RETRASO, a code for modeling reactive transport in saturated and unsaturated porous media

The code RETRASO (REactive TRAnsport of SOlutes) simulates reactive transport of dissolved and gaseous species in non-isothermal saturated or unsaturated problems. Possible chemical reactions include aqueous complexation (including redox reactions), sorption, precipitation-dissolution of minerals and gas dissolution. Various models for sorption of solutes on solids are available, from experimental relationships (linear KD, Freundlich and Langmuir isotherms) to cation exchange and surface complexation models (constant capacitance, diffuse layer and triple layer models). Precipitation-dissolution and aqueous complexation can be modelled in equilibrium or according to kinetic laws. For the numerical solution of the reactive transport equations it uses the Direct Substitution Approach. The use of the code is demonstrated by three examples. The first example models various sorption processes in a smectite barrier. The second example models a complex chemical system in a two dimensional cross-section. The last example models pyrite weathering in an unsaturated medium

Modelling and simulation framework for reactive transport of organic contaminants in bed-sediments using a pure java object - oriented paradigm

Numerical modelling and simulation of organic contaminant reactive transport in the environment is being increasingly relied upon for a wide range of tasks associated with risk-based decision-making, such as prediction of contaminant profiles, optimisation of remediation methods, and monitoring of changes resulting from an implemented remediation scheme. The lack of integration of multiple mechanistic models to a single modelling framework, however, has prevented the field of reactive transport modelling in bed-sediments from developing a cohesive understanding of contaminant fate and behaviour in the aquatic sediment environment. This paper will investigate the problems involved in the model integration process, discuss modelling and software development approaches, and present preliminary results from use of CORETRANS, a predictive modelling framework that simulates 1-dimensional organic contaminant reaction and transport in bed-sediments

Modeling Transport of Non Aqueous Wastes in Unsaturated Soils.

In evaluating risks associated with chemical spills on the ground surface or leaks from underground storage tanks, it is required to know the extent and degree of contamination in the subsurface. In many cases pure organics are spilled and due to their low miscibility with water they remain pure or concentrated for some distance or time from the source. This dissertation is aimed at developing a model of the multiphase (air, water, organic) migration processes. The particular focus is on modeling organic infiltration in the unsaturated zone where the transport is largely vertical. Sand-column experiments using a variety of immiscible and miscible organics indicated that the organic infiltration front after a \u27spill\u27 was sharp and that little residual water was displaced by an infiltrating immiscible organic. Based upon these assumptions, the multiphase transport problem was essentially modeled as a single phase infiltration under the influence of gravity and capillary forces. The resulting model describing organic phase infiltration rate contained two parameters, an effective medium permeability and an effective capillary suction at the wetting front. For the case of a fully infiltrated organic, an effective capillary suction at the drainage front was also required. The boundary element method (BEM) is used to solve the governing quasi-steady differential equations. Good agreement between the experimental data and the model was observed taking the effective medium permeability equal to the saturated flow permeability and using measured values of the capillary suction parameters. Many groundwater contamination incidents begin with the release of an essentially immiscible fluid into the subsurface environment. Once in the subsurface, an immiscible fluid participates in a complex pattern of transport processes. For immiscible fluids that are commonly found in contaminated groundwater environments the interphase mass transfer between the nonaqueous liquid phase and the aqueous phase is an important process. A model capable of exploring the effect of interphase mass transfer on in-situ extraction is also presented

An in-situ capping design for the remediation of petroleum contaminated sediments

Historical disposal practices used by oil companies have caused the accumulation of contaminated sediments in their nearby lakes and ponds. These companies are now faced with the challenge of remediating the bodies of water that contain these contaminated sediments. The contaminants that remain in the sediment continue to pose a threat to human health and the environment. For example, high concentrations of polycyclic aromatic hydrocarbons (PAHs), which are still present in the bottom sediments can have toxic effects on aquatic life. One form of remediation for this problem is In-Situ Capping (ISC), which is defined as a method whereby material is used as a covering or cap for placement over contaminated sediment located under a body of water. This work focuses on evaluating ISC as a remediation method for oil contaminated sediments. Bench-scale laboratory experiments were conducted on oil contaminated sediment samples to observe the effect of consolidation, contaminant migration, gas generation, and ground water migration on the caps ability to contain the contaminants. It was found that, overall, ISC could be used as an effective remediation method for the oil contaminated sediments tested. However, there was some migration of PAHs into the first few centimeters of the cap in all columns tested due to a combination of intermixing during cap placement, non-aqueous phase liquid migration, and retarded transport of certain PAHs. It was also observed that contaminant migration increased when gas bubbles, which simulated gas generated by the contaminated sediment, were injected into the column experiments over an approximately one month period. These results demonstrate that site-specific adjustments to ISC designs are necessary for the cap to most effectively contain contaminant migration in the field

Modelling of chemical migration under the overlapping impact of multiple and diverse pollution sources in the area of the “Zachem” Chemical Plant (Bydgoszcz, northern Poland)

Modeling studies of chemical migration in the area of the “Zachem” Chemical Plant in Bydgoszcz started from the analyses of the production profile. Those studies were conducted to investigate the potential contaminants. Organic compounds still represent a substantial concentration in soil and water environment, including total organic carbon (TOC) reaching values above 1600 mg/L, aniline, nitrobenzene and phenol (up to 500-800 mg/L), organochloride and organometallic compounds, as well as hydrocarbons, such as benzene, toluene and PAHs. Groundwater contains most of the major ions (chlorides, sulphates and bicarbonates, sodium and calcium) and trace elements (Al, Co, Cr and Ni).A reliable conceptual model of the geological structure was constructed for 3 continuous layers with variable bottom morphology. This model represents the complex structure containing permeable and impermeable Quaternary and Neogene deposits. A hydrogeological numerical model was created for the area of the “Zachem” Chemical Plant using the Visual MODFLOW program. Low values of two key statistical measures confirm a good model fitness to the measured conditions: root mean square (RMS) amounts to only about 1.5 m and normalized RMS reaches only about 4.4%. The differences between measured and calculated values are normally distributed. A Modpath module was used to analyze the potential extent of contaminant plume. Accurate hydrogeological 3D sampling was conducted using a “low flow” technique.The results of full and reliable modeling of the chemical migration under the overlapping impact of multiple and diverse pollution sources in the area of the “Zachem” Chemical Plant are essential for further planning of remedial strategies

Site characterization of Riverfront Park, Kansas City, Missouri, for the purpose of hazardous waste site remediation

Riverfront Park, Kansas City, Missouri is located on a point bar along the Missouri River. Portions of the site have historically been used (1950 - 1973) as a municipal landfill receiving residential, commercial and industrial wastes. Relatively high concentrations of elemental lead have been found in small areas of the surface soil within the limits of the Park. Chemicals that may be present in the landfill wastes create a potential for groundwater contamination. A Remedial Investigation, including a series of groundwater monitoring wells is necessary to characterize groundwater geochemistry and flood-induced changes in groundwater flow direction, and to assess any potential environmental problems. During monitoring well installation and groundwater sampling, measures should be taken to obtain parameters for calibration of a computer program that could be used to simulate rates and magnitude of contaminant transport in site groundwater, if such is found to be present. Historical information gathered and data evaluation should be of applied value in determining future sampling or possible remedial action to be utilized at Riverfront Park --Abstract, page ii