1. B-17, in: R.R. Sirabian and R. Darlington (Chairs), Bioremediation and Sustainable Environmental Technologies—2013.
Second International Symposium on Bioremediation and Sustainable Environmental Technologies (Jacksonville, FL;
June 10–13, 2013). ISBN 978-0-9819730-7-4, Battelle Memorial Institute, Columbus, OH. www.battelle.org/biosymp
Field Testing Amendments for Rejuvenation
of Biowalls at High-Sulfate Sites
Erik McPeek (emcpeek@brwncald.com) (Brown and Caldwell, Columbus, Ohio, USA)
Karnam Ramanand (kramanand@brwncald.com)
(Brown and Caldwell, Upper Saddle River, New Jersey, USA)
Adria Bodour (adria.bodour.1@us.af.mil) (AFCEC TDV, Lackland AFB, Texas, USA)
Bruce Alleman (bruce.alleman@noblis.org) (Noblis, Columbus, Ohio)
John Wilson (Wilson.JohnT@epamail.epa.gov), Cherri Adair
(adair.cherri@epamail.epa.gov), and John Skender (Skender.John@epamail.epa.gov)
(U.S. EPA, Ada, Oklahoma, USA)
Background/Objectives. Numerous mulch-based biowalls have been installed to suc-
cessfully treat chlorinated solvents in contaminated groundwater. The Air Force installed
an approximately 7,500-foot (ft) long by 2-ft thick by 30 ft deep biowall at Altus AFB
(AAFB) to support long-term anaerobic biological treatment of trichloroethene, cis-1,2-
Dichloroethene, 1,1-Dichloroethene, vinyl chloride, 1,2-Dichloroethane, and carbon
tetrachloride.
AAFB groundwater contains sulfate concentrations exceeding 2,000 mg/L, and sul-
fide produced during sulfate reduction is inhibitory to the dechlorinating microorganisms
and adversely affects the biowall’s performance. Recent studies have shown that ferrous
iron can precipitate out the sulfide as iron sulfide to “buffer” the sulfide toxicity.
Research also has demonstrated that certain forms of the precipitated iron sulfides were
capable of abiotic degradation of chlorinated solvent contaminants. To take advantage of
these findings, addition of iron supplements to the emulsified vegetable oil used to
replenish the available carbon substrate in the biowall was evaluated on a portion of the
pilot-scale biowall at AAFB to determine if the iron addition could reduce the sulfide
toxicity and improve the biotic as well as abiotic contaminant removal performance for
implementation during “rejuvenation” of the full-scale biowall at Altus or biowall at
other high-sulfate sites.
Approach/Activities. Several forms of iron were tested in the laboratory to ensure that
they did not adversely impact the stability of the vegetable oil emulsion, and that they
would not form large particles, which could cause injection problems. A combination of
ferrous lactate and nanoscale hematite was formulated to maximize the amount of iron
added during each biowall rejuvenation event without causing any injection problems.
The amendment formulation was injected into a portion of the pilot biowall in May 2011.
A separate section of the pilot biowall was amended with the EVO only to provide the
data against which any iron supplement enhancements could be measured. Groundwater
samples were collected from monitoring wells located up gradient of the biowall, inside
the biowall, and downgradient from the biowall before injection and then periodically for
12 months following injection. Parent compound and biotic and abiotic degradation
product concentrations, competing electron acceptors and geochemical and micro-
biological indicator parameters were measured in the collected samples.

2. Results/Lessons Learned. Following injection, sulfide concentrations in the iron-
supplemented portion of the biowall showed immediate response having decreased from
300mg/L to below 1 mg/L, and remaining at this lowered level over the 12 months.
Sulfide concentrations in the EVO only portion did not respond as quickly, but did
decrease to below 7 mg/L over the 12 months. Geochemical data from within the biowall
suggested that anaerobic conditions were sustained and that biotic dechlorination of COC
was occurring despite the persistently high sulfate concentrations. COC concentrations
within the biowall decreased quickly following EVO addition, most likely due to
partitioning of contaminant into the oil phase, but a marked decrease in COC
concentrations has continued within the biowall and 5 ft downgradient of each plot
through 12 months of monitoring. COC concentration trends 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.