the test well, and the lateral and vertical position of the observation interval. Using a 0.05-m test well, response data with a reasonable signal to noise ratio were obtained at observation intervals separated from the test well by over 11 m laterally and up to 3 m vertically. The results of these tests indicate that DP cross-hole slug tests could be a valuable tool for a variety of applications ranging from estimation of bulk aquifer properties to monitoring of temporal changes in the hydraulic properties of permeable reactive barriers. This approach is particularly well-suited for providing information about anisotropy in hydraulic conductivity, a quantity that is rarely known but often of considerable practical importance, especially for the design of remediation systems.
H21E-1050 0800h
Comparison of hydraulic parameters measured at multiple scales in a synthetic heterogeneous aquifer
Estimates of hydraulic parameters such as hydraulic conductivity (K) and specific storage (Ss) are needed to investigate a variety of problems including the evaluation of water supply, contaminant source zone delineation, and modeling of contaminant transport in heterogeneous porous and fractured media. A large number of field studies show that there is evidence that hydraulic parameter estimates vary with location and scale. Such studies are very important and have yielded considerable insight but the underlying cause(s) of the scale effects in hydraulic parameters is still unclear because of a large number of unknown factors that can affect field results. Here, we conduct a laboratory study under highly controlled conditions to examine the scale dependence of hydraulic parameters. We obtain measurements of hydraulic parameters at 5 different scales in a synthetic laboratory aquifer with a known heterogeneity distribution. Estimates of hydraulic parameters were obtained by: 1) constant head experiments on core samples extracted from 48 ports within the flow cell; 2) slug tests at each of the 48 ports; 3) single-hole tests at each of the 48 ports; 4) pumping tests conducted in a tomographic manner with pumping and observation taking place at each of the 48 ports; and, 5) a flow experiment through the entire synthetic aquifer to obtain an estimate of effective K. We analyzed the experimental results using a finite element code VSAFT2 (Yeh et al. 1993) by matching the simulation results to transient data. Results show that the geometric mean values of K are in general comparable for the core, single-hole tests, large-scale pumping tests, and the flow experiments through the entire synthetic aquifer, but the results from the slug tests are considerably lower. We find that the estimates of hydraulic parameters obtained from the pumping tests are unique but the values from the slug tests are not. For the slug test, we are only able to obtain a unique estimate of aquifer diffusivity which is the ratio between K and Ss. These results collectively suggest that pumping tests conducted in a heterogeneous formation with interpretation assuming that the medium is homogenous yields accurate values of equivalent K and Ss that approach the effective values when the pumping test is conducted long enough.
H21E-1051 0800h
A CYCLIC APPROACH FOR THE QUANTIFICATION AND REMEDIATION OF SUBSURFACE CONTAMINATION
A new approach to contaminated land assessment and revitalisation, focusing on groundwater quality and complex contamination patterns at urban industrial megasites was developed. The new approach comprises three cycles: (a) the assessment of groundwater contamination using an integral mass flux based investigation method at the scale of entire industrial sites, (b) the delimiting of potential contamination source zones using backtracking and contaminant fingerprinting techniques, and (c) the development of emission oriented remediation strategies. The major advantage of the new approach is that the number of areas to be considered for further investigation and remediation is reduced from one cycle to the next. Consequently, a large potentially contaminated area is screened initially, but only a small area may be finally remediated, yielding a significant reduction of costs. The results from the integral investigation at the scale of entire megasites can be used for risk assessment purposes, for the quantification of the natural attenuation potential, as well as for the development of priorities for clean-up and / or further investigations and for the design of remediation measures. In addition, a consistent quantification of uncertainties in the results from the application of the integral groundwater investigation method is possible. Finally, the delimiting of the source zone extent and its uncertainty allows to define priorities for further investigation measures at a smaller scale, and to develop cost-optimized clean-up strategies. In this contribution, the focus will be on the three cycles of the new approach. Also, examples of application will be presented.
H21E-1052 0800h
Partial Derivative Modeling of Shallow Seismic Refraction Tomography Data, Fort Wainwright, Fairbanks, Alaska
Site characterization studies performed at Fort Wainwright in Fairbanks AK, suggest that contaminant migration in the area is controlled by fracture flow. Shallow seismic refraction tomography surveys were undertaken at this site to further characterize the nature of the bedrock aquifer and to identify structural features that may contribute to groundwater flow and contaminant migration. Two individual surveys were completed; the original survey was conducted in 2002 and during the following field season (2003) a second survey was carried out to address the remaining data gaps. The 2002 and 2003 profiles show the same trends in velocity in areas where they overlap. The similarity of the 2002 and 2003 profiles demonstrates the soundness of both data sets. In addition, several of the prominent seismic features were defined by profiles collected at different orientations (multiple directions) providing further confirmation of data quality. The 2002 and 2003 seismic surveys have different geometries. In 2002, the profiles were 180 meters in length, and, in 2003, they were 300 meters in length. Because of the varying profile lengths and the subsequent change in the number of seismic shots per profile, these data sets have different resolutions. In order to use these data sets together it was necessary to normalize the data. Therefore, partial derivatives (rate of change in velocity per unit of distance) were calculated. The resulting partial derivative profiles highlight differences in the seismic velocity profiles but are not dependent on specific velocity values. These differences are geologic in nature and interpreted to be structural. Differences are referred to as contrast zones and/or lineations. Dynamic Graphic's software EarthVision was used for the partial derivative modeling. Discrete bedrock zones were delineated by the relative contrast in the seismic profiles. Both high and low contrast zones were identified at Birch Hill. The high contrast bedrock zones are defined by several lineations with varying orientation throughout the vertical extent of the profile. The lineations in the high contrast zones were interpreted to be geologic structures, such as fractures and shear zones, which may influence contaminant behavior at the site. Low contrast profiles typically have a single pronounced lateral reflector with minimal variation below and suggest more competent bedrock. The partial derivative models confirm properties suggested by the non-normalized data and allow quantification of the structures.
