Blowerless Air Sparging
Air Sparging With No Aboveground Blower System
Blowerless Air Sparging (BAS) is a simple patent-pending
technology that sparges the aquifer with air (or other sparging
fluid) as in traditional air sparging. BAS uses recirculating
wells to accomplish the compression of the air and to deliver
the air to the sparging depth. Recirculating wells enable
BAS to treat large capture widths.
There are several differences between BAS and traditional air sparging:
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No blower system or other aboveground equipment. BAS
uses no blower, compressor, or air pump of any kind;
it uses no aboveground equipment other than a control
panel.
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Power consumption is a small fraction of the power
consumption of traditional air sparging. In
a typical positive displacement blower system operating
at 15 psig, more than 75% of the energy used is wasted,
largely in generation of useless heat. In BAS,
compression of the air is isothermal, eliminating the
generation of waste heat.
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Sparging is possible at much greater depths. In
traditional air sparging, sparging is limited to perhaps
20 feet below groundwater surface. With Blowerless
Air Sparging, sparging depths of 100 feet below groundwater
surface are possible, depending on depth to groundwater.
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Greater radius of influence. The radius
of influence of sparging wells is difficult to establish
in the field, but experiments tend to indicate 20 feet
as the maximum in typical settings. Taking advantage
of the large radius of influence of recirculating wells,
with Blowerless Air Sparging, the sparging air is carried
much farther from the well, greatly increasing well spacing
over traditional air sparging. Far fewer wells
are required.
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More effective stripping and aeration of the water. In
traditional air sparging, the nature and effectiveness
of the interaction of the water and the air are unknown
because the interaction happens in the aquifer under unknown
conditions. With Blowerless Air Sparging, the water
and air are initially brought together in the well, where
they are mixed under extremely vigorous conditions. Stripping
and aeration of the water by the air are both highly
effective.
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Less disruption of the aquifer. In traditional
air sparging, large quantities of air are forced out into
the aquifer, where the air displaces the water from some
fraction of the porosity of the aquifer, thus reducing
the available flow paths for the water. The
air and water occupy different spaces in the aquifer. After
a brief period of operation, it is often necessary to turn
off the sparging air and allow the water to return to the
flow paths from which it has been displaced (cycling). With
Blowerless Air Sparging, much less air can be used ad still
achieve the same level of effectiveness in stripping contaminants
from the water and adding oxygen to the water. This
also reduces the need to capture the sparging air with
soil vapor extraction.
Dissolved contaminants (e.g., BTEX, MTBE) are removed from
the groundwater by the stripping action of the air, which
occurs both inside the well and in the aquifer. The
groundwater is pumped more vigorously than in a traditional
air sparging approach, circulated several times through a
large treatment zone established around the BAS well, and
treated for removal of contaminants and saturation of the
water with oxygen during each of several passes through the
well.
The entire process is completed below ground, with the
only aboveground expression of the system being a small manhole
cover and a power pole with a power meter and a small control
panel. BAS systems can be located virtually anywhere
a drill rig can drill a well, even in an active driveway
or the middle of a busy street.
While there are numerous possible configurations, each
optimized for a different set of geologic conditions, the
most basic approach is also the most commonly used. Figure
1 shows the basic configuration.
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The BAS well penetrates to the maximum depth of the
dissolved contamination, or to a depth chosen to achieve
a desired capture width. An inlet screen is set
at or near the top of the groundwater.
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The BAS well incorporates a second screen, an outlet
screen, usually at or near the bottom of the well.
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The inlet portion of the well is separated from the outlet
portion by a packer.
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The water is pumped by a submersible pump (or other means)
to a point above the static groundwater level, where its
direction reverses and it begins to travel back down the
well toward the outlet screen.
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As the water flows downward, a partial vacuum is formed
in the down pipe.
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At a point along the downward path, a metered amount
of air is admitted to the down pipe, where it mixes vigorously
and thoroughly with the water.
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The water and air (bubble) mixture travel downward to
the outlet portion of the well. As the water and
air (bubble) mixture descend in the down pipe, the pressure
increases to above atmospheric pressure, which increases
the saturation concentration of oxygen in water, resulting
in the water being oversaturated with oxygen when it
reaches the outlet screen.
