This is a quick introduction to subsurface remediation,
specifically, Soil Vapor Extraction and Vapor Treatment. Basically,
this term refers to the process of pulling harmful compounds out of
the ground (soil or water) and treating the compounds so they can
be safely discharged to the atmosphere. These harmful compounds
come from leaking underground storage tanks, oil spills, chemical
leaks and old dumping sites. Soil Vapor Extraction and Treatment
allows removal and on-site destruction of these compounds without
having to dig up and handle the contaminated soil.
There are three basic steps to remediating a site:
Extracting (Vapor Extraction) the compounds from the
ground, Separating (Water/Liquid Removal) the liquid
constituents and Treating (Vapor Treatment) the
contaminants so they are harmless to the environment.
The Remediation Handboook is broken
down into four sections, and you can jump ahead at any time.
Vapor
Extraction
Soil Vapor Extraction (SVE) is an in situ (in the soil)
remediation process that removes the contaminants from the ground.
The term vacuum extraction references the fact that the
contaminants are pulled out of the soil with a vacuum-like process.
It allows us to treat the contaminants without having to excavate
and haul the soil from the site to a landfill.
The contaminants are Volatile Organic Compounds (VOCs). An organic
compound is considered volatile if it produces a vapor (a gas) at
room temperature and normal atmospheric pressure (think of the
fumes you see on gasoline pumps without vapor recovery nozzles).
Some of these vapors are dangerous to humans when inhaled in great
quantities or over a long period of time, and also form harmful
ozone.
The volatility of the compounds is what makes them so dangerous,
but it is also the reason we can treat them. An extraction system
uses a powerful vacuum and a network of wells to pull the volatile
compounds out of the soil. The extraction process involves digging
wells into the ground and connecting the extraction system to the
wells. With the tremendous pull of the vacuum, the volatile
compounds readily move toward the wells while the heavier soil
stays in place.
The diagram above shows how the air moves towards the wells. Each
well has a Radius of Influence (ROI) determined by the vacuum and
the soil conditions. For example, a very sandy and porous soil will
likely have a larger Radius of Influence (ROI) than tight clay, or
any other nonporous soil. Wells are often placed in a site to cover
the maximum amount of contaminated space with the minimum number of
wells. There are many factors that influence the type of extraction
system that is required. These factors are interconnected and
impact one another: the size of the plume (the contaminated area),
the number of wells, the placement of wells, the soil conditions,
the time constraints, the contaminant concentrations and the pilot
test results. An environmental engineer will assess these
factors.
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Water/Liquid
Removal
When the contaminants are pulled from the ground, they often carry
with them the moisture that was present in the soil or the water
table and needs to be separated. The air and entrained water come
up from the wells and spins around a cylindrical knockout pot.
Internal baffles in the pot help the centrifugal force separate the
water from the air. On its way to the blower and the treatment
device, the air rises in the pot and passes through a mist
eliminator, a thick mesh of stainless steel. As the air passes
through the steel mesh, additional water droplets collect. As more
moisture collects, the water forms heavy beads that drop to the
bottom of the pot. The amount of water that is collected varies
greatly from site to site based on the depth of the local water
table and the amount of rainfall. A large volume of water, for
instance, may necessitate further treatment.
The air that remains consists of the VOCs pulled from the
subsurface. These VOCs are just as harmful to the air as they were
to the water table, so they cannot be pumped into the atmosphere.
First, they must be treated.
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Vapor
Treatment
Often, the most effective way to treat the airstream containing
VOCs is to oxidize them. Oxidation causes compounds to break up and
re-form into new (in this case, safe) compounds. Add the right
amount of heat and oxygen and oxidation occurs (the process is
Cn H2m + (n + m/2) O2 Þ n
CO2 + H2O + Heat )
Breaking the harmful compounds into harmless compounds and energy
is the basic premise to all oxidation technologies. In the thermal
oxidation process, the contaminated air is heated, breaking apart
the contaminated compounds. The compounds will re-form naturally,
bonding into the harmless compounds of carbon dioxide and water
vapor while also releasing energy. During catalytic oxidation, the
contaminated compounds in the air react with a catalyst material
(platinum, palladium, rhodium, etc.) which helps break apart the
VOCs at a lower temperature than thermal oxidation.
After the VOCs have been oxidized, the air can be discharged into
the atmosphere. The remediation process is now complete: the VOCs
have been extracted from the area that was contaminated, liquid
constituents have been separated, and the VOCs have been turned
into harmless compounds.
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Through the Global Technologies
product line, Anguil provides the following
technologies specifically for the vapor treatment from
contaminated sites: Remedi-Cat,
Chloro-Cat,
Dual
Therm-Cat and optional Scrubber Module