United States
Environmental Protection
Agency
Water Engineering
Research Laboratory
Cincinnati OH 45268
Research and Development
EPA/600/S2-88/020 Apr. 1988
<>EPA Project Summary
Control of Volatile
Organic Contaminants in
Groundwater by In-Well
Aeration
Judith A. Coyle, Harry J. Borchers, Jr., and Richard J. Miltner
At a 0.1 million gallon per day well
contaminated with several volatile
organic compounds (VOC's),
principally trichloroethylene (TCE),
several in-well aeration schemes
were evaluated as control
technologies. The well was logged by
the USGS to define possible zones of
VOC entry. A straddle packer and
pump apparatus were utilized to
isolate those zones and define their
yield and level of VOC concentration.
The technical literature together with
this knowledge of the well were used
to design an air lift pump. Operation
of the air lift pump confirmed
literature prediction of its low wire-
to-water efficiency. Removal of TCE
did not exceed 65%. Mass transfer
occurred in the pump's eductor. Air
lift pumping coupled with in-well
diffused aeration increased TCE
removal to 78%. When in-well
diffused aeration was used with an
electric submersible pump, TCE
removal averaged 83%. In the latter
two schemes, mass transfer
occurred utilizing the well as a
countercurrent stripper. These
technologies are limited by the
volume of air that can be transferred
to the well (air-to-water ratios
below 12:1) and the cost of
compressing air under high head.
Thus, these technologies are not
cost-effective compared to packed
tower aeration. They are, however,
quickly put on-line, easy to operate,
and can serve as short-term
remedies while above-ground
technologies are under design and
construction.
This Project Summary was
developed by EPA's Water Engineering
Research Laboratory, Cincinnati, OH,
to announce key findings of the
research project that is fully
documented in a separate report of
the same title (see Project Report
ordering information at back).
Introduction
Contamination of groundwater with
volatile organic compounds (VOC's) has
become common throughout the United
States. Southeastern Pennsylvania and
the North Penn Water Authority (NPWA)
have not escaped this problem. In 1979,
a large amount of trichloroethylene (TCE)
was spilled in nearby Collegeville, PA.
The Authority sampled all 34 of their
operating wells and found 8 to be
contaminated with TCE and other VOC's.
These wells were shut down, resulting in
a loss of approximately one-third of the
system's total pumping capacity.
Since that time NPWA has been
actively pursuing various methods of
dealing with the VOC problem. Surface
water was purchased from a neighboring
water supplier, a granular activated
carbon treatment plant was installed at
one well, and packed tower aerators were
installed at others. This investigation was
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carried out to evaluate in-well aeration
techniques.
This investigation covered the design
and operation of various in-well aeration
configurations examined by NPWA
during the time period of January 1982
to May 1985. The configurations included
air-lift pumping with and without in-
well diffused aeration, i.e., sparging, as
well as electric submersible pumping
with in-well diffused aeration.
The well selected for this study was
Lansdale number 8 (well L-8). This well
was heavily contaminated with VOC's
and was being pumped to waste in an
attempt to control the contamination
plume. In addition to TCE, well L-8
contained vinyl chloride; carbon tetra-
chloride; tetrachloroethylene; cis-1,2-
dichloroethylene; 1,1 -dichloroethylene;
and 1,1,1-trichloroethane. It is 286 ft
deep and in a mixed resi-
dential/commercial area, with homes in
close proximity to the well house.
Shortly after the discovery of VOC
pollution at NPWA, a series of
preliminary tests were performed using
an air lift pump and an electric
submersible pump with a sparger. No
attempt was made to record air-to-
water ratios or operating conditions;
however, even under these uncontrolled
conditions, nearly 80% removal was
observed for TCE. This provided the
incentive for further study of in-well
aeration.
In-Well Aeration
The air lift pump used for this study
was similar in design to pumps used by
the Lartsdale Municipal Authority
(predecessor to NPWA) in the 1920's.