H21E-1053 0800h
Thermohydrologic Modeling: Coupling Navier-Stokes Models of Gas, Moisture, and Heat Flow in Underground Engineered Systems with Porous-Media Models in Fractured Rocks
Combined free and porous flows occur in a wide range of natural and engineered systems such as coupled transport processes driven by underground-engineered systems. One potential application for modeling these coupled flow processes is related to the emplacement of heat-generating radioactive waste package in tunnels lying above the water table. This example involves the flow of gas and moisture in large open tunnel and gas- and liquid-phase flow in the surrounding fractured, porous rocks. This study aims to develop a method of coupling the Navier-Stokes equations and the Darcy's law to achieve a more rigorous representation of all major flow and transport processes in underground tunnels and surrounding fractured host-rocks. While the thermohydrologic (TH) processes in host-rocks are treated based on porous-medium Darcy-flow approximations, the Navier-Stokes modeling is applied to describe in-tunnel flow behaviors (natural convection, realistic gas/moisture movement, turbulent flow conditions, etc.). The governing equations are numerically solved by a finite-element scheme in the NUFT code. Some numerical simulation results shown in this presentation provide environmental conditions that engineered systems would experience, which, therefore, may be useful for engineered system design analysis and performance assessment. This work was performed under the auspices of the U.S. Department of Energy by University of California Lawrence Livermore National Laboratory under contract No. W-7405-Eng-48.
H21E-1054 0800h
Determination of the Hydraulic Properties of Sub-Sea Formations Using Continuous Measurements of Pore Pressure at Submarine-Groundwater-Discharge Area
The potential field and the distributions of hydraulic properties of sub-sea formation govern the groundwater flow, and control the location and the flux of the submarine groundwater discharge (SGD). In this study, we developed a new method to determine the ambient pore pressures and to estimate the hydraulic diffusivity of sub-sea formation using in-site continuous measurements of pore pressures at two different depths and pressure on the sea floor. The device was set up in an unconfined sand layer. The pore pressures were measured at three water depths; 9m (site A), 6.6m (site B) and 5.1m (site C), offshore Kurobe alluvial fan, Japan, where fresh ground water discharge has been discovered. The depths of the pore pressure measurements were 1.0 meters below sea floor (mbsf) and 2.0 mbsf at the Site A, and 0.5 and 1.0 mbsf at the sites B and C. Pressures were measured every 30 minutes for a month, and to evaluate the effect of water wave loading, we measured pressures data with 2 Hz frequency two times per day. The pore pressures in excess of hydrostatic pressure were determined to be 0.12 to 0.55 kPa at all locations except at 1.0mbsf of the site B. The average upward hydraulic gradients are 0.023 at the site A, 0.032 at the site B and 0.027 at the site C, which was consistent with the existence of fresh groundwater discharge at the location. The hydraulic diffusivities were estimated to be 1.3 m$^{2}$/s at site A, 0.21 m$^{2}$/s at site B and 0.17 m$^{2}$/s at site C from the analysis of the pore pressure responses to the water wave loading based on the theory of poroelasticity. The fluxes of submarine groundwater discharge were estimated to be 5.1_~10$^{-6}$ to 3.6_~10$^{-4}$ m/s from the average hydraulic gradients, the hydraulic diffusivities and the assumed specific storage of the formation, which was consistent with the direct measurement (1.6_~10$^{-6}$ to 3.9_~10$^{-5}$ m/s) using the chemical-mixing based seepage meter.
H21E-1055 0800h
Traditional Aquifer Tests: Comparing Apples to Oranges?
Traditional interpretation of aquifer tests rely on fitting the observed hydrograph at one observation well to Theis type curve or Jacob's approximation solution, which assumes aquifer homogeneity. Recent studies based on Jacob's approach show that transmissivity estimates obtain from late time data converge to effective transmissivity value for uniform flow while the corresponding estimates for storativity exhibits strong spatial variability. Using Monte Carlos simulations, we investigate effects of heterogeneity on the analysis of aquifer tests using the Theis approaches. First, we develop a method that is consistent with the homogeneity assumption to estimate the effective transmissivity and storativity values for radial flow. Results using this method indicate that the effective transmissivity and storativity for radial flow are time variables but converge to geometric means at large time. This suggests the existence of REV for radial flow in the cases we examined. However, the estimated transmissivity based on the drawdown from a single observation well reflects the local heterogeneity surrounding the observation well but varies with pumping time. At large time, the estimated transimisivity value converges to the geometric mean of the flow domain while the storativity estimate fluctuates and do not approach the geometric mean. The estimate of storativity eventually approaches the local average values of storativity near the observation well. Finally, we use sensitivity analysis to explain the results of our numerical experiments and to determine the pumping time required to reach the geometric mean of the transmssivity field. Keywords: pumping test, heterogeneity, distance drawdown curve, time drawdown curve.
H21E-1056 0800h
Data Analysis and Simulation of In-Situ Permeable Flow Sensors for Measuring Groundwater Velocity
We have monitored data from three Hydrotechnics in-situ permeable flow sensors (ISPFSs) installed in a shallow aquifer at the former Fort Ord Army Base near Monterey, California. The in-situ permeable flow sensor operates by constant heating of a nearly one-meter-long, 5 cm diameter cylindrical probe which contains 30 thermistors in direct contact with the formation that has fully collapsed around the instrument during installation. The temperature evolution at each thermistor can be inverted to obtain an estimate of the groundwater flow velocity vector (i.e., horizontal and vertical components, and azimuth). The unconfined aquifer we monitored is in unconsolidated dune sand bounded below by a clay aquitard. The magnitudes of the vertical velocities were expected to be much less than the horizontal velocities at this site because of the underlying clay layer. However, standard data analysis of the ISPFS data suggested a strong and unexpected component of downward flow. We have carried out numerical simulations with TOUGH2 of three-dimensional non-isothermal flow around the instrument to investigate temperature profiles along the instrument that might give rise to spurious indications of downward flow. We studied the effects of different combinations of permeability and thermal conductivity around the instrument. A decrease in the thermal conductivity or permeability of the formation near the bottom of the sensor can perturb the temperature profiles along the instrument in such a manner that the temperature shift could be interpreted as downward flow. The TOUGH2 simulations demonstrate that estimates of downward velocities from the flow sensors should be interpreted with caution and compared with estimates from other methods if possible. This work was supported by U.C. Santa Cruz through the U.S. Army Construction Engineering Reseach Laboratories, and by the U.S. Department of Energy under contract No. DE-AC03-76SF00098.
