1,200

1,000

800

CFC-12

600

MILLIVOLTS

400

TCA & CFC-113

CFC-11

200

Carbon tetrachloride

‘Chloroform
TCE
PCE

=

0 2 4 6 8 10 12 14 16 18 20
ELUTION TIME, IN MINUTES

10,000,000

9,000,000

p-or m-xylene

8,000,000

p- or mexylene

7,000,000

6,000,000

cis-1,2-dichloroethane
Ethylbenzene

5,000,000

COUNTS

Chlorodifluoromethane

Chlorofluoromethane

4,000,000

Benzene
PCE

3,000,000

Chlorobenzene

2,000,000

Dichlorofluoromethane
TCE

1,1-dichloroethane

1,000,000

m (arr Vera Fann Berney

0 5 10 15 20 25
ELUTION TIME, IN MINUTES

Figure 6. Example of (a) GC-ECD and (b) GC-MS analyses for a sample with numerous VOC peaks from a community-
supply well in a fractured-rock aquifer in Virginia. Note scale of y-axis relative to scale of y-axis in figures four and
five.

14 OCCURRENCE OF VOLATILE ORGANIC COMPOUNDS IN DRINKING WATER FROM THE UNITED STATES


Three of the six primary compounds that
appear on the CFC chromatograms included in this
study (TCA, TCE, and PCE) are in the top four
chlorinated solvents with the highest demand (Harte
and others, 1991), which indicates that, as expected,
the compounds with the highest demand, or most
uses, are the most pervasive contaminants. The
VOCs most commonly determined in this investi-
gation are the same compounds that have been
identified as those most frequently detected in many
previous drinking-water investigations (Grady and
Casey, 2001; Moran and others, 2001; Rowe and
others, 2001; Squillace and others, 1999; Westrick,
1990; and Zogorski and others, 2001). It should be
noted that one peak found in a small percentage of
samples is likely N,O, and not a VOC. This peak was
still included if the area was greater than 100,000
because numerous VOC peaks can appear in the
chromatograms around this peak, and due to changes
in the elution time, it cannot be said with certainty
that this peak is always NO. The percentage of sites
that had this peak was not significant, and including
or excluding this peak does not alter the conclusions
made in this investigation.

Utilizing all of the VOC peaks detected by
the GC-ECD, 70% of the samples contained at least
one VOC. This value increases to 98% if the CFC
data are included. These percentages should be
viewed as minimum estimates because the entire data
set was utilized, and as discussed previously, only
peaks with areas greater than 100,000 counts were
included, some of the samples were only analyzed for
six to eight minutes, and many of the samples were
analyzed on GC-2.

Comparison of GC-ECD VOC Peaks with
VOC Concentrations from NAWOA
Investigations

For 124 of the sites from this study, a
comparison was made between CFCs concentrations
and VOC peak areas detected in this investigation (by
GC-ECD) and CFC and VOC concentrations from
USGS NAWQA investigations (appendix 4; John
Zogorski, written communication, 2001). This
comparison is useful in order to determine the
concentration ranges for VOCs identified as a by-
product of CFC analyses. Data for the samples from
NAWQA investigations were obtained using purge-
and-trap GC-MS with a capillary column. For 99 of

these sites, the sampling for the NAWQA investiga-
tions was done on the same day as the sampling for
CFC analyses by the USGS Chlorofluorocarbon
Laboratory. For the remaining sites, the offset
between sampling events is from 3 to 353 days (a cut-
off of one year was chosen to minimize hydrologic
differences).

For the CFCs, the concentrations determined
in this investigation using the GC-ECD are as much
as five orders of magnitude lower than the minimum
reporting level for the samples analyzed in the
NAWQA studies. For example, CFC-11 and/or CFC-
12 concentrations are reported for only 12 NAWQA
samples (appendix 4). In all other samples, the
concentrations reported from NAWQA investigations
were below the minimum reporting level. For these
twelve samples, however, concentrations determined
in the USGS Chlorofluorocarbon Laboratory were as
much as two orders of magnitude above the calibra-
tion range of the GC-ECD, and all except one are
reported in appendix 4 with either a ‘>’ symbol
indicating that the concentration is likely higher, but
was too far above the calibration range to be deter-
mined more accurately, or were reported as ‘NA,’
because in these cases, the concentration was so far
above the calibration range of the instrument that
even a relative number could not be assigned. For
example, in this investigation, site 2614 had a CFC-
12 concentration of >71,100 pg/kg, which is more
than an order of magnitude above the calibration
range for the USGS Chlorofluorocarbon Laboratory.
The concentration reported from a NAWQA study for
this site is 1.04 pg/L, or 1,040,000 pg/kg. This
discrepancy occurs for the other CFC concentrations
reported in NAWQA investigations; however, the
lowest detectable concentrations reported in various
NAWQA investigations correlate with the highest
concentrations measured in the USGS Chlorofluoro-
carbon Laboratory. The difference in the detection
levels between the USGS Chlorofluorocarbon
Laboratory and the NAWQA investigations results
from the different sampling and analysis methods
used by the two groups. Samples collected for CFC
analysis at the USGS Chlorofluorocarbon Laboratory
were collected using metal tubing and fused in
borosilicate ampoules without contacting air.
Samples were analyzed using GC-ECD methods
again without contacting air, thereby eliminating any
chance of atmospheric exchange and allowing the
detection of VOCs at levels that are below modern
atmospheric air-water equilibrium (Busenberg and
Plummer, 1992).

8 OCCURRENCE OF VOLATILE ORGANIC COMPOUNDS IN DRINKING WATER FROM THE UNITED STATES


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Abstract.
Introduction
Purpose and Scope.
Acknowledgements.
Approach.......

Length of Analysis Time
Analysis Conditions
Gas Chromatograph
Identification and Quantification of VOC Peaks in GC-ECD Chromatograms
GC-ECD Chromatograms..............
Comparison of GC-ECD VOC Peaks with VOC Concentrations from NAWQA Investigations.
Identification and Quantification of VOC Peaks in GC-MS Chromatograms.
GC-MS Chromatograms
Comparison of GC-MS VOC Peaks with GC-ECD VOC Peaks and VOC Concentrations from NAWQA
Investigations.
Co-occurrence of VOCs in Dri
Summary and Conclusions
References Cited
Appendixes [In pocket on CD-ROM]
Appendix 1. Field information for all samples included in this investigation
Appendix 2. Codes used in appendix 1 developed by the USGS Chlorofluorocarbon Laboratory to aid in
the interpretation of CFC-modeled ages
Appendix 3. Results of GC-ECD analyses for all samples included in this investigation
Appendix 4. Comparison of GC-ECD concentrations for CFCs and peak areas for selected VOCs with
concentrations from NAWQA investigations
Appendix 5. List of compounds identified in the 85 samples analyzed by GC-MS (also noted are results of
GC-ECD measurements and NAWQA investigations)

SSMIAINNUDAAADAA SE EWNE

Figures

Figure 1. Map of the United States showing the locations of sample sites ve
2. The number of samples that had a VOC peak (other than CFC-11, CFC-12, and CFC-113) ata given

elution time...

3. GC-ECD peak areas versus concentrations from NAWQA investigations for 1,1-dichloroethylene

4, Example of (a) GC-ECD and (b) GC-MS analyses for a sample without many VOC peaks from a

non-community supply well in Hawaii....

5. Example of (a) GC-ECD and (b) GC-MS analyses for a sample without many VOC peaks from a

domestic well in Maine.