Compressed air was introduced by an air
line into an open-ended pipe in the well
called an eductor. The aerated water in
the eductor was less dense than the
surrounding water in the well and was,
therefore, forced up the eductor and out
of the well as a result of the density
gradient. Mass transfer of VOC's
occurred in the eductor. Air and stripped
VOC's were removed in an open tank at
the surface called a separator. When
sparging, a pipe was used to introduce
compressed air into the well at the
desired depth. VOC mass transfer
occurred utilizing the well as a counter-
or cocurrent stripper. The in-well
aeration equipment used in this study
was easily constructed from materials
already in NPWA stock.
Objectives
When a well is found to be
contaminated it is common practice to
pump to waste in order to prevent the
contamination plume from spreading
throughout the aquifer. In-well aeration
can treat the water as it is being
pumped. This may reduce the amount of
pollutants being discharged into the
sewer system as at well L-8 or, in some
cases, may treat the water to potability.
Treating the water while pumping
eliminates the need for construction of
above-ground treatment devices. This
investigation was undertaken to evaluate
the cost effectiveness of in-well aeration
as an alternative to above-ground
technologies.
Well Characterization
The first stage of the in-well aeration
system design in this investigation was
characterization of well L-8.This was
done by the U.S. Geological Survey
(USGS) with a series of well loggings.
These tests included caliper,
conductivity, temperature, radiological,
and brine trace logs, among others. The
USGS study determined possible water
entry zones.
Inflatable straddle packers and a
pump were placed in the well to isolate
these zones. Each zone was analyzed for
VOC's and specific capacity. Three
different depths for in-well aeration
equipment were evaluated at well L-8,
based on the results of the well
characterization and air lift pump theory.
Scope of Work
Parameters measured in the field
during in-well aeration testing included
air pressure, air temperature, air flow
rate, water flow rate, and water level in
the well. These parameters allowed
calculations of pumping efficiencies and
air-to-water ratios. The in-well
aeration systems tested were evaluated
based on these findings, as well as on
VOC removal and cost.
Certain secondary effects of in-well
aeration treatment techniques were also
examined. Off-gases in the well house
were tested to determine whether
hazardous conditions were present. The
air outside the well house in the adjacent
residential area was also tested for
VOC's. Bacteriological changes as well
as corrosion related factors (changes in
pH or dissolved oxygen with aeration)
were examined.
Results
Well Characterization
The USGS well logging identified t
major and five minor potential water en
zones into the well. The packer test
accounted for 81% of the well's spec
capacity. That capacity was observed
the upper 200 ft of the well. T
remaining 19% of the specific capac
was contributed by zones not isolated
packer testing. Seventy-four percent
the well's specific capacity was in i
upper 130 ft. Differences in V(
concentrations were observed in t
isolated zones. The two most heav
VOC-contaminated zones were abc
130 ft and were also the largest wa
producing zones.
An open borehole pumping t(
showed that VOC concentration chang
considerably with time. Over short-te
tests, such as the in-well aeration te
performed, large concentration variatic
could be expected.
Footpiece Tests
Two air lift pump footpieces w«
tested. In one, the air line was op
ended and produced large bubbles in 1
eductor; in the other, the end of the
line was coupled to a diffusing dev
and produced small bubbles. The t
footpieces showed no significe
difference in air lift pump efficieni
There was no difference in VOC remo
brought about by changing from a lar
bubble to small bubble footpie
suggesting that small bubbles coalesc
above the footpiece. The small bubl
footpiece caused greater operati
pressure. The pressure difference w
greatest at higher air-to-water rati
(5:1 to 12:1). The most efficient operati
of an air lift pump was found to be
agreement with the literature at a mi
lower air-to-water ratio (1.5:1) wh«
the pressure differences between t
footpieces were very small. If the air
pump was operated at its maximi
pumping efficiency, there would be 111
difference in operating pressure betwe
the two footpieces. If, however, the pur
were operated at a higher air-to-wa
ratio in order to obtain better V(
removal, the small bubble footpie
would have greater operating pressi
and greater operating cost. Since th(
was no difference in VOC remo1
between the two footpieces, and sir
the small bubble footpiece would
potentially more expensive to opera
the small bubble configuration w
abandoned and the large bubt
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footpiece was used for all in-well
aeration testing.