H21E-1057 0800h
Influence of Coarse-Grained Incised Valley Fill on Ground-Water Flow in Fluvial Fan Deposits, Stanislaus County, California, USA
A relatively coarse-grained incised valley-fill deposit was identified within the Tuolumne River fluvial fan beneath the city of Modesto, Stanislaus County, California, USA. Incised valley fill deposits in the eastern San Joaquin Valley resulted from rapid decreases and increases in sediment supply during interglacial and glacial periods. Ground-water flow and contaminant transport modeling of similar deposits on the Kings River fan near Fresno, California, indicate the potential for (1) relatively high ground-water production rates, (2) rapid contaminant transport within incised valley-fill sediments, and (3) rapid contaminant movement through the incised valley-fill sediments into adjacent aquifer sediments. If these characteristics also apply to the incised valley fill beneath Modesto, then it may have implications for ground-water quality and potential artificial recharge to city supply wells and wells in the surrounding region. We identified the location of the incised valley fill and surrounding deposits in the subsurface through the use of drillers' well logs, geophysical well logs, and core samples, and compared the spatial dimensions of the subsurface incised valley fill to the modern Tuolumne River incised valley. Because the interpretation of drillers' well logs leaves uncertainty regarding the geometry of the subsurface incised valley fill, we assumed that the three-dimensional geometry of the subsurface valley fill is similar to the modern Tuolumne River valley. From this analysis, we estimate the incised valley fill (1) is 0.7 to 1.6 kilometers wide, (2) ranges from approximately 30 meters thick at the apex of the fan to approximately 0.3 meters thick at the toe of the fan, and (3) has a 5 to 9-meter-thick gravel base near the fan apex that thins downfan. Our regional geologic model uses digital elevation model (DEM) and subsurface lithologic data to describe the approximate geometry, subsurface location, and permeability of the incised valley fill. The geologic model will be used to provide a framework for a ground-water flow model that will test whether the incised valley fill enhances flow for prospective artificial recharge and increases potential for contaminant transport to drinking-water wells in the region.
H21E-1058 0800h
Kriging Plume Volumes: Sensitivity of Search Parameters
Geostatistical methods such as kriging are commonly used to estimate the concentration distribution of compounds in a ground water plume. Plume volume estimates can also be obtained by summing the volume of kriged cells with an estimated concentration above some threshold (e.g. MCL). Similarly, estimated concentrations can be used to estimated the total plume mass, assuming that the average estimated concentration is present in pore water within the estimated volume. Estimating the total mass with ordinary kriging has the advantage of being non-sensitive to the concentration at individual points, but careful restriction of the search parameters must be applied to accurately delineate the volume of the plume. In this study we evaluated the effect of search radii and octant criteria restriction on plume volume and mass estimates using the ok3d routine (Deutsch and Journel, 1998). Data from the Borden field tracer experiment were used, and the resulting mass estimates were compared to the initial injected mass, and to mass estimates obtained using spatial moment analysis and geometrical averaging. Ordinary kriging can be used to estimate the mass and volume of a compound in a ground water plume with results that correlate well with other techniques, but the method is highly sensitive to the octant search parameters. We found that the method should require data from at least five octants, with no more than one data point per octant. This prevents extrapolation beyond the plume boundary, while allowing sufficient coverage within the plume. The method is not highly sensitive to variogram parameters, but requires careful selection of search radii. The optimal search radius is between one and two well spacings. If the search radius is lower, plume mass is underestimated, and if the search radius is less than one well spacing the estimate may be completely invalid. A larger search radius tends to result in an overestimation of the plume mass and volume. However, when the octant criteria is adopted, the method is less sensitive to overly large search radii.
H21E-1059 0800h
Natural Radioactive Characterization by Gamma Ray Mapping in Relation with Radon-222, Radium-226 Contents in the Atmosphere, Dripping Groundwater and Mineral in a Dead-end Horizontal Tunnel
The concentration of radon-222 has been monitored since 1995 in the atmosphere of a 2 m transverse dimension, 128 m long, dead-end horizontal tunnel located in the French Alps, at an altitude of 1600 m. The total volume of the tunnel is about 496 m$^{3}$ with an estimated total wall surface area of 1041 m$^{2}$. Most of the time, the radon concentration is stable, with an average value ranging from 200 Bq m$^{-3}$ near the entrance to about 1000 Bq m$^{-3}$ in the most confined section, and with an equilibrium factor F between radon and its short-lived decay products varying from 0.61 to 0.78. However, radon bursts are repeatedly observed, with amplitudes reaching up to 36 x 10$^{3}$ Bq m$^{-3}$ and durations varying from one to several weeks, with similar spatial variations along the tunnel as the background concentration. These spatial variations are qualitatively interpreted in terms of natural ventilation. To understand the source term, we realised a comprehensive 3D map of total gamma emission of rock on all surfaces of the tunnel, i.e., floor, wall and roof, representing 700 measurements points with a section of eight points by two-meter steps along the tunnel. Dose rate varies from 100 to 350 nSv h$^{-1}$ and reveals two major contrasted geological structures, correlated with the radon-222 profile in the air along the tunnel (230 Bq m$^{-3}$ at the entrance to 770 Bq m$^{-3}$ at the end, measured during a period of background radon level), and with other profiles measured in previous work. In addition, a correlation is evidenced with the radon-222 contents in dripping groundwater and with the radon precursors - i.e., the daughters of uranium-238 (radium-226, for example) - content in rocks. The radon and radium contents in water and rocks, and the study of flow rate of the dripping groundwater are in direct relation with the mechanism of radon gas transport by water in porous media. By interpreting all available measurements, it is now possible to model the time variation of radon-222 in the tunnel, and to constrain the origin of the radon peaks generated in the gallery. The bursts result from transient radon exhalation upsurges at the tunnel wall, that could be due to meteorological effects, or possibly to combined hydrological and mechanical forcing associated with the water level variations of the nearby Roselend reservoir lake.
