# Occurrence and Temporal Variability of Methyl tert -Butyl Ether (MTBE) and Other Volatile Organic Compounds in Select Sources of Drinking Water: Results of the Focused Survey

Water-Resources Investigations Report 02-4084

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

# NATIONAL WATER-QUALITY ASSESSMENT PROGRAM NATIONAL SYNTHESIS ON VOLATILE ORGANIC COMPOUNDS

Prepared in cooperation with the Metropolitan Water District of Southern California, Oregon Health & Science University, and the American Water Works Association Research Foundation

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

# Occurrence and Temporal Variability of Methyl tert -Butyl Ether (MTBE) and Other Volatile Organic Compounds in Select Sources of Drinking Water: Results of the Focused Survey

By Gregory C. Delzer and Tamara Ivahnenko

Water-Resources Investig ations Report 02-4084

Prepared in cooperation with the Me tropolitan Water District of Southern California, Oregon Health & Science University, and the American Water Works Ass ociation Research Foundation

# U.S. Department of the Interior GALE A. NORTON, Secretary U.S. Geological Survey Charles G. Groat, Director

The use of firm, trade, and brand names in th is report is for ident ification purpose s only and doe s not consti

tute endorsement by the U.S. Government.
Rapid City, Sout h Dakota: 2003

For additional information write to: District Chief U.S. Geological Survey 1608 Mt. View Road Rapid City, SD 57702 Copies of this report can be purchased from: U.S. Geological Survey Information Services Building 810 Box 25286, Federal Center Denver, CO 80225-0286**Foreword III** 

# FOREWORD The U.S. Geological Survey (USGS) is committed to providing the Nation with accurate and timely scientific informatio n that helps enhance and protect the overall quality of life and that facilitates effective management of water, biological, energy, and mineral resources (http://www.usgs.gov/). Information on the quality of the Nation’s water resources is critical to assuring the long- term availability of water that is safe for drinking and recreation and suitable for industry, irrigation, and hab itat for fish and wildlife. Population growth and increasing demands for multiple water uses make water availability, now measured in terms of quantity and quality, even more essential to the long-term sustainability of our communities an d ecosystems.The USGS implemented the National WaterQuality Assessment (NAWQA) Program in 1991 to support national, regional, and local information needs and decisions related to water-quality management and policy (http://water.usg s.gov/nawqa). Shaped by and coordinated with ongoing efforts of other Federal, State, and local agencies, the NAWQA Program is designed to answer: What is the condition of our Nation’s streams and ground water? How are the conditions changing over time? How do natural features and human activities affect the quality of streams and ground water, and where are those effects most pronounced? By combining information on water chemistry, physical characteristics, stream habitat, and aquatic life, the NAWQA Program aims to provide science-based insights for current and emerging water issues and priorities. From 1991-2001, the NAWQA Program completed interdisciplinary assessments in 51 of the Nation’s major river basins and aquifer systems, referred to as Study Units (http://water.usgs.gov/ nawqa/studyu.html). Baseline conditions were established for comparison tofuture assessments, and long-term monitoring was in itiated in many of the basins. During the next decade, 42 of the 51 Study Units will be reassessed so that 10 years of comparable monitoring data will be available to determine trends at many of the Nation’s streams and aquifers. The next 10 years of study also will fill in critical gaps in characterizing water-quality conditions, enhance understanding of factors that affect water quality, and establish links between sources of contaminants, the transport of those contaminants through the hydrologic system, and the potential effects of contaminants on humans and aquatic ecosystems. The USGS aims to disseminate credible, timely, and relevant science inform ation to inform practical and effective water-resource management and strategies that protect and restore water quality. We hope this NAWQA publication will provide you with insights and information to meet your needs, and will foster increased citizen aw areness and involvement in the protection and restoration of our Nation’s waters. The USGS recognizes that a national assessment by a single program cannot address all water-resource issues of interest. External coordination at all levels is critical for a fullyintegrated understanding of watersheds and for costeffective management, regulation, and conservation of our Nation’s water resources. The NAWQA Program, therefore, depends on advice and information from other agencies—Federal, State, interstate, Tribal, and local—as well as nongovernmental organizations, industry, academia, and other stakeholder groups. Your assistance and suggestions are greatly appreciated.

Robert M. Hirsch Associate Director for Water**Contents V** 

# CONTENTS

Abstract....................................................................................................................... ........................................................... 1 Introduction ................................................................................................................... ........................................................ 2 Purpose and Scope.............................................................................................................. ......................................... 6 Acknowledgments ................................................................................................................ ....................................... 6 Study Design................................................................................................................... ....................................................... 7 Site Selection ................................................................................................................. .............................................. 7 Sample Collection.............................................................................................................. .......................................... 9 Occurrence and Temporal Variability of Volatile Organic Compounds .............

.............. .............. ............ ......... .................. 10 Occurrence and Comparison to the Ran dom Survey................................................................................. .................. 10 Temporal Variability ........................................................................................................... ......................................... 19 Ground Water................................................................................................................... .................................. 20 Reservoirs and Lakes........................................................................................................... .............................. 22 Rivers and Streams ............................................................................................................. ............................... 23 Anthropogenic Factors Associated with MTBE, Gasoline Oxygenates, and Trihalomethanes ........................................... . 25 MTBE and Gasoline Oxygenates ................................................................................................... ............................. 25 Trihalomethanes ................................................................................................................ .......................................... 28 Summary and Conclusions ........................................................................................................ ............................................ 29 References ..................................................................................................................... ........................................................ 31 Appendixes ..................................................................................................................... ....................................................... 33 A. Number of community water system sources sampled per State ................................................................. ......... 35 B. Detailed review of field quality-control data ..

............................................................................ ........................... 39 C. Data acceptance criteria using quality-control data ........................................................................ ....................... 53 D. Summary of VOC concentrations in the Focused Survey ........................................................................ ............. 61
FIGURES 1. Map showing methyl tert-butyl ether (MTBE) high-use areas and location of source waters sampled in the Focused Survey.................................................................................................. ................................. 8 2-8. Graphs showing: 2. Detection frequency at or above the minimum reporting level of individual volatile organic compounds in source waters sampled in the Focused Surveyversus the Random Survey..

.............. ........... ..... 11 3. Detection frequency at or above the minimum reporting level of volatile organic compound subgroups in community water system source waters sampled in the Focused Survey and the Random Survey .......................................................................................................... ........................... 15 4. Detection frequency at or above the minimum reporting level of any volatile organic compound (VOC) and subgroup of VOCs in ground-water sources sampled in the Focused Survey and Random Survey by size of community water system...........
.............. .............. ........... ..... 17 5. Detection frequency at or above the minimum reporting level of any volatile organic compound (VOC) and subgroup of VOCs in surface-water sources sampled in the Focused Survey and Random Survey by size of community water system...........
.............. .............. ........... ..... 18 6. Number of surface-water samples collected by source ty pe and season ......

.............. ............... .............. ......... . 19 7. Detection frequency at or above the minimum reporting level of any volatile organic compound (VOC) and by subgroup of VOCs in community water system source waters by source type.......................................................................................................... ............................... 20 8. Comparison of the detection frequency of at least one volatile organic compound (VOC) at or above the method detection limit by subgroup of VOCs in the first and second sampling of ground-water source water.......................................................................................... ................... 21**VI Contents** 

### FIGURES—Continued

9. Boxplots of detected concentr ations of volatile organic compound subgroups in ground-water source water collected in the first and second samples .

........................................................................ ..................... 21 10. Graph showing detection frequency of at least one volatile organic compound (VOC) at or above the method detection limit by subgroup of VOCs in reservoir and lake source waters by s eason........ .............. ....... 22 11. Boxplots of detected concentrations of volatile organic compound subgroups in reservoir and lake source waters by season............................................................................................... ................................ 23 12. Graph showing detection frequency of at least one volatile organic compound (VOC) at or above the method detection limit by subgroup of VOCs in river and stream source waters by seas on .......... .............. ....... 24 13. Boxplots of detected concentrations of volatile organic compound subgroups in river and stream source waters by season............................................................................................. .............................. 24 14. Boxplots of detected concentrations of methyl tert-butyl ether (MTBE) in reservoir and lake source waters by location in MTBE low- and high-use areas ................................................................. ........... 26 15. Boxplots of detected concentrations of methyl tert-butyl ether (MTBE) in river and stream source waters by location in MTBE low- and high-use areas...................................................................... .............. 27 16. Graph showing average sum of gasoline oxygenate concentrati ons versus watercraft-use f actor........
.............. ....... 27 17. Boxplots of average concentrations of gasoline oxygenate s by watercraft-use quartiles ....................................... ... 28 B1. Graph showing concentration of methyl tert-butyl ether in field duplicate and s ource-water samples..................... 47
TABLES 1. Volatile organic compounds (VOCs) analyzed as part of the Focused Survey and related information by subgroups of VOCs............................................................................................... ......................... 4 2. Summary of number of source waters sampled, frequency of sample collection, and number of samples collected during the Focu sed Survey................................................................................. ................... 9 3. Summary of the frequency and number of quality-contro l samples collected during the Focused Survey ........... 9 4. Summary of detection frequencies of any volatile organic compound (VOC), any subgroup of VOCs, and individual VOCs in source waters sampled in the Focu sed and Random Surveys.......................................... 12 5. Distribution of source waters sampled in the Focused and Random Surveys by source-type and size of community water system based on population served .

.......................................................................... ............ 16 A1. Number of Community Water System source waters sampled that were suspected of having concentrations of methyl tert-butyl ether, by State and so urce-size category ........................................................ 36 A2. Number of Community Water System source waters sampled with known concentrations of methyl tert-butyl ether, by State and source-si ze category................................................................................ ..... 37 A3. Number of Community Water System source waters sampled as control sites where methyl tert-butyl ether would likely not be present, by State and source-size category .................................................... 37 B1. Summary of volatile organic compounds detected in field-equipment blanks, field-reagent blanks, and trip-reagent blanks ........................................................................................................ ................................... 41 B2. Relation between concentrations of volatile organic compounds in 292 companion field blank samples and trip blank samples ...

.............................................................................................. ............................. 48 B3. Relation between concentrations of volatile organic compounds in 27 companion field equipment blank samples and field reagent blank samples.................................................................................. .................... 49 B4. Relation between concentrations of volatile organic compounds in 27 companion field equipment blank samples and trip reagent blank samples................................................................................... ..................... 50 B5. Statistical comparison of concentrations of volatile organic compounds in source-water and duplicate samples.............................................................................................................. ...................................... 51 C1. Schematic diagram for adjusting the frequency of detection of volatile organic compounds in source-water samples to reflect possible random sample c ontamination........................................................... .... 54 C2. Number of source-water samples that meet specified conditions at the method detection limit, with respect to the possibility of random contaminatio n........................................................................ ................ 56 C3. Detection frequency of volatile organic compounds detected at or above the method detection level in source water before and after applying the quality-control screening process.......................................... 58 C4. Schematic diagram for adjusting the frequency of detection of methyl tert-butyl ether in source-water samples to reflect possible random sample c ontamination........................................................... .... 60 D1. Statistical summary of volatile organic compounds in source-water samples in the Focu sed Survey...... ............. 62**Abstract 1** 

# Occurrence and Temporal Variability of Methyl tert -Butyl Ether (MTBE) and Other Volatile Organic Compounds in Select Sources of Drinking Water: Results of the Focused Survey By Gregory C. Delzer and Tamara Ivahnenko
ABSTRACT The large-scale use of the gasoline oxygen

ate methyl tert-butyl ether (MTBE), and its high solubility, low soil ad sorption, and low biodegrad

ability, has resulted in its detection in ground water and surface water in many places throughout the United States. Studies by numerous researchers, as well as many State and local environmental agencies, have discovered high levels of MTBE in soils and ground water at leaking underground gasoline-storage-tank s ites and frequent occur

rence of low to intermediate levels of MTBE in reservoirs used for both public water supply and recreational boating. In response to these findings, the American Water Works Association Research Foundation sponsored an investigation of MTBE and other volatile organic compounds (VOCs) in the Nation’s sources of drinking water. The goal of the investigation was to provide additional informa

tion on the frequency of occurrence, concentra

tion, and temporal variability of MTBE and other VOCs in source water used by community water systems (CWSs). The investigation was completed in two stages: (1) reviews of available literature and (2) the collection of new data. Two surveys were associated with the collection of new data. The first, termed the Random Survey, employed a statistically stratified design for sampling source water from 954 randomly selected CWSs. The second, which is the focus of this report, is termed the Focused Survey, which included samples col

lected from 134 CWS source waters, including ground water, reservoirs, lakes, rivers, and streams, that were suspected or known to contain MTBE. The general intent of the Focused Survey was to compare results with the Random Survey and provide an improved understanding of the occurrence, concentration, temporal variability, and anthropogenic factors associated with fre

quently detected VOCs. Each sample collected was analyzed for 66 VOCs, including MTBE and three other ether gas

oline oxygenates (hereafter termed gasoline oxy

genates). As part of the Focused Survey, 451source-water samples and 744 field qualitycontrol (QC) samples were collected from 78 ground-water, 39 reservoir and (or) lake, and 17 river and (or) stream source waters at fixed inter

vals for a period of 1 year. Using a common assessment level of 0.2 μ g/L (micrograms per liter) (2.0 μ g/L for methyl ethyl ketone), 37 of the 66 VOCs analyzed were detected in both surveys. However, VOCs, especially MTBE and other gasoline oxygenates, were detected more frequently in the Focused Survey than in the Random Survey. MTBE was detected in 55.5 percent of the CWSs sampled in the Focused Survey and in 8.7 percent of those sampled in the Random Survey. Little difference in occurrence, however, was observed for triha

lomethanes (THMs), which were detected in 16.4 and 14.8 percent of Focused Survey and**2 Occurrence and Temporal Variability of MTBE a nd Other VOCs in Select Sources of Drinking Water**  

## Random Survey CWSs, respectively. This may indicate a pervasive occurrence of THMs in several source-water types, regardless of CWS size or geographic location. Using data at or abovethe method detection limit to assess temporal variability and anthropo

genic factors associated with frequent detection of select VOCs, concentrations in the Focused Survey in ground-water, reservoir, and river source waters were typically less than 1 μ g/L. Also, at a 95-percent confidence interval, no statistically significant differences were observed in compar

ing concentrations in the first and second groundwater sample. A weak seasonal pattern was observed in samples collected from reservoirs and lakes where gasoline oxygenates and other gaso

line compounds were detected more frequently during spring and summer, presumedly a result of increased use of motorized watercraft during these seasons. In contrast, seas onal patterns were not observed in samples collected from rivers and streams. The lack of s easonal differences in river and stream source waters sampled may indicate a common and continuous source of contamination. The most frequently detected VOC (MTBE) and the two most frequently occurring subgroups of VOCs (gasoline oxygenates and THMs) detected in CWS source waters were further char

acterized to evaluate so me anthropogenic factors that may better explain their frequent occurrence. Gasoline oxygenates weredetected in 73.9 percent of all CWSs sampled. The concentration of gaso

line oxygenates was slightlycorrelated with water

craft use on reservoirs inside MTBE high-use areas (r2 

## =0.3783) but not outside of these areas (r2 

## =0.0242). In general, the concentration of gaso

line oxygenates increased as watercraft use increased. THMs were detected in 47.8 percent of the CWSs supplied by surface water. The frequent occurrence of THMs in re servoir source waters was determined to be an artifact of disinfection and the recycling of chlorinated water to these reser

voirs. All CWSs with frequent occurrence of THMs served by a reservoir indicated that chlorine was added to waters for various reasons and that the chlorinated water was then released back to, or upstream of, the reservoir or lake that was sampled. 

## INTRODUCTION The gasoline oxygenate methyl tert-butyl ether (MTBE) has been added to gasoline to enhance octane levels since the late 1970’s, and in 1990, the Clean AirAct (CAA) Amendments mandated seasonal or yearround use of oxygenated compounds (oxygenates) in gasoline in specific parts of the United States. Oxygen

ates are added to gasoline to increase the oxygen content, which enhances combustion and decreases vehicular carbon monoxide emissions. Oxygenatesalso reduce the need for benzene and other ozoneforming, aromatic compound s in gasoline. MTBE is the most commonly used oxygenate, followed by ethanol. Oxygenates are added to gasoline during the winter months in areas where winter concentrations of carbon monoxide exceed es tablished air-quality stan

dards. This gasoline is called oxygenated (OXY) gaso

line, which contains oxygenates at 2.7 percent by weight (15 percent by volume for MTBE) (U.S. Envi

ronmental Protection Agency, 1999b). In select areas, oxygenates are added to gasoline year round to abate ozone pollution during the summer months and carbon monoxide pollution during the winter months (U.S. Environmental Protection Agency, 1999a). This gaso

line is called reformulated gasoline (RFG), which con

tains oxygenates at 2 percent by weight (11 percent by volume for MTBE). The implementation of the CAA Amendments resulted in a substantial increase in the production and use of MTBE during the 1990’s. For example, MTBE went from the 39th highest produced organic chemical in the United States in 1970 to the fourth highest in 1998 (Johnson and others, 2000). During that period, the aggregate production of MTBE was 60 million metric tons. In 1998, 39.7 million liters per day were used in the United States, 40 percent of which was used in California alone. Most of MTBE use is associated with RFG. MTBE is used in only about 3 percent of OXY gasoline, whereas MTBE is used in about 85 percent of all RFG (Wigglesworth, 1999). MTBE is a possible human carcinogen. The U.S. Environmental Protection Agency (USEPA) has issued a taste and odor drinking water advisory of concentra

tions in the range of 20 to 40 μ g/L (micrograms per liter) to avert unpleasant taste and odor effects in drinking water causing it to become non-potable (U.S. Environmental Protection Agency, 1997). The chem

ical properties of MTBE, such as high solubility in water, low soil-sorption properties, and low biodegrad

ability in ground water may result in contamination of**Introduction 3** 

### some private and public source waters, and some cities have lost substantial amounts of drinking-water sup

plies to MTBE contamination. For example, in Santa Monica, California, 75 percent of the drinking-water wells are now unusable due to MTBE; in South Lake Tahoe, California, one-third of the city's 34 drinkingwater wells have been shut down because of MTBE contamination; in Windham, Maine, wells have been taken offline; and Los Angeles, San Francisco, Santa Clara Valley, and Sacramento in California all have wells affected by MTBE (Bourelle, 1998; State of Maine, 1998; City of Santa Monica, 1999; California Department of Health Services, 2001). La Crosse, Kansas, also has had wells affected by MTBE; how

ever, officials there have taken steps to remediate the problem and to treat the water rather than to remove the wells from service (Hattan, 2000). Although isolated instances of MTBE contami

nation have been observed, the overall extent of MTBE occurrence in the Nation's drinking-water supplies has not been fully evaluated. The Interagency Assessment of Oxygenated Fuels (Zogorski and others, 1997) attempted to address the national occurrence of MTBE in drinking-water supplies, but was unable to do so due to insufficient data. As a result, additional assessments were recommended. One such assessment, the focus of this report, was sponsored by the American Water Works Associa

tion Research Foundation (AWWARF), an organization that sponsors numerous rese arch studies for the benefit of the drinking-water community. This assessment of MTBE in the Nation's drinking-water supplies was completed by the Metropolitan Water District of Southern California (MWDSC), the U.S. Geological Survey (USGS) National Water-Quality Assessment (NAWQA) Program, and the Oregon Health & Science University (OHSU). This assessment studied not only MTBE but also 65 other volatile organic compounds (VOCs), including other ether gasoline oxygenates(hereafter termed gasoline oxygenates) in drinkingwater supplies (table 1), and tert-butyl alcohol (TBA)—a degradation by-product of MTBE. However, TBA results are not presented herein. Drinking-water supplies studied were specifi

cally termed source waters. Source water is defined by the American Water Works A ssociation as “the supply of water for a water utility [that] is usually treated before distribution to consumers.” A source water can be a river, brook, stream, lake, reservoir, impoundment, spring, or aquifer from which a supply of water is obtained. As such, the assessment did not study any waters that are within a distribution line or after treat

ment processes have beenapplied to the water. The complete list of comp ounds included in this assessment also included 13 VOCs that are on the USEPA’s Contaminant Candidate List (CCL) (U.S. Environmental Protection Agency, 1998). The CCL is a list of contaminants not currently regulated by a National Primary Drinking Water Standard. Addi

tional data on these compounds are needed before a regulatory determination canbe made. This national assessment of MTBE and other VOCs began in September 1998. The national assessment of MTBE and other VOCs in source-water supp lies was accomplished by a two-phase approach: (1) reviews of available litera

ture, and (2) the collection of new drinking-waterquality data. The literature review was conducted in two phases. One review focused on MTBE taste and odor threshold concentratio ns and their relevance to aesthetic effects and possib le water-treatment require

ments. The second review concentrated on the occur

rence of MTBE in public and domestic drinking-water supplies reported by national, regional, or statewide assessments (Delzer and Ivahnenko, 2003). Two surveys were associated with the collection of new drinking-water data. The first survey, termed the Random Source-Water Survey (hereafter termed Random Survey), employed a statistically stratified design for sampling source water from 954 commu

nity water systems (CWSs) randomly selected on the basis of the total number of systems within five popu

lation served-size categories, source-water type, and the total number of peopleserved by each of the source-size categories used within the United States. Findings of the Random Survey are reported else

where (Rowe and others, 2001; Grady, 2003). The second survey, which is the focus of this report, is termed the Focused Source-W ater Survey (hereafter termed Focused Survey). The Focused Survey included samples collectedfrom CWS source waters that were selected on the basi s of factors that appear to be or are known to be related to the frequent detection of MTBE in water. The Focused Survey provides an improved understanding of the occurrence, concentra

tion, temporal variability, and anthropogenic factors associated with the detection of MTBE and other fre

quently identified VOCs. It is important to note, for both the Random Survey and the Focused Survey, that CWSs were promised anonymity in presenting results. Specific information on the design of the Random and Focused Surveys is detailed in Ivahnenko and others (2001).**4 Occurrence and Temporal Variability of MTBE a nd Other VOCs in Select Sources of Drinking Water**  **Table 1**

