vvEPA
United States
Environmental Protection
Agency
d Water Issue
Ground Water Sample Preservation at In-Situ Chemical Oxidation
Sites - Recommended Guidelines
Saebom Ko1, Scott G. Huling2'*, Bruce Pivetz3
Table of Contents
1. Introduction 1
1.1 Reasons to Sample and Analyze Binary Mixtures 2
1.2 Binary Mixtures of Oxidant and Organic
Contaminants in Ground Water Samples 2
1.3 Impact of Binary Mixtures -Previous Studies 2
2. Ground Water Sample Collection, Oxidant
Measurement, and Oxidant Neutralization/Sample
Preservation 4
2.1 Permanganate (MnO4) 5
2.1.1 Analysis by Visual Observation 5
2.1.2 Spectrophotometric Analysis 5
2.1.3 Results 6
2.1.4 Oxidant Neutralization and Sample
Preservation 6
2.2 Persulfate (S2O82 ) 7
2.2.1 Analysis by Field Test Kit Colorimetry 7
2.2.2 Analysis by Spectrophotometric Analysis
(Ferrous Ammonium Sulfate Method) 7
2.2.3 Results 7
2.2.4 Oxidant Neutralization and Sample
Preservation 8
3. Additional Information 9
4. References 9
5. Acknowledgements 10
Appendix - Recommended Operating Procedures -
Preservation of Ground Water Samples at ISCO
Sites Using Ascorbic Acid 11
Figures
Figure 1. Conceptual model of hydrogeologic, and oxidant
and contaminant fate and transport conditions
that contribute to binary mixture ground water
samples. 3
Figure 2. MnO4 Calibration Curve. 6
Figure 3. Calibration curve for S2O82 (Ferrous Ammonium
Sulfate Method). 8
Tables
Table 1. Permanganate concentration, Spectrophotometric
absorbance, ascorbic acid. 5
Table 2. Persulfate concentration, Spectrophotometric
absorbance, ascorbic acid. 8
Table A1. Corresponding concentration of sodium
permanganate and potassium permanganate to
permanganate. 13
Table A2. Corresponding concentration of sodium
persulfate to persulfate (S2O82). 14
1 National Research Council, Robert S. Kerr Environmental
Research Center, P.O. Box 1198, Ada, OK, 74820; Phone:
(580) 436-8742; ko.saebomepa.aov
2" (Corresponding Author) U.S. Environmental Protection
Agency, National Risk Management Research Laboratory,
Robert S. Kerr Environmental Research Center, P.O. Box
1198, Ada OK, 74820; Phone: (580) 436-8610; huling.scotm
epa.gov
3 Shaw Environmental & Infrastructure, Inc., Robert S. Kerr
Environmental Research Center, P.O. Box 1198, Ada, OK,
74820; Phone: (580) 436-8998; E-mail: pivetz.bruce@epa.gov
1. INTRODUCTION
In-situ chemical oxidation (ISCO) involves the introduction of a
chemical oxidant into the subsurface for the purpose of transforming
ground water and/or soil contaminants into less harmful chemical by-
products (Huling and Pivetz, 2006; Rivas, 2006; Ferrarese etal., 2008;
Kao etal., 2008). Often, ground water samples collected specifically to
analyze organic contaminants may contain the oxidant and the organic
contaminants in a "binary mixture" (Huling etal., 201 la; Johnson et
al., 2012). When organic contaminants and oxidants are commingled
in the ground water sample, there is significant potential for oxidative
transformation of contaminants to occur after the sample is collected
and the results of the sample analysis to become non-representative of
in-situ conditions at the time of sampling. Consequently, the quality
of the ground water sample may be compromised and a false negative
result may occur.
An integral component of ISCO is the collection and analysis of
ground water samples to assess ISCO treatment performance. A
technical issue faced by Remedial Project Managers is the collection
and analysis of representative, high quality ground water samples that
can be used to support a site assessment and remedial performance
monitoring at sites where ISCO is being deployed. The purpose of this
Issue Paper is to provide background information and general guidelines
involving methods and procedures that can be used to detect whether
an oxidant (i.e., permanganate or persulfate) is present in ground water,
to approximate the oxidant concentration, and to estimate and deliver
the volume or mass of preservative, specifically ascorbic acid, required
to preserve the binary mixture ground water sample. The focus of this
Issue Paper is on permanganate and persulfate, two oxidants that can
persist for long periods of time in the subsurface and therefore represent
the greatest potential for binary mixture ground water samples. An
Appendix to this Issue Paper (Recommended Operating Procedures -
Preservation of Ground Water Samples at ISCO Sites Using Ascorbic
Acid) provides specific details regarding the preservation procedures for
use by EPA Regional personnel, contractors, and other environmental
professionals engaged in ground water sample collection and analysis.
The guidelines are also applicable to bench-scale studies where oxi-
dants are used to investigate the feasibility of ISCO treatment. For
-------
example, aqueous samples collected from bench-scale
soil reactors are analyzed for organic contaminants, but
may also contain the oxidant amended to the reactor to
destroy the contaminant. Consequently, the guidelines
described below also extend to bench-scale studies where
the potential for binary mixture aqueous samples may
occur, and are analyzed for organic contaminants.
7.7. Reasons to Sample and Analyze Binary
Mixtures
It is often desirable for oxidants in ground water to fully
react prior to collecting and analyzing ground water
samples for organic contaminants. However, there are
circumstances where the collection and analysis of binary
mixture ground water samples may not be avoided.
These reasons vary widely and some examples include
the need to:
(1) conduct an immediate preliminary assessment of
ISCO to validate in-progress treatment performance,
(2) establish design parameters from interim ISCO
pilot-scale studies needed to design full-scale ISCO
deployment,
(3) assess the potential redistribution of the ground water
contaminant plume as affected by ISCO activities,
and
(4) evaluate reaction kinetics during oxidative treatment.
Rapid turnaround of field data and information may be
needed to meet specified milestones and deadlines for
full-scale remedy selection, design, construction, and
implementation. In addition, regulatory-driven goals
and associated timelines may require rapid completion
of pilot-scale testing and full-scale deployment of ISCO.
Therefore, a significant emphasis may be placed on the
collection of ground water samples at ISCO sites prior to
complete reaction of the oxidant (Huling et al, 201 la).
7.2. Binary Mixtures of Oxidant and Organic
Contaminants in Ground Water Samples
Heterogeneous distribution of oxidant and contami-
nants, and hydraulic conductivity variations in hetero-
geneous aquifers are two main causes of binary mixtures
(Figure 1) (Huling etctl, 201 la). For example, oxidants
and contaminants can enter a monitoring well screen
from different lithologic zones. These solutes may be
captured as separate solutes from different lithologic
zones, or as separate or commingled solutes from the
same lithologic zone. Insufficient contact time (i.e., reac-
tion time) between the oxidant and contaminants prior
to, or after, entering the well leads to binary mixtures in
the ground water sample.