6. Example of a) GC-ECD and (b) GC-MS analyses for a sample with numerous VOC peaks froma

community-supply well in a fractured-rock aquifer in Virginia

7. Example of a) GC-ECD and (b) GC-MS analyses for a sample with numerous VOC peaks froma

community-supply well in unconsolidated Coastal Plan aquifer in Virginia.....

CONTENTS | iii


COUNTS

1,200

14,000

800

600

MILLIVOLTS

400

200 4

CFC-11

Carbon tetrachloride

CFC-113
Chloroform
PCE

a

4 6 8 10 12 14 16 18 20

ELUTION TIME, IN MINUTES

10,000,000

9,000,000

8,000,000

7,000,000

6,000,000

5,000,000

4,000,000

3,000,000

2,000,000

1,000,000

PCE

Various hydrocarbons

Hexachlorobutadiene

Pentachlorobutadiene

Trichlorobenzene

Carbon tetrachloride
TCE
m- or p-xylene

Styrene
Dodecane

Chloroform
Tridecane

5 10 15 20 25

ELUTION TIME, IN MINUTES

Figure 7. Example of (a) GC-ECD and (b) GC-MS analyses for a sample with numerous VOC peaks from a community-
supply well in an unconsolidated Coastal Plain aquifer in Virginia. Note scale of y-axis relative to scale of y-axis in

figures four and five.

IDENTIFICATION AND QUANTIFICATION OF VOC PEAKS IN GC-MS CHROMATOGRAMS 15


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SUMMARY AND CONCLUSIONS 17


COUNTS

4.0

3.5

3.0

CFC-11

25

2.0

Carbon tetrachloride

MILLIVOLTS

Chloroform

CFC-12
PCE

05

0.0 +
0 2 4 6 8 10 12 14 16 18 20

ELUTION TIME, IN MINUTES

10,000

8,000

Xenon

7,000

1,2,4-trichlorobenzene
Hexachlorobutadiene

6,000

Trimethylbenzene

5,000
4,000
3,000

2,000

me "0 ee

i) 5 10 15 20 25

ELUTION TIME, IN MINUTES.

Figure 4. Example of GC-ECD (a) and GC-MS (b) analyses for a sample without many VOC peaks from a non-
community supply well in Hawaii. Note scale of y-axis relative to scale of y-axis in figures six and seven.

12 OCCURRENCE OF VOLATILE ORGANIC COMPOUNDS IN DRINKING WATER FROM THE UNITED STATES


to 4°C, and analysis within 14 days; Rose and others,
1998). Degradation of CFCs and other VOCs in the
archived samples was assessed using GC-ECD
analyses of hundreds of water samples stored for as
much as 4 years and is typically negligible.

This investigation is based on samples that
were originally collected for analysis of CFC
concentrations and were not originally intended for
identifying other specific VOCs or quantifying other
VOC concentrations. Nevertheless, a significant
amount of information about numerous VOCs is
available from this existing database, because it is an
unusually large data set from sites sampled and
analyzed with consistent protocols from throughout
the U.S. The collection and analysis procedures
utilized by the USGS Chlorofluorocarbon Laboratory
allow for significantly lower detection limits than
previous investigations and eliminate the problem of
inconsistent or unknown collection and analysis
procedures that have proven problematic in previous
retrospective investigations. It should be noted that
although CFCs are considered VOCs, throughout this
report, the use of the term VOC refers to those VOCs
that are not measured quantitatively in the USGS
Chlorofluorocarbon Laboratory (those other than
CFC-11, CFC-12, and CFC-113).

Acknowledgments

The authors gratefully acknowledge USGS
colleagues Gerolamo C. Casile and Julian E. Wayland
for CFC analyses, and Sarah E. Parnes for GC-MS
analyses. The insightful reviews of the manuscript by
James F. Pankow (Oregon Health & Science
University, Beaverton, Oregon) and David L. Nelms
(USGS, Richmond, Virginia) are greatly appreciated.
In addition, the participation of the USGS district
office personnel in populating the database for their
projects is greatly appreciated.

APPROACH

The VOC data in this investigation are from
chromatograms from past CFC analyses and from the
analysis of water samples archived until the present
investigation in flame-sealed borosilicate ampoules.
This section describes the criteria for selecting
specific data, and how the data were affected by
procedures and conditions in the laboratory over time.

Sample Selection

Wells

Samples collected from ground-water wells
or springs in the U.S. were selected for the present
study from the USGS Chlorofluorocarbon Laboratory
database and sample archive if they were represen-
tative of drinking water supplies. The wells or
springs either were a direct source of drinking water
(community-supply, non-community supply such as
for restaurants, and domestic wells) or they tapped
aquifers used for drinking water (monitoring,
irrigation, and stock wells near drinking-water wells).
A total of 2,672 water samples are included in this
study, including 2,354 samples from ground-water
wells, 317 samples from springs, and one sample
from a surface-water site associated with a drinking—
water supply (appendix 1). The water samples were
collected from 35 states (fig. 1). The largest number
of samples was from Virginia (487 samples).

Only samples that fit the above requirements
were included. The data are often clustered, and
cannot be viewed as a random sampling of drinking-
water sites throughout the U.S. because many of the
samples were collected as part of large studies to
delineate ground-water-flow paths and ages near
major public-supply areas, and because samples were
included from multiple sampling events over several
months or years at specific sites. It should be noted
that all samples are considered raw water samples and
were collected prior to any chlorination or treatment,
thereby eliminating the possibility of formation of
trihalomethanes as a result of treatment processes.

Information collected at each site includes,
where available, site name and USGS identification
number (neither is shown in appendix 1 in the interest
of privacy to well owners), state location, county
location (not shown), latitude and longitude (not
shown), depth of well, length of open interval, land-
surface elevation, aquifer name (not shown), water
temperature, water level, length of the water column
above the open interval, ground-water use, local land
use, geochemical conditions during sampling,
hydrologic conditions, sampling method, field
conditions, materials that contacted the sample, and
other ancillary data. Not all information was
available at every site. Categories such as ground-
water use, local land use, geochemical conditions
during sampling, hydrologic conditions, sampling
method, field conditions, and materials that contacted
the sample were populated using codes

4 OCCURRENCE OF VOLATILE ORGANIC COMPOUNDS IN DRINKING WATER FROM THE UNITED STATES


Occurrence of Volatile Organic Compounds in Drinking Water from the
United States: Results from Archived Chromatograms and Water Samples,

1989-2000

By Stephanie Dunkle Shapiro, L. Niel Plummer, Michael J. Focazio, Eurybiades Busenberg, Wandee Kirkland,

and Mario Fernandez Jr.

ABSTRACT

Archived chromatograms from more than
2,600 untreated ground-water samples representing
drinking water collected from throughout the U.S.
between 1989 and 2000 were used to assess the
occurrence of selected halogenated volatile organic
compounds (VOCs). The archived chromatograms
were from water samples originally collected for
chlorofluorocarbon (CFC) analyses by gas chroma-
tography with an electron capture detector (GC-ECD)
by the United States Geological Survey (USGS)
Chlorofluorocarbon Laboratory in Reston, Virginia.
In addition, 85 archived water samples, which were
duplicates remaining from the CFC analyses, were
analyzed by gas chromatography in combination with
mass spectrometry (GC-MS), to verify the identity of
the frequently detected VOCs found on the CFC
chromatograms, as well as non-halogenated VOCs
that are not detected by the GC-ECD. All samples
were flame-sealed in borosilicate ampoules at the
sampling site prior to any treatment process, using a
consistent protocol that eliminates contact with air.