. Volatile organic compounds (VOCs) analyzed as part of t he Focused Survey and related information by subgroups of VOCs [IUPAC, International Union of Pure and App lied Chemistry; --, none; CCL, compound islisted on the U.S. Environmental Protecti on Agency’s Contami

nant Candidate List] **Compound name (used**

**throughout report) Chemical**  **abstract service number**  **IUPAC name Other common names**  **Chemical formula**  Gasoline Oxygenates tert-Amyl methyl ether (TAME) 994-05-8 2-Methoxy-2-methylbutane

-- C 6 H 14 O Diisopropyl ether (DIPE) 108-20-3 2,2 ′ -oxybis[propane]

-- C 6 H 14 O Ethyl tert-butyl ether (ETBE) 637-92-3 2-Ethoxy-2-methylpropane

-- C 6 H 14 O Methyl tert-butyl ether (MTBE) CCL 1634-04-4 2-Methoxy-2-methylpropane

-- C 5 H 12 O Other Gasoline Compounds Benzene 71-43-2 Benzene

-- C 6 H 6
n -Butylbenzene 104-51-8 n -Butylbenzene 1-Phenylbutane C 10H 14
sec -Butylbenzene 135-98-8 (1-Methylpropyl)benzene

-- C 10H 14 tert-Butylbenzene 98-06-6 (1,1-Dimethylethyl)benzene

-- C 10H 14 Ethylbenzene 100-41-4 Ethylbenzene Phenylethane C 8 H 10 Naphthalene CCL 91-20-3 Naphthalene

-- C 10H 8 Toluene 108-88-3 Methylbenzene

-- C 7 H 8 1,3,5-Trimethylbenzene 108-67-8 1,3,5-Trimethylbenzene Mesitylene C 9 H 12
m ,

p -Xylene 108-38-3/ 106-42-3 1,3-Dimethylbenzene and 1,4-Dimethylbenzene m -Xylene, p -Xylene C 8 H 10

o -Xylene 95-47-6 1,2-Dimethylbenzene

-- C 8 H 10 Trihalomethanes Bromodichloromethane 75-27-4 Bromodichloromethane Dichlorobromomethane CHBrCl 2 Bromoform 75-25-2 Tribromomethane

-- CHBr 3 Chlorodibromomethane 124-48-1 Chlorodibromomethane Dibromochloromethane CHBr2 Cl Chloroform 67-66-3 Trichloromethane

-- CHCl 3 Solvents Bromobenzene CCL 108-86-1 Bromobenzene Phenyl bromide C 6 H 5 Br Carbon tetrachloride 56-23-5 Tetrachloromethane

-- CCl 4 Chlorobenzene 108-90-7 Chlorobenzene Monochlorobenzene C 6 H 5 Cl Chloroethane 75-00-3 Chloroethane Ethyl chloride C 2H 5 Cl 2-Chlorotoluene 95-49-8 1-Chloro-2-methylbenzene o -chlorotoluene C 7 H 7 Cl 4-Chlorotoluene 106-43-4 1-Chloro-4-methylbenzene p -chlorotoluene C 7 H 7 Cl Dibromomethane 74-95-3 Dibromomethane Methylene bromide CH 2Br2 1,2-Dichlorobenzene 95-50-1 1,2-Dichlorobenzene o -Dichlorobenzene C 6 H4 Cl 2 1,3-Dichlorobenzene 541-73-1 1,3-Dichlorobenzene m -dichlorobenzene C 6 H4 Cl 2 1,1-Dichloroethane CCL 75-34-3 1,1-Dichloroethane Ethylidene chloride C 2H4 Cl 2**Introduction 5** Solvents—Continued 1,2-Dichloroethane 107-06-2 1,2-Dichloroethane Ethylene dichloride C 2H4 Cl 2 1,1-Dichloroethene 75-35-4 1,1-Dichloroethene Vinylidene chloride C 2H 2 Cl 2 cis -1,2-Dichloroethene 156-59-2 cis -1,2-Dichloroethene (Z)-1,2-dichloroethene C 2H 2 Cl 2 trans -1,2-Dichloroethene 156-60-5 trans -1,2-Dichloroethene (E)-1,2-dichloroethene C 2H 2 Cl 2 1,2-Dichloropropane 78-87-5 1,2-Dichloropropane Propylene dichloride C 3 H 6 Cl 2 Hexachloroethane 67-72-1 1,1,1,2,2,2-Hexachloroethane Carbon hexachloride C 2 Cl 6 Methylene chloride 75-09-2 Dichloromethane

-- CH 2 Cl 2 Methyl ethyl ketone (MEK) 78-93-3 2-Butanone

-- C 4 H 8 O

n -Propylbenzene 103-65-1 n -Propylbenzene 1-Phenylpropane C 9 H 12 1,1,1,2-Tetrachloroethane 630-20-6 1,1,1,2-Tetrachloroethane

-- C 2H 2 Cl 4 1,1,2,2-Tetrachloroethane CCL 79-34-5 1,1,2,2-Tetrachloroethane

-- C 2H 2 Cl 4 Tetrachloroethene 127-18-4 Tetrachloroethene Perchloroethene, PCE C 2 Cl 4 1,2,4-Trichlorobenzene 120-82-1 1,2,4-Trichlorobenzene

-- C 6 H 3 Cl 3 1,1,1-Trichloroethane 71-55-6 1,1,1-Trichloroethane Methyl chloroform C 2H 3 Cl 3 1,1,2-Trichloroethane 79-00-5 1,1,2-Trichloroethane Vinyl trichloride C 2H 3 Cl 3 Trichloroethene (TCE) 79-01-6 Trichloroethene Trichloroethylene C 2HCl 3 1,2,3-Trichloropropane 96-18-4 1,2,3-Trichloropropane Allyl trichloride C 3 H 5 Cl 3 Organic Synthesis Acrylonitrile 107-13-1 2-Propenenitrile

-- C 3 H 3 N Bromochloromethane 74-97-5 Bromochloromethane Methylene chlorobromide CH 2BrCl 1,3-Dichloropropane CCL 142-28-9 1,3-Dichloropropane Trimethylene dichloride C 3 H 6 Cl 2 2,2-Dichloropropane CCL 594-20-7 2,2-Dichloropropane

-- C 3 H 6 Cl 2 1,1-Dichloropropene CCL 563-58-6 1,1-Dichloropropene

-- C 3 H4 Cl 2 Hexachlorobutadiene CCL 87-68-3 1,1,2,3,4,4-Hexachloro-1,3-butadiene

-- C 4 Cl 6 Isopropylbenzene 98-82-8 (1-Methylethyl)benzene Cumene C 9 H 12 p -Isopropyltoluene CCL 99-87-6 1-Isopropyl-4-methylbenzene

-- C 10H 14 Styrene 100-42-5 Ethenylbenzene Vinyl benzene C 8 H 8 1,2,3-Trichlorobenzene 87-61-6 1,2,3-Trichlorobenzene

-- C 6 H 3 Cl 3 1,2,4-Trimethylbenzene CCL 95-63-6 1,2,4-Trimethylbenzene Pseudocumene C 9 H 12 Vinyl bromide 593-60-2 Bromoethene

-- C 2H 3 Br Vinyl chloride 75-01-4 Chloroethene

-- C 2H 3 Cl **Table 1** . Volatile organic compounds (VOCs) analyzed as part of the Focused Survey and relat ed information by subgroups of VOCs—Continued [IUPAC, International Union of Pure and App lied Chemistry; --, none; CCL, compound is listed on the U.S. Environmental Protecti on Agency’s Contaminant Candidate List] **Compound name (used**

**throughout report) Chemical**  **abstract service number**  **IUPAC name Other common names Chemical**  **formula 6 Occurrence and Temporal Variability of MTBE a**  **nd Other VOCs in Select Sources of Drinking Water** Fumigants Bromomethane CCL 74-83-9 Bromomethane Methyl bromide CH 3 Br 1,4-Dichlorobenzene 106-46-7 1,4-Dichlorobenzene p -Dichlorobenzene C 6 H4 Cl 2 cis -1,3-Dichloropropene CCL,1 10061-01-5 cis -1,3-Dichloropropene (Z)-1,3-Dichloropropene C 3 H4 Cl 2 trans -1,3-Dichloropropene CCL,1 10061-02-6 trans -1,3-Dichloropropene (E)-1,3-Dichloropropene C 3 H4 Cl 2 Refrigerants Chloromethane 74-87-3 Chloromethane Methyl chloride CH 3 Cl Dichlorodifluoromethane 75-71-8 Dichlorodifluoromethane CFC 12, Freon 12 CCl 2F2 Trichlorofluoromethane 75-69-4 Trichlorofluoromethane CFC 11, Freon 11 CCl 3 F1,1,2-Trichloro-1,2,2-trifluoroethane 76-13-1 1,1,2-Trichloro-1,2,2-trifluoroethane CFC 113, Freon 113 C 2 Cl 3 F 3

1 The CCL lists only 1,3-dichlo ropropene. The two isomers, cis - and trans -, are measured separately in the an alytical method usedin this study. **Table 1** . Volatile organic compounds (VOCs) analyzed as part of the Focused Survey and related information by subgroups of VOCs—Continued [IUPAC, International Union of Pure and App lied Chemistry; --, none; CCL, compound islisted on the U.S. Environmental Protecti on Agency’s Contaminant Candidate List] **Compound name (used**

**throughout report) Chemical**  **abstract service number**  **IUPAC name Other common names Chemical**  **formula**



## Purpose and Scope This report describes the occurrence and tem

poral variability of MTBE and other VOCs in CWS source water suspected or known to contain MTBE as part of the Focused Survey. In addition, comparisons between results of the Focused and Random Surveys on the occurrence of MTBE and other VOCs are summa

rized. This report also analyzes anthropogenic factors associated with the frequent occurrence of MTBE, other gasoline oxygenates, and trihalomethanes (THMs). The 451 samples were colle cted at fixed intervals from 78 ground-water, 39 reservoir and (or) lake, and 17 river and (or) stream source waters in selected areas of the Nation. In addition, 744 field quality-control (QC) samples were collected, including trip-reagent blanks, field-reagent blanks, field-equipment blanks, and duplicate samples. All data underwent a thorough quality-control review process to accept or reject source-water data for inclus ion in the Focused Survey. The resulting source-water data set included VOC con

centrations greater than the method detection limit (MDL). However, an assessment level equal to the min

imum reporting level (MRL) was used for comparing Focused Survey and Random Survey results. Temporal variability of subgroups of VOCs was characterized for CWSs supplied by surface water by examining the frequency of occurrence and detected concentrations by season of the year. VOC subgroups include gasoline oxygenates, other gasoline com

pounds (excluding gasoline oxygenates), THMs, sol

vents, organic synthesis compounds, fumigants, and refrigerants. Anthropogenic factors and their relation to concentrations of MTBE and two frequently occurring subgroups of VOCs—gasoline oxygenates and THMs—were examined. These factors include MTBE high-use areas, watercraft density, and ancillary infor

mation obtained from CWS personnel. These factors were characterized to determine their potential signifi

cance with respect to MTBE , gasoline oxygenates, and THM contamination. 

## Acknowledgments
The authors would like to thank the AWWARF and Kenan Ozekin for their support and oversight of this study. Also, the AWWARF project advisory com

mittee, consisting of Homer C. Emery of the San Antonio Water System, David Lipsky of the New York**Study Design 7** 

### City Department of Environmental Protection, and Howard Weinberg of the University of North Carolina, are recognized for their technical advice. Importantly, this assessment would not have been possible without the cooperation and assistance of the owners, operators, and staff of the CWSs that allowed access to sample their source waters. The cooperation and assistance of the 31 USGS District offices that collected samples and worked directly with CWSs is greatlyappreciated. All chemicalanalyses for volatile organic compounds in sourcewater samples were conducted at the MWDSC labora

tory in LaVerne, California, under the direction of Bart Koch and Melissa Dale. The authors would like to thank John Zogorski, Stephen Grady, Rick Clawges, and Barbara Rowe of the USGS, Bart Koch of the MWDSC, and Paul Tratnyek of the Oregon Health & Science University for their technical questions, com

ments, and suggestions during the design and imple

mentation of this study. Bart Koch of the MWDSC and Ryan Thompson and Stephen Grady of the USGS are thanked for pro

viding thorough technical review and insight to this report. Finally, Janet Carter, Ella Decker, Connie Ross, and Chester Zenone of the USGS provided valuable editorial review and assistance in completing this report.


## STUDY DESIGN The Focused Survey was designed to sample source waters suspected or known to be contaminated with MTBE. An equal number of samples was intended to be collected from ground-water, reservoir and (or) lake, and river and (or) stream source waters. Further

more, a fixed-interval samp ling was followed in orderto better understand temporal variability. Groundwater, reservoir and (or) lake, and river and (or) stream source waters were sampled biannually, quarterly, and eight times per year for one year, respectively. Finally, a rigorous field QC sampling regime and data interpre

tation process was followed in order to ensure that the samples collected were representative of the source water being sampled. Data from these field QC samples were used to accept or reject source-water data from the analyses presented in this report. 

## Site Selection The original design of the Focused Survey called for 480 samples to be collected at fixed intervals from 140 CWS source waters. Specifically, 80 ground-water, 40 reservoir and (or) lake, and 20 river and (or) stream source waters were to be sampled. CWS source waters were selected for sampling if MTBE was suspected or know n to occur in the source water. Source waters suspected to be contaminated with MTBE included those in highly urbanized, highpopulation-density settings, usually in MTBE highuse areas. Occasionally, a source water was suspected to be contaminated with MTBE for other reasons. For example, reservoirs near MTBE high-use areas that allowed the use of motorized watercraft were sus

pected to be contaminated with MTBE. Source waters known to contain MTBE wereidentified on the basis of recently completed report s (Delzer and Ivahnenko, 2003) and discussions with local, State, or other Federal agency personnel. In addition, source waters analyzed as part of the Random Survey of this study in which concentrations of MTBE were greater than 0.5 μ g/L also were selected for sampling. Further information on site selec tion and the design of the Focused Survey is presented in Ivahnenko and others (2001). The final selection resulted in 134 CWS source waters sampled. The geographic distribution of the 134 source waters sampled inthe Focused Survey with respect to the location of MTBE high-use areas, is shown in figure 1. MTBE high-use areas were defined as areas within the RFG Program that use MTBE in gasoline (U.S. Environmental Protection Agency, 1999a). Areas designated as “high use” had a median content of MTBE in ga soline greater than 9 percent by volume in at least one year or season from 1995 through 1999. Medians of MTBE content by volume in gasoline were determinedfrom yearly data from the Reformulated Gasoline Survey (Stuart Romanow, U.S. Environmental Protection Agency, written commun., 1999) and season al (winter and summer) data from Motor Gasoline surveys conducted by the National Institute for Petrol eum and Energy Research (Cheryl Dickson, TRW Systems & Information Tech

nology Group, written commun., 2001). All areas cur

rently (2002) in the Federal RFG Program were considered MTBE high-use areas, with the exception of the Chicago and Milwaukee metropolitan areas, which use ethanol in gaso line to meet Federal oxy

genate requirements. Two areas that were previously**8 Occurrence and Temporal Variability of MTBE a nd Other VOCs in Select Sources of Drinking Water**  **Figure 1**

. Methyl tert -butyl ether (MTBE) high-use areas and location ofsource waters sampled in the Focused Survey. 250 500 MILES
250 500 KILOMETERS 0 0 Base modified from U.S. Geological Survey digital data 1:200,000, 1994 Albers Equal Area Conic projection Standard Parallels: 29o30', 45o30' Central Meridan: 96o W

AREAS WHERE HIGH-VOLUME MTBE USE HAS OCCURRED GROUND-WATER SAMPLING SITE SURFACE-WATER SAMPLING SITE 

### EXPLANATION



### in the Federal RFG Program also were considered MTBE high-use areas for this analysis. Areas of south

ern Maine voluntarily entered (opted into) the RFG Program in 1995 and opted out in 1999. Phoenix, Ari

zona, voluntarily entered th e RFG Program in 1997 and opted out in June 1998. Both of these areas have shown significant MTBE use (greater than 9 percent by vol

ume) during the period 1995-99. Two other areas also were considered MTBE high-use areas for this analysis. All areas in the State of California, including those outside Federal RFG Program areas, are considered to be MTBE high-useareas because of documented statewide MTBE highuse in state wintertime oxygenate and (or) California Cleaner Gasoline requirements (California Environ

mental Protection Agency, 1997; California Senate, 1998). Additionally, Yuma and Mohave Counties in Arizona are considered MTBE high-use areas because they likely receive gasoline containing high volumes of MTBE from California distribution sources (Arizona Department of Environmental Quality, 1999). Seventy-seven source waters selected were sus

pected to contain MTBE. Of these, about 50 percent were ground-water source waters and 50 percent were surface-water source waters. Fifty-seven source waters selected were known to contain MTBE. Of these, 67 percent were ground-water source waters and 33 percent were surface-water source waters. In addi

tion to the 134 CWS sources sampled, four source waters (two wells, one reservoir, and one river) were selected as control sites where MTBE was not sus

pected to be present. A summary of source waters sampled in each State by size of CWS is presented in Appendix A. Excluding the control sites, the 78 ground-water, 39 reservoir and (or) lake, and 17 river and (or) stream source waters were selected for partici

pation in the Focused Survey.**Study Design 9** 

## Sample Collection Sample collection and analysis began in September 1999 and was completed in April 2001. Samples were collected by USGS personnel usingUSGS protocols prior to any water treatment. Groundwater samples were collectedfrom water-supply wellsas described by Koterba and others (1995). Surfacewater samples were collected as close to the intake as was reasonable and safe within 5 feet of the surface using a VOC hand-sampler as described by Shelton (1997) and Halde and others (1998). The 451 samples were co llected and analyzedfrom the 134 source waters selected—160 groundwater samples, 155 reservoir and (or) lake samples, and 136 river and (or) stream samples (table 2). The scheduled number of samples was collected from most of the sites. However, 2 samples collected from reser

voirs were lost in shipment , 5 (instead of 4) samples were collected from one reservoir, and 3 (instead of 2) samples were collected from three wells over the sampling period.

The 744 field QC samples were collected as part of the Focused Survey (table 3). One hundred percent of source-water samples werecollected in association with a trip-reagent blank (TRB). TRB samples were prepared at the MWDSC laboratory by filling sampling vials with VOC-free water and sending them to the field office that would conduct the sampling. TRB samples were never opened to the atmosphere and traveled with all other samples from the field site to the laboratory for analysis. TRB samples were intended to document if VOC contamination of the so urce-water samples could **Table 2**

. Summary of number of s ource waters sampled, frequency of sample collection, and number of samples collected during the Focused Survey [CWS, community water system; --, not applicable]

**Source-water type**  **Number of CWS**  **sources sampled**  **Frequency of sample**  **collection (number**  **per year) Total**  **number of samples**  **collected** Ground water 78 2 160 Reservoir and (or) lake 39 4 155 River and (or) stream 17 8 136 Total 134

-- 451 

### have occurred in transit and, thus, were analyzed only if VOCs were detected inthe corresponding sourcewater sample. As such, 304 TRB samples were analyzed.

Field-reagent blank (FRB) samples also were collected in association with 100 percent of sourcewater samples during most of the study. However, FRB samples were collected only in association with about 15 percent of source-water samples during the first three months of samp ling. The 321 FRB samples were prepared by pouring VOC-free water into a sam

pling vial at the field site and were sent to the labora

tory for analyses. These bl ank samples were intended to document all aspects of contamination including sample collection, proces sing, shipment, and anal

yses. Field-equipment blank (FEB) samples and duplicate source-water samples were prepared in asso

ciation with 15 percent of source-water samples col

lected. Fifty FEB samples were collected at surfacewater sites as described by Shelton (1997) by passing VOC-free water through the USGS VOC hand sam

pler and filling the vials accordingly. FEB samples were not collected at ground-water sites because the supply wells sampled had dedicated, submersible pumps. Finally, 69 duplicate samples were collected and analyzed. Ground-water duplicates were collected sequentially, and surface-water duplicates were collected concurrently. **Table 3**

. Summary of the frequency and number of quality-control sa mples collected during the Focused Survey [--, not applicable]
**Quality-control**

**sample type Frequency of**  **quality-control sample collection**  **(percent) Number of**  **quality-control samples**  **analyzed** Trip-reagent blank 100 304 Field-reagent blank 1 100 321 Field-equipment blank 15 50 Duplicate source-water

samples 15 69
Total

-- 744 1 Sample frequency was 15 percent during the first three months of sample collection and 100 percent thereafter.**10 Occurrence and Temporal Variability of MTBE and Other VOCs in Select Sources of Drinking Water** 

### Review of the QC data indicates no systematic contamination of samples. Detected VOC concentra

tions in blank samples typically were less than 0.2 μ g/L, and very little variability was associated with the sample collection, tran sportation, and analytical processes for the majority of VOCs included in this study. A detailed review of these QC data is presented in Appendix B.


