A newsletter about soil, sediment, and groundwater characterization and remediation technologies
Technology
News & Trends
SEPA
EPA 542-N-12-006 | Issue No. 62, December 2012
This issue of Technology News & Trends highlights the use of in situ bioremediation to
address groundwater contamination caused by past releases of organic contaminants.
Implementation of bioremediation at these sites involves biostimulation techniques in which
amendments are administered to the subsurface to provide nutrition for microorganisms
capable of consuming and consequently biodegrading the contaminants, as well as
bioaugmentation techniques involving subsurface injection of biodegrading microorganisms
that may not already exist onsite.
FEATURED ARTICLES
Treatability Testing: Biostimulation and Bioaugmentation of a
TCE Groundwater Plume on Tribal Land
Contributed bv Fred McDonald. Tulalip Tribes: Denise Baker-Kircher. U.S. Environmental
Protection Agency Region 10; Carl M. Bach, The Boeing Company; Clint Jacob and Christoohe
Venot, Landau Associates Inc.
The Boeing Company is performing an in situ treatability test on a groundwater plume
containing trichloroethene (TCE) and TCE breakdown products at the companyTdVis former
aerospace test facility near Seattle, Washington. The treatability test evaluates
bioremediation efficacy as part of a remedial investigation and feasibility study (RI/FS) for
four dissolved-phase TCE plumes affecting 26 acres of this 525-acre site. The RI/FS is
conducted under a Superfund alternative approach,that involved negotiation with the U.S.
Environmental Protection Agency to use Superfund processes and standards but without site
listing on the National Priorities List. Preliminary treatability test results along with earlier
pilot-scale testing indicate that effective sequential reductive dechlorination of TCE and
breakdown products can be achieved through biostimulation and bioaugmentation.
The site is located within the Tulalip Tribes Indian Reservation in Marysville, Washington, and
was leased by Boeing from the Tribes in 1960 to 2001. Bioremediation testing focuses on one
4.3-acre groundwater plume originating from a former aeronautical test area and septic tank.
This plume contains the highest TCE concentration in groundwater, with a maximum
concentration of 500 ug/L identified during 1999-2010 remedial investigation. TCE breakdown
productc/s-l,2-dichloroethene (c/s-DCE) was present at baseline concentrations reaching 200
ug/L. However, breakdown products vinyl chloride (VC), ethene, and ethane were not
detected.
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The plume extends nearly 900 feet in length and 25 to 45 feet in depth in an unconfined,
glacial sand aquifer with low organic carbon. Average groundwater seepage velocity in this
area is 0.5 to 1 foot/day. Prior to pilot testing, baseline aquifer redox conditions were aerobic
to mildly reducing. The distribution of higher TCE concentrations downgradient of suspected
source areas suggests that the site'idVis four plumes resulted from releases of aqueous rather
than dense non-aqueous phase liquid.
Legend
Direct Push Boring
Monitoring Well
Row of Injection Welts
Target Treatment Area
Pilot Injection Wells
•
Figure 1. Feasibility study area with seven rows of wells to
inject electron donor substrate and bacterial inocolum.
Pilot testing was performed intermittently from 2000 through 2010 to identify an optimal
electron donor substrate for biostimulation, evaluate use of bioaugmentation to overcome
c/s-DCE reduction "stall" (no further degradation), and obtain design parameters for potential
full-scale bioremediation. Testing evaluated the use of a single row of injection wells oriented
perpendicular to the plume axis (Figure 1) and relied on natural groundwater flow to distribute
the substrate. An emulsion of sodium lactate (1.5%) and soybean oil (2%) was the most
effective of various electron donor substrates tested alone and in combinations, including
HRC,™ chitin, and other vegetable oil and lactate products. Use of the optimal lactate and oil
substrate resulted in highly reducing (i.e., sulfate-reducing to methanogenic) conditions,
complete dechlorination, and more than six months of donor longevity between injections.