The six most frequently detected VOCs on
the CFC chromatograms include the chlorinated
solvents 1,1-dichloroethylene (DCE), 1,1,1-
trichloroethane (TCA), carbon tetrachloride (CClj),
chloroform, trichloroethylene (TCE), and
tetrachloroethylene (PCE). These compounds were
identified on the basis of a limited number of VOC
standards used on the GC-ECD, and were tentatively
quantified on the basis of comparisons of peak areas
from GC-ECD chromatograms with concentrations
from USGS National Water-Quality Assessment
(NAWQA) data that were analyzed by GC-MS using
purge and trap procedures, and a capillary column.

A total of 91 compounds were identified in
the 85 samples analyzed by GC-MS. Eleven of these
compounds were identified in 30% or more of the

samples, including 1,1,2,3,4,4-hexachloro-1 ,3-
butadiene, 1,2,4-trichlorobenzene, 1,2,4-
trimethylbenzene, 1,2-dichlorobenzene, 1,3,5-
trimethylbenzene, 1,3-dichlorobenzene, 1,4-
dichlorobenzene, chloroform, m-, p-, and/or o-xylene,
PCE, and TCE. These eleven compounds, as well as
CCls, which was frequently detected by GC-ECD,
routinely co-occur in water samples; however, this is
likely only the result of their pervasive use and
continuous atmospheric presence.

Though the analyses are qualitative, the
detection levels for many of the halogenated VOCs
were significantly lower (parts per quadrillion) than
those of previous studies of drinking water samples in
the U.S. due to the use of the GC-ECD in this
investigation. For example, CCl, was detected in
almost every sample analyzed in the USGS Chloro-
fluorocarbon Laboratory; however, CCl, has been
infrequently detected in other investigations. In
addition to lower detection limits, the data were all
obtained with the same collection and analysis
procedures, making it a naturally consistent database,
unlike many previous national studies that have relied
on a combination of data sources. The low-level
detections of VOCs in drinking water in this
investigation resulted in higher percentages of sites
affected by at least trace levels of one or more
chlorinated VOC than previously recognized.
Seventy percent of the samples contained at least one
VOC, and if the CFC data are included, 98% of the
samples contained at least one VOC. Most samples
analyzed meet United States Environmental
Protection Agency (USEPA) drinking-water
standards; however, the low-level detections of VOCs
can provide a measure of aquifer susceptibility to
anthropogenic contamination, and early warning of
potential contamination problems.

ABSTRACT 1


Tables

Table 1. List of the 12 most commonly found compounds (other than CFCs) by GC-ECD and GC-MS from this
investigation for the 85 sites analyzed by GC-MS. Shaded columns indicate sites where
measurements from NAWQA investigations were made (see text for details) .....

Abbreviations and Acronyms

CCl, Carbon tetrachloride

CFC Chlorofluorocarbon

CFC-11 Trichloromonofluoromethane

CFC-12 Dichlorodifluoromethane

CFC-113 1,1,2-trichloro-1,2,2-trifluoromethane

DCE 1,1-dichloroethylene

GC-ECD Gas Chromatograph-Electron Capture Detector
GC-MS Gas Chromatograph-Mass Spectrometer
MTBE Methyl tert-Butyl Ether

NAWQA National Water-Quality Assessment Program
PCE Tetrachloroethylene

TCA 1,1,1-trichloroethane

TCE Trichloroethylene

USEPA United States Environmental Protection Agency
USGS United States Geological Survey

VOC Volatile Organic Compound

pg/L Micrograms per liter

pg/kg Picograms per kilogram

iv OCCURRENCE OF VOLATILE ORGANIC COMPOUNDS IN DRINKING WATER FROM THE UNITED STATES


COUNTS

12
a
10 CFC-12
8 3
o 2
: :
> 6 3
F z
4 €
° 5 2
=
oO
LLIN LA nm Pr cred \ carne
0.
0 2 4 6 8 10 12 14 16 18 20
ELUTION TIME, IN MINUTES
40,000
9,000
8,000 Fs
, 8
8
7,000 4
5
=
6,000 3
=
5,000 x
4,000
3,000
2,000
4,000
o4 u
0 5 10 15 20 25

ELUTION TIME, IN MINUTES

Figure 5. Example of GC-ECD (a) and GC-MS (b) analyses for a sample without many VOC peaks from a domestic
well in Maine. Note scale of y-axis relative to scale of y-axis in figures six and seven.

IDENTIFICATION AND QUANTIFICATION OF VOC PEAKS IN GC-MS CHROMATOGRAMS 13


drinking water and focused on the co-occurrence of
multiple contaminants, but was unable to assess the
quality of the ground-water resource, because VOCs
can be added or lost during the treatment and/or
distribution processes.

As part of the USGS NAWQA Program,
which consists of investigations of surface- and
ground-water quality, a national synthesis component
to assess the occurrence, sources, and processes
affecting VOCs in surface and ground water was
added in 1994 (Bender and others, 1999). In the first
phase of the NAWQA synthesis, 55 VOCs were
included on the basis of which compounds could be
analyzed routinely by purge-and-trap gas chromato-
graphy/mass spectrometry, and focusing on those
compounds that were regulated by the USEPA
(Bender and others, 1999). As a subsequent part of
the NAWQA synthesis, a retrospective investigation
was conducted for 60 VOCs with a minimum
reporting level of 0.2-1.0 g/L in untreated ambient
ground water from 2,948 drinking-water and non-
drinking-water wells in urban and rural areas between
1985 and 1995 (Squillace and others, 1999). The data
for the Squillace and others (1999) investigation were
compiled from studies conducted by the USGS and
by state, local, and other Federal agencies. Squillace
and others (1999) found that five compounds had
detection frequencies of 3% or more at the 0.2 ug/L
detection limit in drinking-water and non-drinking-
water wells in urban and/or rural areas between 1985
and 1995. Westrick (1990) found that five VOCs
(cis- and/or trans-1,2-dichloroethylene, TCA, CCly,
TCE, and PCE) occurred in water samples from at
least 5% of large water-supply systems, while
aromatics, especially xylene, had a higher frequency
of detection in water from small water-supply systems
than in samples from large water-supply systems.

In 1999, the USGS Chlorofluorocarbon
Laboratory, located in Reston, Virginia, in cooper-
ation with the U.S. Environmental Protection Agency
Office of Ground Water and Drinking Water, began
an investigation to assess the presence of low-level
detections of VOCs in drinking water utilizing
archived chromatograms and water samples that were
originally used for measurements of CFC concentra-
tions. The large database from sites sampled and
analyzed with consistent protocols from throughout
the U.S. between 1989 and 2000, combined with
detection levels in the parts per quadrillion range,
provides a significant amount of new information for
assessing aquifer susceptibility to anthropogenic
contamination.