## OCCURRENCE AND TEMPORAL VARIABILITY OF VOLATILE ORGANIC COMPOUNDSThe results of the chemical analyses of sourcewater samples collected for the Focused Survey were evaluated for the occurrence an d temporal variability of individual VOCs and subgroups of VOCs (table 1). VOC subgroups examined include gasoline oxygen

ates, other gasoline related compounds (excluding the oxygenates), THMs, solvents, organic synthesis com

pounds, fumigants, and refrigerants. All source-water data used in these analyses have undergone an exten

sive QC screening procedure. This systematic proce

dure compares source-water data with respective FRB samples to ultimately accept or reject the source-water data. Thus, only those source -water data that met dataquality criteria were accepte d and included in these analyses. Details of this screening procedure are presented in Appendix C. Detection frequencies resulting from the QC screening process for each VOC detected in the Focused Survey also are presented in Appendix C. The detection frequencies in Appendix C are for all 467 samples collected from the three source-water types (includes data from four contro l sites). It is important to note, however, that the analytical method reports all detections above the MDL. Thus, the detection fre

quencies in Appendix C were calculated using data that were not censored to a statistically determined MRL. The MDL concentrations typically were less than 0.05 μ g/L and ranged from 0.014 μ g/L for 1,1,2- trichloroethane to 0.645 μ g/L for methyl ethyl ketone (MEK) (Ivahnenko and others, 2001). The MRL was 0.2 μ g/L for all compounds except MEK, which had a MRL of 2.0 μ g/L. Concentrations of VOCs detected in the Focused Survey generally were less than 1 μ g/L (Appendix D);however, the concentrations of benzene, tetrachloroethene, and trichloroethene in some samples exceeded the USEPA Maximum Contamin ant Levels (MCLs) set for those compounds. It is important to note that MCLs are established for finished drinking water and not for source water. MCLs for benzene, tetrachloroethene, and trichloroethene have been set at 5 μ g/L for each compound (U.S. Environmental Protection Agency, 2001). Benzene concentrations exceeded the MCL in 4 samples, tetrachloroethen e in 13 samples, and trichloroethene in 7 samples. Concentrations of MTBE detected in the Focused Survey exceeded the lower limit of the USEPA Drinking Water Advisory of 20 to 40 μ g/L (U.S. Environmental Protection Agency, 1997) in 12 samples. All samples in which concentra

tions exceeded MCLs or the Drinking Water Advisory for MTBE were collected from ground-water source waters. Of the 4 control s ites—2 wells, 1 reservoir, 1 river—that were selected because MTBE was not suspected to be detected, MTBE was detected only in 1 ground-water sample at a concentration of 0.05 μ g/L. Control site data are not included in table 4. 

## Occurrence and Comparison to the Random Survey One objective of the Random Survey was to pro

vide a statistically representative assessment of the quality of the source water of the Nation’s public drinking-water supplies with respect to the occurrence of MTBE and other VOCs. This objective differs mark

edly from that of the Focu sed Survey, which intention

ally sampled source waters suspected or known to be contaminated with MTBE. Some comparisons between the two surveys, however, may augment conclusions drawn from both surveys. Results from the Random Survey (Rowe and others, 2001; Grady, 2003) were based on the analyses of source water obtained from 954 randomly selected CWSs sampled between May 3, 1999, and October 23, 2000. The Random Survey data underwent the same QC screening process that wa s applied to data from the Focused Survey. VOC concentrations detected during the Random Survey, however, were only reported at or above the MRL. As such, any meaningful comparisons between the two surveys had to be conducted with a common assessment level. Thus, the Focused Survey data were also censored at the MRL in order to make comparisons with the Random Survey. Additional adjustments to Focused Survey data were needed in order to co mpare findings between the two surveys. Results from the Random Survey were commonly presented such that reservoir, lake, river, and stream source waters were combined into one**Occurrence and Temporal Variability of Volatile Organic Compounds 11** 

### surface-water category. Thus, all Focused Survey surface-water data were combined into one category. Finally, in the Random Survey one sample was col

lected from each CWS source water, whereas in the Focused Survey multiple samples were collected from the same CWS source water. Because concentrations may change from one sample to the next at the same site, one sample was randomly selected from each source water sampled as part of the Focused Survey and used for comparing re sults with the Random Survey. As expected, most VOCs were detected more frequently in the Focused Survey than in the Random Survey (fig. 2). The Focused Survey sampled source waters suspected or known to contain MTBE whereas the Random Survey did not. Thus, MTBE was detected much more frequently at s ites sampled in the Focused Survey than in the Random Survey. MTBE was detected in 60 and 49.1 percent of CWSs supplied by ground and surface water, respectively, in the Focused Survey and in 5.4 and 13.8 percent of CWSs supplied by ground and surface water, respectively, in the Random Survey. MTBE was detected in 55.5 percent of the 134 CWSs sampled in the Focused Survey and in 8.7 percent of 954 CWSs sampled in the Random Survey (table 4). In addition to MTBE, numerous other VOCs were detected more frequently in the Focused Survey than in the Random Survey (fig. 2). This may be explained by population densityin areas sampled in the Focused Survey. High-population density, which was one factor associated with the selection of a site to be sampled as part of the Focused Survey, has been shown to be related to increased VOC detection frequencies (Reiser and O’Brien, 1998; Squillace and others, 1999; Bush and others, 2000; Lopes and Furlong, 2001). Sim

ilarly, results from the Random Survey concluded that the occurrence of VOCs was greatest in the largest ground-water CWSs serving populations greater than 50,000 people and medium-sized surface-water CWSs serving populations of 3,001 to 10,000 people. Individual VOC detection frequencies in CWSs sampled as part of the Focused and Random Surveys are presented in table 4. Detection frequencies are pre

sented for data at or above the MRL for both surveys and also at or above the MDL for the Focused Survey. Detection frequencies are lower when using data at or above the MRL because detections of VOCs at or above the MDL, yet below th e MRL, were not included in the calculation (Appendix C).

**Figure 2**

. Detection frequency at or above the minimum reporting level of individual volatile organic compounds in source waters sampled in th e Focused Survey versus the Random Survey. 0 10 20 30 40 50 60 70

0 5 10 15 2 0 FREQUENCY OF DETECTION IN THE RANDOM SURVEY, IN PERCENTFREQUENCY OF DETECTION IN THE FOCUSED SURVEY,IN PERCENT

1:1 Line Ground water Surface water Methyl tert -butyl ether**12 Occurrence and Temporal Variability of MTBE and Other VOCs in Select Sources of Drinking Water Table 4** 

. Summary of detection frequencies of any volatile organic compound (VOC), any subgroup of VOCs, and individual VOCs in source waters sampled in the Focused and Random Surveys [VOC, volatile organic compound; CWS, community water system; n, number of samples]

**Volatile organic compound subgroup**  **and individual compound name**  **Focused Survey Random Survey**  **Detection frequency at or above the MDL (percent)**  **Detection frequency at or above the MRL (percent)**  **Detection frequency at or above the MRL (percent)**  **All CWSs (n=134)**  **Ground water**  **(n=78) Surface**  **water (n=56)**  **All CWSs (n=134)**  **Ground water**  **(n=78) Surface**  **water (n=56)**  **All CWSs (n=954)**  **Ground water**  **(n=579) Surface**  **water (n=375)**  Any VOC 92.5 92.3 92.9 61.2 66.7 53.6 26.9 25.2 29.6 Gasoline Oxygenates tert-Amyl methyl ether 20.3 20.8 19.6 4.5 6.5 1.8 0.2 0.4 0.0 Diisopropyl ether 6.0 10.3 0.0 3.0 5.1 0.0 0.2 0.4 0.0 Ethyl tert-butyl ether 1.5 2.6 0.0 0.7 1.3 0.0 0.1 0.2 0.0 Methyl tert-butyl ether 77.3 68.0 90.6 55.5 60.0 49.1 8.7 5.4 13.8 Any gasoline oxygenate 73.9 65.4 85.7 53.7 59.0 46.4 8.5 5.3 13.3 Other Gasoline Compounds Benzene 22.0 15.8 30.4 7.6 6.6 8.9 0.3 0.4 0.3

n -Butylbenzene 1.5 1.3 1.8 0.0 0.0 0.0 0.1 0.2 0.0

sec -Butylbenzene 1.5 2.6 0.0 0.0 0.0 0.0 0.0 0.0 0.0
tert-Butylbenzene 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 Ethylbenzene 4.8 4.1 6.0 1.6 1.4 2.0 0.5 0.5 0.5 Naphthalene 9.9 10.5 9.1 2.3 3.9 0.0 0.2 0.2 0.3 Toluene 18.3 9.4 31.1 5.5 1.6 11.1 1.1 0.5 1.9 1,3,5-Trimethylbenzene 4.5 1.3 8.9 2.2 1.3 3.6 0.0 0.0 0.0

m ,

p -Xylene 8.6 5.3 13.5 3.1 1.3 5.8 0.8 0.7 0.8

o -Xylene 14.2 10.8 18.9 3.9 1.4 7.5 0.6 0.7 0.5 Any gasoline compound 35.8 29.5 44.6 9.0 7.7 10.7 2.2 1.9 2.7 Trihalomethanes Bromoform 4.5 5.1 3.6 2.2 3.8 0.0 3.4 4.7 1.3 Bromodichloromethane 20.9 15.4 28.6 2.2 2.6 1.8 6.4 5.9 7.2 Chlorodibromomethane 12.7 10.3 16.1 1.5 2.6 0.0 5.5 6.1 4.5 Chloroform 48.4 55.6 38.9 17.5 23.6 9.3 12.7 11.8 14.0 Any trihalomethane 47.8 53.8 39.3 16.4 21.8 8.9 14.8 15.2 14.0 Solvents Bromobenzene 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 Carbon tetrachloride 2.2 3.8 0.0 1.5 2.6 0.0 0.7 0.9 0.5 Chlorobenzene 3.7 5.1 1.8 1.5 2.6 0.0 0.1 0.2 0.0 Chloroethane 0.7 1.3 0.0 0.0 0.0 0.0 0.1 0.2 0.0 2-Chlorotoluene 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 4-Chlorotoluene 0.7 1.3 0.0 0.0 0.0 0.0 0.0 0.0 0.0**Occurrence and Temporal Variability of Volatile Organic Compounds 13** Solvents—Continued Dibromomethane 0.7 1.3 0.0 0.7 1.3 0.0 0.2 0.4 0.0 1,2-Dichlorobenzene 1.5 2.6 0.0 0.7 1.3 0.0 0.1 0.2 0.0 1,3-Dichlorobenzene 2.2 3.8 0.0 0.0 0.0 0.0 0.0 0.0 0.0 1,1-Dichloroethane 15.9 26.3 1.8 5.3 9.2 0.0 1.2 1.4 0.0 1,2-Dichloroethane 11.9 20.5 0.0 4.5 7.7 0.0 0.3 0.5 0.0 1,1-Dichloroethene 6.0 10.3 0.0 3.7 6.4 0.0 0.8 1.4 0.0 cis -1,2-Dichloroethene 12.8 22.1 0.0 6.8 11.7 0.0 1.3 1.9 0.3
trans -1,2-Dichloroethene 4.5 7.7 0.0 2.2 3.8 0.0 0.0 0.0 0.0 1,2-Dichloropropane 3.7 6.4 0.0 0.7 1.3 0.0 0.1 0.2 0.0 Hexachloroethane 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 Methylene chloride 0.8 1.4 0.0 0.8 1.4 0.0 0.2 0.2 0.3 Methyl ethyl ketone 0.8 1.3 0.0 0.0 0.0 0.0 0.5 0.4 0.8

n -Propylbenzene 3.0 1.3 5.4 0.8 1.3 0.0 0.1 0.0 0.3 1,1,1,2-Tetrachloroethane 1.5 2.6 0.0 0.0 0.0 0.0 0.0 0.0 0.0 Tetrachloroethene 21.1 36.4 0.0 13.5 23.4 0.0 2.8 4.2 0.8 1,1,2,2-Tetrachloroethane 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 1,2,4-Trichlorobenzene 3.0 2.6 3.6 0.0 0.0 0.0 0.0 0.0 0.0 1,1,1-Trichloroethane 14.2 24.4 0.0 7.5 12.8 0.0 1.0 1.7 0.0 1,1,2-Trichloroethane 1.5 2.6 0.0 0.0 0.0 0.0 0.0 0.0 0.0 Trichloroethene 17.3 29.9 0.0 10.5 18.2 0.0 2.3 3.3 0.8 1,2,3-Trichloropropane 3.8 3.8 3.7 0.0 0.0 0.0 0.1 0.2 0.0 Any solvent 41.8 61.5 14.3 21.6 37.2 0.0 6.3 8.8 2.4 Organic Synthesis Acrylonitrile 0.7 1.3 0.0 0.7 1.3 0.0 0.0 0.0 0.0 Bromochloromethane 3.7 5.1 1.8 0.0 0.0 0.0 0.0 0.0 0.0 1,3-Dichloropropane 3.0 2.6 3.6 0.7 1.3 0.0 0.0 0.0 0.0 2,2-Dichloropropane 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 1,1-Dichloropropene 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 Hexachlorobutadiene 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 Isopropylbenzene 3.8 5.2 1.8 0.8 1.3 0.0 0.2 0.2 0.3 p -Isopropyltoluene 0.7 0.0 1.8 0.0 0.0 0.0 0.0 0.0 0.0 **Table 4** . Summary of detection frequencies of any volatile organi c compound (VOC), any subgroup of VOCs, and individual VOCs in source waters sampled in the Focused and Random Surveys—Continued [VOC, volatile organic compound; CWS, community water system; n, number of samples]

**Volatile organic compound subgroup**  **and individual compound name**  **Focused Survey Random Survey Detection frequency at or above**  **the MDL (percent) Detection frequency at or above**  **the MRL (percent) Detection frequency at or above**  **the MRL (percent) All CWSs**  **(n=134) Ground**  **water (n=78)**  **Surface water**  **(n=56) All CWSs**  **(n=134) Ground**  **water (n=78)**  **Surface water**  **(n=56) All CWSs**  **(n=954) Ground**  **water (n=579)**  **Surface water**  **(n=375) 14 Occurrence and Temporal Variability of MTBE and Other VOCs in Select Sources of Drinking Water**  Organic Synthesis—Continued Styrene 16.3 21.3 9.3 3.8 6.6 0.0 0.5 0.4 0.8 1,2,4-Trimethylbenzene 7.6 1.3 16.7 1.5 1.3 1.9 0.4 0.2 0.8 1,2,3-Trichlorobenzene 5.2 6.4 3.6 0.0 0.0 0.0 0.0 0.0 0.0 Vinyl bromide 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 Vinyl chloride 2.2 3.8 0.0 2.2 3.8 0.0 0.1 0.2 0.0 Any organic synthesis 32.8 33.3 32.1 7.5 11.5 1.8 1.0 0.7 1.6 Fumigants Bromomethane 3.0 3.8 1.8 0.0 0.0 0.0 0.2 0.2 0.3 1,4-Dichlorobenzene 4.5 6.5 1.8 0.8 1.3 0.0 0.3 0.2 0.5 cis -1,3-Dichloropropene 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0
trans -1,3-Dichloropropene 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 Any fumigant 7.5 10.3 3.6 0.7 1.3 0.0 0.5 0.4 0.8 Refrigerants Chloromethane 3.0 3.8 1.8 0.7 1.3 0.0 0.3 0.5 0.0 Dichlorodifluoromethane 0.7 1.3 0.0 0.7 1.3 0.0 0.4 0.7 0.01,1,2-Trichloro1,2,2-trifluoroethane 0.7 1.3 0.0 0.7 1.3 0.0 0.1 0.2 0.0
Trichlorofluoromethane 2.2 3.8 0.0 2.2 3.8 0.0 0.5 0.9 0.0 Any refrigerant 5.2 7.7 1.8 3.0 5.1 0.0 1.0 1.7 0.0 **Table 4** . Summary of detection frequencies of any volatile organi c compound (VOC), any subgroup of VOCs, and individual VOCs in source waters sampled in t he Focused and Random Surv eys—Continued [VOC, volatile organic compound; CWS, community water system; n, number of samples]

**Volatile organic compound subgroup**  **and individual compound name**  **Focused Survey Random Survey Detection frequency at or above**  **the MDL (percent) Detection frequency at or above**  **the MRL (percent) Detection frequency at or above**  **the MRL (percent) All CWSs**  **(n=134) Ground**  **water (n=78)**  **Surface water**  **(n=56) All CWSs**  **(n=134) Ground**  **water (n=78)**  **Surface water**  **(n=56) All CWSs**  **(n=954) Ground**  **water (n=579)**  **Surface water**  **(n=375)**



### When considering data above the MDL and MRL as part of the Focused Survey, about 93 and 61 percent of all source waters sampled contained at least one of the 66 VOCs an alyzed, respectively. This compares to about 27 percent detected in source waters sampled as part of the Random Survey. Although detec

tion frequencies were less in the Random Survey than in the Focused Survey, a similar number of VOCs were detected in both surveys. Fifty-eight and 41 VOCs were detected at least one time in the Focused Survey above the MDL and MRL, respectively, whereas, 42 were detected at levels above the MRL in the Random Survey. Thirty-seven of the 41 VOCs detected in the Focused Survey also were detected in the Random Survey. Again, only the dete ction frequencies above the MRL should be used for comparison to the Random Survey. A summary of detected concentrations of VOCs collected as part of the Focused Survey is pre

sented in Appendix D. Additional discussion of the occurrence of VOCs in the Focused Survey above the MDL is included in the next section—Temporal Variability. Each subgroup of VOCs wa s detected at or above the MRL at a higher frequency in the Focused Survey than in the Random Survey (table 4, fig. 3). The largest difference in detection frequencies was found in the gasoline oxygenate subgroup, wherein these com

pounds were detected in 53.7 percent of CWSs sampled**Occurrence and Temporal Variability of Volatile Organic Compounds 15** 

### in the Focused Survey but in only 8.5 percent of CWSs sampled in the Random Survey. This difference is due to the intentional selection of sites with suspected or known occurrence of MTBE in the Focused Survey. A slightly higher detectio n frequency for gasoline oxygenates was found in ground-water source waters (59.0 percent) than in surface-water source waters (46.4 percent) in the Focused Survey. This pattern was reversed, however, for samples collected in the Random Survey, where gasoline oxygenates were detected in 5.3 and 13.3 percent of ground and surface water, respectively. MTBEwas the most frequently detected gasoline oxygenate in source waters sampled in the Focused and Random Surveys, occurring in 55.5 and 8.7 percent, respectively. A second large differen ce was found in the solvent subgroup, again with the larger detection frequency occurring in the Fo cused Survey. In both sur

veys, most of the solvent detections were in groundwater source waters (table 4). This may be due to sol

vents degrading slower in ground water than in surface water. The difference in detection frequency between the two surveys (fig. 3) may be due, in part, to inten

tionally sampling ground-water sites as part of the Focused Survey that were considered more vulnerable than other sites. That is, preference was given to sam

pling ground-water source waters withdrawn from shallow, unconsolidated, unconfined aquifers in urban areas serving large populati ons. The solvents detected most frequently in both surveys were tetrachloroethene and trichloroethene. Interestingly, THMs were detected in the Focused and Random Surveys at approximately similar frequencies—16.4 and 14.8 percent of CWSs, respec

tively. Chloroform was the most frequently detected THM in both surveys. However, chloroform was detected more frequently in ground-water source waters in the Focused Survey (23.6 percent) than in the Random Survey (11.8 percent). Similar THM detection frequencies in both surveys indicates a pervasive occur

rence of THMs in several source-water types regardless of CWS size or location. Other gasoline compounds, organic synthesis compounds, fumigants, an d refrigerants all were detected at or above the MRL in less than 10 percent of CWSs sampled in each survey. Although the gasoline oxygenate MTBE was detected frequently in the Focused Survey, VOCs in the other gasoline compound subgroup were detected in only 9 percent of CWS source waters. This may be due to these compounds

**Figure 3**

. Detection frequency at or above the minimum reporting level of volatile organic compound subgroups in community water system source waters sampled in the Focused Survey and the Random Survey. 0 10 20 30 40 50 60FREQUENCY OF DETECTION, IN PERCENT

Gasoline oxygenates Solvents Trihalomethanes Other gasoline compounds Organic synthesis Refrigerants Fumigants

VOC SUBGROUP Focused Survey Random Survey**16 Occurrence and Temporal Variability of MTBE and Other VOCs in Select Sources of Drinking Water** 

### degrading and (or) volatilizing more rapidly in ground and surface water in comparison to MTBE. Organic synthesis compounds also were detected more fre

quently in the Focused Survey (7.5 percent) than in the Random Survey (1.0 percent). The majority of detec

tions in the Focused Survey were found in groundwater source waters (11.5 percent) rather than in surface-water source waters (1.8 percent). Again, this may be due to the Focused Survey’s sampling urban ground-water source waters inshallow, unconsolidated, unconfined aquifers that may be susceptible to contam

ination. Very little differencein detection frequencies between either survey was observed for fumigants and refrigerants. CWSs were subdivided into five size categories based on population served: (1) very small (serves 25 to 500 people); (2) small (serves 501 to 3,300 people); (3) medium (serves 3,301 to 10,000 people); (4) large (serves 10,001 to 50,000 people); and (5) very large (serves more than 50,000 people). Table 5 lists the rel

ative percent of CWSs per sizeof system sampled in the Focused and Random Surveys. A summary of source waters sampled per State by size of CWS is presented in Appendix A. A fairly equal distribution of ground-water CWS sizes was sampled in the Focused Survey—from 10.4 to 26 percent of each size category—whereas the majority of ground-water source waters sampled (50.4 percent) in the Random Survey were very small systems. The abundance of very small ground-water source waters in the Random Survey is due to the rela

tive abundance of very small ground-water supplied CWSs on a national basis and reflects the random selection process used in the Random Survey. A dispro

portionate number of very large CWSs supplied by sur

face water were sampled (85.7 percent) in the Focused Survey. Similarly, the majority of CWSs supplied by surface water sampled (81.9 percent) as part of the Random Survey were large or very large CWSs. The abundance of large and very large surface-water systems sampled as part of the Random Survey was due to the cumulative population served, which was one weighting factor used in the design of that survey (Ivahnenko and others, 2001). The highest VOC detec tion frequency in the Random Survey for each subgroup of VOCs (except THMs) was found in the very large CWSs supplied by ground water (fig. 4). THMs were detected slightly more often in the very small CWSs than in the very large CWSs. This likely reflects the fact that many more of the larger systems have source waters within high-population density, urban areas than do the smaller CWSs. This pattern was not evident in the Focused Survey for gasolin e oxygenates, other gaso

line compounds, solvents, and refrigerants (fig. 4). This is likely due to the fact that the source waters selected were considered more vulnerable to VOC contamina

tion and MTBE was suspected or known to occur in the source, regardless of CWS size. In the Random Survey, gasoline oxygenates and other gasoline compounds were detected more fre

quently in the very large CWSs supplied by surface water than in other size categories (fig. 5). This pattern was generally observed in the Focused Survey. Although the Focused and Random Surveys each sam

pled disproportionately more large and very large CWSs than other size categories, gasoline oxygenates, other gasoline compounds, solvents, THMs, and organic synthesis compounds were detected in virtually every size category sampled in the Random Survey. This was not observed in the Focused Survey. Gasoline oxygenates primarily were detected in large and very large CWSs; however, solvents, THMs, and organic synthesis compounds were not detected at all or only detected in a few sizes of CWSs. The reason for this difference is not known.