Commingling of organic contaminants and oxidants
in the ground water sample impacts the quality of the
ground water sample, but may also impact the analyti-
cal instruments used to measure the concentration of
analyte(s) in the ground water sample (Johnson et al.,
2012). Although rarely reported and documented,
the impact of oxidants on analytical instruments is
exclusively reported for permanganate and predomi-
nantly involves instrument malfunction resulting from
MnO2(s)-clogged lines and ports. No information was
found that documented the impact of hydrogen peroxide
or persulfate on analytical instruments despite numerous
studies where binary mixtures were analyzed.
7.3. Impact of Binary Mixtures - Previous
Studies
A detailed study involving the impact of residual
persulfate on the quality of ground water samples was
performed (Huling et al., 201 la). A significant decline
(49 to 100 percent (%)) in volatile organic compound
(VOC) concentrations was measured in unpreserved
binary mixture samples using gas chromatography
(GC) purge and trap, and GC mass spectroscopy (MS)
headspace analytical methods. In that study, preservation
of the binary mixture samples was achieved through the
addition of ascorbic acid and resulted in 99 to 100%
VOC average recovery relative to oxidant-free control
samples. Adding high concentrations of ascorbic acid (42
to 420 millimolar (mM)) to the samples did not interfere
in the measurement of the VOCs and did not negatively
impact the analytical instruments. These results indicated
that if persulfate is present in the sample, and the binary
sample is not appropriately preserved, the quality of
the sample will be compromised. A companion study
involving the impact of permanganate on the quality of
ground water samples and analytical instruments, and
the use of ascorbic acid yielded similar results (Johnson
et al., 2012). The results of these studies (Huling et al.,
2011 a; Johnson et al., 2012) serve as the basis for the
guidelines provided in this Issue Paper.
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Ground Water Sample Preservation at ISCO Sites
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Oxidant Injection Well,
Well Point, or Other Oxidant
Injection Method
Monitoring
Well
HYDRAULIC
CONDUCTIVITY
LOW
VERY
LOW
HIGH
MEDIUM
LOW
VERY
HIGH
VERY
LOW
SANDY CLAY
CLAY
SAND
SANDY CLAY
SAND/GRAVEL
CLAY
Figure 1. Conceptual model of hydrogeologic, and oxidant and contaminant fate and transport conditions that contribute
to binary mixture ground water samples. The oxidant illustrated in purple, conceptually represents any oxidant
(permanganate, persulfate) used for in-situ chemical oxidation (Ruling etal., 201 la).
The analytical methods used in these studies are com-
monly used in commercial analytical laboratories. The
analytes, including benzene, toluene, xylene (BTX),
perchloroethylene (PCE), and trichloroethylene (TCE),
are representative of contaminants commonly found at
hazardous waste sites. Similarly, empirical results were
obtained in the analysis of binary mixtures comprised
of persulfate and pentachlorophenol (PCP) by high
performance liquid chromatography (HPLC) where
significant loss of PCP was measured in unpreserved
samples relative to persulfate-free control samples and
ascorbic acid-preserved samples (data not included).
Currently, we do not have a firm explanation for a viable
mechanism responsible for persulfate activation and PCP
oxidation in these samples.
Overall, results are applicable to a broad set of analytical
methods, analytes, and site conditions. It is unclear to
what extent these results extend to analytical methods
and contaminants that were not tested in these studies,
however. Additional specific studies are needed in cases
where different analytical methods and ground water
contaminants are involved.
Specifically, analysis involved the measurement of
(1) BTX, PCE, and TCE using the GC/MS headspace
method, and (2) BTX using the GC purge and trap
method (Huling et al, 201 la). The GC/MS headspace
method is involved in EPA Method Nos. 8260C and
5021 A. The automated headspace GC/MS method is
used to confirm the identity and quantity of purgeable
VOCs in water samples in 40 mL volatile organic
analysis (VOA) vials. This method is used to quantify
over sixty VOCs in drinking water, including aromat-
ics, haloalkenes, haloalkanes, haloaromatics, and fuel
oxygenates. This automated method involves the transfer
of an aqueous sub-sample (10 mL) to a sealed headspace
vial which is heated from room temperature to 80
degrees Celsius (°C) in 30 minutes. A sample of the
headspace gas is then transferred to the capillary column
in the GC. After separation on the GC column and
introduction into the MS, the VOCs are identified and
Ground Water Sample Preservation at /SCO Sites
-------
quantified using the MS. We propose that contaminant
loss occurs during the heating step of the sub-sample
where residual persulfate is thermally activated resulting
in VOC oxidation.
The automated purge and trap GC (Agilent, Model 6890,
Wilmington, DE) method was used to quantify BTX
in water samples (40 mL VOA vials). This method is
most similar to EPA Methods 602 and 8020, but shares
similarities with several other EPA methods that involve
purge and trap, including: EPA 501, 502.2, 503.1, 524.2,
601, 602, 624, 8010, 8020, 8021, 8240, and 8260. In
this method, a sub-sample (10 mL) is transferred to a
sparge chamber and purged with helium (6 minutes). The
VOCs are transferred to a K VOCARB 3000 Encon trap
and dry purged with helium to remove water vapor. The
VOCs are thermally desorbed and transferred to the GC
column for separation and measurement. Sample transfer
is through a heated 1.9 mmxl.O m Silcosteel (Restek,
Bellefonte, PA) transfer line coupled directly to the
analytical column. Following separation on the column,
the presence of VOCs is determined and quantified with
photoionization and flame ionization detectors. It was
proposed that the contaminant loss was due to the helium
sparging step where aerosols are formed containing
persulfate and are transfered to the VOC granular acti-
vated carbon trap (Huling etal., 201 la). Subsequently,
during the VOC thermal desorption step where the trap
is heated from room temperature to 260 °C (25 min),
the persulfate residing in the trap is thermally activated
resulting in the oxidation of the VOCs immobilized and
concentrated on the trap. Similarly, highly efficient oxida-
tion of organics immobilized in solid media (i.e., granular
activated carbon) by thermally activated persulfate has
been demonstrated (Huling etal., 201 Ib).
The impact of residual permanganate was evaluated
in water samples prepared in the lab using a multi-
component standard, and in ground water samples
collected at ISCO sites (Johnson et al., 2012). Binary
mixture aqueous samples were prepared that contained
a 52-component standard of organic compounds and
permanganate. Ascorbic acid was added to the binary
mixture which reacted rapidly with the MnO4 , pre-
served the sample, and limited the reaction between
MnO4 and the organic compounds. Consequently, the
concentrations of the majority of the compounds in
the multi-component standard were within the control
limits established for quality assurance. However, despite
timely efforts to preserve the laboratory-prepared binary
mixture samples, the quality of the sample was impacted;
concentrations were generally lower than oxidant-free
controls, and the concentration of several compounds
(r»-l,3-dichloropropene, styrene, ?rara-l,2-dichloro-
ethene, ?rara-l,3-dichloropropene, vinyl chloride) fell
below the applicable lower control limit.
