RITZ is a menu-driven U.S. EPA model which permits decision makers to simulate the movement and fate of hazardous chemicals during land treatment of oily wastes. RITZ incorporates the influence of oil in sludge, water movement, volatilization, and degradation upon the transport and fate of a hazardous chemical. Soil water content is related to hydraulic conductivity by the Clapp and Hornberger function. Features include interactive data entry and both graphical and tabular output.
The Regulatory and Investigative Treatment Zone Model, RITZ, was developed to help decision makers systematically estimate the movement and fate of hazardous chemicals during land treatment of oily wastes. The model considers the downward movement of the pollutant with the soil solution, volatilization and loss to the atmosphere, and degradation. RITZ incorporates the influence of oil upon the transport and fate of the pollutant. This RITZ model forms the basis of this interactive software system. The software enables users to conveniently enter the required soil, chemical, environmental, and management parameters and checks the validity of these entries. The user may then select graphical and tabular outputs of the quantities of interest.
A land treatment site is imagined. The treatment site consists of two soil layers called the plow zone and the treatment zone. The sludge (waste material) containing oil and pollutant is applied to the plow zone. It is thoroughly mixed with the soil in that layer. As time passes, the pollutant and oil are degraded. Some of the pollutant is carried down through the soil with percolating water. Some of the pollutant is volatilized and moves into the air above the treatment site.
The following assumptions were made in developing this model:
- Waste material is uniformly mixed in the plow zone.
- The oil in the waste material is immobile. It never leaves the plow zone. Only the pollutant moves with the soil water.
- The soil properties are uniform from the soil surface to the bottom of the treatment zone. This assumption will rarely, if ever, be met in the field. The user can estimate the impact of non-uniform soils by comparing results for several simulations covering the range of soil properties present at the site.
- The flux of water is uniform throughout the treatment site and throughout time. This assumption will rarely be met in the field.
- Hydrodynamic dispersion is insignificant and can be neglected. This assumption gives rise to sharp leading and trailing edges in the pollutant slug. These sharp fronts will not exist in soils. As a result, the pollutant will likely reach any depth in the treatment zone before the time predicted and it will remain at that depth longer than predicted by the model.
- Linear isotherms describe the partitioning of the pollutant between the liquid, soil, vapor, and oil phases. Local equilibrium between phases is assumed.
- First-order degradation of the pollutant and oil are assumed. Degradation constants do not change with soil depth or time. This assumption ignores changes in biological activity with soil depth. It also ignores the influence of loading rate, temperature, and the quality of the environment for microorganisms upon the degradation rate.
- The pollutant partitions between the soil, oil, water, and soil vapor and does not partition to the remaining fractions of the sludge.
- The sludge does not measurably change the properties of the soil water or the soil so the pore liquid behaves as water.
RITZ presents results for the specific parameters entered without any measure of uncertainty in the calculated values. The user is encouraged to compare results for a series of simulations using parameters in the expected ranges for the site to obtain an estimate of this uncertainty. For example, if the site contains two soil layers, the user may want to run the simulation twice, once for the soil properties of each layer.
RITZ Input Data
The RITZ program is menu driven. The data, including soil parameters, properties of the pollutant and oil, and environmental and management parameters, is entered using a series of data entry screens. The input data includes:
- Identification Code - Character string to identify this set of data for the user's reference.
- Soil name - This serves to identify the soil at the treatment site.
- Fraction organic carbon - Ratio of the mass of organic carbon in the soil to the mass of soil solids.
- Bulk density - Ratio of the mass of soil solids to the total volume of the soil; that is, it is the ratio of the mass of solids to the volume of solids, liquids, and gases in the soil.
- Saturated water content - Ratio of the volume of water in the soil to the total volume of the soil when the soil pores are filled with water.
- Saturated hydraulic conductivity - The hydraulic conductivity of the soil when all of the soil pores are filled with water.
- Clapp and Hornberger constant.
Oil and Pollutant Properties
- Name of the pollutant in sludge - This name is for identifying output tables and graphs.
- CAS number - Chemical Abstracts Number may be entered to provide positive identification for the pollutant being modeled. This number is also displayed with the outputs.
- Concentration of pollutant in sludge - Concentration of the pollutant in the sludge when it was applied to the soil.
- Organic carbon-water partition coefficient - Partition coefficient between the pollutant in soil and water normalized to the soil's organic carbon content.
- Oil-water partition coefficient - Partition coefficient for the pollutant between the oil and water phases.
- Henry's law constant - The constant for partitioning the pollutant between the vapor and water phases.
- Diffusion coefficient. of pollutant in air - The diffusion coefficient of the pollutant in air is used to determine pollutant losses in the vapor phase.
- Half-life of the pollutant - Time required for one-half of the original amount of pollutant to be transformed to some other product.
- Concentration of oil in the sludge - The concentration of oil in the sludge at the time of application.
- Density of oil - The density of the oil in the sludge. This is the mass of oil per unit volume of oil.
- Half-life of oil - The time required for one-half of the original amount of oil in the sludge to be biologically degraded.
Operational and Environmental Factors
- Sludge application rate - The mass of sludge or waste material applied per hectare of land area.
- Plow zone depth - The depth of the bottom of the soil material is incorporated.
- Treatment zone depth - The depth of the bottom of the soil considered to be part of the treatment zone. Chemical movement below this depth is lost from the system and is considered as leached.
- Recharge rate - The average downward flux density of water through the treatment zone.
- Evaporation rate - The average flux density of water evaporating from the soil.
- Air temperature - The average air temperature at the site.
- Relative humidity - The average relative humidity at the site expressed as a fraction.
- Diffusion coefficient of water vapor in air - This diffusion coefficient of water vapor in air is used to estimate the vapor losses of the pollutant.
RITZ Output Options
- Mass balance - Displays a pie chart of the relative amount of the pollutant degraded, leached, and volatilized.
- Pollutant volatilized vs. time - Displays a graph of the flux density of pollutant removed from the treatment site in the vapor phase as a function of time.
- Pollutant leached vs. time - Displays a graph of the flux density of pollutant leached from the treatment zone as a function of time.
- Position of pollutant vs. time - Displays a graph of the location of the top and bottom of the pollutant as a function of time.
- Concentration vs. time at selected depths - Graphs of the total concentration of pollutant and concentrations in water, soil, vapor, and oil phases are displayed sequentially.
- Concentration vs. depth at selected times.
- Concentration bar graphs - Presents a series of bars representing the treatment zone. Within each bar the concentration of pollutant in one phase at a particular time is displayed qualitatively using one of six patterns.
- Input parameters - Displays the parameters entered by the user to define the current scenario.
- Calculated parameters - This table contains selected chemical and physical parameters calculated from the input parameters.
- Mass balance - This table lists the absolute and relative amounts of pollutant degraded, volatilized, and leached along with the mass balance error.
- Pollutant volatilized vs. time - Table of the flux density of pollutant leaving the treatment site in the vapor phase as a function of time.
- Pollutant leached vs. time - Table of flux density of pollutant leached from the treatment zone as a function of time.
- Position of pollutant vs. time - This table displays the location of the top and bottom of the pollutant slug at different times.
RITZ includes the executable and source codes and technical support.