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In cooperation with the Texas Natural Resource Conservation Commission
Volatile Organic Compound and Pesticide
Data for Public Water-Supply Reservoirs
and Wells, Texas, 1999–2001
Open-File Report 02–093
U.S. Department of the Interior
U.S. Geological Survey
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Volatile Organic Compound and Pesticide Data for Public Water-Supply
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Reservoirs and Wells, Texas, 1999-2001
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U.S. Department of the Interior
U.S. Geological Survey
Volatile Organic Compound and Pesticide
Data for Public Water-Supply Reservoirs
and Wells, Texas, 1999–2001
By B.J. Mahler, M.O. Gary, M.G. Canova, Eric W. Strom,
Lynne Fahlquist, and Michael E. Dorsey
U.S. GEOLOGICAL SURVEY
Open-File Report 02–093
In cooperation with the Texas Natural Resource Conservation Commission
Austin, Texas
2002
U.S. DEPARTMENT OF THE INTERIOR
Gale A. Norton, Secretary
U.S. GEOLOGICAL SURVEY
Charles G. Groat, Director
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For additional information write to
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Box 25286
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E-mail: [email protected]
ii
CONTENTS
Abstract ................................................................................................................................................................................ 1
Introduction .......................................................................................................................................................................... 1
Purpose and Scope .................................................................................................................................................... 1
Site Selection ............................................................................................................................................................ 2
Acknowledgments .................................................................................................................................................... 2
Volatile Organic Compound and Pesticide Data .................................................................................................................. 2
Collection of Samples ............................................................................................................................................... 2
Reservoir Samples ......................................................................................................................................... 3
Well Samples ................................................................................................................................................. 3
Quality-Control Samples ............................................................................................................................... 4
Analysis of Data ....................................................................................................................................................... 4
Methods ......................................................................................................................................................... 4
Environmental Samples ................................................................................................................................ 5
Reservoirs ......................................................................................................................................... 5
Wells .................................................................................................................................................. 6
Quality-Control Samples ............................................................................................................................... 6
Reservoirs ......................................................................................................................................... 6
Wells .................................................................................................................................................. 7
Summary .............................................................................................................................................................................. 8
References Cited .................................................................................................................................................................. 9
FIGURES
1. Map showing locations of public water-supply reservoirs sampled in Texas, June–July 1999 ........................... 2
2. Map showing locations of public water-supply wells sampled in Texas, November 1999–January 2001 .......... 3
3. Boxplots showing percent recovery of spikes and surrogates for reservoir samples ........................................... 6
4. Graph showing comparison of concentrations of pesticides detected in environmental and replicate
samples from reservoirs ........................................................................................................................................ 7
5. Boxplots showing percent recovery of spikes and surrogates for well samples ................................................... 7
6. Graph showing comparison of concentrations of pesticides detected in environmental and replicate
samples from wells ............................................................................................................................................... 8
TABLES
1. Concentrations of volatile organic compounds in public water-supply reservoirs sampled in Texas,
June–July 1999 ..................................................................................................................................................... 10
2. Concentrations of soluble pesticides in public water-supply reservoirs sampled in Texas, June–
July 1999 .............................................................................................................................................................. 12
3. Summary of soluble pesticides in samples collected from public water-supply reservoirs in Texas,
June–July 1999 ..................................................................................................................................................... 44
4. Concentrations of volatile organic compounds, nitrite plus nitrate, and tritium in public water-supply
wells sampled in Texas, November 1999–January 2001 ...................................................................................... 45
5. Concentrations of soluble pesticides in public water-supply wells sampled in Texas, November 1999–
January 2001 ......................................................................................................................................................... 51
6. Summary of soluble pesticides in samples collected from public water-supply wells in Texas, November
1999–January 2001 ............................................................................................................................................... 105
CONTENTS iii
Volatile Organic Compound and Pesticide Data
for Public Water-Supply Reservoirs and Wells,
Texas, 1999–2001
By B.J. Mahler, M.O. Gary, M.G. Canova, Eric W. Strom, Lynne Fahlquist, and
Michael E. Dorsey
Abstract tion of substantial potential contamination sources and
to compile information regarding the susceptibility of
To provide data for the Texas Source-Water
systems to contamination. This information will, in
Assessment and Protection Program, the U.S. Geo- turn, help identify systems that might be eligible for
logical Survey conducted a synoptic survey of reduced monitoring or that might require additional
48 public water-supply reservoirs and 174 public monitoring. Assessment of susceptibility to contamina-
water-supply wells during 1999–2001. The tion would enable more efficient use of monitoring and
surface-water samples were analyzed for volatile protection dollars.
organic compounds and soluble pesticides. The The assessment of the susceptibility of water sup-
plies to contamination requires accurate, consistent, and
ground-water samples were analyzed for volatile
technically defensible data on the occurrence of volatile
organic compounds and soluble pesticides, as well
organic compounds (VOCs) and pesticides at low detec-
as nitrite plus nitrate nitrogen and tritium.
tion levels in source waters for public water supply
One or more volatile organic compounds
(PWS). These data are needed to determine what factors
were detected in 75 percent of the reservoirs and in
or activities might contribute to contamination, which
9 percent of the wells. Methyl tert-butyl ether was
source waters are most vulnerable to contamination, and
detected most frequently in reservoirs, and toluene where, and for which pollutants, monitoring should be
was detected most frequently in wells. One or more intensified or reduced. The Texas Natural Resource
pesticides were detected in 96 percent of the reser- Conservation Commission therefore requested the U.S.
voirs and in 33 percent of the wells. Atrazine or its Geological Survey (USGS) to collect water samples
breakdown product deethylatrazine was the most from PWS reservoirs and wells in Texas for VOC and
frequently detected pesticide. pesticide analysis. The database of VOC and pesticide
detections in PWS reservoirs and wells presented in this
Volatile organic compounds and pesticides
report represents a critical contribution to the Texas
were not detected at concentrations exceeding the
SWAP nonpoint-source pollution component for both
maximum contaminant level allowed in drinking
ground-water and surface-water supplies.
water. The only constituent sampled for that
exceeded its maximum contaminant level (10 mil- Purpose and Scope
ligrams per liter) was nitrate nitrogen (in 8 percent
The purpose of this report is to present chemical
of the 174 wells).
data from the analysis of samples from surface and
ground waters that are sources for PWS in Texas. Forty-
INTRODUCTION
eight reservoirs across Texas that are PWS source
Evaluation of the susceptibility of drinking water waters were sampled during June–July 1999 (fig. 1).
supplies to chemical contamination is of nationwide The surface-water samples were analyzed for VOCs and
interest. The U.S. Environmental Protection Agency a suite of soluble pesticides. One hundred and seventy-
(USEPA), through the Safe Drinking Water Act four wells that are PWS source waters were sampled
Amendments of 1996, therefore required that each state during November 1999–January 2001 (fig. 2). The
complete a Source-Water Assessment and Protection ground-water samples were analyzed for VOCs, a suite
(SWAP) Program. The SWAPs are to include identifica- of soluble pesticides, nitrite plus nitrate nitrogen, and
INTRODUCTION 1
102o 100o
36o
OKLAHOMA
98o 96o
34o 94o
ARKANSAS
NEW MEXICO
106o 104o
32o
A
N
A
SI
TEXAS UI
O
L
30o
U
NI
T
MEXICOED S2T8AoTES G ULF OF M EXIC O
0 50 100 150 200 MILES
Figure 1. Locations of public water-supply reservoirs sampled in Texas, June–July 1999.
tritium. The data presented in this report will be used by chosen to represent a broad range of environmental
the Texas SWAP to determine, to the extent possible, characteristics such as land use, depth to water, amount
statistical relations between explanatory variables such of precipitation, and soil characteristics. These environ-
as land-use characteristics of the contributing area of the mental characteristics are potential explanatory vari-
supply and occurrence of a contaminant. ables that might be statistically related to the occurrence
of one or more contaminants.
Site Selection
Acknowledgments
Only reservoirs that are a PWS for one or more
utilities and that have a volume of 5,000 acre-feet or
The authors acknowledge the cooperation of the
more were considered for sampling. The only excep-
PWS well managers and operators who allowed sam-
tions were two small reservoirs in south Texas, La Feria
ples to be collected during this investigation.