H21E-1060 0800h
Characterization of Geochemical Factors Controlling PCE Sorption to Carbonaceous Matter by Lithofacies
Understanding the heterogeneous distribution of aquifer geochemical properties that affect contaminant transport, such as sorption, is essential to accurate contaminant transport prediction and maximizing remediation efficiency. Previous work by our group identified a correlation between the sorption coefficient (Kd) measured for a probe contaminant, perchloroethylene or PCE, and lithofacies, mapped based on sediment characteristics, for aquifer material from Canadian Forces Base Borden. The Kd distributions for the 11 mapped lithofacies were determined from a total of approximately 350 samples. The distribution of variance was the primary difference between the Kd distributions by lithofacies. We hypothesize that carbonaceous matter (CM) associated with granule-size and larger carbonate lithic fragments concentrated within particular lithofacies is primarily responsible for greater and more nonlinear sorption observed in certain lithofacies. Our idea is tested by obtaining the fraction organic carbon (foc), carbonate contents, and the PCE Kd at two concentrations ($\sim$ 7 ug/L and $\sim$ 1600 ug/L) for high-sorbing and low-sorbing subsamples of four of the lithofacies, and 2 to 4 mm carbonate granule material ($\sim$ 70% CaCO3-C) sieved from bulk Borden aquifer material. With this data, we test the influence that this carbonate-associated CM has on sorption. The Kd and Koc (= Kd/foc) values are greatest for the carbonate granule material, followed by the two lithofacies that contain greater organic carbon and carbonate contents, and are characterized by a larger mean grain size and poorer sorting than the other lithofacies. For all lithofacies measured, the low concentration Kd is greater than the high concentration Kd, demonstrating that all samples exhibit nonlinear sorption. Thin section analysis was used to qualitatively determine the proportion of sparry versus micritic carbonate granules within the sediment. Our results suggest that in addition to CM external to carbonate lithic fragments, the CM associated with the carbonate material affects sorption nonlinearity, contributing significantly to total sorption.
H21E-1061 0800h
A Method for Detecting Submarine Groundwater Discharge by Thermal Infra-Red Measurement
Submarine Groundwater Discharge (SGD) has been considered to be one of the important pathways for the transport of freshwater and dissolved constituents from land to coastal ocean. To better understand the importance of SGD, it is necessary to determine spatial distribution, flux, and chemistry of SGD. In this study, Thermal Infra-Red (TIR) survey was conducted to evaluate the ability of this technique for detecting the discharge points. The sea surface temperatures were measured by a TIR sensor with high spatial resolution (1~2cm) and with high frequency (1Hz) at the intertidal zone where groundwater discharge has been found and described. The temperature of discharged freshwater was about 14 $\deg$ C lower than that of ambient seawater because this measurement were done in August. The discharge flux was about 1.3$\sim$6.4$\times$10$^{-6}$m$^{3}$/s, and the area of discharge was about 0.64m$^{2}$. The measurements were conducted from sunset to late at night to remove the effects of sunlight on the sea surface temperature. During the half-day measurements, seawater depth changed from 0 to 1.5m caused by the tidal fluctuation, which enabled us to discuss the water depth-dependant change of sea surface temperature variation. The lower temperature region at sea surface due to the effect of SGD was observed, and the maximum temperature drops were 1.1 and 0.4 $\deg$ C where water depths were 0.5 and 1.1m, respectively. The maximum water depth where we could detect the signal by SGD was 1.3m in this study. The areas of the lower temperature region tended to decrease as the water depth increased. For example, the area of lower temperature (0.6 $\deg$ C) region was about 0.7m$^{2}$ in the case where the water depth was about 0.3m, and it reduced to be about 0.3m$^{2}$ in the case of 0.5m water depth. Using the obtained results from this study, we analyzed the required spatial resolution for TIR survey to detect the existence of the studied SGD with the sensor of which temperature resolution is 0.1 $\deg$ C, which is the standard temperature resolution for airborne TIR survey. It was concluded that the studied SGD could be detected by TIR survey with 50cm spatial resolution even though this resolution has not been achieved in the present airborne TIR survey. However, by using balloon sonde or powered paraglider, we can provide the above mentioned resolution and could use the TIR technique for capturing the spatial distribution of SGD.
H21E-1062 0800h
Effects of Biodegradation and Hydrodynamic Dispersion on Contaminant Plume Development
A two-dimensional biodegradation model is considered including simultaneous transport and biodegradation of an organic contaminant, electron acceptor and moreover growth and decay of micro-organisms. The problem studied relates to the continuous injection of a contaminant at a point source in an aquifer. Initially, electron acceptor and biomass are present in the entire flow domain, while contaminant is absent. Injection of the contaminant leads to the development of a dispersive mixing zone between the zone where the biomass is activated and the inactive, uncontaminated zone. Mathematically the model consists of three coupled nonlinear partial differential equations. For the transient case, these three equations are reduced to an auxiliary linear equation. The solution of this auxiliary problem is used to recast the three equations into two coupled equations. For the stationary case, the problem is reduced further to a single PDE in terms of one of the dependent variables only. Both transient and stationary cases are solved numerically and comparison of the numerical model and laboratory data show good agreement. In the stationary case, results demonstrate that biodegradation and transversal dispersion are competing processes which control mixing between electron acceptor and injected contaminant.
H21E-1063 0800h
Wavelet Analysis of Permeability Anisotropy of Massillon Sandstone
An accurate representation of the permeability anisotropy of a porous medium is needed to successfully predict the magnitude and direction of groundwater flow. We use wavelet analysis to identify principal directions of anisotropy in a heterogeneous porous medium. Wavelet analysis involves the integral transform of a permeability field using a kernel function (wavelet) that can be shifted, stretched, and rotated. The magnitude of the resulting wavelet coefficient provides information about the dominant scales (via stretching) and dominant orientations (via rotation) at various spatial positions in the permeability field. We use a fully-anisotropic Morlet wavelet to successfully identify dominant scales and orientations of a 1m x 1m face of Massillon sandstone. In addition, we demonstrate that wavelet analysis can identify localized features that are not identifiable through geostatistical analysis.