Concentrations of VOCs measured in field-preserved
binary mixture ground water samples were greater than
in replicate samples refrigerated in the field and preserved
with ascorbic acid upon arrival at the lab (Johnson etal.,
2012). These results indicate that the VOCs reacted
in transit despite refrigeration. Excess ascorbic acid
did not negatively impact the quality of the simulated
ground water samples containing a 52-component stock
standard, or actual ground water samples collected from
two field sites, and did not negatively impact the GC/MS
instruments used in the analysis.
2. GROUND WATER SAMPLE COLLECTION,
OXIDANT MEASUREMENT, AND OXIDANT
NEUTRALIZATION/SAMPLE PRESERVATION
Specific details regarding the procedures used in amend-
ing ground water samples with ascorbic acid are provided
in the Appendix entitled, "Recommended Operating
Procedures - Preservation of Ground Water Samples at
ISCO Sites Using Ascorbic Acid".
It is recommended that a representative ground water
sample be collected at the well head in a test vial for the
specific purpose of measuring the oxidant concentration.
Ground water sample collection for this purpose should
follow the normal ground water sampling protocol
established at the site. This initial screening ground water
sample is not collected for the purpose of measuring
organic contaminant concentrations. If contaminant
analysis of the ground water sample is desired, additional
samples must be subsequently collected and preserved,
if necessary. Normal sampling procedures appropriate
for site conditions and regulatory acceptance are recom-
mended. Sample preservation and handling requirements
are based on the type of analyses being performed and
should be specified in project-specific documents such
as the quality assurance project plan, field sampling
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Ground Water Sample Preservation at ISCO Sites
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plan, or in general EPA documents such as the Resource
Conservation and Recovery Act (RCRA) guidance docu-
ment (U.S. EPA, 1992) or EPA SW-846 (U.S. EPA,
1982). Additional direction on ground water sampling
techniques can be found in Yeskis and Zavala (2002).
2.1. Permanganate (MnO4)
Data and information presented below are reported in
terms of the permanganate anion (MnO4; 118.9 grams
per mole (g/mol)). Permanganate is purchased either
as sodium permanganate (NaMnO4; 141.9 g/mol) or
potassium permanganate (KMnO4; 158.0 g/mol) and as
a result conversion to the permanganate anion concentra-
tion is needed to determine sample preservation needs as
per the Issue Paper. Specifically, the ratios 118.9/141.9
(g-mole/g-mole) and 118.9/158.0 (g-mole/g-mole) are
used to convert NaMnO4 and KMnO4, respectively to
MnO4.
2.1.1. Analysis by Visual Observation
The characteristic pink or purple color of MnO4 in a
40 mL VOA vial can be used as a general guideline to
estimate the concentration by using the MnO4 colori-
metric scale (Table 1). This method should be used with
caution because ground water turbidity and colloidal
manganese dioxide solids (MnO2(s)) can affect sample
color and result in deviations from the tabulated color
scale. Field filtration can help minimize these interfer-
ences, but may not fully remove all color if sub-micron
colloidal and/or dissolved constituents are present.
2.1.2. Spectrophotometric Analysis
The permanganate concentration can be determined
using commercially available field test kits (SenSafe M,
2011; CHEMetrics, 2011). Additionally, an accurate
measurement of the permanganate concentrations can be
determined using a field spectrophotometer (maximum
absorbance wavelength (A,) = 525 nanometers (nm)
(A525)) and a calibration curve involving a linear correla-
tion between MnO4 concentration and A525 (Figure 2,
Table 1). Filtered samples (0.2-0.45 micron) may be
required to eliminate background colloidal or suspended
solid materials that can absorb light at 525 nm and inter-
fere with permanganate measurement. Volatilization of
Table 1. Permanganate concentration, Spectrophotometric absorbance at 525 nm, and required amount of ascorbic acid
required to neutralize the oxidant in a 40 mL vial. The color scale represents actual photos of MnO4" vials and is
included for conceptual guidance. Actual colors vary based on background lighting, and color printers. Additionally,
photographs of low concentrations (i.e., clear solutions) do not accurately capture transparency.
[MnO4~] (mg/L) (millimolar in parentheses)
0
(0)
0.75
(0.01)
3.8
(0.03)
7.5
(0.06)
11.3
(0.09)
18.8
(0.16)
30.1
(0.25)
37.6
(0.32)
56.4
(0.47)
75.3
(0.63)
113
(0.95)
151
(1.27)
188
(1.58)
376
(3.16)
Absorbance(1), wavelength (X) = 525 nm
0
0.011
0.059
0.134
0.197
0.329
0.516
0.627
NL
NL
NL
NL
NL
NL
Ascorbic Acid Stock Solution (M)(2)
-
0.015
0.015
0.15
0.15
0.15
0.15
0.15
1.5
1.5
1.5
1.5
1.5
1.5
Volume of Ascorbic Acid solution (\iL)
0
30
150
30
46
76
121
152
23
30
46
61
76
152
Mass of Ascorbic Acid (mg)
0
0.08
0.4
0.79
1.21
2.1
3.32
4.17
6.1
7.9
12.2
16.1
20.1
40.2
(1) [MnO4~] (mg/L) = 58.8 x A525', A525 is the absorbance at 525 nm; non-linear above 38 mg/L MnO4".
(2) To minimize sample dilution, the ascorbic acid stock solution used was 0.015, 0.15, and 1.5 M.
Ground Water Sample Preservation at /SCO Sites
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contaminants is not a concern since the initial screening
ground water sample is used specifically to determine the
concentration of permanganate.
0.7 -i
20 30
[Mn04-] (mg/L)
Figure 2. Calibration curve of MnO4~ concentration versus
absorbance at wavelength (A,) of 525 nm.
2.7.3. Results
If MnO4 is not detected in the ground water sample,
it is recommended that normal ground water sampling
and analysis procedures be used. If MnO4 is detected,
there are two general options to consider. The first
option is to delay the collection and analysis of the
ground water sample for a sufficient time allowing the
MnO4 concentration to fully diminish in the subsurface,
if desired. In some cases, MnO4 persistence is lengthy
and this option is not possible (as discussed above in
Section 1.1). Due to the site-specific time-dependency
of contaminant mass transfer and transport, the time
required to approach chemical equilibrium in ground
water will likely require additional time after the oxidant
is fully consumed. Subsequently, ground water sampling
would follow routine guidelines and requirements. The
second option is to collect and preserve the ground water
sample (i.e., neutralize the oxidant) prior to analysis to
minimize the impact of the commingled oxidant. The
second option may be desirable for a number of reasons
described in Section 1.1.
2.1.4. Oxidant Neutralization and Sample
Preservation
Given the MnO4 concentration, the volume of ascorbic
acid stock solution (0.015,0.15, or 1.5 mol/L), orweight
of crystalline ascorbic acid (176.12 g/mol) required
to preserve the binary mixture is determined (Table
1). Sample preservation involves the addition of the
appropriate amount of ascorbic acid to preserve a binary
mixture in a 40 mL VOA vial. In a lab study (Johnson et
ctl, 2012), the mass of ascorbic acid required to neutralize
MnO4 ranging in concentration from 1-750 milligrams
per liter (mg/L) was determined empirically. The aver-
age molar ratio (n=l4) was 1.64 mol ascorbic acid/mol
MnO4 and values ranged from 1.45 to 1.75 mol/mol.
