The evaluation of groundwater quality has become increasingly important as more industrial waste and solid domestic refuse comes into contact with groundwater. Often the quantity and extent of contamination is determined by direct sampling of the groundwater and soil. An alternative method of detecting contaminated groundwater is by noting the electrical resistivity of the contaminated soil. The feasibility of logging resistivity while conducting cone penetrometer testing has been investigated in this research. To this end a two stage program was devised, consisting of lab testing and then field tests of a working tool. Lab testing was carried out using a prototype probe designed to evaluate the feasibility of the project. The lab testing consisted of determining the resistivity of a number of different soil, electrolyte, and organic contaminant mixtures while varying the configuration of the probe. On the basis of lab testing the necessary requirements for the module dimensions and electronics were chosen and were fine tuned by field tests. The module itself consists of an insulated four electrode array and is mounted behind a standard 15 sq cm piezo-cone (CPTU). Upon completion of the development phase the instrument was tested at four different sites. From field testing it was determined that the resistivity cone (RCPTU) was able to accurately map changes in groundwater chemistry on the basis of resistivity measurements. The results of the resistivity testing were verified by groundwater sampling. It was also found that changes in lithological properties, as determined by the cone penetration test (CPT), could influence the resistivity. Basic guidelines for the use of the RCPTU in contaminant investigations are presented. / Applied Science, Faculty of / Civil Engineering, Department of / Graduate

A field study was conducted to determine the applicability of multivariate geostatistical methods to the problem of estimating and simulating pesticide concentrations in groundwater from measured concentrations of nitrate and pesticide, when pesticide is undersampled. Prior to this study, no published attempt had been made to apply multivariate geostatistics to groundwater contamination. The study was divided into two complementary aspects of geostatistics: estimation and simulation. The use of kriging and cokriging to estimate nitrate and the herbicide dimethyl tetrachloroterepthalate (DCPA) contaminant densities is described in Chapter I. Measured concentrations of nitrate and the DCPA were obtained for 42 wells in a shallow unconfined alluvial and basin-fill aquifer in a 16.5 km² agricultural area in eastern Oregon. The correlation coefficient between log(nitrate) and log(DCPA) was 0.74. Isotropic, spherical models were fitted to experimental direct- and cross-semivariograms with correlation ranges and sliding neighborhoods of 4 km. The relative gain for estimates obtained by cokriging ranged from 14 to 34%. Additional sample locations were selected for nitrate and DCPA using the fictitious point method. A simple economic analysis demonstrated that additional nitrate samples would be more beneficial in reducing estimation variances than additional DCPA samples, unless the costs of nitrate and DCPA analysis were identical. These estimates are by definition, the Best Linear Unbiased Estimates (i.e., the estimates with minimized estimation variance), however the requirement of minimized variance smoothes the variability of contaminant values. The application of conditional simulations to groundwater contamination is described in Chapter 11. Conditional simulation allows the degree of fluctuation of nitrate and DCPA between sample points to be assesed. With knowledge of both the 'best' estimates and the of the variability between sample points, nitrate and DCPA groundwater contamination in the study area can be characterized Based on the semivariogram models found in Chapter I, univariate and multivariate conditional simulations of nitrate and DCPA were generated using the turning bands method and the kriging or cokriging system. Kriging was used to condition the univariate simulations, while cokriging was used to cross-correlate and condition the multivariate simulations. The mean of 25 conditional and coconditional simulations at 8 different locations in the study area were generated and compared to kriging and cokriging estimates and 95% confidence intervals. Both conditional and coconditional simulation of the DCPA and nitrate contaminant densities showed large variations when values in different simulations were compared. The fluctuation in values demonstrate the uncertainties in the contaminant distributions when sample sizes are small. As a result of this unkown component, simulated values vary widely. Coconditional simulation displayed the cross-correlation imposed by using the cokriging system to condition the simulations. After 25 simulations, the mean remained unstable indicating that more simulations would be required to enable comparisons with kriging and cokriging estimates. / Graduation date: 1989

Chapter I presents an investigation of a TCE-contaminated aquifer beneath Tucson International Airport, Arizona. Shallow soil gas (< 2m deep) was collected and analyzed for halocarbon contaminants to determine the relationship with vadose zone and groundwater contamination directly below. The TCE plume in shallow soil gas was mapped with 46 probes and spanned 3 orders of magnitude in concentration (< 0.001 to 2.0 μg/L). TCE concentrations in water from 5 monitoring wells around the Airport property ranged from 4 to 2800 ppb and had a correlation coefficient (r) of 0.90 with TCE concentrations in shallow soil gas. Vertical borings were completed to the water table at four locations in order to obtain profiles of soil gas contamination, air porosity, and water saturation. Vertical concentration gradients and effective diffusion coefficients were used to calculate flux rates for volatile organic contaminants (VOC's). Flux values ranged from 0.094 to 680 pg/day per m² for the four borings, and an annual mass transfer of TCE from groundwater to the atmosphere was estimated at 4 kg over the 0.5 km² site. Contaminant concentrations in shallow soil gas provided an accurate indication (r = 0.94) of vadose zone flux on a site-specific basis. The success in delineating the areal extent of subsurface contamination via soil gas sampling is not diminished by geologic or hydrologic anomalies if they are not laterally extensive compared to the plume. Chapter II introduces an environmental rates model which provides an estimate of the subsurface fate of volatile organic chemicals. Six hydrochemical indices are estimated (dissolved flow retardation, immiscible flow retardation, air-water partitioning, soil gas diffusion, hydrolysis, biodegradation) from compound-specific properties and site-specific characteristics. In addition, the carcinogenic potential and metabolic intermediates (two biochemical indices) of 75 volatile organic chemicals are estimated from the compounds' chemical structure. The model output is designed to assist water resource and environmental decision-makers in assessing the severity of existing problems and in avoiding potential problems.