**Table 5**

. Distribution of source waters sampled in the Focused and Random Surveys by source-type and size of community water system based on population served

**Community water system size (based**  **on population served)**  **System**
**Focused Random**  Percent of ground-water systems sampled Very small 10.4 50.4 Small 16.8 20.9 Medium 20.8 8.6 Large 26.0 10.9 Very large 26.0 9.2 Total 100.0 100.0 Percent of surface-water systems sampled Very small 0.0 3.2 Small 7.1 6.9 Medium 1.8 8.0 Large 5.4 21.0 Very large 85.7 60.9 Total 100.0 100.0**Occurrence and Temporal Variability of Volatile Organic Compounds 17 Figure 4** 

. Detection frequency at or above the minimu m reporting level of any volatile organic compound (VOC) and subgroup of VOCs in ground-water sources sampled in the Focused Survey and Random Survey by size of community water system.FREQUENCY OF DETECTION, IN PERCENT

Gasoline oxygenates Solvents Trihalomethanes Other gasoline compounds Organic synthesis Refrigerants Fumigants Focused Survey

0 10 20 30 40 50 60 70 80

Any VOCFREQUENCY OF DETECTION, IN PERCENT

Gasoline oxygenates Solvents Trihalomethanes Other gasoline compounds Organic synthesis Refrigerants Fumigants Random Survey

0 10 20 30 40 50 60 70 80

Any VOC VOC SUBGROUP

VOC SUBGROUP Very small (25 to 500) Small (501 to 3,300) Medium (3,301 to 10,000) Large (10,001 to 50,000) Very large (more than 50,000)

Very small (25 to 500) Small (501 to 3,300) Medium (3,301 to 10,000) Large (10,001 to 50,000) Very large (more than 50,000)**18 Occurrence and Temporal Variability of MTBE and Other VOCs in Select Sources of Drinking Water Figure 5** 

. Detection frequency at or above the minimum reporting level of any volatile organic compound (VOC) and subgroup of VOCs in surf ace-water sources sampled in the Focused Survey and Random Survey by size of community water system.FREQUENCY OF DETECTION, IN PERCENT

Gasoline oxygenates Solvents Trihalomethanes Gasoline compounds Organic synthesis Refrigerants Fumigants Focused Survey

0 10 20 30 40 50 60

Any VOCFREQUENCY OF DETECTION, IN PERCENT

Gasoline oxygenates Solvents Trihalomethanes Gasoline compounds Organic synthesis Refrigerants Fumigants Random Survey

Any VOC 0 10 20 30 40 50 60 VOC SUBGROUP

VOC SUBGROUP Very small (25 to 500) Small (501 to 3,300) Medium (3,301 to 10,000) Large (10,001 to 50,000) Very large (more than 50,000)

Very small (25 to 500) Small (501 to 3,300) Medium (3,301 to 10,000) Large (10,001 to 50,000) Very large (more than 50,000)**Occurrence and Temporal Variability of Volatile Organic Compounds 19** 

## Temporal Variability Samples were collected for one year at fixed intervals during the Focused Survey. Ground-water source waters were sample d biannually, reservoir and (or) lake source waters were sampled quarterly, and river and (or) stream sourcewaters were sampled eight times per year (table 2). The intent of the fixed-interval sampling was to obtain sufficient data to evaluate tem

poral variability of VOCs in each source-water type. To do so, samples were collected more frequently in sur

face-water source waters than in ground-water source waters to account for likely changes in water quality caused by temperature and other seasonal affects. The ground-water sampling design did not spe

cifically distribute samples seasonally as was done for surface-water sampling. Ground-water samples were collected approximately six months apart and only two samples were collected from each well. Because of the slow movement of ground water, the elapsed time between samples was presumed insufficient to allow for significant changes inground-water quality tooccur. Thus, analyses of temporal variability in groundwater source waters in this report compare only the first sample to the second sample and do not evaluate seasonal patterns. In contrast, the analyses of temporal variability in surface-water source waters do evaluate seasonal patterns. The four seasons considered in the temporal analyses were defined as spring (April-June), summer (July-September), fall (October-December), and winter (January-March). The numb er of reservoir and (or) lake source-water samples collected were distributed fairly evenly among the different seasons (fig. 6). The number of reservoir and lake samples collected ranged from 37 during winter to 46 in the spring. However, more samples were collectedfrom river and (or) stream source waters during winter than in other seasons; about 30 river and (or) stre am samples were collected during the spring, summer, and fall, and 52 samples were collected during the winter. Generally, this may result in an increase in VOC occurrence in rivers andstreams during the winter months due to higher air-towater partitioning and decreased volatility of VOCs at winter temperatures. Temporal analyses were performed to examine seasonal and concentration differences in those sub

groups of VOCs that occur most frequently in CWS source water. It is important to note that all data above the MDL were used in the temporal analyses to maxi

mize the number of VOC detections that are available for analyses. A summary of concentrations detected in source water is presented in Appendix D.

**Figure 6**

. Number of surface-water samples collected by source type and season. 0 10 20 30 40 50 60 70 80 90 100NUMBER OF SAMPLES COLLECTED

Spring Summer Fall Winter SEASON Reservoirs and (or) lakes Rivers and (or) streams Total**20 Occurrence and Temporal Variability of MTBE and Other VOCs in Select Sources of Drinking Water** 

### Analyses of the data from the 134 CWS source waters previously used for comparing the Focused Survey to the Random Survey (table 4) showed that at least 1 of the 66 VOCs analyzed was detected in more than 90 percent of the source waters sampled as part of the Focused Survey (fig. 7). Each of the 17 CWSs sup

plied by rivers or streams contained at least one VOC, a result of the detection of a gasoline oxygenate in each of the 17 CWS river and (or) stream source waters. In addition, gasoline oxygen ates, other gasoline com

pounds, THMs, and organic synthesis compounds were detected more frequently inCWSs supplied by river source waters than in any other source water sampled. This may be due to the presence of point sources upstream from the sampling site that provide a fairly continuous source of contamination. Gasoline oxygenates, other gasoline compounds, THMs, and organic synthesis compounds were detected in more than 25 percent of CWSs served by ground-water, reservoir and (or) lake, and river and (or) stream source waters (fig. 7). Therefore, these four sub

groups of VOCs were used in subsequent temporal analyses. In addition, solvents were evaluated only in ground-water source waters because they were not detected frequently in surface-water source waters. Fumigants and refrigerants were not analyzed for tem

poral variability due to th eir infrequent detection.
Ground Water Analyses of data from all 78 ground-water source waters sampled biannu ally revealed that detec

tion frequencies of VOC subgroups did not change sig

nificantly from the first samplecollected to the second sample (fig. 8). Similarly, no statistically significant differences in detected concentrations of VOCs were found at the 95-percent co nfidence level using the Wilcoxon rank sum test (Helsel and Hirsch, 1992) (fig. 9). Because samples were collected approximately 6 months apart, it is presumed that an insufficient amount of time passed to show any significant changes in ground-water quality. Although these subgroups of VOCs occur fre

quently in the source waters sampled, the concentra

tions detected were small, typically less than 1 μ g/L. However, some higher concentrations were observed—maximum concentrations of MTBE, tetra

chloroethene, and trichloroethene in ground-water source waters were 924, 290, and 165 μ g/L, respec

tively.

**Figure 7**

. Detection frequency at or above the minimu m reporting level of any volatile organic compound (VOC) and by subgroup of VOCs in co mmunity water system source waters by source type. 0 20 40 60 80 100 120FREQUENCY OF DETECTION, IN PERCENT

Gasoline oxygenates Any VOC SolventsTrihalomethanes Other gasoline compounds Organic synthesis Refrigerants Fumigants

VOC SUBGROUP All source types Ground water Reservoirs and (or) lakes Rivers and (or) streams**Occurrence and Temporal Variability of Volatile Organic Compounds 21 Figure 8** 

. Comparison of the detection frequency of atleast one volatile organic compound (VOC) at or above the method detection limit by subgr oup of VOCs in the first and second sampling of ground-water source water.

**Figure 9**

. Detected concentrations of volatile organic compound subgroups in ground-water source water collected in the first and second samples. 0 10 20 30 40 50 60 70 80FREQUENCY OF DETECTION, IN PERCENT

Gasoline oxygenates Solvents Trihalomethanes Other gasoline

compounds Organic synthesis
VOC SUBGROUP First sample Second sample

0.01

0.1

1 10 100 1,000 10,000CONCENTRATIONS, IN MICROGRAMS PER LITER

Gasoline oxygenates Solvents Trihalomethanes Other gasoline

compounds Organic synthesis 50 52 22 19 45 41 50 47 28 23



### x x

x x

x o

x x x x x

x 30 Number of values 

### EXPLANATION



### x

x o

75th percentile
Median 25th percentile
Lower outside Upper detached A AA AA AA AA AA

Populations that share the same letter are not significantly dif- ferent at a 95-percent confidence interval
Upper outside First sample Second sample

VOC SUBGROUP**22 Occurrence and Temporal Variability of MTBE and Other VOCs in Select Sources of Drinking Water** 

### Reservoirs and Lakes A slight seasonal pattern was evident in the occurrence of gasoline oxygenates and other gasoline compounds (fig. 10) in reservoir and lake source waters. Analyses of data from all 39 reservoirs and (or) lakes sampled quarterly revealed that both of these sub

groups of VOCs were detected more frequently in the spring and summer than in the fall and winter. How

ever, these compounds were still fairly prevalent during the fall and winter, when they were detected in at least 27 percent of samples. Thirty-three of the 39 reservoirs sampled allow motorized watercraft. Thus, the greater detection of gasoline-relate d compounds in the spring and summer is presumed to be related to the increased use of motorized watercraft during these seasons. The continued detection of these compounds during fall and winter may be due, in part, to the continued use of watercraft containing reformulated gasoline during these seasons in areas with warmer climates, and the chemical characteristics of MTBE, which allow it to persist longer in water in comparison to other VOCs. Trihalomethanes and organic synthesis com

pounds were detected in about 30 percent of samples collected throughout the yearwith no significant trend identified. The lack of any substantial, seasonal variability in THMs and organic synthesis compounds indicates the possibility of a common and continuous source of contamination for these compounds. Concentrations of VOCs detected in reservoir and lake source waters weretypically less than 1 μ g/L 

## , and very few statistically significant differences in seasonal concentrations were identified (fig. 11). Although gasoline oxygenates and other gasoline com

pounds were detected more frequently in the spring and summer than in fall and winter, statistically significant differences in detected median concentrations of VOCs typically were not identified by the Wilcoxon rank sum test at an alpha of 0.05. There were no statistically sig

nificant differences between seasonal concentrations of gasoline oxygenates and THMs. Statistically signifi

cant differences were found for other gasoline com

pounds and organic synthesis compounds. For these VOC subgroups, winter and (or) fall concentrations were significantly less than spring and (or) summer concentrations.

**Figure 10**

. Detection frequency of at least one volatile organic compound (VOC) at or above the method detection limit by subgroup of VOCs in reservoir and lake source waters by season. 0 20
10 30 40 50 60 70 80 90 100FREQUENCY OF DETECTION, IN PERCENT

Gasoline oxygenates Trihalomethanes Other gasoline

compounds Organic synthesis VOC SUBGROUP Spring Summer Fall Winter**Occurrence and Temporal Variability of Volatile Organic Compounds 23 Figure 11** 

. Detected concentrations of volatile organic compound subgroups in reservoir and lake source waters by season. 0.01

0.1

1 10 100CONCENTRATIONS, IN MICROGRAMS PER LITER

Gasoline oxygenates Trihalomethanes Other gasoline

compounds Organic synthesis 20 Number of values 

### EXPLANATION



### x o

75th percentile
Median 25th percentile Upper detached A A A A A AB B AC C A A A A A A B AB

Populations that share the same letter are not significantly dif- ferent at a 95-percent confidence interval
Upper outside Spring Summer Fall Winter

VOC SUBGROUP 43 46 31 29 69 58 20 27 18 21 23 29 16 15 8 11



### x x x

o

Rivers and Streams No seasonal pattern was evident for any of the more frequently occurring subgroups of VOCs in river and stream source waters (fig. 12). The detection of gasoline oxygenates was found to drop slightly from spring to winter; however, these VOCs were found to be consistently present in the source waters sam

pled—in at least 78 percent of the samples. This may be indicative of a common source of gasoline oxygen

ates to the source waters sampled. Other gasoline com

pounds, THMs, and organic synthesis compounds also were detected at similar frequencies throughout the year. Other gasoline compounds and THMs were detected in more than 50 percent of all samples, and organic synthesis compounds were detected in more than 20 percent of all samples co llected throughout the year. Again, the absence of seasonal differences for these subgroups of compounds may indicate an unknown, but common and continuous source of contamination. Concentrations of the VOCs (subgroups) most frequently detected in river and stream source waters were typically less than 1 μ g/L, and few statistically significant differences in co ncentrations were noticed on a seasonal basis (fig. 13). Although these subgroups of VOCs were found frequently year round (fig. 12), the only statistically signif icant differences in the con

centrations of VOCs were within the gasoline oxy

genate subgroup, which were found at slightly greater concentrations during the summer than during the winter season.**24 Occurrence and Temporal Variability of MTBE and Other VOCs in Select Sources of Drinking Water Figure 12** 

. Detection frequency of at least one volatile organic compound (VOC) at or above the method detection limit by subgroup of VOCs in river and stream source waters by season.

**Figure 13**

. Detected concentrations of volatile organic compound su bgroups in river and stream source waters by season. 0 20
10 30 40 50 60 70 80 90 100FREQUENCY OF DETECTION, IN PERCENT

Gasoline oxygenates Trihalomethanes Other gasoline

compounds Organic synthesis VOC SUBGROUP Spring Summer Fall Winter

0.01

0.1

1 10 100CONCENTRATIONS, IN MICROGRAMS PER LITER

Gasoline oxygenates Trihalomethanes Other gasoline

compounds Organic synthesis 20 Number of values 

### EXPLANATION



### x o

75th percentile
Median 25th percentile Upper detached A AB B BC AC A A A A A A A A A A A A

Populations that share the same letter are not significantly dif- ferent at a 95-percent confidence interval
Upper outside Spring Summer Fall Winter



### x x x

x x x x x x x x x
x x x x o o

x x

VOC SUBGROUP 35 29 28 48 34 30 38 46 28 33 26 80 14 6 14 9**Anthropogenic Factors Associated with MTBE, Gasoline Oxygenates, and Trihalomethanes 25**  

## ANTHROPOGENIC FACTORS ASSOCIATED WITH MTBE, GASOLINE OXYGENATES, AND TRIHALOMETHANES Few temporal patterns were found when exam

ining occurrence and concentrations of VOC subgroups in source waters where MTBE was suspected or known to occur. One apparent trend was found in reservoirs and lakes, where gasoline oxygenates and other gaso

line compounds were detected more frequently during the spring and summer. This was likely associated with the increased use of motorize d watercraft on the reser

voirs during these seasons. However, no significant statistical differences were noticed when examining MTBE concentrations alone on a seasonal basis. Although one or two VOCstypically dominate the occurrence within VOC subgroups (table 4), the increased number of potential detections in subgroups should be beneficial in dete cting significant trends not otherwise noticed when ex amining individual VOCs. As such, the most frequently detected VOC (MTBE) and the two most frequently occurring subgroups of VOCs (gasoline oxygenates and THMs) in the Focused Survey were further characterized to evaluate anthropo

genic factors that may better explain and (or) to under

stand their frequent occurrence. The two most frequently occurring subgroups of VOCs in the Focused Survey were gasoline oxygenates and THMs; these subgroups were detected in 73.9 and 47.8 percent of CWS source waters sampled, respec

tively (table 4). In CWS source waters, MTBE was the most frequently detected gasoline oxygenate (77.3 percent) followed by TAME (20.3 percent). Chlo

roform and bromodichloromethane were the two most frequently detected THMs, occurring in 48.4 and 20.9 percent of CWS source waters, respectively. Anthropogenic factors associated with gasolineoxygenates were evaluated on the basis of MTBE highuse areas for CWSs served by ground-water, reservoir and (or) lake, and river and (or) stream source waters, and on watercraft use on re servoirs and lakes. Anthro

pogenic factors associated with THMs detected in reservoir source waters were evaluated on the basis of ancillary data provided byCWS personnel. All anal

yses were performed using data at or above the MDL. 

## MTBE and Gasoline Oxygenates
Detected concentrationsof MTBE in groundwater source waters inside and outside of MTBE highuse areas were compared. Fifty-five wells were within MTBE high-use areas and 23 were outside of these areas. MTBE was detected more frequently in MTBE low-use areas than in MTBE high-use areas. When both samples collected fro m individual wells were considered, MTBE was detected in 73.9 percent (34 of46) of ground-water samples collected in MTBE lowuse areas and in 62.7 percent (69 of 110) of groundwater samples collected in MTBE high-use areas. The differences in occurrence and concentration may be explained, in part, by how these sites were selected. Thirty-eight CWS wells wereselected because of the suspected occurrence of MTBEand 37 were selected because of a known occurrence (Appendix A). How

ever, 21 of the 37 sites where MTBE was known to occur were not in areas of MTBE high use. This com

parison is then skewed toward those sites outside of MTBE high-use areas and is merely a result of inten

tionally selecting wells witha known occurrence of MTBE. For this reason, statistical comparisons were not completed. Concentrations of MTBE in reservoir and (or)lake source waters inside and outside of MTBE highuse areas were compared seasonally (fig. 14). Twentyfive reservoir and (or) lake sources were inside MTBE high-use areas and 14 were outside of these areas. MTBE was detected more frequently and concentra

tions were greater in MTBEhigh-use areas than in MTBE low-use areas. This is likely due, in part, to the much larger percentage of MTBE volume/volume present in gasoline in MTBE high-use areas than in other areas. However, because as few as four detec

tions of MTBE were found in reservoir and (or) lake source waters in MTBE low-areas, statistical compar

isons were not completed. Concentrations of MTBE in river and (or) stream source waters inside and outside of MTBE high-use areas also werecompared seasonally (fig. 15). Eleven of the river and (or) stream intakes were inside MTBE high-use areas and six were out

side of these areas. Similar to reservoir and (or) lake source waters, MTBE was detected more frequently and concentrations were greater in MTBE high-use areas than in MTBE low-use areas. However, because as few as three detections of MTBE were found in river and (or) stream sources in MTBE low-use areas, statistical comparisons were not completed.**26 Occurrence and Temporal Variability of MTBE and Other VOCs in Select Sources of Drinking Water Figure 14** 

. Detected concentrations of methyl tert -butyl ether (MTBE) in reservoir and lake source waters by location in MTBE low- and high-use areas. 0.01

0.1

1 10 100CONCENTRATIONS, IN MICROGRAMS PER LITER

Spring Winter Fall Summer 4 20 12 20 7 14 4 17

30 Number of values 

### EXPLANATION



### x

x 75th percentile
Median 25th percentile
Lower outside Upper outside MTBE low-use area MTBE high-use are a



### x x

SEASON



### Gasoline oxygenates were analyzed in relation to watercraft use as reported in an ancillary data form completed by personnel at each CWS (Ivahnenko and others, 2001). The average number of watercraft per reservoir per year was divided by the surface area (in acres) of each respective reservoir to obtain a water

craft-use factor (number of boats per acre per year). In order to characterize the effect of watercraft on the occurrence and concentration of gasoline oxygenates, the sum of the average dete cted concentration of all gasoline oxygenates for each reservoir was plotted relative to the watercraft-use factor in MTBE high- and low-use areas (fig. 16). Linear regression analyses indicated a weak pos

itive trend associated with the average gasoline oxy

genate concentration and watercraft use in MTBE highuse areas. The relation between the average gasoline oxygenate concentration and watercraft use in reser

voirs inside MTBE high-use areas resulted in an r2

### of 0.3783. However, no relation was observed for reser

voirs in MTBE low-use areas (r2 

### =0.0242). In general, as watercraft use increased in areas of MTBE high-use, the average concentration of gasoline oxygenates also increased. All watercraft-use values (inside and outside of MTBE high-use areas) were then divided into four quartile categories: (1) 0 to 25th percentile; (2) 26th to 50th percentile; (3) 51st to 75th percentile; and (4) 76th to 100th percentile. The average gasoline oxygenate concentrations were then pl otted per quartile category (fig. 17). Again, the average concentration of gasoline oxygenates increased as watercraft use increased.**Anthropogenic Factors Associated with MTBE, Gasoline Oxygenates, and Trihalomethanes 27**  **Figure 15**

. Detected concentrations of methyl tert -butyl ether (MTBE) in river and st ream source waters by location in MTBE low- and high-use areas.