Therefore, the weight of ascorbic acid that corresponded
with the MnO4 colorimetric scale was conservatively
based on a stoichiometric ratio of 1.8 mol ascorbic
acid/mol MnO4, since, as noted below, no negative
side-effects were noted with over-dosing. Detailed
recommended operating procedures are provided in the
Appendix to estimate the volume of crystalline ascorbic
acid or ascorbic acid stock solution required to neutralize
the MnO4. Once the oxidant is neutralized, it is recom-
mended that normal ground water sample handling and
procedures be followed.
The recommended volume and mass of ascorbic acid
included in Table 1 is a guideline. The addition of
ascorbic acid will rapidly reduce the MnO4 concentra-
tion and eliminate the pink/purple color. The formation
of colloidal or particulate MnO2(s) (i.e., Mn+ ) may
occur causing a brown tinge appearance of the solution.
Incremental amendment of ascorbic acid is required
to further reduce the Mn+ to Mn+2, and eliminate the
brownish tinge color. Mn+2 is highly soluble and the most
desirable form of Mn to minimize the impact of col-
loidal or particulate matter on the laboratory analytical
instruments. Overall, Table 1 is used as a guideline but
the actual amount of ascorbic acid to be added should
be based on the amount required to fully eliminate the
MnO4 and MnO2(s), and to achieve a clear solution.
Excess ascorbic acid did not have a negative impact on
the quality of the ground water sample involving GC and
GC/MS analysis of a broad range of organic chemicals
(Johnson et al., 2012). The volume of ascorbic acid
solution added to the sample vial should be recorded so
Ground Water Issue
Ground Water Sample Preservation at /SCO Sites
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appropriate dilution calculations can be performed to
obtain an accurate estimate of the contaminant concen-
trations. Pre-amending sample vials with ascorbic acid is
also an option and is discussed further in Section 7.F of
the Appendix. Other sample preservation requirements
are based on the analyses being performed and are speci-
fied in the quality assurance project plan, field sampling
plan, RCRA guidance document (U.S. EPA, 1992) or
EPA SW-846 (U.S. EPA, 1982). Additional direction
on ground water sampling techniques can be found in
Yeskis and Zavala (2002)
2.2. Persulfate (SzOf)
The data and information below are presented in terms
of the persulfate anion (S2O82~; 192.0 g/mol). However,
persulfate is predominantly purchased as sodium per-
sulfate (Na2S2O8; 238.1 g/mol). As a result, conversion
of sodium persulfate to persulfate anion concentrations
is necessary to determine sample preservation needs as
per the Issue Paper. Specifically, the ratio of 192.0/238.1
(g-mol/g-mol) is used to convert Na2S2O8 to S2O82".
Persulfate is colorless and requires field measurement at
the well head to determine its presence and concentration
in the ground water sample.
2.2.1. Analysis by Field Test Kit Colorimetry
Field test kits are commercially available to measure per-
sulfate concentration in aqueous samples (CHEMetrics,
2011; FMC, 2012). CHEMetrics persulfate test kits
are available for two sodium persulfate concentration
ranges (0-7,7-70 mg/L). Given the high concentrations
of persulfate injected into the subsurface at ISCO sites,
significant dilution may be required in the use of these
test kits. FMC commercial test kits are dependent on
whether the persulfate activator is base or thermal (test kit
"K"), or whether persulfate is activated by iron chelates
or H2O2 (test kit "C") (FMC, 2012). The lower detection
limit of persulfate using the current FMC test kits is
500 mg/L, a sufficient quantity of oxidant to significantly
impact the concentrations of VOCs and the quality of
the sample. Based on the current detection limit using
the FMC test kit, it is recommended that the minimum
amount of ascorbic acid added to the sample vessel
should conservatively account for 500 mg/L persulfate.
2.2.2. Analysis by Spectrophotometric Analysis
(Ferrous Ammonium Sulfate (FAS) Method)
A Spectrophotometric method can be used to analyze the
persulfate concentration in aqueous samples. The ground
water sample should be filtered (0.2-0.45 micron) to
eliminate background material (i.e., turbidity) that may
interfere with S2O8" analysis. A small volume of de-ion-
ized (DI) water (0.9 mL) and sulfuric acid (H2SO4) (10
mL, 2.5 normal (N)) (or, add 10.9 mL of 2.3 N H2SO4)
is placed in a 20 mL glass or plastic test vessel. These can
be prepared prior to transport to the field. A blank is
prepared by mixing 1 mL DI water with H2SO4 (10 mL,
2.5 N). The filtered sample (0.1 mL) is placed in the test
vessel, followed by the addition of ferrous ammonium
sulfate (FAS) (Fe(SO4)2(NH4)2.6H2O) (0.1 mL, 0.4
N) (prepared immediately before use). Adding a couple
drops of H2SO4 (cone.) to the FAS reagent increases the
stability of the ferrous iron for several more hours (5 to
10 hours). The mixture is swirled/mixed and allowed to
react for 30 to 40 minutes. Subsequently, the mixture is
amended with ammonium thiocyanate (NH4SCN) (0.2
mL, 0.6 N) and the absorbance of the solution is analyzed
immediately with a spectrophotometer at a wavelength
of A, = 450 nm (A450) (Huang etal., 2002; Huling etctl,
201 la; b). The general colorimetric scale provided below
can be used to estimate the persulfate concentration in
a ground water sample (Table 2) analyzed by the FAS
method. Alternatively, a calibration curve involving a
linear correlation between S2O8" concentration and A450
can be used to determine a more precise estimate of the
persulfate concentration (Figure 3).
2.2.3. Results
If S2O8" is not detected in the ground water sample, it
is recommended to proceed using normal ground water
sampling and analysis procedures. If S2O82" is detected,
there are two general options to consider. The first is to
delay collection and analysis of the ground water sample
for sufficient time which allows the persulfate concentra-
tion to fully diminish in the subsurface, if desired. Due
to the site-specific time-dependency of contaminant mass
transfer and transport, the time required to approach
chemical equilibrium in ground water will likely require
additional time after the oxidant is fully consumed.
Subsequently, ground water sampling would follow
routine guidelines. The second option is to collect and
Ground Water Sample Preservation at ISCO Sites
Ground Water Issue
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Table 2. Persulfate concentrations resulting from the ferrous ammonium sulfate analytical method involving the
spectrophotometric measurement (A, = 450 nm) of the solution, and the required amount of ascorbic acid required
to neutralize the oxidant in a 40 mL vial. The color scale represents actual photos of S2O82" vials and is included for
conceptual guidance. Actual colors vary based on background lighting, and color printers. Additionally, photographs
of low concentrations (i.e., clear solutions) do not accurately capture transparency.
