Course Introduction
Getting Started

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Module I
Introduction
Session I-1
Session I-2
Session I-3
Session I-4
Session I-5
Session I-6
Session I-7

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Module II
Introduction
Session II-1
Session II-2
Session II-3
Session II-4
Session II-5

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Models
Equilibrium Partitioning Model

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Tutorials
Equilibrium Partitioning Model

 

SUBSURFACE CONTAMINANT BIOREMEDIATION

MODULE I: ABIOTIC PROCESSES

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SESSION I-7. SUMMARY AND APPLICATION

Module I presents many important abiotic concepts related to ground water contamination. Although the focus is on fuels and chlorinated solvents, please keep in mind that much of the Module I content may be applied to other organic compounds including pesticides and landfill leachate.

Our coverage begins with the introduction of NAPL-phase contaminants into the subsurface, usually in the NAPL phase. Downward migration of LNAPLs and DNAPLs, subject to the effects of capillary forces and geologic heterogeneity, results in the establishment of the source zone (source area) in the vadose zone as well as at and below the water table. Organic compounds initially in the NAPL phase now begin to partition into the surrounding soil, water, and possibly air phases. The Equilibrium Partitioning Model provides a computational tool for studying the partitioning process for different contaminants, soil types, and saturation levels.

Partitioning theory leads into the subject of dissolved contaminant plume formation and migration. As NAPL phase compounds dissolve (partition) into the aqueous phase, a contaminant plume is formed which will now migrate with the flowing ground water. A short summary of basic ground water flow principles is presented followed by in-depth development of the one-dimensional mass transport equations which govern contaminant concentration with time and space during plume migration. The intention here is to sufficiently discuss each mass transport process (i.e. advection, dispersion, sorption, and biodegradation) such that their individual and collective influence on plume behavior can be appreciated. Recall that these concepts form the conceptual basis for the popular remediation strategy referred to as “Monitored Natural Attenuation”. The BIOSCREEN Model provides a very useful computational tool for evaluating contaminant plume behavior (and Monitored Natural Attenuation) in a one-dimensional flow system.

The following list of questions may be helpful in reviewing the contents of Module I:

• How are key subsurface parameters such as hydraulic conductivity, porosity, and dispersivity influenced by the “scale” at which they are observed? (This question related to the “scales of observation” concept presented in Module I. It suggests that the value used to define bulk media properties may change considerably depending on the size of the volume which those properties represent.)

• How do NAPLs distribute in the subsurface and how do subsurface heterogeneities  influence the outcome?
• Why do we focus primarily on BTEX compounds from releases of gasoline when BTEX compounds comprise only about 5 – 15% of the gasoline itself?
• Is there always recoverable DNAPL in pools at chlorinated solvent release sites? Why is DNAPL so hard to find compared to LNAPL?
• What site characteristics (e.g. hydrogeologic, soil, population density) would favor each of the following remediation strategies for a gasoline spill? For a release of TCE?
• Soil vapor extraction
• Pump and surface treatment of ground water
• Monitored Natural Attenuation
• Soil excavation and treatment via land farming
• phytoremediation