H21E-1064 0800h
Hyperspectral Remote Sensing and Groundwater Simulation for Detecting Riparian Wetness Gradients
Groundwater is a precious resource of limited extent. The importance of determining and describing hydrological groundwater flow systems is one of the most important aspects for the management and development of ecological values, especially in valleys of river basin. Knowledge about discharge and recharge zones forms the basis for sound, quantitatively and qualitatively, water management of groundwater flow systems. Determination of discharge-recharge zones using hydrological models needs a large volume of data from various sources. Integrated Hyperspectral remote sensed data and GIS can provide an effective tool in characterizing groundwater flow systems and discharge-recharge relationships. In the present study, an integrated hyperspectral remote sensing and GIS based methodology is developed and tested for the evaluation of groundwater flow system of Doode Bemde wetland in the valley of the Dijle River, Belgium. There are three components of the study; (a) Development of groundwater model using the three dimensional groundwater model, MODFLOW, (b) Extraction of information about the groundwater flow system from CASI-SWIR hyperspectral data using ENVI 3.5 software and, (c) Comparison of each individual CASI-SWIR band with the simulated groundwater depth and discharge-recharge zones. The simulated discharge areas are verified by hyperspectral remote sensed data. The first principle component is found to be the best for identification of recharge zones in study area. An area cross-tabulation two-dimensional table that summarizes the areal overlap of all the possible combination of the two input maps (from the hydrological model and the image) or an error matrix is applied for expressing classification accuracy. The correlation values between 0.6 and 0.65 are observed on the wavelength domain from 0.90 to 1.30m and on the first principle component with the groundwater depth. These bands are among the best for use as a source of information for shallow groundwater depth (up to 1.5m) for natural grasslands.
H21E-1065 0800h
Simultaneous Determination of the Hydraulic Conductivity and Specific Storage of A Test Specimen From Laboratory Permeability Tests
Laboratory testing of representative specimens has been a very useful and widely adopted approach for characterizing the physical properties of geological materials. One of the particular challenges in geotechnical and/or geoenvironmental laboratory testing is the accurate determination of the hydraulic properties of low-permeability geological materials such as clays, intact rocks and the mixtures of sand and clay. These materials are now being studied in increasing detail because of their importance in retarding the transport of hazardous wastes, including radioactive nuclear wastes. Although laboratory permeability tests are thought to be well-established, most methods can obtain only the value of hydraulic conductivity and the specific storage, another important parameter related to the transient flow, is disregarded in the analyses. In addition, conventional test methods require relatively-long times for testing low-permeability geological materials. In this study, we present a set of rigorous solutions to three kinds of laboratory permeability tests: the constant-head, rising tail-water elevation; the falling-head, constant tail-water elevation; and the falling-head, rising tail-water elevation. A new system that can implement any of these three test methods is also introduced. This new system permits automated recording of the heads in up and down streams, eliminating the effects of temperature variation and evaporation on flow rate measurements. The applicabilities and advantages of these improved technologies are demonstrated using a series of experimental data derived from a compacted mixture of sand and clay. The results indicated that using the rigorous solutions to analyze unsteady or transient-phase data obtained from individual permeability tests permits the test durations to be shorted without sacrificing accuracy in estimating both the hydraulic conductivity and the specific storage of a test specimen.
H21E-1066 0800h
Analysis of a Micro-Pumping Test Conducted Within a Saprolitic Aquifer
Field research on biostimulation for remediation of uranium contamination in groundwater is ongoing at a field site near Oak Ridge, TN. As part of the site characterization program, a low-stress pumping test was conducted within a relatively low-permeability fractured saprolite aquifer underlying the site. Despite the low pumping rate used (~25 ml/min), clearly discernable water-level responses were observed as far as 30 meters from the stress well. The pumping test provided areal characterization information in the presence of observable natural stress effects from barometric pressure fluctuations and precipitation events. Although the aquifer is shallow (less than 10 meters), a strong barometric pressure response was observed in all wells. The response model patterns are indicative of a dual-porosity medium, which is consistent with the fractured character of the saprolite materials. The observed water levels were successfully corrected for barometric response, which exhibited time-lag dependences extending to 44 to 48 hours for the four wells analyzed. A variable, areal drawdown dependence for test responses was exhibited at observation wells as a function of direction from the stress well, indicating horizontal anisotropic aquifer conditions. Most of the monitor wells also exhibited a distinct loading response to significant rainfall events that occurred during the pumping test characterization period. This loading phenomenon can be analyzed to determine the vertical hydraulic diffusivity of the overlying bed.
H21E-1067 0800h
Applied Dual-gas Tracing of a Fissured Sandstone Aquifer
Dissolved noble gas tracing is being used in the Environmental Tracers Laboratory at Queen's University Belfast as a novel 'environmentally-friendly' approach to characterise subsurface structure and transport properties for aquifer systems. A single-borehole slug injection (so-called 'push-pull') tracer test has been conducted in the fissured, permeable Sherwood Sandstone aquifer using both dissolved Krypton (Kr) and Xenon (Xe) gases applied simultaneously in a "push" phase lasting 12 hours. Input concentrations (C0) for both tracers initially were chosen to be equimolar specifically to test for the possible role of diffusive exchange between fissures and matrix systems over advective exchange. The simultaneous breakthrough curves show two characteristic peaks and long-tailing, which clearly demonstrate the dual-permeability nature of this important aquifer over the spatial and temporal scale investigated.
http://www.prb-net.qub.ac.uk/eerg/eerg.htm
H21E-1068 0800h
Numerical Simulation of Field-Scale Transport and Biogeochemical Reactions Using a Particle-Based Method
Field research on biostimulation for remediation of uranium contamination in groundwater is ongoing at a field site near Oak Ridge, TN. Several alternative approaches to numerical simulation of field-scale transport and biogeochemical reactions have been implemented to support design and interpretation of field tracer and biostimulation experiments. One such approach involves simulation of advective-dispersive transport, kinetic mass transfer between advection-dominated and diffusion-dominated subdomains, and microbial utilization of carbon source amendments using a discrete particle-based method in which reactions are formulated in terms of particle transformation probabilities rather than concentration changes. We describe the method, demonstrate its application to pre- and post-modeling of tracer and electron donor injection events, and compare model results to field observations.