**Figure 16**

. Average sum of gasoline oxygenate concentrations versus watercraft-use factor. 0.01

0.1

1 10CONCENTRATIONS, IN MICROGRAMS PER LITER

Spring Winter Fall Summer 4 21 5 18 3 17 4 23

30 Number of values 

### EXPLANATION



### x
75th percentile
Median 25th percentile
Lower detached Upper outside MTBE low-use area MTBE high-use are a



### o o x

SEASON

0 1 2 3 4 5 6 7 8

0 5 10 15 20 25 30 35 40 4 5 WATERCRAFT USE FACTOR, IN NUMBER OF BOATS PER ACRE PER YEARCONCENTRATION, IN MICROGRAMS PER LITER

r2= 0.3783

r2= 0.0242 MTBE high-use area MTBE low-use area

Linear (MTBE high-use area) Linear (MTBE low-use area )**28 Occurrence and Temporal Variability of MTBE and Other VOCs in Select Sources of Drinking Water Figure 17** 

. Average concentrations of gasoline o xygenates by watercraft-use quartiles. 0.01

0.1

1 10CONCENTRATIONS, IN MICROGRAMS PER LITER

Quartile 1 Quartile 2 Quartile 3 Quartile 4 9 10 9 9

10 Number of values 

### EXPLANATION

WATERCRAFT USE 75th percentile
Median 25th percentile A A AB BC C

Populations that share the same letter are not significantly dif- ferent at a 95-percent confidence interval



## Trihalomethanes
Trihalomethanes were detected in 11 of the reservoirs and (or) lakes sampled in the Focused Survey. The most frequently detected THM was chloro

form, which was found in 10 of the 39 reservoirs and (or) lakes (25.6 percent), followed by bromodichlo

romethane, which was found in7 of the 39 reservoirs and (or) lakes (17.9 percent). Seven reservoirs and (or) lakes serving CWSs contained detectable concentra

tions of at least two THMs. THMs commonly are referred to as disinfection by-products because they can occur in drinking water thathas been treated with chlo

rine. Because samples in the Focused Survey were col

lected directly from the source water—not finished drinking water—each of these seven CWSs were con

tacted to better understand the occurrence of these com

pounds, and each provided input to the occurrence and likely source of THMs in their source water. CWS personnel indicated that THMs were present in their source water as disinfection by-prod

ucts. Three of the CWSs return filter backwash to the source-water reservoir; one disinfects water from other sources with chlorine and th en releases the disinfected water to the reservoir; one CWS adds chlorine upstream of the source reservoir for algae control; one CWS has a powerplant that withdraws water from the reservoir, disinfects the water with chlorine for algal control, uses the water for cooling purpos es, and then releases the water back to the reservoir. Lastly, one CWS indicated that the source of THMs in the source water could be due to a wastewater treatment facility discharging upstream of the reservoir. THMs were detected in 11 of the 17 rivers and (or) streams sampled in the Focused Survey. Chloro

form was the most frequentlydetected THM, occurring in 11 of the 17 rivers and (or) streams (64.7 percent). Nine of these 11 rivers and (or) streams contained at least two THMs.**Summary and Conclusions 29** 

### The CWSs that obtain their source water from the rivers and (or) streams with more than one detectable concentration of any THM were not contacted for addi

tional information to better understand the occurrence of the THMs. It is presumed, however, that the sources of these compounds may include point-source dis

charges upstream from the CWS intakes. Discharges could include those from wastewater treatment plants, power plants, and industrial discharge. Nonpoint sources, such as runoff of treated irrigation water from lawns, inflow of ground water containing THMs, and combined sewer overflows that are chlorinated prior to discharge, also could explain the occurrence of these compounds.



## SUMMARY AND CONCLUSIONSThe U.S. Geological Survey National WaterQuality Assessment Program in cooperatio n with the Metropolitan Water District of Southern California (MWDSC) and the Oregon Health & Science Univer

sity completed an investigation of the Nation’s drinking-water supplies. The study was sponsored by the American Water Works Association Research Foundation to provide inform ation on the occurrence, concentration, and temporal variability of methyl tert

butyl ether (MTBE) and other volatile organic com

pounds (VOCs) in source waters used by community water systems (CWSs). The national investigation was completed in two stages: (1) reviews of available literature, and (2) the collection of new drinking-water data. Two surveyswere completed for the collection of new drinkingwater data. The first, termed the Random Survey, employed a statistically stratified design for sampling source waters from 954 randomly selected CWSs based on the total number of systems within five populationserved size categories, source-water type, and the total number of people served by each of the source-size categories used within the United States. The second survey, which is the focus of this report, is termed the Focused Survey, which included samples collected from CWS source waters that are suspected or known to contain MTBE. The intent of the Focused Survey was to provide an improved un derstanding of the occur

rence, concentration, temp oral variability, and some anthropogenic factors associated with the frequent occurrence of MTBE and other frequently identified VOCs. Each sample collected was analyzed for 66 VOCs, including MTBE and three other ether gasoline oxygenates (hereafter termed gasoline oxygenates), at the MWDSC laboratory. The 451 samples were col

lected at fixed intervals for one year from 78 groundwater, 39 reservoir and (or) lake, and 17 river and (or) stream source waters in select areas of the Nation. Ground-water source waters were sampled biannually, reservoirs and lakes were sampled quarterly, and rivers and streams were sampled eight times per year. In addition, 744 field quality-control (QC) samples, including trip-reagent blanks, field-reagent blanks, field-equipment blanks, and duplicate samples were collected. All data underwent an exhaustive QC review process to accept or reject source-water data for inclusion in the Focused Survey’s findings. Occurrence data from the Focused Survey were compared to results obtain ed from the Random Survey using a common asse ssment level of 0.2 μg/L. Fortyone and 42 individual VOCs were detected in the Focused Survey and Random Survey, respectively, 37 of which were detected in both surveys. However, the detection frequency of many VOCs was greater in samples collected as part of the Focused Survey than in the Random Survey. Because source waters sus

pected or known to contain MTBE were sampled in the Focused Survey, MTBE was detected in 55.5 percent of the 134 CWSs sampled in the Focused Survey, whereas MTBE was detected in only 8.7 percent of 954 CWSs sampled in the Random Survey. The increased detection frequency of other VOCs in the Focused Survey may be explained by high-population density, which was one factor associ

ated with the selection of source waters to be sampled as part of the Focused Survey. The 66 VOCs analyzed were subdivided into seven subgroups of VOCs, based mainly on the pri

mary use of the compounds. Each subgroup of VOCs was found more frequently inthe Focused Survey than in the Random Survey. The gasoline oxygenate sub

group, which includes MTBE, was found most fre

quently and was detected in 53.7 percent of CWSs in the Focused Survey and in 8.5 percent of CWSs sam

pled in the Random Survey. Again, this difference is due largely to the selection of sites with suspected or known occurrence of MTBE. A large difference in occurrence also was observedin the solvent subgroup; solvents were detected in 21.6 percent and 6.3 percent of CWSs sampled in the Fo cused and Random Survey, respectively. The two mostfrequently detected sol

vents in both surveys were tetrachloroethene and**30 Occurrence and Temporal Variability of MTBE and Other VOCs in Select Sources of Drinking Water** 

### trichloroethene; however, these compounds were mainly detected only in CWSs supplied by ground water. Little difference inoccurrence was observed for the THM subgroup; these comp ounds were detected in 16.4 percent of Focused Survey and 14.8 Random Survey CWSs, respectively. This may indicate a perva

sive occurrence of THMs in source waters, regardless of CWS size or geographic location. In contrast to results of the Random Survey, the occurrence of subgroups of VOCs does not appear to be related to the size (based on population served) of CWSs in the Focused Survey supplied by ground water. In the Focused Survey, each subgroup of VOCs was detected at similar frequencies in each CWS size cate

gory. However, there were some differences in CWSs supplied by surface water in that the gasoline oxy

genate and other gasoline compound subgroups were predominantly detected in the Focused Survey, whereas solvents, THMs, and organic synthesis compounds were detected more frequently in several sizes of CWSs sampled in the Random Survey. Only two samples were collected from each ground-water source water included in the Focused Survey; thus, temporal variations on a seasonal basis could not be identified. However, comparisons were made between the first samp le and the second sample collected from 78 CWSs. No apparent differences were observed for any subgroup of VOCs between the first and second ground-water source water samples ana

lyzed. It is presumed that aninsufficient amount of time passed between the collectio n of the first and second ground-water sample, typically 6 months, to observe any significant changes in ground-water quality. The occurrence of each subgroup of VOCs was virtually identical between the two samples, and no statistically significant differences at an alpha of 0.05 were noticed in the detected VOC concentrations. Detected concen

trations were small, typically less than 1 μ g/L. How

ever, the maximum concentrations of MTBE, tetrachloroethene, and trichl oroethene in ground-water source waters were 924, 290, and 165 μ g/L, respec

tively. On the basis of data at or above the method detection limit, concentrationsof VOCs detected in the Focused Survey in reservoir and (or) lake source waters were typically small (less than 1 μ g/L 

## ) . Furthermore, very few statistically signific ant differences in detected concentrations were noticed on a seasonal basis among subgroups of VOCs. However, a slight seasonal pattern was evident for the occurrenc e of gasoline oxygenates and other gasoline compounds in the 39 reservoirs and lakes sampled. Both of these subgroups of VOCs were detected more frequently during spring and summer than in fall and winter. Thirty-three of the 39 reservoir and (or) lakes sampled allow motorized watercraft. Thus, the greater occurrence of these compounds during spring and summer is presumed to be related to the increased use of watercraft during these seasons. No seasonal pattern was observed for the THMs or organic synthesis subgroups. This indicates the possi

bility of a common and continuous source of contami

nation for these VOCs. As in ground-water and reservoir and (or) lake source waters, concentrations of VOCs in river and (or) stream source waters typically were small (less than 1 μ g/L 

## ) , and very few statistically significant differ

ences in detected concentrations were observed on a seasonal basis among subgroups of VOCs. Similarly, a seasonal pattern was not evident for the detection fre

quency of any subgroup of VOCs in the 17 river and (or) stream source waters sampled. Gasoline oxygen

ates, other gasoline compounds, THMs, and organic synthesis compounds were detected at similar frequen

cies within their respective subgroups year-round. The lack of seasonal differences for these subgroups of compounds may indicate a common and continuous source of contamination upstream of the intake loca

tion. The most frequently detected VOC (MTBE) and the two most frequently occurring subgroups of VOCs (gasoline oxygenates and THMs) detected in CWS source waters sampled in th e Focused Survey were fur

ther characterized to evaluate some anthropogenic fac

tors that may better explain their frequent occurrence. MTBE, gasoline oxygenates, and THMs were detected in 77.3, 73.9, and 47.8 percent of CWS source waters sampled, respectively. Fifty-five of 78 wells, 25 of 39 reservoirs and (or) lakes, and 11 of 17 rivers and streams were inside MTBE high-use areas. Concentrations of MTBE in res

ervoir and (or) lake and river and (or) stream source waters inside and outside of MTBE high-use areas were also compared seasonally. MTBE was detected more frequently and concentrations were greater in MTBE high-use areas than in MTBE low-use areas. However, because as few as three detections of MTBE were found in surface-water source waters in MTBE low-use areas, statistical comparisons were not com

pleted.**References 31** 

### The concentration of gasoline oxygenates in reservoirs was slightly correlated with watercraft use (boats/year/acre) on reservoirs inside MTBE high-use areas (r2 

### =0.3783). As watercraft use increased, the average concentration of gasoline oxygenates also increased. No relation betw een gasoline oxygenates in reservoirs and watercraft use was observed in reservoirs outside of MTBE high-use areas (r2 

### =0.0242). Trihalomethanes were detected in 11 of the reservoirs and (or) lakes sampled. Seven of these reser

voirs contained detectable concentrations of more than one THM. Attempts were made to contact each of the seven CWSs with multiple THM detections. Each CWS provided additional information on reasons why THMs may occur in their source water. In all cases, the pres

ence of THMs were the result of the addition of chlo

rine to waters that ultimately recycled back to, or upstream of, the reservoir that was sampled.



## REFERENCES Arizona Department of Environmental Quality, 1999, Report on methyl tertiary butyl ether (MTBE), October 1, 1999: Arizona Department of Environmental Quality, accessed March 1, 2002, at URL http://www.adeq.state.az.us/environ/waste/ust/ mtbe.html Bourelle, Andy, 1998, MTBE—A real concern for South Lake Tahoe: Tahoe Daily Tribune, August 28, 1998, accessed December 6, 2000, at URL http://www.tahoe.com/tribune/stories.8.28.98/news/ mt28Aug1347.html Bush, P.W., Ardis, A.F., Fahlquist, Lynne, Ging, P.B., Hornig, C.E., and Lanning-Rush, Jennifer, 2000, Water quality in south-central Texas, 1996-98: U.S. Geologi

cal Survey Circular 1212, 32 p. California Department of Health Services, 2001, MTBE in California drinking water: accessed December 6, 2000, at URL http://www.dhs.cahwnet.gov/ps/ddwem/ chemicals/MTBE/mtbeindex.htm California Environmental Protection Agency, 1997, MTBE (methyl tertiary butyl ether), Briefing paper prepared by the California Environmental Protection Agency, April 24, 1997 (updated September 3, 1998): accessed February 28, 2002, at URL http://www.arb.ca.gov/cbg/oxy/oxy.htm California Senate, 1998, Does California need MTBE?, prepared by Kip Wiley, February 1998: accessed February 28, 2002, at URL http://www.sen.ca.gov/ftp/sen/sor/environ/98mtbe.htm City of Santa Monica, 1999, MTBE issue featured on “60 Minutes”: accessed December 6, 2000, at URL http://epwm.santamonica.org/epwm/ watquality/1999report/waterweb/news05.htm Delzer, G.C., and Ivahnenko, Tamara, 2003, A review of literature for methyl tert-butyl ether in sources of drinking water in the United States: U.S. Geological Survey Open-File Report 01-322, 19 p. Grady, S.J., 2003, A national survey of methyl tert-butyl ether and other volatile organic compounds in drinking-water sources—Results of the random survey: U.S. Geological Survey Water-Resources Investigations Report 02-4079, 85 p. Halde, M.J., Delzer, G.C., and Zogorski, J.S., 1998, Study design and analytical resu lts used to evaluate a surface-water point sampler for volatile organic compounds: U.S. Geological Survey Open-File Report 98-651, 31 p. Hattan, Greg, 2000, MTBE treatment systems in Kansas: Association of State and Territorial Solid Waste Management Officials, MTBE and Fuel Oxygenates Workgroup Newsletter, v. 3, no. 1, 31 p. Helsel, D.R., and Hirsch, R.M., 1992, Statistical methods in water resources: New York, Elsevier, 529 p. Ivahnenko, Tamara, Grady, S.J., and Delzer, G.C., 2001, Design of a national survey of methyl tert-butyl etherand other volatile organic compounds in drinkingwater sources: U.S. Geological Survey Open-File Report 01-271, 42 p. Johnson, R.L., Pankow, J.F., Bender, D.A., Price, C.V., and Zogorski, J.S., 2000, MTBE—To what extent will past releases contaminate community water supply wells?: Environmental Science & Technology, v. 34, no. 9, p. 2A-9A. Koterba, M.T., Wilde, F.D., and Lapham, W.W., 1995, Ground-water data collection protocols and proce

dures for the National Water-Quality AssessmentProgram—Collection and documentation of waterquality samples and related data: U.S. Geological Survey Open-File Report 95-399, 113 p. Lopes, T.J., and Furlong, E.T., 2001, Occurrence and poten

tial adverse effects of semivolatile organic compounds in streambed sediment, United States, 1992-1995: Environmental Toxicology and Chemistry, v. 20, no. 4, p. 727-737. Reiser, R.G., and O’Brien, A.K., 1998, Occurrence and seasonal variability of volatile organic compounds in seven New Jersey streams: U.S. Geological Survey Water-Resources Investigations Report 98-4074, 11 p. Rowe, B.L., Grady, S.J., Zogorski, J.S., Koch, Bart, Tratnyek, Paul, 2001, Initial findings—National survey of MTBE, other ether oxygenates, and other VOCs in community drinking-water sources: U.S. Geological Survey Open-File Report 01-399, 1 p.**32 Occurrence and Temporal Variability of MTBE and Other VOCs in Select Sources of Drinking Water** 

### Shelton, L.R., 1997, Field guide for collecting samples for analysis of volatile organic compounds in stream water of the National Water-Quality Assessment Program: U.S. Geological Survey Open-File Report 97-401, 14 p. Squillace, P.J., Moran, M.J., Lapham, W.W., Price, C.V., Clawges, R.C., and Zogorski, J.S., 1999, Volatile organic compounds in untreated ambient groundwater of the United States, 1985-1995: Environmental Science & Technology, v. 33, no. 23, p. 4176- 4187. State of Maine, 1998, The presence of MTBE and other gasoline compounds in Maine's drinking water, prelim

inary report, October 13, State of Maine, Bureau of Health, Bureau of Waste Management and Remedia

tion, Maine Geological Survey: Augusta, State of Maine, 23 p. U.S. Environmental Protection Agency, 1997, Drinking water advisory—Consumer acceptability advice and health effects analysis on methyl tertiary-butyl ether (MTBE): Office of Water, EPA-822-F-97-009, 4 p. ———1998, Announcement of the drinking water contami

nant candidate list, notice (March 12, 1998): Federal Register, v. 63, no. 40, p. 10273-10287. ———1999a, List of reformulated gasoline program areas: Office of Mobile Sources, accessed April 5, 1999, at URL http://www.epa.gov/oms/rfgarea.htm ———1999b, Winter oxygenated fuels program: Office of Mobile Sources, accessed June 16, 1999, at URL http://www.epa.gov/oms/fuels.htm ———2001, National Primary Drinking Water Standards: Office of Water, EPA-816-F-01-007, 4 p. U.S. Geological Survey, 1990, Digital line graphs from 1:2,000,000-scale maps, data users guide 3: U.S. Geological Survey National Mapping Program Techni

cal Instructions, 70 p., accessed March 25, 2002, at URL ftp://mapping.usgs.gov/pub/ti/DLG/2mdlgguide Wigglesworth, Terry, 1999, MTBE—A watertight case: Chemistry and Industry, no. 10, p. 408. Zogorski, J.S., Morduchowitz, A.M., Baehr, A.L., Bauman, B.J., Conrad, D.L., Drew, R.T., Korte, N.E., Lapham, W.W., Pankow, J.F., and Washington, E.R., 1997, Fuel oxygenates and water quality, chapter 2 of the Inter

agency Assessment of Oxygenated Fuels: Washington, D.C., National Science and Technology Council, Office of Science and Technology Policy, p. 2-1 to 2-80.