When sparging in the well, large and
small bubble air lines, identical to the air
lines used for air lift pumping, were
compared. The small bubble sparger had
a higher operating pressure, and
therefore, a higher operating cost than
the large bubble sparger. There was no
differences in VOC removal between the
large and small bubble spargers. As with
the air lift pump, the large bubble
sparger was used for all testing.
Reproducibility
Raw water VOC concentration varied
within a given test, which confirmed the
findings of the pumping test conducted
during well characterization. Even though
VOC concentrations varied over time in
the short term, test results were found to
be reproducible from one day to the
next, thereby giving confidence to the
procedures employed. In the short term,
static water levels were consistent.
Test results generally were not
reproducible when conducted months
apart. Raw water VOC concentrations
varied from one test to another over time.
Over the long term, static water levels
changed. It is possible that with changes
in static water level, the yield within a
water entry zone changed slightly and
made reproducibility difficult. Changes in
static water level .cause changes in
submergence which, in turn, cause
changes in pump efficiency. A given air
flow rate produced different water flow
rates and air-to-water ratios over the
long term.
Air Lift Pump Tests
Based on well characterization, the air
lift pump was studied at 130, 200, and
280 ft depths. The 130 ft depth coincided
with 65% submergence, which is
reported as optimum for air lift pump
efficiency. Operation of the air lift pump
confirmed its highest efficiency at 65%
submergence. The maximum efficiency
was found to be 30% to 35%. The
efficiency decreased as submergence
increased, also confirming the
predictions of the literature. VOC removal
was poorer at the 280 ft setting than it
was at 130 ft or 200 ft. Best VOC control
for the air lift pump ranged from 90% for
vinyl chloride (VC) with the highest
Henry's Law constant to 47% for cis-
1,2-dichloroethylene (cis-1,2-DCE)
with the lowest constant. Percent
removal of the other VOC's was
consistent with their Henry's Law
constants. TCE was 65% removed by air
lift pumping. This level of control
occurred at the higher, more expensive,
air-to-water ratios.
Tests with Sparging and Air Lift
Pumping
In these tests, the air lift pump was
located at 130, 200, and 280 ft depths.
While the air lift pump was fixed in the
well, the air sparger was located at 130,
200, or 280 ft depths.
Sparging air into the well decreased
the pumping efficiency of the air lift
pump because the density gradient
between the well and the eductor was
diminished. However, the efficiency of
the combined devices was higher than if
all of the air had been delivered to the air
lift pump alone. Therefore, in terms of
efficiency and cost, it was better to
operate an air lift pump and sparger
combination than the air lift pump alone.
The air lift pump and sparger
combination yielded VOC removal
percentages ranging from 99% for VC to
65% for cis-1,2-DCE, with TCE having
78% removal. A higher air-to-water
ratio was obtained by using the air lift
pump and sparger combination than by
using the air lift pump alone. This
accounted for the higher VOC removal.
The highest air-to-water ratios
obtained were 10.6:1 for the air lift pump
alone and 17:1 for the air lift pump and
sparger combination. When sparging, the
air-to-water ratio was limited to the
point at which water actually bubbled out
of the well. In a well with a wider bore,
the air-to-water ratio might be higher
because water would not be forced out of
the well as readily. At well L-8, some of
the cross section was taken up by test
equipment, e.g., sample pump and water
level probe, which would not be in the
well during regular operation.
No significant removal differences
were observed when the equipment was
operated at different depths. This was
attributed to poor reproducibility of
sparger tests over long periods of time.
Tests with Sparging and Electric
Pumping
An electric submersible pump was
operated at 200 ft with sparger testing
being conducted at 130, 200, and 280 ft.
The best VOC control was observed with
the sparger at 130 ft. Sparging at the 200
ft depth gave the poorest control. VOC
control was consistent with what was
expected from well characterization.
Sparging at 130 ft caused counter-
current stripping as water from the most
contaminated zone waspulled past the
bubbles on its way to the pump. A
counter- and cocurrent stripper would
have been created by the 280 ft sparger,
with at least some of the air being pulled
into the pump before it reached the most
heavily contaminated zone. With the
sparge directly adjacent to the pump,
most of the air could have been pulled
into the pump before any stripping
occurred in the well.