H21E-1069 0800h
On the Equivalence of Two Models for Biodegradation During Contaminant Transport in Groundwater
Biodegradation is one of the most important processes affecting contaminant fate and transport in groundwater. Not surprisingly, then, several models have been developed for describing or modeling biodegradation during contaminant transport. Here we compare two such models: a ``simple'' model that is based upon macroscropic properties only, and a ``biofilm'' model that accounts for contaminant diffusion and reaction in biofilms. We demonstrate that the two models are, in fact, equivalent at the macroscopic scale when steady-state conditions prevail. Under these conditions, the equivalent macroscopic first-order degradation rate $k$ can be related to microscopic rate parameters that describe mass transfer across a boundary layer, diffusion within the biofilm, and reaction within the biofilm. Under transient (non-steady-state) conditions, the two models are not strictly equivalent. However, even under these conditions, the error between the two models is negligible in almost all cases. Therefore, in order to describe or predict concentrations at the macroscopic scale, the more sophisticated biofilm model offers little or no advantage over the simple model. To describe concentrations at the microscopic scale, the biofilm model is, of course, still needed.
H21E-1070 0800h
Using Airborne and Ground Electromagnetic Surveys and DC Resistivity Surveys to Delineate a Plume of Conductive Water at an In-Channel Coalbed Methane Produced Water Impoundment Near the Powder River, Wyoming
Development of coal bed methane (CBM) in the Powder River Basin of Wyoming and Montana has significantly increased since 1997. Production of CBM involves withdrawing groundwater from the coal bed to lower the hydrostatic pressure thereby allowing methane to desorb from the coal. The water co-produced with CBM is managed by storing it in impoundments until it can infiltrate to the groundwater, be used for beneficial purposes, or be discharged to surface streams. Skewed Reservoir was constructed as a research site to evaluate disposal of CBM water through infiltration ponds constructed by damming ephemeral streams. Geochemical data collected from monitoring wells placed downgradient of the reservoir detected a plume of water with total dissolved solids concentrations an order of magnitude higher than the CBM water stored in the impoundment. Infiltrating CBM water is suspected to have dissolved salts that were present in the unconsolidated materials beneath the reservoir. A geophysical investigation of the Skewed Reservoir area was conducted in July of 2004 to map the horizontal and vertical extent of the plume and to possibly identify the source of solutes to the infiltrating water. The Department of Energy's National Energy Technology Laboratory contracted Fugro Airborne Surveys to fly their RESOLVE frequency domain airborne electromagnetic (AEM) system with 50-m line spacing at the site. A ground investigation was completed at the same time as the airborne survey. Five 2-D dipole-dipole resistivity surveys and one 3-D pole-dipole survey were conducted using the AGI SuperSting R8/IP multi-channel resistivity imaging system. Additionally, ground conductivity measurements were recorded along each resistivity line using a Geophex GEM-2 multi-frequency ground conductivity meter. All geoelectrical measurements were inverted to obtain the subsurface conductivity distribution. Inversions were constrained using results of downhole borehole induction logs. Results were compared to geological and geochemical data collected from on-site monitoring wells. The geophysical methods accurately delineated the CBM water plume. Differences in the inversion results were observed and are discussed. The AEM data may also prove useful in identifying potential problem areas for locating future in-channel storage impoundments.
H21E-1071 0800h
Assembly and Comparison of Different Equations of State for Multiphase Carbon Dioxide in the Subsurface
Sequestration of carbon dioxide in deep saline aquifers has been suggested as a possible means for reducing greenhouse gas concentrations in the atmosphere. For geological sequestration, an accurate equation-of-state (EOS) is critical for evaluating and estimating migration and ultimate diagenetic effects on permeability and porosity. We assembled, coded, and compared two different EOS algorithms. One is the modified Redlich-Kwong (MRK) EOS, which employs modification of the attractive term from van der Waals equation. The other is Span and Wagner's (SW) EOS, an empirical representation of the fundamental equation of Helmholtz energy. Using these fundamentally different EOS, the density, fugacity, and enthalpy of carbon dioxide in the gas and supercritical phases were simulated for several test case models. Results included some disparities between simulated and experimental data. Furthermore, for some simulations small errors were compounded and induced very significant impacts on ultimate carbon dioxide plume migration and associated subsurface chemical reactions. In particular, aqueous carbon dioxide solubility calculations by the two EOS algorithms reflected large differences, especially during longer time-scale simulations. In sum, results suggest that even small differences in thermodynamic properties of carbon dioxide, as calculated between the MRK and SW EOS, may produce magnified differences in ultimate projections of subsurface plume histories and associated chemical reaction processes.
H21E-1072 0800h
Recharge, Upflux, and Water Table Fluctuations for Shallow Water Table Conditions
Recharge to groundwater and upflux were estimated for shallow water tables that have unexpectedly high rises in response to small water input. This phenomenon, known as the reverse Wieringermeer effect, renders the conventional recharge and upflux calculations, using specific yield, inaccurate. Water balance and soil moisture data from five large lysimeters, were used to develop a method for calculating recharge and upflux. Regression analysis was used to correlate the water table fluctuations to rainfall and irrigation input and withdrawals for the lysimeters. Three lysimeters (drip lysimeters) were irrigated through a combination of drip and seepage irrigation and two lysimeters (seepage lysimeters) were irrigated using seepage irrigation method. Rainfall and seepage irrigation input was highly correlated with water table rise in all lysimeters. Drip irrigation input had a low correlation for all lysimeters because of the effect of evaporation on the percolation rate. Drainage was highly correlated with water table drops in drip lysimeters while the correlation in the seepage lysimeters was low. The low correlation for seepage lysimeters is attributed to air entrapment in the groundwater during the high volume seepage irrigation events. These relationships could provide effective prediction tools for irrigation and drainage management under shallow water table conditions.
