in situ remediation basics

In-Situ Remediation ApplicationsIn-Situ Remediation Applications1

Key Factors for Success The Right Chemistry

fundamental understanding of geochemistry and microbiology to pick right chemistry

Good Delivery contact with the contamination intensity of the delivery and distribution

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Understand the Site Hydrogeology Geochemistry Contaminants Microbial populations

A good understanding of contaminant source, contaminant migration, means a better design for remediation plan

Metals Objective: change the valence state to bind metals and

restrict migration VOCs:

Petroleum: can use biodegradation, either aerobic (oxygen) or anaerobic (sulfate); oxidation; inject heat to volatilize and enhance extraction

Chlorinated: anaerobic bio; oxidation; chemicalreduction

SVOCs: oxidation PCBs: oxidation

Concentrations Define source area Delineate dissolved plume

Transformations Degradation products of solvents indicate the

types of bacteria present, can they be utilized or need to be augmentedWill there be complete degradation to

ethene/ethane, a stall at cis-DCE, or a vinyl chloride build-up

Chemical Oxidation Chemical Reduction

(zero valent iron) Aerobic Bioremediation Anaerobic Bioremediation Thermal (steam) injection Metals Stabilization

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Chemical Oxidation Direct chemical destruction of volatile organics,

petroleum and chlorinated hydrocarbons Typical oxidants:

Potassium and sodium permanganate Sodium persulfate Hydrogen peroxide, Fenton’s chemistry Ozone

Typical response time: immediate to 4 months

Chemical Reduction Direct destruction of volatile organics through

abiotic reduction Zero valent iron (ZVI)

Typically injected, placed as a reactive wall or barrier

Commonly used for chlorinated hydrocarbons

Typical response time: immediate to years

Aerobic Bioremediation Addition of oxygen source to feed bacteria

that consume petroleum hydrocarbonsAir spargingOxygen release productsOxygenated water injection

Typical effective treatment: 1 to 6 months, or the length of sparging period

Anaerobic Bioremediation Sulfate reduction of petroleum

Magnesium sulfate (Epsom salt, EAS®), gypsum Chlorinated hydrocarbon enhanced reductive

dechlorination (ERD)Adding hydrogen source to feed bacteria

Fatty acids Edible oil Sodium/ethyl lactate esters Molasses and sugars

Typical effective treatment: 6 to 24 months

Why enhanced? Aquifers are sometimes limited by carbon (or

food) source for bacteria In some instances, the proper bacteria (e.g.

dehalogenators) are not present Can bioaugment with Dehalococcoides ethenogenes

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Lactates, fatty acids , edible oils ferment anaerobically:

Hydrogen is produced plus a new shortened fatty acid (lactic, linoleic, palmitic, propionitic acids); the shortened fatty acid is then cleaved, forming more hydrogen and acetic acid. The acetic acid breaks down to methane and carbon dioxide

Breakdown product acids degrade under lower hydrogen partial pressures, serve as a hydrogen storage, provide a longer hydrogen source

Does not overstimulate (typical problem when using sugars): Sugar overstimulates methanogens; much slower breakdown,

incomplete degradation, excess methane gas produced (health hazard)

Anaerobic microorganisms that degrade chlorinated organics (halorespirers) use the hydrogen as an electron donor and the chlorinated organics as electron acceptors

First notice a decline in parent material (PCE, TCE, TCA) with a corresponding increase in cis-DCE; then vinyl chloride. Then degradation products are degraded, resulting in ethenes/ethanes.

Can use a mixture of hydrogen source plus ZVI Combines anaerobic bioremediation and

chemical reduction (from ZVI) Less likely to form vinyl chloride Adventus holds patent to add ZVI to

carbon amendment

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Volume, rates of injection are monitored for each well for the duration of the injection

Direct Push (Geoprobe) Injection