# APPENDIXES

# Appendix A - Number of community water system sources sampled per State**36 Occurrence and Temporal Variability of MTBE and Other VOCs in Select Sources of Drinking Water Table A1** 

. Number of community water system source waters sampled that were sus pected of having co ncentrations of methyl tert -butyl ether, by State and source-size category [GW, ground water; SW, surface water; VSM, very small; SM, small; MED, medium; LRG, large; VLRG, very large]

**State 1**  **Source-size category Total**  **GW- VSM**  **GW SM**  **GW MED**  **GW LRG**  **GW VLRG**  **SW VSM**  **SW SM**  **SW MED**  **SW LRG**  **SW VLRG**  CA 0 0 2 4 6 0 0 0 1 6 19 CO 0 0 0 0 0 0 0 0 0 1 1 CT 0 0 0 2 1 0 1 0 0 0 4 DE 2 2 3 1 1 0 0 0 0 2 11 GA 0 0 0 1 0 0 0 0 0 2 3 IN 0 0 0 0 0 0 0 0 0 1 1 KY 0 0 0 2 0 0 0 0 0 1 3 LA 0 0 0 0 0 0 0 0 0 1 1 MA 0 0 0 0 0 0 0 0 0 2 2 MD 0 0 0 0 0 0 0 0 0 1 1 MS 0 0 0 0 0 0 0 0 0 1 1 NJ 0 0 0 0 0 0 0 0 0 1 1 NV 0 0 0 0 0 0 0 0 0 1 1 NY 0 0 0 0 4 0 0 0 0 0 4 OK 0 0 0 0 0 0 0 0 0 2 2 OR 0 0 1 3 0 0 1 1 0 0 6 PA 0 0 0 0 0 0 0 0 0 3 3 RI 0 0 0 0 0 0 0 0 0 1 1 TX 0 1 0 0 2 0 0 0 0 3 6 VA 0 0 0 0 1 0 0 0 0 3 4 VT 0 0 0 0 0 0 0 0 0 1 1 WV 0 0 2 0 0 0 0 0 0 0 2 Total 2 3 8 13 15 0 2 1 1 33 78 1 Postal Service State abbreviation.**Appendix A 37 Table A2** 

. Number of community wa ter system source waters sampled with known concentrations of methyl tert -butyl ether, by State and source-size category [GW, ground water; SW, surface water; VSM, very small; SM, small; MED, medium; LRG, large; VLRG, very large]

**State 1**  **Source-size category Total**  **GW- VSM**  **GW SM**  **GW MED**  **GW LRG**  **GW VLRG**  **SW VSM**  **SW SM**  **SW MED**  **SW LRG**  **SW VLRG**  AZ 0 0 0 1 0 0 0 0 0 1 2 CA 0 0 0 0 0 0 1 0 0 8 9 CT 1 0 0 0 0 0 0 0 0 0 1 FL 0 0 0 0 2 0 0 0 0 1 3 IA 0 2 0 0 0 0 0 0 0 0 2 IL 0 2 2 0 0 0 0 0 0 0 4 KY 1 0 0 0 0 0 0 0 0 0 1 KS 0 2 1 1 0 0 0 0 0 0 4 MA 1 0 0 1 0 0 0 0 0 0 2 MD 0 1 1 1 0 0 0 0 0 0 3 ME 0 1 2 1 0 0 0 0 0 0 4 NC 0 0 1 0 0 0 0 0 0 1 2 NH 0 0 1 1 0 0 0 0 1 1 4 NJ 0 0 0 2 2 0 0 0 0 0 4 NY 0 0 0 0 1 0 0 0 0 0 1 OH 0 1 0 0 0 0 0 0 0 0 1 OR 2 0 0 0 0 0 0 0 0 0 2 PA 1 0 0 0 0 0 0 0 0 1 2 TN 0 0 0 0 0 0 0 0 1 0 1 TX 0 0 0 0 0 0 1 0 0 2 3 VA 0 1 0 0 0 0 0 0 0 0 1 Total 6 10 8 8 5 0 2 0 2 15 56 1 Postal Service State abbreviation.

**Table A3**

. Number of community wa ter system source waters sampled as control sites where methyl tert -butyl ether would likely not be present, by State and source-size category [GW, ground water; SW, surface water; VSM, very small; SM, small; MED, medium; LRG, large; VLRG, very large]

**State 1**  **Source-size category Total** **GW VSM**  **GW SM**  **GW MED**  **GW LRG**  **GW VLRG**  **SW VSM**  **SW SM**  **SW MED**  **SW LRG**  **SW VLRG**  SD 0 0 0 0 0 0 0 0 0 1 1 MN 0 0 0 1 1 0 0 0 0 1 3
1 Postal Service State abbreviation.

# Appendix B - Detailed review of field quality-control data**40 Occurrence and Temporal Variability of MTBE and Other VOCs in Select Sources of Drinking Water** 

## SUMMARY OF QUALITY-CONTROL SAMPLES A review of the field quality-control (QC) data collected in the Focused Survey has been conducted with parallel protocols as those of the Random Survey. Field-reagent blank (FRB) and trip-reagent blank (TRB) samples were collected in both surveys; how

ever, duplicate samples and field-equipment blank (FEB) samples also were collected in the Focused Survey. FEB samples were co llected only for surfacewater samples. As in the Random Survey, FRB samples were used to measure contamin ation from the environment around the sampling site and during sample shipment. In the Focused Survey, a bottle containing VOC-free water was provided to U.S. Geological Survey (USGS) field personnel with each sample kit. FRB samples were prepared by directly filling VOC 40 mL (millili

ters) vials labeled “Field Bl ank” at each sampling site with VOC-free water immediately prior to or following the collection of the source-water sample. USGS field personnel preserved the FRB sample with a 1:1 hydro

chloric acid solution to a pH of 2. It is important to note that FRB samples are used extensively to accept or reject detected concentrations of volatile organic com

pounds (VOCs) in source-water samples in the fol

lowing appendix (Appendix C). TRB samples, however, were prepared at the laboratory by filling vials with VOC-free water. TRB samples were placed in each sample kit and travel ed along with the sourcewater samples back to the Metropolitan Water District of Southern California (MWDSC) laboratory. TRB samples were never opened and were intended to mea

sure any contamination associated with samples during shipment. Because ground-water samples were col

lected from permanently installed pumps, FEB samples were collected only for surface-water source waters. FEBs were intended to represent all contamination associated with the surface -water sampling process, sampling equipment, processing, transportation, and laboratory handling/analys is. FEB samples were col

lected by passing VOC-free water through the USGS VOC hand sampler and filling the vials accordingly. FEB sample collection pro cedures for the VOC hand sampler are described by Shelton (1997). Field dupli

cate source-water samples were collected at about 15 percent of the surface- and ground-water sites to characterize variability associated with sampling, pro

cessing, transportation, and analysis. Ground-water duplicates were collectedsequentially, and surfacewater duplicates were collected concurrently with their respective source-water sample. 

## Field-Reagent Blank Samples
In addition to data for 467 (451 source-water samples plus 16 from control sites) source-water samples analyzed as part of the Focused Survey, the MWDSC laboratory reported VOC analysis for 321 FRB samples. For the first three months of sampling, FRB samples were not collected with 100 percent of the source-water samples. Subsequently, a FRB accom

panied all source-water samples. Forty-six VOCs were detected in one or moreof the 321 FRB samples (table B1) with a concentration range of 0.03 to 17.0 μ g/L for all VOCs detected. Detection frequencies ranged from 0.31 percent for several VOCs to 75.4 percent for toluene. As in the Random Survey, toluene and methylene chloride were the most frequently detected compounds, reported in nearly two-thirds of the FRB samples. Seven other VOCs, including MTBE, ethylbenzene, m ,

p -xylene, o -xylene, chloroform, styrene, and 1,2,4- trimethylbenzene were reported in 10 percent of the FRB samples (table B1). Up to 67 percent of the detec

tions in the FRBs were less than 0.2 μ g/L. 

## Trip-Reagent Blank Samples TRB samples were sent with 100 percent of the source-water samples; however, TRB samples were analyzed only when a VOC was detected in the sourcewater sample. The MWDSC la boratory analyzed 304 TRB samples. There were 163 source-water samples with no VOCs detected in the source-water sample, thus the accompanying TRB sample was not analyzed. Concentrations of the detected VOCs in the TRB samples ranged from 0.03 to 2.56 μ g/L (table B1). Detection frequencies ranged from 0.3 percent for sev

eral VOCs to 58.9 percent for toluene. Thirty-five of the 66 VOC compounds analy zed were detected in the 304 TRB samples. As with the FRB sample s in both the Focused and Random Surveys, methylene chloride (58.0 percent) and toluene (58.9 percent) were the most frequently detected compounds, reported in nearly two-thirds of the TRB sample s. Similarly, six (MTBE, ethylbenzene, m , p -xylene, o -xylene, styrene, and 1,2,4- trimethylbenzene) of the seven VOCs detected in FRB samples also were detected in TRB samples. Up to 54.7 percent of the detected c oncentrations in the TRBs were less than 0.2 μ g/L.**Appendix B 41 Table B1** 

. Summary of volatile organic compounds detected in field- equipment blanks, field-reagent blanks, and trip-reagent blanks [FEB, field-equipment blank; FRB, field-reagent blank; TRB, trip-reagent blank; ND, not detected; --, not applicable]
**Volatile organic compound Type of**  **blank Number of**  **samples Number of**  **detections Range in**  **concentration (micrograms per liter)**  **Detection frequency (percent)**  Gasoline Oxygenates tert-Amyl methyl ether (TAME) FRB 321 7 0.04-0.42 2.2 TRB 304 4 0.04-0.05 1.3 FEB 50 ND

-- -- Diisopropyl ether (DIPE) FRB 321 ND

-- -- TRB 304 ND

-- -- FEB 50 ND

-- -- Ethyl tert-butyl ether (ETBE) FRB 321 ND

-- -- TRB 304 ND

-- -- FEB 50 ND

-- -- Methyl tert-butyl ether (MTBE) FRB 321 143 0.04-17.02 44.6 TRB 304 153 0.04-1.62 50.3 FEB 50 9 0.04-1.74 18.0 Other Gasoline Compounds Benzene FRB 321 11 0.03-9.46 3.4 TRB 304 5 0.03-0.08 1.6 FEB 50 2 0.05-2.01 4.0

n -Butylbenzene FRB 321 1 0.07 0.3 TRB 304 ND

-- -- FEB 50 1 0.07 2.0

sec -Butylbenzene FRB 321 1 0.05 0.3 TRB 304 ND

-- -- FEB 50 ND

-- -- tert-Butylbenzene FRB 321 1 0.04 0.3 TRB 304 ND

-- -- FEB 50 ND

-- -- Ethylbenzene FRB 321 125 0.04-0.79 38.9 TRB 304 50 0.04-0.3 16.4 FEB 50 9 0.04-0.88 18.0 Naphthalene FRB 321 22 0.06-0.15 6.9 TRB 304 15 0.06-0.13 4.9 FEB 50 7 0.06-0.38 14.0 Toluene FRB 321 242 0.03-6.95 75.4 TRB 304 179 0.03-0.62 58.9 FEB 50 17 0.03-6.01 34.0**42 Occurrence and Temporal Variability of MTBE and Other VOCs in Select Sources of Drinking Water** Other Gasoline Compounds—Continued 1,3,5-Trimethylbenzene FRB 321 2 0.05-0.18 0.6 TRB 304 ND

-- -- FEB 50 2 0.03-0.29 4.0

m ,

p -Xylene FRB 321 123 0.07-1.49 38.3 TRB 304 57 0.07-0.76 18.8 FEB 50 7 0.07-3.73 14.0

o -Xylene FRB 321 103 0.03-0.88 32.1 TRB 304 37 0.03-0.23 12.2 FEB 50 6 0.03-1.68 12.0 Trihalomethanes Bromodichloromethane FRB 321 2 0.02-0.03 0.6 TRB 304 ND

-- -- FEB 50 ND

-- -- Bromoform FRB 321 ND

-- -- TRB 304 ND

-- -- FEB 50 ND

-- -- Chlorodibromomethane FRB 321 2 0.02-0.03 0.6 TRB 304 ND

-- -- FEB 50 ND

-- -- Chloroform FRB 321 45 0.03-5.7 14.0 TRB 304 13 0.03-0.06 4.3 FEB 50 4 0.03-0.18 8.0 Solvents Bromobenzene FRB 321 1 0.03 0.3 TRB 304 1 0.03 0.3 FEB 50 ND

-- -- Carbon tetrachloride FRB 321 1 0.28 0.3 TRB 304 ND

-- -- FEB 50 ND

-- -- Chlorobenzene FRB 321 ND

-- -- TRB 304 ND

-- -- FEB 50 ND

-- -- Chloroethane FRB 321 2 0.34-0.84 0.6 TRB 304 ND

-- -- FEB 50 ND

-- -- **Table B1** . Summary of volatile organic compounds detected in fiel d-equipment blanks, field-reagent blanks, and trip-reagent blanks—Continued [FEB, field-equipment blank; FRB, field-reagent blank; TRB, trip-reagent blank; ND, not detected; --, not applicable]
**Volatile organic compound Type of**  **blank Number of**  **samples Number of**  **detections Range in**  **concentration (micrograms per liter)**  **Detection frequency (percent)** **Appendix B 43** Solvents—Continued 2-Chlorotoluene FRB 321 ND

-- -- TRB 304 ND

-- -- FEB 50 1 0.14 2.0 4-Chlorotoluene FRB 321 1 0.03 0.3 TRB 304 ND

-- -- FEB 50 1 0.04 2.0 Dibromomethane FRB 321 ND

-- -- TRB 304 ND

-- -- FEB 50 ND

-- -- 1,2-Dichlorobenzene FRB 321 ND

-- -- TRB 304 ND

-- -- FEB 50 ND

-- -- 1,3-Dichlorobenzene FRB 321 ND

-- -- TRB 304 ND

-- -- FEB 50 ND

-- -- 1,1-Dichloroethane FRB 321 3 0.04-0.08 0.9 TRB 304 1 0.04 0.3 FEB 50 ND

-- -- 1,2-Dichloroethane FRB 321 1 0.32 0.3 TRB 304 ND

-- -- FEB 50 ND

-- -- 1,1-Dichloroethene FRB 321 1 0.1 0.3 TRB 304 ND

-- -- FEB 50 ND

-- -- cis -1,2-Dichloroethene FRB 321 3 0.03-0.09 0.9 TRB 304 ND

-- -- FEB 50 ND

-- -- trans -1,2-Dichloroethene FRB 321 ND

-- -- TRB 304 ND

-- -- FEB 50 ND

-- -- 1,2-Dichloropropane FRB 321 1 0.03 0.3 TRB 304 ND

-- -- FEB 50 ND

-- -- **Table B1** . Summary of volatile organic compounds detected in fiel d-equipment blanks, field-reagent blanks, and trip-reagent blanks—Continued [FEB, field-equipment blank; FRB, field-reagent blank; TRB, trip-reagent blank; ND, not detected; --, not applicable]
**Volatile organic compound Type of**  **blank Number of**  **samples Number of**  **detections Range in**  **concentration (micrograms per liter)**  **Detection frequency (percent)** **44 Occurrence and Temporal Variability of MTBE and Other VOCs in Select Sources of Drinking Water** Solvents—Continued Hexachloroethane FRB 321 ND

-- -- TRB 304 ND

-- -- FEB 50 ND

-- -- Methylene chloride FRB 318 191 0.03-1.18 60.1 TRB 300 174 0.03-0.71 58.0 FEB 50 31 0.03-0.54 62.0 Methyl ethyl ketone FRB 321 13 0.8-2.87 4.0 TRB 304 11 0.71-1.09 3.6 FEB 50 1 0.85 2.0

n -Propylbenzene FRB 321 20 0.05-0.26 6.2 TRB 304 8 0.05-0.11 2.6 FEB 50 2 0.14-0.17 4.0 1,1,1,2-Tetrachloroethane FRB 321 1 0.02 0.3 TRB 304 ND

-- -- FEB 50 ND

-- -- 1,1,2,2-Tetrachloroethane FRB 321 1 0.1 0.3 TRB 304 ND

-- -- FEB 50 ND

-- -- Tetrachloroethene FRB 321 6 0.05-1.1 1.9 TRB 304 1 0.05 0.3 FEB 50 ND

-- -- 1,2,4-Trichlorobenzene FRB 321 10 0.05-0.13 3.1 TRB 304 1 0.05 0.3 FEB 50 4 0.05-0.14 8.0 1,1,1-Trichloroethane FRB 321 1 0.4 0.3 TRB 304 ND

-- -- FEB 50 ND

-- -- 1,1,2-Trichloroethane FRB 321 ND

-- -- TRB 304 ND

-- -- FEB 50 ND

-- -- Trichloroethene FRB 321 1 0.25 0.3 TRB 304 ND

-- -- FEB 50 ND

-- -- **Table B1** . Summary of volatile organic compounds detected in fiel d-equipment blanks, field-reagent blanks, and trip-reagent blanks—Continued [FEB, field-equipment blank; FRB, field-reagent blank; TRB, trip-reagent blank; ND, not detected; --, not applicable]
**Volatile organic compound Type of**  **blank Number of**  **samples Number of**  **detections Range in**  **concentration (micrograms per liter)**  **Detection frequency (percent)** **Appendix B 45** Solvents—Continued 1,2,3-Trichloropropane FRB 321 7 0.03-0.1 2.2 TRB 304 ND

-- -- FEB 50 4 0.03-0.09 8.0 Organic Synthesis Acrylonitrile FRB 321 1 0.31 0.3 TRB 304 ND

-- -- FEB 50 ND

-- -- Bromochloromethane FRB 321 1 0.04 0.3 TRB 304 ND

-- -- FEB 50 ND

-- -- 1,3-Dichloropropane FRB 321 3 0.04-0.15 0.9 TRB 304 6 0.03-0.23 2.0 FEB 50 1 0.03 2.0 2,2-Dichloropropane FRB 321 1 0.07 0.3 TRB 304 1 0.29 0.3 FEB 50 ND

-- -- 1,1-Dichloropropene FRB 321 ND

-- -- TRB 304 ND

-- -- FEB 50 ND

-- -- Hexachlorobutadiene FRB 321 1 0.11 0.3 TRB 304 ND

-- -- FEB 50 ND

-- -- Isopropylbenzene FRB 321 29 0.04-0.34 9.0 TRB 304 9 0.04-0.12 2.6 FEB 50 2 0.04-0.31 4.0 p -Isopropyltoluene FRB 321 ND

-- -- TRB 304 8 0.04-0.1 3.0 FEB 50 ND

-- -- Styrene FRB 321 230 0.03-8.61 71.7 TRB 304 154 0.03-2.56 50.7 FEB 50 20 0.03-0.87 40.0 1,2,3-Trichlorobenzene FRB 321 11 0.05-0.11 3.4 TRB 304 7 0.05-0.1 2.3 FEB 50 3 0.06-0.1 6.0 **Table B1** . Summary of volatile organic compounds detected in fiel d-equipment blanks, field-reagent blanks, and trip-reagent blanks—Continued [FEB, field-equipment blank; FRB, field-reagent blank; TRB, trip-reagent blank; ND, not detected; --, not applicable]
**Volatile organic compound Type of**  **blank Number of**  **samples Number of**  **detections Range in**  **concentration (micrograms per liter)**  **Detection frequency (percent)** **46 Occurrence and Temporal Variability of MTBE and Other VOCs in Select Sources of Drinking Water** Organic Synthesis—Continued 1,2,4-Trimethylbenzene FRB 321 49 0.03-0.58 15.3 TRB 304 31 0.03-0.06 10.2 FEB 50 6 0.03-1.34 12.0 Vinyl bromide FRB 321 ND

-- -- TRB 304 ND

-- -- FEB 50 ND

-- -- Vinyl chloride FRB 321 ND

-- -- TRB 304 ND

-- -- FEB 50 ND

-- -- Fumigants Bromomethane FRB 319 6 0.1-0.18 1.9 TRB 299 5 0.09-0.13 1.7 FEB 50 ND

-- -- 1,4-Dichlorobenzene FRB 321 4 0.04-0.11 1.3 TRB 304 1 0.06 0.3 FEB 50 ND

-- -- cis -1,3-Dichloropropene FRB 321 ND

-- -- TRB 304 ND

-- -- FEB 50 ND

-- -- trans -1,3-Dichloropropene FRB 321 ND

-- -- TRB 304 ND

-- -- FEB 50 ND

-- -- Refrigerants Chloromethane FRB 321 8 0.13-1.53 2.5 TRB 304 ND

-- -- FEB 50 2 0.13-0.18 4.0 Dichlorodifluoromethane FRB 321 ND

-- -- TRB 304 ND

-- -- FEB 50 ND

-- -- Trichlorofluoromethane FRB 321 ND

-- -- TRB 304 ND

-- -- FEB 50 ND

-- -- 1,1,2-Trichloro-1,2,2-trifluoroethane FRB 321 ND

-- -- TRB 304 ND

-- -- FEB 50 ND

-- -- **Table B1** . Summary of volatile organic compounds detected in fiel d-equipment blanks, field-reagent blanks, and trip-reagent blanks—Continued [FEB, field-equipment blank; FRB, field-reagent blank; TRB, trip-reagent blank; ND, not detected; --, not applicable]
**Volatile organic compound Type of**  **blank Number of**  **samples Number of**  **detections Range in**  **concentration (micrograms per liter)**  **Detection frequency (percent)** **Appendix B 47** 

## FIELD-EQUIPMENT BLANK SAMPLES FEB samples were collectedonly for equipment used to collect samples atsurface-water sites by passing VOC-free water through the USGS VOC hand sampler and filling the vial s accordingly. Fifty FEB samples were collected. Twenty-three VOCs were reported in one or more of the FEB samples. Concen

trations of these VOCs ranged from 0.03 to 6.01 μ g/L. Detection frequencies (table B1) ranged from 2 percent for several VOCs to 62 percent for methylene chloride. 