H21E-1073 0800h
Optimal Sampling Strategy for Parameters Estimation
In groundwater modeling problems, parameter estimation constitutes one of the main uncertain items that must be taken into account, as inverse solution techniques are blocked by several inherent difficulties (i. e. ill-posedness and insufficient quantity and quality of observation data). The easiest way to minimize this uncertainty is to collect great amounts of data. The aim of this work is to build and test a decision model able to locate the position of a fixed number of sample points in order to obtain the "optimal" parameters estimation minimizing the parameters uncertainty and the overall cost of the experimental campaign. This decision model is applied to the estimation of the longitudinal and transversal dispersivity coefficients from simulated field experiments. The classical design of experiment techniques are based on the optimization of the amount of information obtained from experimental data with the hypothesis that the sample domain is defined on a continuous space over time and position (Altmann-Dieses et al. (2002), Carrera, J. at al. (1984), Jacquez, J.A. (1998)). Since this assumption does not always reflect the real situation, especially when field campaigns are to be performed or when the piezometric wells are already present on the site, an approach based on discrete and iterative optimization over a fixed grid of possible sampling points is proposed. The estimates are updated with a Bayesian approach and the iterative process is stopped when the imposed convergence criterium based on the analysis of the variance is reached. The decision model is tested on a bidimensional transport problem considering a bunch of different boundary conditions often found in reality. The concentration experimental data are generated perturbing some rigorous analytical solutions of the advection-dispersion model with a normally distributed experimental error with given variance (a Monte Carlo based technique is used to generate normally distributed random variables). In order to define the optimal sampling points in the porous medium, binary decision variables are introduced: they assume value one when the concentration is measured at a specific point and time, zero otherwise. The objective function is iteratively minimized with a genetic algorithm and it is proportional to the calculated covariance of the estimated parameters and the decision variables. The formalized constraints regard the possible number of measures, according to the available budget.
H21E-1074 0800h
ASEST - a Convenient Software Package for Subsurface Problems
In February 2004, Shans' Groundwater published a two-volume book, Analytical Solutions in Excel for Subsurface Transport (abbreviated as ASEST). Authored by C. Shan, the book has a large collection of analytical solutions for flow of water (or gas) and transport of chemicals in the subsurface. Solutions for aquifer problems are in Volume I, and solutions for vadose zone in Volume II. For each of the selected problems, the book gives the corresponding assumptions, the governing equation, the boundary/initial conditions, and the analytical solution. All analytical solutions are programmed in Microsoft Excel ('97 version), which are loaded on a CD (totally 60 programs). The procedures, tips, and examples for running these programs are given in the book. To run a program, users simply open the Excel file and go to Sheet1, type input data in a table, and click a run button below the table. It usually takes a few seconds or minutes to run the program, which outputs the resulting data on Sheet2. For a two-column output, a figure is usually shown on Sheet3. ASEST is a convenient software package for solving many kinds of subsurface problems. It is also designed for everyone: university professors can use it in preparing their lectures, graduate students can use it in their course study and thesis preparation, researchers can use it to analyze data from laboratory or field experiments, code developers can use it to verify their numerical programs, and consultant engineers can use it to obtain some first-cut results for their projects. More detailed information about the book is given at the website: http://www.shans-groundwater.com .
http://www.shans-groundwater.com
H21E-1075 0800h
Three Model-Independent Algorithms for Optimal Selection of Monitoring Wells
Contamination of groundwater is quantified by sampling the aquifer at a number of wells and mathematically interpolating or physically modeling discrete values into maps of contaminant plumes. The apparent shape of the contaminant plume is extremely sensitive to the choice of wells. The objective of this work is to develop an algorithm which would choose the optimal wells for sampling. The optimization algorithms developed as part of this work can receive input (i.e. contaminant concentrations, pumping discharges, and concentration uncertainty estimates) from a variety of external models and recommend where to sample, i.e. which input the model should demand from the real world. The well utility function (WUF) simply weighs the input according to user-defined weights: given n available samples, the n wells with the highest well utilities are chosen for sampling. The cell utility function (CUF) ranks rectangular area cells by summing up the individual WUFs included in each cell. Consequently, each cell is assigned a number of samples according to its rank. Inside each cell it is much easier to allocate samples, mainly because there is a much smaller pool of wells to choose from. The major contribution of this work was the Utility Density Function. The UDF was defined as a continuous function, whose integral over an area returned that area's utility for sampling. A genetic algorithm found the best partition of the aquifer, in which the variance of the utility functions of the different polygonal cells was minimal. In the next step, one well was chosen for sampling in each cell. This ensured that no cell was allotted redundant samples (as all had the same utility). The three algorithms (WUF, CUF, UDF) were tested on several environmental settings, and in general the performance of each algorithm surpassed its precedents; i.e. sampling at the recommended sites resulted in better model predictions. This was also seen in sensitivity analyses, in which different parameters were taken to extremes.
H21E-1076 0800h
Approximate Solutions to Certain Nonlinear Diffusion Equations Appearing in Groundwater Flows.
We consider the Boussinesq equation and its generalization the porous medium equation. The Boussinesq equation describes unconfined groundwater flow, while the porous medium equation describes the filtration of moisture in case of the power-law diffusivity. For certain types of initial and boundary conditions there are approximate solutions techniques. We analyze one-dimensional semi-infinite initially dry aquifer with boundary conditions at the inlet. Solutions would propagate with the finite speed in this case, and the constructed approximate solutions would preserve certain scaling properties of the original problems.
H21E-1077 0800h
Pressure and Displacement Responses During Slug Tests in Deformable Fractures
Slug tests are a common method of estimating the transmissivity of aquifers, but limited work has been done on how to interpret these tests in fractured media. We have conducted suites of air-slug tests using straddle packers and a highly sensitive extensometer to evaluate the distribution of aquifer properties in fractured biotite gneiss at a site in Clemson, SC. Pressure was measured as a function of time, and the extensometer allowed us to also measure transient changes in fracture aperture during the tests. Results show pressure signals similar to that predicted by the Cooper, Bredehoeft, Papadapolous (1967) solution, but the pressure drops slightly faster than predicted by that solution during about half of the tests. Moreover, the slug-out pressure responses commonly differ from the slug-in responses at the same depth. Fracture apertures open by 1 to 20 microns during slug-in tests, depending on the applied air pressure, and the maximum aperture lags behind the maximum pressure by up to several tens of seconds. The field results were modeled using a hydrid-finite difference numerical code designed to simulate coupled flow and deformation of a single, idealized fracture. The model predicts the field data remarkably well. The compiled results of 25 slug tests along the length of a single well show that there are three conductive intervals (K ͙ 10-3 cm/s) separated by relatively low conductivity material (K<10-5 cm/s). Hydraulic conductivity estimates for slug-in tests are as much as 1.25 times greater than estimates from slug-out tests at the same depth. These differences are consistent with pressure-induced aperture changes at the wellbore predicted by the model. Transient changes in fracture aperture measured with the extensometer can be used to improve the estimate of specific storage during slug tests. Pressure and displacement data were inverted to estimate the locations of permeable zones intersecting the fractures. These results indicate that steeply dipping fractures occur within several meters of the borehole at most depths.
