5
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/A newsletter about soil, sediment, and groundwater characterization and remediation technologies
Issue 46
7)zis is-SHe o/Technology News and Trends highlights the use of compound specific isotope analysis
(CSIA), an environmental forensics technique used to characterize contaminated sites and the
progress of bioremediation and natural attenuation. CSIA measures and compares the ratios of
stable isotopes found in compounds of suspected contaminant sources or plumes as well as the
feedstock or manufacturing process of materials historically used in a site's vicinity. Isotopic
analysis can help discern the potential for multiple spills of the same compound based on their
different isotopic "signatures. " An isotopic signature can be used to associate a contaminant
plume with a particular spill or potentially responsible party. It also can be used to evaluate the
extent of contaminant degradation caused by microbes during natural attenuation.
CSIA at the Bandera Road Site Reveals a Second Contaminant Source
February 2010
The U.S. Environmental Protection Agency
(EPA) Region 6 office recently conducted a
CSIA investigation at the Bandera Road
Groundwater Plume Superfund site in Leon
Valley, TX, just outside San Antonio.
Previous groundwater investigations
identified chlorinated solvents exceeding
groundwater standards. Determining the
carbon isotope ratios (13C/12C) for
tetrachloroethene (PCE), trichloroethene
(TCE), andcw-l,2-dichloroethene (cDCE) in
groundwater samples helped to distinguish
release sources and assess biodegradation.
Gas chromatography-isotope ratio mass
spectrometry (GC-IRMS) and sample
preparation techniques that could detect
chlorinated solvents at concentrations as
low as 20 ppb were used.
Many processes affecting contaminants in
groundwater, such as dilution, sorption,
and volatilization, have little or no effect
on isotopic ratios. Processes such as
biodegradation and abiotic degradation,
however, are associated with significant
isotopic fractionation. In addition, the
isotopic ratios of PCE and TCE vary
depending on the manufacturer. As a
result, CSIA can be used at a contaminated
site to identify sources of chlorinated
solvent; help determine the sequence of
multiple releases; and identify,
characterize, and quantify biotic and abiotic
transformation reactions.
The study area encompassed approximately
162 acres in a commercial area with nearby
residences. Potential contaminant sources
included several dry cleaners, automotive
businesses, and a former municipal airfield.
The primary contaminants of concern are
PCE, TCE, and cDCE due to their detection
frequency and concentrations in local
groundwater. Of the 10 wells with PCE or TCE
concentrations exceeding the 5 ppb federal
drinking water standard, four had been
plugged and abandoned prior to CSIA work
because they were open to the Edwards
Aquifer, the sole-source drinking water
aquifer for the San Antonio area.
The other six impacted wells extend to water-
bearing formations (Austin Chalk and Buda
Limestone) above the Edwards Aquifer. The
highest PCE concentration of 11,600 ppb was
detected in an Austin Chalk monitoring well
(USGS-42) adjacent to a former dry cleaning
facility. Another Austin Chalk well (DW-404)
approximately 150 feet from an operating dry
cleaning facility exhibited PCE concentrations
as high as 1,100 ppb.
CSIA was conducted in June 2009, in
accordance with EPA's Guide for Assessing
[continued on page 2]
Contents
CSIA at the Bandera
Road Site Reveals a
Second Contaminant
Source page 1
Combined Dual
Isotope and Dissolved
Gas Analyses Used to
Evaluate Nitrate
Contamination at
LLNL Site 300 page 3
CSIA Discounts PCE
Biodegradation as
Source of TCE in
Municipal Wellfield page 4
CLU-IN Resources
EPA's CLU-IN Web host
provides information on methods
and standard operating
procedures for site character-
ization, such as A Guide for
Assessing Biodegradation and
Source Identification of
Organic Groundwater Contami-
nants Using Compound
Specific Isotope Analysis
(CSIA) (EPA600/R-08/148), at:
www.cluin.org/characterization/.
CLU-IN information on the
related issue of natural
attenuation is available in
guidance such as Monitored
Natural Attenuation of Inorganic
Contaminants in Ground
Water (Volumes 1 and 2, EPA
600-R-07-139 and EPA600-R-
07-140), at: www.cluin.org/
remediation/.