Purpose and Scope

This report provides a retrospective synthesis
of VOC data from selected sites that are representa-
tive of drinking water sources throughout the U.S.
The data were obtained from chromatograms
compiled between 1989 and 2000 by the USGS
Chlorofluorocarbon Laboratory, as a by-product of
CFC analyses, and from archived water samples
analyzed during this investigation. Concentrations of
CFCs in surface- and ground-water samples from
throughout the U.S., as well as in several other
countries, have been measured in the USGS Chloro-
fluorocarbon Laboratory using purge-and-trap
GC-ECD since 1989 (see Busenberg and Plummer,
1992; Plummer and Friedman, 1999;
http://water.usgs.gov/lab/cfc). Samples come from a
wide variety of hydrogeologic and land-use settings,
and geochemical conditions. All samples were
collected prior to treatment using metal tubing and
were fused in borosilicate ampoules without
contacting air (Busenberg and Plummer, 1992).
Typically, three separate ampoules from each site
were analyzed, also without contacting air, and
similar results were obtained from all three samples.
The CFC analytical detection limit was somewhat
variable between samples depending on laboratory
and sample conditions, but was typically in the range
of 0.3 to 1.0 picograms per kilogram of water
(0.3x10"” to 1.0x10"” grams per kilogram, or 0.3 to
1.0 parts per quadrillion). The concentrations can be
converted to atmospheric partial pressures and related
to historical atmospheric concentrations of CFCs to
estimate the year when a water sample was recharged
to a ground-water flow system (“apparent recharge
year,” see, for example, Busenberg and Plummer,
1992; Plummer and Friedman, 1999; Plummer and
Busenberg, 2000; http://water.usgs.gov/lab/cfc).
Chromatograms from the CFC analyses include
information on a variety of other VOCs, and can be
used to qualitatively assess low-level occurrences of
additional VOCs.

In this investigation, data from chromato-
grams from previous CFC analyses by GC-ECD are
used to identify, and in some cases, tentatively
quantify, additional VOCs. In addition to GC-ECD
analysis, selected archived water samples were also
analyzed by GC-MS. Some of the VOCs identified in
this investigation are likely degradation products, as
the samples were not acidified or chilled (USEPA
requires immediate acidification to a pH of 2, chilling

INTRODUCTION 3


investigations that utilized data from numerous
sources that had different collection and analysis
procedures. While concentrations for VOCs other
than CFC-11, CFC-12, and CFC-113 are not
quantified in this investigation, the detections provide
evidence for aquifer susceptibility to anthropogenic
contamination, and early warning of potential
contamination problems. Previous non-detects by
other methods that do not have the same low
detection limits have been used to support claims of
safety in water supplies; however, the detections of
various VOCs at the parts per quadrillion level using
the GC-ECD should be viewed as evidence of
anthropogenic influence on water supplies.

REFERENCES CITED

Bender, D.A., Zogorski, J.S., Halde, M.J., Rowe,
B.L., 1999, Selection Procedure and Salient
Information for Volatile Organic Compounds
Emphasized in the National Water-Quality
Assessment Program: U.S. Geological Survey
Open-File Report 99-182, 32 p.

Busenberg, E. and Plummer, L.N., 1992, Use of
chlorofluorocarbons (CC1,F and CC1,F2) as
hydrologic tracers and age-dating tools: The
alluvium and terrace system of Central
Oklahoma: Water Resources Research, v. 28,
no. 9, p. 2257-2283.

Devaux, P., and Guiochon, G., 1967, in Zlatkis, A.,
ed., Advances in Gas Chromatography 1967.

Dinicola, R.S., Cox, S.E., and Bradley, P.M., 2000,
Natural Attenuation of Chlorinated Volatile
Organic Compounds in Ground Water at Area
6, Naval Air Station Whidbey Island,
Washington: U.S. Geological Survey Water-
Resources Investigations Report 00-4060, 86 p.

Grady, S.J., and Casey, G.D., 2001, Occurrence and
Distribution of Methyl tert-Butyl Ether and
Other Volatile Organic Compounds in Drinking
Water in the Northeast and Mid-Atlantic
Regions of the United States, 1993-98: U.S.
Geological Survey Water-Resources
Investigations Report 00-4228, 123 p.

Harte, J., Holdren, C., Schneider, R., and Shirley, C.,
1991, Toxics A to Z: A Guide to Everyday

Pollution Hazards: Berkeley, University of
California Press, 479 p.

Jeffers, P.M., Ward, L.M., Woytowitch, L.M., and
Wolf, N.L., 1989, Homogeneous hydrolysis rate
constants for selected chlorinated methanes,
ethanes, ethenes, and propanes: Environmental
Science and Technology, v. 23, no. 8, p. 965-
969.

Lappé, M., 1991, Chemical Deception, The Toxic
Threat to Health and the Environment: San
Francisco, Sierra Club Books, 360 p.

Mlay, M., 1990, Management Controls of Volatile
Organic Compounds in Groundwater
Protection, in Ram, N.M., Christman, R.F., and
Cantor, K.P., eds., Significance and Treatment
of Volatile Organic Compounds in Water
Supplies, Lewis Publishers, Inc., p. 15-36.

Moran, M., Grady S., and Zogorski J., 2001,
Occurrence and Distribution of Volatile Organic
Compounds in Drinking Water Supplied by
Community Water Systems in the Northeast and
Mid-Atlantic Regions of the United States,
1993-98; U.S. Geological Survey Fact Sheet
FS-089-01.

Plummer, L.N., and Busenberg, E., 2000,
Chlorofluorocarbons, in Cook, P.G., and
Herzeg, A., eds., Environmental Tracers in
Subsurface Hydrology, Chapter 15, Kluwer
Academic Press, p. 441-478.

Plummer, L.N. and Friedman, L.C., 1999, Tracing
and Dating Young Ground Water: U.S.
Geological Survey Fact Sheet 134-99.

Rathbun, R.E., 1998, Transport, Behavior, and Fate
of Volatile Organic Compounds in Streams:
U.S. Geological Survey Professional Paper
1589, 151 p.

Rose, D.L., Connor, B.F., Abney, S.R., and Raese,
J.W., 1998, Laboratory Method for Analysis of
Small Concentrations of Methyl tert-Butyl Ether
and Other Ether Gasoline Oxygenates in Water:
US. Geological Survey Fact Sheet 086-98.

Rowe, B., Grady S., Zogorski, J., Koch B., and
Tratnyek P., 2001, National Survey of MTBE,

REFERENCES CITED 19


ZUSGS

science for a changing world

Occurrence of Volatile Organic Compounds in
Drinking Water from the United States: Results
from Archived Chromatograms and Water
Samples, 1989-2000 Po

1 S81 0 2003

4.9.

“TE 7ED

Water-Resources Investigations Report 02-4173
C2

Prepared in cooperation with the U.S. Environmental Protection Agency, Office of Ground Water &
Drinking Water

1,200

1,000

800

400

200

Chloroform

MILLIVOLTS.
— "ss ore-12
CFC-11
TCA & CFC-113
Carbon tetrachloride

TCE
PCE

uA |

i} 2 4 6 8 10 12 14 16 18 20
ELUTION TIME, IN MINUTES

U.S. Department of the Interior
US. Gealoaical Survev


developed by the USGS Chlorofluorocarbon
Laboratory to aid in the interpretation of CFC
concentrations. These codes are shown in appendix 2
and are discussed below.

Chromatograms

The primary objective of this investigation
was to tabulate VOC peaks that appear in all archived
chromatograms from samples analyzed for CFCs by
the USGS Chlorofluorocarbon Laboratory since 1989
that fit the drinking-water criteria described above.
Typically, three ampoules were historically analyzed
in the USGS Chlorofluorocarbon Laboratory per
sampling site; however, only one chromatogram was
selected in this investigation for interpretation at each
site. This chromatogram was not necessarily the one
with the most VOC peaks on the chromatogram, but
the one interpreted to be most representative of stable
conditions during pumping. For example, the first
sample collected at any given site occasionally has
higher concentrations of CFCs as well as additional
VOC peaks, as a consequence of insufficient purge
time or flushing of the sampling apparatus.