Following various donor injections but prior to bioaugmentation, c/s-DCE stall was indicated
by increasing c/s-DCE concentrations of up to 1,400 ug/L.
Pilot-scale bioaugmentation tests began after the third donor injection by injecting the
Bachman Road strain (BAV1) of Dehalococcoides (DHC) bacteria. DHC are the only
microorganisms known to reductively dechlorinatec/s-DCE and were not detected in the
plume prior to bioaugmentation. Substantial VC and ethene production occurred after one
injection of DHC BAV1. This increase had not been observed following injections of lactate and
oil alone. Near the end of testing, two to three times as much ethene as VC (on a molar basis)
was measured at three monitoring wells downgradient of the injection wells (Figure 2). Four
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years after the bioaugmentation, DHC BAV1 were found more than 350 feet downgradient
from the injection wells, at densities of 104 to 105 cells per milliliter (ml). Overall results of
the pilot-scale test and aquifer tracer tests indicated that effective full-scale treatment of the
plume could likely be achieved with injection wells on 15-foot centers in rows 150 feet apart
across the plume axis.
1" Pilot-Test
Injection Donor Pilot-Testing
100% -I
Bioaugmentation
Bioaugmentation Pilot-Testing
Ethene+ Ethane = 2-3x VC
Incomplete Treatment,
c/s-DCE stall
VC Produced,
BAV1gene count
increases
47 59 71
Months Elapsed
83
95
107 119
(NOV2010)
Figure 2. Pilot-test averages for three monitoring wells located 25-75 feet
downgradient of injection wells.
Treatability testing was designed and implemented based on the pilot results. In 2010, 78
injection wells were installed in seven rows across the plume to target all zones containing
TCE and breakdown products at concentrations exceeding maximum contaminant levels
(MCLs) (Figure 1). A total of 134 injection intervals were achieved with 10-foot-long nested
shallow and deep screens (25 and 40 feet below ground surface [bgs], respectively) in 56 of
the wells.
A total of 955,000 gallons of donor fluid was injected during three events in 2011 and 2012
(Figure 3). The fluid consisted of an emulsion of tap water and LactOil™ donor substrate
containing slow-release soybean oil and fast-release ethyl lactate at concentrations similar to
those used successfully in the pilot test. For cost savings and ease of handling, the substrate
was purchased in bulk quantity and delivered in 10 tank trucks carrying a total of 53,000
gallons (461,000 pounds). The donor fluid was batch-mixed with tap water onsite in
temporary 6,500-gallon tanks. To expedite injection, a manifold was constructed to meter
emulsion flow to six wells simultaneously. Each injection event lasted approximately two
months, with events starting about six months apart.
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Figure 3. Electron donor injection to multiple wells within a row.
Treatability study bioaugmentation was conducted concurrent with the second biostimulation
(donor) injection, using groundwater extracted from the pilot area as inoculum. The
groundwater inoculum contained DHC BAV1 at densities exceeding 104 cells/ml (lower than
the 106 cells/ml common in commercially available inocula) and was used in agreement with
the pilot test inoculum vendor. To prevent DHC mortality caused by contact with dissolved
oxygen, donor solution was biologically reduced prior to injection by adding a concentrated
anaerobic culture grown from site groundwater and storing the mixture overnight in a
separate tank. The solution was injected immediately before and after the groundwater
inoculum injection.
Aquifer chemistry and weather conditions presented challenges for plume treatment. Donor
addition to a sand aquifer with low buffering capacity reduced the pH to below optimal
conditions necessary for bioactivity, resulting in decreased ethane production. Low pH was
addressed by using lower donor concentrations for the third injection. Also, thickening and
some separation of the concentrated donor substrate occurred at low winter temperatures
(<20°F) during the first injection. This problem was avoided during the third injection by
storing deliveries of hot (up to 140°C) substrate in an insulated tank and optimizing delivery
timing for immediate use. Lastly, some surfacing of injection fluid was observed during winter
injection in areas with groundwater less than 1 foot bgs; this was addressed by injecting
donor solution at a slower rate in these wells and shifting part of the injection volume to
adjacent wells.