Over the last decades, arsenic (As) contamination of soil-plant-water systems has become a major concern for Bangladesh and West Bengal, India. The geochemistry of the sediment depositional environment which subsequently, on sediment burial, give rise to elevated As in Holocene groundwater’s of Southeast Asia, may provide clues to unravelling the mechanistic basis and spatial heterogeneity of this phenomenon. The Sundarbans mangrove ecosystem, Bangladesh, is a modern analogue, and indeed forms a continuum with, the Holocene sediments of concern and thus studying As cycling in surface Sundarbans sediments. Similarly, rice paddy fields in many regions of the Bengal Basin form a continuum with Holocene sediments. Sediment cores were collected from a wide range of locations within the Sundarbans to study surface spatial, as well as down the profile (~1 m), As distribution and it’s association with other geochemical parameters. Pore and surface water, and Diffusive Gradients in Thin films (DGT) were sampled from 4 different interlocked sub-habitats over 0.29 km2: major river bank, main tributary, forest floor and minor tributary. Further experiments were conducted to observe As dynamics in mangrove surface sediments on application of mangrove detritus. Finally 3 interlinked experiments (field manuring, soil batch culture, greenhouse growth trials) were conducted to assess the effect of farm-yard manure (FYM) and rice straw, at a field application rate practised in Bangladesh (5 t/ha), on As mobilization in soil and subsequent assimilation by rice. As concentration in mangrove sediment down the profile was found to be more associated with elevated Fe and Mn than with organic matter (OM), with significant spatial variations among the locations. Sediment particle size was an important factor determining As retention and mobilization, which is also true for deeper Bengal Bay sediments. Proximity to mangrove vegetation and to water bodies was found to have significant effect on As dynamics. Porewaters from coarse textured, low OM riverbank sediment were high in As, but with only a small pool of As for resupply from the solid phase, showing similarities with grey aquifer sediments compared to fine textured and high OM content forest floor sediments. The As column dynamics study showed that As release into porewater was strongly associated with Fe release, indicating the strong association of the 2 elements, with OM playing a major role in their dissolution. The desorption studies also showed OM driving As mobilization within short time. Due to strong redox cycling very little evidence of As methylation was observed in biologically active mangrove porewaters. But we found 10-fold increase in dimethylarsinic acid (DMA) production compared to a non-amended control using the same sediments treated with mangrove detritus in the laboratory. OM amendments lead to considerable mobilization of As into both soil porewaters and standing surface waters in rice paddy. In a greenhouse rice cultivation experiment, flooding initially caused greatly enhanced As mobilization in porewater (< 24 d), but the effects of flooding on As mobilization decreased during later rice growth, particularly at grain fill. However, OM amendment did not cause significant As accumulation in grain and straw compared to control. It was noted in field trials and greenhouse studies that OM fertilization greatly enhanced As mobility to surface waters, which may have major implications for fate of As in paddy agronomic ecosystems.

The rate of removal of benzene, toluene, ethylbenzene and the xylene isomers (BTEX) from contaminated groundwater is needed to design remediation processes. Benzylsuccinic acid (BSA) and methyl-benzylsuccinic acid (methyl BSA) are unambiguous metabolites of anaerobic BTEX biodegradation. An analytical method for quantitative determination of BSA in groundwater samples was developed. Samples containing BSA and methyl BSA were extracted onto 0.5 g of styrene-divinylbenzene, eluted with ethyl acetate, and methylated with diazomethane. Gas chromatography coupled to mass spectrometry with electron impact ionization was used for separation and detection. The recovery from spiked 1 L groundwater samples was 88 to 100 %. The precision of the method, indicated by the relative standard error was ± 4% with a method detection limit of 0.2 μg/L. The method was then used to analyze samples from single-well push-pull tests conducted by injecting deuterated toluene and xylene into BTEX-contaminated wells in order to demonstrate in-situ biodegradation. Unambiguous evidence for deuterated toluene and xylene biodegradation was obtained with the observation of deuterated BSA and methyl BSA coupled with the utilization of nitrate presumably due to denitrification as terminal-electron-accepting process. Minimum first-order degradation rates for deuterated toluene estimated from formation of BSA were 0.0004 to 0.001 day⁻¹. Rates of methyl BSA formation were not calculated because methyl BSA, although detected, was not above the quantitation limit. Removal rates of deuterated toluene and o-xylene were not directly measurable because the rates were too low to measure significant changes in parent compound concentrations. Wells for which the formation of deuterated BSA and methyl BSA were observed had lower relative concentrations of toluene and xylenes relative to total BTEX than wells for which no deuterated BSA and methyl BSA were observed. Retardation factors for injected deuterated toluene and background toluene of 2 and 14, respectively, were obtained from push-pull tests conducted to determine toluene transport properties. Differences in retardation factors for injected and background toluene indicate differences between injected and background solute transport and is a topic that requires further study. / Graduation date: 2002