Limitations

The CFC analyses conducted by the USGS
Chlorofluorocarbon Laboratory were designed to
provide picogram per liter detections of CFCs for the
purpose of determining modeled recharge dates and
ages, but were not designed to give optimum results
in determining additional VOCs. Three major
analytical issues that significantly affect this
investigation include (1) the length of the analysis,
(2) the instrument conditions, and (3) the specific
GC-ECD instrument that was used for the analyses.
These three limitations are detailed below; however,
even with the three major limitations in analytical
procedures, a large amount of information can be
extracted from these data that is relevant to VOC
occurrence in drinking water throughout the U.S.

Length of Analysis Time

From 1989 through mid 1992, CFC-113 was
not measured, and analyses were conducted for only
about 6-8 minutes, therefore eliminating the chance
of finding additional VOC peaks with elution times
greater than 6-8 minutes (Busenberg and Plummer,
1992; http:/Avater.usgs.gov/lab/cfe). Over the years, the
analysis time has been increased to about 20 minutes,
and additional VOC peaks have routinely appeared in

the chromatograms. In compiling the data for this
investigation, the samples with short analysis times
appear to have fewer VOC peaks compared to the
samples with long analysis times, when in fact they
may have had numerous peaks with late elution
times. The effect of the analysis time increasing over
the years of operation of the USGS Chlorofluoro-
carbon Laboratory is that the percentage of sites with
0 peaks decreases as analysis time increases (79% for
6-8 minute analyses versus 13% for 18-20 minute
analyses) and the total number of peaks measured
increases as the analysis time increases (0% with 10
peaks for 6-8 minute analyses versus 0.2% with 10
peaks for 18-20 minute analyses).

Analysis Conditions

There are numerous conditions in the GC-
ECD that can vary over time and affect the elution
times of the measured compounds. These conditions
include variations in the composition and/or quality
of the material used to separate the compounds of
interest, in the flow rate of the gas used in the system,
or in the temperature of the oven (Busenberg and
Plummer, 1992; http:/Avater.usys.gov/lab/cfc). These
effects and others can alter the elution times of the
compounds on the chromatograms; however, the
identity of the predominant compounds remains
certain, and the relative elution times remain nearly
unchanged for specific compounds.

It should be noted that the CFC data remain
quantitative throughout any changes in the USGS
Chlorofluorocarbon Laboratory; however, because the
GC-ECD used in the USGS Chlorofluorocarbon
Laboratory is not designed for the quantitative
analysis of other VOCs, the peak areas for the other
VOCs are not meaningful. Changes in the oven
temperature, in the length of time each VOC is
trapped, or in how much of a VOC is being back-
flushed, can significantly affect how much of a given
compound, particularly those with late elution times,
is moving into the detector. Only peaks with areas
greater than approximately 100,000 counts are
included. Using this threshold, the number of peaks
is limited, because it is typical to get just a few counts
to tens of thousands of counts on many compounds.

It should also be noted that when peaks for
individual VOCs become large, two or more peaks
sometimes combine into one very large peak with an
elution time between the times that the two individual
peaks would have had alone. In such cases, it would
appear that there are fewer peaks than are really

6 OCCURRENCE OF VOLATILE ORGANIC COMPOUNDS IN DRINKING WATER FROM THE UNITED STATES


“SaUis ajdwies jo suoijed0] ay) Buimoys sajes payiur) ay) jo dey *p aanBiy

APPROACH 5


INTRODUCTION

Approximately 50% of all U.S. citizens, and
97% of U.S. citizens in rural areas, rely on ground
water as a source of drinking water (Mlay, 1990).
Ground water is susceptible to contamination due to
the large number of potential sources of contaminants
in contact with or in close proximity to aquifers.
Potential contaminant sources across the U.S. include
hazardous waste sites, septic systems, surface
impoundments, hazardous-waste landfills, municipal
and commercial landfills, underground storage tanks,
and underground injection wells. In 1984, the
USEPA estimated that 75% of the 30,000 to 50,000
hazardous-waste sites across the United States were
leaking toxic contaminants into ground water (Lappé,
1991). Countless other sources of potential contami-
nation to ground water include sewage treatment
plant outfall, storm water runoff, outfall or dumping
from chemical factories, dry-cleaning facilities,
application of millions of tons of pesticides and
fertilizers to agricultural lands, emissions or spills
from motor vehicles as well as refueling stations, and
spills or dumping by individual homeowners. All of
these potential sources could contaminate ground
water with thousands of chemical constituents, of
which Federal drinking water standards exist for only
a subset.

One group of hazardous substances, referred
to as volatile organic compounds (VOCs), is of
particular concern to human health. VOCs are among
the most toxic environmental pollutants, and many
are known or are suspected carcinogens (Lappé,
1991; Thomas, 1990). VOCs generally have low
molecular weights, high vapor pressures, and low-to-
medium water solubilities (Rathbun, 1998). Because
they can aid in the dissolution of many other organic
compounds, VOCs are widely used as degreasers,
solvents, and cleaning and liquefying agents in fuels,
as well as in polishes, cosmetics, drugs, and dry-
cleaning solutions. According to Bender and others
(1999), VOCs constitute 10 of the top 20 chemical
compounds with the largest releases into the environ-
ment. Westrick (1990) reports that the ten most
frequently identified VOCs include vinyl chloride,
1,2-dichloroethane, 1,2-dichloropropane, DCE, CCl4,
1,1-dichloroethane, cis/trans-1,2-dichloroethylene,
TCA, PCE, and TCE. These ten compounds are
chlorinated solvents that are used in many industrial
applications as well as in many consumer products.
Only 1% are reused or recycled, while the rest are

eventually released into the environment, where they
are mobile, toxic, and very persistent in soil and
water, leading to bioconcentration and ground-water
contamination (Harte and others, 1991). In addition,
some of these compounds can degrade in the
environment into more toxic compounds, such as
PCE and TCE, which can degrade to vinyl chloride
(Harte and others, 1991).

Attenuation of VOCs in most ground-water
flow systems is minimal. Non-destructive processes
for the attenuation of VOCs in ground water include
evaporation, dispersion and sorption. Numerous
destructive processes could work to alter concentra-
tions of VOCs over time in the ground. Reductive
dechlorination, which is most efficient under sulfate-
reducing or methanogenic conditions, could occur if
sufficient organic matter such as aquifer material,
major fuel hydrocarbons, or landfill leachate is
available (Dinicola and others, 2000). Another
process, abiotic degradation, is not typical in normal
ground-water environments, and half lives for some
chlorinated ethenes by abiotic degradation can be as
long as 10° to 10° years (Jeffers and others, 1989).
Mineralization, or direct oxidation, of VOCs occurs
under aerobic conditions, and is negligible under
methanogenic conditions (Dinicola and others, 2000).

National surveys of VOCs in ground water at
the microgram per liter level or lower could provide
valuable information to water-resources managers
regarding aquifer susceptibility and the potential for
concentrations of VOCs to exceed drinking water
standards in specific areas. The extent of occurrence
in drinking-water supplies from a wide range of
VOCs is largely unknown. Large water-supply
systems monitor for compounds that are regulated by
the USEPA, but typically do not monitor for unregu-
lated compounds. Small water-supply systems and
private homeowners are not required to monitor even
for regulated compounds. In addition, monitoring for
low levels of VOCs provides a database from which
research can be conducted on the long-term
cumulative and synergistic effects of low concentra-
tions of numerous VOCs on human health and the
environment. Little is known about these effects, as
research is usually conducted on individual com-
pounds, and regulations are compound-specific.

The USEPA conducted a national survey of
VOCs in treated drinking water from ground- and
surface-water sources at the 0.2 microgram per liter
(ug/L) level from 1975-1981 (Westrick, 1990). This
survey documented the occurrence of VOCs in treated

2 OCCURRENCE OF VOLATILE ORGANIC COMPOUNDS IN DRINKING WATER FROM THE UNITED STATES


CO-OCCURRENCE OF VOCs IN
DRINKING WATER

Another issue of great importance with
regard to VOCs in drinking water is that of co-
occurrence of numerous VOCs, and the combined
effect of the multiple VOCs even when individual
concentrations are low. Thomas (1990) reports that
VOCs should be treated as a class of substances due
to the similarities of toxicity between individual
VOCs and the similarities in target organs. Grady
and Casey (2001) found that two or more VOCs
occurred together in more than half of drinking water
samples with VOC detections in the Northeast and
Mid-Atlantic regions of the U.S., four or five
compounds occurred together in 12% of the samples
with VOC detections, and more than five compounds
occurred together in 3% of samples with VOC
detections. Squillace and others (1999) found that
MTBE, PCE, TCE, and trichloromethane often occur
together, likely because of widespread occurrence,
not necessarily that they are used together. Westrick
(1990) also found that the co-occurrence of
numerous VOCs was common, but concluded that
the co-occurrence was likely the result of common
usage/disposal practices or from biotransformations
of parent VOCs to common daughter products.

Utilizing non-CFC detections by both GC-
ECD and GC-MS techniques, 12 compounds
appeared in 30% or more of the samples (table 1).
The NAWQA data are also included in table 1 in
order to demonstrate that the co-occurrence of these
compounds is being detected by all three methods for
at least a few of the compounds (e.g. CCl,
chloroform, PCE, and TCE). The 12 compounds that
appeared in 30% or more of samples include
1,1,2,3,4,4-hexachloro-1,3-butadiene, 1,2,4-
trichlorobenzene, 1,2,4-trimethylbenzene, 1,2-
dichlorobenzene, 1,3,5-trimethylbenzene, 1,3-
dichlorobenzene, 1,4-dichlorobenzene, CCl,,
chloroform, and m-, p-, and/or o-xylene, PCE, and
TCE. Many of the 85 samples analyzed by GC-MS
have most, if not all, of the 12 compounds present
(for example, sites 414 and 415). The results from
the present investigation are consistent with those of
Moran and others (2001), Rowe and others (2001),
Squillace and others (1999), Westrick (1990), and
Zogorski and others (2001) indicating that the
predominant organic contaminants in ground water
throughout the United States commonly co-occur and

are compounds used as solvents, in gasoline, as
refrigerants, and in organic synthesis.

SUMMARY AND CONCLUSIONS

An investigation to assess the occurrence of
selected VOCs from sources of drinking water
around the U.S. was conducted by the USGS
Chlorofluorocarbon Laboratory using archived
chromatograms and water samples originally from
CFC analyses conducted between 1989 and 2000.
Chromatograms from the CFC analyses were used to
assess the occurrence of halogenated VOCs in water
from 2,672 sites. The VOCs identified most
frequently in this investigation using GC-ECD are
the chlorinated solvents DCE, TCA, CCl,,
chloroform, TCE, and PCE. Seventy percent of the
samples contained at least one VOC, and if the CFC
data are included, 98% of the samples contained at
least one VOC.

Archived water samples stored in flame-
sealed borosilicate ampoules were analyzed using
GC-MS to verify the identity of the frequently
detected VOCs found on the CFC chromatograms as
well as to identify non-halogenated VOCs that would
not be detected by the GC-ECD. A total of 91
compounds were identified in the 85 samples
analyzed by GC-MS. Twelve non-CFC compounds
were identified in 30% or more of the samples
analyzed by GC-ECD and GC-MS, including
1,1,2,3,4,4-hexachloro-1,3-butadiene, 1,2,4-
trichlorobenzene, 1,2,4-trimethylbenzene, 1,2-
dichlorobenzene, 1,3,5-trimethylbenzene, 1,3-
dichlorobenzene, 1,4-dichlorobenzene, CCl,,
chloroform, m-, p-, and/or o-xylene, PCE, and TCE.
These twelve compounds routinely co-occur in water
samples, however, this is likely the result of their
pervasive use and continuous atmospheric presence,
not necessarily that they are used in combination.

Results of the present investigation are
consistent with those of numerous other state and
national surveys in terms of the specific VOCs
identified. A significant difference between this
study and previous investigations, however, is the
lower analytical detection limits (up to 5 orders of
magnitude lower than the reporting level in previous
investigations) achieved with the collection and
analysis methods utilized by the USGS Chlorofluoro-
carbon Laboratory, and the fact that the data are
internally consistent, unlike other national synthesis

16 OCCURRENCE OF VOLATILE ORGANIC COMPOUNDS IN DRINKING WATER FROM THE UNITED STATES


U.S. Department of the Interior
GALE A. NORTON, Secretary

U.S. Geological Survey
Charles G. Groat, Director

The use of trade, product, or firm names in this publication is for identification purposes only and does not
imply endorsement by the U.S. Government.

For additional information write to: Copies of this report can be purchased from:
Chief, Branch of Regional Research, Eastern U.S. Geological Survey
Region Information Services
U.S. Geological Survey Box 25286, Federal Center
432 National Center Denver, CO 80225
12201 Sunrise Valley Drive e-mail: infoservices@usgs.gov

Reston, VA 20192


PEAK AREA FROM CFC CHROMATOGRAM,

A comparison was made of concentrations of
DCE measured in NAWQA studies and peak areas
from the GC-ECD chromatograms; the DCE peak
appears just before CFC-113 and is not back-flushed
or lost during the GC-ECD analysis. Of all the VOC
peaks (other than CFC-11, CFC-12, and CFC-113)
identified conclusively in this investigation, the DCE
peak is the most quantitative. The peak areas from
the CFC chromatograms increase linearly as the
concentration reported from NAWQA studies
increases (fig. 3). Using this correlation,
concentrations for numerous samples with smaller
peak areas than those used to make the correlation can
be estimated and are in the range of 0 to 0.008 ug/L
(fig. 3).

Direct comparisons between VOC peaks
(other than CFC-11, CFC-12, and CFC-113, and
DCE) in this investigation and those from the
NAWQA studies are difficult for several reasons. For
example, not all of the 124 sites for which there is
overlap between data from this investigation and data
from the NAWQA studies were analyzed for 20
minutes, in which case peaks with late elution times
would not appear. In numerous cases, chloroform
and/or PCE are reported in NAWQA studies, when

due to insufficient run time, no peaks are reported for
chloroform or PCE from the GC-ECD chromato-
grams (appendix 4). For samples with high
concentrations of any VOC, other VOCs can be
masked on the GC-ECD chromatograms by the large
peaks and do not appear to be present. For example,
if CFC-113 is high, TCA can be masked. If
concentrations of chloroform, TCE and/or PCE are
high, they can combine into one large peak with an
elution time that is shifted to the mid-point of the
combined peak (for example, for site 1644, for which
NAWQA investigations detected chloroform (1.8
pg/L), TCE (3.957 pg/L), and PCE (0.1639 pg/L), all
three peaks on the chromatogram are merged, and the
detector labels two at 13.92 and 17.65 minutes,
instead of three at ~14, 15, and 18 minutes). Also, if
the concentration of a VOC is high enough, the
detector becomes saturated and no other peaks are
seen (for example, site 413, for which NAWQA
investigations detected chloroform (0.1122 ug/L),
TCE (20.44 g/L), and PCE (0.3556 j1g/L), and the
chromatogram shows that the detector is ‘saturated’
after 13 minutes). It is generally possible to assess if
there is more than one compound present in the
GC-ECD chromatogram, especially if multiple

IN MILLIONS:

0 0.02 0.04

0.06

04

0.08 0.12

NAWQA CONCENTRATION, IN MICROGRAMS PER LITER

Figure 3. GC-ECD peak areas versus concentrations from NAWOA investigations for 1,1-dichloroethylene.

IDENTIFICATION AND QUANTIFICATION OF VOC PEAKS IN GC-ECD CHROMATOGRAMS 9


methanogenic conditions; however, the sample
appears to be representative of water that is relatively
unaffected by anthropogenic activity.

If the GC-ECD chromatogram had many
peaks other than the CFCs, numerous VOCs were
also identified by GC-MS (figs. 6 and 7). Figure 6
shows GC-ECD (6a) and GC-MS (6b) chromato-
grams from a 625-foot deep community-supply well
in Virginia that is completed in an unconfined,
fractured-rock aquifer beneath an urban area (Site
#1992). The water is methanogenic, has numerous
VOC peaks, and has a modeled CFC-11 recharge
year of 1975, but CFC-12 and CFC-113 concentra-
tions are above modern air-water equilibrium (i.e.,
contaminated). This well is likely contaminated and
the older CFC-11 modeled-age is likely the result of
degradation of CFC-11. Figure 7 shows GC-ECD
(7a) and GC-MS (7b) chromatograms from a 59-foot
deep community-supply well in Virginia, in a
discharge area of an unconfined aquifer (Site #1909).
The water is oxygenated, contains tens of VOC
peaks, has a modeled CFC-11 recharge year of 1988,
but CFC-12 and CFC-113 concentrations are above
modern air-water equilibrium (i.e., contaminated),
and has a fairly high tritium value (9.51 TU). This
water has likely been recharged in approximately the
last 5 years and has many indicators of anthropogenic
inputs.

Eleven compounds were identified in 30% or
more of the samples analyzed by GC-MS. These
eleven include 1,1,2,3,4,4-hexachloro-1,3-butadiene
(77.6%), 1,2,4-trichlorobenzene (74.1%), 1,2,4-
trimethyl-benzene (62.4%), 1,2-dichlorobenzene
(62.4%), 1,3,5-trimethylbenzene (38.8%), 1,3-
dichloro-benzene (62.4%), 1,4-dichlorobenzene
(61.2%), chloroform (31.8%), m-, p-, and/or o-xylene
(35.3%), PCE (32.9%), and TCE (34.1%). Three of
these were also in the six most frequently detected
compounds identified using the GC-ECD chromato-
grams (chloroform, TCE, and PCE). Carbon tetra-
chloride was the most frequently detected compound
on the GC-ECD chromatograms, but was detected in
only seven of the GC-MS samples. The sensitivity to
CCl, of the GC-MS could be increased if the range of
the scan for each sample were decreased to focus on
the period when CCl, would appear.

Comparison of GC-MS VOC Peaks with
GC-ECD VOC Peaks and VOC
Concentrations from NAWOQA
Investigations

For 55 of the sites from this study, a
comparison was made between CFCs and VOCs
detected in this investigation by GC-ECD and by
GC-MS, and CFC and VOC concentrations from
NAWQA studies (appendix 5). In appendix 5, data
from NAWQA investigations are available only for
the shaded samples and are reported as N or NE,
depending on whether the concentration was actual
(above the minimum reporting level) or estimated.
The compounds for which there is overlap with all
three methods of detection include CCl,, chloroform,
TCA, 1,1-dichloroethane, DCE, PCE, and TCE. This
would be expected because these compounds can be
detected by all three methods (unlike some of the
other compounds listed), and they are among the
most commonly used and detected VOCs.

While all three methods can detect numerous
compounds, each method appears to be particularly
useful for detecting certain compounds. The
GC-ECD appears to be most useful in detecting
concentrations of CFCs, CCly, chloroform, PCE, and
TCE in the parts per quadrillion range. The GC-ECD
data for VOCs other than CFC-11, CFC-12, and
CFC-113 are not quantified, but can be utilized for
surveying low-level contamination in aquifers. The
GC-MS appears to be most useful in detecting
1,1,2,3,4,4-hexachloro-1,3-butadiene, 1,2,4-
trichlorobenzene, 1,2,4-trimethylbenzene, 1,2-
dichlorobenzene, 1,3,5-trimethylbenzene, 1,3-
dichlorobenzene, 1,4-dichlorobenzene, and m-, p-,
and/or o-xylene. NAWQA investigations routinely
provide quantitative measurements of a wide array of
the VOCs, but at concentrations typically greater

than 0.1 pg/L.

IDENTIFICATION AND QUANTIFICATION OF VOC PEAKS IN GC-MS CHROMATOGRAMS 11


U.S. Department of the Interior
U.S. Geological Survey

Occurrence of Volatile Organic Compounds in
Drinking Water from the United States: Results
from Archived Chromatograms and Water
Samples, 1989-2000

By Stephanie Dunkle Shapiro', L. Niel Plummer’, Michael J. Focazio', Eurybiades
Busenberg', Wandee Kirkland', and Mario Fernandez Jr2

Water-Resources Investigations Report 02-4173

Prepared in cooperation with the
U.S. Environmental Protection Agency, Office of Ground Water & Drinking Water

Reston, Virginia
2003

' U.S. Geological Survey, Reston, VA 20192
? U.S. Geological Survey, Tampa, FL 33612


Other Ether Oxygenates, and Other VOCs in
Community Drinking-Water Sources: U.S.
Geological Survey Open File Report 01-399.

Squillace, P.J., Moran, M.J., Lapham, W.W., Price,
C.V., Clawges, R.M., and Zogorski, J.S., 1999,
Volatile Organic Compounds in Untreated
Ambient Groundwater of the United States,
1985-95: Environmental Science and
Technology, v. 33, no. 23, p. 4176-4187.

Thomas, R.D., 1990, Evaluation of Toxicity of
Volatile Organic Chemicals: General
Considerations, in Ram, N.M., Christman, R.F.,
and Cantor, K.P., eds., Significance and
Treatment of Volatile Organic Compounds in
Water Supplies, Lewis Publishers, Inc., p. 451-
463.

Westrick, J.J., 1990, National Surveys of Volatile
Organic Compounds in Ground and Surface
Waters, in Ram, N.M., Christman, R.F., and
Cantor, K.P., eds., Significance and Treatment
of Volatile Organic Compounds in Water
Supplies, Lewis Publishers, Inc., p. 103-125.

Zogorski, J., Morgan M.J., and Hamilton P.A., 2001,
MTBE and Other Volatile Organic Compounds-
New Findings and Implications on the Quality
of Source Waters Used for Drinking-Water
Supplies: U.S. Geological Survey Fact Sheet
FS-105-01.

20 OCCURRENCE OF VOLATILE ORGANIC COMPOUNDS IN DRINKING WATER FROM THE UNITED STATES


Cover graphic: Example of a GC-ECD chromatogram for a sample with numerous VOC peaks from a
community-supply well in a fractured-rock aquifer in Virginia.


present. This situation will be addressed in more
detail in subsequent sections. Finally, it should be
noted that the VOC peak areas are affected by
variations in the headspace in the ampoule. A
correction for this is made when determining CFC
concentrations, however, the peak areas for individual
VOCs are not corrected. The effect of the headspace
variation depends on the Henry’s law constant of a
specific compound and is typically negligible, but the
VOCs have not been quantified in this investigation
anyway, and the relative peak areas are still
meaningful.

Gas Chromatograph
The majority of the CFC analyses were

conducted on one instrument that has been in use
since 1989 (GC-1). A second instrument (GC-2),
added in 1996, was designed to optimize efficiency,
and VOCs with elution times that are greater than
those of the CFC compounds of interest are flushed
out of the system after the CFC compounds have
passed into the analytical column. Except for those
compounds with exceedingly high concentrations,
most of the VOCs are lost from the system.
Comparisons of samples from the same site run on
both GCs show that samples analyzed on GC-2 had
fewer extra VOC peaks and lower peak areas than
samples run on GC-1. GC-2 had a larger percentage
of samples (79%) with 0 and 1 peak as compared to
GC-1 (56%), and a smaller percentage of samples
(7%) with more than 2 peaks as compared to GC-1
(28%).

IDENTIFICATION AND
QUANTIFICATION OF VOC PEAKS IN
GC-ECD CHROMATOGRAMS

In this section, the VOC peaks from the
archived CFC chromatograms analyzed by GC-ECD
are identified and tentatively quantified on the basis
of a limited number of standards analyzed on the GC-
ECD, and by comparisons to VOC concentrations
from the same wells as determined by USGS
NAWOQA investigations (John Zogorski, U.S.
Geological Survey, written communication, 2001).

GC-ECD Chromatograms

The VOC peaks (other than CFC-11, CFC-
12, and CFC-113) from all CFC chromatograms
analyzed since 1989 are shown in figure 2 and are
tabulated in appendix 3. It is difficult to specify that
a peak appearing on a CFC chromatogram is a
particular compound due to the lack of standards used
for specific VOCs and to variations in the conditions
of the instrument over time. However, several
groupings of peaks are evident and were identified on
the basis of a limited number of VOC standards
analyzed by GC-ECD.

Referring again to figure 2, the group with an
elution time just before 6 minutes is DCE, followed
by TCA just after 6 minutes, CCl, around 9-10
minutes (the cluster just after 10 minutes is still CCl,
from analyses in 1994), chloroform around 14
minutes, TCE just after 15 minutes, and PCE around
18 minutes. In this investigation, CCl, was detected
most frequently, followed by chloroform, which is
primarily because of the high sensitivity of the GC-
ECD to these compounds. The ECD is as much as
five orders of magnitude more sensitive to CCl,, for
example, than it is to various other VOCs (Devaux
and Guiochon, 1967).

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8 12
ELUTION TIME, IN MINUTES

Figure 2. Number of samples that had a VOC peak (other than
CFC-11, C, CFC-12, and CFC-113) at a given elution time.

IDENTIFICATION AND QUANTIFICATION OF VOC PEAKS IN GC-ECD CHROMATOGRAMS 7


ampoules are analyzed; however, this cannot be done
with certainty.

Individual peaks can be separated when the
concentrations are small. For example, for site 1005,
the USGS Chlorofluorocarbon Laboratory detects
individual peaks for TCE and PCE that have
NAWQ4A-reported concentrations of 0.0094 ug/L,
and 0,048 g/L, respectively. For site 2593, the
USGS Chlorofluorocarbon Laboratory detects
individual peaks for chloroform, TCE, and PCE, for
NAWQA-reported concentrations of 0.04 pg/L,
0.006 pg/L, and 0.123 pg/L, respectively. The
GC-ECD peaks for the lowest reported concentra-
tions for chloroform, TCE, and PCE are hundreds of
thousands of counts, millions of counts, and tens of
millions of counts, respectively. The GC-ECD
appears to be most useful for chloroform, TCE, and
PCE concentrations below about 0.04, 0.01, and 0.05
ug/L, respectively. Carbon tetrachloride is detected
in almost every sample analyzed in the USGS Chlor-
ofluorocarbon Laboratory; however, in NAWQA
investigations, CCl, is detected in only five samples
(as low as ~0.1 jig/L). For the lowest concentrations
reported from NAWQA investigations for CCl,, the
GC-ECD peaks are so large that peak areas cannot be
assigned. The discrepancy between the laboratories
for the detection of CCl, is a function of the sensi-
tivity of the GC-ECD to CCl, as discussed above.

IDENTIFICATION AND
QUANTIFICATION OF VOC PEAKS IN
GC-MS CHROMATOGRAMS

A subset of stored samples was selected for
analysis by GC-MS. About half of these samples
were collected from domestic and community/non-
community-supply wells in five states. These wells
were sampled in the year 2000 and were selected to
minimize any effects from storage in the ampoules.
The second set of samples, which were stored in
ampoules for up to four years, were selected because
they had numerous VOC peaks on the GC-ECD
chromatograms. The GC-MS analyses were used to
corroborate the identity of the VOCs detected on the
GC-ECD, as well as to identify non-halogenated
VOCs that are not detected by the GC-ECD.

GC-MS Chromatograms

Archived ampoules from 85 sites were
analyzed by GC-MS. A Hewlett Packard (HP) 5973
mass selective detector with a mass range of 34 to
550 atomic mass units was used in combination with
an HP 6890 gas chromatograph. The VOCs were
preconcentrated using purge and trap procedures,
cryofocused, and injected into a 60m x 0.32mm x
1.8um HP-VOC/MS capillary column. Specific
VOCs were tentatively identified, but not quantified,
using the National Institute of Standards (NIST)
Mass Spectral Library (version 1.6) which has more
than 61,000 chemical structures and MS spectra.
Specific peaks were considered positively identified
if there was a 90% or greater chance that the mass
spectrum matched a specific spectrum in the library
(appendix 5). These are listed in appendix 5 as GS,
GM, or GL depending on whether the peak area was
<10,000, 10,000-19,999, or >20,000, respectively. In
addition, other compounds were tentatively identified
and listed if the peak correlated with a peak
identified in the standard (appendix 5). These
compounds are listed similarly to those positively
identified, except that an ‘E’ was added (GES, GEM,
GEL). A total of 91 compounds were identified in
the 85 samples analyzed by GC-MS (appendix 5).

In general, if the GC-ECD chromatogram
had no peaks other than the CFCs, few peaks were
detected by GC-MS (figs. 4 and 5). Figure 4 shows
GC-ECD (4a) and GC-MS (4b) chromatograms from
an 870-foot deep drinking-water well in Hawaii,
completed in an unconfined, fractured-rock aquifer
beneath an urban/residential area (Site #408). The
water is oxygenated, contains virtually no VOCs, has
modeled CFC-11, CFC-12, and CFC-113 recharge
years of 1954, 1952, and <1955, respectively, has a
low tritium value (0.11 TU), and has an 85-year old
>H~He modeled age, which is beyond the practical
dating range of the method. This water is relatively
old and is unaffected by modern anthropogenic
inputs. Figure 5 shows GC-ECD (5a) and GC-MS
(5b) chromatograms from a 182-foot deep domestic
well in Maine, which is completed in a semi-
confined, fractured-rock aquifer beneath a residential
area (Site #988). The water is methanogenic,
contains virtually no VOC peaks, and has modeled
CFC-11, CFC-12, and CFC-113 recharge years of
<1945, 1964, and <1955, respectively. The
concentrations of VOCs in this water may be affected
by degradation processes, as is typical under

10 OCCURRENCE OF VOLATILE ORGANIC COMPOUNDS IN DRINKING WATER FROM THE UNITED STATES