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Liquid waste has been injected into a permeable part of the lower limestone of the Floridan aquifer since 1963, raising hydraulic head in the injection zone throughout a region of northwestern Florida. The injection zone consists of a moderately permeable limestone, hydraulically isolated from overlying aquifers by a thick layer of clay. The formation fluid is saline, but becomes fresher up dip, northward where the limestone crops out. Numerical simulations were performed at regional and local scales to assess the regional pressure increase, to analyze the movement of the 10,000 mg/1 total dissolved solids (TDS) isopleth (formation fluid) in the lower limestone of the Floridan aquifer, and to analyze the migration of the injection fluid, both historically and predictively, in the injection formation. This work is based largely on previous work by Merritt (1984), but uses the SWIFT code. Modifications to Merritt's work include increasing the hydraulic conductivity near the injection wells and using more recent injection rates; extensions include particle tracking and solute transport modeling. The simulations indicate that regional pressure increases should be much less than previously predicted. Using the new results, by the year 2033, the average movement of the 10,000 mg/1 TDS isopleth due to injection is expected to be approximately 2200 ft (671 m). Additionally, by the year 2033, the indiluted injection fluid (95% of injection concentration) should migrate to an approximate diameter of 2.1 mi (3.4 km) from the injection wells.

A one-dimensional, finite-difference model for simulating biodegradation and sorption processes in saturated porous media is developed. The model formulation is general and capable of accommodating a variety of boundary conditions and process theories. Advective and dispersive transport of a substrate and an electron acceptor are considered. Aerobic biodegradation is modeled using a modified Monod function; anaerobic biodegradation is modeled using Michaelis-Menten kinetics. In addition, first-order degradation is allowed for both substances. Sorption can be incorporated using linear, Freundlich, or Langmuir equilibrium isotherms for either substance. Dirichlet, Neumann, or Cauchy boundary conditions are allowed, where they are constant in time, or include first-order degradation. The resulting nonlinear problem is solved using a Newton-Raphson iterative technique. Model verification is achieved through a series of simulations, two of which arc included. In addition, three applications demonstrate the utility of the model.

The numerical models used in ground-water studies are general computer programs that can be applied to a variety of hydrogeological conditions. These programs are based on approximations to the governing partial differential equations for ground-water flow and transport. To use these models requires an understanding of the physical problem and field data. Although program input data and output results are quantitative, the appropriate application of numerical models remains a partly subjective procedure. To use models, the hydrologist must assess the merits of alternative numerical methods, evaluate available data, estimate data where missing or absent, and interpret computed results. The review of previous model applications can provide valuable insight on how these tasks may be approached.

During the two-week period from March 12 through March 26, 1982, a preliminary conceptual design analysis on various remedial measures for the Lipari Landfill, New Jersey, was performed. This site is currently ranked at the top of the EPA's Superfund Cleanup List. This report demonstrates the practical benefits and limitations of applying models (both analytical and numerical) to a hazardous waste site in a restricted period of time. The numerical model was used to simulate current flow conditions at the site and provide initial conditions for a series of sensitivity simulations. These sensitivity simulations were designed to test (1) a slurry wall, (2) drain location, (3) drain depth, and (4) a clay cap. Analytical solutions were designed to analyze (1) water in place, (2) flow through an underlying layer, the lower Cohansey, (3) draining the lower Cohansey, (4) flushing the contaminated area using wells, and (5) convective arrival time of contaminants to drains. This analysis quantified discharge to drains, flow rates to a swamp downstream of the landfill, time required to drain the landfill, and contaminant travel times that would result from the implementation of each of the remedial measures that were suggested. The conclusions from this study were used by engineers and planners who incorporated, economics and engineering decisions for the various remedial measures considered.