Recycled/Recy cl abl e
Printed with Soy/Canola Ink on paper that
contains at least 50% recycled fiber
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Carbon Isotope Ratio and Concentrations of Chlorinated Hydrocarbons
Sample ID
USGS-42
DW-408
DW-404
DW-407
DW-47
DW-36
PCE
(813C)
-23.45
-20.29
-26.38
-24.92
-23.24
-24.95
PCE
(ppb)
1 1 ,600
86
1,100
135
6.8
32
TCE
(513C)
-27.00
-25.92
-29.23
-26.61
-27.79
TCE
(ppb)
1,560
28
41
2.9
<1
1.1
cDCE
(513C)
-22.00
-14.8
-24.88
-23.03
-22.90
-24.00
cDCE
(ppb)
2,600
50
51
2.7
<1
<1
Table 1. Results ofCSIAfor PCE and its degradation products in groundwater samples helped identify a second source of
contamination at the Bandera Road site.
[continued from page 1]
Biodegradation and Source Identification
of Organic Groundwater Contaminants
Using CSIA. The guidance allows for a
typical analytical uncertainty of ±0.5%o for
carbon isotopes. Results of the analysis are
reported as 813C, which represents a
comparison between the ratio of 13C to 12C
in a sample and the ratio in an international
standard, expressed in parts per thousand
(%o). A813C of-30%o, for example, indicates
that the ratio of 13C to 12C for the sample is
3% lower than the standard. Biodegradation
induces a shift of the residual compound to
less negative values of 813C; the more
negative the CSIA values are, the closer to
the source and/or the more recent the
contaminant release is likely to be.
Techniques for collecting and preserving
groundwater samples for CSIA are
identical to those used in collecting
samples for volatile organic analysis
using EPAMethod 8260. All samples are
packed in the same manner and then
shipped to an offsite laboratory. For
Bandera Road CSIA, laboratory costs
averaged $600 per sample.
Comparison of carbon isotope ratios for
PCE indicates that monitoring well
USGS-42 contains the highest PCE
concentration, but well DW-404 has a
Figure 1. Spatial distribution of CSIA
results at Bandera Road suggests the
presence of two or more contaminant
more negative 813C value (Table 1). This
indicates that either a more recent release
has taken place near DW-404 and/or less
degradation is occurring near this well.
Subsequent passive soil gas sampling at
the operating dry cleaner near DW-404
identified PCE, TCE, cDCE, and vinyl
chloride contamination in soil gas.
The spatial distribution of 813C for PCE
and its degradation products (TCE and
cDCE) and standard sampling results were
examined to determine potential trends in
biodegradation (Figure 1). Biodegradation
impacts also were observed in well DW-
408, which is located approximately 400
feet from the former dry cleaner and
monitoring well USGS-42. CSIA data and
contaminant ratios indicate that
contamination in other wells (DW-407
and DW-36) may originate from a source
other than than the former dry cleaner.
Using the CSIA results, Region 6 plans to
conduct a tracer study to help identify
contaminant migration pathways. Analysis
of additional CSIA techniques involving
chlorine and hydrogen istopes (39C1/37C1
and 2H/1H) may be used to further
distinguish and delineate the plumes.
Contributed by Chris Villarreal, EPA
Region 6 (villarreal.chris(q)epa.gov or
214-665-6758) andYi Wang, Ph.D., DPRA-
ZymaXForensics (vi.wang(a>zvmaxusa.com
or 760-781-3338)
Operating Dry Cleaner
^y/
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Combined Dual Isotope and Dissolved Gas Analyses Used to Evaluate Nitrate Contamination at LLNL Site 300
Lawrence Livermore National Laboratory
(LLNL) developed an integrated approach
using groundwater nitrate (NO3) isotopic
composition and dissolved gas analyses
to help identify nitrate sources and
demonstrate natural attenuation at the
LLNL Site 300 Superfund site, east of San
Francisco Bay, CA. The U.S. Department
of Energy has conducted high explosives
(HE) formulation and testing at Site 300
since 1955. In the 1990s, site
investigations identified nitrate in
groundwater at concentrations reaching
90 mg/L (as NO3), significantly higher
than the average 30 mg/L background
level at Site 300. As a result, the HE
process area was studied to determine
whether elevated groundwater nitrate
was due to degradation of past releases
of HE to unlined rinse-water lagoons and
landfills, effluent from site septic
discharge systems, or natural nitrate
from soil and bedrock. The extent to
which nitrate was being attenuated once
it entered underlying groundwater also
was evaluated.
