Ferrous carbonate has been studied in batch reactions under rigorously anoxic conditions to determine thermodynamic and kinetic information about the compound. This information is particularly of interest in corrosion control and in the comparison of FeCO$\sb3$ to CaCO$\sb3$, a compound which has been studied extensively. The enthalpy of the dissolution reaction has been calculated to be $-22.8$ $\pm$ 0.6 kJ/mole, which is close to the NBS (1) reported value. The precipitation kinetics fit an empirical second order rate law with an activation energy of (9.31 $\pm$ 1.47) $\times$ $10\sp4$ J/mole, indicating surface reaction control. The dissolution kinetics fit an empirical second order rate law more closely than a first order rate law; however, more research is needed to decisively determine the reaction order. With either rate law, the activation energy for dissolution is large enough to suggest surface reaction control.

Natural biodegradation is occurring at a Gulf Coast Refinery based on results of a field program that showed a statistically significant relationship between DO depression and BTEX contamination and that microbes capable of degrading BTEX are present in the soils at the site. Natural biodegradation is shown to have the potential to be a viable remedial technique at the Refinery based on modeling of the site using BIOPLUME II, a two dimensional ground water transport and biodegradation model. Natural biodegradation was shown and observed to be a viable remedial technique at a site in Traverse City, Michigan where contaminant remediation of the off-site plume occurred in less than three years. BIOPLUME II model results indicated that hydraulic flushing alone could not account for the observed declines in BTEX concentrations at three wells downgradient of an interdiction well field, but that biodegradation and vertical reaeration were processes required to accurately model the site.

Leading researchers in methods of Spatial Statistics advocate applying kriging methods to samples of 100 or more observations. However, in practice it is not uncommon to have as few as 20 observations from which to estimate a surface. The focus of this thesis is to compare various kriging models, given a small number of observations and develop a method for finding a lag at which to fit a variogram model. Specifically, the spherical, rational quadratic, and exponential variogram models are examined. A comparison among kriging methods and kernel methods is presented.

A true ecological architecture acts comprehensively, on all scales, from urban form to building materials. While suburbia is the urban form most destructive to the natural environment as well as to diverse human culture, it persists in the collective American desire. Present proposals exist to turn new suburban development into tight pedestrian communities, but the question remains what to do with the deteriorating fabric of American cities. Medium density, mixed-use urban infill that carefully plans for multiple types of transportation while providing some of the attractive aspects of suburbia, such as personal privacy and security, offers an escape from auto-centric existence. When augmented with the selection of local, non-toxic building materials from renewable resources, passive heating and cooling techniques, and provisions for usable open green-space, mixed-use infill will allow our cities to avoid utopian social engineering on the way to ecological soundness.

The influence of Natural Organic Matter (NOM) on the removal of atrazine by nanofiltration was studied using pressurized dead-end filtration cells. The effect of several parameters, physical and chemical, was investigated to identify the interactions between the NOM and atrazine. Any changes of the physical parameters leading to an increase in concentration polarization, such as stopping the stirring, produced a decrease in rejection of atrazine. No significant pressure effect was observed for the conditions evaluated in this study. The chemistry of the feed solution also influenced the removal of atrazine. The presence of organic material appeared to enhance atrazine rejection by the membrane. The extent of this process varied with several factors: the atrazine to TOC ratio (smaller effect at higher atrazine to TOC ratio), the nature of the organic matter (higher removal observed for tannic acid compared to the NOM) and the calcium concentration at low ionic strength in the presence of tannic acid. The model presented in this work consistently underestimated the initial concentration of atrazine. It also gave better predictions in the absence of organic matter and failed to predict most of the data obtained with tannic acid.

No description available.

Hydrilla (Hydrilla verticillata Royle) is an exotic aquatic angiosperm which has become a problematic weed throughout the southern United States. Infestation by aquatic weeds like hydrilla increase loss of valuable water through evapotranspiration, choke waterways used for transportation, depress real estate values, and may present health hazards. Control strategies including herbicide treatment and mechanical harvesting have proven costly and of short term benefit. One reason for this is the vegetative dormant buds which allow the plant to overwinter and reestablish rapidly after attempts at control. This research focuses on elucidation of the bud formation process in hydrilla to provide the basis for development of a control strategy which combines use of herbicides with disruption of bud formation and hence the capacity for regrowth. The environmental and hormonal control of vegetative dormant bud formation was studied in the laboratory using algal-free cultures of hydrilla. Bud formation is stimulated by a photoperiod of less than 12 hours. This environmental stimulus appears to be sensed by the phytochrome system and hormonally induced by abscisic acid. Field sampling at Lake Conroe, Texas, confirmed, where possible, laboratory results and indicated that artificially prolonged photoperiods prevent bud formation. Ethylene, both in laboratory and greenhouse cultures, significantly reduced bud formation at a dose rate of 0.1 mg/l every two days. Coumarin significantly reduced bud formation when applied at 10('-6) M but information in the literature indicates that the mode of action of coumarin may be induced ethylene formation in the plant (Morgan and Cowell, 1970). Growth characteristics of hydrilla make it suitable for use in a bioassay for the assessment of the relative phytotoxicity of aquatic pollutants. Algae-free cultures of hydrilla were grown in the laboratory in 10% Hoagland's medium. Evaluation of chemical toxicity was obtained starting from two different life stages of the plant: dormant buds and apical fragments. Dormant bud production was also monitored in order to evaluate the potential for life cycle and chronic studies. Hydrilla appeared more sensitive to ammonium carbamate than were duckweeds and more sensitive to phenol than was a unicellular green alga. Growth rate was not quantitatively related to toxicant concentration, but yield, dormant bud sprouting, and dormant bud production were related. . . . (Author's abstract exceeds stipulated maximum length. Discontinued here with permission of school.) UMI

