This document discusses optimizing in situ remediation of groundwater contamination using advanced diagnostic tools. It describes compound specific isotope analysis (CSIA) and molecular biological tools (MBT) that can definitively identify contaminant destruction and the microbial mechanisms involved. CSIA tracks stable isotopes to determine if degradation occurred, while MBTs quantify microbial populations and activity. These tools provide better information for selecting and applying in situ remediation technologies like bioremediation and chemical oxidation. When used during remedy selection and performance monitoring, they result in more successful application of in situ groundwater treatment.

1. Optimizing In Situ Remediation
Using Advanced Diagnostics
Presented by: Matt Burns
Contact Information:
WSP Environment & Energy
300 Trade Center, Suite 4690
Woburn, MA, 01801
781/933-7340
matt.burns@wspgroup.com
http://www.linkedin.com/in/mattburns
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Introduction
In situ remediation has been widely applied
to address groundwater contamination over
the past 10 years. Unfortunately, the barrier
to applying the technology is low and poorly
conceived and planned applications are
affecting the credibility of the technology.
Successful selection and application of in situ technologies begins with
a conceptual model that is not biased by preconceived or irrelevant
factors and is tested analytically. The limitations of potential remedies
should be given as much consideration as their potential benefits,
keeping in mind the concepts of integrated site remediation that bundle
complementary technologies for sequential application.
Analytical Assessment Tools
Analytical testing of proposed in situ remedies is complicated
by two key facts:
x The mechanisms of degradation are unseen and not
well understood.
x The physical effects of amendment application (e.g.,
dilution and displacement) can affect concentration
data in a manner similar to the desired reactive
mechanism.

2. Until recently, analytical testing protocols to better understand in
situ degradation processes have been limited by cost, timeliness,
and data tangential what is really necessary:
x Will the proposed amendment application destroy the
contaminant or just push around and dilute it?
x What is the mechanism of destruction and can it be
monitored directly?
New cost-effective analytical tools are now commercially available to answer these questions.
Compound specific isotope analysis (CSIA) provides definitive information on contaminant
destruction that is not concentration related and molecular biological tools (MBTs) identify
microbial-mediated mechanisms of destruction. Proper use of these tools during remedy
selection and performance monitoring results in better application of technologies such as
monitored natural attenuation, bioremediation and in situ chemical oxidation and reduction.
These tools also have applications for environmental forensics that, for example, can segregate
comingled groundwater plumes or identify vapor intrusion sources as originating from above or
below the slab.
Compound Specific Isotope Analysis
CSIA distinguishes destructive reactions from non-destructive processes by tracking the fate of
heavy stable isotopes. Stable isotopes are naturally occurring and not radioactive. Carbon for
example, has two stable isotopes 13C and 12C (note the 14C is radioactive and not stable). The
natural abundance of these isotopes is about 99 percent and 1 percent respectively. The basis
of CSIA as a degradation assessment tool is that heavier isotopes (e.g., 13C) form stronger
bonds. Therefore, the degradation rate of contaminant molecules that contain heavy isotopes is
slower than contaminant molecules composed solely of lighter isotopes (e.g., 12C). The slower
reactivity results in an accumulation of heavier isotopes which are measured by CSIA.
Degradation rate and reaction percent completion can be calculated using CSIA data.
Chocolate Fractionation used with
permission from Dr. Mike Hyman,
Department of Microbiology
North Carolina State University

3. CSIA measures the ratio of heavy isotopes to light isotopes. The analytically derived ratio is
normalized to an international standard and reported in units as part per thousand (per mil or
‰), expressed as the difference (del or δ) from the standard.
Key concepts of CSIA data
interpretation include:
x parent compound fractionation is
unequivocal proof of degradation
x daughter product fractionation
alone does not prove daughter
product degradation
x the non-degrading daughter
product can get no heavier than
the initial signature of the parent
x daughter product isotopic
signature greater than the initial
signature of the parent
compound indicates daughter
product degradation
Molecular Biological Tools
MBTs quantify microbial populations and their activity by assessing unique nucleic acid based
or lipid based biomarkers. Many analytical techniques that quantify these biomarkers are
available with quantitative polymerase chain reaction (qPCR) and phospholipid fatty acid (PLFA)
being the most commonly used for environmental applications. MBTs can be used to answer
site specific questions to assess naturally occurring conditions directly or experimentally by
manipulating local conditions with proposed remediation amendments before their use.
MBT samples can be collected discretely
from extracted and filtered groundwater or
a time-integrated sample can be collected
using a growth matrix such as a bio-trap®
sampler (manufactured by Microseeps of
Rockford, Tennessee). Both sampling
methods are capable of collecting microbes
for MBT evaluation of existing conditions.
Bio-trap samplers have the added utility of
being amendable to test proposed remedial
strategies and answer site-specific
questions. Electron acceptors (e.g., ORC),
electron donors (e.g., HRC), microbial
augments (e.g., SDC-9), contaminant
analogs (e.g., trichlorofluroethene), and
isotopically labeled contaminants can be
incorporated within the bio-trap® matrix. Comparing amended bio-trap® data to non-amended
(i.e., control) bio-trap® data provides information on the potential success of field-scale
application of remediation amendments.

4. Amending specifically manufactured contaminants that contain isotopically enriched carbon (i.e.,
13
C at a very high abundance) is referred to as stable isotope probing (SIP). SIP can provide
the most definitive evidence of attenuation available. The SIP technique involves tracking the
fate of the carbon that comprise the contaminant into biomass and/or dissolved inorganic
carbon. SIP is only applicable where the contaminant is used as a source of cellular synthesis
or for energy derivation.
Conclusions
Advanced diagnostic tools optimize in situ
remediation by definitively identifying
contaminant destruction and the
microbial-mediated mechanism of
destruction. The tools are versatile and
with proper experimental construction can
answer site questions. Overall,
incorporation of advanced diagnostics
within the remedial selection and remedy
performance process leads to better
decisions and increased success rates of
in situ technologies.
Additional Resources
A Guide for Assessing
Biodegradation and Source
Identification of Organic Ground
Water Contaminants using
Compound Specific Isotope
Analysis (CSIA) (December
2008).
Burns, M. and Myers, C. (2010),
Evolution of predictive tools for
in situ bioremediation and
natural attenuation evaluations.
Remediation Journal, 20: 5–16.
doi: 10.1002/rem.20259
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