[S2O8 ] (mg/L) (millimolar in parentheses)
80
(0.42
200
(1.1)
400
(2.1)
610
(3.2)
810
(4.2)
1210
(6.3)
1610
(8.4)
2020
(10.5)
2420
(12.6)
2820
(14.7)
3230
(16.8)
3630
(18.9)
4030
(21.0)
Absorbance(1), wavelength (1) = 450 nm
0.011 0.019 0.04 0.062 0.076 0.121 0.164 0.204
0.245
0.275 0.313
0.349 0.397
Volume of Ascorbic Acid solution (mL)
0.04 0.11 0.22 0.34 0.45 0.67 0.89 1.12 1.34 1.57 1.79 2.02 2.24
Mass of Ascorbic Acid (176.12 g/mol) (g)
0
0.01 I 0.03 | 0.06 | 0.09 | 0.12 | 0.18 | 0.24 0.3 | 0.35 | 0.41 | 0.47 | 0.53 | 0.59
(1) Solubility of ascorbic acid in water = 330 g/L (1.87 mol/L); 80% solubility (1.5 mol/L) used as stock
solution; [S2O82~] (mg/L) = 10,000 x A45o; where A450 is the absorbance at 450 nm.
preserve the ground water sample prior to analysis to
minimize the impact of persulfate on the ground water
sample. The second option may be desirable for a number
of reasons described in Section 1.1.
0.45
0.4 -
0.35
0.3 -
0.25
0.2 -
0.15
0.1 -
0.05
0
Y = 1.0e-4x; R2 = 0.999
[S20821 (mg/L) = 10,000 xA450
0 1000 2000 3000 4000 5000
[S2082 ] (mg/L)
Figure 3. Calibration curve for S2O8" concentration versus
absorbance at wavelength 450 nm using the ferrous
ammonium sulfate method.
2.2.4. Oxidant Neutralization and Sample
Preservation
Guidelines for the volume of ascorbic acid stock solution
(1.5 mol/L) or the weight of crystalline ascorbic acid
(176.1 g/mol) required to preserve the binary mixture in
a 40 mL sample vial are provided (Table 2). The mass of
ascorbic acid that corresponds with the persulfate colo-
rimetric scale is based on a stoichiometric ratio of 4 mol
ascorbic acid/mol persulfate and was determined empiri-
cally in a laboratory study (Hiding etal., 2011a). Detailed
recommended operating procedures are provided in the
Appendix to estimate the volume of crystalline ascorbic
acid or ascorbic acid stock solution required to neutralize
the S2O82". This stoichiometric ratio is in excess of the
ideal stoichiometry for mineralization of persulfate by
ascorbic acid. Excess ascorbic acid (4 - 40 mol ascorbic
acid/mol persulfate) did not have a negative impact on
the quality of the ground water sample involving GC
and GC/MS analysis of BTX, TCE, and PCE (Huling
et al., 201 la). The basis for this quantity of ascorbic
acid is to achieve favorable reaction kinetics between
•SO4 and ascorbic acid, relative to the reaction between
the sulfate radical (-SO4~) and the VOCs. Following
oxidant neutralization, it is recommended that other
approved sample preservation and handling methods
,
Ground Water Sample Preservation at /SCO Sites
-------
in ground water sample handling be performed. For
example, acidification of the sample is normally carried
out to minimize biochemical and reduction reactions.
Other sample preservation requirements are based on the
analyses being performed and are specified in the qual-
ity assurance project plan, field sampling plan, RCRA
guidance document (U.S. EPA, 1992) or EPA SW-846
(U.S. EPA, 1982). Additional direction on ground water
sampling techniques can be found in Yeskis and Zavala
(2002).
3. ADDITIONAL INFORMATION
It is recommended that the analytical laboratory be noti-
fied that the aqueous samples contain residual persulfate
or permanganate and were preserved with ascorbic acid.
The volume of ascorbic acid solution added to the sample
should be recorded so the appropriate calculations can
be used to correct for dilutions. If MnO2(s) has settled
on the bottom of the VOA vial, it is important that the
sample not be disturbed prior to analysis. This precau-
tion in sample handling prevents the suspension of
the MnO2(s) particles and the potential for accidental
injection into the analytical instruments.
Other preservatives have been used to successfully
neutralize these oxidants, but may negatively impact
the quality of the sample (Huling etal., 201 la). Despite
efforts used to neutralize the oxidant and to preserve
the quality of the ground water sample, the presence of
oxidant in ground water samples introduces uncertainty
in the precise measurement of contaminant concentra-
tions in the subsurface. This is attributed to the potential
impact of the oxidant on contaminant concentrations
in the ground water sample prior to neutralization, the
transient nature of contaminant fate and transport in the
subsurface where ISCO activities were deployed, and the
site-specific oxidant injection and hydrogeologic condi-
tions contributing to binary mixtures. Consequently,
additional ground water sample collection and analysis
will likely be required to achieve an accurate evaluation
of post-ISCO performance, and regulatory adherence
with US EPA ground water compliance monitoring
requirements.
Numerous examples exist where elevated permanganate
and VOC concentrations have been measured in ground
water samples collected over extended periods of time at
hazardous waste sites. It can be concluded from a simple
kinetic analysis that long term VOC persistence can
primarily be explained by spatial separation between the
ground water containing the oxidant and contaminant
(Figure 1) (Johnson etal., 2012). Ground water samples
derived from wells screened over spatially separate vertical
intervals indicate an in-well mixture of ground water
containing either oxidants or contaminants. Limited
contact between the oxidant and contaminant within the
same lithologic unit can be due to specific mass transfer
or mass transport conditions including the dissolution
of non-aqueous phase liquids (NAPLs) or slow diffusion
of contaminants from low permeability materials. These
fate and transport conditions indicate the oxidant has not
been uniformly delivered to the contaminated zone(s).
A critical analysis of screened intervals, injection inter-
vals, contaminated intervals, oxidant and contaminant
transport characteristics, and ground water sample results
from analyzing preserved binary mixtures, could provide
valuable insight for the development of a more accurate
site conceptual model that could be used to design and
deploy a more effective oxidant delivery system.
4. REFERENCES
CHEMetrics. 2011. http://www. chemetrics. com/Persulfate.
Ferrarese, E., Andreottola, G., and Oprea, LA. 2008.
Remediation of PAH-contaminated sediments by
chemical oxidation./. Haz. Mat. 152(1), 128-139.
FMC Environmental Solutions. 2012. Field Measurement
http://environmental.fmc.com/solutions/soil-g'round-
remediation/field-measurement.
Huang, K.C., Couttenye, R.A., and Hoag, G.E. 2002.
Kinetics of heat-assisted persulfate oxidation of methyl
tert-butylether (MTBE). Chemosphere 49(4),413-420.
Huling, S.G., and Pivetz, B. 2006. In-Situ Chemical
Oxidation - Engineering Issue. US Environmental
Protection Agency, National Risk Management
Research Laboratory, R.S. Kerr Environmental
Research Center, Ada, OK. EPA/600/R-06/072. http://
www. epa.pov/nrmrl/nuerd/publicatiom. html#oxidation.
