1. A-36, in: H.V. Rectanus and R. Sirabian (Chairs), Bioremediation and Sustainable Environmental Technologies—2011.
International Symposium on Bioremediation and Sustainable Environmental Technologies (Reno, NV; June 27–30, 2011).
ISBN 978-0-9819730-4-3, Battelle Memorial Institute, Columbus, OH. www.battelle.org/biosymp
Selection and Testing of Biowall Amendments for
Effective Rejuvenation of Biowalls at High-Sulfate Sites
Erik McPeek (emcpeek@brwncald.com) and James Peeples (jpeeples@brwncald.com)
(Brown and Caldwell, Columbus, Ohio, USA)
Adria Bodour (adria.bodour.1@us.af.mil) and
Javier Santillan (javier.santillan@us.af.mil)
(AFCEE TDV, Lackland AFB, Texas, USA)
Bruce Alleman (Bruce.Alleman@noblis.org) (Noblis, Columbus, Ohio, USA)
John Wilson (Wilson.JohnT@epamail.epa.gov) and
John Skender (Skender.John@epamail.epa.gov) (U.S. EPA, Ada, Oklahoma, USA)
Azra Bilgin (abilgin@brwncald.com) (Brown and Caldwell, Denver, Colorado, USA)
Background/Objectives. Mulch-based biowalls have been demonstrated successful
as a remedial technology for chlorinated groundwater contaminants. The Air Force, as
well as other branches of the Department of Defense and private firms, has invested in
the development of this technology, as they have installed full-scale biowalls at several
bases as the selected remedial technology. Altus Air Force Base (AAFB) was one of the
first Bases to incorporate biowall treatment into their remedial program. The AAFB
biowall is approximately 7,500 feet (ft) long, two ft thick, and installed to a depth of
approximately 30 ft. The primary contaminants of concern (COCs) at AAFB include
trichloroethene (TCE), 1,2-dichloroethene (total) (DCE), 1,1-DCE, vinyl chloride (VC),
1,2-dichloroethane (DCA), and carbon tetrachloride (CT).
Groundwater at AAFB is characterized with sulfate concentrations exceeding
2,000 mg/L. The full-scale biowall removes contaminants through microbially-mediated
reductive dechlorination and abiotic degradation. Approximately two to three years
following installation, the readily available electron donor from the biowall materials had
been depleted and the biowall was amended with emulsified vegetable oil as a source of
slow-release donor. A data review found that sulfide produced during sulfate reduction in
the biowall appeared to be inhibitory to dechlorinating microorganisms. This led to an
investigation into potential biowall amendments that could reduce the sulfide toxicity and
improve the remedial performance of the biowall.
Approach/Activities. The investigation focused on iron sources that could be
combined with the vegetable oil and added during the biowall rejuvenation events. The
investigation included laboratory testing of several iron source materials, which were
tested alone and in combination at varying concentrations to determine their com-
patibility with the emulsified oil. Iron was selected because of its known ability to
precipitate out sulfide and buffer toxicity as well as the potential side benefit of possibly
catalyzing abiotic degradation of the AAFB COCs. The combination of ferrous lactate
and nano-scale hematite was shown to be compatible and to enhance the emulsion
stability and was selected for field testing. The field tests are being conducted at the
Operable Unit 1 pilot-scale biowall at AAFB; this biowall has been used extensively in
developing the biowall technology and is outfitted with an extensive monitoring well
network. Testing includes two conditions: vegetable oil only, and vegetable oil with the
iron additives.
Results/Lessons Learned. The data are being reviewed to assess enhancement in
both biotic and abiotic reductive dechlorination performance when the iron additives are

2. included over the vegetable oil only amendment. Field testing will continue for
12 months. The presentation will include the laboratory testing and preliminary results
from the field test. Trends in COC concentrations and geochemical changes imparted by
the iron additives will be discussed relative to dechlorination enhancement. The study
results will determine whether iron-based additives should be included in the AAFB
biowall rejuvenation protocol, as well as the potential for using this approach at other
high-sulfate sites that experience sulfide toxicity of reductive dechlorination.