Reservoir and Donna Reservoir. Of the 205 candidate
reservoirs, 48 were selected to give as much spatial cov-
VOLATILE ORGANIC COMPOUND AND
erage of the State as possible and to reflect both urban
and agricultural land uses in their watersheds. PESTICIDE DATA
The wells sampled are PWS wells that have well-
log information and that are screened primarily in Collection of Samples
unconfined aquifers. About 470 of about 18,000 PWS
wells in Texas were candidates for sampling. From Samples were collected following protocols
those 470 wells, 174 were selected to represent, in rela- established by the USGS National Water-Quality
tive proportion, the variety of aquifer materials found in Assessment (NAWQA) Program or developed in
the State (for example, unconsolidated sediment, lime- consultation with NAWQA water-quality specialists.
stone, and alluvium) and to give as much spatial cover- These sampling protocols are briefly described below
age of the State as possible. Additionally, the wells were and the appropriate reference cited.
2 Volatile Organic Compound and Pesticide Data for Public Water-Supply Reservoirs and Wells, Texas, 1999–2001
102o 100o
36o
OKLAHOMA
98o 96o
34o 94o
ARKANSAS
NEW MEXICO
106o 104o
32o
A
N
A
SI
TEXAS UI
O
L
30o
U
NI
T
MEXICOED S2T8AoTES G ULF OF M EXIC O
0 50 100 150 200 MILES
Figure 2. Locations of public water-supply wells sampled in Texas, November 1999–January 2001.
Reservoir Samples 1 L into each of two 1-L baked glass amber bottles using
a baked 0.7-micrometer (µm) pore-size glass-fiber filter
The VOC sample was collected first at each reser- in a stainless steel or aluminum holder and Teflon tub-
voir site. Once the approximate sampling site location ing. The samples were preserved on ice until and during
was reached, the boat motor was turned off and the boat shipping to the laboratory.
allowed to drift upwind as far as possible (at least 50
Dissolved oxygen, pH, specific conductance, and
feet [ft]) before the sample was collected to avoid con-
temperature were measured as a vertical profile in each
tamination by boat exhaust. The sample was collected
reservoir concurrent with collection of each pesticide
by dipping three pre-cleaned 40-milliliter (mL) amber
sample. Measurements were taken at each of the sam-
glass VOC vials about 0.5 m below the water surface
pling intervals using a Hydrolab and flow cell. Measure-
and allowing them to fill. The samples were preserved
ments were made by pumping lake water from the
on ice after being acidified with hydrochloric acid, agi-
interval through the flow cell on the boat and using
tated, and checked to make sure no air bubbles were
measurement probes inserted into the cell.
trapped inside (Shelton, 1997).
The pesticide sample was collected as a vertical Well Samples
composite. The total depth at the sampling site was
divided into 10 discrete depth intervals, and one-tenth of All well samples collected were raw water
the 3-liter (L) sample was pumped from the center of samples, that is, they were collected before the water
each interval into a Teflon bottle using a peristaltic had been filtered, chlorinated, or treated in any way.
pump fitted with Teflon tubing. The minimum sampling Sampling procedures followed those of the USGS
interval was 2 ft, so in shallow lakes (less than 20-ft NAWQA Program as described in Koterba and others
deep), fewer than 10 intervals were sampled. The col- (1995) and Koterba (1998).
lected water was processed following NAWQA protocol Field properties were monitored using a Hydrolab
(Shelton, 1994, p. 23). Briefly, the approach was to filter and flow cell. The well was purged until dissolved
VOLATILE ORGANIC COMPOUND AND PESTICIDE DATA 3
oxygen, pH, specific conductance, and temperature the constituents regulated by the Safe Drinking Water
stabilized. Samples were not collected until the purging Act.
was completed. Samples were collected directly from The pesticides analyzed include many of those
the well discharge, ensuring that the water had not regulated by the Safe Drinking Water Act, as well as
undergone any sort of treatment (for example, filtration others that are under consideration for regulation. Most
or chlorination) prior to collection. of these pesticides are very soluble in water thus more
VOC vials were filled from a cleaned brass con- likely to occur in source waters. Most of these pesticides
nection screwed to the well spigot. The purpose of the also are widely used and include the herbicides atrazine
brass connection was to protect the sample from contact and 2,4-D and the insecticides carbaryl and dieldrin.
with the atmosphere. Hydrochloric acid was immedi- In this report, nitrate refers to the sum of nitrite
ately added to each vial to lower the pH to <2.0, as a pre- plus nitrate nitrogen, which consists primarily of nitrate
servative. Vials were agitated and checked to make sure with negligible amounts of nitrite. Nitrite plus nitrate
no air bubbles were trapped inside, then stored on ice. nitrogen was analyzed in the samples from 174 PWS
Samples for pesticide analysis were either filtered wells because the presence of nitrate could be an indica-
in-line, when possible, or collected in a 3-L Teflon tor of other types of contamination. For example, nitrate
bottle and filtered off-site. In either case, water was is commonly used in fertilizer, and its occurrence in
filtered into two 1-L baked glass amber bottles using a high concentrations in drinking water might indicate
baked 0.7-µm pore-size glass-fiber filter in a stainless contamination by agricultural runoff. In addition, con-
steel or aluminum filter apparatus. Samples were chilled centrations of nitrate exceed the U.S. Environmental
on ice and returned to the USGS laboratory in Austin, Protection Agency (1996) maximum contaminant level
Tex., for solid-phase extraction. (MCL) of 10 milligrams per liter (mg/L) in drinking
water relatively often (U.S. Geological Survey, 2001).
The nitrite plus nitrate sample was collected by
repeatedly filling a 40-mL syringe fitted with a polypro- Tritium was analyzed in ground water as an indi-
pylene filter holder and filtering the sample through a cation of the age of the water (Schlosser and others,
0.5-µm pore-size cellulose-acetate filter into a 125-mL 1988). Tritium is a radionuclide produced naturally in
high-density polyethylene (HDPE) bottle. Nitrite plus the outer atmosphere. It is also produced by nuclear
nitrate samples were stored on ice for shipping to the reactors and nuclear-weapons testing. It is incorporated
laboratory. The 1-L tritium sample was collected in a into the water molecule and has a half-life of 12.3 years,
HDPE bottle; no filtering or treatment was required for two characteristics that make it useful as an indicator of
this sample. ground-water age, particularly for differentiating
between older (pre-1953) and younger (post-1953)
Quality-Control Samples water. The analysis of tritium was included in this study
to assist the SWAP in determining if the occurrence of
Quality-control samples for this study included tritium, a sign of relatively young waters, might be a
trip blanks (for VOCs in reservoirs only), field blanks, useful indicator of contamination.
replicate samples, and spiked samples. The number of
quality-control samples collected is about 20 percent of Methods
the number of environmental samples collected.
The VOCs were analyzed at the USGS National
Water Quality Laboratory (NWQL) in Denver, Colo.,
Analysis of Data
by gas chromatograph/mass spectrometry (GC/MS) at a
The VOCs analyzed were methyl tert-butyl minimum reporting level (MRL) of 0.2 microgram per
ether (MTBE, a gasoline oxygenate) and the BTEX liter (µg/L). The procedures are described by Connor
compounds (benzene, toluene, ethylbenzene, and total, and others (1998). Samples for pesticide analysis were
o-, and m- and p-xylene). These compounds were first extracted onto solid-phase columns at the USGS
chosen because there is currently much interest in the laboratory in Austin, then submitted to the NWQL for
occurrence of MTBE in the environment and because analysis by GC/MS. Pesticide analytical procedures are
the BTEX compounds are among the more commonly described by Zaugg and others (1995) and Werner and
occurring VOCs in surface and ground water (Grady others (1996). Nitrite plus nitrate was analyzed at the
and Casey, 2000). The BTEX compounds are among NWQL by colorimetry and cadmium reduction and by
4 Volatile Organic Compound and Pesticide Data for Public Water-Supply Reservoirs and Wells, Texas, 1999–2001
diazotization, as described by Fishman (1993), at an 6 reservoirs, and xylenes in 11 reservoirs. The highest
MRL of 0.05 mg/L. Tritium was analyzed at the USGS concentrations of BTEX compounds were 0.75 µg/L of
National Research Program Laboratory in Menlo Park, benzene, 2.9 µg/L of toluene, 0.44 µg/L of ethylben-
Calif. Tritium analysis was done by electrolytic enrich- zene, and 2.2 µg/L of total xylene in a sample from Lake
ment and liquid scintillation (Thatcher and others, Medina. These concentrations are well below the MCLs
1977) at an MRL of 2.5 picocuries per liter (pCi/L). of 5.0 µg/L for benzene, 1,000 µg/L for toluene, 700
Analytical results are listed in tables 1–6 (at end µg/L for ethylbenzene, and 10,000 µg/L for total xylene.
of report). Concentrations are reported as less-than
Concentrations of BTEX also were affected by high rec-
values, estimated values, or actual sample values. Less-
reational use of lakes over the Fourth of July weekend.
than values are reported when the constituent was not
Toluene concentrations in three of the four reservoirs
detected above a specified concentration. Less-than
and xylene concentrations in two reservoirs were higher
values are based on the MRL, defined as the lowest con-
following the high-use weekend; in two reservoirs, ben-
centration of a constituent that can be identified and
zene and ethylbenzene were not detected before the
quantitated within known statistical limits. The MRL
high-use weekend but were detected afterward at con-
could be raised as a result of high concentrations of tar-
centrations less than the MRL. On the basis of the Sign
get or non-target constituents. Estimated values are con-
Test for matched pairs, these differences are not signifi-
centrations that are less than the MRL but greater than
cant at alpha = 0.1.
the laboratory method detection limit. These concentra-
tions are identified as estimated values because of the One or more pesticides were detected in 46 of the
uncertainty associated with concentrations less than the 48 reservoirs (96 percent) (table 2). The pesticide detec-
MRL. Estimated values thus are counted as a detection, tions are summarized in table 3. Of the 10 pesticides
but quantification of the concentration is uncertain as analyzed for which MCLs have been established, only 4
estimated values are typically outside of the calibration pesticides were detected, and concentrations did not
range of the method.
exceed those respective MCLs. Atrazine, the most com-
monly detected pesticide, was detected in every reser-
Environmental Samples
voir except two, Lakes Murvaul and Sweetwater; no
Reservoirs pesticides were detected in samples from those two
lakes. The highest atrazine concentration was 1.4 µg/L
One or more VOCs were detected in 36 of the
from Granger Lake. The MCL for atrazine is 3.0 µg/L.
48 PWS reservoirs (75 percent) during the June–July
Deethylatrazine, a breakdown product of atrazine, was
1999 sampling (table 1). MTBE was detected in 34 of
detected in 43 reservoirs.
the 48 reservoirs; all concentrations were well below the
USEPA drinking-water advisory level of 20 to 40 µg/L The next two most commonly detected pesticides
issued for reasons of taste and smell (U.S. Environmen- were simazine and metolachlor, detected in 29 and 28
tal Protection Agency, 1997). Eleven reservoirs had reservoirs, respectively. The highest concentration of
MTBE concentrations exceeding 1.0 µg/L. The highest simazine was 0.52 µg/L in Lake Ray Hubbard. The
concentration of MTBE detected during this investiga- MCL for simazine is 4.0 µg/L, and the U.S. Environ-
tion was 4.1 µg/L in a sample from Grapevine Lake. mental Protection Agency (1996) lifetime Health Advi-
To investigate the influence of recreational use of sory (HA) level is 1.0 µg/L. The highest concentration
gasoline-powered vehicles on MTBE concentrations, of metolachlor was 0.29 µg/L in Aquilla Lake. The HA
four reservoirs with high recreational use (Granger for metolachlor is 70 µg/L.
Lake, Lake Belton, Lake Travis, and Lake Waco) were
The most pesticides detected in any reservoir was
sampled before and after the Fourth of July weekend. In
each case, the MTBE concentration after the high-use 12, in Lake Texana. Other reservoirs with eight or more
weekend was greater than that analyzed previously. On pesticides detected were Buffalo Springs Lake, Granger
the basis of the Sign Test for matched pairs (Helsel and Lake, Lake Houston, Lavon Lake, and Livingston
Hirsch, 1992), the difference is significant at p = 0.06. Reservoir. Of the 46 reservoirs with pesticide detec-
Occurrence of the BTEX compounds was less tions, 45 reservoirs (94 percent) had detections of two or
widespread than that of MTBE. Benzene was detected more pesticides, and 27 reservoirs (59 percent) had
in 6 reservoirs, toluene in 19 reservoirs, ethylbenzene in detections of five or more pesticides.
VOLATILE ORGANIC COMPOUND AND PESTICIDE DATA 5