Fifty stable-isotope and dissolved-gas
analyses were performed on groundwater
samples collected from depths of 100 to
170 feet below ground surface (bgs) in an
underlying bedrock aquifer. Stable isotope
ratios of nitrogen and oxygen were
measured in groundwater nitrate and in
potential source materials, including
barium nitrate (a mock explosive), RDX (a
high explosive formulated and tested at
Site 300), and nitric acid (which may have
been present in waste disposed in the
onsite landfills). Use of both nitrate-N and
nitrate-O isotopic composition (the dual
isotope approach) allowed greater
differentiation among nitrate sources than
analysis of nitrate-N isotopic composition
alone. The approach also provided
evidence of denitrification, the dominant
subsurface degradation process for
nitrate. Biologically mediated
denitrification typically favors lighter
isotopes, systematically shifting the
isotopic composition of both nitrogen and
oxygen in residual nitrate along a
characteristic trend line.
The approach used to determine nitrate
isotopic composition relied on a specific
strain of denitrifying bacteria. The
denitrifier approach can be two to three
orders of magnitude more sensitive, less
subject to contaminated groundwater
matrix interferences such as sulfate, and
less labor-intensive than other methods for
isotope composition analysis. The
technique also allowed collection of sample
volumes as small as 40 mL and
determination of nitrate isotopic
composition in low-nitrate groundwater,
where denitrification effects on isotopic
composition are most pronounced.
Dissolved gases were measured in the
same set of samples to more conclusively
assess the role of saturated-zone
denitrification in attenuating nitrate transport.
Analyses showed excess concentrations of
dissolved gases resulting from atmospheric
gases, which were determined by argon
measurement. LLNL constructed a simple,
portable, gas analyzer to determine the
dissolved nitrogen, argon, and oxygen gas
concentrations in groundwater samples in the
field. Costs for combined isotope and
dissolved gas analysis averaged
approximately $600 per sample.
Dissolved nitrate isotopic compositions
in the samples were consistent with a
natural source (non-impacted soil and
bedrock) or a septic effluent source.
In addition, groundwater isotopic
signatures differed markedly from
isotopic signatures of materials used in
onsite HE operations, including nitric acid,
barium nitrate, and degraded RDX.
Although the HE materials dataset is too
small to be definitive, it supports
determination of a non-HE source for site
nitrate contamination.
Groundwater sampled in the upgradient
unconfined aquifer had high concentrations
of nitrate and oxygen and no excess
nitrogen. In the downgradient confined
aquifer, concentrations of dissolved
oxygen and nitrate decrease and excess
nitrogen increases, a pattern consistent
with saturated-zone denitrification (Figure 2).
The isotopic composition of both nitrogen
and oxygen in groundwater nitrate shifts
to heavier values in the downgradient
aquifer. On a nitrate isotopic composition
plot, 15N and 18O are positively correlated
[continued on page 4]
-> 100-r
I
*w
tfi
Upgradient -
(uncor fined)
Downgradient
(confined)
V
-------
Figure 3. Nitrate isotopic compositions
measured in Site 300 groundwater and
operations provided discrete markers, as
compared to range values of nitrate
isotopic compositions of soil, septic
effluent, and precipitation reported in
[continued from page 3]
with a linear regression slope of 0.5 that is
characteristic of denitrification (Figure 3).
The combined stable isotope and
dissolved-gas analyses provided
evidence of saturated-zone denitrification
by way of microbial degradation, rather
than dispersion and dilution, as the
primary attenuation mechanism for low
nitrate concentrations in downgradient
groundwater. As a result, monitored
natural attenuation (MNA) was selected
as a remedy for nitrate in this area. More
information about the use of this
approach is available in EPA guidance,
Monitored Natural Attenuation of
Inorganic Contaminants in Ground
Water, Volume 2.
70n
60-
50-
40-
1 z 3°-
1 0 20-
"> 10-
o-
-10-
-20-
-30-
Precipitation
- - n^
Soil— (-*•[_*« .
(^J.