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The water and air (bubble) mixture flows through the
outlet screen and into the aquifer through the sand pack
and the aquifer materials.
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At the exit screen, higher than normal pressures are
formed, resulting in higher head values near the well.
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The treated water, containing the dissolved oxygen (and
other components of air), flows outward from the well
and upward under the influence of the vertical gradients
created by the extraction process at the top of the well. Because
aquifer materials are typically anisotropic, allowing
horizontal flows more readily than vertical flows, the
flows tend to be even more outward than upward.
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A recirculation zone is created that typically returns
the majority of the treated water to the inlet screen. The
treated depth, the hydraulic gradient, the hydraulic
conductivity, the anisotropy of the aquifer, and the
pumping rate largely determine the shape and size of
the treatment zone.
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As the water circulates upward through the aquifer,
the pressure decreases. The excess air dissolved in the
water due to the higher pressures in the lower region of
the well effuses out of the water, turning the water a
milky-white color. It is by this mechanism that
sparging is effected at distances much greater than the
20 feet maximum typical of traditional air sparging wells.
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The water cycles through the treatment zone and the
well several times, on average, before escaping down
gradient.
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There are no above-ground systems or equipment. Typically,
the only above-ground expression of a BAS system is a
manhole with an adjacent power pole that has a utility
meter and a small control panel.
While the basic configuration and process are straightforward,
even for this simplest case there are many considerations
in designing and installing Blowerless Air Sparging (BAS)
systems. Well diameter, optimal pumping rate, number
of wells and well placement, length of the inlet and outlet
screens, special development procedures, controls and instrumentation,
in-well plumbing configuration, other pumping methods, constructability,
and many other factors must be addressed in developing a
complete design. For more complex or challenging geology,
there are additional considerations such as confined aquifer
configurations and multiple rows of wells.
The major advantages of Blowerless Air Sparging technology
are discussed below.
Figure 1 - Blowerless Air
Sparging - Click
to see a larger image (Patent
Pending)
Major Advantages Of Blowerless Air Sparging
with Recirculating Wells
No Surface Equipment
Faster
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Faster than traditional air sparging. Pumping
the water in an established treatment cell around the
well and treating it on several passes through the well
is much more thorough than the largely unknowable treatment
process of an air sparging well.
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More vigorous than traditional air sparging approaches. Air
sparging flows air through paths of least resistance, often
treating only a portion of the water that flows through
the treatment zone. However, re-circulating wells
induce vertical gradients to vigorously circulate and
treat all
of the water in the aquifer multiple times. While
the interaction between the air and water in a traditional
air sparging system is not well understood, or subject
to modeling or calculation, the exact opposite is true
for recirculating wells. The stripping and aeration
processes are thorough and rapid, affecting all of the
water in the treatment cell.
Cheaper
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Lower initial capital costs, lower maintenance costs,
and faster cleanups result in lower life-cycle costs.
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BAS wells are typically three-inch PVC construction,
not much more expensive than traditional air sparging
wells. But,
the equipment in the well costs only a small fraction
of the cost of a blower system in an enclosure.
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Fewer wells. Well spacing typically 2 to 5 times
depth of contamination. At a site with 50 feet
of saturated zone, well spacing can be 200+ feet.
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Lower energy costs. Because BAS involves pumping
an incompressible fluid (water instead of air), and because
the air is compressed isothermally, energy costs are
much lower than for traditional air sparging.
More Flexible
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Large well spacings at many sites allow great flexibility
in placing wells. Placing wells at a gas station
site, for example, can be quite flexible.
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Tolerant of variable geology. Rather than being
impeded by thin silt lenses and discontinuous clay layers
as traditional air sparging systems can be, re-circulation
patterns are enhanced by these typical real-world features.
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Pumping rates (skimmer pump and submersible pump) can
be adjusted after installation to match actual aquifer
response. Pumping rates can also be modified to
meet changing conditions during cleanup.
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Does not affect adjacent plumes. Because groundwater
is not extracted, adjacent plumes are not drawn toward
a re-circulating well. Specific plumes or parts
of a plume can be targeted.
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Compatible with soil vapor extraction systems.
Regulatory Advantages
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