A numerical model is presented that solves the partial differential equations describing the motion of salt water and fresh water separated by a sharp interface. The areal equations are based on the Dupuit approximation and are obtained from partial integration over the vertical dimension. Finite-difference techniques are applied and the utility of several solution schemes is tested. The most efficient and accurate solution scheme uses block line-successive over-relaxation. Examples are given to: (1) test the model, (2) evaluate the Dupuit approximation, and (3) demonstrate the application to a field situation. The results show that the model is in good agreement with an analytical solution, but under severe conditions the Dupuit approximation may be inappropriate. The model is applied to a field area near Kahului, Maui, Hawaii and results extend the analysis of the problem beyond previous efforts.

Ground-water modeling is an area of current research. As such, new techniques and applications continually evolve. In addition to being influenced by the necessity to solve certain problems, recent developments in modeling are influenced by the state of model evolution and computer capabilities.

Ground-water modeling is a tool that can help analyze many ground-water problems. Models are useful for reconnaissance studies preceding field investigations, for interpretive studies following the field program, and for predictive studies to estimate future field behavior. In addition to these applications, models are useful for studying various types of flow behavior by examining hypothetical aquifer problems. Before attempting such studies, however, one must be familiar with ground-water modeling concepts, model usage, and modeling limitations.

Volusia County, in east central Florida, comprises approximately 1,200 square miles situated between the St. Johns River and the Atlantic Ocean. Most of the County is underlain by a three-aquifer system. Population centers in Volusia County, which create a large water demand, are located near the coast. Saltwater intrusion into the ground water near these population centers has led to relocation of public water supply wells further inland. Regional management of the county's water resources commissioned construction of a three-dimensional computer model of the county. Predevelopment simulation results were used as initial conditions for the development simulations, which included well discharge data. The predevelopment model calibration consisted of reproducing field-determined potentiometric surfaces. As part of the calibration process, sensitivity analyses were performed on boundary conditions, recharge rates, permeability, and leakage properties. Results of the model study indicate the utility of computer models as a management tool for the complex ground-water system in Volusia County.

1. Extrahypothalamic thermosensitivity at normal (39 degrees C) and lowered (33.8 degrees C) hypothalamic clamp temperatures has been measured in cold exposed rabbits equipped with chronically implanted hypothalamic perfusion thermodes. The animals were subjected to body core cooling by means of cold perfused thermodes placed in the colon. 2. At lowered hypothalamic temperature the threshold core temperature for increased metabolic heat production due to body core cooling was significantly increased as compared to that at normal hypothalamic temperature. However, the slope of the response relating increased metabolic rate to body core temperature was significantly reduced. 3. The experimental results compare well with those predicted from a mathematical model, which takes into account the effect of temperature on synaptic transmission of afferent information in the hypothalamus.

The City of Hallandale, located on the east coast of Florida, has documented over the past decade an increase in chloride in the monitoring well network surrounding its wellfield. Data indicate that the salt-water front is currently located within 1,200 ft of the wellfield and is still moving inland. Suspected causes of the intrusion are: (1) increased pumpage by Hallandale, (2) increased pumpage from neighboring wellfields, (3) cumulative deficiency in rainfall over the past decade, and (4) reduction of canal stages that control water-table elevations. The inability of standard methods to characterize the salt-water intrusion led to the use of numerical modeling to aid in understanding the processes occurring at Hallandale. A series of three models were used in the study. A cross-sectional model was used to conceptualize the flow system, and a regional model synthesized input for the third model, the wellfield model. The wellfield model was eventually used to assess the relative merits of proposed water management alternatives. Although the modeling did not isolate a specific cause of the intrusion, it did show the extreme sensitivity of the hydrologic system. Long-term water-level declines of only a few tenths of a foot were shown to result in a significant movement of the salt-water front. There is a distinct time lag, however, between lowering of the hydraulic heads and movement of the salt-water front, which has many implications for water management decisions and in the construction and calibration of a numerical model. These observations, as well as others made in the course of this study, can be applied generally to coastal water management programs.