• Groundwater
n Nitric acid
A Barium nitrate (mock explosive)
O RDX (explosive)
Downgradient wells
(low NO3, high N^K,
Septic
i
r Denitrification
trend line
0 10 20 30 40
_
Upgradient wells
_+ (high N03, low N2) g15N (0/ooj
The U.S. Air Force Center for Engineering
and the Environment (AFCEE) has begun
using dual-isotope and dissolved gas
analyses at several bases, including Edwards
Air Force Base (AFB), CA, andKirtlandAFB,
NM. At Edwards AFB, this technique will be
used to evaluate potential sources including
naturally occurring nitrate, explosive
ordnance disposal, septic waste, and
hydrazine (a nitrate-containing component of
rocket fuel) and to assess possibility of
implementing an MNA remedy.
Contributed by Bradley Esser, Ph.D.,
LLNL (bkesserCdi.llnl.sov or 925-422-
5247), Edward Brown, AFCEE
(edward.brown.3(q),us.af.mil or 210-
536-5239), and Robert Ferry, Brown
and Caldwell (rferrv(q)brwncald. com
or 925-872-7264)
CSIA Discounts PCE Biodegradation as Source of TCE in Municipal Wellf ield
U.S. EPAs Region 10 conducted CSIA in
2006 to help refine the conceptual site
model at the Palermo Wellfield Superfund
site in Tumwater, WA, located just south
of Olympia. Following detection of TCE in
the municipal water supply in 1993,
groundwater investigations identified
dissolved contaminant plumes of TCE and
PCE in area groundwater and several
potential source areas. Results of CSIA
using stable carbon isotopes indicated
that upgradient locations of Washington
Department of Transportation (WDOT)
laboratories, rather than biodegradation of
PCE released from a dry cleaner, were the
likely source of TCE in the well field.
The Palermo Wellfield lies within the
Deschutes River Valley, east of a 60-foot-
high bluff atop which sit several
commercial businesses and potential
source areas. The Palermo neighborhood
borders the wellfield to the northwest
(Figure 4). Municipal wells of the wellfield
are completed in fluvial sand and gravel,
while the upland area is underlain by glacial
outwash sands and till. The glacial deposits
are unconfined and hydraulically
connected to the fluvial sediments in the
valley. Depth to groundwater in the
uplands ranges from 10 to 55 feet bgs and
from 4 to 8 feet bgs in the valley, with
groundwater flow to the northeast.
Early detections of TCE in the wellfield
ranged from 0.9 to 14 |Ig/L TCE, exceeding
the 5 (Ig/L drinking water standard.
Detection of TCE prompted a 1997 removal
action involving wellhead treatment of the
municipal water supply by air stripping. A
subsequent groundwater investigation
initially identified an upgradient dry
cleaning facility as a potential source of
TCE due to the past disposal of PCE in
an onsite dry well and suspected
biodegradation of the PCE to TCE through
anaerobic dechlorination. Concentrations
of PCE measured in soil at the dry cleaners
were as high as 63.2 mg/kg. As part of a
1998 removal action, a soil vapor extraction
(SVE) system was installed to remove PCE
from soil at the property.
In the subsequent remedial investigation,
the TCE plume was found to originate in
the uplands west of the wellfield and west
of the dry cleaners. The plume extends east-
northeast for about a half mile beneath the
Palermo neighborhood and wellfield where
it is intercepted by the municipal well. The
PCE plume, however, was found to be
smaller (about 750 feet long), extending
[continued on page 5]
-------
•J,
5000 Bldo
•«~"7 ^
x.
I ft '"".li1
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t
Paogo'n Towing
and Aulo Rnpnlr
•
LEGEND
• ..:.i-
C'-MI
Monitoring Well Sampled
Monitoring Well Not Sampled
Groundwater Elevation (ft)
' TCE Value (ng/L)
Figure 4. The plume
of TCE follows the
direction of
groundwater flow
from the former WDO
facility until it is
tured bv the
Palermo Wellfleld.
[continued from page 4]
northeast from the parking lot of the dry
cleaners to the edge of the bluff. The plume
stops short of the homes and wellfield.
Furthermore, subsurface conditions at the
dry cleaners did not appear conducive to
anaerobic biodegradation as areas of low
dissolved oxygen and oxidation reduction
potential were limited. In addition,
detections of reductive dechlorination
daughter products such as cDCE and vinyl
chloride were sporadic, further
discounting the dry cleaner as the source
of wellfield TCE. The 1999 record of
decision (ROD) called for continued
operation of wellhead and SVE treatment.
The SVE system was shut down in 2000.