Groundwater monitoring is performed quarterly to semiannually. Analytical parameters
include total organic carbon; aquifer redox; TCE and its breakdown products and end
products; and microbial DNA analysis via quantified polymerase chain reaction (qPCR),
including functional gene analysis. Monitoring results show that breakdown product c/s-DCE
has replaced TCE in predominance at most wells upgradient of the former pilot area. At a
representative upgradient monitoring well, TCE decreased from 110 to 7 ug/L while c/s-DCE
increased from 26 to 590 ug/L, and a low level (1.5 ug/L) of ethene was detected. End
products ethene and ethane are now the only compounds detected within the farthest
upgradient injection row, indicating complete dechlorination in the immediate vicinity of
bioaugmented wells. Although the number and extent of DHC BAV1 in upgradient areas have
not yet increased substantially, an increase is anticipated over time.
Downgradient of the pilot area, TCE and c/s-DCE concentrations have decreased to below
MCLs (5 ug/L and 70 ug/L, respectively) and VC, ethene, and ethane predominate. At the
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plume's leading edge, VC concentrations are below the MCL of 2 ug/L. These results indicate
complete dechlorination within the treatment zone, with no migration of TCE or breakdown
products to wells beyond the treatment area.
Additional donor injection may be needed as electron donor is consumed, but further
bioaugmentation injection is not anticipated. The cost to plan, implement, and monitor this
treatability test (excluding earlier pilot testing) over the first three years was approximately
$1.4 million. This includes $640,000 to purchase the donor substrate and $192,000 to
construct the 78 injection and seven additional monitoring wells, representing a cost of $5.25
per cubic yard of the target treatment zone.
Full-Scale Application: Source Area Biostimulation Combined
with a Biobarrier
Contributed by Greg Gilmore, Georgia Environmental Protection Division; Kevin Morris, ERM
A full-scale approach for stimulating indigenous microbes to achieve anaerobic reductive
dechlorination of trichloroethene (TCE) in groundwater was implemented recently at Rummel
Fibre, an industrial facility in northern Georgia. The biostimulation design involved source-area
treatment to address elevated TCE concentrations remaining after ex situ groundwater
treatment and a permeable injection biobarrier to mitigate offsite migration of
dissolved-phase TCE. Results to date indicate that injection of a vegetable oil substrate is
significantly accelerating the site's cleanup closure.
Soil and groundwater contamination at this 30-acre site resulted from TCE releases that
occurred between 1970 and 1980 during manufacturing operations. Site lithology comprises
silty saprolite overlying bedrock at 25 to 70 feet below ground surface (bgs). A 1993
investigation revealed TCE impacts to perched groundwater in the shallow (10-15 bgs)
saprolite and some impact to groundwater in fractured bedrock. The highest identified TCE
concentration in groundwater was 78,000 ug/L. Groundwater seepage velocity in this area is
estimated at 90 feet per year but varies seasonally. A naturally occurring drainage swale
bisects the source area. Prior to bioremediation, cleanup strategies included 1998-2002
operation of a groundwater pump-and-treat system followed by an in situ electro-chemical
geo-oxidation (ECGO) system that began treating soil in 2003.
Initial biostimulation involved an onsite pilot study that used biotraps to collect data on the
indigenous microbial community. Analysis of biotraps deployed in site groundwater revealed a
healthy population of Dehalococcoides ethenogenes. Based on this finding, a small-scale
substrate injection test was conducted in 2006. Test results indicated that complete reductive
dechlorination of TCE could be achieved by using a commercially available substrate
containing emulsified soybean oil (NewmanZone™). Monitoring indicated subsurface reducing
conditions that persisted for nearly five years after the small injection, with no detection of
TCE or evidence of contaminant rebound. For the past two years, biodegradation daughter
products/s-dichloroethene, vinyl chloride, ethane, and ethane in the pilot test area have
remained below maximum contaminant levels (MCLs).
