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The remediation of contaminated sediments can be quite challenging. The sediments are difficult to get to; can be located in high energy systems, such as rapidly flowing streams and rivers; can be in fresh water, salt water, or brackish conditions; can be near surface or hundreds of feet below water; and can be contaminated with hard to treat viscous NAPLs and metals, as well as conventional petroleum hydrocarbons and chlorinated solvents.

Chemical oxidants and reductants react quickly and effectively with many organic contaminants, including petroleum hydrocarbons and chlorinated solvents. The challenge is getting the reagents to contact the contaminant, often over an extended time frame. Practitioners refer to chemical oxidation and reduction in the subsurface as a `contact sport.` Applied correctly, the process can reduce contaminant levels and flux efficiently. It is important to note that chemical oxidation and reduction occur primarily in the aqueous phase. Because there is equilibrium between the non-aqueous and aqueous phases, by lowering the aqueous phase concentrations directly adjacent to the non-aqueous phase liquid (NAPL), you will enable more rapid NAPL dissolution.

As people eat food and breathe air to derive energy for growth, so do the subsurface microbes that can beneficially remediate various contaminants. Fundamentally, bioremediation involves creating geochemical conditions conducive to microbial growth. As long as these organisms, sometimes called bugs, have something to eat and breathe, they will continue to grow and degrade the contaminants. The challenge, of course, is maintaining favorable subsurface, geochemical conditions over an extended time period.

If you want to solve a three dimensional contaminant problem, you need to understand the three dimensional distribution of hydraulic head and contaminant concentrations. One of the problems faced by environmental scientists and engineers is that it is extremely expensive to collect subsurface data. As a result, these professionals are often tasked with characterizing a site to develop a conceptual model with a paucity of data. Furthermore, contaminant and hydraulic head measurements taken over large screened intervals may not provide useful information, if the predominant flow regimes and contaminant loading are in specific hydrogeologic units.