In pursuit of another line of evidence, EPA
performed CSIA in 2006 to confirm that the
Figure 5. S3C measured in monitoring wells
dry cleaner was not the source of TCE and
to identify other potential sources of the
TCE. Groundwater samples were collected
as part of semi-annual, long-term
groundwater monitoring required by the
ROD. Twenty-seven wells and piezometers
were sampled for chlorinated solvents and
13C/12C analysis. The quantitation limits for
CSIA were estimated to be 20 |lg/L for TCE
and 30 (Ig/L for PCE using a purge and trap
technique combined with GC-IRMS. TCE
concentrations in 10 samples were
sufficient to run CSIA. The 813C values
ranged from -22.7%o to -28.8%o. TCE with
813C values in the range of -26%o was
detected in wells downgradient of the
former WDOT facility at the western
extent of the plume (Figure 5), in wells
near the WDOT testing lab further
[continued on page 6]
Wellfield Superfund site show little change
with distance downgradient of the former
WDOT facility and the WDOT testing lab.
The shaded area represents the minimum
isotopic distinction needed to demonstrate a
change in the isotopic signature of TCE
from that measured inMW-109.
•
-25-
1
• * '
-30-
-35-
X
OTCE
Former
WDOT
^ aci I y
WDOT
Lab9
| MW-1 1 1 MW-ES-05
Palermo
Neighborhood
P2-728 O
-L
j ^ ^> MW-ES-09
MW-109Y MW-ES-02Y PZ'721,£, YPZ"724
MW-ES-03^
Dry Cleaners
? MW-ES-04
*
> MW-ES-10
Distance from MW-UI, the Monitoring Well at the
Former WDOT Facility (feet)
Taken from Vlassopoulos. (May 2006)
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Solid Waste and
Emergency Response
(5203P)
EPA 542-N-10-001
February 2010
Issue No. 46
United States
Environmental Protection Agency
National Service Center for Environmental Publications
P.O. Box 42419
Cincinnati, OH 45242
Presorted Standard
Postage and Fees Paid
EPA "
Permit No. G-35
Official Business
Penalty for Private Use $300
[continued from page 5]
downgradient and wells in the Palermo
neighborhood near the well field. The PCE
detected near the dry cleaners had a 813C
of-33%o.
The similarity of 813C values with
increasing distance downgradient
supports the conceptual site model
suggesting that little degradation of
TCE is occurring. That, together with
the marked difference between TCE and
PCE values, indicates that degradation
of PCE from the dry cleaners is not the
source of TCE in the Palermo Wellfield
or neighborhood. Instead, the former
and current WDOT facilities are the
likely sources.
A second five-year review in 2008
indicated that, due to the lack of
conditions amenable to biodegradation,
the TCE plume will degrade as quickly as
anticipated; therefore, groundwater will
not be restored within the 5- to 30-year
timeframe predicted in the ROD. EPA is
recommending that the conceptual site
model and remedial action objectives be
re-evaluated since natural attenuation is
not a significant process for reducing
TCE and PCE concentrations in the
groundwater.
Contributed by Bernie Zavala, EPA
Region 10 (zavala.bernie@epa.gov or
206-553-1562)
Upcoming Green Remediation Conference
Registration is now open for the international conference on Green Remediation:
Environment, Energy, and Economics on June 15-17, 2010 at the University of
Massachusetts in Amherst, MA. View the preliminary agenda and find more online
information through The Environmental Institute at: www.umass.edu/tei/.
Contact Us
Technology News and Trends
is on the NET! View, download,
subscribe, and unsubscribe at:
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www.clu-in.orq/newsletters
Contributions may be submitted to:
John Quander
Office of Superfund Remediation
and Technology Innovation
U.S. Environmental Protection Agency
Phone:703-603-7198
quander.iohn@.epa.qov
Strategy for Characterizing DNAPL
EPA's Office of Research and Develop-
ment, with assistance from EPA's
Ground Water Forum, recently
published Assessment and Delineation
of DNAPL Source Zones at Hazard-
ous Waste Sites, which provides a
framework for assessing the pres-
ence of dense non-aqueous phase
liquids (DNAPLS) and delineating the
spatial extent of a DNAPL source zone
(www.epa.qov/ada/pubs/issue.html).
EPA is publishing this newsletter as a means of disseminating useful information regarding innovative and alternative treatment techniques and
technologies. The Agency does not endorse specific technology vendors.
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