A series of soil column tests and field experiments were designed to evaluate microbial removal of trace organics during rapid infiltration recharge of ground water. Field experiments demonstrated that operation of rapid infiltration systems using either primary or secondary wastewater can contribute trace organics to associated ground waters although concentrations of individual compounds can be reduced by the treatment process. Most of the removal occurred in the upper meter of the soil. Soil column tests demonstrated that trace organic removal from either primary or secondary wastewater was minimal when non-acclimated soil was conditioned by continuous flooding to eliminate adsorption as a removal mechanism. Batch tests indicated that most of the removal occurred in the wastewater prior to infiltration. Conversely, column tests using acclimated soil from an operational system demonstrated good removal of trace organics. Increased concentrations of target compounds in the feed did not always result in corresponding increases in the column effluent. Microbial adaptation was evident for some compounds. Other compounds appeared to exhibit a minimum concentration below which biodegradation did not proceed. Microbial activity was confirmed as a fate mechanism for several target compounds using radiolabels. In direct correlation with field results, the induction of anaerobiosis in the soil columns resulted in increased fractional breakthrough of trace organics.

A ground water humic material has been isolated using XAD-8 adsorption chromatography (Thurman and Malcolm, 1981). Partitioning studies for DDT, hexachlorobenzene (HCB), and bis(2-ethylhexyl)phthalate (BEHP) and soil column studies for HCB and anthracene have been completed. Partition coefficients for DDT, HCB and BEHP are 10('5.99), 10('4.64) and 10('3.66), respectively. A linear relationship between log solubility (mole fraction) and log partition coefficient (Kp) exists where: log Kp = -0.91 log S (mole fraction) -3.34 (R = 0.9984). These values are in agreement with those determined for soil sediments for compounds whose water solubilities are in the range of 1 (mu)g-l('-1), but are lower by an order of magnitude for compounds whose water solubilities are on the order of 500 (mu)g-l('-1) (Karickhoff, 1979). The classical contaminant retardation equation was modified to account for mediated transport by dissolved organic carbon (DOC). Soil column experiments exhibited mediated transport of HCB and anthracene by the humic material and provided strong evidence that the compounds move as an irreversible humic/organic complex. The implications and magnitude of this mediation of organic transport by ground water humics is discussed. The existence of such a complex may account for the enhanced migration of certain trace level organics in ground water.

To prevent the deterioration of groundwater quality, mathematical simulation models have been formulated to predict the transport of contaminants in complex aquifer systems and to design remedial schemes for the problems. Existing analytical and numerical approaches have serious disadvantages for large-scale nonhomogeneous field problems where well-pumping or injection is involved. The major difficulties relate to numerical dispersion and oscillations in highly advective-dominated simulations, computational accuracy, excessive computer expense, grid orientation problems, and an inability for simulating with random conductivity fields. Recent work by Ewing, Russell, and Wheeler (1983) has produced a very efficient and accurate method for miscible displacement in oil reservoirs. Their concept was adapted and then applied to groundwater contaminant transport problems in this thesis. The highly efficient code combines a mixed finite element procedure for groundwater flow and a modified method of characteristics and finite element procedure (MMOC) for the parabolic transport equation. The preconditioned conjugate gradient method was used to solve the resulting matrices for both equations. The method has been compared with two analytical solutions on a homogeneous domain. Excellent agreements were demonstrated through relative concentration contours and breakthrough curves. The method has also been compared with the currently popular USGS Solute Transport model. More accurate resolutions were achieved for the MMOC method than for the USGS Solute Transport model. In addition, much larger time steps were allowed in the MMOC method than the USGS Solute Transport model obtaining similar resolutions. The method has been applied to highly advective-dominated problems on a CRAY-XMP supercomputer and the results showed there are no dispersion or oscillation problems common in many existing numerical codes. The method has also been used to simulate cases with random hydraulic conductivity fields that were simulated from Turning Bands Method. Fingering phenomena developed because the concentration front is transported more rapidly in the zones of higher hydraulic conductivity. The method has been shown to be superior in many respects to currently used models in groundwater transport, especially in the presence of strong pumping or injection centers or heterogeneities in the flow field.