Huling, S.G., Ko, S., and Pivetz, B. 201 la. Ground
water sampling at ISCO sites - Binary mixtures of
volatile organic compounds and persulfate. Ground
Water Monit. Remed. 31(2), Spring 72-79.
Huling, S.G., Ko, S., Park, S., and Kan, E. 201 Ib.
Persulfate-driven oxidation of contaminant-spent
granular activated carbon. /. Haz. Mat. 192(3),
1484-1490.
Ground Water Sample Preservation at ISCO Sites
Ground Water Issue
-------
Johnson, K.T., Wickham-St. Germain, M., Ko, S. and International) for graphics preparation and Ms. Martha
Hiding, S.G. 2012. Binary Mixtures of Permanganate Williams (SRA International) for desktop publishing.
and Chlorinated Volatile Organic Compounds in A rtable document format (PDF) version of this
Groundwater samples: oample Preservation and , . ., , , r , , ,. r
Analysis. GroundWaterMonit. Remed., 32(3), Summer document is available for viewing or downloading from
g4_92. http://www.epct.govlnrmrllgwerdlpubliccttiom.html (please
Kao, C.M., Huang, K.D., Wang, J.Y., Chen, T.Y., ffer l° "In Situ Chemical Oxidation; "Issue Paper"; or
and Chien, H.Y. 2008. Application of potassium "2012").
permanganate as an oxidant for in-situ oxidation
of tricmoroethylene-contaminated groundwater: A
laboratory and kinetics study. /. Haz. Mat. 153(3),
919-927.
Rivas, F.J. 2006. Polycyclic aromatic hydrocarbons sorbed
on soils: A short review of chemical oxidation based
treatments./. Haz. Mat. 138(2), 234-251.
SenSafe, 2011. http://www.sensafe. com/product.
php?recordID=481 138.
U.S. EPA. 1982. Test Methods for Evaluating Solid Waste,
Physical/Chemical Methods, EPA SW-846. Office of
Solid Waste and Emergency Response, Washington,
D.C. http://www.epa.mv/epawaste/hazard/testmethods/
sw846/online/index. htm.
U.S. EPA. 1992. RCRA Ground-Water Monitoring:
Draft Technical Guidance. Office of Solid Waste,
Washington, DC EPA/530/R-93/001, NTIS PB 93-
139350.
Yeskis, D., andZavala, B. 2002. Ground-Water Sampling
Guidelines for Superfund and RCRA Project Managers
- Ground Water Forum Issue Paper. Office of Solid
Waste and Emergency Response, Washington, D.C.
EPA 542-S-02-001 May 2002. http://www.epa.yov/
tio/tsp/download/?w sampling guide.pdf.
5. ACKNOWLEDGEMENTS
This Ground Water Issue Paper was prepared for the
U.S. Environmental Protection Agency, Office of
Research and Development, National Risk Management
Research Laboratory. The authors were Dr. Saebom Ko
(National Research Council), Dr. Scott G. Huling (U.S.
EPA) and Dr. Bruce E. Pivetz (Shaw Environmental &
Infrastructure Inc.). The authors acknowledge the U.S.
EPA Ground Water Forum members for their valuable
input and peer review comments. The authors also wish
to acknowledge the valuable input and peer review
comments provided by Dr. Phil Block (FMC Corp.),
Dr. Daniel Cassidy (Western Michigan University),
Dr. Wilson Clayton (TriHydro Corporation), Mr. Tom
Palaia (CH2M Hill), and Mr. Mike Wireman (U.S. EPA
Region 8). The authors thank Ms. KathyTynsky (SRA
10 Ground Water Issue
Ground Water Sample Preservation at /SCO Sites
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Appendix
Recommended Operating
Procedures -
Preservation of Ground Water
Samples at ISCO Sites Using
Ascorbic Acid
Table of Contents
1. Purpose (Scope and Application) 11
2. Method Summary 11
3. Reagents 11
4. Equipment/Apparatus 11
5. Health and Safety Precautions 11
6. Interferences 12
7. Procedures 12
A. Ascorbic Acid 12
B. Sample Filtration 12
C. Concentration Measurement 12
1) Commercially available test kits 12
a. Permanganate 12
b. Persulfate 12
2) UV-VIS absorbance 12
a. Permanganate 12
b. Persulfate 12
3) Colorimetric scales 12
D. Quality Assurance and Quality Control (QA/QC) 12
E. Calculations 12
1) Concentration conversion 12
a. Permanganate 12
b. Persulfate 13
2) Required volume and mass of ascorbic acid to
neutralize oxidants 13
a. Permanganate 13
b. Persulfate 14
F. Pre-amending Sample Vials With Preservative 14
8. References 15
9. Disclaimer 15
1. PURPOSE (SCOPE AND APPLICATION)
The commingling of organic contaminants and oxidants
in ground water or aqueous samples represents a condi-
tion in which there is significant potential for oxidative
transformation of the contaminants after the sample
is collected. Consequently, the quality of the ground
water or aqueous sample may be compromised and a
false negative result may occur. These recommended
operating procedures describe the steps used to preserve
ground water samples containing the oxidants per-
manganate (MnO4), or persulfate (S2O8~) and organic
contaminants of concern (COCs) prior to analysis. It is
applicable for ground water samples containing volatile
and non-volatile organic contaminants to be analyzed by
gas chromatography (GC), or gas chromatography-mass
spectroscopy (GC-MS), using either the purge and trap
or headspace sample introduction methods, and high
performance liquid chromatography (HPLC).
These procedures are also applicable to bench-scale stud-
ies where oxidants are used to investigate the feasibility of
ISCO treatment. For example, aqueous samples collected
from bench-scale soil reactors are analyzed for organic
contaminants, but may also contain the oxidant amended
to the reactor to destroy the contaminant. Consequently,
the guidelines and general procedures described below
also extend to bench-scale studies where the potential
for binary mixture aqueous samples may occur, and are
analyzed for organic contaminants.
2. METHOD SUMMARY
Based on the measured or estimated oxidant concentra-
tion in a ground water or aqueous sample, a specific
quantity of the preservative, ascorbic acid, is added to the
ground water or aqueous sample to either neutralize or
to limit the impact of the residual oxidant on the quality
of the sample. Tables 1 and 2 in the Issue Paperare used
as guidelines to estimate the amount of ascorbic acid to
add to a 40 mL VOA vial to preserve binary mixture
ground water and/or aqueous samples.
3. REAGENTS
Ascorbic Acid (C6H8O6; 176.1 g mol"1)
De-ionized (DI) water
Ferrous amonium sulfate (FAS) reagents - sulfuric
acid (H2SO4), ferrous ammonium sulfate
(Fe(SO4)2(NH4)2-6H2O), ammonium thiocyanate
(NH4SCN).
4. EQUIPMENT/APPARATUS
Pipette, volumetric flasks, spectrophotometer (or field
test kits)
SenSafe or CHEMetrics field test kits for permanganate
measurement (if used), or direct measurement.