In preparation for full-scale biostimulation, 70 injection wells were installed in December
2008. Thirty-five injection points were constructed at a spacing of 15 feet in the approximate
150- by 120-foot TCE source area. The injection points were installed through 20 to 50 feet of
saprolite overburden to the top of bedrock. To create the permeable biobarrier that intersects
groundwater flowing downgradient of the primary source area, an additional 35 injection
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points were installed at the same spacing over a linear distance of approximately 500 feet.
The barrier injection points also were installed to the top of bedrock.
Figure 1. Delivery of substrate from a single
500-gallon tank into four injection points via a
positive displacement pump.
In January and February 2009, the emulsified vegetable oil solution was injected into each
point at a rate of 2-4 gallons per minute under a pressure below 30 pounds per square inch
gauge (Figure 1). This low flow and pressure helped minimize potential short-circuiting to the
ground surface (daylighting). Using a manifold system, up to four points were injected
simultaneously. Substrate injections were conducted in the barrier line first to assure that a
treatment zone was established prior to injecting into the source area.
The total combined injection volume for all 70 injection points was 98,000 gallons of solution
containing 95,000 gallons of water and 3,000 gallons of the substrate. A total of
approximately 7,000 gallons (100 gallons per point) of chase water was injected immediately
after the substrate injection to assure that biofouling did not become a problem in the event
additional injections are necessary. Since onsite groundwater is generally more compatible
with indigenous anaerobic microorganisms, the water needed to administer the injection
consisted of groundwater that was pumped from an onsite bedrock well and mixed with
hydrant water.
Intermittent freezing temperatures during the full-scale injection caused some difficulty in
handling the water, pumps, and hoses. Also, some daylighting occurred, primarily in the
shallowest (<20 feet bgs) injection points. Any point displaying visual sign of daylighting was
immediately valved off to minimize the amount of substrate escaping to ground surface.
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5.000
4.500
4.000
3,500
ECGO system startup
I nrtiatioo ol full-sea te
bioslimulation irjoctio-is
dichloroethcne
linear
(Irichloroethene)
Mar-02 Mar-03 Mar-04
Mar-06 Mar-07 Mar.06 Mar-09 Mar-10 Mar-11 Mar-12
Date
Figure 2. Average TCE concentrations in source area groundwater before
and after vegetable oil injection.
Post-injection monitoring in the source area showed evidence of reductive dechlorination
within three months (Figure 2), with dissolved oxygen below 0.5 mg/L and pH maintained at
about 6.5. Within six months, TCE concentrations had decreased from the pre-injection
average of 3,000 ug/L to below the MCL of 5 ug/L. Reductive dechlorination end products
ethene and ethane have been detected at concentrations reaching 200 ug/L, with an average
concentration of approximately 100 T«i1/2g/L in the source area. This represents a significant
increase from the highest concentrations of ethane and ethane prior to full-scale
biostimulation, which were below 1 ug/L.
Monitoring of overburden groundwater downgradient of the permeable barrier shows similar
trends (Figure 3). Reducing conditions were observed in the groundwater within six months
after injection completion. Within nine months, ethane and ethane were detected for the first
time in two downgradient wells. Currently, these downgradient locations show an average
TCE concentration of 40 ug/L, the lowest concentration in nearly 20 years.
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12.000
10,000
s
-ECGO s-ystem startup
Initiation of full-scale
injections
- •*- OS-1,2-
dicftioroetten*
• tnehloroethefie
—*—vinyl ehtonde
-linear
(triqhioraetnene)
Mar-02 Mar-03 Mar-04 Mar-OS Mar-Q6 Mar-07 Mar-06 Mar-09 Mar-10 Mar-11 Mar-12
Date
Figure 3. Average TCE concentrations in groundwater downgradient of the
biobarrier before and after vegetable oil injection.
