ELECTRON ACCEPTOR SELECTION FOR ENHANCED
BIOREMEDIATION OF NON-CHLORINATED
HYDROCARBONS
Michael Branson, P.G. ([email protected])
and M. Tony Lieberman, RSM, PMP
Solutions-IES, Inc., (SIES), Raleigh, NC
Background/ Objectives
 NCDOT contracted SIES assess and remediate BTEX
(benzene, toluene, ethylbenzene, and xylenes)
contamination at a former gas station site located in
Cabarrus County, North Carolina.
 Three gasoline USTs and one kerosene UST were
removed from the site in 1995 to accommodate
widening of an adjacent highway.
 A Comprehensive Site Assessment (CSA) was
conducted in 2001 and 2002 which identified
petroleum contamination in soil and groundwater from
the former UST system.
 13 water supply wells within 1500 ft
 The former tank basin is located within the grassy
area between eastbound and westbound lanes of the
highway.
 Groundwater plume extends onto neighboring
property to south with a water supply well within 250
ft. of release.
o Geology: sands and clay
above partially weathered
bedrock
o Groundwater flow velocity
to the southeast ~ 1.8 ft/yr.
o Former UST pit now in
highway median
o Sulfate-reducing
conditions confirmed by
groundwater analysis.
 REAGENT /TECHNOLOGY OPTIONS:
 Mobil Multiphase Petroleum Extraction (MMPE)
 In Situ Chemical Oxidation with Na Persulfate
 Air Sparge/Soil Vacuum Extraction (AS/SVE)
 Bioremediation – Aerobic (Oxygen) vs. Anaerobic
(Alternate Electron Acceptor)
 MMPE performed three times successfully, but left
residual BTEX & naphthalene
 ISCO and AS/SVE too expensive and disruptive.
 ANAEROBIC BIOREMEDIATION SELECTED
Approach/Activities
 SULFATE-DEPENDENT ANAEROBIC BIOREMEDIATION
 EAS™ is a sulfate-based electron acceptor solution.
 It enhances ongoing anaerobic microbial processes that
facilitate biodegradation of PHCs (BTEX, aromatic
hydrocarbons, MTBE) in the subsurface.
 Its application takes advantage of prevailing (reducing)
subsurface geochemistry.
 Easy to inject into partially weathered rock.
 It stimulates biodegradation by providing a soluble,
readily available electron acceptor. (i.e., sulfate)
 In the presence of elevated sulfate, anaerobic
groundwater bacteria use the PHCs for carbon and
energy while mineralizing the hydrocarbons to carbon
dioxide and water.
Results
 Sulfate Radius of Influence: 3 ft after 1 month; 5 ft
after 3 months (> gw flow vel.)
 Concentration Changes (compared to baseline) 6
Months Post-Injection:
PIW-1
PMW-1
PMW-3
B
T
E
X
BTEX
-21%
-7%
-37%
-98%
-9%
-65%
-34%
-20%
-47%
-87%
-4%
+19%
-80%
-9%
-21%
 Concentration Changes (compared to baseline) 16
Months Post-Injection:
B
T
E
X
BTEX
PIW-1
-10%
-86%
+33%
-59%
-56%
PMW-1
PMW-3
-70%
+118%
-82%
-71%
+21%
+96%
-34%
+63%
-39%
+72%
MW-13
-78%
-82%
-70%
-81%
-78%
Discussion
Pilot Study
o Wells screened 10–20 ft bgs
o Injection well (PIW-1)
o Performance monitor wells:
 PMW-1 (3 ft
downgradient)
 PMW-2 (5 ft
downgradient)
 PMW-3 (10 ft
downgradient)
o Network monitor wells:
 MW-4 (20 ft east of
PIW-1)
 MW-13 (25 ft SW of
PIW-1)
 INJECTION: SIES gravity-fed 52.5 gallons of EAS™ into
PIW-1 located in the former tank pit.
 ~1000 ppm Sulfate added to aquifer
 Feed rate = 0.6 to 0.7 gpm.
 MONITORING:
 pH, ORP, DO, sulfate, BTEX, MTBE, naphthalene
 Sulfate-reducing bacteria
EAS™ was provided by from EOS Remediation, LLC (Raleigh, NC)
 6.1 to 9.5 x 104 cells/mL sulfate-reducing bacteria
present in aquifer
 Within 6 months, positive impact of EAS™
enhancement observed within 5 to 10 ft of injection.
 After 16 months, positive impact of EAS™ declining,
but benzene, toluene and xylenes still reduced
compared to baseline.
 Subsurface heterogeneity and preferential pathways
influence transport of EAS™
 MW-13 showing 78% total BTEX decrease 16 months
post EAS™ injection 25 ft to NE (subsurface
heterogeneity and favorable pathways).
Conclusions
 EAS™ impact declined after 6
months with some rebound
observed.
 Sufficient longevity was
observed to warrant full
scale application.
 Multiple injections will likely
be required to sustain
enhancement.