H21E-1078 0800h
A Dipole Flow In Situ Reactor: Initial Modeling and Experimental Results
Knowledge of aquifer material characteristics is necessary to make informed decisions about trigger levels for restoration and selecting remediation options. In particular, aquifer property measurement techniques for groundwater transport and reactions are too costly or not-representative of in situ conditions and therefore there is an over-reliance on literature values or model assumptions. This results in overly uncertain predictions of in situ performance and therefore unnecessarily cautious risk assessment and costly remediation strategies. Therefore, cost-effective site investigative tools that have the capability of producing high quality characterization data are required. The dipole flow test which circulates groundwater between isolated injection (source) and extraction (sink) chambers within a single borehole has been used successfully by others to delineate heterogeneous hydraulic properties in both highly permeable and fractured rock aquifers. A project is presently underway that extends this approach by adding a suite of reactive tracers into a dipole flow field to assess various aquifer properties (e.g., geochemical properties and biodegradation potential). If successful this will provide a method to ascertain site-specific parameters for use in appropriate reactive transport models, and to support remedial technology selection and design. This project involves: (1) the construction of a laboratory-scale physical model of a dipole probe to investigate the utility of this dipole flow and reactive tracer test as an site assessment tool; (2) the execution of a host of field trials; and (3) the development of a stand-alone multi-phase reactive transport model that can be used to interpret the generated breakthrough curves. In addition to an overview of this project, initial experimental and model results will be discussed.
H21E-1079 0800h
Geochemical and Isotopic Constraints on Deep Ground Waters in the Bluegrass Region of Central Kentucky
The Cambro-Ordovician Knox Group Aquifer is a regionally extensive paleokarst ground water system that underlies much of the Interior Low Plateau and neighboring Central Lowland province of the United States. The geology and hydrology of the aquifer in the Bluegrass region of central Kentucky are regionally controlled by the north-trending Cincinnati Arch, and are locally controlled by the Jessamine Dome, the northeast-trending Kentucky River Fault and West Hickman Fault systems, and a system of northwest-trending fractures. Previous hydrological investigations elucidated two distinct zones of water within the aquifer as it occurs throughout the Bluegrass. A zone of low conductivity waters straddles the axis of the Cincinnati Arch north of the Kentucky River, which cuts across the axis of the Arch in the southern portion of the Bluegrass. Low conductivity waters are thought to be related to leakage of the Kentucky River into the top of the aquifer, and to vertical leakage that occurs along fracture and fault systems. High conductivity waters occur along the eastern and western flanks of the Arch. The purpose of the present investigation is to utilize the geochemical and isotopic characteristics of Knox Group Aquifer waters to assess local and regional flow dynamics (recharge/discharge/velocity) and hydrogeochemical evolution of waters in a structurally complex setting. Preliminary results from deep wells ($>$260 meters) indicate a dynamic range in chloride (10 to 412 ppm), sulfate (13 to 143 ppm), and fluoride (undetectable to 6 ppm), suggesting significant geochemical evolution of ground waters over short horizontal flow paths. Alkalinity concentrations range from 260 to 290 mg/L CaCO$_{3}$. Preliminary $\delta$$^{18}$O results from wells in the central and southwest Bluegrass are similar to the annual average $\delta$$^{18}$O of regional meteoric ($\sim$-7.0$\permil$).
H21E-1080 0800h
A Geophysical Study of Fissures in Pahrump, Nevada
Earth fissures are surface expressions of deep fracturing subsidence systems caused by groundwater withdrawl greater than aquifer recharge. This type of subsidence is most common in arid environments of the south western U.S. such as, Las Vegas, NV, Phoenix, AZ, and areas in New Mexico. In addition, fissures have recently been identified in the Pahrump Valley in southwestern Nevada just west of Las Vegas. The city of Pahrump has experienced an increase in population and economic growth. This growth has lead to a higher demand in the use of the areas natural resources. One major concern is groundwater pumping and over-watering of the land surface. Pahrump has experienced significant differential subsidence within the valley causing significant structural damage to infrastructure. This differential subsidence is most readily identified by its surface expression as fissures. Earth fissures are not only shallow surface features but can be 10's of meters deep and 100's of meters long. These ground failures can be exacerbated by faults at depth, shallow bedrock, and/or differential compaction. However, the most significant cause is from groundwater withdrawl. Several geophysical methods were performed on the fissures to better understand their subsurface expression, trend, and ultimately their affect on the city of Pahrump. Seismic refraction, reflection, ground penetrating radar (GPR), and gravity measurements were performed on the fissures and surrounding area including local faults. Our initial studies show the fissures propagating for long distances, in a variety of shapes, and trending in a north-south direction. Initial GPR studies show high fissure reflections at approximately 1 and 1.5 meters along with general slumping features below these reflections. Fissures are an unmitigatable problem. Our results will help identify fissures in the area that do not have a surface expression as well as mapping the current fissures and their extent. These results can be used to increase standards in the building of infrastructure and in designating land use zonation.
H21E-1081 0800h
A new method of measuring 81Kr and 85Kr abundances in environmental samples
We demonstrate a new method for determining the 81Kr/Kr ratio in environmental samples based upon two measurements: the 85Kr/81Kr ratio measured by Atom Trap Trace Analysis (ATTA) and the 85Kr/Kr ratio measured by Low-Level Counting (LLC). This method can be used to determine the mean residence time of groundwater in the range of 100,000 - 1000,000 years. It requires a sample of 100 micro-l STP of Kr extracted from approximately two tons of water. With modern atmospheric Kr samples, we demonstrate that the ratios measured by ATTA and LLC are directly proportional to each other within the measurement error of ±10%; we calibrate the 81Kr/Kr ratio of modern air measured using this method; and we show that the 81Kr/Kr ratios of samples extracted from air before and after the development of the nuclear industry are identical within the measurement error.
http://www-mep.phy.anl.gov/atta/