The ECGO system was shut down in 2010, following 12 months of evidence that anaerobic
reductive dechlorination continued to occur in the source area and downgradient
groundwater. Due to overall success of the biostimulation, the Georgia Environmental
Protection Division (GAEPD) has agreed to modify the monitoring program from a quarterly to
a semi-annual schedule.
The approximate costs to implement full-scale bioremediation at this site currently total
$575,000. This includes $35,000 to purchase the electron-donor substrate, $260,000 to install
the 70 injection points and administer the injections over two months, and $280,000 for four
years of monitoring. Currently, the GAEPD is considering a two-year monitored natural
attenuation as a final remedy. Cleanup closure is anticipated in 2015-2016, approximately 20
years ahead of original estimates.
CLU-IN Website: Bioremediation of Chlorinated Solvents
This remediation technology area of CLU-IN provides an overview and compendium of
reference materials, application reports, and other information resources on in situ and ex situ
methods of using bioremediation.
Upcoming Report: Superfund Remedy Report (14th edition)
EPA's Office of Superfund Remediation and Technology Innovation anticipates release of the
14th edition of this report in January 2013. The report presents an analysis of Superfund
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remedial actions documented in records of decision (ROD), ROD amendments, and
explanations of significant differences for fiscal year (FY) 2005 through FY 2012 and identifies
general trends in Superfund remedy selection over the past 20 years. Information compiled
for the!3th edition revealed that 61% of the remedies selected for in situ treatment of
groundwater in FY 2005 through FY 2008 involved bioremediation.
ESTCP Cost & Performance Report: Application of Nucleic
Acid-Based Tools for Monitoring Monitored Natural
Attenuation (MNA), Biostimulation and Bioaugmentation at
Chlorinated Solvent Sites
This report (ER-200518) from the U.S. Department of Defense Environmental Security
Technology Certification Program provides results from a recent project that: demonstrates
correlations between dechlorination of chlorinated ethenes and the presence and abundance of
Dehalococcoides sp. biomarker genes; defines limitations of the deoxyribonucleic acid
biomarker-based approach and specifies conditions where quantitative real-time polymerase
chain reaction (qPCR) assay offers or fails to provide meaningful information; and develops a
guidance protocol for practitioners to apply this tool.
A Citizen's Guide: Bioremediation
As one of a 22-document series, this two-page fact sheet answers general questions about
using bioremediation for contaminated site cleanup. The 2012 update to "A Citizen's Guide to
Bioremediation" (EPA 542-F-12-003) explains how bioremediation works and aspects such as
typical duration, safety, and benefits of this technology. Other topics addressed in thecitizen's
guide series include pump and treat, in situ chemical oxidation, evapotranspiration covers,
fracturing for site cleanup, and vapor intrusion mitigation.
Upcoming Training: Low-Cost Remediation Strategies for
Contaminated Soil and Groundwater
The National Groundwater Association offers this three-day course on February 6-8, 2013, in
Denver, Colorado, to help participants select a remedial technology for a site and determine
how to properly design, install, and monitor the technology. Technologies covered in this
course include enhanced bioremediation, air sparging, phytoremediation, and natural
attenuation for remediation of contaminated groundwater, bioventing for remediation of
contaminated soil, and bioslurping for removal of light non-aqueous phase liquids.
Conference Proceedings: 5th International Symposium on
Biosorption and Bioremediation
Proceedings from the 5th International Symposium on Biosorption and Bioremediation held in
Prague this past June are now available online from the Institute of Chemical Technology.
Topics addressed at this conference include biodegradation of recalcitrant organic compounds,
phytoremediation, heavy metal sorption, use of genetically modified organisms, and microbial
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ecology in contaminated environments. The National Technical Library of the Czech Republic
and the non-profit European Federation of Biotechnology are among the event sponsors.
EPA is publishing this newsletter as a means or disseminating useful information regarding innovative and alternative
treatment technologies and techniques. The Agency does not endorse specific technology vendors.
Contact Us
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