# The Analysis of Occurrence Data from the Unregulated Contaminant Monitoring Program (UCM) and National Inorganics and Radionuclides Survey (NIRS) in Support of Regulatory Determinations for the Second Drinking Water Contaminant Candidate List (CCL 2)

Office of Water (4607M) EPA 815-R-08-014 June 2008 www.epa.gov/safewater

### EPA – OGWDW Analysis of Occurrence Data from th e UCM and NIRS for CCL 2 June 2008



# Disclaimer

This document is designed to provid e technical background information for the regulatory determinations being made on the sec ond drinking water Contaminant Candidate List (CCL 2).

This document is not a regulation itself, and it does not substitute for the Safe Drinking Water Act (SDWA) or the Environmental Protecti on Agency’s (EPA’s) regulations. Mention of trade names or commercial products does not cons titute endorsement or recommendation for use.

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# Acknowledgments

The compilation and analysis of data presen ted in this report were undertaken by EPA’s Office of Ground Water and Drinking Wate r (OGWDW) in support of the regulatory determinations for specific contaminants listed on CCL 2. This effort was directed by Mr. Clifton Townsend and Ms. Yvette Selby-M ohamadu of OGWDW’s St andards and Risk Management Division (SRMD) Targeting and Analysis Branch (TAB). Yvette SelbyMohamadu served as the Team Lead for the CCL 2 final regulatory determinations under the guidance of Wynne Miller (TAB Associate Branch Chief), Eric Burneson (TAB Branch Chief), Phil Oshida (SRMD Deputy Divi sion Director), Pamela Barr (SRMD Division Director) and Cynthia Dougherty (OGWDW Office Director).

We would like to thank the many States, as well as the American Water Works Service Company, that contributed data se ts and valuable advice. Thanks also to the many public water systems that conducted the monitoring that provi ded the contaminant occurrence data used in this report.

The Cadmus Group, Inc., served as the prime contractor for this project, supporting the data management, analysis, and report deve lopment under Contract # 68-C-02-026. The major contributions of Morgan Tingley, Erin Mateo, Alison Cullity, Brent Ra nalli, and Dr. George Hallberg are gratefully acknowle dged. Dr. Jonathan Koplos served as the Cadmus Project Manager.

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# Executive Summary

The Unregulated Contaminant Monitoring (UCM) program (Rounds 1 and 2) and the National Inorganics and Radionuclides Survey (NIRS) were important sources of data considered by the United States Environmenta l Protection Agency (EPA) when evaluating the occurrence of unregulated contam inants on the second Contaminan t Candidate List (CCL 2). This report presents EPA’s anal ysis of national occu rrence of CCL 2 contaminants with data from those sources. Detailed occurrence analyses are presented in this re port to support the EPA regulatory determinations for the four CCL 2 contaminants with Round 1, Round 2 and NIRS data: boron, metolachlor, 1,3- dichloropropene, and 1,1,2,2-tetr achloroethane. Detailed descriptions are presented of the data sources, data editing and management, development of national cross-sections using UCM Round 1 and R ound 2 data from States, and the analytical approaches used to assess the occurrence data.

The UCM Round 1 monitoring data represen t public water system (PWS) monitoring results from 1988 to 1992 for unregulated contamin ants collected under the authority of Safe Drinking Water Act (SDWA). Forty States/pri macy entities have submitted PWS monitoring data for Round 1. Subsequent UCM Round 2 mo nitoring data collected from 1993 to 1997 were reported by 35 States/entities. Th e raw data from these two databa ses were reviewed and edited for data quality considerations to ensure consis tency and repeatability in the analyses. A data management approach was developed to construc t representative national cross-sections using the State data sets determined to be of the highest quality and most complete.

The development of the UCM Round 1 a nd Round 2 national cross-sections enabled occurrence analyses that were i ndicative of national occurrence us ing data from these two large databases. All States with monitoring data we re first evaluated by their distribution across a range of pollution potential indicators and spatia l/hydrogeologic diversity. A select group of States, representing a balanced distribution across these polluti on potential measures and across the nation geographically, was then used to cons truct national cross-sections (one using Round 1 data, the other Round 2 data) that would provi de reasonable representations of national occurrence. While the Round 1 and Round 2 nati onal cross-sections cannot be presented as “statistically representative,” they comprise very large samples (24 and 20 States, respectively), provide analytical occurrence re sults that are clear indications of central tendency of the occurrence data, and are gene rally indicative of national contaminant occurrence.

The NIRS provides contaminant occurrence data from 1984 through 1986 from a group of statistically selecte d, nationally representative PWSs serv ed by ground water. These data are from 49 States (there are no data from Hawaii), as well as Puerto Rico. Given the statistical design of NIRS, the resulting cont aminant occurrence analyses can be considered representative of national occurrence in PW Ss served by ground water.

Occurrence analyses of the UCM Rounds 1 a nd 2 and the NIRS data are conducted using a two-stage analytical approach. In Stage 1, th e data are first reviewed, quality-checked and characterized, and then analyzed to generate simple, clear non-parametric estimates of contaminant occurrence. The Stage 1 analysis, based on maximum sample analytical values, is inherently conservative; it is careful not to underestimate oc currence toward the goal ofprotecting public health. Simple counts are made of the number of systems, and populationsvii

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# served by those systems, with at least one an alytical result above a specified concentration threshold. Any contaminant found to have signif icant occurrence at or near health reference level (HRL) concentrations based on the Stage 1 analysis can addi tionally be analyzed using the Stage 2 analysis. In Stage 2, statistical mode ling is used to generate national probability estimates of contaminant occurrence based on estimated annual mean concentrations of contaminants while providing statistical meas ures of uncertainty and error. Because no contaminants in this report were found with si gnificant levels of cont aminant occurrence at or near the HRLs of concern based on the Stage 1 an alyses, the Stage 2 analyses were not warranted for any of the contaminants.

Stage 1 assessments of occurrence are presen ted in several ways for each contaminant to characterize different aspects of occurrence. For each contaminant, occurrence statistics presented include the number a nd percent of samples with labo ratory analytical detections, which are quantified analytical values above the laboratory method re porting limit or minimum reporting level (MRL). All anal ytical detections are summari zed by calculating and presenting the minimum, median, and 99 th 

# percentile values of detections for each contaminant. At the system level, the number and percent of systems w ith at least one detectio n at or above the MRL, and the number and percent of systems with at least two detectio ns at or above the MRL, are presented. For contaminants with HRLs, simila r types of occurrence assessments are presented relative to the concentration values of the HR L. The occurrence of the four contaminants described in this report is summarized as follows:

• For boron, 989 total samples (1 sample per system) were collected by the NIRS. Boron was detected at or above the MRL of 0.005 mg/L in 810 (81.9% of) systems. The maximum detection was 3.95 mg/L and th e median detection was 0.047 mg/L. Detections were found in PWSs in all Stat es that conducted sampling, with the exception of Rhode Island. Seventeen PWSs had dete ctions greater than the boron HRL of 1.4 mg/L, and 43 PWSs detected concentrations greater than 1⁄2 HRL (0.7 mg/L). A national extrapolation from the sta tistical sample of PWSs finds that 48,682 ground water systems, serving more than 75.5 million people, are estimated to have at least one sample detection of boron. Approximately 2,584 ground water systems, serving nearly 2.5 million people are estimated to have at least one sample detection of boron above the 1⁄2 HRL and approximately 1,022 ground water systems, serving approximately 372,000 people are estimated to have at least one sample detecti on of boron above the HRL of 1.4 mg/L.

• For metolachlor, a total of 33,930 samples we re collected by the R ound 2 cross-section. Metolachlor was detected at or above the MRL in 108 (0.83% of) systems. (MRLs varied from system to system. They ranged from 0.01 to 52 μg/L. The modal MRL value was 0.2 μg/L.) Although occurrence wa s relatively widespread, the metolachlor concentrations found were consistently low. In the Round 2 cross-section, the maximum detection was 13.8 μg/L, the 99 th 

# percentile of detections was 7.1 μg/L, and the median detection was 0.61 μg/L. Detections were found in PWSs in 12 of the 19 Round 2 crosssection States. The proportion of surface wa ter systems with metolachlor detections (6.55%) was much greater than that for ground water systems (0.11%). A national extrapolation from the Round 2 cross-section results estimates that 542 systems, serving approximately 24.7 million people, have at least one sample detection of metolachlor.

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# No analytical results in the Round 2 database were greater than the metolachlor HRL of 70 μg/L. Metolachlor was not monitored under the UCM Round 1.

• For 1,3-dicloropropene, in the Round 1 nati onal cross-section, a total of 31,104 samples were collected from 9,164 PWSs. 1,3-Dichlo ropropene was detected at or above the MRL in 15 (0.16% of) systems. (MRLs varied from system to system. They ranged from 0.02 to 10 μg/L. The modal MRL value was 0.5 μg/L.) The maximum detection in the Round 1 cross-section was 2.0 μg/L and the median detection was 1.0 μg/L. Detections were found in PWSs in 5 of th e Round 1 cross-section States. A national extrapolation from the Round 1 cross-section results estimates 106 systems, serving approximately 1.8 million people, have at least one sample detection of 1,3- dichloropropene. All PWSs with detections of 1,3-dichlorpropane in Round 1 also had detections greater than the 1⁄2 HR L (0.2 μg/L) and HRL (0.4 μg/L).

For 1,3-dicloropropene, in the Round 2 nati onal cross-section, a total of 70,631 samples were collected from 16,787 PWSs. 1,3-Dichlo ropropene was detected at or above the MRL in 58 (0.35% of) systems. (MRLs varied from system to system. They ranged from 0.08 to 1 μg/L. The modal MRL value was 0.5 μg/L.) The maximum detection in the Round 2 cross-section was 39 μg/L and the median detection was 0.5 μg/L. Detections were found in PWSs in 7 of the Round 2 cross-section States. Fifty PWSs had detections of 1,3-dichloropropene greater than 1⁄2 HRL (0.2 μg/L) and 38 PWSs had detections greater than HRL of 0.4 μg/L. All 7 Round 2 States had at least one PWS with a detection greater than the HRL. A na tional extrapolation from the Round 2 crosssection results estimates 225 systems, servi ng approximately 1.2 million people, have at least one sample detection of 1,3-dichloropropene. Approximately 194 systems, serving approximately 894,000 people are estimated to have at least one sample detection of 1,3- dichloropropene greater than the 1⁄2 HRL and approximately 147 systems, serving approximately 703,000 people are estimated to have at least one sample detection greater than the HRL.

• For 1,1,2,2-tetrachloroethane, in the Round 1 national cross-section, a total of 67,688 samples were collected from 20,407 PWSs. 1,1, 2,2-Tetrachloroethane was detected at or above the MRL in 91 (0.45% of) systems. (MRL s varied from system to system. They ranged from 0.01 to 10 μg/L. The modal MR L value was 0.5 μg/L.) The maximum detection in the Round 1 cro ss-section was 200 μg/L and th e median detection was 0.5 μg/L. Detections were found in PWSs in 13 of the Round 1 cross-se ction States. Fortyone PWSs had detections of 1,1,2,2-tetrachloroethane greater than the HRL of 0.4 μg/L and 44 PWSs had detections greater than the 1⁄2 HRL (0.2 μg/L.). 1,1,2,2- Tetrachloroethane detections greater than the HRL were found in PWSs in 9 of the Round 1 cross-section States. A national ex trapolation from the Round 1 cross-section results estimates 290 systems, serving approxi mately 4.0 million people, have at least one sample detection of 1,1,2,2-te trachloroethane. Approximately 140 systems, serving approximately 3.6 million people are estimated to have at least one sample detection of 1,1,2,2-tetrachloroethane greate r than the 1⁄2 HRL and approximately 131 systems, serving approximately 3.5 million people are estimated to have at least one sample detection greater than the HRL.

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# • For 1,1,2,2-tetrachloroethane, in the Round 2 national cross-section, a total of 98,911 samples were collected from 24,800 PWSs. 1,1, 2,2-Tetrachloroethane was detected at or above the MRL in 19 (0.08% of) systems. (MRL s varied from system to system. They ranged from 0.1 to 2.5 μg/L. The modal MR L value was 0.5 μg/L.) The maximum detection in the Round 2 cro ss-section was 2 μg/L and the median detection was 0.5 μg/L. Detections were found in PWSs in 9 of the Round 2 cross-secti on States. Eighteen PWSs had detections of 1,1,2,2-tetrachloroeth ane greater than 1⁄2 HR L (0.2 μg/L) and 17 PWSs had detections of 1,1,2,2-tetrachloroeth ane greater than HRL of 0.4 μg/L. 1,1,2,2- Tetrachloroethane detections greater than the HRL were found in PWSs in 7 of the Round 2 cross-section States. A national ex trapolation from the Round 2 cross-section results estimates 50 systems, serving approximately 5.6 million people, have at least one sample detection of 1,1,2,2-te trachloroethane. Approximately 47 systems, serving approximately 1.1 million people are estimated to have at least one sample detection of 1,1,2,2-tetrachloroethane greater than 1⁄2 the HRL and approximately 45 systems, serving approximately 168,000 people are estimated to have at least one sample detection greater than the HRL.

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# Contents

Disclaimer..................................................................................................................... .................iii Acknowledgments........................................................................................................................... v Executive Summary.............................................................................................................. ........ vii
Exhibits ....................................................................................................................... .................xiii Appendices.................................................................................................................................... xv Acronyms....................................................................................................................... ............. xvii
1. Introduction................................................................................................................................. 1 1.1 Regulatory Background................................................................................................... 1 1.2 Sources of Data Used for Analysis.................................................................................. 2 1.3 Threshold Evaluations ..................................................................................................... 5 1.4 General Description of the Two-Stage Analytical Approach.......................................... 6 1.5 Detailed Description of the St age 1 Analytical Methodology......................................... 7 1.6 Analytical Tools ........................................................................................................... ... 8
2. UCM Round 1 Data Overview ................................................................................................... 9 2.1 Description of Data........................................................................................................ .. 9 2.2 Data Management and Data Quality ............................................................................. 10 2.3 Round 1 Data Bias and Representativeness: Further Data Quality Review and Editing 11 2.4 Data Characteristics Overview ...................................................................................... 14
3. UCM Round 2 Data Overview ................................................................................................. 19 3.1 Description of Data........................................................................................................ 19 3.2 Data Management and Data Quality ............................................................................. 19 3.3 Round 2 Data Bias and Representativeness: Further Data Quality Review and Editing 20 3.4 Data Characteristics Overview ...................................................................................... 23 4. National Inorganics And Radionuc lides Survey (NIRS) Data ................................................. 27 4.1 Description of Data........................................................................................................ 27 4.2 Representativeness ........................................................................................................ 2 7 4.3 Data Characteristics Overview ...................................................................................... 28 4.4 Supplemental IOC Data................................................................................................. 29 5. Developing a Nationally Repr esentative Perspective............................................................... 31 6. Analysis of National Occurrence............................................................................................. . 35
6.1 Round 1 Contaminant Occurrence ................................................................................ 35 6.2 Round 2 Contaminant Occurrence ................................................................................ 36 6.3 NIRS Contaminant Occurrence..................................................................................... 38 6.4 National Extrapolation of St age 1 Occurrence Measures.............................................. 39 6.5 Comparing Data Coverage of Round 1 and Round 2.................................................... 40

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# 7. Graphical and Spatial Assessments of the C ontaminants Considered During CCL 2 Regulatory Determinations................................................................................................................. ............. 43
7.1 Metolachlor................................................................................................................ .... 44 7.2 1,3-Dichloropropene...................................................................................................... 47 7.3 1,1,2,2-Tetrachloroethane.............................................................................................. 52
8. References................................................................................................................................. 59

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# Exhibits

Exhibit 1.2.a. Diagram of th e Inter-Relationship of the Da tabases, Monitoring Rounds and Contaminant Lists Discussed in the Report............................................................ 3 Exhibit 1.2.b. List and Description of C ontaminants with Round 1 and Round 2 Data Considered During CCL 2 Re gulatory Determinations.......................................... 4 Exhibit 1.2.c. Description of the Inorganic Chem ical with data in NI RS Considered During CCL 2 Regulatory Determinations ......................................................................... 5 Exhibit 1.5.a. Total Number Systems and Popul ation Served Systems Used in All National Extrapolations ......................................................................................................... 8 Exhibit 2.3.a. Summary of Round 1 Data Quan tity and Quality for the States, Tribes and Territories.............................................................................................................. 13 Exhibit 2.3.b. Summary of Round 1 Data Quant ity and Quality for the States, Tribes and Territories.............................................................................................................. 14
Exhibit 2.4.a. Round 1 Data – Number of Records and Systems by Source Water Type.......... 15 Exhibit 2.4.b. Round 1 Data – Number of Records and Systems by System Type.................... 16 Exhibit 2.4.c. Round 1 Data – Number of Records by Year and Source Water Type ............... 17
Exhibit 2.4.d. Round 1 Data – Number of Records by Month and Source Water Type ............ 17 Exhibit 3.3.a. Summary of Round 2 Data Quanti ty and Quality for the States, Tribes and Territories.............................................................................................................. 22 Exhibit 3.3.b. Summary of Round 2 Data Quant ity and Quality for the States, Tribes and Territories.............................................................................................................. 22
Exhibit 3.4.a. Round 2 Data – Number of Records and Systems by Source Water Type........... 24 Exhibit 3.4.b. Round 2 Data – Number of Records and Systems by System Type.................... 24
Exhibit 3.4.c. Round 2 Data – Number of Records by Year and Source Water Type ................ 25
Exhibit 3.4.d. Round 2 Data – Number of Records by Month and Source Water Type ............ 25 Exhibit 4.3.a. NIRS Data – Number of Records by Year............................................................ 28
Exhibit 4.3.b. NIRS Data – Nu mber of Records by Month......................................................... 28
Exhibit 5.a. 24 Round 1 Cross-Sect ion States and States Not In cluded in the Cross-Section . 33
Exhibit 5.b. 20 Round 2 Cross-Sect ion States and States Not In cluded in the Cross-Section . 33
Exhibit 6.1.a. Round 1 Data – 24-State Cross- Section Summary of System-Level Occurrence for Contaminants Considered During CCL 2 Regulatory Determinations........... 36
Exhibit 6.1.b. Round 1 Data – 24-State Cross- Section Summary of Population Served-Level Occurrence for Contaminants Considered During CCL 2 Regulatory Determinations...................................................................................................... 36
Exhibit 6.2.a. Round 2 Data – 20-State Cross- Section Summary of System-Level Occurrence for Contaminants Considered During CCL 2 Regulatory Determinations........... 37

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# Exhibit 6.2.b. Round 2 Data – 20-State Cross-S ection Summary of Population Served-Level Occurrence for Contaminants Considered During CCL 2 Regulatory Determinations...................................................................................................... 38 Exhibit 6.3.a. NIRS Data – Summary of Bo ron Occurrence in Surveyed Ground Water Systems - Based on the System Level................................................................................. 39 Exhibit 6.3.b. NIRS Data – Summary of Bor on Occurrence in Surveyed Ground Water Systems - Based on Population Served............................................................................... 39 Exhibit 6.4. National Extrapolation of Stage 1 Occurrence Measures.................................... 40
Exhibit 6.5. States Common to Both Round 1 and Round 2, and Respective Cross-Sections. 41 Exhibit 7.1.a. Geographic Distribution of Meto lachlor Detections in Both Cross-Section and Non-Cross-Section States (Round 2 Data) ........................................................... 45 Exhibit 7.1.b. Geographic Distribu tion of Metolachlor Detection Frequencies in Cross-Section States (Round 2 Data) ........................................................................................... 45 Exhibit 7.1.c. Annual Frequency of Metolachlor Detections By Year (1992-1997) from the 19-State Round 2 Cross-Section ........................................................................... 46 Exhibit 7.2.a. Geographic Dist ribution of 1,3-Dichloropropene Detections in Both CrossSection and Non-Cross-Section Stat es (Combined Rounds 1 and 2) ................... 47 Exhibit 7.2.b. Geographic Distri bution of 1,3-Dichloropropene De tection Frequencies in CrossSection States (Upper Map: Round 1; Lower Map: Round 2).............................. 48 Exhibit 7.2.c. Geographic Distri bution of 1,3-Dichloropropene Det ection Frequencies (upper map) and HRL Exceedance Frequencies (lower map) for All Round 1 and Round 2 Cross-Section States ........................................................................ 50 Exhibit 7.2.d. Annual Frequency of 1,3-Dich loropropene Detections (left) and HRL Exceedances (right), 1985 - 1997, in Select Cross-Section States ....................... 51 Exhibit 7.2.e. Distribution of 1,3-Dichloropr opene Detections (left) and HRL Exceedances (right) Among Select Cr oss-Section States........................................................... 51 Exhibit 7.3.a. Geographic Distri bution of 1,1,2,2-Tetrachloroethane De tections in Both Cross-Section and Non-Cr oss-Section States (Combined Rounds 1 and 2)......... 52 Exhibit 7.3.b. Geographic Distri bution of 1,1,2,2-Tetrachloroethan e Detection Frequencies in Cross-Section States (Upper Map: Round 1; Lower Map: Round 2) ................... 53 Exhibit 7.3.c. Geographic Di stribution of 1,1,2,2-Tetrachloroe thane Detection Frequencies (upper map) and HRL Exceedance Frequencies (lower map) for All Round 1 and Round 2 Cross-Section States............................................................................... 55 Exhibit 7.3.d. Annual Frequenc y of 1,1,2,2-Tetrachloroethane De tections (left) and HRL Exceedances (right), 1985 - 1997, in Select Cross-Section States ....................... 56
Exhibit 7.3.e. Distribution of 1,1,2,2-Tetrachloroethane Detections (left) and HRL Exceedances (right) Among Select Cr oss-Section States........................................................... 57

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# Appendices

APPENDIX A. Development of Health Reference Levels

APPENDIX B. Detailed Round 1 Data Summary for 1,3-Dich loropropene, and 1,1,2,2- Tetrachloroethane

APPENDIX C. Detailed Round 2 Data Summ ary for Metolachlor, 1,3-Dichloropropene, and 1,1,2,2-Tetrachloroethane

APPENDIX D. Detailed NIRS Data Summary for Boron

APPENDIX E. Data Summaries of Occu rrence and Population Served for Four Contaminants Considered During CCL 2 Regulatory Determinations

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# Acronyms

AWWARF American Water Works Association Research Foundation

CAS Chemical Abstract Services

CCL Contaminant Candidate List

CCL 1 EPA’s First Cont aminant Candidate List

CCL 2 EPA’s Second Contaminant Candidate List

CMR Chemical Monitoring Reform

CWS Community Water System

DCPA Dimethyl Tetrachloroterephthalate (Dacthal)

DDE 1,1-Dichloro-2,2-bis( p-chlorophenyl)ethylene

EPA Environmental Protection Agency

EPTC s-Ethyl Dipropylthiocarbamate

GWUDI Ground Water under Direct Influence

GW Ground Water

HRL Health Reference Level

IOC Inorganic Compound

MRL Minimum Reporting Leve l or Method Reporting Limit

MTBE Methyl Tertiary Butyl Ether

NCWS Non-Community (or Transient) Water System

NCFAP National Center for Food and Agricultural Policy

NIRS National Inorganic and Radionuclides Survey

NPDWR National Primary Drinking Water Regulation

NTNCWS Non-Transient Non-Community Water System

OGWDW Office of Ground Wate r and Drinking Water

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## xviii 

# PWS Public Water System

PWSID Public Water System Identifier

SDWA Safe Drinking Water Act

SDWIS Safe Drinking Water Information System

SDWIS/FED Safe Drinking Water Info rmation System/Federal Version

SOC Synthetic Organic Compound

SRMD Standards and Risk Management Division

SW Surface Water

TAB Targeting and Analysis Branch

UCM Unregulated Contaminant Monitoring

UCMR Unregulated Contamin ant Monitoring Regulation

URCIS Unregulated Contaminant Monitoring Information System

VOC Volatile Organic Compound

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# 1. Introduction

This report presents an analys is of national occurrence in pu blic drinking water systems of four unregulated contaminants: one inorga nic compound (IOC), boron; one synthetic organic compound (SOC), metolachlor, and two volatile organic compounds (VOCs), 1,3- dichloropropene and 1,1,2,2-tetrachloroethane. These four contaminants are on the second Contaminant Candidate List ( CCL 2) for which the United States Environmental Protection Agency (EPA) is currently considering during the CCL 2 regulatory determination process.

Drinking water contaminant occurrence findings developed in this report are based on three different data sets. The Unregulated Contaminant Monitoring (UCM) program Round 1 and Round 2 monitoring data sets were collected under provisions of the Safe Drinking Water Act (SDWA). These data sets provide occu rrence data for 1,1,2,2- tetrachloroethane, 1,3- dichloropropene, and metolachlor. The occu rrence data for boron were collected through the National Inorganics and Radionuclides Survey (NIRS). Reviews of these unregulated contaminant occurrence data sets, as we ll as detailed occurrence findings for 1,1,2,2- tetrachlroethane, 1,3-dichloropropene, metolachlo r and boron, are presented in this report. Additionally, the CCL 2 includes several contaminants monitored under the first Unregulated Contaminant Monitoring Regula tion (UCMR 1). EPA presents the occurrence findings for ten UCMR 1 contaminants (1,1-dichloro-2,2-bis(p- chlorophenyl)ethylene, also known as DDE; the mono- and di-acid degradates of dimethyl tetrachloroterephthal ate, also known as DCPA or dacthal; 1,3-dichloropropene; 2,4-dinitr otoluene; 2,6-dinitr otoluene; s-ethyl dipropylthiocarbamate, also known as EPTC; fonofos; methyl tertiary butyl ether, also known as MTBE; and terbacil) in a separate report entitled The Analysis of Occurrence Data from the First Unregulated Contaminant Monitoring Regul ation (UCMR 1) in Support of Regulatory Determinations for the Second Drin king Water Contaminant Candidate List (USEPA, 2008a).

For those contaminants considered as part of the CCL 2 regulatory determinations, a Regulatory Determinations Support Document (U SEPA, 2008b) provides contaminant-specific information regarding chemical and physical pr operties, use and rele ase, and supplemental occurrence data and analyses. Based on contam inant occurrence, exposure, and other risk considerations, EPA must determine if regulatin g these contaminants will present a meaningful opportunity to reduce public health risk.


# 1.1 Regulatory Background

Under §1412(b)(1) of the SDWA Amendments , EPA was required to publish a list of contaminants (the CCL) to assist in priority-set ting efforts. The contaminants included on a CCL are not subject to any current or proposed National Primary Drinking Water Regulation (NPDWR). CCL contaminants may pose risks fo r drinking water, and therefore may require regulation under SDWA.

The first CCL (CCL 1) contained 60 contam inants, including 50 chemicals or chemical groups and 10 microbiological contaminants or mi crobial groups. In 2003, EPA released final regulatory decisions on nine of these contaminants (68 FR 42898). The second and current CCL (CCL 2: 70 FR 9071) contains 51 contaminants, c onsisting of all the contaminants from CCL 1 that did not progress to regulat ory determination. The 1996 SDWA Amendments require EPA to make determinations on whether or not to regul ate at least five contaminants on a five-year

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# cycle, or three and a half y ears after each CCL. This report presents contaminant occurrence findings that serve to support the s econd round of regulatory determinations.


# 1.2 Sources of Data Used for Analysis

Brief descriptions of the occurrence data sour ces used in this repor t are provided in this section (see Sections 2, 3, 4, and 5 for more deta ils on data management). Occurrence data for three of the contaminants evaluated in this report (metolachlor, 1,3- dichloropropene, and 1,1,2,2- tetrachloroethane) were collected as part of the UCM program. The SDWA, Amendments of 1986 required public water systems (PWSs) to mon itor for specified unre gulated contaminants on a five-year cycle, and to report the monitoring re sults to the States. Data from the first round of monitoring starting in 1988 were stored in the Unregulated C ontaminant Monitoring Information System (URCIS) database, referr ed to in this report as the UCM “Round 1 database.” In 1993, Congress amended SDWA to add new unregulated contaminants for monitoring. Data from this second round of mon itoring, starting in 1993, were stored in the Safe Drinking Water Information System/Federal version (SDWIS/FED 1 

# ) database, referred to in this report as the UCM “Round 2 database.” Occurrence data for the fourth contaminant evaluated in this report, boron, is derived from the occurren ce data collected under the National Inorganic and Radionuclides Survey.

Unregulated contaminants are contaminants that do not have an established or proposed NPDWR, but they may be formally listed and scheduled for monitoring under Federal regulations. The intent of the m onitoring is to gather scientific information on the occurrence of these contaminants, to enable a decision rega rding whether regulations were needed. EPA required all non-purchased community water sy stems (CWSs) and non-purchased non-transient non-community water systems (NTNCWSs) with more than 150 service connections to participate in this UCM. Smaller systems were not universally required to participate in the monitoring, but they were require d to be available for monitoring if the State decided such monitoring was necessary. (As ev ident in the data, many States did collect data from small systems as well.)

The 1993 SDWA Amendments added other contaminants to the unregulated contaminant list for required monitoring, and the 1996 SDWA Amendments directed EPA to develop a revised program for such monito ring. This new program was fo rmally published in the Federal Register on September 17, 1999 (64 FR 50556), as the UCMR 1. The UCMR 1, and related rules, replaced the older (UCM) requirements, pu tting forth a new list of contaminants, a new set of rules about which systems must monitor, a new structure to the monitoring program, and a new framework to ensure that all the monitori ng results are reported to EPA. Monitoring under UCMR 1 began in 2001. Every five years EP A must develop a new list of unregulated contaminants for UCMR monitoring.

Exhibit 1.2.a diagrams the inte r-relationship of the various databases, monitoring rounds and contaminant lists related to the UCM R ound 1 and Round 2 data. The Round 1 and Round 2 databases contain occurrence data from other cont aminants besides those re quired as part of the UCM in 1987 (referred to as UCM [1987]) or as amended in 1993 (referred to as UCM [1993]).

1 

## SDWIS/FED is the official da tabase repository of data provided by public drinking water systems, and includes data from earlier EPA public water system databases.

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# Also, although each database primarily contains da ta collected during the years of the two formal monitoring periods (1988-1992 a nd 1993-1997), there are some ear lier “grandfathered” data from years that pre-date the beginning of each of the respective monitoring periods.

Exhibit 1.2.a. Diagram of the Inter-Relationship of the Databases, Monitoring Rounds and Contaminant Lists Discussed in the Report

-UCM (1987) Chemicals

-28 Additional Chemicals •20 Mandatory VOCs •14 Discretionary VOCs

•21 Phase I VOCs •2 Regulated SOCs

•5 Miscellaneous Contaminants



## -34 Chemicals from UCM (1987)

-14 Additional Chemicals •20 Mandatory VOCs (Group 3) •14 Discretionary VOCs (Group 4)

•13 SOCs (Group 1) •1 IOC (Group 2) 

## UCM (1993) Chemicals Monitoring Period: 1988-1992

Monitoring Period: 1993-1997 -UCM (1987) Chemicals

-28 Additional Chemicals •20 Mandatory VOCs •14 Discretionary VOCs

•21 Phase I VOCs •2 Regulated SOCs

•5 Miscellaneous Contaminants



## -34 Chemicals from UCM (1987)

-14 Additional Chemicals •20 Mandatory VOCs (Group 3) •14 Discretionary VOCs (Group 4)

•13 SOCs (Group 1) •1 IOC (Group 2) 

## UCM (1993) Chemicals Monitoring Period: 1988-1992

Monitoring Period: 1993-1997



# The UCM (1987) contaminants included 34 VOCs, divided into two groups: one with 20 VOCs for mandatory monitoring, and the other wi th 14 VOCs for discretionary monitoring. The UCM (1987) contaminants were first monitore d coincident with the Phase I regulated contaminants, during the 1988-1992 period. This period is referred to as the “Round 1” monitoring period. The monitoring data collected by the PWSs were reported to the States (as primacy agents), but there was no pr otocol in place that defined re porting of these data to EPA.

The Round 1 data were stored in the URCIS (or “Round 1”) database. Most of the Phase 1 regulated contaminants were also VOCs. Both the unregulated and regulated VOCs are analyzed using the same sample and the same laboratory methods. Hence, the Round 1 database included data on all of these 62 Round 1 cont aminants: the 34 UCM (1987) VOCs; the 21 regulated Phase I VOCs; 2 regulated SOCs; a nd 5 miscellaneous contaminants that were voluntarily reported by some States (e.g., isomers of other organic contaminants). Details of the Round 1 database, its contained data, data quantity and quality, etc., are disc ussed in Section 2 of this report.

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# Monitoring for the UCM (1993) contaminants began coincident with the Phase II-V regulated contaminants in 1993 through 1998. This is often referred to as “Round 2” monitoring. The UCM (1987) contaminants were also includ ed in the Round 2 monitoring. In the updated listing for the unregulated contaminants re quired for the monitoring, the UCM (1993) contaminants were listed as: Group 1 (13 SOCs ); Group 2 (1 IOC); Group 3 (the 20 mandatory VOCs in UCM (1987)); and Group 4 (the 14 disc retionary VOCs in UCM (1987)). The group numbering is somewhat reversed, with the firs t unregulated contaminants, from UCM (1987), in the last two groups. Data from Round 2 monitoring were stored in the SDWIS/FED (or “Round 2”) database. Further details of the Round 2 data base, its data and management, are discussed in Section 3 of this report.

Exhibit 1.2.b presents the list of three contaminants evaluated during CCL 2 regulatory determinations contained in the Round 1 and Round 2 databases. This table includes Chemical Abstract Services (CAS) number and Safe Drinking Water Information System (SDWIS) contaminant code, and indicates the monitori ng Rounds and Group reference numbers for the contaminants. Note that the minimum repor ting levels (MRLs) were not uniform for metolachlor, 1,3-dichloropropene , or 1,1,2,2-tetrachloroethane, as several analytical methods were used in analyzing these data. MRLs for metolachlor varied from 0.01 to 52 μg/L with a modal value of 0.2 μg/L. MRLs for 1,3-dichloropr opene varied from 0.02 to 10 μg/L in Round 1 and from 0.08 to 1 μg/L in Round 2. The modal MRL in both rounds was 0.5 μg/L. MRLs for 1,1,2,2-tetrachloroethane varied from 0.01 μg/L to 10 μg/L in Round 1 and from 0.01 μg/L to 2.5 μg/L in Round 2. The modal MRL in both rounds was 0.5 μg/L.

Exhibit 1.2.b. List and Description of Contaminants with Round 1 and Round 2 Data Considered During CCL 2 Regulatory Determinations

Contaminant CAS Number SDWIS ID Modal MRL ( μ g/L) HRL ( μ g/L) UCM Round Common Sources of Contaminant
Synthetic Organic Chemicals

Metolachlor 51218-45-2 2045 0.2 70

– 2 Herbicide for corn, soybeans, peanuts, cotton, pod crops Volatile Organic Chemicals
1,3-Dichloropropene 542-75-6 2413 0.5 0.4 1 2 Solvent, used as fungicide

1,1,2,2- Tetrachloroethane 79-34-5 2988 0.5 0.4 1 2 Used in paint manufacturing;cement; paint removers; mothproofing

Modal MRL = Because different laboratory analytical methods were used during the approximately ten years of Round 1 and 2 monitoring, the resulting sample concent ration data reflect a range of MRLs; the modal value is the most common MRL. HRL = Health Reference Level (concent ration values used only as reference le vels for analyses in this report) UCM Round = data included in Round 1 and/or Round 2 monitoring and database.



# The third and final database used in this re port is the NIRS database. Data used for analysis of the remaining IOC (boron) comes from this database. The NIRS data, collected for a statistically designed, nationally representative survey, can be used directly for national

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# contaminant occurrence analyses with very few, if any, data quality or use issues. One limitation, however, is that the NIRS data are from groundwater systems only. The NIRS data, and assessments of supplemental IOC data, are discussed in detail in Section 4.

The NIRS survey was designed and conducted by EPA specifically to provide data on the occurrence of a select set of ra dionuclides and IOCs being cons idered for NPDWRs. The NIRS provides contaminant occurrence data from approximately 989 nationally representative community PWSs served by ground water. Each of these statistically randomly selected PWSs was sampled a single time between 1984 and 1986. Exhibit 1.2.c describes the single IOC for which occurrence was assessed in this report. The MRL for boron in the NIRS was always 0.005 mg/L.

Exhibit 1.2.c. Description of the Inorganic Chemical with Data in NIRS Considered During CCL 2 Regulatory Determinations

Contaminant CAS Number MRL (mg/L) HRL (mg/L) Common Sources of Contaminant

Inorganic Chemicals

Boron 7440-42-8 0.005 1.4 Naturally occurring in environment as borates, widely used in production of industrial and household goods



# 1.3 Threshold Evaluations

Assessments of contaminant occurrence incl uded in this report ar e conducted relative to the MRL. Analytical detections are samples w ith contaminants detected at concentrations equal to or greater than the MRL. An analytical non-detecti on is a sample that either had no contaminant present and therefore detected no co ntaminant or had the contaminant present at a concentration less than the MRL (and therefore was undetected). Evaluations of occurrence relative to the MRL provide the ba seline measure of occurrence.

Detections of the contaminants are also evaluated relative to at least two other concentration thresholds: the health reference level (HRL) and one-half the HRL (1⁄2 HRL). The HRL is an EPA-defined benchmark for evalua ting contaminant occurrence based on health effects information. By conducting occurrence asse ssments relative to se veral thresholds (such as the MRL, 1⁄2 HRL, and HRL), additional inform ation is provided on the degree as well as the frequency of contaminant occurrence. This serv es to better characte rize the distribution of

occurrence.
EPA evaluated the best available, peer-reviewed assessments and studies to characterize the human health effects that may result from ex posure to individual contaminants when found in drinking water. Based on this characteri zation, the Agency estim ated an HRL for each contaminant. For more details regarding the de velopment of the HRLs, see Appendix A in this report.

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# It is important to note that HRL values ha ve been derived by EPA as a means to provide additional information regarding the distributi on of occurrence and occurrence relative to concentrations of potenti al health effects.

Some contaminants with analytical detects ma y not have been detected at concentrations greater than their re spective HRL or 1⁄2 HRL. Although ma ny of the 1,3-dichloropropene and 1,1,2,2-tetrachloroethane occurrence data in the cross-section were generated using analytical methods with MRLs that were higher than the HRL, all MRLs did fall within (or below) the risk range of 10 -6 

# to 10 -4 

# used by EPA to evaluate carcinogens. It is possible, though, that monitoring failed to identify some HRL exceedances at the participating systems. Using the Stage 1 analytical approach, direct o ccurrence measures cannot be made relative to concentration thresholds below (less than) the MRL. Thus, th e HRL analyses might reflect underestimates of actual occurrence at concentrations above the 1⁄2 HRL and below the MRL. If warranted, the Stage 2 analytical approach (probabilistic modeling) can estimate system m ean concentrations at any level above or below the MRL. 2



# 1.4 General Description of the Two-Stage Analytical Approach

A two-stage analytical approach is used to evaluate the UCM Round 1 and 2 and NIRS contaminant occurrence data. The first stage of an alysis provides a straightforward evaluation of occurrence of all contaminants under considera tion. This “Stage 1 analysis” of occurrence assesses the data sources, quality, and characteristics, and then us es the data to conduct simple, non-parametric, and conservative assessments for a broad evaluation of contaminant

occurrence. 3 

# Occurrence analyses for each contaminant are assessed for samples, systems, and population served by systems. A typical Stage 1 analysis is a simple count of the number (or percentage) of systems with at least one analytical detection of a specific contaminant, or at least one analytical detection with a c oncentration greater than an HRL.

Any contaminant found to have significant occurrence at or near HRL concentrations based on the Stage 1 analysis can additionally be analyzed using the “Stage 2 analysis.” The Stage 2 analysis generates an estimated num ber of systems with a mean contaminant concentration exceeding a specified threshold and includes measures of uncertainty (corresponding confidence intervals based on calculat ed standard errors). The Stage 2 analysis uses statistical modeling to gene rate national probability estimates of contaminant occurrence by generating estimated annual mean concentrations of contaminants at PWSs. This provides an occurrence analysis that is less conservative since it is based on estimated annual mean concentrations rather than maximu m sample concentration results as in the Stage 1 analysis. The Stage 2 analysis also provides more direct es timates of potential chro nic exposure since it is based on estimated annual (long-term) mean concen trations of contaminant occurrence. In a general sense, the Stage 1 analysis reflects an ap proximation of peak analytical results while the Stage 2 analysis estimates l ong-term, average occurrence.

2 

## Stage 2 analysis allows an assessment of systems with me an, rather than peak, concen trations estimated to exceed the HRL and 1⁄2 the HRL. Because the Stage 2 mean concentr ation estimates are based on annual, or longer-term, occurrence data, the Stage 2 analyses may be more approp riate for contaminants with chronic health effects.

3 

## These analyses are conservative in the sense that they ar e protective of human health (i .e., they are more likely to overestimate risks to human health than underestimate them).

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# Because none of the contaminants discusse d in this report were found with significant levels of contaminant occurrence at or near th e HRLs of concern based on the Stage 1 analyses, Stage 2 analyses were not warranted for any of the contaminants. 4 

# The two-stage analytical approach was previously developed for othe r EPA Office of Ground Water and Drinking Water (OGWDW) national occurrence stud ies, including the first Six- Year Review of NPDWRs (see USEPA, 2003a). This data management and o ccurrence analytical approach was previously peer-reviewed for use under the Six-Year Revi ew and, partly for c onsistency across OGWDW projects, has been adapted for the analyses of the CCL 2 regulatory de termination occurrence data. A detailed description of the Stage 1 analyti cal approach is included in Section 1.5 below. For more details on the Stage 2 analytical approach, see Section 5 and Appendix B of The Analysis of Occurrence Data from the First Unregulated Contaminant Monitoring Regulation (UCMR 1) In Support of Regulatory Determinati ons for the Second Drinking Water Contaminant Candidate List (USEPA, 2008a).


# 1.5 Detailed Description of the St age 1 Analytical Methodology

Stage 1 analysis provides a conservative assessment of occurrence for each contaminant by counting the number of PWSs with at least one analytical result that equals or exceeds the MRL, or exceeds the 1⁄2 HRL or the HRL. Hence, these Stage 1 analyses are essentially based on the single maximum analytical value recorded at each PWS. The Stage 1 analyses are conservative – cautious regarding pu blic health concerns – in the sense that they are descriptive statistics based on peak, rather than long-term mean, concentrati ons of contaminants. The Stage 1 analyses are conducted at both the system le vel and the population-se rved level, allowing exposure to be characterized both in terms of the number and per cent of systems with detections, and the number and percent of popul ation-served by systems with detections. Estimates based on the population served by PWSs provide a rudime ntary characteristic of exposure potential.

By conducting the Stage 1 analyses at the syst em level and not the sample level, several biases of the Round 1 and Round 2 sampling methodology are avoided. During Round 1 and Round 2 monitoring, when detects were found in a system, sampling frequency increased for that system. Conducting Stage 1 analyses at the sample level, consequently, would bias the results toward increased detection frequencies. As such, the detection fre quency portion of Stage 1 analyses was conducted only on systems and th e population-served. The only sample-level analyses that were conducted were calculations of the mini mum, median, maximum, and 99 th 

# percentile values. Note that due to the inherent vulnerability , occurrence pattern, and some regulatory differences between surface wa ter-supplied and ground water-supplied PWSs, separate analyses were generated for surf ace water (SW) systems and ground water (GW) systems. All Stage 1 analytical findings are presented in Ap pendix B (for Round 1), Appendix C (for Round 2), and Appendix D (for the NIRS). At the beginning of the Appendices section, the “List of Appendix Tables” identifies all tables included in each of the three appendices.

4 

## It is important to note that Stage 2 analysis would not have been appropriate for the NIRS data. Stage 2 uses multiple records for a specific contamin ant per system to model a system’s long-term mean concentration. As the NIRS only contains one record per co ntaminant per system, Stage 2 analyses were therefore not appropriate for the NIRS data set.

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# 1.5.1 Extrapolation of National Cross-Section Results

The development of the UCM Round 1 a nd Round 2 national cross-sections enables occurrence analyses that are indi cative of national occurrence. In addition, the NIRS data were collected for a statistically desi gned, nationally representative surv ey. Extrapolations provide the best available estimate of contaminant occurr ence on a nationwide scale. To calculate the extrapolations, the total nationa l number of systems (or population served by systems) estimated to exceed a specified threshold is generated by multiplying the representative cross-section (or NIRS) percentage of systems with a threshol d exceedance (e.g., % sy stems > 1⁄2 HRL) by the national numbers for systems (and population served by systems) documented in the Water Industry Baseline Handbook, Second Edition - 2000 (USEPA, 2000).

Exhibit 1.5.a. Total Number System s and Population Served Systems Used in All National Extrapolations

National Inventory of CWSs plus NTNCWSs Source Water Type Systems Population
Ground Water 59,440 85,681,696 Surface Water 5,590 127,326,486 Total 65,030 213,008,182

Source: USEPA, 2000

.



# To estimate the national number of ground water systems with a detec tion of metolachlor, for example, the percentage of ground water systems from the Round 2 cross-section with detections of metolachlor (0.113%) is multiplie d by the total number of ground water systems nationally (59,440 systems). The resulting estimate equals 67 systems (59,440*0.00113=67). The national estimate of population exposed to a gi ven contaminant is extrapolated in a similar fashion (i.e., the proportion of population served by a system with a threshold exceedance is multiplied by the total population served nationa lly). Extrapolated results are presented in Section 6.4 and Appendix E.


# 1.6 Analytical Tools

All statistical analyses, and most mana gement efforts, were conducted with SAS ® 

# statistical software. Some data forma tting problems were corrected in Microsoft ® 

# Excel with the aid of specialized programs written in Visual Basic ® 

# or were corrected directly in SAS before the analysis began. 5 

# After analysis, results were typica lly exported into Excel for secondary analysis, sorting, or the development of report tables.

5 

## SAS is a registered trademark of the SAS Institute, Inc. Excel and Visual Basic are trademarks of the Microsoft Corporation.

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# 2. UCM Round 1 Data Overview

In this section of the re port, the monitoring results for the UCM program Round 1 data (from approximately 1988-1992) are reviewed. Th e data were derived from EPA’s Unregulated Contaminant Information System database. As de scribed previously, this report refers to URCIS as the Round 1 database.


# 2.1 Description of Data

The Round 1 database is a compilation of PWS monitoring results for unregulated contaminants, collected under the authority of SDWA, and reported to the States (as the primacy agents for SDWA). EPA requested that the States submit these data to EPA in the early 1990s, but no formal protocol or format had been established for reporting. Given the evolving nature of data management during this era various prob lems were encountered. The data were supplied by States on a variety of media, ranging from photo copies of hand-written files to electronic files on magnetic tape or diskettes of various kinds, and in many different formats and software configurations. Some data were electronically transferable, ot her data had to be manually entered or re-entered. EPA worked on the entry, cleanup, and analysis of these data during the 1990s. Through this long effort, many critical data quality problems were resolved (such as getting the data into consistent , standard units of measure). 6



# Data from Round 1 were reviewed, edited, and analyzed by the EPA in several other studies. Some initial analyses of the Round 1 data were presented in the occurrence data report produced for EPA’s OGWDW Chemical Monito ring Reform (CMR) project. That report, A Review of Contaminant Occurre nce in Public Water Systems (USEPA, 1999), is referred to as the “CMR Report.” Additionally, an occurrence review of select unregulated contaminants based on the Round 1 and Round 2 data is presented within the EPA report Analysis of National Occurrence of the 1998 Contaminant Candidate List (CCL) Regulat ory Determination Priority Contaminants in Public Water Systems (USEPA, 2002), referred to as the “ Priority Contaminants Report. ” The Priority Contaminants Report presents a comprehensive overview of national occurrence data fo r eight contaminants on the 1998 CCL. It was followed by the Analysis of National Occurre nce of 14 Contaminants from the 1998 Contaminants Candidate List (CCL) (USEPA, 2003), referred to as the “ Occurrence of 14 Report .” The Occurrence of 14 Report contains Round 1 analyses for two of the cont aminants discussed in this current report (1,3-dichloropropene and 1,1,2,2-tetrach loroethane). As descripti ons of occurrence based on the Round 1 database have been cove red thoroughly elsewhere, this cu rrent report presents only the information related to understa nding occurrence findings for the contaminants evaluated for CCL 2 regulatory determinations. For the most co mprehensive description of the creation and management of the Round 1 database, refer to Section II of the Priority Contaminants Report

.
The version of the Round 1 database used as the basis for this current analysis was the same final edited version developed and used fo r the regulatory determinations made on the 1998

6 

## For examples of data problem resolution, see Fallon, Fran, 1994 (November), “Unregulated Contaminants Information System (URCIS) System Inventory;” Computer Sciences Corp, 1993 (March), “Unregulated Contaminants Maintenance Manual;” Fallon, Fran, 1993 (December), “Unreg ulated Contaminants Maintenance Manual Supplement;” and, Computer Sciences Corp, 1992 (July), “A Statistical Survey of the Unregulated Contaminant Data.” (All of these internal reports contain many pages of text, sometimes unnumbered, and typically many pages of unnumbered tabulated data and/or computer code.)

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# CCL 1 contaminants. Some of the actual analyt ical findings developed and presented in the Occurrence of 14 Report (USEPA, 2003) are used in the current report. Other analyses, including new analyses using upda ted HRLs, have been conducted for and are presented for the first time in this current report.

The Round 1 database (as noted in Section 1) includes information on 62 contaminants, including: 34 unregulated VOCs; 2 regulated SO Cs and 21 regulated VOCs; and 5 miscellaneous contaminants reported by the States. The data were reported from 38 States, Washington, D.C., and the Virgin Islands. The data are from the first round of required UCM initiated in 1987 (i.e., UCM (1987)), but also include ol der data that are comparable to, but predate, the formal beginning of first round monitoring.


# 2.2 Data Management and Data Quality

During 1997-1998, the Round 1 database was revi ewed for various data quality problems and subsequently edited to remove problematic data to ensure the quality of the data used in the analysis. In the process of in itial database download and translat ion, unreadable lines of text and characters were apparently introduced into the data set and were subsequently deleted. (These lines did not appear to be actual data, but were artifacts related to the download, translation, and merger of various data sets.) Additionally, data from 946 systems of unknown source water type were eliminated. (Other systems had no sour ce type specified, but this missing inventory information was supplemented with SDWIS in ventory data.) Five observations with contaminant concentrations greater than 9,000 μg/L were excluded from the analysis (as presumed errors; this outlier editing was c onsistent with other processing that EPA has completed, see USEPA, 1999). Another 1,503 observ ations with erroneous sampling dates (e.g., years indicated as 00, 01, 39, etc.) were eliminated. In addition to these, a variety of other postdownload editing procedures were conducted to fill in data gaps, eliminate inconsistencies, and reduce potential sources of error. A more detailed description of these proc edures is discussed in Section II.B of the Priority Contaminants Report (USEPA, 2002). After these data management and editing efforts, the Round 1 database contained 3,452,530 analytical records for 62 contaminants.

Even with these management endeavors, ther e are still potential data quality problems given the diverse sources of the data and the sheer size of the database (i.e., 3.5 million records). Sources of problems may include some data reco rded in incorrect units , (e.g., the results are actually in mg/L, but are recorded as μg/L) or da ta units mistakenly converted in the original compilation of the data (e.g., the data units were ac tually in μg/L, were in correctly assumed to be in mg/L, and were then mistakenly ‘converted’ to μg/L as if they were mg/L). Reviews of the original database found that th is did not affect many data. There are a few apparently high analytical results (outliers) th at may be caused by this units problem. While outliers affect a review of the maximum concentrat ion values of a contaminant, there are few such data and they will have limited impact on other occurrence statistics reviewed in this report. (For most analytical summaries included in this report, the value of the 99 th 

# percentile is presented to avoid this problem.)

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# 2.3 Round 1 Data Bias and Representa tiveness: Further Data Quality Review and Editing

Subsequent to the major editing efforts on this database, a basic analysis of the 3.5 million records was undertaken. As a first step, various descriptive statistics were compiled by State to enable a further data review for bias and representativeness. Some State data, as will be described, are so incomplete that their use would introduce bias into the analyses. These data are used in certain parts of this repo rt to provide context or reference, but not to make determinations based on their occurrence analyses.

Exhibits 2.3.a. and 2.3.b summarize some key results from this next stage of data review. Together, they summarize the data availability for 57 primacy entities considered under SDWA: the 50 States, 5 territories, the District of Columbia, and an aggregate entry for the Native American Tribes. Within the Round 1 database th ere are data for 38 States, the Virgin Islands, and Washington, D.C., and no data for 17 primacy en tities. Some States only reported data for detections. For eight States (identified in E xhibit 2.3.b as “Entities with Data sets with 100% Detects”), the percent of samples with analytical detections (i.e., analytical results equal to or greater than the MRL) ranged fr om 80-100%. These States only reported data for detections and, hence, are highly biased (they did not repor t the majority of the monitoring sample results for which there were no detections above the MRL) . As presented in Exhibit 2.3.a, the percent of samples with detections (aggr egating all the data), typically ranged from 1-5% for States with complete data reporting.

The number of unique PWSs included in each State’s data record is shown in Exhibit 2.3.a. The number of PWSs included were co mpared to the total number of non-purchased CWSs and NTNCWSs in the curre nt State inventory, and to the number of non-purchased CWSs and NTNCWSs serving more than 500 people (s ince not all small systems may have had to conduct this monitori ng). The States identified as “Mos t Complete Data Sets” in Exhibit 2.3.b all approximated or exceeded 100% of one of these numbers (i.e., New Mexico’s Round 1 PWS numbers were only 70% of thei r current total inventory, but equaled 300% of the number of systems serving more than 500 persons). The States identified as “Significantly Too Few Systems” had far less representativeness. Fo r example, Colorado only has Round 1 data for 60 PWSs. This represents only 24% of the reporte d number of systems in their inventory lists. Also, Colorado data show 34% of all sample data are detections. Further review suggests that their data mainly include records for systems that had detections, but that analytical records were provided for all samples for these systems. This partial, selective reporting lowers the percent of sample records that represent detections (to less than 100% detection), but still reflects biased reporting and creates a biased an alytical record, since not all non-detection records have been reported (such as records from the likely large nu mber of systems with non-detections). In other cases, it is not clear what the data represent. Nevada’s reported percent samples with detections suggests the data may be complete, but there is only data for 10 systems – about 3% of systems as based on State inventory reco rds. Another five States ar e identified as having too few systems.
Exhibit 2.3.a also presents the number of samples per PWS in each State’s data. This summary statistic provides a perspective on the re lative completeness of reporting. For example, the States reporting only samples with detections typically report ed 2 to 10 samples per PWS. For most States, approximately 100 to 300 samples were collected a nd reported per PWS.

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# The last category in Exhibit 2.3.b identifies States with data records that are not complete (i.e., less than 100% of systems reported as base d on inventory listings), but that have other parameters (e.g., “Percent Sample Detections,” “S amples per PWS,” etc.) that suggest that the data are balanced and perhaps complete for th e systems that did repor t. The relatively low system numbers may simply relate to how the State implemented the program (e.g., implementation related to system size or other waiv ers, etc.). For exampl e, Florida reported data for 855 PWSs, a substantive number, but it’s on ly a small share of th eir relatively large inventory. Nevertheless, the whol e data picture for Florida (e.g., th e total detecti on rate) appears balanced.

In summary, of the 40 States/territories w ith Round 1 data, 21 States had records that appear relatively complete and balanced, and another 6 had record s that likely are balanced and with a substantial (though not complete) number of systems. The data from these 27 States should provide the most complete and unbiased summary of the occurrence data; the remaining 13 States are clearly biased sin ce results were reported only (or primarily) for detections. To present a national summary of the data, the 27 primacy entities with most complete records were evaluated for their national repres entativeness (to be discussed in Section 4) and considered for inclusion in the subsequent analyses.

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# Exhibit 2.3.a. Summary of Round 1 Data Quantity and Quality for the States, Tribes and Territories

States/ Tribes/

Territories Total Unique PWSs Percent Sample Detections Samples per PWS States/ Tribes/ Territories Total Unique PWSs Percent Sample Detections Samples per PWS

1 Alabama 152 5% 136 30 Nebraska 214 100% 6

2 Alaska 748 2% 132 31 Nevada 10 2% 860

3 American Samoa

- 32 New Hampshire 201 100% 5

4 Arizona 973 1% 151 33 New Jersey 1,551 2% 94

5 Arkansas 6 100% 5 34 New Mexico 617 0% 151

6 California 4,167 7% 111 35 New York 357 1% 348

7 Colorado 60 34% 38 36 North Carolina 298 2% 134

8 Connecticut

- 37 North Dakota

- 9 Delaware 13 6% 1,207 38 Ohio 2,657 1% 313

10 Florida 855 20% 14 39 Oklahoma

- 11 Georgia 1,165 2% 120 40 Oregon

- 12 Guam

- 41 Pennsylvania

- 13 Hawaii 127 1% 370 42 Puerto Rico

- 14 Idaho

- 43 Rhode Island

- 15 Illinois 1,307 5% 147 44 South Carolina

- 16 Indiana 415 4% 292 45 South Dakota 335 4% 52

17 Iowa 1,002 5% 62 46 Tennessee 306 4% 197

18 Kansas

- 47 Texas 124 98% 2

19 Kentucky 525 3% 273 48 Tribes

- 20 Louisiana 13 3% 95 49 Utah 430 1% 150

21 Maine

- 50 Vermont 133 82% 10

22 Mariana Is.

- 51 Virgin Islands 3 9% 186

23 Maryland 998 2% 105 52 Virginia

- 24 Massachusetts 220 91% 14 53 Washington 992 1% 229

25 Michigan 139 100% 16 54 Washington, D.C. 1 5% 3,432

26 Minnesota 1,565 1% 100 55 West Virginia 139 6% 157

27 Mississippi 206 100% 6 56 Wisconsin

- 28 Missouri 85 1% 215 57 Wyoming 145 3% 125

29 Montana 565 2% 94 TOTAL 23,819 2.9% 146



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# Exhibit 2.3.b. Summary of Round 1 Data Quantity and Quality for the States, Tribes and Territories

From the 27 States with reas onably complete data, three primacy entities were removed. Washington, D.C. and the Virgin Islands were re moved because they are not States, and the New York State data were excluded because there we re various and numerous problems associated with the data and metadata. For example, Ne w York did not use standard PWS identifiers (PWSIDs) that could be associat ed with SDWIS records, and the total number of reporting PWSs in the New York data set represented only 12 to 40% of the expected number of PWSs as based on the State’s inventory numbers. Also, there were some embedded errors in the data that sometimes caused data processing problems. Therefore, as summarized in Section 6, data are aggregated for a representative cross-section of 24 States (the 27 entities less Washington, D.C., the Virgin Islands, and New York), as well as for all 40 entities (which includes all entities; those with complete and balanced records, as well as the entities with biased records).



# 2.4 Data Characteristics Overview

After data management and editing, 3.45 m illion records were available for analysis representing more than 24,000 PWSs from the 40 States/enti ties. For the 24 States comprising the Round 1 representative cross- section (see Section 6 for a disc ussion regarding cross-section), the analytical results total 3.27 million records, from 22,034 PWSs.

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# For both all states and the 24-state cross- section, Exhibit 2.4.a re ports the number and percentage of sample records and systems relate d to source water type: 87% of the systems are classified as ground water and 13% as using surf ace water. The Round 1 data were collected before “ground water under the direct influen ce of surface water” (GWUDI) was introduced as a source definition. The classificati on used follows the regulatory gui delines: if a system uses any surface water, the system is classified, and is required to monitor, as a surface water system.

Exhibit 2.4.a. Round 1 Data – Number of Records and Systems by Source Water Type

RECORDS SYSTEMS SOURCE TYPE NUMBER PERCENT NUMBER PERCENT
All States - Ground Water 2,950,618 85.5% 21,046 87.1%
All States - Surface Water 501,912 14.5% 3,130 12.9%
All States - Total 3,452,530 100.0% 23,819 1 

## 100.0%
24 States - Ground Water 2,814,472 86.1% 19,637 87.9%
24 States - Surface Water 453,173 13.9% 2,695 12.1%
24 States - Total 3,267,645 100.0% 22,034 1 

## 100.0%

1. Because some water systems have more than one source water type, the total number of systems does not equal the sum of the ground water systems plus surface water systems.



# For both all states and the 24-state cross- section, Exhibit 2.4.b s hows the number and percent of records and systems by system type. About 7% of systems were coded as “NCWS,” a SDWIS code typically used for non-community wate r systems, or transient systems. Transient PWSs were not required by Federal rule to m onitor, but may have been required to by some States. Also, about 7% of the systems did not in dicate a system type (and the type could not be determined by SDWIS inventory records). These data remained in the database for the first stages of analysis, because other data elements were complete.

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# Exhibit 2.4.b. Round 1 Data – Number of Records and Systems by System Type

RECORDS SYSTEMS SYSTEM TYPE NUMBER PERCENT NUMBER PERCENT
All States - CWS 1 

## 2,608,840 75.6% 15,562 65.3%
All States - NCWS 2 

## 89,707 2.6% 1,771 7.4%
All States - NTNCWS 3 

## 516,047 14.9% 4,872 20.5%
All States - UNKNOWN 237,936 6.9% 1,614 6.8%
All States - Total 3,452,530 100.0% 23,819 100.0%
24 States - CWS 1 

## 2,546,144 77.9% 14,260 64.7%
24 States - NCWS 2 

## 89,533 2.7% 1,746 7.9%
24 States - NTNCWS 3 

## 515,807 15.8% 4,774 21.7%
24 States - UNKNOWN 116,161 3.6% 1,254 5.7%
24 States - Total 3,267,645 100.0% 22,034 100.0%

1. CWS = Community Water System 2. NCWS = Non-Community (Transient) Water System 3. NTNCWS = Non-Transient Non-Community Water System



# Exhibits 2.4.c and 2.4.d show the distribution of data by year and by month for States in the 24-State cross-section for the years 1983-1992. This period includes the compliance cycle (1988-1992) when the majority of data were colle cted, with a peak of data collection in 1991. Records prior to 1988 predate the formal begi nning of first round monitoring, but represent comparable data, and are therefore included to ex pand the coverage of these analyses. Exhibit 2.4.c shows the distribution of records for the years 1983-1992 7 

# , while Exhibit 2.4.d shows the monthly distribution of all the records used in the Round 1 anal yses for the same time period.

Records were well distributed throughout th e year, with an average of 272,304 records per month for the 24-State cross-section. Althou gh in the month of Marc h there is a slightly greater monthly percentage of data, there is no significant difference, suggesting that there should be no seasonal bias due to monthly differe nces in reporting. For Round 1 data from the 24-State cross-section, the tota l number of records during the compliance period of 1988 to 1992 ranged between a minimum of 321,618 records in 1988 and a maximum of 1,280,797 records in 1991, with an average of 573,945 records per year. By month for the 24-State cross-section, the total number of records ranged between 221,314 (Jul y) and 371,492 (March), with an average of 272,304 records per month. For a more detailed coverage of these numbers and other Round 1 data statistics, refer to Section II.D of the Priority Contaminants Report (USEPA, 2002).

7 

## Some data contained in the Round 1 data set are older, “grandfathered” data that predate the formal beginning of the 1988-1992 Round 1 monitoring period.

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# Exhibit 2.4.c. Round 1 Data – Number of Records by Year and Source Water Type

YEAR # SURFACE WATER RECORDS # GROUND WATER RECORDS TOTAL # RECORDS % OF TOTAL RECORDS

24 States - 1983 0 5 5 0.0% 24 States - 1984 30 43,837 43,867 1.3% 24 States - 1985 175 78,696 78,871 2.4% 24 States - 1986 1,852 140,155 142,007 4.3% 24 States - 1987 12,867 120,292 133,168 4.1% 24 States - 1988 107,428 214,190 321,618 9.8% 24 States - 1989 111,979 337,068 449,047 13.7% 24 States - 1990 87,273 509,889 597,162 18.3% 24 States - 1991 106,338 1,174,459 1,280,797 39.2% 24 States - 1992 25,222 195,881 221,103 6.8% 24 States - Total 453,164 2,814,472 3,267,645 100.0%



# Exhibit 2.4.d. Round 1 Data – Number of Records by Month and Source Water Type

MONTH # SURFACE WATER RECORDS # GROUND WATER RECORDS TOTAL # OF RECORDS % OF TOTAL RECORDS
24 States - January 33,315 266,685 300,000 9.2% 24 States - February 42,774 259,528 302,302 9.3% 24 States - March 42,903 328,589 371,492 11.4% 24 States - April 33,625 262,270 295,895 9.1% 24 States - May 45,221 254,900 300,121 9.2% 24 States - June 38,140 190,791 228,931 7.0% 24 States - July 31,060 190,254 221,314 6.8% 24 States - August 40,967 185,958 226,925 6.9% 24 States - September 33,214 209,679 242,893 7.4% 24 States - October 35,756 222,984 258,740 7.9% 24 States - November 39,480 215,372 254,852 7.8% 24 States - December 36,718 227,462 264,180 8.1% 24 States - Total 453,173 2,814,472 3,267,645 100.0%



# The analytical findings of the 24-State Round 1 cross-section o ccurrence data for 1,3- dichloropropene and 1,1,2,2-tetrachlo roethane are developed and summarized in Section 6 of this report.

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# 3. UCM Round 2 Data Overview

In this section of th e report, the monitoring results for the UCM (1993) list of unregulated contaminants, from Round 2 (approximately 1992-1997), are analyzed and reviewed. These Round 2 data (as discussed in Section 1) we re derived from the SDWIS/FED (or “Round 2”) database. Significant data review, formatti ng, and data quality checking and editing were required of these Round 2 data to enable the evaluations and analyses conducted.


# 3.1 Description of Data

The analyses in this section of the repor t are based on Round 2 data derived from the monitoring data collected between 1992 and 1997 and subsequently submitted to EPA. (Although the Round 2 monitoring period was forma lly initiated in 1993, data in the Round 2 data set include some older, “grandfathered” data from 1992.) The Round 2 database includes information on 48 contaminants, including: 1 IOC, 13 SOCs, 20 mandatory VOCs and 14 discretionary VOCs. These data ar e from 35 States/primacy entities

. Like the Round 1 data, much of the Round 2 data analyses and all of the data management and editing was conducted and descri bed previously in several EPA reports. The two most relevant of these reports are the Analysis of National Occurrence of the 1998 Contaminant Candidate List (CCL ) Regulatory Determination Prio rity Contaminants in Public Water Systems (the “Priority Contaminants Report;” USEPA, 2002), which contains more detailed information on data management a nd analysis of the Round 2 database, and the Analysis of National Occurrence of 14 Contaminants from the 1998 Cont aminant Candidate List (CCL) (the “Occurrence of 14 Report;” USEPA, 2003), which contains Round 2 analyses for 3 of the contaminants discussed in this report (1,3- dichloropropene, 1,1,2,2-tetrachlorethane, and metolachlor). For the most comprehensive description of the creation, management, and maintenance of the Round 2 database , refer to Section III of the Priority Contaminants Report (USEPA, 2002). Some of the actual analytical findings deve loped and presented in USEPA (2003) are used in this current report. Other analyses, incl uding those based on updated HRLs, have been conducted for, and are pr esented in, this current report.


# 3.2 Data Management and Data Quality

The raw Round 2 data from the 35 States/pri macy entities contai ned a total of 4,350,874 records. An important and substantial component of the Priority Contaminants Report (USEPA, 2002) consisted of the detailed and extensive review of these data records for numerous data quality considerations includi ng reporting consistencies, un iform and valid coding, data completeness, correct and consistent use of anal ytical units, and any inhe rent bias in the raw records. To ensure data quality for sound a nd dependable occurrence an alysis, extensive data review, checking, and editing were required. This data management and quality review process identified and addressed problema tic data or data that could no t be uniquely categorized. For more information on the types of problematic data encountered and how they were managed, refer to Section III.B of the Priority Contaminants Report (USEPA, 2002). With these data quality improvements, the initia l 4,350,874 analytical records from the 35 States/primacy entities for the 48 contaminants decreased to 4,211,446 anal ytical records for this Round 2 analysis.

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# 3.3 Round 2 Data Bias an d Representativeness: Furt her Data Quality Review and Editing

Subsequent to this initial editing and filtering of the data , a basic analysis of the 4.21 million records was undertaken. Similar to the R ound 1 data, various descriptive statistics were compiled by State to enable a further more de tailed data review to assess data bias and representativeness. Some State data, as described below, ar e seriously biased because they are so incomplete, and should only be used with cau tion for any statistical summary of occurrence.

Exhibits 3.3.a and 3.3.b summarize some key resu lts from this next stage of Round 2 data review. Together, they summarize the data avai lability and data quality for 57 primacy entities considered under SDWA (the 50 States, 5 territ ories and the District of Columbia, and an aggregate entry for the Native American Tribes). Of the 57 primacy entities in Round 2, 35 have reported Round 2 data and 22 have not. Exhibit 3.3.a also provides an overview of data quality, while Exhibit 3.3.b presents the 20 States (the States identified with data sets of adequate quality and completeness) that comprise the 20- State cross-section for Round 2 data.

Of the 35 States with Round 2 data, 15 States have incomplete data and/or data of inadequate quality. For two States (Alabama and Mississippi), the percent of samples with detections (with analytical results equal to or greater than the MRL; “Percent Sample Detections”) ranged from 70-100%. These States are identified in Exhib it 3.3.b as “Entities with Data Sets with 100% Detects.” These States re ported only (or mainly) analytical records for detections and, hence, their data sets are highly biased (over-r epresenting occurrence) and are therefore excluded from additional analysis. As shown in Exhibit 3.3.a, the percent samples with detections typically rang e from 1% to 8% for States with almost complete data reporting. An additional secondary check on these two States reporting only analytical detections is the measure of the number of samples per PWS. The numbers of samples per PWS for Alabama (2 samples/PWS) and Mississippi (4 samples/PWS) are significantly below the common range of 50 to 250 samples per PWS in most States.

The number of unique PWSs included in each State’s data sets, and the number of samples per PWS, are also included in Exhib it 3.3.a. These summary statistics provide a perspective on the relative completeness of repo rting. The number of PWSs included were compared to the total number of non-purchas ed CWSs and NTNCWSs in the current State inventory, and to the number of non-purchas ed CWSs and NTNCWSs serving more than 500 people (since not all small systems may have ha d to conduct this monitoring). Most States approximated or exceeded 100% of one of these comparative inventory numbers. The States (entities) identified with “Signi ficantly Too Few Systems” in E xhibit 3.3.b have data reported from far fewer systems than listed in the curren t State inventory. For ex ample, New Jersey (17 PWSs) and California (67 PWSs) have far too few systems with Round 2 data based on this comparison. Therefore, to reduce potential analytical results bias, New Jersey, California, and seven other States were excluded from the analyses since a signifi cant portion of PWSs in these States do not have contaminant occurrence data for Round 2.

Exhibit 3.3.b also indicates States with data quality problems. Th e data from Louisiana, Pennsylvania, South Carolina, and Vermont were very problematic. For instance, 100% of the data reported by Louisiana (for a very larg e number of systems and samples) were nondetections. There were no positive analytical findings of contaminant occurrence in the 164,492

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# sample results reported. Data fr om the other three States were very inconsistent (e.g., data for VOCs within a single State appeared to be reported in mixed units ). The data from these four States were excluded from the analysis and are identified as “Data Quality Problems”. The last category in Exhibit 3.3.b, “Entities Usable for Cross- section,” identifies Stat es with data records that are reasonably balanced and perhaps comple te for the systems that did report. These 20 Round 2 primacy entities with adequate and unbiased data were further considered for occurrence analyses.

The next level of data evaluation assessed th e analytical results fo r each State in even more detail. For example, the minimum, median, 99 th 

# percentile, and maximum analytical values were determined for every contaminant in each State. With this more in-depth level of analysis, some additional data quality problems we re identified within the data sets of the 20 Round 2 cross-section States. Most of these probl ems were determined to be specific to certain contaminants (or contaminant groups). With add itional data editing efforts, these problems have either been resolved or the problematic porti on of data omitted from further analysis. For additional discussion of specific prob lems, refer to Section III.C of the Priority Contaminants Report (USEPA, 2002).

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# Exhibit 3.3.a. Summary of Round 2 Data Quantity and Quality for the States, Tribes and Territories

State/ Tribes/

Territories Total Unique PWSs Percent Sample Detections Samples per PWS State/ Tribes/ Territories Total Unique PWSs Percent Sample Detections Samples per PWS

1 Alabama 314 94.08% 2 30 Nebraska

- 2 Alaska 625 3.10% 194 31 Nevada

- 3 American Samoa

- 32 New Hampshire 849 5.45% 23
4 Arizona 123 2.75% 55 33 New Jersey 17 2.32% 28
5 Arkansas 577 7.29% 118 34 New Mexico 755 0.75% 277
6 California 67 6.75% 44 35 New York

- 7 Colorado 833 3.72% 143 36 North Carolina 2,263 2.05% 55
8 Connecticut 87 4.53% 921 37 North Dakota 296 7.73% 59
9 Delaware

- 38 Ohio 2,259 3.45% 291
10 Florida

- 39 Oklahoma 888 3.99% 180
11 Georgia

- 40 Oregon 1,168 1.66% 75
12 Guam

- 41 Pennsylvania 1,424 10.32% 16
13 Hawaii

- 42 Puerto Rico

- 14 Idaho

- 43 Rhode Island 117 0.30% 136
15 Illinois

- 44 South Carolina 1,047 0.33% 147
16 Indiana 120 2.26% 58 45 South Dakota 27 2.34% 40
17 Iowa

- 46 Tennessee 78 9.31% 147
18 Kansas

- 47 Texas 4,863 1.23% 124
19 Kentucky 445 7.50% 125 48 Tribes 26 1.22% 57
20 Louisiana 1,394 0.00% 118 49 Utah

- 21 Maine 745 0.89% 163 50 Vermont 636 2.65% 74
22 Mariana Is.

- 51 Virgin Islands

- 23 Maryland 1,015 0.62% 140 52 Virginia

- 24 Massachusetts 506 3.12% 125 53 Washington 2,680 2.23% 123
25 Michigan 3,209 7.26% 97 54 Washington, D.C.

- 26 Minnesota 1,581 1.66% 198 55 West Virginia

- 27 Mississippi 1,155 71.27% 4 56 Wisconsin 225 1.41% 51
28 Missouri 1,434 6.08% 109 57 Wyoming

- 29 Montana

- TOTAL 33,848 2.95% 124



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# Exhibit 3.3.b. Summary of Round 2 Data Quantity and Quality for the States, Tribes and Territories



# 3.4 Data Characteristics Overview

A descriptive overview of the Round 2 data is presented in Exhibits 3.4.a through 3.4.d to provide additional insight and pe rspective on the results. As noted, after the initial data management and editing, 4.21 million records were available for analysis from more than 33,000 PWSs in the 35 States/entities. The Round 2 cro ss-section States total 3.69 million records from slightly more than 27,000 PWSs. These 20 States, therefore, contain nearly 88% of all available Round 2 State contaminant occurrence data.

Exhibit 3.4.a shows the number and percentage of sample records and systems according to source water type: approximately 89% of the systems in the 20-State cross-section are classified as ground water and 11% as surface water. These source water percentages are essentially the same for the entire data set usi ng all 35 States/entities. The Round 2 data contains systems using GWUDI as a source definition. Th e classification used follows the regulatory guidelines: if a system uses any surface water (s uch as a GWUDI), it is classified as a surface water system.

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# Exhibit 3.4.a. Round 2 Data – Number of Records and Systems by Source Water Type

RECORDS SYSTEMS SOURCE TYPE NUMBER PERCENT NUMBER PERCENT
All States - Ground Water 3,479,102 82.6% 30,085 88.9%
All States - Surface Water 732,344 17.4% 3,763 11.1%
All States - Total 4,211,446 100.0% 33,848 100.0%
20 States - Ground Water 3,085,266 83.5% 24,199 89.3%
20 States - Surface Water 609,619 16.5% 2,909 10.7%
20 States - Total 3,694,885 100.0% 27,108 100.0%



# Exhibit 3.4.b shows the number and percentage of records and systems by system type. Approximately 70% of systems in the 20-Stat e cross-section were CWSs and 30% were NTNCWSs. The CWS percentage was slightly highe r for the entire 35 States/entities data set, and the percentage for NTNCWS corresponding ly lower. Systems coded as NCWSs (or transients) were excluded from these analyses.

Exhibit 3.4.b. Round 2 Data – Number of Records and Systems by System Type

RECORDS SYSTEMS SYSTEM TYPE NUMBER PERCENT NUMBER PERCENT
All States - CWS 1 

## 3,255,222 77.3% 24,357 72.0%
All States - NTNCWS 2 

## 956,224 22.7% 9,491 28.0%
All States - Total 4,211,446 100.0% 33,848 100.0%
20 States - CWS 1 

## 2,808,341 76.0% 19,055 70.3%
20 States - NTNCWS 2 

## 886,544 24.0% 8,053 29.7%
20 States - Total 3,694,885 100.0% 27,108 100.0%

1. CWS = Community Water System 2. NTNCWS = Non-Transient Non-Community Water System



# Exhibits 3.4.c and 3.4.d show the distributi on of data by years and by month (based on actual sample collection or analysis date). Thes e tables only present the 20-State cross-section data. Exhibit 3.4.c indicates the amount of data annually collect ed during the 1993-1997 compliance cycle (including some 1992 “grandfathered” data). For Round 2 data from the 20- State cross-section, the total number of records ranged between 220,745 in 1992 and 823,587 in 1995, with an average of 615,814 records per year. In Exhibit 3.4.d, a fairly uniform distribution of occurrence data by month is shown, suggesting th at there should be no inherent seasonal bias in the data. For the 20-State cross-section, the total number of records ranged between 259,787 (November) and 371,122 (March), with an averag e of 307,907 records per month. Trends were similar for the entire 35 States/entities data se t as for the 20-State cro ss-section. For a more

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# detailed summary of these numbers, refer to Section III.D of the Priority Contaminants Report (USEPA, 2002).

Exhibit 3.4.c. Round 2 Data – Number of Records by Year and Source Water Type

YEAR # SURFACE WATER RECORDS # GROUND WATER RECORDS TOTAL # OF RECORDS % OF TOTAL RECORDS

20 States - 1992 33,187 187,558 220,745 6.0% 20 States - 1993 115,859 592,555 708,414 19.2% 20 States - 1994 105,673 504,410 610,083 16.5% 20 States - 1995 112,144 711,443 823,587 22.3% 20 States - 1996 136,182 589,788 725,970 19.6% 20 States - 1997 106,574 499,512 606,086 16.4% 20 States - Total 609,619 3,085,266 3,694,885 100.0%



# Exhibit 3.4.d. Round 2 Data – Number of Records by Month and Source Water Type

MONTH # SURFACE WATER RECORDS # GROUND WATER RECORDS TOTAL # OF RECORDS % OF TOTAL RECORDS
20 States - January 40,939 221,420 262,359 7.1% 20 States - February 49,405 211,499 260,904 7.1% 20 States - March 65,525 305,597 371,122 10.0% 20 States - April 41,692 257,085 298,777 8.1% 20 States - May 44,374 245,051 289,425 7.8% 20 States - June 55,612 285,159 340,771 9.2% 20 States - July 44,174 262,611 306,785 8.3% 20 States - August 52,087 266,475 318,562 8.6% 20 States - September 65,814 293,692 359,506 9.7% 20 States - October 46,113 254,688 300,801 8.1% 20 States - November 46,492 213,295 259,787 7.0% 20 States - December 57,392 268,694 326,086 8.8% 20 States - Total 609,619 3,085,266 3,694,885 100.0%



# The analytical findings of the 20-State Round 2 cross-section o ccurrence data for 1,3- dichloropropene, 1,1,2,2-tetrachlore thane, metolachlor are devel oped and summarized in Section 6 of this report.

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# 4. National Inorganics And Ra dionuclides Survey (NIRS) Data

The EPA’s NIRS occurrence data are assessed for one contaminant considered during CCL 2 regulatory determinations, boron, and ar e only applicable for PWSs served by ground water.


# 4.1 Description of Data

The NIRS survey was conducted by EPA speci fically to provide data on the occurrence of a select set of radionuclides and IOCs be ing considered for NPDWRs. The NIRS provides contaminant occurrence data from 989 CWSs se rved by ground water sources. Each of these randomly selected PWSs was sampled a single time between 1984 and 1986. The selection of this group of PWSs was designed so that the c ontaminant occurrence results from these PWSs are representative of national occurrence of contaminants in ground water systems. Further description of the NIRS survey can be found in Longtin (1988).

The NIRS sample design included random sel ection of a number of systems from each size category in proportion to the number of PWSs in those size categories nationally. NIRS was structured as a stratified, ra ndom sampling of the nation’s co mmunity ground water supplies as they existed in the mid-1980s. The stratification for sample selection was based on system size. However, the sampling frame used in NIRS was not specifically designed to be representative of ground water supplies on a State-by- State, regional, or other geographic basis. The resulting sample of systems represents approximately 2% of the nation’s community ground water supply in each system size category. Therefore, since ther e are many more small than large PWSs in the US, most of the NIRS data are from smaller syst ems. In aggregate, approximately 95% of the analytical sample results in the entire NIRS da tabase indicate no detectio ns of the contaminants sampled and analyzed. The NIRS database incl udes information on 42 contaminants, including: 36 IOCs (including 10 regulated IOCs), 2 re gulated radionuclides, and 4 unregulated radionuclides. The data are from 49 States (there are no data fr om Hawaii), as well as Puerto Rico. One contaminant from the NIRS is evaluate d in this report: boron. Concentration values for boron are presented in milligrams per liter (mg/L), not micrograms per liter (μg/L).


# 4.2 Representativeness

By design, the data collected and containe d in the NIRS database are nationally representative of ground water systems, and furt hermore, can be divided into strata based on system size for additional statistical resolution. Especially when compared to the Round 1 and 2 databases, there are few contaminant occurrence data quality or completeness issues with the NIRS data set. The NIRS contai ns analytical results that were specifically collected to establish a nationally representative sample, so the sample is “complete and adequate” simply by correct implementation of the sample selection design. Al so, there are often com putational (statistical) problems resulting from multiple laboratory analytic al detection limits that must be addressed in the analysis of occurrence data. In the case of NIRS (for the IOC being evaluated in this report) analytical methods with uniform detection lim its were employed. Therefore, the extensive concerns and problems with data quality, comple teness, and representati veness encountered in the use of Round 1 or 2 data are not issues when considering the us e of the NIRS data.

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# 4.3 Data Characteristics Overview

A descriptive overview of the data is presented in two tables to provide additional insight and perspective on the results. Summary results for all States are included in the following results tables. For more descriptive informati on on the NIRS data characteristics, refer to Section IV.C of the Priority Contaminants Report (USEPA, 2002).

Exhibits 4.3.a and 4.3.b show the distributi on of data by years and by month across all years. The data were collect ed between 1984 and 1986, with a peak of data collection in 1985. Somewhat more samples were collected in 198 5, and a somewhat larger proportion of samples was collected in the fall months of September, October, and November (though seasonal effects for the occurrence of IOCs in groundwater is lik ely not high). The analytical findings of the occurrence data for boron are developed and summarized in Section 6.3 of this report.

Exhibit 4.3.a. NIRS Data – Number of Records by Year

YEAR # OF RECORDS % OF TOTAL RECORDS

1984 268 27.1% 1985 466 47.1% 1986 255 25.8% Total 989 100.0%



# Exhibit 4.3.b. NIRS Data – Number of Records by Month

MONTH # OF RECORDS % OF TOTAL RECORDS January 19 1.9% February 29 2.9%

March 63 6.4% April 92 9.3% May 70 7.1% June 68 6.9% July 92 9.3% August 94 9.5% September 118 11.9%

October 153 15.5% November 132 13.3% December 59 6.0% Total 989 100.0%

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# 4.4 Supplemental IOC Data

Efforts were made to identify data sources from surface water systems to supplement the ground water data in the NIRS data. Boron was not monitored in either the UCM or UCMR. To gain a better understanding of th e potential occurrence of boron in surface water systems, EPA evaluated a report funded by the American Wa ter Works Associati on Research Foundation (AWWARF; Frey et al. , 2004). The AWWARF study recruited 189 PWSs representing 407 source waters that covered 41 states. Of these 407 PWS source water samples, 342 were returned and 341 were analyzed for boron. Of these 341 samples, approximately 67% (or 228) represented ground water sources and 33% (or 113) represented surface water sources. None of the 113 surface water sources exceeded the bor on HRL of 1.4 mg/L and the maximum concentration observed in surface water was 0.345 mg/L . Extrapolation of the data indicates that 95% of the ground water detections had bor on levels less than 1.054 mg/L; the maximum observed concentration in ground water was ap proximately 3.3 mg/L. Seven of the 228 ground water sources (from 5 systems) had boron concen trations greater than 1.4 mg/L (Seidel, 2006).

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# 5. Developing a Nationally Representative Perspective

As discussed in previous sections of this report, the Round 1 and Round 2 databases contain contaminant occurrence da ta from a total of 40 and 35 St ates/entities, respectively. However, data from many of these States ar e incomplete, problematic , and/or biased. An evaluation of these data suggested that data from certa in States were most complete and might, therefore, be used to generate summary statistic s indicative of national contaminant occurrence. The representativeness of the State data was ev aluated across a range of potential contaminant occurrence and across the spatial/hydrologic divers ity of the nation. Based on these assessments, a cross-section of States was developed for each database to provide a reasonable indication of national occurrence.

The approach used for the construction of the cross-sections in this analysis was originally developed for the CMR report (USEPA , 1999). The approach to establish national cross-sections from State SDWA contaminant da tabases was supported by peer reviewers and by stakeholders as providing a clear, replicab le, and understandable approach. Although this approach cannot provide a statistically repres entative sample (since th e data could not be selected in a statistically random manner), the resultant data pr ovide a clear indication of the central tendency of national o ccurrence. The methods by which the national cross-section was developed and tested for representativeness will be summarized in this report in a condensed form. For a detailed description of the methods used to develop the nationally-representative cross-sections, see Section V of the Priority Contaminants Report (USEPA, 2002).

States selected for the nati onal cross-section were evalua ted along two main criteria. First, the States had to provide the best data quality and completeness. Evaluation of this criterion has been discussed previously in this report. Second, the States had to provide a balanced national cross-section of occurrence data , requiring them to be representative of other characteristics as well. Determination of cr oss-sectional balance wa s based on evaluating the States’ pollution potential and geogr aphic coverage in relation to all States. Pollution potential was included to ensure the selection of states that represent the range of likely contaminant occurrence and a balance with regard to lik ely high and low occurrence. Geographic consideration was included so that the wide range of clima tic and hydrogeologic conditions across the United States would be represented, agai n balancing the varied conditions that affect transport and fate of contaminants. Two primar y indicators were chosen to represent pollution potential in each State: the num ber of manufacturing establishments per square mile, and the total farm agricultural chemical expenses. Sources of information for the first indicator were the 1995 Annual Survey of Manufactures (USDOC, 1997) and the 1992 Census of Manufactures (USDOC, 1996), while data for the s econd indicator was taken from the 1992 Census of Agriculture (USDOC, 1994).

The states were divided into quartiles base d on their pollution poten tial rankings for the two indicators, and the cr oss-section states were chosen to ensure equitable representation from each quartile. In addition, some secondary pollu tion potential indicators were considered to further ensure that the cross-section states incl uded the spectrum of pollu tion potential conditions (high to low). At the same time, care was ta ken to ensure that the cross-section provided representative coverage across all geographic regions of the United States.

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# The product of the data quality screening, pollution potential rankings, and geographic coverage analysis was a nationa l cross-section of 24 Round 1 stat es and a national cross-section of 20 Round 2 states (see Exhibit 5.a-b). Th e Round 1 24-State cross-section includes about 49% of the PWSs nationally and about 56% of the population served by PWSs. By comparison, the Round 2 20-State cross-secti on includes more than 41% of the PWSs nationally and about 34% of the population served by PWSs. In each case, the cross-section states provide good representation of the nation's va ried climatic and hydrogeologic regimes and the breadth of pollution potential for the contaminant groups.

To assess the representativeness of the Round 1 24-State cross-se ction, and the crosssection methodology in general, cross-sections of 4, 8, and 13 States were developed and contaminant statistics for each cross-section were compared to the 24-State cross section. These statistics were also compared to contaminant statistics derive d from cross-sections including biased data. Following this comparison, the 24-Stat e cross-section appeared to be a successful balance between the problems associated with too little data (unrepresentative sampling) and those associated with to o much data (including “bad” or bi ased data). Consequently, although they are not “statistically representative,” both th e 20- and 24-State cross-sections were used for further analyses of occurrence data. For more information on the construction and validation of both the Round 1 and Round 2 cross-s ections, see Section V of the Priority Contaminants Report (USEPA, 2002).

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# Exhibit 5.a. 24 Round 1 Cross-Section States and States Not Included in the Cross-Section

Exhibit 5.b. 20 Round 2 Cross-Section States and States Not Included in the Cross-Section

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# 6. Analysis of National Occurrence

This section of the report contains detailed occurrence assessments of four contaminants considered during CCL 2 regulatory determina tions: data for 1,3-dichloropropene and 1,1,2,2- tetrachloroethane are found in the Round 1 and Round 2 databases, data for metolachlor are found in the Round 2 database, and data for boron are found in the NIRS database. In the following section (Section 7), a se ries of graphs and maps are presented as a complimentary graphical evaluation of the occurr ence of these four contaminants.

The summary data developed for the occurr ence assessments are presented in detail in Appendices B through E. Appendix B contains analyses of the two Round 1 contaminants. Appendix C contains analyses of the three R ound 2 contaminants. Appendix D presents an analysis of the NIRS data for boron. Detailed su mmaries of all four contaminants are presented in Appendix E. At the beginning of the Appe ndices section, a complete “List of Appendix Tables” identifies all tables included in the f our appendices. Also included are “Notes to Accompany Unregulated Contaminant Occurrence Da ta Tables” which presents definitions of terms and phrases commonly used in the many tables, graphs, and maps included in this report and its appendices.



# 6.1 Round 1 Contaminant Occurrence

Exhibits 6.1.a and 6.1.b summarize the Round 1 24-State cross-sec tion occurrence data for 1,3-dichloropropene and 1,1,2,2- tetrachloroethane. For bo th 1,3-dichloropropene and 1,1,2,2-tetrachloroethane, less than 1% of PWSs in the cross-section States have analytical detections in the Round 1 databa se. Approximately 2% of the population served by PWSs had analytical detections of 1,1,2,2-te trachloroethane while less than 1% of the population served by PWSs had detections of 1,3-dich loropropene. While detection fr equencies of both contaminants suggest very low levels of national occurren ce, both contaminants also were found more frequently in surface water PWSs than ground wate r PWSs. This pattern is found at both the detection ( ≥ MRL) and threshold (> HRL) level.

Nevertheless, the low percentage of systems with at least one sample analytical result exceeding the HRL (< 0.6% for both contaminan ts in surface water) suggests that both contaminants are only very rarely found in con centrations surpassing the defined health-based thresholds. Because much of the 1,1,2,2-tetrach loroethane and 1,3-dichloropropene occurrence data were generated using labor atory methods with MRLs higher than the respective HRLs and 1⁄2 HRLs, it is likely that occurrence analys es did not identify some HRL and 1⁄2 HRL exceedances at the participating systems. Given this, the analyses may potentially underestimate actual 1,1,2,2-tetrachloroethane a nd 1,3-dichloropropene occurrence relative to their respective HRLs and 1⁄2 HRLs. Although many of the MR Ls used in the cross-section for 1,3- dichloropropene and 1,1,2,2-tetrachloroethane were higher than the HRL, all MRLs did fall within (or below) the risk range of 10 -6 

# to 10 -4 

# used by EPA to evaluate carcinogens. A complete presentation of the occurrence data for the two contaminants considered during CCL 2 regulatory determinations in Round 1 is provided in Appendix B.

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# Exhibit 6.1.a. Round 1 Data – 24-State Cross-Section Summary of System-Level Occurrence for Contaminants Considered During CCL 2 Regulatory Determinations

# of PWSs % PWSs ≥ MRL % PWSs > HRL 99th

CHEMICAL NAME (HRL in μ g/L) Percentile Value ( μ g/L) Total GW SW Total GW SW Total GW SW

VOCs

1,3-Dichloropropene (HRL=0.4) 9,164 8,303 898 0.16% 0.12% 0.56% 0.16% 0.12% 0.56% < MRL

1,1,2,2- Tetrachloroethane 20,407 18,693 1,867 0.45% 0.39% 1.02% 0.20% 0.17% 0.48% < MRL (HRL=0.4)

PWS = Public Water System; GW = Ground Water; SW = Surface Wa ter; MRL = Minimum Reporting Limit (for laboratory analyses); HRL = Health Reference Level (con centration values used only as re ference levels for analyses in this report). “% PWSs > HRL” indicates the proportion of systems with any analytical result s exceeding the concentration value of the HRL. 99th Percentile Value = the 99th percentile of all samples, not just detects.



# Exhibit 6.1.b. Round 1 Data – 24-State Cross-Section Summary of Population Served-Level Occurrence for Contaminants Considered During CCL 2 Regulatory Determinations

CHEMICAL NAME (HRL in μ g/L) Total Population Served by PWSs % Population Served by PWSs ≥ MRL % Population Served by PWSs > HRL

Total GW SW Total GW SW Total GW SW

VOCs 1,3- Dichloropropene ( HRL=0.4 ) 50,917,006 24,660,968 29,271,833 0.86% 0.59% 0.99% 0.86% 0.59% 0.99%

1,1,2,2- Tetrachloroethane 94,710,065 55,763,644 43,763,942 1.86% 1.82% 1.70% 1.63% 1.53% 1.58% (HRL=0.4)

PWS = Public Water System; GW = Ground Water; SW = Surface Wa ter; MRL = Minimum Reporting Limit (for laboratory analyses); HRL = Health Reference Level (c oncentration values used only as reference levels for analyses in this report). “% Population Served by PWSs > HRL” indicates the proportion of population se rved by systems with any analytical results exceeding the concentration value of the HRL.



# 6.2 Round 2 Contaminant Occurrence

The Round 2 20-state cross-secti on data are discussed in Secti on 5 of this report, and are identified in Exhibit 5.b. Exhibit 6.2.a su mmarizes the Round 2 20-state cross-section occurrence data for metolachlo r, 1,3-dichloropropene, and 1, 1,2,2-tetrachloroethane. For all three contaminants, less than 1% of PWSs in the cross-section States have analytical detections. Analytical detections of 1,1,2,2- tetrachloroethane are found in less than 0.1% of PWSs, suggesting very low levels of national occurrence for this contaminant. However, based on the percentage of population served by systems, al most 12% of the population served by PWSs had detections of metolachlor, less than 1% of the population served by PWSs had detections of 1,3-

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# dichloropropene, and slightly more than 2.5% of the population served by PWSs had detections of 1,1,2,2-tetrachloroethane. The percent of systems with at least one sample analytical result greater than the HRL for 1,3-di chloropropene and 1,1,2,2-tetrachlo roethane is less than 0.25%, suggesting that these contaminants are only very rarely found in concen trations surpassing the defined HRL. No PWSs had any analytical results of metolach lor greater than the HRL of 70 μg/L

. Appendix C contains complete occurrence summaries for these three contaminants contained in Round 2 data.

Exhibit 6.2.a. Round 2 Data – 20-State Cross-Section Summary of System-Level Occurrence for Contaminants Considered During CCL 2 Regulatory Determinations

CHEMICAL NAME (HRL in μ g/L) # of PWSs % PWSs ≥ MRL % PWSs > HRL 99th Percentile

Value ( μ g/L) Total GW SW Total GW SW Total GW SW

SOCs

Metolachlor 1 

### (HRL=70) 12,953 11,503 1,450 0.83% 0.11% 6.55% 0.00% 0.00% 0.00% < MRL

VOCs 1,3- Dichloropropene (HRL=0.4) 16,787 15,178 1,609 0.35% 0.32% 0.62% 0.23% 0.19% 0.56% < MRL

1,1,2,2- Tetrachloroethane 24,800 22,106 2,694 0.08% 0.05% 0.30% 0.07% 0.05% 0.22% < MRL (HRL=0.4)

1. Massachusetts data not included in summar y statistics for this contaminant.
PWS = Public Water System; GW = Ground Water; SW = Surface Wa ter; MRL = Minimum Reporting Limit (for laboratory analyses); HRL = Health Reference Level (con centration values used only as re ference levels for analyses in this report). “% PWSs > HRL” indicates the proportion of systems with any analytical results exceeding the concentration value of the HRL. 99 th 

### Percentile Value = the 99 th 

### percentile of all samples, not just those with detections.



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# Exhibit 6.2.b. Round 2 Data – 20-State Cross-Section Summary of Population Served-Level Occurrence for Contaminants Considered During CCL 2 Regulatory Determinations

CHEMICAL NAME (HRL in μ g/L) Total Population Served by PWSs % Population Served by PWSs ≥ MRL % Population Served by PWSs > HRL

Total GW SW Total GW SW Total GW SW

SOCs

Metolachlor 1 

### (HRL=70) 47,098,573 14,279,627 32,818,946 11.58% 0.70% 16.31% 0.00% 0.00% 0.00%

VOCs
1,3- Dichloropropene (HRL=0.4) 45,951,052 17,423,030 28,528,022 0.55% 1.13% 0.19% 0.33% 0.57% 0.18%

1,1,2,2- Tetrachloroethane (HRL=0.4) 71,294,263 25,978,359 45,315,904 2.61% 0.09% 4.06% 0.08% 0.09% 0.07%

1. Massachusetts data not included in summary statistics for this contaminant.
PWS = Public Water System; GW = Ground Water; SW = Surface Wa ter; MRL = Minimum Reporting Limit (for laboratory analyses); HRL = Health Reference Level (c oncentration values used only as reference levels for analyses in this report). “% Population Served by PWSs > HRL” indicates the proportion of systems with any analytical results exceeding the concentration value of the HRL.



# 6.3 NIRS Contaminant Occurrence

The NIRS data are discussed in Section 4 of this report. Exhibit 6.3.a summarizes the occurrence data of the NIRS (f or ground water systems only) fo r boron. Nearly 82% of PWSs, serving 88% of the population served, had analytical detections of boron. This is consistent with the known widespread natural occu rrence of boron in soil and mi nerals. The percentage of systems with at least one sample analytical resu lt greater than the HRL (1.7%) is higher than the other contaminants analyzed, again indicating bo ron’s widespread nature. (Note that these results are for ground water systems only, and that the NIRS survey was designed to provide statistically valid results for ground water syst ems nationally.) Appendix D summarizes the NIRS data coverage for boron.

Since the NIRS data were collected from a select group of nationally representative PWSs (served by ground water), the percentage of samples (or systems) exceeding various thresholds are also estimates of national occurrence. For exam ple, since 1.7% of NIRS systems sampled for boron have detections greater than the HRL (of 1.4 mg/L ), it can be concluded that approximately 1.7% of ground water systems sa mpled nationally for boron will also have detections greater than the specified HRL. Furt hermore, it can be concluded that approximately 0.4% of the population served by ground water systems sampled nationally for boron will also have detections greater th an the specified HRL.

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# Exhibit 6.3.a. NIRS Data – Summary of Boron Occurrence in Surveyed Ground Water Systems - Based on the System Level

CHEMICAL NAME Total No. Percent PWS Percent PWS Percent PWS 99th Percentile

(HRL in mg/L) PWS ≥ MRL > 1⁄2 HRL > HRL Value (mg/L)
Inorganic Chemicals
Boron ( HRL=1.4 ) 989 81.90% 4.32% 1.72% 2.44

PWS = Public Water System; MRL = Minimum Reporting Limit (for laboratory analyses); HRL = Health Reference Level (concentration values used only as reference levels for analyses in this report) . 99th Percentile Value = the 99th percentile o f all samples, not just those with detections.



# Exhibit 6.3.b. NIRS Data – Summary of Boron Occurrence in Surveyed Ground Water Systems - Based on Population Served

CHEMICAL NAME (HRL in mg/L) Total Population Served by PWSs % Population Served by PWSs ≥ MRL % Population Served by PWS > 1⁄2 HRL % Population Served by PWS > HRL Inorganic Chemicals
Boron ( HRL=1.4 ) 1,482,153 88.10% 2.90% 0.40%

PWS = Public Water System; M RL = Minimum Reporting Limit (for laboratory analyses); HRL = Health Reference Level (concentration values used only as referenc e levels for analyses in this report).



# 6.4 National Extrapolation of Stage 1 Occurrence Measures

As stated earlier, both the Round 1 and R ound 2 cross-sections, as well as the NIRS database, were developed to be nationally representative. Nati onal estimates of the contaminant occurrence data can be genera ted via extrapolations. Exhibit 6.4 presents the national extrapolations of the Stage 1 occurrence measur es from the UCM Rounds 1 and 2 cross-sections and the NIRS data. These national extrapolations were calculated by multiplying the percentages of systems (or population served by systems) with threshold exceedances (presented in Exhibits 6.1.a through 6.3.b) by the number of systems and population served by systems nationally (presented in Exhibit 1.51).

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# Exhibit 6.4. National Extrapolati on of Stage 1 Occurrence Measures

Detec t ion s ( ≥ M RL) Detec t ion s > 1⁄2 HRL Chemi cal Na me Source (HRL ) Wat e r T y pe Popula t io n Popula t io n S y s t ems S y s t ems Ser v e d Ser v e d

Natio n al Extr ap olati on o f R o u n d 1 24-S t ate Cro ss-Secti on Data

GW 72 508,000 72 508,000 1,3- Dichloropropen e SW 31 1,262,000 31 1,262,000 (0.4 μ g/L) Total 106 1,825,000 106 1,825,000

GW 229 1,564,000 105 1,329,000 1,1,2,2- Tetrachloro etha ne SW 57 2,166,000 33 2,131,000 (0.4 μ g/L) Total 290 3,963,000 140 3,592,000 Detec t ion s > H RL

Popula t io n S y s t ems Ser v e d

72 508,000

31 1,262,000

106 1,825,000

102 1,309,000

27 2,013,000

131 3,472,000

Natio n al Extr ap olati on o f R o u n d 2 20-S t ate Cro ss-Secti on Data

GW 67 596,000 0.00% 0.00% 0.00% 0.00%

SW 366 20,769,000 0.00% 0.00% 0.00% 0.00% Metolachlor (70 μ g/L )
Total 542 24,660,000 0.00% 0.00% 0.00% 0.00%

GW 188 969,000 161 695,000 114 492,000

SW 35 248,000 31 230,000 31 230,000 1,3- Dichloropropen e (0.4 μ g/L) Total 225 1,171,000 194 894,000 147 703,000

GW 30 80,000 30 80,000 30 80,000

SW 17 5,164,000 15 950,000 12 90,000 1,1,2,2- Tetrachloro etha ne (0.4 μ g/L) Total 50 5,563,000 47 1,082,000 45 168,000

Natio n al Extr ap olati on o f NI RS Data

Boron (1.4 mg/L ) GW (onl y) 48,682 75,501,000 2,584 2,469,000 1,022 372,000



# 6.5 Comparing Data Coverage of Round 1 and Round 2

The Round 1 and Round 2 data were evaluated to determine if comparable States, PWSs, and contaminants are contained in both database s. As previously noted, Round 1 consisted of data from 40 States/territorie s and Round 2 consisted of data from 35 States/territories.

Exhibit 6.4 illustrates the Stat es in Round 1 and 2, identifying the States common to both. Although 25 States are common to both Rounds 1 and 2, most of these States could not be considered for this analysis because of data quali ty issues (see Exhibit 2.3.a and Exhibit 3.3.a). Many States reported analytical re sults from a very low proportion of systems, reported results in mixed units, and/or reported only analytical detections (highly censo red reporting) in Round 1 and/or Round 2.

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# Of the 25 States in both Round 1 and 2 (i dentified in Exhibit 6.4), only eight were determined to be sufficiently complete for use in this comparison analysis. Alaska, Kentucky, Maryland, Minnesota, North Carolina, New Mexic o, Ohio, and Washington were contained in both databases and have data of adequate quality for analyses and comparisons.

Exhibit 6.5. States Common to Both R ound 1 and Round 2, and Respective CrossSections

In addition to the States that have data in both the Round 1 and Round 2 databases, a determination was made regarding actual PWSs that are common to both databases. Thirty-one percent of all PWSs in Round 1 are also in Round 2, while only 22% of all Round 2 PWSs are common to both rounds. This is, in part, be cause there are many more systems reporting analytical results in Round 2 than in Round 1.

Michigan, for example, has only 139 systems in Round 1, and 123 of those systems (88%) are also in Round 2. In Round 2, Michigan has a total of 3,209 systems. Of these Round 2 systems, 123 (approximately 4%) are in Roun d 1. The number of PWSs in Alaska is problematic because the PWSIDs from Round 1 do not match the PWSIDs in Round 2. A few States do have a higher percen tage of systems common to both rounds. Kentucky, Maryland, Minnesota, New Mexico, and Ohio each have over 70% of their total number of systems common to both Round 1 and Round 2. Coincidently, these are five of the States used for the comparison of occurrence data in States common in Round 1 and Round 2, which makes this

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# analysis more representative for comparison of the States for each contaminant. For specific numbers associated with each State, refer to Section IV.D of the Priority Contaminants Report (USEPA, 2002).

Comparisons of contaminants in Round 1 and Round 2 indicated that there were no common IOCs (Group 1) or SOCs (Regulated or Group 2) reported in both databases. In contrast, all of the unregulat ed Group 3 and Group 4 VOCs reported in Round 2 were also reported in Round 1. None of the regulated VOC s reported in Round 1, however, were reported in Round 2. Summary data for the two VO Cs considered during CCL 2 regulatory determinations (1,3-dichloropropene and 1,1,2,2- tetrachloroethane) common to both Round 1 and Round 2 are presented in Appendix E (Table s E.3 and E.4) and comparisons between the rounds can be made. Further comparisons, in gr aphical form, are presen ted in Sections 7.2 and 7.3 of this report.

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# 7. Graphical and Spatial Assessments of the Contaminants Considered During CCL 2 Regulatory Determinations

This section presents graphical assessments of the contamin ants considered during CCL 2 regulatory determinations with data in the R ound 1 and Round 2 cross-section States. Most of the Section 7 exhibits (maps and graphs) present analytical results based on these cross-section States. Some exhibits (discussed below) use addi tional State data to incr ease spatial coverage. The occurrence data used for all of the followi ng maps and graphs ar e found in the occurrence summary tables in Appendix B and Appendix C of this report.

The development of the nationally representative cross-sections is an important aspect of the Round 1 and Round 2 data that must be consider ed as part of any conclusions drawn from the maps and graphs in this report. This deve lopment was discussed for Round 1 and Round 2 data in Section 5. The national cr oss-sections are developed from PWSs’ contaminant monitoring data with the intent that, in aggregate, the cro ss-section States’ occurrence findings are indicative of national occurrence. (Various occurrenc e comparisons between the Round 1 and Round 2 data, as well as comparisons to other State data sets, indicate that these cross-section States do provide contaminant occurrence data that are reasonable indications of national occurrence.)

Although sub-national occurrence findings, such as regional or multi-State occurrence patterns, can be useful for these initial assessments, any regional occurrence patterns (or absence of patterns) should be considered in the contex t of the source and coverage of the State crosssection data. With half (or more) of the States excluded from the cross-sections because they lack adequate data, regional pa tterns may be difficult to char acterize and must be interpreted with caution. Supplemental info rmation should be collected and used, whenever possible, to assist in evaluating the significance of any appa rent regional patterns. For example, when assessing a particular pesticide occurrence pattern in this report , supplemental State or regional pesticide-use information could be reviewed to determine how the possible absence of a pesticide high-use State might affect interpretati on of any occurrence pattern in the cross-section State maps.

The NIRS, designed to provide a single national occurrence assessment, is based on significantly less data th an that provided by the Round 1 or Round 2 databases. Also, the NIRS data reflect a single sample per system (in cont rast to 5 or 6 years of monitoring data from systems in the Round 1 and Round 2 databases). The NIRS survey results should only be reviewed in aggregate (i.e., at th e national level and not at any regi onal or State level); therefore, no maps or graphs using the NIRS data for boron are included.

Most of the exhibits below that illustra te distribution of occurrence are based on nonbiased data; for these exhibits only the cross-sec tion State data are used to develop the maps and graphs. However, to increase the spatial coverage of the exhibits th at broadly identify contaminant occurrence (Exhi bits 7.1.a, 7.2.a, and 7.3.a), all data from all States with data in Round 1 and Round 2 are used. Therefore, in th ese exhibits the data from non-cross-section States (i.e., States with limited or biased data) are included, in addition to data from the crosssection States. This more extensive use of the data in the databases can be appropriate when a simple ‘yes or no’ identification of States with any PWS contaminant detection is of interest.

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# 7.1 Metolachlor

There are only Round 2 occurrence data for metolachlor. Based on these data, metolachlor appears to o ccur throughout the United States, especi ally in the eastern half of the country. Fifteen of the 24 States with metolach lor data in Round 2 had at least one PWS with at least one analytical detection of this contaminant (see Exhibit 7.1.a, which includes all States, both cross-section and non-cross- section States, from the Round 2 database). In Exhibit 7.1.b, occurrence relative to the MRL is presented fo r only the Round 2 cross-section States. (MRLs varied from system to system. They ranged from 0.01 to 52 μg/L. The modal MRL value was 0.2 μg/L.) There is no apparent geographic tr end among the States with the highest proportion of analytical detections of metolachlor. The States with the highest percentage (between 10.1% and 20%) of metolachlor analytic al detections are Kentucky and Rhode Island. No States had any analytical results of metolachlor greater than the HR L of 70 μg/L. A lthough occurrence is relatively widespread, the degree of occurrence (as measured by concentration) appears low.

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# Exhibit 7.1.a. Geographic Di stribution of Metolachlor De tections in Both CrossSection and Non-Cross-Sect ion States (Round 2 Data)

Exhibit 7.1.b. Geographic Di stribution of Metolachlor Detection Frequencies in Cross-Section States (Round 2 Data)

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# Metolachlor occurrence over time, relative to the MRL, is presente d in Exhibit 7.1.c. Based on these data, the highest percentage of PW Ss had analytical detections of metolachlor equal to or greater than the MRL in 1992 and 1997. Note: Significantly fewer PWSs collected metolachlor data in 1992, as compared to subseque nt years; however, ther e were about the same number of PWSs with detections in 1992 as in other years, causing an elevated percentage of PWSs with metolachlor detections for 1992. A much smaller percentage of PWSs had analytical detections of metolachlor in 1993 through 1996. The increased percentage of PWSs with metolachlor detections in 1997 could be due to the increased use of metolachlor between 1992 and 1997. According to the National Center fo r Food and Agricultural Policy (NCFAP), around 1992 approximately 59.4 million pounds of metolachlo r active ingredient (a.i.) were applied annually to 16 types of crops on 32.4 million ac res, and around 1997 approximately 67.3 million pounds of metolachlor a.i. were applied annua lly to 21 types of crops on 36.7 million acres (NCFAP, 2004 as cited in Chapter 12 of USEPA, 2008b)

.

Exhibit 7.1.c. Annual Frequency of Metola chlor Detections By Year (1992-1997) from the 19-State Round 2 Cross-Section

Percent PWSs > MRL

0.0% 0.3% 0.6% 0.9% 1.2% 1.5% 1.8% 2.1%

1992 1993 1994 1995 1996 1997



## 46

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# 7.2 1,3-Dichloropropene

There are 1,3-dichloropropene occurrence data in both Round 1 and Round 2. Based on these data, the States with detections of 1,3-di chloropropene are widely distributed across theUnited States (see Exhibit 7.2.a, which includes all States, both cross-section and non-crosssection States, from both the Round 1 and 2 databa ses). Fourteen of the 37 States with 1,3- dichloropropene data in Round 1 and Round 2 had at least one PWS with at least one analytical detection. In Exhibit 7.2.b, occurrence relative to the MRL is presented for the Round 1 crosssection States in the left map and the Round 2 cross-section States in the right map. (MRLs varied from system to system. They ranged from 0.02 to 10 μg/L in the Round 1 cross-section and from 0.08 to 1 μg/L in the Round 2 cross- section. The modal MRL value was 0.5 μg/L in both cross-sections.) Utah and Minnesota have a higher percentage of 1,3-dichloropropene detections (between 1% and 3%) relative to other States.

Exhibit 7.2.a. Geographic Di stribution of 1,3-Dichloropr opene Detections in Both Cross-Section and Non-Cross-Section States (Combined Rounds 1 and 2)

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# Exhibit 7.2.b. Geographi c Distribution of 1,3-Di chloropropene Detection Frequencies in Cross-Section States (U pper Map: Round 1; Lower Map: Round 2)

48

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# Exhibit 7.2.c presents the co mbined Round 1 and Round 2 Cross-Section States with analytical detections of 1,3-dichloropropene equa l to or greater than the MRL (upper map) and greater than the HRL (lower map). Each State shows the highest percentage of detections for either Round 1 or Round 2 – State detection frequencie s for the maps below are not averages of Round 1 and Round 2 data. The States with the hi ghest percentage (between 1% and 3%) of 1,3- dichloropropene analytical detections are Minnesota and Utah. PWSs in several States detected concentrations above the HRL of 0.4 μg/L. The States with the highest percentage (between 0.51% and 1.75%) of 1,3-dichloropropene concentr ations greater than the HRL are Minnesota, Utah, Illinois, Alabama, and North Carolina. Minnesota and Utah, consequently, exhibit both elevated numbers of detections for 1,3-dichloropr opene, and elevated con centrations, relative to the other States in the cross-sections.

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# Exhibit 7.2.c. Geographi c Distribution of 1,3-Di chloropropene Detection Frequencies (upper map) and HRL Exceeda nce Frequencies (lower map) for All Round 1 and Round 2 Cr oss-Section States

1,3-Dichloropropene occurrence over time is presented in Exhibits 7.2.d and 7.2.e. The data used in these two exhibits were from the eight States that had 1,3-Dichloropropene

50

### EPA – OGWDW Analysis of Occurrence Data from th e UCM and NIRS for CCL 2 June 2008



# occurrence data in both the Round 1 and R ound 2 databases (Alaska, Kentucky, Maryland, Minnesota, North Carolina, New Mexico, Ohio and Washington). In both exhibits, occurrence is measured relative to the MRL in the left graph and relative to the HRL in the right graph. In Exhibit 7.2.d, the graphs suggest annual variab ility in occurrence between 1991 and 1997, with an increase in concentrations starting in 1992. Note: Significantly fewer PWSs collected 1,3- dichloropropene data in 1992, as compared to s ubsequent years so the single detection of 1,3- dichloropropene in 1992 caused the overall percentage of PWSs with detections in that year to appear high. However, it is unclear why there is an increase in occu rrence between 1992 and 1994; the use and release of 1,3- dichloropropene decreased thr oughout the 1990s (Chapter 6 of USEPA, 2008b). Exhibit 7.2.e presents the occu rrence of 1,3-dichloroprop ene by State. With the exception of Ohio, none of the eight States had any detections in the Round 1 data.

Exhibit 7.2.d. Annual Freque ncy of 1,3-Dichloropropene Detections (left) and HRL Exceedances (right), 1985 - 1997, in Select Cross-Section States

Percent PWSs > MRL

0.00% 0.10% 0.20% 0.30% 0.40% 0.50% 0.60% 0.70% 0.80%

1985 1986 1987 1988 1989 1990 1991 1992 1992 1993 1994 1995 1996 1997

Round 1 Round 2 Percent PWSs > HRL

0.00% 0.10% 0.20% 0.30% 0.40% 0.50% 0.60% 0.70% 0.80%

1985 1986 1987 1988 1989 1990 1991 1992 1992 1993 1994 1995 1996 1997
Round 1 Round 2



### Summary statistics by year are from 8 States: AK, KY, MD, MN , NC, NM, OH and WA. These are the only Cross-Section States with PWS 1,3-dichloropropene data in both Round 1 and Round 2. There are data for 1992 in both the Round 1 and Round 2 databases. The HRL used for 1,3-dichloropropene is 0.4 μ g/L.



# Exhibit 7.2.e. Distribution of 1,3-Dichloropropene Detections (left) and HRL Exceedances (right) Among Sel ect Cross-Section States

Percent PWSs > MRL

0.0% 0.5% 1.0% 1.5% 2.0% 2.5% 3.0%

AK KY MD MN NC NM OH WA

Round 1 Round 2 

### Percent PWSs >HRL

0.0% 0.5% 1.0% 1.5% 2.0% 2.5% 3.0%

AK KY MD MN NC NM OH WA

Round 1 Round 2



### These are the only Cross-Section States with PWS 1,3-dichlo ropropene data in both Round 1 and Round 2. The Health Reference Level (HRL) used for 1,3-dichloropropene is 0.4 μ g/L.



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# 7.3 1,1,2,2-Tetrachloroethane

Both Round 1 and Round 2 contain occurren ce data for 1,1,2,2-tetrachloroethane. Based on these data, 1,1,2,2-tetrachloroethane appears to occur throughout the United States. However, its occurrence does not appear to have a distinct geographic pa ttern (see Exhibit 7.3.a, which includes all States, both cro ss-section and non-cross-section States, from both Round 1 and 2 databases). Twenty-five of 46 States with 1,1,2,2-tetrachloroethane da ta in Round 1 and Round 2 had at least one PWS with at least one analytical detection of the contaminant. In Exhibit 7.3.b, occurrence relative to the MRL is presented fo r the Round 1 cross-secti on States in the left map and the Round 2 cross-section States in th e right map. (MRLs varied from system to system. They ranged from 0.01 to 10 μg/L in the Round 1 cross-section and ranged from 0.1 to 2.5 μg/L in the Round 2 cross-section. The modal MRL value was 0.5 μg/L in both crosssections.) Generally, the maps reflect 1,1,2,2-tetrachloroethane’s broad occurrence. There is no apparent geographic trend among the States with the highest proporti on of analytical detections. South Dakota has an especially hi gh percentage of detections w ith 11.64%. Florida is the second highest with 4.15%.

Exhibit 7.3.a. Geographic Di stribution of 1,1,2,2-Tetrach loroethane Detections in Both Cross-Section and Non-Cross-Sect ion States (Combined Rounds 1 and 2)

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# Exhibit 7.3.b. Geographic Distribution of 1,1,2,2-Te trachloroethane Detection Frequencies in Cross-Section States (U pper Map: Round 1; Lower Map: Round 2)

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# Exhibit 7.3.c presents the combined Round 1 and Round 2 States with analytical detections of 1,1,2,2-tetrachloroetha ne equal to or greater than the MRL (upper map) and greater than the HRL (lower map). Each State shows th e highest percentage of system detections for either Round 1 or Round 2 – State detection frequencie s for the maps below are not averages of Round 1 and Round 2 data. As presented previousl y, the two States with the highest percentage (between 4.15% and 11.6%) of 1,1,2,2-tetrachloroethane analytical detections are South Dakota and Florida. PWSs in several States detected concentrations above the HRL of 0.4 μg/L. The States with the highest percentage (bet ween 0.65% and 2.76%) of 1,1,2,2-tetrachloroethane concentrations greater than the HRL are Utah, Alabama, a nd Florida. In Round 2, North Carolina is the only State to have more than 0.5 0% system detections greater than the HRL.

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# Exhibit 7.3.c. Geographic Distribution of 1,1,2,2-Te trachloroethane Detection Frequencies (upper map) and HRL Exceeda nce Frequencies (lower map) for All Round 1 and Round 2 Cr oss-Section States

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# 1,1,2,2-Tetrachloroethane occurr ence over time is presented in Exhibits 7.3.d and 7.3.e for the cross-section States. The data used in these two exhibits are from the eight States that had 1,1,2,2-tetrachloroethane occurrence data in both the Round 1 and Round 2 databases (Alaska, Kentucky, Maryland, Minnesota, North Ca rolina, New Mexico, Ohio and Washington). In both exhibits, occurrence is measured relative to the MRL in the left graph and relative to the HRL in the right graph. In Exhibit 7.3.d, the gr aphs suggest annual vari ability in occurrence between 1988 and 1997, with a spike in concentrations in 1994. Detections greater than the HRL were disproportionately observed in 1988 (R ound 1) and 1994 (Round 2). Many fewer PWSs collected 1,1,2,2-tetrachloroetha ne samples in Round 1 compared to Round 2; thus, any detections that occurred in th e Round 1 data caused the overall percentage of PWSs with 1,1,2,2- tetrachloroethane detections to a ppear elevated. It is unclear why there were more detections of 1,1,2,2-tetrachloroethane in 1994 comp ared to other years. Production for commercial uses in the United States ceased by the late 1980’s and re leases of the contaminant steadily declined from 1989 to 2003 (Chapter 11 of USEPA, 2008b). Exhibit 7.3.e presents the occurrence of 1,1,2,2-tetrachloroethane by State. No trend is evident between 1,1,2,2-tetrachloroethane occurrence in Round 1 and Round 2, based on these graphs.

Exhibit 7.3.d. Annual Frequenc y of 1,1,2,2-Tetrachloroethane Detections (left) and HRL Exceedances (right), 1985 - 1997, in Select Cro ss-Section States

Percent PWSs > MRL

0.00% 0.05% 0.10% 0.15% 0.20% 0.25%

1985 1986 1987 1988 1989 1990 1991 1992 1992 1993 1994 1995 1996 1997

Round 1 Round 2 Percent PWSs > HRL

0.00% 0.05% 0.10% 0.15% 0.20% 0.25%

1985 1986 1987 1988 1989 1990 1991 1992 1992 1993 1994 1995 1996 1997

Round 1 Round 2



### Summary statistics by year are from 8 States: AK, KY, MD, MN , NC, NM, OH and WA. These are the only Cross-Section States with PWS 1,1,2,2-tetrachloroethane data in both Round 1 and Round 2. There are data for 1992 in both the Round 1 and Round 2 databases. The HRL used for 1,1,2,2-tetrachloroethane is 0.4 μ g/L.



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# Exhibit 7.3.e. Distribution of 1,1,2,2-Tetrachloroethane Detections (left) and HRL Exceedances (right) Among Sel ect Cross-Section States

Percent PWSs > MRL

0.00% 0.10% 0.20% 0.30% 0.40% 0.50% 0.60%

AK KY MD MN NC NM OH WA

Round 1 Round 2 Percent PWSs > HRL

0.00% 0.10% 0.20% 0.30% 0.40% 0.50% 0.60%

AK KY MD MN NC NM OH WA

Round 1 Round 2



### These are the only Cross-Section States with PWS 1,1,2,2- tetrachloroethane data in both Round 1 and Round 2. The Health Reference Level (HRL) used for 1, 1,2,2-tetrachloroethane is 0.4 μ g/L.



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## 58

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## 59 

# 8. References

Frey, M.M., C. Seidel, M. Edwards, J. Parks, and L. McNeill. 2004. Occurrence Survey for Boron and Hexavalent Chromium. AwwaRF Report 91044F.

Longtin, J. P. 1988. Occurrence of Radon, Radium, and Uranium in Groundwater. Journal of the American Water Works Association . 80(7):84-93.

National Center for Food and Agricultural Po licy (NCFAP). 2004. National Pesticide Use Database. Available on the Internet at: http://www.ncfap.org/database/default.htm

. Seidel, C. 2006. Email Communication to Brent Ranalli at The Cadmus Group, Inc. [concerning boron data from an AwwaRF-spons ored study, with data in an attached spreadsheet]. Denver, CO: McGuire Malcolm Pirnie; May 19, 2006.

U.S. Department of Commerce (USDOC), Bu reau of the Census. 1994. 1992 Census of Agriculture. Washington, D.C.: U.S. Government Printing Office.

USDOC, Bureau of the Census. 1996. 1992 Census of Manufactures. Washington, D.C.: U.S. Government Printing Office.

USDOC, Bureau of the Census. 1997. 1995 A nnual Survey of Manufactures. Washington, D.C.: U.S. Government Printing Office.

U.S. Environmental Protection Agency (USEPA). 1999. A Review of Contaminant Occurrence in Public Water Systems . EPA 816-R-99-006. Office of Water. 78 pp.

USEPA. 2000. Water Industry Baseline Handbook, Second Edition (Draft).

USEPA. 2002. Analysis of National Occurrence of the 1998 Contaminant Candidate List (CCL) Regulatory Determination Priority C ontaminants in Public Water Systems . EPA 815-D01-002. Office of Water. 77 pp.

USEPA. 2003. Analysis of National Occurrence of 14 Contaminants from the 1998 Contaminant Candidate List (CCL) . Office of Water. 58 pp.

USEPA. 2008a. The Analysis of Occurrence Data from the First Unregulated Contaminant Monitoring Regulation (UCMR 1) in Support of Regulatory Determinations for the Second Drinking Water C ontaminant Candidate List . EPA 815-R-08-013. June 2008.

USEPA. 2008b. Regulatory Determinations Support Docu ment for Selected Contaminants from the Second Drinking Water Contaminant Candidate List (CCL 2). EPA 815-R-08-012. June 2008.

# APPENDICES

# APPENDICES

APPENDIX A. Development of He alth Reference Levels (HRLs)

APPENDIX B. Detailed Ro und 1 Data Summary for 1,3-Dichloropropene, a nd 1,1,2,2-Tetrachloroethane

APPENDIX C. Detailed Round 2 Data Summary for Metolachlor, 1,3-Dichloropropene, a nd 1,1,2,2-Tetrachloroethane

APPENDIX D. Detailed NIRS Data Summary for Boron

APPENDIX E. Data Summaries of Oc currence and Population Served for Four Contaminants Considered During CCL 2 Regulatory Determinations

# Notes to Accompany Appendix Tables

The following tables present a summary of the analytical results and occurrence for the listed contaminants. The various measures and descriptive statistics shown on the tables include:

Total # Samples = the total number of analytical records for the contaminant in the state (or in the portion of the data indicated).

Total Unique PWS = the total number of public water systems with records for the contaminant in the state (or in the portion of the data indicated).

Total Pop Served = the total summation of population served-by values for all public water systems with records for the contaminant in the state (or in the portion of the data indicated).

Minimum Value = the minimum analytical value of all analytical results for the contaminant in the state data set (or in the portion of the data indicated).

99th Value = the concentration value of the 99th percentile of all analytical results for the contaminant in the state data set (or in the portion of the data indicated).

Maximum Value = the maximum analytical value of all analytical results for the contaminant in the state data set (or in the portion of the data indicated).

Minimum Detects = the minimum analytical value of all the detections (analytical results greater than the Minimum Reporting Level) for the contaminant in the state dataset (or in the portion of the data indicated).

Median Detects = the median analytical value of all the detections (analytical results greater than the Minimum Reporting Level) for the contaminant in the state dataset (or in the portion of the data indicated).

% PWS (or POP) > MRL = percent of the total number of (or population served-by) public water systems with at least one analytical result equal to or greater than the Minimum Reporting Level.

% PWS (or POP) > 1⁄2 HRL = percent of the total number of (or population served-by) public water systems with at least one analytical result that exceeded half the Health Reference Level.

% PWS (or POP) > HRL = percent of the total number of (or population served-by) public water systems with at least one analytical result that exceeded the Health Reference Level.

# Total = the total number of samples, unique PWSs, and percent PWSs exceeding the MRL, 1⁄2 HRL, or HRL are the summation of all values for all the states for the contaminant; i.e. Total = all data from 40 states/territories; 24 States = all data from cross-section of 24 states. The values indicated as “totals” for the analytical results , e.g. minimum value, 99th percentile value, etc., are similarly the value derived from the data from all states, or 24 states respectively.

Concentration values for Round 1 and Round 2 data are measured in micrograms per liter (μg/L).

Concentration values for NIRS data are measured in milligrams per liter (mg/L).

# Appendix A. Development of He alth Reference Levels (HRLs)

## Appendix A. Development of Health Reference Levels



# Appendix A. Development of Health Reference Levels

Section 1412(b)(1)(A)(i) of SDWA requires EPA to determine whether each candidate contaminant may have an adverse effect on public health. This append ix describes the overall process the Agency used to evaluate health eff ects information, the approach used to estimate a contaminant health reference level or HRL (a benchmark against which to conduct the initial evaluation of the occurrence data), and the approa ch used to identify and evaluate information on hazard and dose-response for the contaminants under consideration.

There are two different approaches to the deri vation of an HRL. One approach is used for chemicals that cause cancer and exhibit a linear response to dose and the other applies to noncarcinogens and carcinoge ns evaluated using a non-linear approach.

Use of Carcinogenicity Data for the De rivation of a Health Reference Level

Two of the contaminants discussed in this re port had data available to classify them as likely or probable human carcinogens. These two contaminants (1,3-dichloropropene and 1,1,2,2-tetrachloroethane) are also the only contaminants for which low dose linear extrapolations were performed. For these cont aminants, EPA evaluated data on the mode of action of the chemical to determine the method of low dose extrapolation. When this analysis indicates that a linear low dose extrapolation is appropriate or when data on the mode of action are lacking, EPA uses a low dose linear extrapolat ion to calculate risk-specific doses. The riskspecific doses are the estimated or al exposures associated with lif etime excess risk levels that range from one cancer in ten thousand (10 -4 

# ) to one cancer in a million (10 -6 

# ). The risk-specific doses (expressed as mg/kg of body weight per da y) are combined with adult body weight and drinking water consumption data to estimate drin king water concentrations corresponding to this risk range. EPA generally used the one-in-a-million (10 -6 

# ) cancer risk in the initial screening of the occurrence data for carcinogens evalua ted using linear low dose extrapolation.

Use of Non-carcinogenic Health Effects Data for Derivation of a Health Reference Level

The remaining contaminant (metolachlor) has not been identified as known, likely or probable carcinogens. For this cont aminant, EPA calculated a refere nce dose (RfD). An RfD is an estimate of a daily oral exposure to the human population (including sensitive subgroups) that is likely to be without an apprec iable risk of deleterious effect s during a lifetime. It can be derived from either a “no-obser ved-adverse-effect le vel” (NOAEL), a “low est-observed-adverseeffect level” (LOAEL), or a benchmark dose, with uncertainty factors applied to reflect limitations of the data used.

EPA used uncertainty factors (UFs) to addr ess uncertainty resulting from incompleteness of the toxicological database. The individual UFs (usually applied as integers of 1, 3, or 10) were multiplied together and used to derive the Rf D from experimental data. Individual UFs are intended to account for:

(1) the variation in sensitivity among th e members of the human population (i.e., intraspecies variability);

A-1

## Appendix A. Development of Health Reference Levels

A-2 

# (2) the uncertainty in extrapolating animal data to humans (i.e., interspecies variability); (3) the uncertainty in extrapolating from data obtained in a study with less-than-lifetime exposure to lifetime exposure (i.e., extrapolating from subchronic to chronic exposure); (4) the uncertainty in extrapolating from a LOAEL rather than from a NOAEL; and/or (5) the uncertainty associated with an incomplete database.

EPA derived the HRLs using the RfD approach as follows:

HRL = [(RfD x BW)/DWI] x RSC

Where: RfD = Reference Dose BW = Body Weight for an adult, a ssumed to be 70 kilograms (kg) DWI = Drinking Water Intake, assumed to be 2 L/day (90 th 

# percentile) RSC = Relative Source Contribution, or the level of exposure believed to result from drinking water when compared to other sources (e.g., food, ambient air). A 20 percent RSC is being used to estimate the HRL and screen the occurren ce data because it is the lowest and most conservative RSC used in the derivation of a maximum contaminant level goal (MCLG) for drinking water.

For metolachlor, EPA used the RfD in conj unction with a 20 per cent RSC to derive a conservative HRL estimate and perform an initial screening of the drinki ng water occurrence data. Since the initial sc reening of the occurrence data at th is conservative HRL value resulted in negligible occurrence findings fo r metolachlor, EPA recognized that it was not necessary to further evaluate the RSC in making the regulatory determination.

# Appendix B. Detailed Round 1 Data Summary for 1,3-Dichloropropene and 1,1,2,2-Tetrachloroethane

Table B 1.a Round 1 Data - 1,3-Dichloroprope ne Occurrence in Public Water Systems - Based on Number of Samples Table B.1.b Round 1 Data - 1,3-Dichloropropene Occurrence in Public Water Systems - Based on Number of Systems Table B.1.c Round 1 Data - 1,3-Dichloroprope ne Occurrence in Public Water Systems - Based on Population Served

Table B.2.a Round 1 Data - 1,1,2,2-Tetrachl oroethane Occurrence in Public Water Systems - Based on Number of Samples Table B.2.b Round 1 Data - 1,1,2,2-Tetrachloroethane Occurrence in Public Water Systems - Based on Number of Systems Table B.2.c Round 1 Data - 1,1,2,2-Tetrachl oroethane Occurrence in Public Water Systems - Based on Population Served

### Appendix B. Detailed Round 1 Data Summary

Table B.1.a. Round 1 Data - 1,3-Dichloropropene Occurrence in Public Water Systems - Based on Number of Samples

STATE TOTAL UNIQUE PWSs TOTAL # SAMPLES # GW SAMPLES # SW SAMPLES % TOTAL SAMPLES

> MRL % GW SAMPLES

> MRL % SW SAMPLES

> MRL MIN VALUE (μg/L) 99% VALUE (μg/L) MAX VALUE (μg/L) MIN DETECTS

(μg/L) MEDIAN DETECTS

(μg/L)

AK 656 1,568 1,283 285 0.00% 0.00% 0.00% < 0.00 < 0.00 < 0.00
AL 131 351 244 107 0.28% 0.41% 0.00% < 0.50 < 0.50 1.60 1.60 1.60
AR
AZ CA 259 1,994 1,862 132 0.00% 0.00% 0.00% < 0.00 < 0.50 < 2.00 CO 5 15 14 1 0.00% 0.00% 0.00% < 0.08 < 5.00 < 5.00 DC
DE 9 280 145 135 0.00% 0.00% 0.00% < 0.50 < 0.80 < 0.80
FL
GA
HI
IA 745 1,055 952 103 0.00% 0.00% 0.00% < 0.20 < 1.00 < 1.00
IL 258 938 624 314 0.21% 0.00% 0.64% < 0.02 < 2.00 2.00 1.20 1.60
IN 146 819 618 201 0.00% 0.00% 0.00% < 0.02 < 1.00 < 1.00
KY
LA 1 1 1 0 0.00% 0.00% 0.00% < 0.50 < 0.50 < 0.50
MA 2 8 5 3 75.00% 60.00% 100.00% < 0.00 17.00 17.00 0.50 1.85
MD 978 1,582 1,275 307 0.00% 0.00% 0.00% < 0.50 < 0.50 < 0.50
MI
MN
MO 85 324 298 26 0.31% 0.34% 0.00% < 0.20 < 2.00 0.20 0.20 0.20 MS
MT 20 35 16 19 0.00% 0.00% 0.00% < 0.50 < 2.00 < 2.00 NC 297 644 569 75 0.00% 0.00% 0.00% < 0.50 < 0.50 < 0.50
NE
NH
NJ 1,455 3,067 2,706 361 0.10% 0.07% 0.28% < 0.00 < 1.00 1.40 1.00 1.30
NM 590 1,595 1,475 120 0.00% 0.00% 0.00% < 0.00 < 1.00 < 5.00
NV 7 125 115 10 0.00% 0.00% 0.00% < 0.20 < 0.20 < 0.20
NY 29 104 28 76 0.00% 0.00% 0.00% < 0.20 < 0.50 < 1.00
OH 2,532 14,328 13,659 669 0.01% 0.01% 0.00% < 0.00 < 1.00 1.00 1.00 1.00 SD 335 444 363 81 0.00% 0.00% 0.00% < 0.50 < 0.50 < 0.50
TN 303 1,220 433 787 0.00% 0.00% 0.00% < 0.02 < 0.50 < 0.50
TX 2 2 2 0 100.00% 100.00% 0.00% 2.00 12.00 12.00 2.00 7.00
UT 400 1,259 1,154 105 0.95% 0.78% 2.86% < 0.00 < 10.00 1.90 0.50 0.50
VI 3 10 0 10 0.00% 0.00% 0.00% < 1.00 < 1.00 < 1.00
VT
WA
WV 58 204 61 143 0.00% 0.00% 0.00% < 0.20 < 4.00 < 4.00
WY 1 1 1 0 0.00% 0.00% 0.00% < 0.00 < 0.00 < 0.00

TOTAL 9,307 31,973 27,903 4,070 0.09% 0.07% 0.22% < 0.00 < 1.00 17.00 0.20 1.00

24 STATES 9,164 31,104 27,295 3,809 0.06% 0.05% 0.16% < 0.00 < 1.00 2.00 0.50 1.00

PWS = Public Water System; GW = Ground Water; SW = Surface Water; MRL= Minimum Reporting Limit; Min, 99%, and Max Value = the m inimum, the 99th percentile value, and the maximum value of all samples; Min and Median Detects = the minimum and median of all sample detects. - The highlighted States are part of the 24-State Round 1 Cross-Section. - Less-than (<) values indicate MRL values. Some systems did not report MRL values. In the data, these MRL values are represented by zeros (e.g "< 0.00").



### B-1

### Appendix B. Detailed Round 1 Data Summary

Table B.1.b. Round 1 Data - 1,3-Dichloropropene Occurrence in Public Water Systems - Based on Number of Systems

STATE TOTAL # SAMPLES TOTAL UNIQUE

PWS # GW PWS # SW PWS % PWS > MRL % GW PWS > MRL % SW PWS > MRL % PWS > 1⁄2 HRL % GW PWS > 1⁄2 HRL % SW PWS > 1⁄2 HRL % PWS > HRL % GW PWS > HRL % SW PWS > HRL

AK 1,568 656 527 134 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00%
AL 351 131 93 42 0.76% 1.08% 0.00% 0.76% 1.08% 0.00% 0.76% 1.08% 0.00%
AR
AZ CA 1,994 259 227 46 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% CO 15 5 4 1 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% DC
DE 280 9 7 2 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00%
FL
GA
HI
IA 1,055 745 716 29 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00%
IL 938 258 185 73 0.78% 0.00% 2.74% 0.78% 0.00% 2.74% 0.78% 0.00% 2.74%
IN 819 146 121 25 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00%
KY
LA 1 1 1 0 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00%
MA 8 2 2 1 50.00% 50.00% 100.00% 50.00% 50.00% 100.00% 50.00% 50.00% 100.00%
MD 1,582 978 935 43 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00%
MI
MN
MO 324 85 71 14 1.18% 1.41% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% MS
MT 35 20 11 9 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% NC 644 297 254 44 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00%
NE
NH
NJ 3,067 1,455 1,430 25 0.21% 0.14% 4.00% 0.21% 0.14% 4.00% 0.21% 0.14% 4.00%
NM 1,595 590 555 35 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00%
NV 125 7 6 2 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00%
NY 104 29 5 26 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00%
OH 14,328 2,532 2,384 150 0.08% 0.08% 0.00% 0.08% 0.08% 0.00% 0.08% 0.08% 0.00% SD 444 335 306 29 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00%
TN 1,220 303 156 147 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00%
TX 2 2 2 0 100.00% 100.00% 0.00% 100.00% 100.00% 0.00% 100.00% 100.00% 0.00%
UT 1,259 400 382 29 1.75% 1.31% 6.90% 1.75% 1.31% 6.90% 1.75% 1.31% 6.90%
VI 10 3 0 3 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00%
VT
WA
WV 204 58 20 38 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00%
WY 1 1 1 0 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00%

TOTAL 31,973 9,307 8,401 947 0.20% 0.17% 0.63% 0.19% 0.15% 0.63% 0.19% 0.15% 0.63%

24 STATES 31,104 9,164 8,303 898 0.16% 0.12% 0.56% 0.16% 0.12% 0.56% 0.16% 0.12% 0.56%

PWS = Public Water System; GW = Ground Water; SW = Surface Water; "% PWS > MRL", "> 1⁄2 HRL", and "> HRL" are the proportion of systems with at least one analytic result equal to or greater than the MRL, exceeding the 1⁄2 HRL benchmark, and exceeding the HRL benchmark, respectively. - The highlighted States are part of the 24-State Round 1 Cross-Section. - The HRL used for 1,3-Dichloropropene is 0.4 μg/L.



### B-2

### Appendix B. Detailed Round 1 Data Summary

Table B.1.c. Round 1 Data - 1,3-Dichloropropene Occurrence in Public Water Systems - Based on Population Served

STATE TOTAL POP SERVED GW POP SERVED SW POP SERVED % POP

> MRL % GW POP > MRL % SW POP > MRL % POP > 1⁄2 HRL % GW POP > 1⁄2 HRL % SW POP > 1⁄2 HRL % POP > HRL % GW POP > HRL % SW POP > HRL

AK 1,086 1,086 0 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00%
AL 2,417,639 1,195,423 1,514,944 0.22% 0.44% 0.00% 0.22% 0.44% 0.00% 0.22% 0.44% 0.00%
AR
AZ CA 9,972,097 9,331,228 2,422,363 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% CO 386,658 349,700 36,958 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% DC
DE 479,534 246,534 233,000 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00%
FL
GA
HI
IA 1,086,985 804,288 282,697 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00%
IL 6,257,995 1,529,195 4,728,800 0.24% 0.00% 0.32% 0.24% 0.00% 0.32% 0.24% 0.00% 0.32%
IN 2,251,503 567,606 1,683,897 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00%
KY
LA 400 400 0 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00%
MA 66,550 66,550 52,050 78.21% 78.21% 100.00% 78.21% 78.21% 100.00% 78.21% 78.21% 100.00%
MD 4,811,057 761,204 4,049,853 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00%
MI
MN
MO 890,030 717,341 172,689 0.36% 0.45% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% MS
MT 190,933 9,861 181,072 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% NC 1,109,397 452,814 656,833 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00%
NE
NH
NJ 5,309,506 1,738,792 3,570,714 4.25% 0.04% 6.30% 4.25% 0.04% 6.30% 4.25% 0.04% 6.30%
NM 1,361,172 1,162,879 198,293 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00%
NV 63,910 56,410 34,560 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00%
NY
OH 8,083,502 3,300,218 4,810,984 0.01% 0.02% 0.00% 0.01% 0.02% 0.00% 0.01% 0.02% 0.00% SD 510,708 230,535 280,173 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00%
TN 3,915,111 1,240,820 2,674,291 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00%
TX 8,973 8,973 0 100.00% 100.00% 0.00% 100.00% 100.00% 0.00% 100.00% 100.00% 0.00% UT 3,098,407 2,276,635 1,735,395 6.12% 6.13% 2.88% 6.12% 6.13% 2.88% 6.12% 6.13% 2.88%
VI 66,000 0 66,000 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00%
VT
WA
WV 539,758 58,234 481,524 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00%
WY 150 150 0 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00%

TOTAL 52,879,061 26,106,876 29,867,090 0.95% 0.81% 1.15% 0.94% 0.79% 1.15% 0.94% 0.79% 1.15%

24 STATES 50,917,006 24,660,968 29,271,833 0.86% 0.59% 0.99% 0.86% 0.59% 0.99% 0.86% 0.59% 0.99%

PWS = Public Water System; GW = Ground Water; SW = Surface Water; "% POP > MRL", "> 1⁄2 HRL", and "> HRL" are the proportion of the total population served by systems with at least one analytic result equal to or greater than the MRL, exceeding the 1⁄2 HRL benchmark, and exceeding the HRL benchmark, respectively. - The highlighted States are part of the 24-State Round 1 Cross-Section. - The HRL used for 1,3-Dichloropropene is 0.4 μg/L.



### B-3

### Appendix B. Detailed Round 1 Data Summary

Table B.2.a. Round 1 Data - 1,1,2,2-Tetrachloroethane Occurrence in Public Water Systems - Based on Number of Samples

STATE TOTAL UNIQUE

PWS TOTAL # SAMPLES # GW SAMPLES # SW SAMPLES % TOTAL SAMPLES

> MRL % GW SAMPLES

> MRL % SW SAMPLES

> MRL MIN DETECTS

(μg/L) MEDIAN DETECTS

(μg/L) MIN VALUE (μg/L) 99% VALUE (μg/L) MAX VALUE (μg/L)

AK 661 1,610 1,323 287 0.12% 0.08% 0.35% < 0.00 < 0.00 200.00 49.00 124.50
AL 131 351 244 107 0.85% 0.82% 0.93% < 0.50 < 0.50 0.90 0.50 0.80
AR
AZ 944 2,932 2,272 660 0.00% 0.00% 0.00% < 0.05 < 2.00 < 10.00 CA 3,522 11,667 11,564 103 0.12% 0.12% 0.00% < 0.00 < 0.50 5.80 0.50 1.55 CO 9 33 30 3 0.00% 0.00% 0.00% < 0.04 < 5.00 < 5.00 DC 1 62 0 62 0.00% 0.00% 0.00% < 0.50 < 0.50 < 0.50
DE 13 333 189 144 0.60% 1.06% 0.00% < 0.20 < 0.50 9.00 0.40 4.70
FL 217 315 70 245 3.17% 4.29% 2.86% < 0.00 1.00 1.00 0.05 0.80 1,161 2,460 1,861 599 0.00% 0.00% 0.00% < 0.50 < 0.50 < 0.50 GA
HI 127 1,221 1,081 140 0.00% 0.00% 0.00% < 0.00 < 0.30 < 0.30
IA 1,002 1,908 1,697 211 0.00% 0.00% 0.00% < 0.40 < 1.00 < 1.00
IL 1,302 6,002 5,035 967 0.10% 0.06% 0.31% < 0.02 < 1.00 2.50 0.11 0.50
IN 311 1,724 1,338 386 0.17% 0.22% 0.00% < 0.10 < 2.00 2.74 0.49 0.88
KY 524 2,076 1,119 957 0.00% 0.00% 0.00% < 0.50 < 1.00 < 1.00
LA 13 22 18 4 0.00% 0.00% 0.00% < 0.50 < 0.50 < 0.50
MA 2211 100.00% 100.00% 100.00% 0.63 2.20 2.20 0.63 1.42
MD 986 1,909 1,441 468 0.05% 0.00% 0.21% < 0.10 < 0.50 0.20 0.20 0.20
MI 1110 100.00% 100.00% 0.00% 13.00 13.00 13.00 13.00 13.00
MN 1,565 2,756 2,677 79 0.11% 0.11% 0.00% < 0.20 < 1.00 0.20 0.20 0.20 MO 85 323 297 26 0.00% 0.00% 0.00% < 0.20 < 2.00 < 2.00 MS
MT 565 1,624 1,376 248 0.00% 0.00% 0.00% < 0.50 < 1.00 < 1.00 NC 297 644 569 75 0.16% 0.18% 0.00% < 0.07 < 0.50 0.07 0.07 0.07
NE 1110 100.00% 100.00% 0.00% 1.20 1.20 1.20 1.20 1.20
NH
NJ 1,511 3,130 2,775 355 0.35% 0.40% 0.00% < 0.00 < 1.00 112.00 0.52 2.80
NM 590 1,595 1,475 120 0.00% 0.00% 0.00% < 0.00 < 1.00 < 5.00
NV 8 148 136 12 0.68% 0.74% 0.00% < 0.00 < 0.20 1.00 1.00 1.00
NY 355 2,160 1,618 542 0.09% 0.06% 0.18% < 0.04 < 1.00 3.00 2.00 2.50 OH 2,656 16,084 15,166 918 0.01% 0.01% 0.00% < 0.00 < 1.00 2.00 2.00 2.00 SD 335 444 363 81 8.78% 9.37% 6.17% < 0.15 0.15 0.22 0.15 0.15
TN 303 1,220 433 787 0.00% 0.00% 0.00% < 0.01 < 0.50 < 0.50
TX
UT 423 1,328 1,215 113 0.83% 0.82% 0.88% < 0.00 5.00 1.00 0.30 0.50
VI 3 10 0 10 0.00% 0.00% 0.00% < 1.00 < 1.00 < 1.00
VT 1110 100.00% 100.00% 0.00% 1.10 1.10 1.10 1.10 1.10
WA 992 3,987 3,656 331 0.00% 0.00% 0.00% < 0.50 < 0.50 < 0.50
WV 137 388 164 224 0.00% 0.00% 0.00% < 0.03 < 4.00 < 4.00
WY 145 313 259 54 0.00% 0.00% 0.00% < 0.20 < 0.40 < 1.00

TOTAL 20,899 70,784 61,465 9,319 0.16% 0.15% 0.23% < 0.00 < 1.00 200.00 0.05 0.50

24 States 20,407 67,688 59,173 8,515 0.16% 0.15% 0.22% < 0.00 < 1.00 200.00 0.05 0.50

PWS = Public Water System; GW = Ground Water; SW = Surface Water; MRL= Minimum Reporting Limit; Min, 99%, and Max Value = the m inimum, the 99th percentile value, and the maximum value of all samples; Min and Median Detects = the minimum and median of all sample detects. - The highlighted States are part of the 24-State Round 1 Cross-Section. - Less-than (<) values indicate MRL values. Some systems did not report MRL values. In the data, these MRL values are represented by zeros (e.g "< 0.00").



### B-4

### Appendix B. Detailed Round 1 Data Summary

Table B.2.b. Round 1 Data - 1,1,2,2-Tetrachloroethane Occurrence in Public Water Systems - Based on Number of Systems

STATE TOTAL SAMPLE # S TOTAL UNIQUE

PWS # GW PWS # SW PWS % PWS > MRL % P > M

GW WS

RL % SW PWS > MR L % PWS > 1⁄2 HR L % GW PWS > 1⁄2 HR L % SW PWS > 1⁄2 HR L % PWS > HRL % GW PWS > HRL % SW PWS > HRL

AK 1,61 0 661 532 134 0.30% 0.19% 0.7 5% 0.30% 0.19 % 0.75% 0.30% 0.19% 0.75%
AL 35 1 131 93 42 2.29% 2.15% 2.3 8% 2.29% 2.15 % 2.38% 2.29% 2.15% 2.38%
AR
AZ 2,93 2 944 874 106 0.00% 0.00% 0.0 0% 0.00% 0.00 % 0.00 % 0.00% 0.00% 0.00% CA 11,66 7 3,522 3,495 37 0.31% 0.31% 0.0 0% 0.31% 0.31 % 0.00% 0.31% 0.31% 0.00% CO 33 9 7 3 0.00% 0.00% 0.0 0% 0.00% 0.00 % 0.00 % 0.00% 0.00% 0.00% DC 62 1 1 0.00% 0.00% 0.0 0% 0.00% 0.00 % 0.00 % 0.00% 0.00% 0.00%
DE 33 3 13 11 2 15.38% 18 .18% 0.0 0% 15.38% 18.18 % 0.00% 7.69% 9.09% 0.00%
FL 31 5 217 42 196 4.15% 4.76% 3.5 7% 2.76% 4.76% 2.04% 2.76% 4.76% 2.04%
GA 2,46 0 1,161 1,052 109 0.00% 0.00% 0.0 0% 0.00% 0.00 % 0.00 % 0.00% 0.00% 0.00%
HI 1,22 1 127 112 16 0.00% 0.00% 0.0 0% 0.00% 0.00 % 0.00 % 0.00% 0.00% 0.00%
IA 1,90 8 1,002 963 39 0.00% 0.00% 0.0 0% 0.00% 0.00 % 0.00 % 0.00% 0.00% 0.00%
IL 6,00 2 1,302 1,187 115 0.46% 0.25% 2.6 1% 0.38% 0.17 % 2.61% 0.31% 0.17% 1.74%
IN 1,72 4 311 280 32 0.64% 0.71% 0.0 0% 0.64% 0.71 % 0.00% 0.64% 0.71% 0.00%
KY 2,07 6 524 291 233 0.00% 0.00% 0.0 0% 0.00% 0.00 % 0.00 % 0.00% 0.00% 0.00%
LA 22 13 9 4 0.00% 0.00% 0.0 0% 0.00% 0.00 % 0.00 % 0.00% 0.00% 0.00%
MA 2 2 1 1 100.00% 100 .00% 100.0 0% 100.00% 100.00% 100.00% 100.00% 100.00% 100.00%
MD 1,90 9 986 940 51 0.10% 0.00% 1.9 6% 0.00% 0.00 % 0.00% 0.00% 0.00% 0.00%
MI 1 1 1 0 100.00% 100 .00% 0.0 0% 100.00% 100.00% 0.00% 100.00% 100.00% 0.00%
MN 2,75 6 1,565 1,540 29 0.19% 0.19% 0.0 0% 0.00% 0.00 % 0.00% 0.00% 0.00% 0.00%
MO 32 3 85 71 14 0.00% 0.00% 0.0 0% 0.00% 0.00 % 0.00 % 0.00% 0.00% 0.00% MS
MT 1,62 4 565 523 57 0.00% 0.00% 0.0 0% 0.00% 0.00 % 0.00 % 0.00% 0.00% 0.00% NC 64 4 297 254 44 0.34% 0.39% 0.0 0% 0.00% 0.00 % 0.00% 0.00% 0.00% 0.00%
NE 1 1 1 0 100.00% 100 .00% 0.0 0% 100.00% 100.00% 0.00% 100.00% 100.00% 0.00%
NH
NJ 3,13 0 1,511 1,486 25 0.40% 0.40% 0.0 0% 0.40% 0.40 % 0.00% 0.40% 0.40% 0.00%
NM 1,59 5 590 555 35 0.00% 0.00% 0.0 0% 0.00% 0.00 % 0.00 % 0.00% 0.00% 0.00%
NV 14 8 8 7 2 12.50% 14 .29% 0.0 0% 12.50% 14.29 % 0.00% 12.50% 14.29% 0.00%
NY 2,16 0 355 252 122 0.56% 0.40% 0.8 2% 0.56% 0.40 % 0.82% 0.56% 0.40% 0.82%
OH 16,08 4 2,656 2,493 167 0.04% 0.04% 0.0 0% 0.04% 0.04 % 0.00% 0.04% 0.04% 0.00% SD 44 4 335 306 29 11.64% 11 .11% 17.2 4% 0.30% 0.00% 3.45% 0.00% 0.00% 0.00%
TN 1,22 0 303 156 147 0.00% 0.00% 0.0 0% 0.00% 0.00 % 0.00 % 0.00% 0.00% 0.00%
TX
UT 1,32 8 423 403 34 1.65% 1.49% 2.9 4% 1.65% 1.49% 2.94% 1.42% 1.24% 2.94%
VI 10 3 0 3 0.00% 0.00% 0.0 0% 0.00% 0.00 % 0.00 % 0.00% 0.00% 0.00%
VT 1 1 1 0 100.00% 100 .00% 0.0 0% 100.00% 100.00% 0.00% 100.00% 100.00% 0.00%
WA 3,98 7 992 937 77 0.00% 0.00% 0.0 0% 0.00% 0.00 % 0.00 % 0.00% 0.00% 0.00%
WV 38 8 137 63 75 0.00% 0.00% 0.0 0% 0.00% 0.00 % 0.00 % 0.00% 0.00% 0.00%
WY 31 3 145 116 38 0.00% 0.00% 0.0 0% 0.00% 0.00 % 0.00 % 0.00% 0.00% 0.00%

TOTAL 70,78 4 20,899 19,054 2,019 0.48% 0.42% 1.0 4% 0.26% 0.22 % 0.64% 0.24% 0.20% 0.54%

24 States 67,68 8 20,407 18,693 1,867 0.45% 0.39% 1.0 2% 0.22% 0.18 % 0.59% 0.20% 0.17% 0.48%

- The highlighted States are part of the 24-State Round 1 Cross-Section. PWS = Public Water System; GW = Ground Water; SW = Surface Water; "% PWS > MRL", "> 1⁄2 HRL", and "> HRL" are the proportion of systems with at least one analytic result equal to or greater than the MRL, exceeding the 1⁄2 HRL benchmark, and exceeding the HRL benchmark, respectively.

- The HRL used for 1,1,2,2-Tetrachloroethane is 0.4 μg/L.



### B-5

### Appendix B. Detailed Round 1 Data Summary

TOTAL 98,334,686 57,663,608 45,776,159 2.16% 2.37% 1.65% 1.99% 2.10% 1.62% 1.90% 2.02% 1.53%

24 States 94,710,065 55,763,644 43,763,942 1.86% 1.82% 1.70% 1.69% 1.55% 1.67% 1.63% 1.53% 1.58% 

### Table B.2.c. Round 1 Data - 1,1,2,2-Tetrachloroethane Occurrence in Public Water Systems - Based on Population Served

STATE TOTAL PO SERVED P GW P SERV OP ED S S W POP

ERVED % POP > MRL % GW POP > MRL % SW POP > MRL % POP > 1⁄2 HRL % GW POP > 1⁄2 HRL % SW POP > 1⁄2 HRL % POP > HRL % GW POP > HRL % SW POP > HRL

AK 1,12 6 1,126 0 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00%
AL 2,417,63 9 1,19 5,423 1,514,944 25.48% 1.34% 39.61% 25.48% 1.34% 39.61% 25.48% 1.34% 39.61%
AR
AZ 4,001,76 2 1,32 3,094 2,909,062 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% CA 26,356,78 3 26,08 5,197 841,643 1.92% 1.94% 0.00% 1.92% 1.94% 0.00% 1.92% 1.94% 0.00% CO 1,681,65 8 64 4,700 1,290,958 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% DC
DE 499,73 2 26 6,732 233,000 40.94% 76.71% 0.00% 40.94% 76.71% 0.00% 34.38% 64.41% 0.00%
FL 4,315,46 6 1,74 5,246 3,704,774 0.64% 1.54% 0.01% 0.63% 1.54% 0.01% 0.63% 1.54% 0.01% GA 4,919,20 8 1,37 3,936 3,545,272 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00%
HI 1,260,60 3 1,21 5,122 81,837 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00%
IA 2,128,42 1 1,49 9,541 628,880 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00%
IL 7,228,37 8 2,44 2,436 4,785,942 3.11% 6.02% 1.63% 1.15% 0.21% 1.63% 0.78% 0.21% 1.07%
IN 2,287,53 4 82 0,099 1,484,247 4.95% 13.80% 0.00% 4.95% 13.80% 0.00% 4.95% 13.80% 0.00%
KY 3,134,69 2 24 1,389 2,893,303 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00%
LA 240,11 5 5 8,905 181,210 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00%
MA 15,72 5 6,425 9,300 100.00% 100.00% 100.00% 100.00% 100.00% 100.00% 100.00% 100.00% 100.00%
MD 4,849,91 1 86 4,423 4,068,878 0.23% 0.00% 0.27% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00%
MI 131,54 6 13 1,546 0 100.00% 100.00% 0.00% 100.00% 100.00% 0.00% 100.00% 100.00% 0.00%
MN 2,303,76 5 2,15 8,522 175,509 0.01% 0.01% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% MO 890,03 0 71 7,341 172,689 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% MS
MT 549,17 2 27 6,682 334,304 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% NC 1,109,39 7 45 2,814 656,833 0.07% 0.18% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00%
NE 98 5 985 0 100.00% 100.00% 0.00% 100.00% 100.00% 0.00% 100.00% 100.00% 0.00%
NH NJ
NM 5,246,07 1,361,17 2 1,67 2 1,16 5,358 2,879 3,570,714 198,293 0.85%
0.00% 2.65%
0.00% 0.00%
0.00% 0.85%
0.00% 2.65%
0.00% 0.00%
0.00% 0.85%
0.00% 2.65%
0.00% 0.00%
0.00%
NV 70,91 0 6 3,410 34,560 6.70% 7.49% 0.00% 6.70% 7.49% 0.00% 6.70% 7.49% 0.00%
NY 27,88 0 9,880 24,500 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% OH 8,745,89 2 3,55 4,348 5,262,754 0.001% 0.002% 0.00% 0.001% 0.002% 0.00% 0.00% 0.00% 0.00% SD 510,70 8 23 0,535 280,173 4.87% 4.28% 5.36% 2.73% 0.00% 4.98% 0.00% 0.00% 0.00%
TN 3,915,11 1 1,24 0,820 2,674,291 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00%
TX UT 3,116,052 2,289,457 1,746,978 6.19% 6.67% 2.30% 6.19% 6.67% 2.30% 5.77% 6.10% 2.30%
VI 66,00 0 0 66,000 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00%
VT 40 40 0 100.00% 100.00% 0.00% 100.00% 100.00% 0.00% 100.00% 100.00% 0.00%
WA 3,801,04 0 3,46 2,027 1,547,480 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00%
WV 777,62 9 18 7,714 594,025 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00%
WY 372,53 2 26 5,456 263,806 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00%

served by systems with at least one analytic result equal to or greater than the MRL, exceeding the 1⁄2 HRL benchmark, and exceeding the HRL benchmark, respectively. - The highlighted States are part of the 24-State Round 1 Cross-Section. - The HRL used for 1,1,2,2-Tetrachloroethane is 0.4 μg/L. PWS = Public Water System; GW = Ground Water; SW = Surface Water; "% POP > MRL", "> 1⁄2 HRL", and "> HRL" are the proportion of the total population



### B-6

# Appendix C. Detailed Round 2 Data Summary for Metolachlor, 1,3-Dichloropropen e and 1,1,2,2-Tetrachloroethane

Table C.1.a Round 2 Data - Metolachlor Occurrence in Public Water Systems - Based on Number of Samples Table C.1.b Round 2 Data - Metolachlor O ccurrence in Public Water Systems - Based on Number of Systems Table C.1.c Round 2 Data - Metolachlor Occurrence in Public Water Systems - Based on Population Served

Table C.2.a Round 2 Data - 1,3-Dichloroprope ne Occurrence in Public Water Systems - Based on Number of Samples Table C 2.b Round 2 Data - 1,3-Dichloropropene Occurrence in Public Water Systems - Based on Number of Systems Table C 2.c Round 2 Data - 1,3-Dichloroprope ne Occurrence in Public Water Systems - Based on Population Served

Table C.3.a Round 2 Data - 1,1,2,2-Tetrachl oroethane Occurrence in Public Water Systems - Based on Number of Samples Table C.3.b Round 2 Data - 1,1,2,2-Tetrachloroethane Occurrence in Public Water Systems - Based on Number of Systems Table C.3.c Round 2 Data - 1,1,2,2-Tetrachl oroethane Occurrence in Public Water Systems - Based on Population ServedAppendix C. Detailed Round 2 Data Summary

Table C.1.a. Round 2 Data - Metolachlor Occurrence in Public Water Systems - Based on Number of Samples

STATE TOTAL UNIQUE

PWS TOTAL # SAMPLES # GW SAMPLES # SW SAMPLES % TOTAL SAMPLES

> MRL % GW SAMPLES

> MRL % SW SAMPLES

> MRL MIN VALUE (μg/L) 99% VALUE (μg/L) MAX VALUE (μg/L) MIN DETECTS

(μg/L) MEDIAN DETECTS

(μg/L)
Tribes (06) 1 3 3 0 0.00% 0.00% 0.00% < 0.07 < 0.07 < 0.07 AK 17 23 19 4 0.00% 0.00% 0.00% < 0.00 < 0.00 < 0.00 AL AR 536 1,610 1,225 385 0.00% 0.00% 0.00% < 0.00 < 0.00 < 0.00 AZ CA CO 750 2,230 1,365 865 0.04% 0.00% 0.12% < 0.00 < 0.00 0.60 0.60 0.60 CT 70 317 116 201 0.63% 1.72% 0.00% < 0.00 < 0.00 4.40 0.59 2.50 IN KY 38 156 65 91 7.69% 0.00% 13.19% < 0.01 0.33 0.70 0.01 0.15 LA MA 54 182 72 110 8.79% 15.28% 4.55% < 0.20 0.33 0.33 0.33 0.33 MD 683 1,135 913 222 0.18% 0.11% 0.45% < 0.05 < 2.00 1.58 1.07 1.33 ME MI 2,650 4,162 3,780 382 0.17% 0.00% 1.83% < 0.00 < 0.00 6.00 1.00 2.00 MN 1,264 5,985 5,706 279 0.37% 0.33% 1.08% < 0.00 < 0.00 2.00 0.50 0.80 MO 538 1,798 780 1,018 2.34% 0.00% 4.13% < 0.50 0.91 13.80 0.50 0.84 MS NC 495 730 694 36 0.14% 0.14% 0.00% < 0.00 < 0.00 0.70 0.70 0.70 ND 296 384 317 67 0.00% 0.00% 0.00% < 0.00 < 0.07 < 0.07 NH 592 612 577 35 0.00% 0.00% 0.00% < 0.00 < 0.00 < 0.00 NJ NM 716 4,288 4,094 194 0.00% 0.00% 0.00% < 0.03 < 0.20 < 0.20 OH 2,202 5,386 4,901 485 0.48% 0.02% 5.15% < 0.01 < 5.00 10.10 0.20 1.20 OK 1 1 0 1 0.00% 0.00% 0.00% < 0.00 < 0.00 < 0.00 OR 1,135 2,528 1,972 556 0.04% 0.05% 0.00% < 0.00 < 0.00 1.00 1.00 1.00 PA 459 2,012 1,157 855 7.55% 6.57% 8.89% < 0.00 3.00 3.00 0.03 1.00 RI 15 188 82 106 3.72% 8.54% 0.00% < 0.00 0.61 0.75 0.17 0.33 SC 940 5,692 4,699 993 0.00% 0.00% 0.00% < 0.00 < 0.00 < 0.00 SD TN 10 50 16 34 0.00% 0.00% 0.00% < 0.00 < 0.00 < 0.00 TX 426 1,545 194 1,351 4.79% 2.58% 5.11% < 0.10 0.67 7.10 0.10 0.30 VT 391 612 483 129 0.16% 0.21% 0.00% < 0.00 < 0.00 0.10 0.10 0.10 WA 599 1,169 967 202 0.00% 0.00% 0.00% < 0.00 < 0.00 < 0.00 WI

TOTAL 14,878 42,798 34,197 8,601 0.86% 0.37% 2.80% < 0.00 < 5.00 13.80 0.01 1.00

20 STATES 13,007 34,112 27,723 6,389 0.62% 0.17% 2.58% < 0.00 < 5.00 13.80 0.01 0.57

19 STATES 1 12,953 33,930 27,651 6,279 0.57% 0.13% 2.55% < 0.00 < 5.00 13.80 0.01 0.61

PWS = Public Water System; GW = Ground Water; SW = Surface Water; MRL= Minimum Reporting Limit; Min, 99%, and Max Value = the m inimum, the 99th percentile value, and the maximum value of all samples; Min and Median Detects = the minimum and median of all sample detects. - Massachusetts data not included in "19 States" summary statistics for Metolachlor. See text for details. - The highlighted States are part of the 20-State Round 2 Cross-Section. - Less-than (<) values indicate MRL values. Some systems did not report MRL values. In the data, these MRL values are represented by zeros (e.g "< 0.00").

C-1

### Appendix C. Detailed Round 2 Data Summary

Table C.1.b. Round 2 Data - Metolachlor Occurrence in Public Water Systems - Based on Number of Systems

STATE TOTAL # SAMPLES TOTAL UNIQUE

PWS # GW PWS # SW PWS % PWS

> MRL % GW PWS

> MRL % SW PWS

> MRL % PWS > 1⁄2 HRL % GW PWS > 1⁄2 HRL % SW PWS > 1⁄2 HRL % PWS > HRL % GW PWS > HRL % SW PWS > HRL
Tribes (06) 3 1 1 0 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% AK 23 17 14 3 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% AL AR 1,610 536 431 105 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% AZ CA CO 2,230 750 538 212 0.13% 0.00% 0.47% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% CT 317 70 35 35 1.43% 2.86% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% IN KY 156 38 18 20 13.16% 0.00% 25.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% LA
MA 182 54 27 27 14.81% 14.81% 14.81% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00%
MD 1,135 683 626 57 0.29% 0.16% 1.75% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00%
ME
MI 4,162 2,650 2,570 80 0.19% 0.00% 6.25% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00%
MN 5,985 1,264 1,234 30 0.40% 0.32% 3.33% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% MO 1,798 538 437 101 4.28% 0.00% 22.77% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% MS NC 730 495 470 25 0.20% 0.21% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% ND 384 296 258 38 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% NH 612 592 559 33 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% NJ NM 4,288 716 687 29 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% OH 5,386 2,202 2,021 181 1.00% 0.05% 11.60% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% OK 1 1 0 1 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% OR 2,528 1,135 984 151 0.09% 0.10% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% PA 2,012 459 313 146 13.07% 8.95% 21.92% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% RI 188 15 6 9 20.00% 50.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% SC 5,692 940 842 98 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% SD TN 50 10 2 8 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% TX 1,545 426 121 305 9.39% 1.65% 12.46% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% VT 612 391 339 52 0.26% 0.29% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% WA 1,169 599 529 70 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% WI

TOTAL 42,798 14,878 13,062 1,816 1.20% 0.36% 7.21% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00%

20 STATES 34,112 13,007 11,530 1,477 0.89% 0.15% 6.70% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00%

19 STATES 1 33,930 12,953 11,503 1,450 0.83% 0.11% 6.55% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00%

PWS = Public Water System; GW = Ground Water; SW = Surface Water; "% PWS > MRL" is the proportion of systems with at least one analytic result equal to or greater than the MRL. - Massachusetts data not included in "19 States" summary statistics for Metolachlor. - The highlighted States are part of the 20-State Round 2 Cross-Section. - The HRL used for metolachlor is 70 μg/L.



### C-2

### Appendix C. Detailed Round 2 Data Summary

Table C.1.c. Round 2 Data - Metolachlor Occurrence in Public Water Systems - Based on Population Served

STATE TOTAL POP SERVED GW POP SERVED SW POP SERVED % POP

> MRL % GW POP > MRL % SW POP > MRL % POP > 1⁄2 HRL % GW POP > 1⁄2 HRL % SW POP > 1⁄2 HRL % POP > HRL % GW POP > HRL % SW POP > HRL
Tribes (06) 9,500 9,500 0 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% AK 26,647 25,947 700 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% AL AR 1,549,257 791,316 757,941 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% AZ CA CO 3,530,819 404,353 3,126,466 0.04% 0.00% 0.05% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% CT 1,802,411 160,372 1,642,039 0.73% 8.19% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% IN KY 184,262 5,795 178,467 30.10% 0.00% 31.08% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% LA
MA 885,780 107,685 778,095 13.47% 16.00% 13.12% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00%
MD 4,350,399 487,444 3,862,955 0.13% 0.12% 0.13% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00%
ME
MI 4,154,030 1,879,382 2,274,648 1.23% 0.00% 2.25% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00%
MN 3,399,893 2,139,231 1,260,662 0.38% 0.07% 0.91% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% MO 1,732,871 590,275 1,142,596 9.94% 0.00% 15.08% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% MS NC 651,824 485,104 166,720 2.74% 3.68% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% ND 478,189 227,270 250,919 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% NH 441,328 138,778 302,550 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% NJ NM 1,352,305 1,211,125 141,180 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% OH 8,917,037 3,102,837 5,814,200 5.50% 0.00% 8.43% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% OK 2,989 0 2,989 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% OR 2,287,248 698,065 1,589,183 0.00% 0.01% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% PA 6,104,554 345,376 5,759,178 48.02% 12.41% 50.15% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% RI 722,671 101,600 621,071 9.62% 68.41% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% SC 2,570,542 735,470 1,835,072 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% SD TN 260,764 3,014 257,750 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% TX 10,304,341 561,815 9,742,526 44.41% 1.76% 46.86% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% VT 369,364 108,156 261,208 0.07% 0.24% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% WA 3,012,463 1,429,290 1,583,173 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% WI

TOTAL 59,101,488 15,749,200 43,352,288 14.41% 1.10% 19.25% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00%

20 STATES 47,984,353 14,387,312 33,597,041 11.61% 0.81% 16.24% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00%

19 STATES 1 47,098,573 14,279,627 32,818,946 11.58% 0.70% 16.31% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00%

PWS = Public Water System; GW = Ground Water; SW = Surface Water; "% POP > MRL" is the proportion of the total population served by systems with at least one analytic result equal to or greater than the MRL. - Massachusetts data not included in "19 States" summary statistics for Metolachlor. - The highlighted States are part of the 20-State Round 2 Cross-Section. - The HRL used for metolachlor is 70 μg/L.



### C-3

### Appendix C. Detailed Round 2 Data Summary

Table C.2.a. Round 2 Data - 1,3-Dichloropropene Occurrence in Public Water Systems - Based on Number of Samples

STATE TOTAL UNIQUE

PWS TOTAL # SAMPLES # GW SAMPLES # SW SAMPLES % TOTAL SAMPLES

> MRL % GW SAMPLES

> MRL % SW SAMPLES

> MRL MIN VALUE (μg/L) 99% VALUE (μg/L) MAX VALUE (μg/L) MIN DETECTS

(μg/L) MEDIAN DETECTS

(μg/L)
Tribes (06) 21 30 29 1 0.00% 0.00% 0.00% < 0.50 < 1.00 < 1.00 AK 625 3,535 2,596 939 0.03% 0.04% 0.00% < 0.00 < 0.00 39.00 39.00 39.00 AL AR 407 1,352 1,078 274 0.00% 0.00% 0.00% < 0.00 < 0.08 < 0.08 AZ CA 16 81 61 20 0.00% 0.00% 0.00% < 0.20 < 0.50 < 0.50 CO 831 2,643 1,693 950 0.00% 0.00% 0.00% < 0.00 < 0.00 < 0.00 CT 86 2,265 934 1,331 0.04% 0.00% 0.08% < 0.00 < 0.00 0.35 0.35 0.35 IN 86 153 147 6 0.00% 0.00% 0.00% < 0.10 < 1.00 < 1.00 KY 181 354 128 226 0.00% 0.00% 0.00% < 0.10 < 1.00 < 1.00 LA 1,310 4,055 3,451 604 0.00% 0.00% 0.00% < 0.50 < 0.50 < 0.50 MA 419 1,822 1,371 451 0.05% 0.07% 0.00% < 0.00 < 0.50 0.99 0.99 0.99 MD 976 4,871 4,320 551 0.02% 0.02% 0.00% < 0.50 < 0.50 0.60 0.60 0.60 ME 744 3,540 3,138 402 0.00% 0.00% 0.00% < 0.00 < 0.00 < 0.00 MI 2,735 13,929 12,281 1,648 0.00% 0.00% 0.00% < 0.00 < 0.00 < 0.00 MN 1,480 6,381 6,205 176 1.00% 0.81% 7.95% < 0.00 0.20 22.00 0.20 0.40 MO 1,053 1,071 980 91 0.00% 0.00% 0.00% < 0.00 < 0.00 < 0.00 MS NC 1,505 2,854 2,455 399 0.32% 0.29% 0.50% < 0.00 < 0.00 0.50 0.50 0.50 ND 296 382 316 66 0.00% 0.00% 0.00% < 0.00 < 1.00 < 1.00 NH 687 944 898 46 0.00% 0.00% 0.00% < 0.00 < 0.00 < 0.00 NJ 12 15 12 3 0.00% 0.00% 0.00% < 0.14 < 1.61 < 1.61 NM 718 4,830 4,613 217 0.00% 0.00% 0.00% < 0.50 < 1.00 < 1.00 OH 2,232 17,788 16,432 1,356 0.02% 0.02% 0.00% < 0.50 < 0.50 1.60 0.62 1.15 OK OR 1,081 2,617 2,071 546 0.04% 0.00% 0.18% < 0.00 < 0.00 0.50 0.50 0.50 PA RI 102 291 241 50 0.00% 0.00% 0.00% < 0.00 < 1.00 < 1.00 SC SD 23 28 22 6 0.00% 0.00% 0.00% < 0.50 < 0.50 < 0.50 TN 77 533 191 342 0.00% 0.00% 0.00% < 0.00 < 0.00 < 0.00 TX VT 526 1,597 1,405 192 0.00% 0.00% 0.00% < 0.00 < 0.00 < 0.00 WA 715 1,427 1,279 148 0.00% 0.00% 0.00% < 0.00 < 0.00 < 0.00 WI

TOTAL 18,944 79,388 68,347 11,041 0.10% 0.09% 0.16% < 0.00 < 0.50 39.00 0.20 0.50

20 STATES 16,787 70,631 62,095 8,536 0.11% 0.10% 0.20% < 0.00 < 0.50 39.00 0.20 0.50

PWS = Public Water System; GW = Ground Water; SW = Surface Water; MRL= Minimum Reporting Limit; Min, 99%, and Max Value = the m inimum, the 99th percentile value, and the maximum value of all samples; Min and Median Detects = the minimum and median of all sample detects. - The highlighted States are part of the 20-State Round 2 Cross-Section. - Less-than (<) values indicate MRL values. Some systems did not report MRL values. In the data, these MRL values are represented by zeros (e.g "< 0.00").



### C-4

### Appendix C. Detailed Round 2 Data Summary

Table C.2.b. Round 2 Data - 1,3-Dichloropropene Occurrence in Public Water Systems - Based on Number of Systems

STATE TOTAL # SAMPLES TOTAL UNIQUE

PWS # GW PWS # SW PWS % PWS

> MRL % GW PWS > MRL % SW PWS > MRL % PWS > 1⁄2 HRL % GW PWS > 1⁄2 HRL % SW PWS > 1⁄2 HRL % PWS > HRL % GW PWS > HRL % SW PWS > HRL
Tribes (06) 30 21 20 1 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% AK 3,535 625 481 144 0.16% 0.21% 0.00% 0.16% 0.21% 0.00% 0.16% 0.21% 0.00% AL AR 1,352 407 319 88 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% AZ CA 81 16 12 4 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% CO 2,643 831 619 212 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% CT 2,265 86 44 42 1.16% 0.00% 2.38% 1.16% 0.00% 2.38% 0.00% 0.00% 0.00% IN 153 86 80 6 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% KY 354 181 84 97 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% LA 4,055 1,310 1,241 69 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% MA 1,822 419 345 74 0.24% 0.29% 0.00% 0.24% 0.29% 0.00% 0.24% 0.29% 0.00% MD 4,871 976 920 56 0.10% 0.11% 0.00% 0.10% 0.11% 0.00% 0.10% 0.11% 0.00% ME 3,540 744 676 68 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% MI 13,929 2,735 2,644 91 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% MN 6,381 1,480 1,450 30 2.91% 2.48% 23.33% 2.36% 2.00% 20.00% 1.55% 1.17% 20.00% MO 1,071 1,053 964 89 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% MS NC 2,854 1,505 1,329 176 0.53% 0.45% 1.14% 0.53% 0.45% 1.14% 0.53% 0.45% 1.14% ND 382 296 258 38 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% NH 944 687 656 31 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% NJ 15 12 10 2 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% NM 4,830 718 692 26 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% OH 17,788 2,232 2,050 182 0.13% 0.15% 0.00% 0.13% 0.15% 0.00% 0.13% 0.15% 0.00% OK OR 2,617 1,081 931 150 0.09% 0.00% 0.67% 0.09% 0.00% 0.67% 0.09% 0.00% 0.67% PA RI 291 102 92 10 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% SC SD 28 23 17 6 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% TN 533 77 30 47 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% TX VT 1,597 526 466 60 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% WA 1,427 715 668 47 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% WI

TOTAL 79,388 18,944 17,098 1,846 0.31% 0.28% 0.60% 0.27% 0.24% 0.54% 0.20% 0.17% 0.49%

20 STATES 70,631 16,787 15,178 1,609 0.35% 0.32% 0.62% 0.30% 0.27% 0.56% 0.23% 0.19% 0.56%

PWS = Public Water System; GW = Ground Water; SW = Surface Water; "% PWS > MRL", "> 1⁄2 HRL", and "> HRL" are the proportion of systems with at least one analytic result equal to or greater than the MRL, exceeding the 1⁄2 HRL benchmark, and exceeding the HRL benchmark, respectively. - The highlighted States are part of the 20-State Round 2 Cross-Section. - The HRL used for 1,3-Dichloropropene is 0.4 μg/L.



### C-5

### Appendix C. Detailed Round 2 Data Summary

Table C.2.c. Round 2 Data - 1,3-Dichloropropene Occurrence in Public Water Systems - Based on Population Served

STATE TOTAL POP SERVED GW POP SERVED SW POP SERVED % POP > MRL % GW POP > MRL % SW POP > MRL % POP > 1⁄2 HRL % GW POP > 1⁄2 HRL % SW POP > 1⁄2 HRL % POP > HRL % GW POP > HRL % SW POP > HRL

Tribes (06) 49,986 41,486 8,500 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% AK 480,068 204,976 275,092 0.83% 1.95% 0.00% 0.83% 1.95% 0.00% 0.83% 1.95% 0.00% AL AR 1,301,907 612,648 689,259 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% AZ CA 1,171,659 529,897 641,762 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% CO 3,576,561 440,514 3,136,047 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% CT 2,330,321 211,367 2,118,954 0.32% 0.00% 0.35% 0.32% 0.00% 0.35% 0.00% 0.00% 0.00% IN 392,657 349,013 43,644 KY 2,212,474 179,998 2,032,476 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% LA 4,535,907 2,598,561 1,937,346 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% MA 3,402,403 1,326,669 2,075,734 0.01% 0.03% 0.00% 0.01% 0.03% 0.00% 0.01% 0.03% 0.00% MD 5,012,575 671,808 4,340,767 0.004% 0.03% 0.00% 0.004% 0.03% 0.00% 0.004% 0.03% 0.00% ME 675,407 244,096 431,311 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% MI 3,237,068 1,920,249 1,316,819 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% MN 3,622,825 2,362,163 1,260,662 5.78% 7.43% 2.69% 4.13% 5.06% 2.37% 2.99% 3.31% 2.37% MO 1,554,953 1,131,780 423,173 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% MS NC 4,690,803 1,186,827 3,503,976 0.55% 0.59% 0.54% 0.55% 0.59% 0.54% 0.55% 0.59% 0.54% ND 478,189 227,270 250,919 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% NH 476,008 169,280 306,728 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% NJ 27,774 5,374 22,400 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% NM 1,351,088 1,212,253 138,835 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% OH 9,095,427 3,311,171 5,784,256 0.11% 0.30% 0.00% 0.11% 0.30% 0.00% 0.11% 0.30% 0.00% OK OR 1,820,043 690,965 1,129,078 0.16% 0.00% 0.26% 0.16% 0.00% 0.26% 0.16% 0.00% 0.26% PA RI 689,332 112,386 576,946 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% SC SD 44,854 21,240 23,614 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% TN 792,356 105,819 686,537 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% TX VT 417,057 160,828 256,229 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% WA 2,273,921 1,417,977 855,944 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% WI

TOTAL 55,713,623 21,446,615 34,267,008 0.47% 0.92% 0.18% 0.36% 0.66% 0.17% 0.27% 0.47% 0.15%

20 STATES 45,951,052 17,423,030 28,528,022 0.55% 1.13% 0.19% 0.42% 0.81% 0.18% 0.33% 0.57% 0.18%

PWS = Public Water System; GW = Ground Water; SW = Surface Water; "% POP > MRL", "> 1⁄2 HRL", and "> HRL" are the proportion of the total population served by systems with at least one analytic result equal to or greater than the MRL, exceeding the 1⁄2 HRL benchmark, and exceeding the HRL benchmark, respectively. - The highlighted States are part of the 20-State Round 2 Cross-Section. - The HRL used for 1,3-Dichloropropene is 0.4 μg/L.



### C-6

### Appendix C. Detailed Round 2 Data Summary

Table C.3.a. Round 2 Data - 1,1,2,2-Tetrachloroethane Occurrence in Public Water Systems - Based on Number of Samples

STATE TOTAL UNIQUE

PWS TOTAL # SAMPLES # GW SAMPLES # SW SAMPLES % TOTAL SAMPLES

> MRL % GW SAMPLES

> MRL % SW SAMPLES

> MRL MIN VALUE (μg/L) 99% VALUE (μg/L) MAX VALUE (μg/L) MIN DETECTS

(μg/L) MEDIAN DETECTS

(μg/L)
Tribes (06) 22 32 31 1 0.00% 0.00% 0.00% < 0.50 < 1.00 < 1.00 AK 625 3,548 2,604 944 0.00% 0.00% 0.00% < 0.00 < 0.00 < 0.00 AL AR 407 1,352 1,078 274 0.00% 0.00% 0.00% < 0.00 < 0.10 < 0.10 AZ 121 244 172 72 0.00% 0.00% 0.00% < 0.20 < 2.00 < 2.00 CA 16 81 61 20 0.00% 0.00% 0.00% < 0.20 < 0.50 < 0.50 CO 831 2,643 1,693 950 0.00% 0.00% 0.00% < 0.00 < 0.00 < 0.00 CT 86 2,280 918 1,362 0.53% 0.22% 0.73% < 0.00 < 0.00 3.90 0.06 0.12 IN 69 142 129 13 0.00% 0.00% 0.00% < 0.50 < 2.00 < 2.00 KY 433 1,972 899 1,073 0.00% 0.00% 0.00% < 0.10 < 2.50 < 2.50 LA 1,310 4,055 3,451 604 0.00% 0.00% 0.00% < 0.50 < 0.50 < 0.50 MA 418 1,823 1,372 451 0.05% 0.07% 0.00% < 0.00 < 0.50 1.40 1.40 1.40 MD 976 4,869 4,319 550 0.02% 0.00% 0.18% < 0.10 < 0.50 0.50 0.10 0.10 ME 744 3,559 3,154 405 0.03% 0.00% 0.25% < 0.00 < 0.00 2.00 2.00 2.00 MI 2,735 6,965 6,141 824 0.01% 0.02% 0.00% < 0.00 < 0.00 0.50 0.50 0.50 MN 1,558 6,864 6,678 186 0.00% 0.00% 0.00% < 0.00 < 0.20 < 0.40 MO 1,413 3,773 3,275 498 0.00% 0.00% 0.00% < 0.00 < 1.00 < 1.00 MS NC 1,785 3,393 2,906 487 0.32% 0.31% 0.41% < 0.00 < 0.00 0.50 0.50 0.50 ND 296 382 316 66 0.00% 0.00% 0.00% < 0.00 < 0.50 < 0.50 NH 681 935 892 43 0.00% 0.00% 0.00% < 0.00 < 0.00 < 0.00 NJ 16 19 16 3 0.00% 0.00% 0.00% < 0.23 < 1.32 < 1.32 NM 716 4,820 4,602 218 0.00% 0.00% 0.00% < 0.50 < 1.00 < 1.00 OH 2,232 17,788 16,432 1,356 0.01% 0.01% 0.00% < 0.50 < 0.50 0.56 0.50 0.53 OK 792 4,746 3,492 1,254 0.02% 0.00% 0.08% < 0.00 < 0.00 0.80 0.80 0.80 OR 1,085 2,658 2,096 562 0.00% 0.00% 0.00% < 0.00 < 0.00 < 0.00 PA RI 114 423 338 85 0.00% 0.00% 0.00% < 0.00 < 1.00 < 1.00 SC 907 3,984 3,424 560 0.00% 0.00% 0.00% < 0.00 < 0.50 < 0.50 SD 27 35 26 9 0.00% 0.00% 0.00% < 0.50 < 0.50 < 0.50 TN 77 531 191 340 0.00% 0.00% 0.00% < 0.00 < 0.00 < 0.00 TX 4,412 16,849 12,190 4,659 0.01% 0.00% 0.04% < 1.00 < 1.00 1.60 1.50 1.55 VT 558 1,806 1,600 206 0.00% 0.00% 0.00% < 0.00 < 0.00 < 0.50 WA 2,547 9,549 8,665 884 0.01% 0.00% 0.11% < 0.00 < 0.00 0.30 0.30 0.30 WI 200 360 356 4 0.00% 0.00% 0.00% < 0.00 < 3.00 < 3.00

TOTAL 28,209 112,480 93,517 18,963 0.03% 0.02% 0.09% < 0.00 < 1.00 3.90 0.06 0.50

20 STATES 24,800 98,911 83,142 15,769 0.02% 0.02% 0.05% < 0.00 < 1.00 2.00 0.10 0.50

PWS = Public Water System; GW = Ground Water; SW = Surface Water; MRL= Minimum Reporting Limit; Min, 99%, and Max Value = the m inimum, the 99th percentile value, and the maximum value of all samples; Min and Median Detects = the minimum and median of all sample detects. - The highlighted States are part of the 20-State Round 2 Cross-Section. - Less-than (<) values indicate MRL values. Some systems did not report MRL values. In the data, these MRL values are represented by zeros (e.g "< 0.00").



### C-7

### Appendix C. Detailed Round 2 Data Summary

Table C.3.b. Round 2 Data - 1,1,2,2-Tetrachloroethane Occurrence in Public Water Systems - Based on Number of Systems

STATE TOTAL # SAMPLES TOTAL UNIQUE

PWS # GW PWS # SW PWS % PWS

> MRL % GW PWS > MRL % SW PWS > MRL % PWS > 1⁄2 HRL % GW PWS > 1⁄2 HRL % SW PWS > 1⁄2 HRL % PWS > HRL % GW PWS > HRL % SW PWS > HRL
Tribes (06) 32 22 21 1 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% AK 3,548 625 481 144 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% AL AR 1,352 407 319 88 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% AZ 244 121 106 15 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% CA 81 16 12 4 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% CO 2,643 831 619 212 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% CT 2,280 86 44 42 3.49% 4.55% 2.38% 1.16% 2.27% 0.00% 1.16% 2.27% 0.00% IN 142 69 62 7 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% KY 1,972 433 208 225 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% LA 4,055 1,310 1,241 69 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% MA 1,823 418 344 74 0.24% 0.29% 0.00% 0.24% 0.29% 0.00% 0.24% 0.29% 0.00% MD 4,869 976 920 56 0.10% 0.00% 1.79% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% ME 3,559 744 676 68 0.13% 0.00% 1.47% 0.13% 0.00% 1.47% 0.13% 0.00% 1.47% MI 6,965 2,735 2,644 91 0.04% 0.04% 0.00% 0.04% 0.04% 0.00% 0.04% 0.04% 0.00% MN 6,864 1,558 1,528 30 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% MO 3,773 1,413 1,297 116 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% MS NC 3,393 1,785 1,592 193 0.50% 0.44% 1.04% 0.50% 0.44% 1.04% 0.50% 0.44% 1.04% ND 382 296 258 38 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% NH 935 681 651 30 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% NJ 19 16 14 2 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% NM 4,820 716 689 27 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% OH 17,788 2,232 2,050 182 0.09% 0.10% 0.00% 0.09% 0.10% 0.00% 0.09% 0.10% 0.00% OK 4,746 792 541 251 0.13% 0.00% 0.40% 0.13% 0.00% 0.40% 0.13% 0.00% 0.40% OR 2,658 1,085 934 151 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% PA RI 423 114 102 12 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% SC 3,984 907 806 101 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% SD 35 27 19 8 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% TN 531 77 30 47 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% TX 16,849 4,412 3,825 587 0.05% 0.00% 0.34% 0.05% 0.00% 0.34% 0.05% 0.00% 0.34% VT 1,806 558 494 64 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% WA 9,549 2,547 2,428 119 0.04% 0.00% 0.84% 0.04% 0.00% 0.84% 0.00% 0.00% 0.00% WI 360 200 197 3 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00%

TOTAL 112,480 28,209 25,152 3,057 0.08% 0.05% 0.29% 0.07% 0.05% 0.23% 0.06% 0.05% 0.20%

20 STATES 98,911 24,800 22,106 2,694 0.08% 0.05% 0.30% 0.07% 0.05% 0.26% 0.07% 0.05% 0.22%

PWS = Public Water System; GW = Ground Water; SW = Surface Water; "% PWS > MRL", "> 1⁄2 HRL", and "> HRL" are the proportion of systems with at least one analytic result equal to or greater than the MRL, exceeding the 1⁄2 HRL benchmark, and exceeding the HRL benchmark, respectively. - The highlighted States are part of the 20-State Round 2 Cross-Section. - The HRL used for 1,1,2,2-Tetrachloroethane is 0.4 μg/L.



### C-8

### Appendix C. Detailed Round 2 Data Summary

Table C.3.c. Round 2 Data - 1,1,2,2-Tetrachloroethane Occurrence in Public Water Systems - Based on Population Served

STATE TOTAL POP SERVED GW POP SERVED SW POP SERVED % POP > MRL % GW POP > MRL % SW POP > MRL % POP > 1⁄2 HRL % GW POP > 1⁄2 HRL % SW POP > 1⁄2 HRL % POP > HRL % GW POP > HRL % SW POP > HRL
Tribes (06) 51,486 42,986 8,500 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% AK 480,068 204,976 275,092 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% AL AR 1,301,907 612,648 689,259 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% AZ 862,408 181,619 680,789 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% CA 1,171,659 529,897 641,762 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% CO 3,576,561 440,514 3,136,047 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% CT 2,330,321 211,367 2,118,954 1.32% 12.98% 0.16% 0.42% 4.67% 0.00% 0.42% 4.67% 0.00% IN 250,248 214,333 35,915 KY 3,047,973 296,772 2,751,201 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% LA 4,535,907 2,598,561 1,937,346 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% MA 3,401,953 1,326,219 2,075,734 0.03% 0.07% 0.00% 0.03% 0.07% 0.00% 0.03% 0.07% 0.00% MD 5,012,575 671,808 4,340,767 29.92% 0.00% 34.56% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% ME 675,407 244,096 431,311 0.32% 0.00% 0.50% 0.32% 0.00% 0.50% 0.32% 0.00% 0.50% MI 3,237,068 1,920,249 1,316,819 0.002% 0.003% 0.00% 0.002% 0.003% 0.00% 0.002% 0.003% 0.00% MN 3,648,944 2,388,282 1,260,662 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% MO 2,297,960 1,477,191 820,769 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% MS NC 4,927,499 1,254,514 3,672,985 0.54% 0.62% 0.51% 0.54% 0.62% 0.51% 0.54% 0.62% 0.51% ND 478,189 227,270 250,919 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% NH 466,045 168,817 297,228 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% NJ 28,130 5,730 22,400 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% NM 1,352,001 1,211,338 140,663 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% OH 9,095,427 3,311,171 5,784,256 0.17% 0.47% 0.00% 0.17% 0.47% 0.00% 0.17% 0.47% 0.00% OK 3,012,419 639,513 2,372,906 0.02% 0.00% 0.03% 0.02% 0.00% 0.03% 0.02% 0.00% 0.03% OR 2,280,323 691,245 1,589,078 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% PA RI 759,625 132,623 627,002 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% SC 2,556,069 708,949 1,847,120 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% SD 57,723 25,359 32,364 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% TN 792,356 105,819 686,537 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% TX 17,945,854 6,369,774 11,576,080 0.06% 0.00% 0.09% 0.06% 0.00% 0.09% 0.06% 0.00% 0.09% VT 419,236 161,487 257,749 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% WA 4,296,465 2,389,339 1,907,126 7.12% 0.00% 16.05% 7.12% 0.00% 16.05% 0.00% 0.00% 0.00% WI 342,561 305,110 37,451 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00%

TOTAL 84,692,367 31,069,576 53,622,791 2.23% 0.17% 3.43% 0.44% 0.11% 0.63% 0.08% 0.11% 0.06%

20 STATES 71,294,263 25,978,359 45,315,904 2.61% 0.09% 4.06% 0.51% 0.09% 0.75% 0.08% 0.09% 0.07%

PWS = Public Water System; GW = Ground Water; SW = Surface Water; "% POP > MRL", "> 1⁄2 HRL", and "> HRL" are the proportion of the total population served by systems with at least one analytic result equal to or greater than the MRL, exceeding the 1⁄2 HRL benchmark, and exceeding the HRL benchmark, respectively. - The highlighted States are part of the 20-State Round 2 Cross-Section. - The HRL used for 1,1,2,2-Tetrachloroethane is 0.4 μg/L.



### C-9

# Appendix D. Detailed NIRS Data Summary for Boron

Table D.1.a NIRS Data - Boron O ccurrence in Public Water Systems

### Appendix D. Detailed NIRS Data Summary

Table D.1. NIRS Data - Boron Occurrence in Public Water Systems

State # Samples # Samples > MRL % Samples

> MRL # Detects > 1⁄2 HRL % Detects > 1⁄2 HRL # Detects > HRL % Detects > HRL Min Value (mg/L) 99% Value (mg/L) Max Value (mg/L) Min Detects (mg/L) Median Detects (mg/L)

AK 8 7 87.50% 0.00% 0.00% < 0.01 0.12 0.12 0.01 0.04 AL 8 3 37.50% 0.00% 0.00% < 0.01 0.41 0.41 0.01 0.01 AR 9 9 100.00% 0.00% 0.00% 0.01 0.60 0.60 0.01 0.09 AZ 14 13 92.86% 1 7.14% 0.00% < 0.01 1.00 1.00 0.01 0.04 CA 60 56 93.33% 5 8.33% 2 3.33% < 0.01 3.89 3.89 0.01 0.07 CO 10 9 90.00% 0.00% 0.00% < 0.01 0.22 0.22 0.01 0.04 CT 23 19 82.61% 0.00% 0.00% < 0.01 0.14 0.14 0.01 0.02 DE 10 8 80.00% 1 10.00% 0.00% < 0.01 0.89 0.89 0.01 0.01 FL 56 55 98.21% 0.00% 0.00% < 0.01 0.24 0.24 0.01 0.02 GA 23 14 60.87% 0.00% 0.00% < 0.01 0.06 0.06 0.01 0.01 IA 28 28 100.00% 1 3.57% 1 3.57% 0.01 1.44 1.44 0.01 0.06 ID 12 8 66.67% 0.00% 0.00% < 0.01 0.13 0.13 0.01 0.04 IL 46 45 97.83% 7 15.22% 1 2.17% < 0.01 1.63 1.63 0.01 0.32 IN 19 19 100.00% 0.00% 0.00% 0.01 0.22 0.22 0.01 0.08 KS 6 6 100.00% 0.00% 0.00% 0.02 0.27 0.27 0.02 0.07 KY 8 7 87.50% 0.00% 0.00% < 0.01 0.12 0.12 0.01 0.02 LA 26 25 96.15% 3 11.54% 1 3.85% < 0.01 2.82 2.82 0.01 0.05 MA 7 4 57.14% 0.00% 0.00% < 0.01 0.02 0.02 0.01 0.01 MD 6 5 83.33% 0.00% 0.00% < 0.01 0.68 0.68 0.08 0.13 ME 7 3 42.86% 0.00% 0.00% < 0.01 0.03 0.03 0.01 0.01 MI 25 25 100.00% 1 4.00% 0.00% 0.01 0.79 0.79 0.01 0.04 MN 19 18 94.74% 1 5.26% 0.00% < 0.01 1.11 1.11 0.01 0.18 MO 21 15 71.43% 0.00% 0.00% < 0.01 0.63 0.63 0.01 0.04 MS 26 19 73.08% 0.00% 0.00% < 0.01 0.50 0.50 0.01 0.13 MT 11 11 100.00% 1 9.09% 0.00% 0.01 1.21 1.21 0.01 0.12 NC 44 17 38.64% 0.00% 0.00% < 0.01 0.64 0.64 0.01 0.02 ND 19 19 100.00% 7 36.84% 5 26.32% 0.02 3.95 3.95 0.02 0.49 NE 19 19 100.00% 0.00% 0.00% 0.01 0.22 0.22 0.01 0.05 NH 10 3 30.00% 0.00% 0.00% < 0.01 0.06 0.06 0.01 0.02 NJ 6 1 16.67% 0.00% 0.00% < 0.01 0.10 0.10 0.10 0.10 NM 7 7 100.00% 0.00% 0.00% 0.02 0.20 0.20 0.02 0.07 NV 2 2 100.00% 0.00% 0.00% 0.01 0.34 0.34 0.01 0.18 NY 57 43 75.44% 1 1.75% 0.00% < 0.01 0.83 0.83 0.01 0.04 OH 25 25 100.00% 0.00% 0.00% 0.01 0.61 0.61 0.01 0.05 OK 12 12 100.00% 0.00% 0.00% 0.01 0.51 0.51 0.01 0.07 OR 8 7 87.50% 0.00% 0.00% < 0.01 0.25 0.25 0.01 0.01 PA 36 29 80.56% 0.00% 0.00% < 0.01 0.41 0.41 0.01 0.05 PR 1 1 100.00% 0.00% 0.00% 0.04 0.04 0.04 0.04 0.04 RI 1 0.00% 0.00% 0.00% < 0.01 < 0.01 < 0.01 SC 18 10 55.56% 1 5.56% 1 5.56% < 0.01 2.44 2.44 0.01 0.01 SD 8 8 100.00% 2 25.00% 1 12.50% 0.06 2.87 2.87 0.06 0.25 TN 9 5 55.56% 0.00% 0.00% < 0.01 0.04 0.04 0.01 0.01 TX 74 74 100.00% 8 10.81% 3 4.05% 0.01 3.15 3.15 0.01 0.17 UT 10 9 90.00% 0.00% 0.00% < 0.01 0.16 0.16 0.01 0.03 VA 30 14 46.67% 2 6.67% 2 6.67% < 0.01 2.12 2.12 0.01 0.14 VT 12 3 25.00% 0.00% 0.00% < 0.01 0.02 0.02 0.01 0.01 WA 52 37 71.15% 1 1.92% 0.00% < 0.01 0.93 0.93 0.01 0.02 WI 30 25 83.33% 0.00% 0.00% < 0.01 0.59 0.59 0.01 0.02 WV 8 6 75.00% 0.00% 0.00% < 0.01 0.12 0.12 0.01 0.03 WY 3 3 100.00% 0.00% 0.00% 0.03 0.39 0.39 0.03 0.06 Total 989 810 81.90% 43 4.35% 17 1.72% < 0.01 2.44 3.95 0.01 0.05

PWS = Public Water System; GW = Ground Water; SW = Surface Water; MRL= Minimum Reporting Limit; "# (or %) PWS > MRL", "> 1⁄2 HRL", and "> HRL" are the number (or proportion) of systems with at least one analytic result equal to or greater than the MRL, exceeding the 1⁄2 HRL benchmark, and exceeding the HRL benchmark, respectively; Min, 99%, and Max Value = the minimum, the 99th percentile value, and the maximu m value of all samples; Min and Median Detects = the minimum and median of all sample detects. - Only one sample was taken per system, so # samples = # systems. - Less-than (<) values indicate MRL values. - The HRL used for boron is 1.4 mg/L.



### D-1

# Appendix E. Data Summaries of Occurrence and Population Served for Four Contaminants Co nsidered During CCL 2 Re gulatory Determinations

Table E.1 Boron Occurrence Summary Sta tistics in Ground Water Surveys (NIRS)

Table E.2 Metolachlor Occurrenc e Summary Statistics (Round 2)

Table E.3.a 1,3-Dichloropropene Occu rrence Summary Statistics (Round 1) Table E.3.b 1,3-Dichloropropene Occu rrence Summary Statistics (Round 2)

Table E.4.a 1,1,2,2-Tetrachloroethane O ccurrence Summary Statistics (Round 1) Table E.4.b 1,1,2,2-Tetrachloroethane O ccurrence Summary Statistics (Round 2)

### Appendix E. Data Summaries of Occurrence Population Served for Four Contaminants Considered During CCL 2 Regulatory Determinations


# Table E.1. Boron Occurrence Summary Statistics in Ground Water Surveys (NIRS)

Frequency Factors NIRS Data on Boron National System & Population Numbers 1



## Total Number of Samples/Systems 989 59,440

99 t h 

## Percentile Concentration (all samples) 2.44 mg/L

-- Health Reference Level (HRL) 1.4 mg/L

-- Minimum Reporting Level (MRL) 0.005 mg/L

-- Maximum Concentration of Detections 3.95 mg/L

99 th 

## Percentile Concentration of Detections 2.6 mg/L

-- Median Concentration of Detections 0.047 mg/L

-- Total Population Served 1,482,153 85,681,696
Occurrence by Sample/System Number Percentage National Extrapolation

Ground Water PWSs with Detections ( > MRL) 810 81.9% 48,682 Range of NIRS States 0 - 74 0 - 100% N/A

Ground Water PWSs > 1⁄2 HRL 43 4.3% 2,584 Range of NIRS States 0 - 8 0 - 37% N/A

Ground Water PWSs > HRL 17 1.7% 1,022 Range of NIRS States 0 - 5 0 - 26% N/A
Occurrence by Population Served

Population Served by GW PWSs with Detections 1,306,048 88.1% 75,501,000 Range of NIRS States 0 - 343,465 0 - 100% N/A Population Served by GW PWSs > 1⁄2 HRL 42,702 2.9% 2,469,000 Range of NIRS States 0 - 20,465 0 - 34% N/A Population Served by GW PWSs > HRL 6,443 0.4% 372,000 Range of NIRS States 0 - 2,500 0 - 34% N/A

1. Total PWS and population numbers are from EPA's March 2000 Water Industry Baseline Handbook, 2nd Edition. National extrapolations are generated by multiplying the system/population percentages and the national Baseline Handbook system/population numbers.

Abbreviations: PWS = Public Water Systems; GW = Ground Water; N/A = Not Applicable; Total Number of Samples/Systems = total number of samples/systems on record for the contaminant; 99th Percentile Concentration = the concentration in the 99th percentile sample (out of either all samples or just samples with detections); Median Concentration of Detections = the concentration in the median sample (out of samples with detections); Total Population Served = the total population served by PWSs for which sampling results are available; Ground Water PWSs with Detections, PWSs >1⁄2HRL, or PWSs >HRL = GW PWSs with at least one sampling result greater than or equal to the MRL, exceeding the 1⁄2HRL benchmark, or exceeding the HRL benchmark, respectively; Population Served by GW PWSs with Detections, by PWSs >1⁄2HRL, or by PWSs >HRL = population served by GW PWSs with at least one sampling result greater than or equal to the MRL, exceeding the 1⁄2HRL benchmark, or exceeding the HRL benchmark, respectively.

Notes: - Only results at or above the MRL were reported as detections. Concentrations below the MRL are considered non-detects.



### E-1Appendix E. Data Summaries of Occurrence Population Served for Four Contaminants Considered During CCL 2 Regulatory Determinations



### Table E.2. Metolachlor Occurrence Summary Statistics (Round 2)

Frequency Factors 19 State Cross-Section 1 All Reporting States 2 National System & Population Numbers 3
Total Number of Sample s 33,930 42,798

- - Percent of Samples with Detection s 0.57% 0.86%

- - 99 t h Percentile Concentration (all samples) < MRL < MRL

-- Health Reference Level (HRL ) 70 70

- - Minimum Reporting Level (MRL) - Range 0.01 - 52 μg/L 0.01 - 52 μg/L

-- - (modal value) 4 0.2 μg/L 0.1 μg/L

Maximum Concentration of Detections 13.8 μg/L 13.8 μg/L

-- 99 t h Percentile Concentration of Detections 7.1 μg/L 6 μg/L

-- Median Concentration of Detections 0.61 μg/L 1.0 μg/L

- - Total Number of PWSs 12,953 14,878 65,030 Number of GW PWSs 11,503 13,062 59,440 Number of SW PWSs 1,450 1,816 5,590 Total Populatio n 47,098,573 59,101,488 213,008,182 Population of GW PWSs 14,279,627 15,749,200 85,681,696 Population of SW PWSs 32,818,946 43,352,288 127,326,486 Occurrence by System Number Percentage Number Percentage National Extra p olation 5 Cross-Section All States PWSs with detections ( > MRL) 108 0.83% 178 1.20% 542 778 Range across States 0 - 40 0 - 20.00% 0 - 60 0 - 20.0% N/ A N/ A GW PWSs with detections 13 0.11% 47 0.36% 67 214 SW PWSs with detections 95 6.55% 131 7.21% 366 403
PWSs > 1⁄2 HRL 0 0.00% 0 0.00% 0 0 Range across States 0 0.00% 0 0.00% 0 N/ A GW PWSs > 1⁄2 HRL 0 0.00% 0 0.00% 0 0 SW PWSs > 1⁄2 HRL 0 0.00% 0 0.00% 0 0
PWSs > HRL 0 0.00% 0 0.00% 0 0 Range across States 0 0.00% 0 0.00% 0 N/ A GW PWSs > HRL 0 0.00% 0 0.00% 0 0 SW PWSs > HRL 0 0.00% 0 0.00% 0 0

Occurrence by Population Served Population served by PWSs with detection s 5
, 452
, 616 11.58% 8
, 516
, 409 14.41% 24,660,000 30,694,000 Range across States 0 - 4
, 575
, 644 0 - 44.41% 0 - 4
, 575
, 644 0 - 48.02% N/ A N/ A Pop. Served by GW PWSs with detection s 99
, 372 0.70% 172
, 839 1.10% 596,000 940,000 Pop. Served by SW PWSs with detection s 5
, 353
, 244 16.31% 8
, 343
, 570 19.25% 20,769,000 24,505,000 Population served by PWSs > 1⁄2 HR L 0 0.00% 0 0.00% 0 0 Range across States 0 0.00% 0 0.00% 0 N/ A Pop. Served by GW PWSs > 1⁄2 HR L 0 0.00% 0 0.00% 0 0 Pop. Served by SW PWSs > 1⁄2 HR L 0 0.00% 0 0.00% 0 0 Population served by PWSs > HR L 0 0.00% 0 0.00% 0 0 Range across States 0 0.00% 0 0.00% 0 N/ A Pop. Served by GW PWSs > HR L 0 0.00% 0 0.00% 0 0 Pop. Served by SW PWSs > HR L 0 0.00% 0 0.00% 0 0

1. Summary Results based on 19-State Cross-Section, UCM Round 2 data. 2. Summary Results based on All Reporting States, UCM Round 2 data. 3. Total PWS and population numbers are from EPA March 2000 Water Industry Baseline Handbook, 2nd Edition. 4. Because several different analytical methods were used, MRLs were not uniform. The modal value is the most common MRL. 5. National extrapolations are generated by multiplying the system/population percentages and the national Baseline Handbook system/population numbers.

Abbreviations: PWS = Public Water Systems; GW = Ground Water; SW = Surface Water; N/A = Not Applicable; Total Number of Samples = total number of samples on record for the contaminant; 99th Percentile Concentration = the concentration in the 99th percentile sample (out of either all samples or just samples with detections); Median Concentration of Detections = the concentration in the median sample (out of samples with detections); Total Number of PWSs = the total number of PWSs for which sampling results are available; Total Population Served = the total population served by PWSs for which sampling results are available; PWSs with Detections, PWSs >1⁄2HRL, or PWSs >HRL = PWSs with at least one sampling result greater than or equal to the MRL, exceeding the 1⁄2HRL benchmark, or exceeding the HRL benchmark, respectively; Population Served by PWSs with Detections, by PWSs >1⁄2HRL, or by PWSs >HRL = population served by PWSs with at least one sampling result greater than or equal to the MRL, exceeding the 1⁄2HRL benchmark, or exceeding the HRL benchmark, respectively.

Notes: - Only results at or above the MRL were reported as detections. Concentrations below the MRL are considered non-detects. - Because some systems were counted as both ground water and surface water systems and others could not be classified, GW and SW figures might not add up to totals. - Due to differences between the ratios of GW and SW systems with monitoring results and the national ratio, extrapolated GW and SW figures might not add up to extrapolated totals.

E-2Appendix E. Data Summaries of Occurrence Population Served for Four Contaminants Considered During CCL 2 Regulatory Determinations



### Table E.3.a. 1,3-Dichloropropene Occurrence Summary Statistics (Round 1)

Frequency Factors 24 State Cross-Section 1 All Reporting States 2 National System & Population Numbers 3

Total Number of Samples 31,104 31,973

- - Percent of Samples with Detections 0.06% 0.09%

- - 99 t h Percentile Concentration (all samples) < MRL < MRL

-- Health Reference Level (HRL ) 0.4 μg/ L 0.4 μg/ L

- - Minimum Reporting Level (MRL) - Range 0.02 - 10 μg/L 0.02 - 10 μg/L

-- - (modal value) 4 (0.5 μg/L) (0.5 μg/L)

Maximum Concentration of Detections 2.0 μg/L 17.0 μg/L

-- 99 t h Percentile Concentration of Detections 2.0 μg/L 15.6 μg/L

-- Median Concentration of Detections 1.0 μg/ L 1.0 μg/ L

- - Total Number of PWS s 9,164 9,307 65,030 Number of GW PWS s 8,303 8,401 59,440 Number of SW PWS s 898 947 5,590 Total Population 50,917,006 52,879,061 213,008,182 Population of GW PWS s 24,660,968 26,106,876 85,681,696 Population of SW PWSs 29,271,833 29,867,090 127,326,486 Occurrence by System Number Percentage Number Percentage National Extra p olatio n 5 Cross-Section All States PWSs with detections ( > ) MRL 15 0.16% 19 0.20% 106 133 Range across States 0 - 7 0 - 1.75% 0 - 7 0 - 100% N/ A N/ A GW PWSs with detection s 10 0.12% 14 0.17% 72 99 SW PWSs with detections 5 0.56% 6 0.63% 31 35
PWSs > 1⁄2 HR L 15 0.16% 18 0.19% 106 126 Range across States 0 - 7 0 - 1.75% 0 - 7 0 - 100% N/ A N/ A GW PWSs > 1⁄2 HR L 10 0.12% 13 0.15% 72 92 SW PWSs > 1⁄2 HR L 5 0.56% 6 0.63% 31 35
PWSs > HR L 15 0.16% 18 0.19% 106 126 Range across States 0 - 7 0 - 1.75% 0 - 7 0 - 100% N/ A N/ A GW PWSs > HR L 10 0.12% 13 0.15% 72 92 SW PWSs > HR L 5 0.56% 6 0.63% 31 35

Occurrence by Population Served Population served by PWSs with detections 436,223 0.86% 500,486 0.95% 1,825,000 2,016,000 Range across States 0 - 225,630 0 - 6.12% 0 - 225,630 0 - 100% N/ A N/ A Pop. Served by GW PWSs with detection s 146,155 0.59% 210,418 0.81% 508,000 691,000 Pop. Served by SW PWSs with detection s 290,068 0.99% 342,118 1.15% 1,262,000 1,458,000 Population served by PWSs > 1⁄2 HR L 436,223 0.86% 497,246 0.94% 1,825,000 2,003,000 Range across States 0 - 225,630 0 - 6.12% 0 - 225,630 0 - 100% N/ A N/ A Pop. Served by GW PWSs > 1⁄2 HR L 146,155 0.59% 207,178 0.79% 508,000 680,000 Pop. Served by SW PWSs > 1⁄2 HR L 290,068 0.99% 342,118 1.15% 1,262,000 1,458,000 Population served by PWSs > HR L 436,223 0.86% 497,246 0.94% 1,825,000 2,003,000 Range across States 0 - 225,630 0 - 6.12% 0 - 225,630 0 - 100% N/ A N/ A Pop. Served by GW PWSs > HR L 146,155 0.59% 207,178 0.79% 508,000 680,000 Pop. Served by SW PWSs > HR L 290,068 0.99% 342,118 1.15% 1,262,000 1,458,000

1. Summary Results based on 24-State Cross-Section, UCM Round 1 data. 2. Summary Results based on All Reporting States, UCM Round 1 data. 3. Total PWS and population numbers are from EPA March 2000 Water Industry Baseline Handbook, 2nd Edition. 4. Because several different analytical methods were used, MRLs were not uniform. The modal value is the most common MRL. 5. National extrapolations are generated by multiplying the system/population percentages and the national Baseline Handbook system/population numbers.

Abbreviations:
PWS = Public Water Systems; GW = Ground Water; SW = Surface Water; N/A = Not Applicable; Total Number of Samples = total number of samples on record for the contaminant; 99th Percentile Concentration = the concentration in the 99th percentile sample (out of either all samples or just samples with detections); Median Concentration of Detections = the concentration in the median sample (out of samples with detections); Total Number of PWSs = the total number of PWSs for which sampling results are available; Total Population Served = the total population served by PWSs for which sampling results are available; PWSs with Detections, PWSs >1⁄2HRL, or PWSs >HRL = PWSs with at least one sampling result greater than or equal to the MRL, exceeding the 1⁄2HRL benchmark, or exceeding the HRL benchmark, respectively; Population Served by PWSs with Detections, by PWSs >1⁄2HRL, or by PWSs >HRL = population served by PWSs with at least one sampling result greater than or equal to the MRL, exceeding the 1⁄2HRL benchmark, or exceeding the HRL benchmark, respectively.

Notes: - Only results at or above the MRL were reported as detections. Concentrations below the MRL are considered non-detects. - Because some systems were counted as both ground water and surface water systems and others could not be classified, GW and SW figures might not add up to totals. - Due to differences between the ratios of GW and SW systems with monitoring results and the national ratio, extrapolated GW and SW figures might not add up to extrapolated totals. - Due to MRL variability, it is likely that the sampling failed to capture some 1⁄2 HRL and HRL exceedances at participating systems, and the 1⁄2 HRL and HRL analyses underestimate actual contaminant occurrence.

E-3Appendix E. Data Summaries of Occurrence Population Served for Four Contaminants Considered During CCL 2 Regulatory Determinations



### Table E.3.b. 1,3-Dichloropropene Occurrence Summary Statistics (Round 2)

Frequency Factors 20 State Cross-Section 1 

### All Reporting States 2 

### National System & Population Numbers 3



### Total Number of Sample s 70,631 79,388

- - Percent of Samples with Detection s 0.11% 0.10%

- - 99 t h 

### Percentile Concentration (all samples) < MRL < MRL

-- Health Reference Level (HRL ) 0.4 μg/ L 0.4 μg/ L

- - Minimum Reporting Level (MRL) - Range 0.08 - 1 μg/L 0.08 - 1 μg/L

-- - (modal value) 4 

### (0.5 μg/L) (0.5 μg/L)

Maximum Concentration of Detections 39 μg/L 39 μg/L

-- 99 t h 

### Percentile Concentration of Detections 39 μg/L 25 μg/L

-- Median Concentration of Detections 0.5 μg/ L 0.5 μg/ L

- - Total Number of PWS s 16,787 18,944 65,030 Number of GW PWS s 15,178 17,098 59,440 Number of SW PWS s 1,609 1,846 5,590 Total Populatio n 45,951,052 55,713,623 213,008,182 Population of GW PWS s 17,423,030 21,446,615 85,681,696 Population of SW PWS s 28,528,022 34,267,008 127,326,486 Occurrence by System Number Percentage Number Percentage National Extra p olation 5 

### Cross-Section All States PWSs with detections (> MRL) 58 0.35% 59 0.31% 225 203 Range across States 0 - 43 0 - 2.91% 0 - 43 0 - 2.91% N/ A N/ A GW PWSs with detections 48 0.32% 48 0.28% 188 167 SW PWSs with detections 10 0.62% 11 0.60% 35 33
PWSs > 1⁄2 HR L 50 0.30% 51 0.27% 194 175 Range across States 0 - 35 0 - 2.36% 0 - 35 0 - 2.36% N/ A N/ A GW PWSs > 1⁄2 HR L 41 0.27% 41 0.24% 161 143 SW PWSs > 1⁄2 HR L 9 0.56% 10 0.54% 31 30
PWSs > HR L 38 0.23% 38 0.20% 147 130 Range across States 0 - 23 0 - 1.55% 0 - 23 0 - 1.55% N/ A N/ A GW PWSs > HR L 29 0.19% 29 0.17% 114 101 SW PWSs > HR L 9 0.56% 9 0.49% 31 27

Occurrence by Population Served Population served by PWSs with detection s 252,643 0.55% 260,157 0.47% 1,171,000 995,000 Range across States 0 - 209,261 0 - 5.78% 0 - 209,261 0 - 5.78% N/ A N/ A Pop. Served by GW PWSs with detection s 197,066 1.13% 197,066 0.92% 969,000 787,000 Pop. Served by SW PWSs with detection s 55,577 0.19% 63,091 0.18% 248,000 234,000 Population served by PWSs > 1⁄2 HR L 192,870 0.42% 200,384 0.36% 894,000 766,000 Range across States 0 - 149,488 0 - 4.13% 0 - 149,488 0 - 4.13% N/ A N/ A Pop. Served by GW PWSs > 1⁄2 HR L 141,275 0.81% 141,275 0.66% 695,000 564,000 Pop. Served by SW PWSs > 1⁄2 HR L 51,595 0.18% 59,109 0.17% 230,000 220,000 Population served by PWSs > HR L 151,553 0.33% 151,553 0.27% 703,000 579,000 Range across States 0 - 108,171 0 - 2.99% 0 - 108,171 0 - 2.99% N/ A N/ A Pop. Served by GW PWSs > HR L 99,958 0.57% 99,958 0.47% 492,000 399,000 Pop. Served by SW PWSs > HR L 51,595 0.18% 51,595 0.15% 230,000 192,000

1. Summary Results based on 20-State Cross-Section, UCM Round 2 data. 2. Summary Results based on All Reporting States, UCM Round 2 data. 3. Total PWS and population numbers are from EPA March 2000 Water Industry Baseline Handbook, 2nd Edition. 4. Because several different analytical methods were used, MRLs were not uniform. The modal value is the most common MRL. 5. National extrapolations are generated by multiplying the system/population percentages and the national Baseline Handbook system/population numbers.

Abbreviations:

PWS = Public Water Systems; GW = Ground Water; SW = Surface Water; N/A = Not Applicable; Total Number of Samples = total number of samples on record for the contaminant; 99th Percentile Concentration = the concentration in the 99th percentile sample (out of either all samples or just samples with detections); Median Concentration of Detections = the concentration in the median sample (out of samples with detections); Total Number of PWSs = the total number of PWSs for which sampling results are available; Total Population Served = the total population served by PWSs for which sampling results are available; PWSs with Detections, PWSs >1⁄2HRL, or PWSs >HRL = PWSs with at least one sampling result greater than or equal to the MRL, exceeding the 1⁄2HRL benchmark, or exceeding the HRL benchmark, respectively; Population Served by PWSs with Detections, by PWSs >1⁄2HRL, or by PWSs >HRL = population served by PWSs with at least one sampling result greater than or equal to the MRL, exceeding the 1⁄2HRL benchmark, or exceeding the HRL benchmark, respectively.

Notes: - Only results at or above the MRL were reported as detections. Concentrations below the MRL are considered non-detects. - Due to differences between the ratios of GW and SW systems with monitoring results and the national ratio, extrapolated GW and SW figures might not add up to extrapolated totals. - Due to MRL variability, it is likely that the sampling failed to capture some 1⁄2 HRL and HRL exceedances at participating systems, and the 1⁄2 HRL and HRL analyses underestimate actual contaminant occurrence.

E-4Appendix E. Data Summaries of Occurrence Population Served for Four Contaminants Considered During CCL 2 Regulatory Determinations



### Table E.4.a. 1,1,2,2-Tetrachloroethane Occurrence Summary Statistics (Round 1)

Frequency Factors 24 State Cross-Section 1 All Reporting States 2 National System & Population Numbers 3

Total Number of Sample s 67,688 70,784

- - Percent of Samples with Detection s 0.16% 0.16%

- - 99 t h Percentile Concentration (all samples) < MRL < MRL

-- Health Reference Level (HRL ) 0.4 μg/L 0.4 μg/L

- - Minimum Reporting Level (MRL) - Range 0.01 - 10 μg/L 0.01 - 10 μg/L

-- - (modal value) 4 (0.5 μg/L) (0.5 μg/L)

Maximum Concentration of Detections 200 μg/L 200 μg/L

-- 99 t h Percentile Concentration of Detections 112 μg/L 112 μg/L

-- Median Concentration of Detections 0.5 μg/L 0.5 μg/L

- - Total Number of PWSs 20,407 20,899 65,030 Number of GW PWSs 18,693 19,054 59,440 Number of SW PWSs 1,867 2,019 5,590 Total Populatio n 94,710,065 98,334,686 213,008,182 Population of GW PWSs 55,763,644 57,663,608 85,681,696 Population of SW PWSs 43,763,942 45,776,159 127,326,486 Occurrence by System Number Percentage Number Percentage National Extra p olation 5 Cross-Section All States PWSs with detections ( > MRL) 91 0.45% 101 0.48% 290 314 Range across States 0 - 39 0 - 11.64% 0 - 39 0 - 100% N/ A N/ A GW PWSs with detections 72 0.39% 80 0.42% 229 250 SW PWSs with detections 19 1.02% 21 1.04% 57 58
PWSs > 1⁄2 HRL 44 0.22% 54 0.26% 140 168 Range across States 0 - 11 0 - 2.76% 0 - 11 0 - 100% N/ A N/ A GW PWSs > 1⁄2 HRL 33 0.18% 41 0.22% 105 128 SW PWSs > 1⁄2 HRL 11 0.59% 13 0.64% 33 36
PWSs > HRL 41 0.20% 50 0.24% 131 156 Range across States 0 - 11 0 - 2.76% 0 - 11 0 - 100% N/ A N/ A GW PWSs > HRL 32 0.17% 39 0.20% 102 122 SW PWSs > HRL 9 0.48% 11 0.54% 27 30

Occurrence by Population Served
Population served by PWSs with detection s 1,762,198 1.86% 2,119,844 2.16% 3,963,000 4,592,000 Range across States 0 - 616,019 0 - 25.48% 0 - 616,019 0 - 100% N/ A N/ A Pop. Served by GW PWSs with detection s 1,017,630 1.82% 1,365,976 2.37% 1,564,000 2,030,000 Pop. Served by SW PWSs with detection s 744,568 1.70% 753,868 1.65% 2,166,000 2,097,000 Population served by PWSs > 1⁄2 HR L 1,597,140 1.69% 1,954,786 1.99% 3,592,000 4,234,000 Range across States 0 - 616,019 0 - 25.48% 0 - 616,019 0 - 100% N/ A N/ A Pop. Served by GW PWSs > 1⁄2 HR L 864,770 1.55% 1,213,116 2.10% 1,329,000 1,803,000 Pop. Served by SW PWSs > 1⁄2 HR L 732,370 1.67% 741,670 1.62% 2,131,000 2,063,000 Population served by PWSs > HR L 1,543,647 1.63% 1,868,493 1.90% 3,472,000 4,047,000 Range across States 0 - 616,019 0 - 25.48% 0 - 616,019 0 - 100% N/ A N/ A Pop. Served by GW PWSs > HR L 851,641 1.53% 1,167,187 2.02% 1,309,000 1,734,000 Pop. Served by SW PWSs > HR L 692,006 1.58% 701,306 1.53% 2,013,000 1,951,000

1. Summary Results based on 24-State Cross-Section, UCM Round 1 data. 2. Summary Results based on All Reporting States, UCM Round 1 data. 3. Total PWS and population numbers are from EPA March 2000 Water Industry Baseline Handbook, 2nd Edition. 4. Because several different analytical methods were used, MRLs were not uniform. The modal value is the most common MRL. 5. National extrapolations are generated by multiplying the system/population percentages and the national Baseline Handbook system/population numbers.

Abbreviations:
PWS = Public Water Systems; GW = Ground Water; SW = Surface Water; N/A = Not Applicable; Total Number of Samples = total number of samples on record for the contaminant; 99th Percentile Concentration = the concentration in the 99th percentile sample (out of either all samples or just samples with detections); Median Concentration of Detections = the concentration in the median sample (out of samples with detections); Total Number of PWSs = the total number of PWSs for which sampling results are available; Total Population Served = the total population served by PWSs for which sampling results are available; PWSs with Detections, PWSs >1⁄2HRL, or PWSs >HRL = PWSs with at least one sampling result greater than or equal to the MRL, exceeding the 1⁄2HRL benchmark, or exceeding the HRL benchmark, respectively; Population Served by PWSs with Detections, by PWSs >1⁄2HRL, or by PWSs >HRL = population served by PWSs with at least one sampling result greater than or equal to the MRL, exceeding the 1⁄2HRL benchmark, or exceeding the HRL benchmark, respectively.

Notes: - Only results at or above the MRL were reported as detections. Concentrations below the MRL are considered non-detects. - Because some systems were counted as both ground water and surface water systems and others could not be classified, GW and SW figures might not add up to totals. - Due to differences between the ratios of GW and SW systems with monitoring results and the national ratio, extrapolated GW and SW figures might not add up to extrapolated totals. - Due to MRL variability, it is likely that the sampling failed to capture some 1⁄2 HRL and HRL exceedances at participating systems, and the 1⁄2 HRL and HRL analyses underestimate actual contaminant occurrence.

E-5Appendix E. Data Summaries of Occurrence Population Served for Four Contaminants Considered During CCL 2 Regulatory Determinations



### Table E.4.b. 1,1,2,2-Tetrachloroethane Occurrence Summary Statistics (Round 2)

Frequency Factors 20 State Cross-Section 1 All Reporting States 2 National System & Population Numbers 3

Total Number of Sample s 98,911 112,480

- - Percent of Samples with Detection s 0.02% 0.03%

- - 99 t h Percentile Concentration (all samples) < MRL < MRL

-- Health Reference Level (HRL ) 0.4 μg/L 0.4 μg/L

- - Minimum Reporting Level (MRL) - Range 0.1 - 2.5 μg/L 0.1 - 2.5 μg/L

-- - (modal value) 4 (0.5 μg/L) (0.5 μg/L)

Maximum Concentration of Detections 2 μg/L 3.9 μg/L

-- 99 t h Percentile Concentration of Detections 2 μg/L 3.9 μg/L

-- Median Concentration of Detections 0.5 μg/L 0.5 μg/L

- - Total Number of PWSs 24,800 28,209 65,030 Number of GW PWSs 22,106 25,152 59,440 Number of SW PWSs 2,694 3,057 5,590 Total Populatio n 71,294,263 84,692,367 213,008,182 Population of GW PWSs 25,978,359 31,069,576 85,681,696 Population of SW PWSs 45,315,904 53,622,791 127,326,486 Occurrence by System Number Percentage Number Percentage National Extra p olation 5 Cross-Section All States PWSs with detections ( > MRL) 19 0.08% 22 0.08% 50 51 Range across States 0 - 9 0 - 0.5% 0 - 9 0 - 3.49% N/ A N/ A GW PWSs with detections 11 0.05% 13 0.05% 30 31 SW PWSs with detections 8 0.30% 9 0.29% 17 16
PWSs > 1⁄2 HRL 18 0.07% 19 0.07% 47 44 Range across States 0 - 9 0 - 0.50% 0 - 9 0 - 1.16% N/ A N/ A GW PWSs > 1⁄2 HRL 11 0.05% 12 0.05% 30 28 SW PWSs > 1⁄2 HRL 7 0.26% 7 0.23% 15 13
PWSs > HRL 17 0.07% 18 0.06% 45 41 Range across States 0 - 9 0 - 0.50% 0 - 9 0 - 1.16% N/ A N/ A GW PWSs > HRL 11 0.05% 12 0.05% 30 28 SW PWSs > HRL 6 0.22% 6 0.20% 12 11

Occurrence by Population Served
Population served by PWSs with detection s 1,862,105 2.61% 1,892,850 2.23% 5,563,000 4,761,000 Range across States 0 - 1,500,000 0 - 29.92% 0 - 1,500,000 0 - 29.92% N/ A N/ A Pop. Served by GW PWSs with detection s 24,115 0.09% 51,543 0.17% 80,000 142,000 Pop. Served by SW PWSs with detection s 1,837,990 4.06% 1,841,307 3.43% 5,164,000 4,372,000 Population served by PWSs > 1⁄2 HR L 362,105 0.51% 371,980 0.44% 1,082,000 936,000 Range across States 0 - 306,000 0 - 7.12% 0 - 306,000 0 - 7.12% N/ A N/ A Pop. Served by GW PWSs > 1⁄2 HR L 24,115 0.09% 33,990 0.11% 80,000 94,000 Pop. Served by SW PWSs > 1⁄2 HR L 337,990 0.75% 337,990 0.63% 950,000 803,000 Population served by PWSs > HR L 56,105 0.08% 65,980 0.08% 168,000 166,000 Range across States 0 - 26,550 0 - 0.54% 0 - 26,550 0 - 0.54% N/ A N/ A Pop. Served by GW PWSs > HR L 24,115 0.09% 33,990 0.11% 80,000 94,000 Pop. Served by SW PWSs > HR L 31,990 0.07% 31,990 0.06% 90,000 76,000

1. Summary Results based on 20-State Cross-Section, UCM Round 2 data. 2. Summary Results based on All Reporting States, UCM Round 2 data. 3. Total PWS and population numbers are from EPA March 2000 Water Industry Baseline Handbook, 2nd Edition. 4. Because several different analytical methods were used, MRLs were not uniform. The modal value is the most common MRL. 5. National extrapolations are generated by multiplying the system/population percentages and the national Baseline Handbook system/population numbers.

Abbreviations: PWS = Public Water Systems; GW = Ground Water; SW = Surface Water; N/A = Not Applicable; Total Number of Samples = total number of samples on record for the contaminant; 99th Percentile Concentration = the concentration in the 99th percentile sample (out of either all samples or just samples with detections); Median Concentration of Detections = the concentration in the median sample (out of samples with detections); Total Number of PWSs = the total number of PWSs for which sampling results are available; Total Population Served = the total population served by PWSs for which sampling results are available; PWSs with Detections, PWSs >1⁄2HRL, or PWSs >HRL = PWSs with at least one sampling result greater than or equal to the MRL, exceeding the 1⁄2HRL benchmark, or exceeding the HRL benchmark, respectively; Population Served by PWSs with Detections, by PWSs >1⁄2HRL, or by PWSs >HRL = population served by PWSs with at least one sampling result greater than or equal to the MRL, exceeding the 1⁄2HRL benchmark, or exceeding the HRL benchmark, respectively.

Notes: - Only results at or above the MRL were reported as detections. Concentrations below the MRL are considered non-detects. - Due to differences between the ratios of GW and SW systems with monitoring results and the national ratio, extrapolated GW and SW figures might not add up to extrapolated totals. - Due to MRL variability, it is likely that the sampling failed to capture some 1⁄2 HRL and HRL exceedances at participating systems, and the 1⁄2 HRL and HRL analyses underestimate actual contaminant occurrence.

E-6