## Duplicate Samples In addition to the FEBs, FRBs, and TRBs, dupli

cate samples were collected sequentially at groundwater sampling sites and concurrently at surface-water sampling sites. Duplicate samples were processed in the same manner as the s ource-water sample and pro

vide an indication of sampling and analytical reproduc

ibility. Sixty-nine source-water samples were collected with field duplicates. Detected concentrations of MTBE in field duplicate samples and corresponding source-water samples are shown in figure B1. Most of the points fall directly on or near the 1:1 line with an r2 

### value of 0.999, indicating very little variation in the concentrations of duplicates and source-water samples.


## STATISTICAL COMPARISON OF QUALITYCONTROL SAMPLES The low-level (less than 0.2 μ g/L) contamination evident in the field quality-control data required further analysis to determine the level of uncertainty associ

ated with VOC detectio ns. Similarities between detected concentrations in different blank types may indicate a common source of contamination, whereas differences may indicate more of a random source. The statistical analyses described below include compari

sons between FRB, TRB, and FEB samples. In addi

tion, duplicate source-water samples are further analyzed.

**Figure B1**

. Concentration of methyl tert -butyl ether in field duplicate and source-water samples. 0 5 10 15 20 25 30 35

0 5 10 15 20 25 30 3 5 CONCENTRATION IN SOURCE-WATER SAMPLES, IN MICROGRAMS PER LITERCONCENTRATION IN DUPLICATE SAMPLES,IN MICROGRAMS PER LITER**48 Occurrence and Temporal Variability of MTBE and Other VOCs in Select Sources of Drinking Water**

## Field-Reagent Blank Samples Versus TripReagent Blank Samples A review of the FRB and TRB sample data was completed to determine if there was a relation between the frequency and concentration of VOC detections in these samples for sites where both quality-control sam

ples were collected. Of the 304 TRB samples collected, 292 had a companion FRB sample. A Wilcoxon signed-rank test (Helsel and Hirsch, 1992), was used to statistic ally determine the relation between concentrations inFRB and TRB samples. VOCs detected in either bl ank type were used in the statistical analysis. Results for all 292 pairs of samples indicated that the concentrations of seven of the VOCs detected in both blanks werestatistically different at the 95-percent confidence level (table B2). These seven VOCs include chloromethan e, methylene chloride, MTBE, n -propylbenzene, styrene, TAME, and toluene. Concentrations of six of these VOCs were found to be statistically greater in the FRB samples than in the TRB samples. This may indicate th at the detections of VOCs might be due to greater exposure of the source water for the FRB samples to conditionsin the field than the TRB samples, which were unopened during field oper

ations. Concentrations of chloromethane were found to be statistically greater in the TRB samples than in the FRB samples, but this compou nd was detected in only 16 source-water samples.

**Table B2**

. Relation between concentrations of volatile organic compounds in 292 companion field-blank samples and tripblank samples [Statistically different results are the 95-percent confidence interval are given in boldface; H o , null hypothesis; FRB, field-reagent blank; TRB, trip-reagent blank; <, less than; >, greater than] **Volatile organic**

**compound Number of**  **detections in FRB samples**  **Number of detections in**  **TRB samples Null hypothesis tested and p-value**  **H o**  **: FRB=TRB 1**  **H o**  **: FRB<TRB 2**  **H o**  **: FRB>TRB 2** 
tert-Amyl methyl ether (TAME) 5 3 0.0457 0.0228 0.9773 Benzene 8 4 0.5394 0.7310 0.2697 Bromomethane 6 5 0.7679 0.3839 0.6169 Chloroform 37 12 0.4377 0.7815 0.2189 Chloromethane 8 0 0.0347 0.9827 0.0174 1,4-Dichlorobenzene 4 1 0.3190 0.0904 0.8413 1,1-Dichloroethane 3 1 0.9989 0.5021 0.4993 Ethylbenzene 115 46 0.3452 0.1726 0.8276 Isopropylbenzene 23 7 0.5298 0.2649 0.7356 p -Isopropyltoluene 0 8 0.1577 0.0788 0.9215 Methyl ethyl ketone 11 10 0.2224 0.1112 0.8891 Methylene chloride 172 166 0.0427 0.0214 0.9787 Methyl tert-butyl ether (MTBE) 131 145 <0.0001 <0.0001 1.0000 Naphthalene 19 13 0.5981 0.7016 0.2990
n -Propylbenzene 16 7 0.0605 0.0303 0.9699 Styrene 213 148 <0.0001 <0.0001 1.0000 Toluene 222 171 <0.0001 <0.0001 1.0000 1,2,3-Trichloropropane 5 0 0.4215 0.7901 0.2108 1,2,4-Trimethylbenzene 42 29 0.8231 0.4116 0.5890

m ,

p -Xylene 112 53 0.2678 0.1339 0.8663
o -Xylene 91 32 0.4475 0.2238 0.7765 1 Two-sided p-values <0.1 significant at 95-percent confidence level. 2 One-sided p-values <0.05 significant at 95-percent confidence level.**Appendix B 49**

## Field-Reagent Blank Samples Versus FieldEquipment Blank Samples
Concentrations of VOCs were statistically com

pared using the Wilcoxon signed-rank test for FEBs and FRBs in 27 paired sets of blank samples. As in the test comparing FRB samples to TRB samples, VOCs detected in either blank type were used in the statistical analysis. Concentrations of MTBE and styrene were found to be statistically different at the 95-percent confidence level (table B3). Concentrations of MTBE were determined to be statistically higher in FEB sam

ples than in FRB samples. Conversely, concentrations of styrene were found to be statistically higher at the 95-percent confidence level inthe FRB samples than in the FEB samples. Concentration differences between FRB samples and FEB samples for all other com

pounds analyzed were not found to be statistically different. 

## Trip-Reagent Blank Samples Versus FieldEquipment Blank Samples Concentrations of FEB samples and TRB sam

ples were also compared for 27 sets of paired blanks. For all compounds analyzed, none were statistically different, nor were any concentrations of compounds statistically higher or lower for any of the blanks (table B4). 

## Duplicate Samples A Wilcoxon signed-rank test for the VOCs was used to test whether there were significant differences between the samples and the duplicates. Results of the test indicated that for the 69 pairs of source-water sam

ples and duplicates, the concentrations of three com

pounds (naphthalene, trichloroethene, and 1,3,5- trimethylbenzene) were significantly different at the 95-percent confidence level (table B5).

**Table B3**

. Relation between concentrations of volatile organic co mpounds in 27 companion field-equipment blank samples and field-reagent blank samples [Statistically different results at the 95-percent confidence interval are given in boldface; H o , null hypothesis; FEB, field- equipment blank; FRB, fieldreagent blank; <, less than; >, greater than] **Volatile organic**

**compounds Number of**  **detections in FEB samples**  **Number of detections in FRB**  **samples Null hypothesis tested and p-value**  **H o**  **: FEB=FRB 1**  **H o**  **: FEB<FRB 2**  **H o**  **: FEB>FRB 2**  Benzene 1 0 0.3356 0.1678 0.8501 Chloroform 2 5 0.1920 0.0960 0.9100 Chloromethane 2 1 0.3356 0.8501 0.1678 Ethylbenzene 3 12 0.9675 0.5270 0.4838 Isopropylbenzene 1 0 0.3356 0.8501 0.1678 Methylene chloride 16 17 0.9796 0.4898 0.5204 Methyl tert-butyl ether (MTBE) 4 9 0.0155 0.0078 0.9928 Naphthalene 4 0 0.9844 0.4922 0.5234

n -Propylbenzene 1 0 0.3356 0.1678 0.8501 Styrene 9 20 0.0013 0.9994 0.0006 Toluene 8 19 0.9802 0.5198 0.4901 1,2,4-Trichlorobenzene 2 0 1.0000 0.5000 0.5213 1,2,3-Trichloropropane 2 2 0.3356 0.8501 0.1678 1,2,4-Trimethylbenzene 4 5 0.5790 0.2895 0.7255

m ,

p -Xylene 2 12 0.2093 0.1047 0.8367
o -Xylene 2 8 0.1267 0.0633 0.9402 1 Two-sided p-values <0.1 significant at 95-percent confidence level. 2 One-sided p-values <0.05 signifi cant at 95-percent confidence level.**50 Occurrence and Temporal Variability of MTBE and Other VOCs in Select Sources of Drinking Water Table B4** 

. Relation between concentrations of volatile organic compounds in 27 companion field-equipment blank samples and trip-reagent blank samples [H o , null hypothesis; FEB, field-equipment blank; TRB, trip-reagent blank; <, less than; >, greater than] **Volatile organic**

**compound Number of**  **detections in FEB samples**  **Number of detections in**  **TRB samples Null hypothesis tested and p-value**  **H o**  **: FEB=TRB 1**  **H o**  **: FEB<TRB 2**  **H o**  **: FEB>TRB 2**  Benzene 1 0 0.3356 0.1678 0.8501 Chloroform 2 2 0.9844 0.5234 0.4922 Chloromethane 2 0 0.1654 0.9252 0.0827 Ethylbenzene 3 6 0.4346 0.2173 0.7923 Isopropylbenzene 1 1 1.0000 0.5213 0.5000 p -Isopropyltoluene 0 2 0.1654 0.0827 0.9252 Methylene chloride 15 19 0.2060 0.1030 0.9014 Methyl tert-butyl ether (MTBE) 4 13 0.5280 0.2640 0.7442 Naphthalene 4 0 0.9687 0.4844 0.5312

n -Propylbenzene 1 0 0.3356 0.1678 0.8501 Styrene 10 15 0.1375 0.9345 0.0688 Toluene 8 14 0.7010 0.3505 0.6590 1,2,3-Trichlorobenzene 3 0 0.6097 0.3049 0.7105 1,2,3-Trichloropropane 2 0 0.1654 0.9252 0.0827 1,2,4-Trimethylbenzene 4 6 0.6097 0.7105 0.3049

m ,

p -Xylene 2 7 0.1548 0.0774 0.9268

o -Xylene 2 3 1.0000 0.5000 0.5156 1 T

wo-sided p-values <0.1 signific ant at 95-percent confidence level. 2 One-sided p-values <0.05 signifi cant at 95-percent confidence level.**Appendix B 51 Table B5** 

. Statistical comparison of concentrations of volatile organic compounds in source-water and duplicate samples [Statistically different results at the 95-percent confidence interval are given in boldface; H o , null hypothesis; ENV, source-water sample; DUP, dupli

cate sample]
**Volatile organic compound Null hypothesis tested**  **and p-value 1**  **H o**  **: ENV=DUP** tert-Amyl methyl ether (TAME) 0.9772 Benzene 0.5970 Bromodichloromethane 0.7101 Bromomethane 0.1604 Carbon tetrachloride 1.0000 Chlorodibromomethane 0.9706 Chloroform 0.3490 Chloromethane 0.3174 1,1-Dichloroethane 0.9820 1,2-Dichloroethane 0.9940 cis -1,2-Dichloroethene 0.2406 1,3-Dichloropropane 0.1604 Ethylbenzene 0.4321 Isopropylbenzene 0.3245 Methylene chloride 0.5811 Methyl tert-butyl ether (MTBE) 0.5230 Naphthalene 0.0620

n -Propylbenzene 0.5754 Styrene 0.5923 1,1,1-Trichloroethane 0.9820 Tetrachloroethene 0.9883 Toluene 0.4417 Trichloroethene 0.0354 1,2,4-Trimethylbenzene 0.6894 1,3,5-Trimethybenzene 0.0848

m ,

p -Xylene 1.0000

o -Xylene 0.8334 1 Two-sided p-values <0.1 signifi cant at 95-percent confidence level shown in bold.

# Appendix C - Data acceptance criteria using quality-control data**54 Occurrence and Temporal Variability of MTBE and Other VOCs in Select Sources of Drinking Water** 

## SOURCE-WATER DATA ACCEPTANCE CRITERIA Two objectives of the Focused Survey include: (1) to determine the temporal variability, and (2) characterize sampling site s that had frequent occur

rence of MTBE and other VOCs in source water. In order to accomplish these tw o objectives, data analyses will involve the use of conc entration values to deter

mine temporal trends as well as a presence/absence approach for site characterizations. The strength of these types of comparisons relies on the amount of data (detections) available for data analyses. That is, if a compound is determined to be present, it may be used in statistical tests to determine if the VOC is associated with some environmental risk factor. However, if the concentration of a compounddetected below the min

imum reporting level (MRL) is censored, low-level temporal trends and explanatory factors could be missed. It is important to no te that data below the MRL can only be used in these analyses if the QC screening process supports those activities. 

## Source-Water Data Screening Process
As with the Random Survey, an analysis of source-water data and field QC data can identify poten

tial contamination of individual VOCs in source-water samples. Subsequently, the frequency of detection can be adjusted to account for possible contamination. The source-water samples were subdivided into seven con

ditions that relate to the level of uncertainty associated with source-water VOC detections. These conditions are described in table C1.

**Table C1**

. Schematic diagram for adjusting the frequency ofdetection of volatile organic compounds in source-water samples to reflect possible random sample contamination [VOCs, volatile organic compounds; <, le ss than; >=, greater than or equal to]
**Condition Possibility of random contamination of**  **source-water samples** Condition A: Source water = no VOCs detected Field blank = no VOCs detected None

Condition B: Source water = no VOCs detected Field blank = VOCs detected None

Condition C: Source water = no VOCs detected Field blank = not analyzed None

Condition D: Source water = VOCs detected Field blank = no VOCs detected None

Condition E1: Source water = VOCs detected Field blank = same VOCs detected, however, source water

concentrations >= 5 times the field blank concentrations None

Condition E2: Source water = VOCs detected Field blank = same VOCs detected, however, source water

concentrations < 5 times the field blank concentrations Random contamination suspected

Condition F: Source water = VOCs detected Field blank = not analyzed Undetermined—Pos sibility of random sample contamination**Appendix C 55** 

### Conditions A, B, C, and D all indicate that random sample contamination of source-water samples above the method detection limit (MDL) is not likely. As presented in table C2, the majority of source-water samples had no detections (conditions A, B, and C), thus, random contamination was not measurable. For example, many source-water samples did not have a detected VOC in the source-water sample or FRB sample (condition A). There also were many sourcewater samples with no VOC detections, but with detec

tions in the corresp onding FRB samples (condition B)—methylene chloride, styrene, and tol

uene were detected in 179, 118, and 111 FRB samples, respectively, but were not detected in the corresponding source-water samples. Concentrations for methylene chloride, styrene, and tolu ene in FRB samples ranged from 0.03 μ g/L for all three compounds to 1.18, 8.61, and 6.95 μ g/L, respectively. This may be an indication that the VOC-free water used in the collection of these FRBs was contaminated wi th those compounds when the FRB sample was collected. Condition C VOCs were not detected in source -water samples, thus they are not considered contaminated and, as stated in the protocol, the FRB samples were not analyzed unless compounds were detected in the source-water samples. Also, chloroform and MTBE were detected in 146 and 134 source-water samples, respectively, but with no detections in the corre sponding FRB samples (condition D). This further indicates contamination associated with those comp ounds under that specific condition is unlikely. The validity of only two categories of data remain in question: (1) the samples that have the same VOCs in the source-water sample as well as the associ

ated FRB sample (conditions E1 and E2); and (2) those source-water samples with VOC detections that do not have an associated FRB sample (condition F). Samples classified into category E1 and E2 have detections of the same VOCs in both the source-water sample and associated FRB sample (table C2). Samples classified as E1 have VOC concentrations 5 times greater than the concentrations in the acc ompanying FRB sample. Sam

ples classified as E2 have VOC concentrations less than 5 times the concentrations in the accompanying FRB sample. The source-water samples that were classified as E1 were judged to have essentially no possibility that the source-water concentration was an artifact of random contamination. These samples were few, except for MTBE, which had 82 samples in this category. In addition, toluene and ethylbenzene had 18 and 3 sam

ples in condition E1, respectively (table C2). For samples with VOCs at concentrations less than five times the FRB sample concentration there was a clear possibility that the source-water detection was due to random contamin ation, especially when concentrations approached a 1:1 ratio for one or more compound. Accordingly, 487 source-water VOC detections that fall under condition E2 (223 of these detections were due to styrene and toluene) were cen

sored from the source-water data and not included in the analyses of VOCs subsequently reported for source water. As in the QC analysis for the Random Survey, this is a conservative approach to reporting VOC occurrence data, and it is recognized that the detection of the same VO C in both the FRB and source-water samples does not definitively indicate that random contamination of the source-water sample has occurred, but indicates that it may have occurred or cannot be ruled out. Source-water samples classified as condition F had a detected VOC in the source-water sample but an associated FRB sample was not available. This condi

tion is considered to have some uncertainty associated with the detection, however, as in the Random Survey, these concentrations werenot censored from the source-water data. Thus, only E2 samples were cen

sored from the data set and are not included in any analyses subsequently reported for source water. 

## Volatile Organic Compound Detection Frequencies
The total number of samples collected, the orig

inal detection frequency be fore adjusting for E2 con

ditions, and the adjusted detection frequency after adjusting for E2 conditions for data at the MDL are listed in table C3. As in the Random Survey analyses, the adjusted detection frequency is equal to the total number of times a VOC was detected minus the number of condition E2 samples divided by the total number of samples minus the number of condition E2 samples. Table C4 illustrates an example of calcu

lating the adjusted detection frequency for MTBE at the MDL. The detection frequency in source-water sam

ples was adjusted downward for 32 of the 58 detected VOCs due to possible random contamination. Only the adjusted samples (those not affected by condition E2) were used in data analyses presented in this report.**56 Occurrence and Temporal Variability of MTBE and Other VOCs in Select Sources of Drinking Water Table C2** 

. Number of source-water sample s that meet specified condit ions at the method detection limit, with respect to the possibility of random contamination

**Possible volatile organic compound contaminant**  **Number of samples per condition 1**  **A B**  **C D**  **E1 E2**  **F** Acrylonitrile 315 1 145 6 0 0 0
tert-Amyl methyl ether (TAME) 227 4 126 88 0 3 19 Benzene 213 6 125 98 1 4 20 Bromobenzene 319 1 145 2 0 0 0 Bromochloromethane 312 1 144 9 0 0 1 Bromodichloromethane 262 2 141 52 0 6 4 Bromoform 306 0 137 15 0 0 8 Bromomethane 306 5 138 10 0 1 5

n -Butylbenzene 313 1 141 8 0 0 1

sec -Butylbenzene 320 0 145 1 0 1 0
tert-Butylbenzene 320 1 145 1 0 0 0 Carbon tetrachloride 313 1 143 8 0 0 2 Chlorobenzene 311 0 141 10 0 0 4 Chlorodibromomethane 274 1 129 46 0 1 16 Chloroethane 318 0 145 2 0 2 0 Chloroform 136 20 88 146 6 14 57 Chloromethane 306 3 142 8 0 5 3 2-Chlorotoluene 321 0 145 0 0 0 0 4-Chlorotoluene 319 1 145 2 0 0 0 Dibromomethane 319 0 145 3 0 0 0 1,2-Dichlorobenzene 316 0 145 5 0 0 1 1,3-Dichlorobenzene 321 0 145 13 1 0 2 1,4-Dichlorobenzene 309 3 142 9 0 1 3 Dichlorodifluoromethane 320 0 144 2 0 0 1 1,1-Dichloroethane 294 0 130 26 0 2 15 1,2-Dichloroethane 291 1 137 30 0 0 8 1,1-Dichloroethene 307 0 145 13 1 0 2 cis -1,2-Dichloroethene 287 0 138 32 1 2 7
trans -1,2-Dichloroethene 312 0 144 10 0 0 1 1,2-Dichloropropane 313 1 144 8 0 0 1 1,3-Dichloropropane 313 3 141 6 0 0 4 2,2-Dichloropropane 321 1 145 0 0 0 0 1,1-Dichloropropene 321 0 145 0 0 0 0 cis -1,3-Dichloropropene 321 0 145 0 0 0 0
trans -1,3-Dichloropropene 321 0 145 0 0 0 0**Appendix C 57** 1 Described in table C1. Diisopropyl ether (DIPE) 307 0 142 15 0 0 3 Ethylbenzene 176 95 140 19 3 29 5 Ethyl tert-butyl ether (ETBE) 318 0 144 4 0 0 1 Hexachlorobutadiene 320 0 145 1 0 1 0 Hexachloroethane 321 0 145 0 0 0 0 Isopropylbenzene 282 25 144 11 0 4 1 p -Isopropyltoluene 321 0 145 1 0 0 0 Methyl ethyl ketone 302 12 141 7 0 1 4 Methylene chloride 124 179 138 3 1 12 7 Methyl tert-butyl ether (MTBE) 43 17 41 134 82 46 104 Naphthalene 280 10 129 23 0 9 16

n -Propylbenzene 292 16 143 10 0 4 2 Styrene 78 118 102 11 1 114 43 1,1,1,2-Tetrachloroethane 318 1 145 3 0 0 0 1,1,2,2-Tetrachloroethane 321 1 145 0 0 0 0 Tetrachloroethene 266 4 131 50 1 1 14 Toluene 52 111 93 32 18 109 52 1,2,3-Trichlorobenzene 301 8 143 10 0 3 4 1,2,4-Trichlorobenzene 302 8 136 10 0 2 9 1,1,1-Trichloroethane 287 0 141 33 0 1 6 1,1,2-Trichloroethane 317 0 145 5 0 0 0 Trichloroethene 273 0 128 48 0 1 17 Trichlorofluoromethane 315 0 141 7 0 0 4 1,2,3-Trichloropropane 307 3 139 8 0 4 6 1,1,2-Trichloro-1,2, 2-trifluoromethane 320 0 144 2 0 0 1 1,2,4-Trimethylbenzene 239 12 140 36 0 35 5 1,3,5-Trimethylbenzene 298 1 143 22 0 1 2 Vinyl bromide 321 0 145 0 0 0 0 Vinyl chloride 317 0 143 5 0 0 2

m ,

p -Xylene 168 91 136 31 3 29 9

o -Xylene 176 65 132 42 0 39 13 **Table C2** . Number of source-water samples that meet specified conditions at the method detection limit, with respect to the possibility of random contamination—Continued

