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

-------
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

-------
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

-------
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

-------
                                                                                            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
         EPA
  PERMIT No. G-35
Official Business
Penalty for Private Use $300

EPA/600/S2-88/020
                           0000329   PS

                           ll  S EMVIR MOTECTXOII  *Gi«CY
                               — ^ j*. «L«  tf  ft V B D A tUP
                           V P IMV IVH  J  L. Jt P T\ W « * __

                           clicieo1**           it   60604

-------