CHEMetrics or FMC field test kits for persulfate measure-
ment (if used), or measurement using FAS method.
5. HEALTH AND SAFETY PRECAUTIONS
The Materials Safety Data Sheet for ascorbic acid indi-
cates potentially acute health effects: slightly hazardous
in case of skin contact (irritant), of eye contact (irritant),
of ingestion, of inhalation. In case of skin contact: wash
Ground Water Sample Preservation at ISCO Sites
Ground Water Issue
11
-------
with soap and water. Cover the irritated skin with an
emollient. Get medical attention if irritation develops.
Cold water may be used. Other guidelines are available
based on exposure (http://www.sciencelab.coml'msds.
php?msdsld=9922972). It is recommended to wear
gloves and safety glasses during all of the procedures
described herein due to the potential for exposure to
oxidants, impacted ground water sample, and other
chemicals involved in these procedures. Always consult
site-specific health and safety plans prior to sampling.
6. INTERFERENCES
Colloidal and/or suspended solids in ground water sam-
ples may adsorb light and interfere with the measurement
of oxidant concentration. For this reason, the ground
water sample may require filtration (0.2-0.45 |J.m) to
eliminate background material (i.e., turbidity).
7. PROCEDURES
A. Ascorbic Add
Prepare ascorbic acid stock solution either in the lab
prior to ground water sampling, or in the field. The
appropriate use of these stock solutions is dependent on
concentrations of the oxidant measured in the ground
water samples. The stock solution should be stored in
a refrigerator or cooler until used, and discarded after
150 days.
High Concentration Stock Solution: 1.5 M ascorbic acid
(e.g., add 264 g of ascorbic acid (MW= 176.1 g/mol) to
1L volumetric flask and fill with DI water). This stock
solution can be diluted in the preparation of 0.015 and
0.15 M ascorbic acid stock solutions.
Medium Concentration Stock Solution: 0.15 M ascorbic
acid: Dilute 1.5 M ascorbic acid stock solution 1:10
(e.g., dilute 100 mL of 1.5 M stock solution to 1L with
DI water).
Low Concentration Stock Solution: 0.015 M ascorbic
acid: Dilute 1.5 M ascorbic acid stock solution 1:100
(e.g., dilute 10 mL of 1.5 M stock solution to 1L with
DI water).
B. Sample Filtration
Filter the ground water or aqueous sample using
0.2-0.45 um filter (as needed in accordance with the
site QAPP or Sampling and Analysis Plan) to eliminate
background material (i.e., turbidity) that may interfere
with oxidant analysis.
C. Concentration Measurement
Determine the oxidant concentrations (permanganate or
persulfate) through one of three methods below.
1) Commercially available test kits
a. Permanganate: SenSafe™ or CHEMetrics
b. Persulfate: CHEMetrics or FMC
measurement):
2) UV-VIS absorbance
a. Permanganate (direct
wavelength = 525 nm
b. Persulfate (Ferrous Ammonium Sulfate method):
wavelength = 450 nm (Huang et al, 2002; Huling
etal.,20U)
3) Colorimetric scales presented in Tables 1 and 2.
Based on the oxidant concentration determined, ascorbic
acid stock solution is added to an empty sample vial
according to Tables 1 and 2.
D. Quality Assurance and Quality Control
(QA/QC)
Quality control includes regularly scheduled analysis of
method blanks and sample replicates, and the verification
of stock solutions of known concentration via the analysis
for concentrations of secondary solutions prepared from
the stocks. Results of the analyses of method blanks,
replicate analyses, and the verification of stock solution
concentrations are logged and maintained in record
books specific to the research being conducted. The
frequency, control limits, and corrective actions should
be appropriately developed for specific applications.
E. Calculations
1) Concentration conversion
a. Permanganate.
The concentrations of permanganate (MnO4~) have
been presented in terms of the permanganate anion
(118.9 g/mol) (Table 1). However, permanganate is
purchased either as sodium permanganate (NaMnO4;
141.9 g/mol) or potassium permanganate (KMnO4;
158.0 g/mol) and as a result conversion to permanga-
nate anion concentrations may be desired to determine
12
Ground Water Issue
Ground Water Sample Preservation at /SCO Sites
-------
adequate sample preservation needs. Specifically, the
ratios 118.9/141.9 (0.84) and 118.9/158.0 (0.75) are
used to convert NaMnO4 and KMnO4 respectively, to
MnO4 (Table Al).
Because 1 mmole of either sodium or potassium perman-
ganate produces 1 mmole of permanganate (Eqs 1 and
2), the molar concentrations of sodium and potassium
permanganate are the same as permanganate (Table 3).
NaMnO4 -» Na+ + MnO4
KMnO, -» K+ + MnO;
(1)
(2)
Converting sodium and potassium permanganate con-
centrations from mg/L to millimolar, and calculating
their permanganate equivalence,
X mg/L NaMnO4 =
(Xmg/L) x (1 mmol/141.9 mg) =
X/l4l.9mMNaMnO4 =
X/141.9 mM MnO4 X/141.9 mM MnO4 =
((X/141.9) mmol/L) x (118.9 mg/mmol) =
0.84X mg/L MnO4
NOTE: 1 mmol = 0.001 mol; mM= mmol/L
Y mg/L KMnO4 =
(Ymg/L) x (1 mmol/158.0 mg) =
Y/158.0mMKMnO4 =
Y/158.0 mM MnO4
Y/158.0mMMnO4 =
((Y/158.0) mmol/L) x (118.9 mg/mmol) =
0.75Y mg/L MnO4
NOTE: 1 mmol = 0.001 mol; mM= mmol/L
b. Persulfate.
The concentration of persulfate is presented in terms of
the persulfate anion (S2O82~; 192.0 g/mol) (Table A2).
However, persulfate is purchased as sodium persulfate
(Na2S2O8; 238.1 g/mol) and as a result a conversion
may be desired to correct for the anionic form of the
oxidant and to determine adequate sample preservation
needs. Specifically, the ratio of 192.0/238.1 (0.81) is
used to convert Na2S2O8 to S2O8 " . Persulfate is color-
less and requires field measurement at the well head to
determine its presence and concentration in the ground
water sample.
Converting sodium persulfate concentrations from mg/L
to millimolar, and calculating the persulfate equivalence,
Na2S2O8 -> 2Na+ +S2O82~
Z mg/L Na2S2O8 =
(Z mg/L) x (1 mmole/238.1 mg) =
Z/238.1 mMNa2S2O8 =
Z/238.1 mMS2O82-
(3)
Z/238.1
(Z/238.1) mmole/L) x (192 mg/mmole) =
0.8 1Z mg/L S2O82~
2) Required volume and mass of ascorbic acid to neutral-
ize oxidants.
a. Permanganate.
1.8 mole ascorbic acid per mole of permanganate was
empirically determined to effectively neutralize perman-
ganate in an aqueous sample containing VOCs (Johnson
etal., 2012). Therefore, the mass balance equation (Eq 4)
can be set up as follows,
V-
MnO4- -
H2A
(4)
Where,
CMn04. = permanganate concentration determined in
step 7.C,
Table Al. Corresponding concentration of sodium permanganate and potassium permanganate to permanganate.