The VOC control obtained during
electric pump and sparger tests averaged
83% for TCE, 80% for cis-1,2-DCE,
and 93% for VC. These removals were
better than those achieved by air lift
pumping with or without a sparger. The
air-to-water ratio used to achieve this
level of control was 8.2:1, which is lower
by half than the maximum air-to-water
ratio used in the tests with the air lift
pump and sparger. Better control
resulted from directing available air to the
in-well sparger than by directing all or a
portion of it to the air lift pump.
Secondary Effects
All configurations of in-well aeration
increased the pH by an average of 0.4
pH units as carbon dioxide was stripped.
Dissolved oxygen (DO) was raised to
saturation by all of the in-well aeration
methods tests as a result of air
introduced under high head. Water
entering the separator was bubbly in
appearance and actually milky white
when sparging, but all of the bubbles
were released by the time the water
passed from the separator.
Bacteriological testing of raw and
treated water was inconclusive, with large
variations in bacterial counts masking any
trends. The R2A method provided
consistently higher recovery of
organisms than the heterotrophic plate
count.
Air sampling showed that in-well
aeration would probably not cause air
quality problems of industrial hygiene
concern; however, it may be considered
an air pollution source and require the
appropriate permits. Venting of VOC off
gases from the separator, and from the
well bore when sparging, may be
prudent.
Conclusions
In-well aeration is limited by the
amount of air that can be transferred to
the well and the cost of compressing air
under high head. With limited air-to-
water ratios, removal will not reach that
achievable with above-ground
technologies.
In-well aeration can be a useful
treatment technique for VOC removal on
a short-term emergency basis. Electric
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submersible pumping with the use of a
sparger is particularly well suited to this
application. The addition of an air
compressor and the installation of an air
sparger was completed for this study in a
matter of a few days with readily
available materials. The sparger should
not be placed directly adjacent to the
pump intake as this will draw the bubbles
into the pump and VOC stripping in the
well will be minimized. Air should be
added in slowly-increasing amounts
until the foaming water is just visible
below the well head. This will produce
the greatest possible air-to-water ratio.
Both an air and water separator and
repumping to the distribution system are
necessary. A chlorine contact chamber
might be easily modified for this
purpose. The time required to build or
put an off-the-shelf tank in place as a
separator may negate the usefulness of
in-well aeration as a short-term
emergency technology. While the cost to
compress air may reach 25C/1.000
gallons depending on the depth of the
sparger, the total cost, assuming 3 mo
emergency service, may reach
$1.90/1,000 gal at 0.1 MGD under
NPWA conditions.
While well characterization was useful
during this project, both for experimental
design and data interpretation, it would
not be a prudent investment in an
emergency situation. Optimum location
of the sparger could be more cost-
effectively determined by trial and error.
As with any aeration technology, air
quality must be considered. The
necessity to treat off gases to remove
VOC's or to vent off gases to limit human
exposure could negate its advantages as
a quickly-installed emergency
technology.
Finally, water saturated with DO may
be corrosive to some distribution system
materials, even in the short term. This
too could negate the advantages of in-
well aeration for emergency treatment.
The full report was submitted in
fulfillment of CR 809758 by the North
Penn Water Authority under the
sponsorship of the U.S. Environmental
Protection Agency.
U. S. GOVERNMENT PRINTING OFFICE: 1988/548-158/67110
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usciJUUI
Judith A. Coyle and Harry J. Borchers, Jr., are with the North Penn Water
Authority, Lansdale, PA 19446; the EPA author Richard J. Miltner (also the
EPA Project Officer, see below) is with the Water Engineering Research
Laboratory, Cincinnati, OH 45268.
The complete report, entitled "Control of Volatile Organic Contaminants in
Groundwater by In-Well Aeration," (Order No. PB 88-180 1121 AS; Cost:
$19.95, subject to change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Water Engineering Research Laboratory
U.S. Environmental Protection Agency
Cincinnati, OH 45268
^JJ .;}
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
BULK RATE
POSTAGE & FEES PAID
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PERMIT No. G-35
Official Business
Penalty for Private Use $300
EPA/600/S2-88/020
0000329 PS
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