Trichloroethene (TCE) is the most frequently detected organic contaminant in groundwater, is classified as a probable human carcinogen, and exhibits toxicological effects on the human endocrine, immune, developmental, and reproductive systems. While significant research efforts have been devoted to the development of strategies for remediating TCE-contaminated groundwater, their advancement is currently hindered by limitations in current methodologies for measuring in situ reductive dechlorination rates, especially for sorbing solutes. This dissertation describes the development, evaluation, and demonstration of a method for measuring in situ reductive dechlorination rates that utilizes single-well, "push-pull" test technology. Initial field tests indicated that trichlorofluoroethene (TCFE) could be used as a surrogate for TCE in push-pull tests since (a) TCE and TCFE were transported similarly and (b) TCFE underwent reductive dechlorination by a pathway analogous to that of TCE while retaining the fluorine label. Because TCFE and TCE experienced sorption at the selected field site, a novel data analysis technique called "forced mass balance" (FMB) was developed to obtain in situ transformation rates of sorbing solutes from push-pull test data. The FMB technique was evaluated by quantifying errors in rates derived by applying FMB to push-pull test data generated by a numerical model. Results from simulated tests indicated that an example in situ rate for the reductive dechlorination of TCFE, which was obtained by applying FMB to field data, was underestimated relative to the true in situ rate by 10%. The utility of the rate-determination method presented in this dissertation was demonstrated by using it to evaluate the effectiveness of a chemical amendment, namely fumarate, at enhancing in situ reductive dechlorination rates in TCE-contaminated groundwater. Reductive dechlorination rates increased following three consecutive additions of fumarate in all five of the tested wells. The development of the rate-determination method described in this dissertation advances the state of bioremediation technology because methods for measuring in situ transformation rates are needed to both assess the potential for natural attenuation and to quantify the effects of bioremediation techniques in the field. / Graduation date: 2003

Graduation date: 1995

Ph.D. / Environmental Science and Engineering / Chromate-containing precipitates can affect the mobility of toxic Cr(VI) in the subsurface, control its concentration in groundwater, limit its bioavailability, and impede remediation of chromium contaminated sites. This dissertation focuses on two iron-chromate precipitates, KFe [subscript 3](CrO4)[subscript 2](OH)[subscript 6] (the chromate analog of the sulfate mineral jarosite) and KFe(CrO4)[subscript 2].2H2O, that we identified in a soil contaminated by chrome plating solutions. The precipitates were identified using scanning and transmission electron microscopy, as well as powder x-ray diffraction. KFe[subscript 3](CrO4)[subscript 2](OH)[subscript 6] occurs as small (2-5 um) crystals interspersed within the bulk soil. KFe(CrO4)[subscript 2].2H2O forms crusts of larger crystals (10-50 um) in cracks and fractures of the soil. / Due to highly mathematical nature of the abstract, only the first paragraph is shown.

Just as children eventually learn that covering their eyes does not make them invisible, we as adults have realized that just because harmful substances are "out-of-site" it does not necessarily mean they are gone for good. As we expanded our ability to think abstractly we began to consider how our actions affect our future and the lives of future generations. For example, we established procedures for the handling and disposal of high level radioactive waste and other hazardous materials because of the threat such materials pose to the environment. To date, however, the effect of atmospheric pollutants on groundwater supplies has been virtually ignored. Atmospheric pollution sources include, but are not limited to, smoke stack emissions, releases from power plants, weapons testing and manufacturing, fires, explosions, and deflation from tailings, spills and playas. This study evaluates the potential for groundwater to be contaminated by a point-source atmospheric emission. Pollutant concentrations in groundwater are estimated using a Gaussian model of atmospheric transport, a transfer function model for transport through the unsaturated zone, and a two-dimensional groundwater flow model based on Darcy's law to simulate transport in the saturated groundwater system. A sensitivity analysis of the composite atmospheric-groundwater transport model suggests that the most important factors influencing the susceptibility of a groundwater system to contamination by an aerosol source are: the concentration of the source, the amount of recharge, the depth to the water-table, and the velocity distribution in the unsaturated zone. This study indicates a significant potential for pollution of groundwater systems by aerosols. Shallow aquifers are especially vulnerable; however, deeper aquifers where rapid travel times through the unsaturated zone exist are also susceptible to aerosol contamination. / text

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