NaMn04
KMn04
Mn04
mg/L
mM
mg/L
mM
mg/L
mM
0.90
0.006
1.00
0.006
0.75
0.006
4.5
0.032
5.0
0.032
3.8
0.032
9.0
0.063
10.0
0.063
7.5
0.063
13.5
0.095
15.0
0.095
11.3
0.095
22.4
0.16
25.0
0.16
18.8
0.16
35.9
0.25
40.0
0.25
30.1
0.25
44.9
0.32
50.0
0.32
37.9
0.32
67.3
0.47
74.9
0.47
56.4
0.47
89.9
0.63
100
0.63
75.3
0.63
135
0.95
150
0.95
113
0.95
180
1.27
201
1.27
151
1.27
224
1.58
250
1.58
188
1.58
449
3.16
500
3.16
376
3.16
Ground Water Sample Preservation at /SCO Sites
Ground Water Issue
13
-------
Table A2. Corresponding concentration of sodium persulfate to persulfate (S2O8").
Na2S208
SA2-
mg/L
mM
mg/L
mM
99
0.42
80
0.42
248
1.0
200
1.0
496
2.1
400
2.1
756
3.2
610
3.2
1004
4.2
810
4.2
1500
6.3
1210
6.3
1996
8.4
1610
8.4
2504
10.5
2020
10.5
3000
12.6
2420
12.6
3496
14.7
2820
14.7
4004
16.8
3230
16.8
4500
18.9
3630
18.9
4996
21.0
4030
21.0
VMno4 = volume of permanganate solution in the VOA
vial (0.04 L),
CH2A = ascorbic acid concentration (0.015, 0.15 or 1.5
M), and
VH2A = volume of ascorbic acid required to neutralize
permanganate.
VH2A can be calculated (Eq 5) through rearranging Eq. (4)
VH2A= (1.8
(5)
For example, a 40 mL permanganate concentration of
1.27mM (151 mg/L) is neutralized using 1.5 M ascorbic
acid. The volume of stock solution and mass of ascorbic
acid can be calculated as follows.
VH2A= (1.8 x 1.27 mmol/L x 0.04L/1.5 mol/L) x
(1 mol/1000 mmol) x (106 ixL/lL) = 61 iiL
MH2A = 1.5 mol/L x 61 ixL x (1L/106 iiL) x
(176.12 g/mol) x (1000 mg/g) = 16.1 mg
Where,
MH2A = mass of ascorbic acid
The formation of colloidal or particulate MnO2(s) (i.e.,
Mn+4) may occur causing a brown tinge appearance of
the solution. Incremental amendment of ascorbic acid
may be required to further reduce the Mn+ to Mn+2,
and eliminate the brownish tinge color. Mn+ is highly
soluble and the most desirable form of Mn to minimize
the impact of colloidal or particulate matter on the
laboratory analytical instruments. Overall, Table 1 is
used as a guideline but the actual amount should be
based on the amount required to fully eliminate the
MnO4 and MnO2(s), and to achieve a clear solution. The
volume of ascorbic acid solution added to the sample vial
should be recorded so appropriate dilution calculations
can be performed to obtain an accurate estimate of the
contaminant concentrations.
b. Persulfate.
4 mole of ascorbic acid per mole of persulfate was
empirically determined to effectively limit the impact
of the oxidant on VOCs in aqueous samples (Huling et
ctl, 2011). Therefore, the mass balance equation (Eq 6)
can be set up as follows,
V'
S2O82- ~
H2A
(6)
Where,
CS2082- = persulfate concentration determined in step 7.C,
VS2082 = volume of persulfate solution in the VOA vial
0.04 L,
CH2A = ascorbic acid concentration (1.5 M),
VH2A = volume of ascorbic acid required to neutralize
persulfate
VH2A can be calculated (Eq 7) through rearranging Eq. (6)
VH2A=(4xC
'S2O82-
' S2O82-
'H2A
(7)
For example, persulfate concentration is 10.5 mM
(2020 mg/L) and neutralized using 1.5 M ascorbic acid.
The volume of stock solution and mass of ascorbic acid
can be calculated as follows.
VH2A= (4 x 10.5 mmol/L x 0.04L / 1.5 mol/L) x
(1 mol/1000 mmol) x (1000 mL/lL)= 1.12 mL
MH2A= 1.5 mol/L x 1.12 mL x
(1 L/1000 mL) x (176.12 g/mol) = 0.3 g
Where,
MH2A = mass of ascorbic acid
The volume of ascorbic acid solution added to the sample
vial should be recorded so appropriate dilution calcula-
tions can be performed to obtain an accurate estimate
of the contaminant concentrations.
F. Pre-amending Sample Vials With Preservative
Pre-amending the 40 mL sample vials prior to per-
forming ground water sample collection in the field is
one step that may help simplify sample preservation
procedures. The advantage is that all sample vials are
14
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Ground Water Sample Preservation at /SCO Sites
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amended with the preservative in a uniform manner,
and this reduces the number of steps and time required
during ground water sampling activities in the field.
Specifically, this would involve amending the sample
vial with an appropriate quantity of ascorbic acid using
the procedures recommended above. Successful sample
preservation would be immediately obvious in the case
with permanganate binary mixtures as the pink/purple
color would disappear and the sample would become
clear. A persistent pink/purple or brown tinge color
would indicate the need for additional preservative.
The immediate visual feedback would not occur in the
preservation of persulfate binary mixtures due to the
absence of oxidant coloration. Success of the preservation
method will most likely require prior knowledge of oxi-
dant concentrations in ground water samples to support
the selection of an appropriate quantity of preservative.
A quality assurance step could include the collection of
duplicate samples, and subsequent analysis for persulfate,
when time permits, to confirm that a sufficient quantity
of preservative was amended. Other appropriate quality
assurance steps could be developed.
8. REFERENCES
Huang, K.C., Couttenye, R.A., and Hoag, G.E. 2002.
Kinetics of heat-assisted persulfate oxidation of methyl
tert-butyl ether, Chemosphere49(4), 413-420.
Huling, S.G., Ko, S., and Pivetz, B. 2011. Ground water
sampling at ISCO sites - binary mixtures of volatile
organic compounds and persulfate. Ground Water
Monit. Remed. 31(2), Spring 72-79.
Johnson, K.T., Wickham-St. Germain, M., Ko, S. and
Huling, S.G. 2012. Binary Mixtures of Permanganate
and Chlorinated Volatile Organic Compounds in
Groundwater Samples: Sample Preservation and
Analysis. GroundWaterMonit. Remed., 32(3), Summer
84-92.
9. DISCLAIMER
This recommended operating procedure has been pre-
pared for general use. This is not an official approved U.S.
Environmental Protection Agency method and has not
undergone the Agency's peer review process.
Ground Water Sample Preservation at ISCO Sites
Ground Water Issue
15
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