**Possible volatile organic compound contaminant**  **Number of samples per condition 1**  **A B C D E1 E2 F 58 Occurrence and Temporal Variability of MTBE and Other VOCs in Select Sources of Drinking Water**  **Table C3**

. Detection frequency of volatile organic compounds detect ed at or above the method detection level in source water before and after applying the quality-control screening process [--, not applicable]

**Volatile organic compound Number of**  **samples Number of**  **original detections**  **Unadjusted detection**  **frequency (percent)**  **Number of samples after** 

**screening process**  **Number of detections after**  **screening process**  **Adjusted detection**  **frequency (percent)**  Acrylonitrile 467 6 1.3 467 6 1.3
tert-Amyl methyl ether (TAME) 467 110 23.6 464 107 23.1 Benzene 467 123 26.3 463 119 25.7 Bromobenzene 467 2 0.4 467 2 0.4 Bromochloromethane 467 10 2.1 467 10 2.1 Bromodichloromethane 467 62 13.3 461 56 12.1 Bromoform 467 23 4.9 467 23 4.9 Bromomethane 465 16 3.4 464 15 3.2

n -Butylbenzene 467 9 1.5 467 9 1.5

sec -Butylbenzene 467 2 0.4 466 1 0.2
tert-Butylbenzene 467 1 0.2 467 1 0.2 Carbon tetrachloride 467 10 2.1 467 10 2.1 Chlorobenzene 467 14 3.0 467 14 3.0 Chlorodibromomethane 467 63 13.5 466 62 13.3 Chloroethane 467 4 0.9 465 2 0.4 Chloroform 467 223 47.8 453 209 46.1 Chloromethane 467 16 3.4 462 11 2.4 4-Chlorotoluene 467 2 0.4 467 2 0.4 Dibromomethane 467 3 0.6 467 3 0.6 1,2-Dichlorobenzene 467 6 1.3 467 6 1.3 1,3-Dichlrobenzene 467 6 1.3 467 6 1.3 1,4-Dichlorobenzene 467 13 2.8 466 12 2.6 Dichlorodifluoromethane 467 3 0.6 467 3 0.6 1,1-Dichloroethane 467 43 9.2 465 41 8.8 1,2-Dichloroethane 467 38 8.1 467 38 8.1 1,1-Dichloroethene 467 16 3.4 467 16 3.4 cis -1,2-Dichloroethene 467 42 9.0 465 40 8.6
trans -1,2-Dichloroethene 467 11 2.4 467 11 2.4 1,2-Dichloropropane 467 9 1.9 467 9 1.9 1,3-Dichloropropane 464 10 2.2 464 10 2.2 Diisopropyl ether (DIPE) 467 19 4.1 467 19 4.1 Ethylbenzene 467 56 12.0 438 27 6.2 Ethyl tert-butyl ether (ETBE) 467 5 1.1 467 5 1.1 Hexachlorobutadiene 467 2 0.4 466 1 0.2**Appendix C 59** Isopropylbenzene 467 16 3.4 463 12 2.6 p -Isopropyltoluene 467 1 0.2 467 1 0.2 Methyl ethyl ketone 467 12 2.6 466 11 2.4 Methylene chloride 464 23 5.0 452 11 2.4 Methyl tert-butyl ether (MTBE) 467 366 78.4 421 320 76.0 Naphthalene 467 48 10.3 458 39 8.5

n -Propylbenzene 467 16 3.4 463 12 2.6 Styrene 467 169 36.2 353 55 15.6 1,1,1,2-Tetrachloroethane 467 3 0.6 467 3 0.6 1,1,2,2-Tetrachloroethane 467 1 0.2 467 1 0.2 Tetrachloroethene 467 66 14.1 466 65 13.9 Toluene 467 211 45.2 358 102 28.5 1,2,3-Trichlorobenzene 467 17 3.6 464 14 3.0 1,2,4-Trichlorobenzene 467 21 4.5 465 19 4.1 1,1,1-Trichloroethane 467 40 8.6 466 39 8.4 1,1,2-Trichloroethane 467 5 1.1 467 5 1.1 Trichloroethene 467 66 14.1 466 65 13.9 Trichlorofluoromethane 467 11 2.4 467 11 2.4 1,2,3-Trichloropropane 467 18 3.9 463 14 3.0 1,1,2-Trichloro-1,2,2-trifluoro

ethane 467 3 0.6 467 3 0.6 1,2,4-Trimethylbenzene 467 76 16.3 432 41 9.5 1,3,5-Trimethylbenzene 467 25 5.4 466 24 5.2 Vinyl chloride 467 7 1.5 467 7 1.5

m ,

p -Xylene 467 72 15.4 438 43 9.8

o -Xylene 467 94 20.1 428 55 12.9 **Table C3** . Detection frequency of volatile organic compounds detected at or above the method detection level in source water before and after applying the quality-control screening process—Continued [--, not applicable]

**Volatile organic compound Number of**  **samples Number of**  **original detections**  **Unadjusted detection**  **frequency (percent)**  **Number of samples after** 

**screening process**  **Number of detections after**  **screening process**  **Adjusted detection**  **frequency (percent)** **60 Occurrence and Temporal Variability of MTBE and Other VOCs in Select Sources of Drinking Water Table C4** 

. Schematic diagram for adjusting the frequency of detection of methyl tert -butyl ether in source-water samples to reflect possible random sample contamination 1 [VOCs, volatile organic compounds; MTBE, methyl tert-butyl ether; <, less than; >=, greater than or equal to] **Possibility of random contamination of source-water samples**  **Condition** No random samplecontamination Condition A : Source water = no VOCs detected Field blank = no VOCs detected For MTBE = 43 samples No random samplecontamination Condition B : Source water = no VOCs detected Field blank = VOCs detected For MTBE = 17 samples No random samplecontamination Condition C : Source water = no VOCs detected Field blank = not analyzed For MTBE = 41 samples No random samplecontamination Condition D : Source water = VOCs detected Field blank = no VOCs detected For MTBE = 134 samples No random samplecontamination Condition E1 : Source water = VOCs detected Field blank = same VOCs detected, and source water con

centrations >= 5 times the field blank concentrations For MTBE = 82 samples Random contamin ation suspected Condition E2 : Source water = VOCs detected Field blank = same VOCs detected, and source water con

centrations < 5 times the field blank concentrations For MTBE = 46 samples Undetermined—Possibi lity of random sample contamination Condition F : Source water = VOCs detected Field blank = not analyzed For MTBE = 104 samples Frequency of detection, unadjusted = (D+E1+E2 +F)/(A+B+C+D+E1+E2+F)

For MTBE = (134+82+46+104)/(43+17+41+1 34+82+46+104) = 366/467 = 78.4 percent Frequency of detection, adjusted = (D+E1+F)/(A+B+C+D+E1+F)

For MTBE = (134+82+104)/(43+17+41+134+ 82+104) = 320/421 = 76.0 percent Estimated frequency of detection that may be attributedto random contamination of source-water samples = frequency of

detection, unadjusted - frequency of detection, adjusted For MTBE = 78.4 percent - 76.0 percent = 2.4 percent
1 Based on all detections greater than or equal to the me thod detection limit.

# Appendix D - Summary of VOC concentrations in the Focused Survey**62 Occurrence and Temporal Variability of MTBE and Other VOCs in Select Sources of Drinking Water Table D1** 

. Statistical summary of volatile organic compoundsin source-water samples in the Focused Survey [Values in micrograms per liter; N, numberof sources sampled; ND, not detected] **Volatile organic**

**compounds All community water systems (N=134)**  **Ground Water (N=78) Mini**  **** **mum 25th**  **Median 75th**  **Maxi**   ** mum** **Mini**   ** mum** **25th Median**  **75th Maxi**  **** **mum** Gasoline oxygenates Diisopropyl ether 0.10 0.14 0.27 0.74 3.93 0.10 0.14 0.27 0.74 3.93 Ethyl tert-butyl ether 0.16 0.17 0.18 0.19 0.20 0.16 0.17 0.18 0.19 0.20 Methyl tert-butyl ether 0.04 0.18 0.68 1.63 924.00 0.04 0.57 0.95 4.73 924.00 tert-Amyl methyl ether 0.03 0.04 0.11 0.18 1.27 0.03 0.06 0.11 0.23 1.27 Other gasoline compounds 1,3,5-Trimethylbenzene 0.03 0.06 0.20 0.33 0.49 0.32 0.32 0.32 0.32 0.32 Benzene 0.03 0.04 0.10 0.30 37.90 0.03 0.09 0.14 0.86 37.90 Ethylbenzene 0.05 0.05 0.07 0.54 2.69 0.05 0.06 0.06 1.38 2.69
m ,

p -Xylene 0.07 0.08 0.09 0.72 3.26 0.07 0.09 0.10 0.89 3.26 Naphthalene 0.06 0.06 0.12 0.17 0.98 0.06 0.11 0.15 0.21 0.98
n -Butylbenzene 0.05 0.09 0.12 0.16 0.19 0.19 0.19 0.19 0.19 0.19
o -Xylene 0.03 0.03 0.04 0.20 1.16 0.03 0.03 0.04 0.09 0.93
sec -Butylbenzene 0.05 0.06 0.06 0.07 0.07 0.05 0.06 0.06 0.07 0.07 tert-Butylbenzene ND ND ND ND ND ND ND ND ND ND Toluene 0.03 0.05 0.09 0.32 4.98 0.03 0.03 0.05 0.18 4.42 Trihalomethanes Bromodichloromethane 0.02 0.02 0.04 0.08 1.27 0.02 0.02 0.03 0.04 1.27 Bromoform 0.03 0.09 0.20 0.28 2.61 0.19 0.21 0.26 0.88 2.61 Chlorodibromomethane 0.02 0.03 0.04 0.07 2.43 0.02 0.03 0.04 0.15 2.43 Chloroform 0.03 0.05 0.12 0.29 5.00 0.03 0.06 0.13 0.30 5.00 Organic synthesis 1,1-Dichloropropene ND ND ND ND ND ND ND ND ND ND 1,2,3-Trichlorobenzene 0.05 0.07 0.08 0.13 0.17 0.05 0.07 0.11 0.14 0.17 1,2,4-Trimethylbenzene 0.03 0.07 0.09 0.15 2.42 2.42 2.42 2.42 2.42 2.42 1,3-Dichloropropane 0.05 0.06 0.10 0.16 0.21 0.05 0.09 0.13 0.17 0.21 2,2-Dichloropropane ND ND ND ND ND ND ND ND ND ND Acrylonitrile 0.75 0.75 0.75 0.75 0.75 0.75 0.75 0.75 0.75 0.75 Bromochloromethane 0.04 0.04 0.04 0.05 0.08 0.04 0.04 0.04 0.06 0.08 Hexachlorobutadiene ND ND ND ND ND ND ND ND ND ND Isopropylbenzene 0.04 0.05 0.05 0.09 0.24 0.04 0.05 0.05 0.10 0.24 p -Isopropyltoluene 0.04 0.04 0.04 0.04 0.04 ND ND ND ND ND Styrene 0.03 0.04 0.07 0.12 1.10 0.03 0.04 0.08 0.21 1.10 Vinyl bromide ND ND ND ND ND ND ND ND ND ND Vinyl chloride 0.61 0.86 1.10 1.18 1.25 0.61 0.86 1.10 1.18 1.25 Solvents 1,1,1,2-Tetrachloroethane 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.02 1,1,1-Trichloroethane 0.06 0.13 0.23 0.67 6.84 0.06 0.13 0.23 0.67 6.84**Appendix D 63 Reservoir (N=39)**  **Rivers (N=17) All surface water (N=56)**  **Mini**   ** mum** **25th Median**  **75th Maxi**  **** **mum Mini**  **** **mum 25th**  **Median 75th**  **Maxi**   ** mum** **Mini**   ** mum** **25th Median**  **75th Maxi**  **** **mum**

ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND 0.04 0.10 0.40 1.18 14.00 0.09 0.14 0.20 0.64 1.65 0.04 0.11 0.26 0.85 14.00 0.03 0.05 0.12 0.12 0.35 0.03 0.04 0.05 0.08 0.11 0.03 0.04 0.11 0.12 0.35

0.33 0.37 0.41 0.45 0.49 0.03 0.05 0.06 0.07 0.07 0.03 0.06 0.07 0.33 0.49 0.03 0.04 0.06 0.26 1.83 0.03 0.03 0.05 0.05 0.30 0.03 0.03 0.05 0.22 1.83 0.05 0.06 0.07 0.39 0.70 ND ND ND ND ND 0.05 0.06 0.07 0.39 0.70 0.07 0.07 0.33 0.79 2.63 0.08 0.08 0.08 0.08 0.08 0.07 0.08 0.08 0.72 2.63 0.07 0.09 0.07 0.12 0.16 0.06 0.06 0.06 0.06 0.06 0.06 0.06 0.06 0.07 0.16 ND ND ND ND ND 0.05 0.05 0.05 0.05 0.05 0.05 0.05 0.05 0.05 0.05 0.03 0.04 0.15 0.37 1.16 0.03 0.03 0.04 0.08 0.21 0.03 0.03 0.04 0.25 1.16 ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND 0.10 0.19 0.35 1.99 4.98 0.03 0.05 0.07 0.11 0.70 0.03 0.06 0.10 0.35 4.98

0.02 0.03 0.04 0.09 0.21 0.02 0.03 0.06 0.10 0.16 0.02 0.03 0.06 0.10 0.21 0.06 0.06 0.06 0.06 0.06 0.03 0.03 0.03 0.03 0.03 0.03 0.04 0.05 0.05 0.06 0.02 0.03 0.05 0.10 0.15 0.02 0.03 0.03 0.04 0.07 0.02 0.03 0.03 0.07 0.15 0.03 0.05 0.07 0.08 0.33 0.03 0.05 0.10 0.25 0.90 0.03 0.05 0.08 0.13 0.90

ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND 0.07 0.07 0.08 0.08 0.07 0.08 0.08 ND ND 0.08 0.07 0.07 0.08 0.08 0.08 0.03 0.06 0.09 0.14 0.99 0.06 0.07 0.08 0.11 0.13 0.03 0.06 0.08 0.13 0.99 0.06 0.08 0.10 0.12 0.14 ND ND ND ND ND 0.06 0.08 0.10 0.12 0.14 ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND 0.04 0.04 0.04 0.04 0.04 0.04 0.04 0.04 0.04 0.04 ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND 0.09 0.09 0.09 0.09 0.09 ND ND ND ND ND 0.09 0.09 0.09 0.09 0.09 0.04 0.04 0.04 0.04 0.04 ND ND ND ND ND 0.04 0.04 0.04 0.04 0.04 0.03 0.03 0.04 0.04 0.04 0.04 0.04 0.04 0.04 0.04 0.03 0.04 0.04 0.04 0.04 ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND

ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND**64 Occurrence and Temporal Variability of MTBE and Other VOCs in Select Sources of Drinking Water Table D1** 

. Statistical summary of volatile organic compounds in source-water samples in the Focused Survey—Continued [Values in micrograms per liter; N, numberof sources sampled; ND, not detected] **Volatile organic**

**compounds All community water systems (N=134)**  **Ground Water (N=78) Mini**  **** **mum 25th**  **Median 75th**  **Maxi**   ** mum** **Mini**   ** mum** **25th Median**  **75th Maxi**  **** **mum** Solvents—Continued 1,1,2,2-Tetrachloroethane ND ND ND ND ND ND ND ND ND ND 1,1,2-Trichloroethane 0.04 0.07 0.10 0.12 0.15 0.04 0.07 0.10 0.12 0.15 1,1-Dichloroethane 0.04 0.05 0.09 0.33 3.85 0.04 0.07 0.10 0.36 3.85 1,1-Dichloroethene 0.10 0.14 0.64 1.53 9.78 0.10 0.14 0.64 1.53 9.78 1,2,3-Trichloropropane 0.03 0.04 0.05 0.08 0.09 0.03 0.04 0.05 0.07 0.08 1,2,4-Trichlorobenzene 0.06 0.06 0.06 0.08 0.14 0.06 0.08 0.10 0.12 0.14 1,2-Dichlorobenzene 0.18 0.19 0.20 0.21 0.22 0.18 0.19 0.20 0.21 0.22 1,2-Dichloroethane 0.03 0.06 0.14 0.39 2.14 0.03 0.06 0.14 0.39 2.14 1,2-Dichloropropane 0.04 0.09 0.11 0.17 1.04 0.04 0.09 0.11 0.17 1.04 1,3-Dichlorobenzene 0.04 0.05 0.05 0.11 0.17 0.04 0.05 0.05 0.11 0.17 2-Chlorotoluene ND ND ND ND ND ND ND ND ND ND 4-Chlorotoluene 0.03 0.03 0.03 0.03 0.03 0.03 0.03 0.03 0.03 0.03 Bromobenzene ND ND ND ND ND ND ND ND ND ND Carbon tetrachloride 0.06 0.41 0.75 0.95 1.15 0.06 0.41 0.75 0.95 1.15 Chlorobenzene 0.05 0.07 0.08 0.56 0.81 0.07 0.08 0.32 0.62 0.81 Chloroethane 0.15 0.15 0.15 0.15 0.15 0.15 0.15 0.15 0.15 0.15 cis -1,2-Dichloroethene 0.03 0.06 0.27 1.38 10.35 0.03 0.06 0.27 1.38 10.35 Dibromomethane 0.30 0.30 0.30 0.30 0.30 0.30 0.30 0.30 0.30 0.30 Hexachloroethane ND ND ND ND ND ND ND ND ND ND Methyl ethyl ketone 1.84 1.84 1.84 1.84 1.84 1.84 1.84 1.84 1.84 1.84 Methylene chloride 0.31 0.31 0.31 0.31 0.31 0.31 0.31 0.31 0.31 0.31
n -Propylbenzene 0.05 0.06 0.13 0.26 0.47 0.47 0.47 0.47 0.47 0.47 Tetrachloroethene 0.05 0.10 0.39 4.24 290.00 0.05 0.10 0.39 4.24 290.00 trans -1,2-Dichloroethene 0.05 0.07 0.19 0.29 0.45 0.05 0.07 0.19 0.29 0.45 Trichloroethene 0.04 0.17 0.43 2.18 165.00 0.04 0.17 0.43 2.18 165.00 Fumigants 1,4-Dichlorobenzene 0.04 0.04 0.06 0.15 0.46 0.04 0.04 0.05 0.18 0.46 Bromomethane 0.09 0.09 0.09 0.10 0.11 0.09 0.09 0.09 0.10 0.11 cis -1,3-Dichloropropene ND ND ND ND ND ND ND ND ND ND trans -1,3-Dichloropropene ND ND ND ND ND ND ND ND ND ND Refrigerants 1,1,2-Trichloro-1,2,2-trifluo

roethane 2.27 2.27 2.27 2.27 2.27 2.27 2.27 2.27 2.27 2.27
Chloromethane 0.11 0.13 0.15 0.78 2.63 0.13 0.15 0.16 1.40 2.63 Dichlorodifluoromethane 0.40 0.40 0.40 0.40 0.40 0.40 0.40 0.40 0.40 0.40 Trichlorofluoromethane 0.23 0.35 0.46 0.48 0.50 0.23 0.35 0.46 0.48 0.50**Appendix D 65 Reservoir (N=39)**  **Rivers (N=17) All surface water (N=56)**  **Mini**   ** mum** **25th Median**  **75th Maxi**  **** **mum Mini**  **** **mum 25th**  **Median 75th**  **Maxi**   ** mum** **Mini**   ** mum** **25th Median**  **75th Maxi**  **** **mum**

ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND 0.04 0.04 0.04 0.04 0.04 0.04 0.04 0.04 0.04 0.04 ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND 0.04 0.05 0.07 0.08 0.09 ND ND ND ND ND 0.04 0.05 0.07 0.08 0.09 0.06 0.06 0.06 0.06 0.06 0.06 0.06 ND ND 0.06 0.06 0.06 0.06 0.06 0.06 ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND 0.05 0.05 0.05 0.05 0.05 0.05 0.05 0.05 0.05 0.05 ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND 0.05 0.09 0.12 0.16 0.19 0.06 0.06 0.06 0.06 0.06 0.05 0.06 0.06 0.13 0.19 ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND

0.06 0.06 0.06 0.06 0.06 ND ND ND ND ND 0.06 0.06 0.06 0.06 0.06 0.09 0.09 0.09 0.09 0.09 ND ND ND ND ND 0.09 0.09 0.09 0.09 0.09 ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND

ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND
ND ND ND ND ND 0.11 0.11 0.11 0.11 0.11 0.11 0.11 0.11 0.11 0.11 ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND