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 the UCM and NIRS for CCL 2 June 2008

Disclaimer 

 This document is designed to provide technical background information for the 

regulatory determinations being made on the second 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 Protection Agency’s (EPA’s) regulations. Mention of 

trade names or commercial products does not constitute endorsement or recommendation for use. 

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

Acknowledgments 

 The compilation and analysis of data presented in this report were undertaken by EPA’s 

Office of Ground Water and Drinking Water (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-Mohamadu of OGWDW’s Standards 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 Division 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 sets and valuable advice. Thanks also to the many public water 

systems that conducted the monitoring that provided 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 development under Contract # 68-C-02-026. The major 

contributions of Morgan Tingley, Erin Mateo, Alison Cullity, Brent Ranalli, and Dr. George 

Hallberg are gratefully acknowledged. Dr. Jonathan Koplos served as the Cadmus Project 

Manager. 

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

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 Environmental Protection Agency (EPA) when evaluating the 

occurrence of unregulated contaminants on the second Contaminant Candidate List (CCL 2). 

This report presents EPA’s analysis of national occurrence of CCL 2 contaminants with data 

from those sources. Detailed occurrence analyses are presented in this report 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-tetrachloroethane. Detailed 

descriptions are presented of the data sources, data editing and management, development of 

national cross-sections using UCM Round 1 and Round 2 data from States, and the analytical 

approaches used to assess the occurrence data. 

 

 The UCM Round 1 monitoring data represent public water system (PWS) monitoring 

results from 1988 to 1992 for unregulated contaminants collected under the authority of Safe 

Drinking Water Act (SDWA). Forty States/primacy entities have submitted PWS monitoring 

data for Round 1. Subsequent UCM Round 2 monitoring data collected from 1993 to 1997 were 

reported by 35 States/entities. The raw data from these two databases were reviewed and edited 

for data quality considerations to ensure consistency and repeatability in the analyses. A data 

management approach was developed to construct 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 and Round 2 national cross-sections enabled 

occurrence analyses that were indicative of national occurrence using data from these two large 

databases. All States with monitoring data were first evaluated by their distribution across a 

range of pollution potential indicators and spatial/hydrogeologic diversity. A select group of 

States, representing a balanced distribution across these pollution potential measures and across 

the nation geographically, was then used to construct national cross-sections (one using Round 1 

data, the other Round 2 data) that would provide reasonable representations of national 

occurrence. While the Round 1 and Round 2 national cross-sections cannot be presented as 

“statistically representative,” they comprise very large samples (24 and 20 States, respectively), 

provide analytical occurrence results that are clear indications of central tendency of the 

occurrence data, and are generally indicative of national contaminant occurrence. 

 The NIRS provides contaminant occurrence data from 1984 through 1986 from a group 

of statistically selected, nationally representative PWSs served 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 contaminant occurrence analyses can be considered representative 

of national occurrence in PWSs served by ground water. 

 

 Occurrence analyses of the UCM Rounds 1 and 2 and the NIRS data are conducted using 

a two-stage analytical approach. In Stage 1, the 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 occurrence toward the goal of 

protecting public health. Simple counts are made of the number of systems, and populationsvii 
EPA – OGWDW Analysis of Occurrence Data from the UCM and NIRS for CCL 2 June 2008

served by those systems, with at least one analytical result above a specified concentration 

threshold. Any contaminant found to have significant occurrence at or near health reference 

level (HRL) concentrations based on the Stage 1 analysis can additionally be analyzed using the 

Stage 2 analysis. In Stage 2, statistical modeling is used to generate national probability 

estimates of contaminant occurrence based on estimated annual mean concentrations of 

contaminants while providing statistical measures of uncertainty and error. Because no 

contaminants in this report were found with significant levels of contaminant occurrence at or 

near the HRLs of concern based on the Stage 1 analyses, the Stage 2 analyses were not warranted 

for any of the contaminants. 

 Stage 1 assessments of occurrence are presented in several ways for each contaminant to 

characterize different aspects of occurrence. For each contaminant, occurrence statistics 

presented include the number and percent of samples with laboratory analytical detections, 

which are quantified analytical values above the laboratory method reporting limit or minimum 

reporting level (MRL). All analytical detections are summarized by calculating and presenting 

the minimum, median, and 99th percentile values of detections for each contaminant. At the 

system level, the number and percent of systems with at least one detection at or above the MRL, 

and the number and percent of systems with at least two detections at or above the MRL, are 

presented. For contaminants with HRLs, similar types of occurrence assessments are presented 

relative to the concentration values of the HRL. 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 the median detection was 0.047 mg/L. 

Detections were found in PWSs in all States that conducted sampling, with the exception 

of Rhode Island. Seventeen PWSs had detections 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 statistical 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 detection of boron above the HRL of 1.4 

mg/L. 

• For metolachlor, a total of 33,930 samples were collected by the Round 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 was relatively widespread, the metolachlor 

concentrations found were consistently low. In the Round 2 cross-section, the maximum 

detection was 13.8 μg/L, the 99th 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 water 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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EPA – OGWDW Analysis of Occurrence Data from the UCM and NIRS for CCL 2 June 2008

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 national cross-section, a total of 31,104 samples 

were collected from 9,164 PWSs. 1,3-Dichloropropene 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 the 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 HRL (0.2 μg/L) and HRL (0.4 μg/L). 

For 1,3-dicloropropene, in the Round 2 national cross-section, a total of 70,631 samples 

were collected from 16,787 PWSs. 1,3-Dichloropropene 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 national extrapolation from the Round 2 crosssection results estimates 225 systems, serving 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. (MRLs varied from system to system. They 

ranged from 0.01 to 10 μg/L. The modal MRL value was 0.5 μg/L.) The maximum 

detection in the Round 1 cross-section was 200 μg/L and the median detection was 0.5 

μg/L. Detections were found in PWSs in 13 of the Round 1 cross-section 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 extrapolation from the Round 1 cross-section 

results estimates 290 systems, serving approximately 4.0 million people, have at least one 

sample detection of 1,1,2,2-tetrachloroethane. Approximately 140 systems, serving 

approximately 3.6 million people are estimated to have at least one sample detection of 

1,1,2,2-tetrachloroethane greater 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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EPA – OGWDW Analysis of Occurrence Data from the UCM and NIRS for CCL 2 June 2008

• 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. (MRLs varied from system to system. They 

ranged from 0.1 to 2.5 μg/L. The modal MRL value was 0.5 μg/L.) The maximum 

detection in the Round 2 cross-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-section States. Eighteen 

PWSs had detections of 1,1,2,2-tetrachloroethane greater than 1⁄2 HRL (0.2 μg/L) and 17 

PWSs had detections of 1,1,2,2-tetrachloroethane 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 extrapolation 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-tetrachloroethane. 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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EPA – OGWDW Analysis of Occurrence Data from the UCM and NIRS for CCL 2 June 2008

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 Stage 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 Radionuclides Survey (NIRS) Data ................................................. 27 

4.1 Description of Data........................................................................................................ 27 

4.2 Representativeness ........................................................................................................ 27 

4.3 Data Characteristics Overview ...................................................................................... 28 

4.4 Supplemental IOC Data................................................................................................. 29 

5. Developing a Nationally Representative 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 Stage 1 Occurrence Measures.............................................. 39 

6.5 Comparing Data Coverage of Round 1 and Round 2.................................................... 40 

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

7. Graphical and Spatial Assessments of the Contaminants 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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EPA – OGWDW Analysis of Occurrence Data from the UCM and NIRS for CCL 2 June 2008

Exhibits 

Exhibit 1.2.a. Diagram of the Inter-Relationship of the Databases, Monitoring Rounds and 

Contaminant Lists Discussed in the Report............................................................ 3 

Exhibit 1.2.b. List and Description of Contaminants with Round 1 and Round 2 Data 

Considered During CCL 2 Regulatory Determinations.......................................... 4 

Exhibit 1.2.c. Description of the Inorganic Chemical with data in NIRS Considered During 

CCL 2 Regulatory Determinations ......................................................................... 5 

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

Extrapolations ......................................................................................................... 8 

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

Territories.............................................................................................................. 13 

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

Territories.............................................................................................................. 22 

Exhibit 3.3.b. Summary of Round 2 Data Quantity 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 – Number of Records by Month......................................................... 28 

Exhibit 5.a. 24 Round 1 Cross-Section States and States Not Included in the Cross-Section . 33 

Exhibit 5.b. 20 Round 2 Cross-Section States and States Not Included 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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EPA – OGWDW Analysis of Occurrence Data from the UCM and NIRS for CCL 2 June 2008

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...................................................................................................... 38 

Exhibit 6.3.a. NIRS Data – Summary of Boron Occurrence in Surveyed Ground Water Systems 

- Based on the System Level................................................................................. 39 

Exhibit 6.3.b. NIRS Data – Summary of Boron 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 Metolachlor Detections in Both Cross-Section and 

Non-Cross-Section States (Round 2 Data) ........................................................... 45 

Exhibit 7.1.b. Geographic Distribution 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 Distribution of 1,3-Dichloropropene Detections in Both CrossSection and Non-Cross-Section States (Combined Rounds 1 and 2) ................... 47 

Exhibit 7.2.b. Geographic Distribution of 1,3-Dichloropropene Detection Frequencies in CrossSection States (Upper Map: Round 1; Lower Map: Round 2).............................. 48 

Exhibit 7.2.c. Geographic Distribution of 1,3-Dichloropropene Detection 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-Dichloropropene Detections (left) and HRL 

Exceedances (right), 1985 - 1997, in Select Cross-Section States ....................... 51 

Exhibit 7.2.e. Distribution of 1,3-Dichloropropene Detections (left) and HRL Exceedances 

(right) Among Select Cross-Section States........................................................... 51 

Exhibit 7.3.a. Geographic Distribution of 1,1,2,2-Tetrachloroethane Detections in Both 

Cross-Section and Non-Cross-Section States (Combined Rounds 1 and 2)......... 52 

Exhibit 7.3.b. Geographic Distribution of 1,1,2,2-Tetrachloroethane Detection Frequencies in 

Cross-Section States (Upper Map: Round 1; Lower Map: Round 2) ................... 53 

Exhibit 7.3.c. Geographic Distribution of 1,1,2,2-Tetrachloroethane 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 Frequency of 1,1,2,2-Tetrachloroethane Detections (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 Cross-Section States........................................................... 57 

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

xv 

Appendices 

APPENDIX A. Development of Health Reference Levels 

APPENDIX B. Detailed Round 1 Data Summary for 1,3-Dichloropropene, and 1,1,2,2-

Tetrachloroethane 

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

and 1,1,2,2-Tetrachloroethane 

APPENDIX D. Detailed NIRS Data Summary for Boron 

APPENDIX E. Data Summaries of Occurrence and Population Served for Four 

Contaminants Considered During CCL 2 Regulatory Determinations 

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

Acronyms

AWWARF American Water Works Association Research Foundation 

CAS Chemical Abstract Services 

CCL Contaminant Candidate List 

CCL 1 EPA’s First Contaminant 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 Level 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 Water and Drinking Water 

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

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 Information 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 Contaminant Monitoring Regulation 

URCIS Unregulated Contaminant Monitoring Information System 

VOC Volatile Organic Compound 
EPA – OGWDW Analysis of Occurrence Data from the UCM and NIRS for CCL 2 June 2008

1. Introduction 

This report presents an analysis of national occurrence in public drinking water systems 

of four unregulated contaminants: one inorganic 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 occurrence data for 1,1,2,2-tetrachloroethane, 1,3-

dichloropropene, and metolachlor. The occurrence data for boron were collected through the 

National Inorganics and Radionuclides Survey (NIRS). Reviews of these unregulated 

contaminant occurrence data sets, as well as detailed occurrence findings for 1,1,2,2-

tetrachlroethane, 1,3-dichloropropene, metolachlor and boron, are presented in this report. 

Additionally, the CCL 2 includes several contaminants monitored under the first Unregulated 

Contaminant Monitoring Regulation (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 tetrachloroterephthalate, also known as DCPA or 

dacthal; 1,3-dichloropropene; 2,4-dinitrotoluene; 2,6-dinitrotoluene; 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 Regulation (UCMR 1) in Support of Regulatory 

Determinations for the Second Drinking Water Contaminant Candidate List (USEPA, 2008a). 

 For those contaminants considered as part of the CCL 2 regulatory determinations, a 

Regulatory Determinations Support Document (USEPA, 2008b) provides contaminant-specific 

information regarding chemical and physical properties, use and release, and supplemental 

occurrence data and analyses. Based on contaminant occurrence, exposure, and other risk 

considerations, EPA must determine if regulating 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-setting 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 for drinking water, and therefore may require 

regulation under SDWA. 

 The first CCL (CCL 1) contained 60 contaminants, including 50 chemicals or chemical 

groups and 10 microbiological contaminants or microbial 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, consisting of all the contaminants from CCL 1 

that did not progress to regulatory determination. The 1996 SDWA Amendments require EPA to 

make determinations on whether or not to regulate at least five contaminants on a five-year 

1 
EPA – OGWDW Analysis of Occurrence Data from the UCM and NIRS for CCL 2 June 2008

cycle, or three and a half years after each CCL. This report presents contaminant occurrence 

findings that serve to support the second round of regulatory determinations. 

1.2 Sources of Data Used for Analysis 

 Brief descriptions of the occurrence data sources used in this report are provided in this 

section (see Sections 2, 3, 4, and 5 for more details 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 monitor for specified unregulated contaminants 

on a five-year cycle, and to report the monitoring results to the States. Data from the first round 

of monitoring starting in 1988 were stored in the Unregulated Contaminant Monitoring 

Information System (URCIS) database, referred 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 monitoring, starting in 1993, were stored in the Safe 

Drinking Water Information System/Federal version (SDWIS/FED1

) 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 occurrence 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 monitoring is to gather scientific information on the occurrence of 

these contaminants, to enable a decision regarding whether regulations were needed. EPA 

required all non-purchased community water systems (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 required to be available for monitoring if the State decided such 

monitoring was necessary. (As evident 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 monitoring. This new program was formally 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, putting 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 monitoring results are reported to EPA. Monitoring under 

UCMR 1 began in 2001. Every five years EPA must develop a new list of unregulated 

contaminants for UCMR monitoring. 

 Exhibit 1.2.a diagrams the inter-relationship of the various databases, monitoring rounds 

and contaminant lists related to the UCM Round 1 and Round 2 data. The Round 1 and Round 2 

databases contain occurrence data from other contaminants besides those required 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 database repository of data provided by public drinking water systems, and includes 

data from earlier EPA public water system databases. 

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

Also, although each database primarily contains data collected during the years of the two formal 

monitoring periods (1988-1992 and 1993-1997), there are some earlier “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 with 14 VOCs for discretionary monitoring. The 

UCM (1987) contaminants were first monitored 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 protocol in place that defined reporting 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 contaminants: the 34 UCM (1987) VOCs; the 21 

regulated Phase I VOCs; 2 regulated SOCs; and 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 discussed in Section 2 of 

this report. 

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

 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 included in the Round 2 monitoring. In the updated 

listing for the unregulated contaminants required 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 discretionary VOCs in UCM (1987)). The group 

numbering is somewhat reversed, with the first 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 database, 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 monitoring Rounds and Group reference numbers for the 

contaminants. Note that the minimum reporting 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-dichloropropene 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 

(μg/L)

HRL 

(μg/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 concentration data reflect a range of MRLs; the modal value is the most common MRL. 

HRL = Health Reference Level (concentration values used only as reference levels 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 report 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 

4 
EPA – OGWDW Analysis of Occurrence Data from the UCM and NIRS for CCL 2 June 2008

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 radionuclides and IOCs being considered 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 included in this report are conducted relative to 

the MRL. Analytical detections are samples with contaminants detected at concentrations equal 

to or greater than the MRL. An analytical non-detection is a sample that either had no 

contaminant present and therefore detected no contaminant 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 baseline 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 evaluating contaminant occurrence based on health 

effects information. By conducting occurrence assessments relative to several thresholds (such 

as the MRL, 1⁄2 HRL, and HRL), additional information is provided on the degree as well as the 

frequency of contaminant occurrence. This serves to better characterize the distribution of 

occurrence. 

 EPA evaluated the best available, peer-reviewed assessments and studies to characterize 

the human health effects that may result from exposure to individual contaminants when found in 

drinking water. Based on this characterization, the Agency estimated an HRL for each 

contaminant. For more details regarding the development of the HRLs, see Appendix A in this 

report.

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

 It is important to note that HRL values have been derived by EPA as a means to provide 

additional information regarding the distribution of occurrence and occurrence relative to 

concentrations of potential health effects. 

 Some contaminants with analytical detects may not have been detected at concentrations 

greater than their respective HRL or 1⁄2 HRL. Although many 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 occurrence measures cannot be made relative to concentration 

thresholds below (less than) the MRL. Thus, the 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 mean 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 analysis provides a straightforward evaluation of 

occurrence of all contaminants under consideration. This “Stage 1 analysis” of occurrence 

assesses the data sources, quality, and characteristics, and then uses 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 concentration 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 number of systems with a mean contaminant 

concentration exceeding a specified threshold and includes measures of uncertainty 

(corresponding confidence intervals based on calculated standard errors). The Stage 2 analysis 

uses statistical modeling to generate 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 maximum sample concentration results as in the Stage 1 analysis. The 

Stage 2 analysis also provides more direct estimates of potential chronic exposure since it is 

based on estimated annual (long-term) mean concentrations of contaminant occurrence. In a 

general sense, the Stage 1 analysis reflects an approximation of peak analytical results while the 

Stage 2 analysis estimates long-term, average occurrence. 

 

2

 Stage 2 analysis allows an assessment of systems with mean, rather than peak, concentrations estimated to exceed 

the HRL and 1⁄2 the HRL. Because the Stage 2 mean concentration estimates are based on annual, or longer-term, 

occurrence data, the Stage 2 analyses may be more appropriate for contaminants with chronic health effects. 

3

 These analyses are conservative in the sense that they are protective of human health (i.e., they are more likely to 

overestimate risks to human health than underestimate them). 

6 
EPA – OGWDW Analysis of Occurrence Data from the UCM and NIRS for CCL 2 June 2008

 Because none of the contaminants discussed in this report were found with significant 

levels of contaminant occurrence at or near the 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 other EPA Office of Ground Water and Drinking Water 

(OGWDW) national occurrence studies, including the first Six-Year Review of NPDWRs (see 

USEPA, 2003a). This data management and occurrence analytical approach was previously 

peer-reviewed for use under the Six-Year Review and, partly for consistency across OGWDW 

projects, has been adapted for the analyses of the CCL 2 regulatory determination occurrence 

data. A detailed description of the Stage 1 analytical 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 Determinations for the Second Drinking Water Contaminant 

Candidate List (USEPA, 2008a). 

1.5 Detailed Description of the Stage 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 public health concerns – in the sense that they are descriptive 

statistics based on peak, rather than long-term mean, concentrations of contaminants. The Stage 

1 analyses are conducted at both the system level and the population-served level, allowing 

exposure to be characterized both in terms of the number and percent of systems with detections, 

and the number and percent of population-served by systems with detections. Estimates based 

on the population served by PWSs provide a rudimentary characteristic of exposure potential. 

By conducting the Stage 1 analyses at the system 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 frequency portion of Stage 1 

analyses was conducted only on systems and the population-served. The only sample-level 

analyses that were conducted were calculations of the minimum, median, maximum, and 99th

percentile values. Note that due to the inherent vulnerability, occurrence pattern, and some 

regulatory differences between surface water-supplied and ground water-supplied PWSs, 

separate analyses were generated for surface water (SW) systems and ground water (GW) 

systems. All Stage 1 analytical findings are presented in Appendix 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 contaminant per system to model a system’s long-term mean concentration. As the 

NIRS only contains one record per contaminant per system, Stage 2 analyses were therefore not appropriate for the 

NIRS data set.

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

1.5.1 Extrapolation of National Cross-Section Results 

 The development of the UCM Round 1 and Round 2 national cross-sections enables 

occurrence analyses that are indicative of national occurrence. In addition, the NIRS data were 

collected for a statistically designed, nationally representative survey. Extrapolations provide the 

best available estimate of contaminant occurrence on a nationwide scale. To calculate the 

extrapolations, the total national 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 threshold exceedance (e.g., % systems > 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 Systems and Population Served Systems 

Used in All National Extrapolations

 

National Inventory of Source Water CWSs plus NTNCWSs 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 detection of metolachlor, 

for example, the percentage of ground water systems from the Round 2 cross-section with 

detections of metolachlor (0.113%) is multiplied 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 given 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 nationally). Extrapolated results are presented in 

Section 6.4 and Appendix E. 

1.6 Analytical Tools 

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

statistical software. Some data formatting 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 typically 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. 

8 
EPA – OGWDW Analysis of Occurrence Data from the UCM and NIRS for CCL 2 June 2008

2. UCM Round 1 Data Overview 

 In this section of the report, the monitoring results for the UCM program Round 1 data 

(from approximately 1988-1992) are reviewed. The data were derived from EPA’s Unregulated 

Contaminant Information System database. As described 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 problems were encountered. The data were supplied 

by States on a variety of media, ranging from photocopies 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, other 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 Monitoring Reform (CMR) project. That report, A 

Review of Contaminant Occurrence 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) Regulatory 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 for eight contaminants on the 1998 CCL. It was followed by the 

Analysis of National Occurrence 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 contaminants discussed in this current report 

(1,3-dichloropropene and 1,1,2,2-tetrachloroethane). As descriptions of occurrence based on the 

Round 1 database have been covered thoroughly elsewhere, this current report presents only the 

information related to understanding occurrence findings for the contaminants evaluated for CCL 

2 regulatory determinations. For the most comprehensive 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 for 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), “Unregulated 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.) 

9 
EPA – OGWDW Analysis of Occurrence Data from the UCM and NIRS for CCL 2 June 2008

CCL 1 contaminants. Some of the actual analytical findings developed and presented in the 

Occurrence of 14 Report (USEPA, 2003) are used in the current report. Other analyses, 

including new analyses using updated 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 SOCs 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 older 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 reviewed 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 initial database download and translation, 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 source type specified, but this missing inventory 

information was supplemented with SDWIS inventory data.) Five observations with 

contaminant concentrations greater than 9,000 μg/L were excluded from the analysis (as 

presumed errors; this outlier editing was consistent with other processing that EPA has 

completed, see USEPA, 1999). Another 1,503 observations 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 procedures 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, there 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 recorded in incorrect units, (e.g., the results are 

actually in mg/L, but are recorded as μg/L) or data units mistakenly converted in the original 

compilation of the data (e.g., the data units were actually in μg/L, were incorrectly 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 this did not affect many data. There are a few apparently high 

analytical results (outliers) that may be caused by this units problem. While outliers affect a 

review of the maximum concentration 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 99th percentile is presented to avoid 

this problem.) 

10 
EPA – OGWDW Analysis of Occurrence Data from the UCM and NIRS for CCL 2 June 2008

2.3 Round 1 Data Bias and Representativeness: 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 report 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 there are data for 38 States, the Virgin Islands, 

and Washington, D.C., and no data for 17 primacy entities. Some States only reported data for 

detections. For eight States (identified in Exhibit 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 from 80-100%. These States only reported data for detections 

and, hence, are highly biased (they did not report 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 (aggregating 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 compared to the total number of non-purchased 

CWSs and NTNCWSs in the current State inventory, and to the number of non-purchased CWSs 

and NTNCWSs serving more than 500 people (since not all small systems may have had to 

conduct this monitoring). The States identified as “Most 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 their 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. For example, Colorado only has Round 1 data for 60 

PWSs. This represents only 24% of the reported 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 analytical record, since not all non-detection records have been 

reported (such as records from the likely large number 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 records. Another five States are 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 relative completeness of reporting. For example, 

the States reporting only samples with detections typically reported 2 to 10 samples per PWS. 

For most States, approximately 100 to 300 samples were collected and reported per PWS. 

11 
EPA – OGWDW Analysis of Occurrence Data from the UCM and NIRS for CCL 2 June 2008

 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 based on inventory listings), but that have other 

parameters (e.g., “Percent Sample Detections,” “Samples per PWS,” etc.) that suggest that the 

data are balanced and perhaps complete for the systems that did report. The relatively low 

system numbers may simply relate to how the State implemented the program (e.g., 

implementation related to system size or other waivers, etc.). For example, Florida reported data 

for 855 PWSs, a substantive number, but it’s only a small share of their relatively large 

inventory. Nevertheless, the whole data picture for Florida (e.g., the total detection rate) appears 

balanced. 

 In summary, of the 40 States/territories with Round 1 data, 21 States had records that 

appear relatively complete and balanced, and another 6 had records 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 since 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 representativeness (to be discussed in Section 4) and considered for 

inclusion in the subsequent analyses. 

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

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

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

Tribes and Territories 

 

From the 27 States with reasonably complete data, three primacy entities were removed. 

Washington, D.C. and the Virgin Islands were removed because they are not States, and the New 

York State data were excluded because there were various and numerous problems associated 

with the data and metadata. For example, New York did not use standard PWS identifiers 

(PWSIDs) that could be associated 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 million records were available for analysis 

representing more than 24,000 PWSs from the 40 States/entities. For the 24 States comprising 

the Round 1 representative cross-section (see Section 6 for a discussion regarding cross-section), 

the analytical results total 3.27 million records, from 22,034 PWSs. 

 

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

 For both all states and the 24-state cross-section, Exhibit 2.4.a reports the number and 

percentage of sample records and systems related to source water type: 87% of the systems are 

classified as ground water and 13% as using surface water. The Round 1 data were collected 

before “ground water under the direct influence of surface water” (GWUDI) was introduced as a 

source definition. The classification used follows the regulatory guidelines: 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 shows 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 water systems, or transient systems. Transient 

PWSs were not required by Federal rule to monitor, but may have been required to by some 

States. Also, about 7% of the systems did not indicate 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. 

15 
EPA – OGWDW Analysis of Occurrence Data from the UCM and NIRS for CCL 2 June 2008

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 collected, with a peak of data collection in 1991. 

Records prior to 1988 predate the formal beginning of first round monitoring, but represent 

comparable data, and are therefore included to expand the coverage of these analyses. Exhibit 

2.4.c shows the distribution of records for the years 1983-19927, while Exhibit 2.4.d shows the 

monthly distribution of all the records used in the Round 1 analyses for the same time period. 

 Records were well distributed throughout the year, with an average of 272,304 records 

per month for the 24-State cross-section. Although in the month of March 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 differences in reporting. For Round 1 data from the 

24-State cross-section, the total 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 (July) 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. 

16 
EPA – OGWDW Analysis of Occurrence Data from the UCM and NIRS for CCL 2 June 2008

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 occurrence data for 1,3-

dichloropropene and 1,1,2,2-tetrachloroethane are developed and summarized in Section 6 of this 

report. 

17 
EPA – OGWDW Analysis of Occurrence Data from the UCM and NIRS for CCL 2 June 2008

18 
EPA – OGWDW Analysis of Occurrence Data from the UCM and NIRS for CCL 2 June 2008

3. UCM Round 2 Data Overview

 In this section of the 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) were derived from the SDWIS/FED (or “Round 2”) 

database. Significant data review, formatting, 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 report 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 formally 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 are 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 described 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 Priority Contaminants in Public 

Water Systems (the “Priority Contaminants Report;” USEPA, 2002), which contains more 

detailed information on data management and analysis of the Round 2 database, and the Analysis 

of National Occurrence of 14 Contaminants from the 1998 Contaminant 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 developed and presented in USEPA 

(2003) are used in this current report. Other analyses, including those based on updated HRLs, 

have been conducted for, and are presented in, this current report. 

3.2 Data Management and Data Quality 

 The raw Round 2 data from the 35 States/primacy entities contained 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 including reporting consistencies, uniform and valid coding, data 

completeness, correct and consistent use of analytical units, and any inherent bias in the raw 

records. To ensure data quality for sound and dependable occurrence analysis, extensive data 

review, checking, and editing were required. This data management and quality review process 

identified and addressed problematic data or data that could not 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 initial 4,350,874 analytical records from the 35 States/primacy entities 

for the 48 contaminants decreased to 4,211,446 analytical records for this Round 2 analysis. 

19 
EPA – OGWDW Analysis of Occurrence Data from the UCM and NIRS for CCL 2 June 2008

3.3 Round 2 Data Bias and Representativeness: Further 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 Round 1 data, various descriptive statistics were 

compiled by State to enable a further more detailed data review to assess data bias and 

representativeness. Some State data, as described below, are seriously biased because they are 

so incomplete, and should only be used with caution for any statistical summary of occurrence. 

 Exhibits 3.3.a and 3.3.b summarize some key results from this next stage of Round 2 data 

review. Together, they summarize the data availability and data quality for 57 primacy entities 

considered under SDWA (the 50 States, 5 territories 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 Exhibit 3.3.b as “Entities with 

Data Sets with 100% Detects.” These States reported only (or mainly) analytical records for 

detections and, hence, their data sets are highly biased (over-representing occurrence) and are 

therefore excluded from additional analysis. As shown in Exhibit 3.3.a, the percent samples with 

detections typically range 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 Exhibit 3.3.a. These summary statistics provide a 

perspective on the relative completeness of reporting. The number of PWSs included were 

compared to the total number of non-purchased CWSs and NTNCWSs in the current State 

inventory, and to the number of non-purchased CWSs and NTNCWSs serving more than 500 

people (since not all small systems may have had to conduct this monitoring). Most States 

approximated or exceeded 100% of one of these comparative inventory numbers. The States 

(entities) identified with “Significantly Too Few Systems” in Exhibit 3.3.b have data reported 

from far fewer systems than listed in the current State inventory. For example, 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 significant 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. The data from Louisiana, 

Pennsylvania, South Carolina, and Vermont were very problematic. For instance, 100% of the 

data reported by Louisiana (for a very large number of systems and samples) were nondetections. There were no positive analytical findings of contaminant occurrence in the 164,492 

20 
EPA – OGWDW Analysis of Occurrence Data from the UCM and NIRS for CCL 2 June 2008

sample results reported. Data from 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 States with data records 

that are reasonably balanced and perhaps complete 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 the analytical results for each State in even 

more detail. For example, the minimum, median, 99th 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 were identified within the data sets of the 20 

Round 2 cross-section States. Most of these problems were determined to be specific to certain 

contaminants (or contaminant groups). With additional data editing efforts, these problems have 

either been resolved or the problematic portion of data omitted from further analysis. For 

additional discussion of specific problems, refer to Section III.C of the Priority Contaminants 

Report (USEPA, 2002). 

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

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

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 perspective 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 cross-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 using all 35 States/entities. The Round 2 data contains 

systems using GWUDI as a source definition. The classification used follows the regulatory 

guidelines: if a system uses any surface water (such as a GWUDI), it is classified as a surface 

water system. 

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

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-State cross-section were CWSs and 30% were 

NTNCWSs. The CWS percentage was slightly higher for the entire 35 States/entities data set, 

and the percentage for NTNCWS correspondingly 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 distribution of data by years and by month (based on 

actual sample collection or analysis date). These tables only present the 20-State cross-section 

data. Exhibit 3.4.c indicates the amount of data annually collected 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 that 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 average of 307,907 records per month. Trends were 

similar for the entire 35 States/entities data set as for the 20-State cross-section. For a more 

24 
EPA – OGWDW Analysis of Occurrence Data from the UCM and NIRS for CCL 2 June 2008

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 occurrence data for 1,3-

dichloropropene, 1,1,2,2-tetrachlorethane, metolachlor are developed and summarized in Section 

6 of this report. 

25 
EPA – OGWDW Analysis of Occurrence Data from the UCM and NIRS for CCL 2 June 2008

26 
EPA – OGWDW Analysis of Occurrence Data from the UCM and NIRS for CCL 2 June 2008

4. National Inorganics And Radionuclides Survey (NIRS) Data 

 The EPA’s NIRS occurrence data are assessed for one contaminant considered during 

CCL 2 regulatory determinations, boron, and are only applicable for PWSs served by ground 

water. 

4.1 Description of Data 

 The NIRS survey was conducted by EPA specifically to provide data on the occurrence 

of a select set of radionuclides and IOCs being considered for NPDWRs. The NIRS provides 

contaminant occurrence data from 989 CWSs served 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 contaminant 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 selection 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, random sampling of the nation’s community 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 there are many more small than large PWSs in the 

US, most of the NIRS data are from smaller systems. In aggregate, approximately 95% of the 

analytical sample results in the entire NIRS database indicate no detections of the contaminants 

sampled and analyzed. The NIRS database includes information on 42 contaminants, including: 

36 IOCs (including 10 regulated IOCs), 2 regulated radionuclides, and 4 unregulated 

radionuclides. The data are from 49 States (there are no data from Hawaii), as well as Puerto 

Rico. One contaminant from the NIRS is evaluated 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 contained in the NIRS database are nationally 

representative of ground water systems, and furthermore, 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 contains 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. Also, there are often computational (statistical) 

problems resulting from multiple laboratory analytical 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 limits were employed. Therefore, the extensive 

concerns and problems with data quality, completeness, and representativeness encountered in 

the use of Round 1 or 2 data are not issues when considering the use of the NIRS data. 

27 
EPA – OGWDW Analysis of Occurrence Data from the UCM and NIRS for CCL 2 June 2008

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 information 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 distribution of data by years and by month across all 

years. The data were collected between 1984 and 1986, with a peak of data collection in 1985. 

Somewhat more samples were collected in 1985, 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 likely 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%

28 
EPA – OGWDW Analysis of Occurrence Data from the UCM and NIRS for CCL 2 June 2008

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 the potential occurrence of boron in surface water systems, EPA 

evaluated a report funded by the American Water Works Association 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 boron 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 boron levels less than 1.054 mg/L; the maximum 

observed concentration in ground water was approximately 3.3 mg/L. Seven of the 228 ground 

water sources (from 5 systems) had boron concentrations greater than 1.4 mg/L (Seidel, 2006). 

29 
EPA – OGWDW Analysis of Occurrence Data from the UCM and NIRS for CCL 2 June 2008

30 
EPA – OGWDW Analysis of Occurrence Data from the UCM and NIRS for CCL 2 June 2008

5. Developing a Nationally Representative Perspective

 As discussed in previous sections of this report, the Round 1 and Round 2 databases 

contain contaminant occurrence data from a total of 40 and 35 States/entities, respectively. 

However, data from many of these States are incomplete, problematic, and/or biased. An 

evaluation of these data suggested that data from certain States were most complete and might, 

therefore, be used to generate summary statistics indicative of national contaminant occurrence. 

The representativeness of the State data was evaluated across a range of potential contaminant 

occurrence and across the spatial/hydrologic diversity 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 databases was supported by peer reviewers and by 

stakeholders as providing a clear, replicable, and understandable approach. Although this 

approach cannot provide a statistically representative sample (since the data could not be 

selected in a statistically random manner), the resultant data provide a clear indication of the 

central tendency of national occurrence. 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 national cross-section were evaluated 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 cross-sectional balance was based on evaluating the 

States’ pollution potential and geographic 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 likely high and low occurrence. Geographic 

consideration was included so that the wide range of climatic and hydrogeologic conditions 

across the United States would be represented, again balancing the varied conditions that affect 

transport and fate of contaminants. Two primary indicators were chosen to represent pollution 

potential in each State: the number 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 second indicator was taken from the 1992 Census of 

Agriculture (USDOC, 1994). 

 The states were divided into quartiles based on their pollution potential rankings for the 

two indicators, and the cross-section states were chosen to ensure equitable representation from 

each quartile. In addition, some secondary pollution potential indicators were considered to 

further ensure that the cross-section states included the spectrum of pollution potential conditions 

(high to low). At the same time, care was taken to ensure that the cross-section provided 

representative coverage across all geographic regions of the United States. 

 

31 
EPA – OGWDW Analysis of Occurrence Data from the UCM and NIRS for CCL 2 June 2008

The product of the data quality screening, pollution potential rankings, and geographic 

coverage analysis was a national cross-section of 24 Round 1 states and a national cross-section 

of 20 Round 2 states (see Exhibit 5.a-b). The 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-section 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 varied 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-section, 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 derived from cross-sections including 

biased data. Following this comparison, the 24-State cross-section appeared to be a successful 

balance between the problems associated with too little data (unrepresentative sampling) and 

those associated with too much data (including “bad” or biased data). Consequently, although 

they are not “statistically representative,” both the 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-sections, see Section V of the Priority Contaminants Report 

(USEPA, 2002). 

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

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 

33 
EPA – OGWDW Analysis of Occurrence Data from the UCM and NIRS for CCL 2 June 2008

34 
EPA – OGWDW Analysis of Occurrence Data from the UCM and NIRS for CCL 2 June 2008

6. Analysis of National Occurrence

 This section of the report contains detailed occurrence assessments of four contaminants 

considered during CCL 2 regulatory determinations: 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 series of graphs and maps are presented as a complimentary 

graphical evaluation of the occurrence of these four contaminants. 

 The summary data developed for the occurrence 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 Round 2 contaminants. Appendix D presents an 

analysis of the NIRS data for boron. Detailed summaries of all four contaminants are presented 

in Appendix E. At the beginning of the Appendices section, a complete “List of Appendix 

Tables” identifies all tables included in the four appendices. Also included are “Notes to 

Accompany Unregulated Contaminant Occurrence Data 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-section occurrence data 

for 1,3-dichloropropene and 1,1,2,2-tetrachloroethane. For both 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 database. Approximately 2% of the population served by PWSs had 

analytical detections of 1,1,2,2-tetrachloroethane while less than 1% of the population served by 

PWSs had detections of 1,3-dichloropropene. While detection frequencies of both contaminants 

suggest very low levels of national occurrence, both contaminants also were found more 

frequently in surface water PWSs than ground water 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 contaminants in surface water) suggests that both 

contaminants are only very rarely found in concentrations surpassing the defined health-based 

thresholds. Because much of the 1,1,2,2-tetrachloroethane and 1,3-dichloropropene occurrence 

data were generated using laboratory methods with MRLs higher than the respective HRLs and 

1⁄2 HRLs, it is likely that occurrence analyses 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 and 1,3-dichloropropene occurrence relative to their respective 

HRLs and 1⁄2 HRLs. Although many of the MRLs 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. 

35 
EPA – OGWDW Analysis of Occurrence Data from the UCM and NIRS for CCL 2 June 2008

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 μg/L)

Percentile 

Value 

(μg/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 Water; MRL = Minimum Reporting Limit (for laboratory analyses); 

HRL = Health Reference Level (concentration values used only as reference levels for analyses in this report). “% PWSs > HRL” 

indicates the proportion of systems with any analytical results 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 μg/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 Water; MRL = Minimum Reporting Limit (for laboratory analyses); 

HRL = Health Reference Level (concentration values used only as reference levels for analyses in this report). “% Population 

Served by PWSs > HRL” indicates the proportion of population served 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-section data are discussed in Section 5 of this report, and are 

identified in Exhibit 5.b. Exhibit 6.2.a summarizes the Round 2 20-state cross-section 

occurrence data for metolachlor, 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, almost 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-

36 
EPA – OGWDW Analysis of Occurrence Data from the UCM and NIRS for CCL 2 June 2008

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-dichloropropene and 1,1,2,2-tetrachloroethane is less than 0.25%, 

suggesting that these contaminants are only very rarely found in concentrations surpassing the 

defined HRL. No PWSs had any analytical results of metolachlor 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 μg/L)

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

Percentile 

Value 

Total GW SW Total GW SW Total GW SW (μg/L)

SOCs

Metolachlor1 

(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 summary statistics for this contaminant. 

PWS = Public Water System; GW = Ground Water; SW = Surface Water; MRL = Minimum Reporting Limit (for laboratory analyses); 

HRL = Health Reference Level (concentration values used only as reference levels for analyses in this report). “% PWSs > HRL” 

indicates the proportion of systems with any analytical results exceeding the concentration value of the HRL. 99th Percentile Value = 

the 99th percentile of all samples, not just those with detections.

37 
EPA – OGWDW Analysis of Occurrence Data from the UCM and NIRS for CCL 2 June 2008

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 μg/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

Metolachlor1 

(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 Water; MRL = Minimum Reporting Limit (for laboratory analyses); 

HRL = Health Reference Level (concentration 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 (for ground water systems only) for boron. Nearly 82% of PWSs, 

serving 88% of the population served, had analytical detections of boron. This is consistent with 

the known widespread natural occurrence of boron in soil and minerals. The percentage of 

systems with at least one sample analytical result greater than the HRL (1.7%) is higher than the 

other contaminants analyzed, again indicating boron’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 systems 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 example, 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 sampled nationally for boron will also have 

detections greater than the specified HRL. Furthermore, 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 than the specified HRL. 

38 
EPA – OGWDW Analysis of Occurrence Data from the UCM and NIRS for CCL 2 June 2008

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 of 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; MRL = Minimum Reporting Limit (for laboratory analyses); HRL = Health Reference Level 

(concentration values used only as reference levels for analyses in this report).

6.4 National Extrapolation of Stage 1 Occurrence Measures 

 As stated earlier, both the Round 1 and Round 2 cross-sections, as well as the NIRS 

database, were developed to be nationally representative. National estimates of the contaminant 

occurrence data can be generated via extrapolations. Exhibit 6.4 presents the national 

extrapolations of the Stage 1 occurrence measures 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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EPA – OGWDW Analysis of Occurrence Data from the UCM and NIRS for CCL 2 June 2008

Exhibit 6.4. National Extrapolation of Stage 1 Occurrence Measures 

Detections (≥ MRL) Detections > 1⁄2 HRL 

Chemical Name Source 

(HRL) Water Type Population Population Systems Systems Served Served

National Extrapolation of Round 1 24-State Cross-Section Data

GW 72 508,000 72 508,000 

 1,3- 

 Dichloropropene SW 31 1,262,000 31 1,262,000 

 (0.4 μg/L) 

Total 106 1,825,000 106 1,825,000 

GW 229 1,564,000 105 1,329,000 

 1,1,2,2- 

 Tetrachloroethane SW 57 2,166,000 33 2,131,000 

 (0.4 μg/L) 

Total 290 3,963,000 140 3,592,000 

Detections > HRL 

Population Systems Served

72 508,000

31 1,262,000

106 1,825,000 

102 1,309,000

27 2,013,000

131 3,472,000 

National Extrapolation of Round 2 20-State Cross-Section 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 μg/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- 

 Dichloropropene 

 (0.4 μg/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- 

 Tetrachloroethane 

 (0.4 μg/L) 

Total 50 5,563,000 47 1,082,000 45 168,000 

National Extrapolation of NIRS Data 

 Boron 

 (1.4 mg/L) GW (only) 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 databases. As previously noted, Round 1 consisted of 

data from 40 States/territories and Round 2 consisted of data from 35 States/territories. 

 

 Exhibit 6.4 illustrates the States 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 quality issues (see Exhibit 2.3.a and Exhibit 3.3.a). 

Many States reported analytical results from a very low proportion of systems, reported results in 

mixed units, and/or reported only analytical detections (highly censored reporting) in Round 1 

and/or Round 2. 

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

 Of the 25 States in both Round 1 and 2 (identified 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 Mexico, 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 Round 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, because 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 Round 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 percentage 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 

41 
EPA – OGWDW Analysis of Occurrence Data from the UCM and NIRS for CCL 2 June 2008

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 unregulated Group 3 and Group 4 VOCs reported in Round 2 were also 

reported in Round 1. None of the regulated VOCs reported in Round 1, however, were reported 

in Round 2. Summary data for the two VOCs 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 (Tables E.3 and E.4) and comparisons between the 

rounds can be made. Further comparisons, in graphical form, are presented in Sections 7.2 and 

7.3 of this report. 

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

7. Graphical and Spatial Assessments of the Contaminants Considered During 

CCL 2 Regulatory Determinations 

This section presents graphical assessments of the contaminants considered during CCL 2 

regulatory determinations with data in the Round 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 additional State data to increase spatial coverage. 

The occurrence data used for all of the following maps and graphs are 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 considered as part of any conclusions drawn from the 

maps and graphs in this report. This development was discussed for Round 1 and Round 2 data 

in Section 5. The national cross-sections are developed from PWSs’ contaminant monitoring 

data with the intent that, in aggregate, the cross-section States’ occurrence findings are indicative 

of national occurrence. (Various occurrence 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 context 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 patterns may be difficult to characterize and must be interpreted 

with caution. Supplemental information should be collected and used, whenever possible, to 

assist in evaluating the significance of any apparent 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 interpretation 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 than that provided by the Round 1 or Round 2 databases. Also, the NIRS 

data reflect a single sample per system (in contrast 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 the national level and not at any regional or State level); therefore, 

no maps or graphs using the NIRS data for boron are included. 

 Most of the exhibits below that illustrate distribution of occurrence are based on nonbiased data; for these exhibits only the cross-section State data are used to develop the maps and 

graphs. However, to increase the spatial coverage of the exhibits that broadly identify 

contaminant occurrence (Exhibits 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 these 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. 

43 
EPA – OGWDW Analysis of Occurrence Data from the UCM and NIRS for CCL 2 June 2008

7.1 Metolachlor 

 There are only Round 2 occurrence data for metolachlor. Based on these data, 

metolachlor appears to occur throughout the United States, especially in the eastern half of the 

country. Fifteen of the 24 States with metolachlor 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 for 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 trend 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 analytical detections are Kentucky and Rhode Island. No States had 

any analytical results of metolachlor greater than the HRL of 70 μg/L. Although occurrence is 

relatively widespread, the degree of occurrence (as measured by concentration) appears low. 

44 
EPA – OGWDW Analysis of Occurrence Data from the UCM and NIRS for CCL 2 June 2008

Exhibit 7.1.a. Geographic Distribution of Metolachlor Detections in Both CrossSection and Non-Cross-Section States (Round 2 Data) 

Exhibit 7.1.b. Geographic Distribution of Metolachlor Detection Frequencies in 

Cross-Section States (Round 2 Data) 

45 
EPA – OGWDW Analysis of Occurrence Data from the UCM and NIRS for CCL 2 June 2008

 Metolachlor occurrence over time, relative to the MRL, is presented in Exhibit 7.1.c. 

Based on these data, the highest percentage of PWSs 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 subsequent years; however, there 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 for Food and Agricultural Policy (NCFAP), around 

1992 approximately 59.4 million pounds of metolachlor active ingredient (a.i.) were applied 

annually to 16 types of crops on 32.4 million acres, and around 1997 approximately 67.3 million 

pounds of metolachlor a.i. were applied annually 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 Metolachlor 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 
EPA – OGWDW Analysis of Occurrence Data from the UCM and NIRS for CCL 2 June 2008

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-dichloropropene are widely distributed across the 

United States (see Exhibit 7.2.a, which includes all States, both cross-section and non-crosssection States, from both the Round 1 and 2 databases). 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 Distribution of 1,3-Dichloropropene Detections in Both 

Cross-Section and Non-Cross-Section States (Combined Rounds 1 and 2) 

47 
EPA – OGWDW Analysis of Occurrence Data from the UCM and NIRS for CCL 2 June 2008

Exhibit 7.2.b. Geographic Distribution of 1,3-Dichloropropene Detection 

Frequencies in Cross-Section States (Upper Map: Round 1; Lower Map: Round 2) 

 

 

48 
EPA – OGWDW Analysis of Occurrence Data from the UCM and NIRS for CCL 2 June 2008

Exhibit 7.2.c presents the combined Round 1 and Round 2 Cross-Section States with 

analytical detections of 1,3-dichloropropene equal 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 frequencies for the maps below are not averages of 

Round 1 and Round 2 data. The States with the highest 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 concentrations 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-dichloropropene, and elevated concentrations, relative to 

the other States in the cross-sections. 

49 
EPA – OGWDW Analysis of Occurrence Data from the UCM and NIRS for CCL 2 June 2008

Exhibit 7.2.c. Geographic Distribution of 1,3-Dichloropropene Detection 

Frequencies (upper map) and HRL Exceedance Frequencies (lower map) for All 

Round 1 and Round 2 Cross-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 the UCM and NIRS for CCL 2 June 2008

occurrence data in both the Round 1 and Round 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 variability 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 subsequent 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 occurrence between 1992 and 

1994; the use and release of 1,3-dichloropropene decreased throughout the 1990s (Chapter 6 of 

USEPA, 2008b). Exhibit 7.2.e presents the occurrence of 1,3-dichloropropene 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 Frequency 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 μg/L. 

Exhibit 7.2.e. Distribution of 1,3-Dichloropropene Detections (left) and HRL 

Exceedances (right) Among Select 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-dichloropropene data in both Round 1 and Round 2. The Health Reference 

Level (HRL) used for 1,3-dichloropropene is 0.4 μg/L. 

51 
EPA – OGWDW Analysis of Occurrence Data from the UCM and NIRS for CCL 2 June 2008

7.3 1,1,2,2-Tetrachloroethane 

 Both Round 1 and Round 2 contain occurrence 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 pattern (see Exhibit 7.3.a, which 

includes all States, both cross-section and non-cross-section States, from both Round 1 and 2 

databases). Twenty-five of 46 States with 1,1,2,2-tetrachloroethane data 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 for the Round 1 cross-section 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 0.01 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 proportion of analytical detections. 

South Dakota has an especially high percentage of detections with 11.64%. Florida is the second 

highest with 4.15%. 

Exhibit 7.3.a. Geographic Distribution of 1,1,2,2-Tetrachloroethane Detections in 

Both Cross-Section and Non-Cross-Section States (Combined Rounds 1 and 2) 

52 
EPA – OGWDW Analysis of Occurrence Data from the UCM and NIRS for CCL 2 June 2008

Exhibit 7.3.b. Geographic Distribution of 1,1,2,2-Tetrachloroethane Detection 

Frequencies in Cross-Section States (Upper Map: Round 1; Lower Map: Round 2) 

 

53 
EPA – OGWDW Analysis of Occurrence Data from the UCM and NIRS for CCL 2 June 2008

Exhibit 7.3.c presents the combined Round 1 and Round 2 States with analytical 

detections of 1,1,2,2-tetrachloroethane equal to or greater than the MRL (upper map) and greater 

than the HRL (lower map). Each State shows the highest percentage of system detections for 

either Round 1 or Round 2 – State detection frequencies for the maps below are not averages of 

Round 1 and Round 2 data. As presented previously, 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 (between 0.65% and 2.76%) of 1,1,2,2-tetrachloroethane 

concentrations greater than the HRL are Utah, Alabama, and Florida. In Round 2, North 

Carolina is the only State to have more than 0.50% system detections greater than the HRL. 

54 
EPA – OGWDW Analysis of Occurrence Data from the UCM and NIRS for CCL 2 June 2008

Exhibit 7.3.c. Geographic Distribution of 1,1,2,2-Tetrachloroethane Detection 

Frequencies (upper map) and HRL Exceedance Frequencies (lower map) for All 

Round 1 and Round 2 Cross-Section States 

 

55 
EPA – OGWDW Analysis of Occurrence Data from the UCM and NIRS for CCL 2 June 2008

1,1,2,2-Tetrachloroethane occurrence 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 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 7.3.d, the graphs suggest annual variability in occurrence 

between 1988 and 1997, with a spike in concentrations in 1994. Detections greater than the HRL 

were disproportionately observed in 1988 (Round 1) and 1994 (Round 2). Many fewer PWSs 

collected 1,1,2,2-tetrachloroethane samples in Round 1 compared to Round 2; thus, any 

detections that occurred in the Round 1 data caused the overall percentage of PWSs with 1,1,2,2-

tetrachloroethane detections to appear elevated. It is unclear why there were more detections of 

1,1,2,2-tetrachloroethane in 1994 compared to other years. Production for commercial uses in 

the United States ceased by the late 1980’s and releases 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 Frequency of 1,1,2,2-Tetrachloroethane Detections (left) and 

HRL Exceedances (right), 1985 - 1997, in Select Cross-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 μg/L. 

56 
EPA – OGWDW Analysis of Occurrence Data from the UCM and NIRS for CCL 2 June 2008

Exhibit 7.3.e. Distribution of 1,1,2,2-Tetrachloroethane Detections (left) and HRL 

Exceedances (right) Among Select 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 μg/L. 

57 
EPA – OGWDW Analysis of Occurrence Data from the UCM and NIRS for CCL 2 June 2008

58 
EPA – OGWDW Analysis of Occurrence Data from the UCM and NIRS for CCL 2 June 2008

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 Policy (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-sponsored study, with data in an attached 

spreadsheet]. Denver, CO: McGuire Malcolm Pirnie; May 19, 2006. 

U.S. Department of Commerce (USDOC), Bureau 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 Annual 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 Contaminants 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 Contaminant Candidate List. EPA 815-R-08-013. June 2008. 

USEPA. 2008b. Regulatory Determinations Support Document 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 Health Reference Levels (HRLs) 

APPENDIX B. Detailed Round 1 Data Summary for 

 1,3-Dichloropropene, and 1,1,2,2-Tetrachloroethane 

APPENDIX C. Detailed Round 2 Data Summary for Metolachlor, 

 1,3-Dichloropropene, and 1,1,2,2-Tetrachloroethane 

APPENDIX D. Detailed NIRS Data Summary for Boron 

APPENDIX E. Data Summaries of Occurrence 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 Health 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 appendix describes the overall 

process the Agency used to evaluate health effects 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 approach used to identify and evaluate information on 

hazard and dose-response for the contaminants under consideration. 

 There are two different approaches to the derivation 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 carcinogens evaluated using a non-linear approach. 

Use of Carcinogenicity Data for the Derivation of a Health Reference Level

 Two of the contaminants discussed in this report 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 contaminants, 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 extrapolation to calculate risk-specific doses. The riskspecific doses are the estimated oral exposures associated with lifetime 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 day) are combined with adult body weight and 

drinking water consumption data to estimate drinking 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 evaluated 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 contaminant, EPA calculated a reference 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 appreciable risk of deleterious effects during a lifetime. It can be 

derived from either a “no-observed-adverse-effect level” (NOAEL), a “lowest-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 address 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 RfD from experimental data. Individual UFs are 

intended to account for: 

(1) the variation in sensitivity among the 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, assumed to be 70 kilograms (kg) 

DWI = Drinking Water Intake, assumed to be 2 L/day (90th 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 occurrence 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 conjunction with a 20 percent RSC to derive a 

conservative HRL estimate and perform an initial screening of the drinking water occurrence 

data. Since the initial screening of the occurrence data at this conservative HRL value resulted in 

negligible occurrence findings for 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-Dichloropropene 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-Dichloropropene Occurrence in Public Water Systems - 

Based on Population Served 

 Table B.2.a Round 1 Data - 1,1,2,2-Tetrachloroethane 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-Tetrachloroethane 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 minimum, 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

GA 1,161 2,460 1,861 599 0.00% 0.00% 0.00% < 0.50 < 0.50 < 0.50

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 minimum, 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

> MRL

% PWS

> 1⁄2 HRL

% GW

PWS 

> 1⁄2 HRL

% SW 

PWS 

> 1⁄2 HRL

% PWS 

> HRL

% GW 

PWS 

> HRL

% SW 

PWS 

> HRL

AK 1,610 661 532 134 0.30% 0.19% 0.75% 0.30% 0.19% 0.75% 0.30% 0.19% 0.75%

AL 351 131 93 42 2.29% 2.15% 2.38% 2.29% 2.15% 2.38% 2.29% 2.15% 2.38%

AR

AZ 2,932 944 874 106 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00%

CA 11,667 3,522 3,495 37 0.31% 0.31% 0.00% 0.31% 0.31% 0.00% 0.31% 0.31% 0.00%

CO 33 9 7 3 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00%

DC 62 1 1 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00%

DE 333 13 11 2 15.38% 18.18% 0.00% 15.38% 18.18% 0.00% 7.69% 9.09% 0.00%

FL 315 217 42 196 4.15% 4.76% 3.57% 2.76% 4.76% 2.04% 2.76% 4.76% 2.04%

GA 2,460 1,161 1,052 109 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00%

HI 1,221 127 112 16 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00%

IA 1,908 1,002 963 39 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00%

IL 6,002 1,302 1,187 115 0.46% 0.25% 2.61% 0.38% 0.17% 2.61% 0.31% 0.17% 1.74%

IN 1,724 311 280 32 0.64% 0.71% 0.00% 0.64% 0.71% 0.00% 0.64% 0.71% 0.00%

KY 2,076 524 291 233 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00%

LA 22 13 9 4 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00%

MA 2 2 1 1 100.00% 100.00% 100.00% 100.00% 100.00% 100.00% 100.00% 100.00% 100.00%

MD 1,909 986 940 51 0.10% 0.00% 1.96% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00%

MI 1 1 1 0 100.00% 100.00% 0.00% 100.00% 100.00% 0.00% 100.00% 100.00% 0.00%

MN 2,756 1,565 1,540 29 0.19% 0.19% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00%

MO 323 85 71 14 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00%

MS

MT 1,624 565 523 57 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00%

NC 644 297 254 44 0.34% 0.39% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00%

NE 1 1 1 0 100.00% 100.00% 0.00% 100.00% 100.00% 0.00% 100.00% 100.00% 0.00%

NH

NJ 3,130 1,511 1,486 25 0.40% 0.40% 0.00% 0.40% 0.40% 0.00% 0.40% 0.40% 0.00%

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 148 8 7 2 12.50% 14.29% 0.00% 12.50% 14.29% 0.00% 12.50% 14.29% 0.00%

NY 2,160 355 252 122 0.56% 0.40% 0.82% 0.56% 0.40% 0.82% 0.56% 0.40% 0.82%

OH 16,084 2,656 2,493 167 0.04% 0.04% 0.00% 0.04% 0.04% 0.00% 0.04% 0.04% 0.00%

SD 444 335 306 29 11.64% 11.11% 17.24% 0.30% 0.00% 3.45% 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

UT 1,328 423 403 34 1.65% 1.49% 2.94% 1.65% 1.49% 2.94% 1.42% 1.24% 2.94%

VI 10 3 0 3 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00%

VT 1 1 1 0 100.00% 100.00% 0.00% 100.00% 100.00% 0.00% 100.00% 100.00% 0.00%

WA 3,987 992 937 77 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00%

WV 388 137 63 75 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00%

WY 313 145 116 38 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00%

TOTAL 70,784 20,899 19,054 2,019 0.48% 0.42% 1.04% 0.26% 0.22% 0.64% 0.24% 0.20% 0.54%

24 States 67,688 20,407 18,693 1,867 0.45% 0.39% 1.02% 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 1,126 1,126 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 25.48% 1.34% 39.61% 25.48% 1.34% 39.61% 25.48% 1.34% 39.61%

AR

AZ 4,001,762 1,323,094 2,909,062 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00%

CA 26,356,783 26,085,197 841,643 1.92% 1.94% 0.00% 1.92% 1.94% 0.00% 1.92% 1.94% 0.00%

CO 1,681,658 644,700 1,290,958 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00%

DC

DE 499,732 266,732 233,000 40.94% 76.71% 0.00% 40.94% 76.71% 0.00% 34.38% 64.41% 0.00%

FL 4,315,466 1,745,246 3,704,774 0.64% 1.54% 0.01% 0.63% 1.54% 0.01% 0.63% 1.54% 0.01%

GA 4,919,208 1,373,936 3,545,272 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00%

HI 1,260,603 1,215,122 81,837 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00%

IA 2,128,421 1,499,541 628,880 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00%

IL 7,228,378 2,442,436 4,785,942 3.11% 6.02% 1.63% 1.15% 0.21% 1.63% 0.78% 0.21% 1.07%

IN 2,287,534 820,099 1,484,247 4.95% 13.80% 0.00% 4.95% 13.80% 0.00% 4.95% 13.80% 0.00%

KY 3,134,692 241,389 2,893,303 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00%

LA 240,115 58,905 181,210 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00%

MA 15,725 6,425 9,300 100.00% 100.00% 100.00% 100.00% 100.00% 100.00% 100.00% 100.00% 100.00%

MD 4,849,911 864,423 4,068,878 0.23% 0.00% 0.27% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00%

MI 131,546 131,546 0 100.00% 100.00% 0.00% 100.00% 100.00% 0.00% 100.00% 100.00% 0.00%

MN 2,303,765 2,158,522 175,509 0.01% 0.01% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00%

MO 890,030 717,341 172,689 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00%

MS

MT 549,172 276,682 334,304 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 0.07% 0.18% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00%

NE 985 985 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 70,910 63,410 34,560 6.70% 7.49% 0.00% 6.70% 7.49% 0.00% 6.70% 7.49% 0.00%

NY 27,880 9,880 24,500 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00%

OH 8,745,892 3,554,348 5,262,754 0.001% 0.002% 0.00% 0.001% 0.002% 0.00% 0.00% 0.00% 0.00%

SD 510,708 230,535 280,173 4.87% 4.28% 5.36% 2.73% 0.00% 4.98% 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

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 66,000 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 3,801,040 3,462,027 1,547,480 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00%

WV 777,629 187,714 594,025 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00%

WY 372,532 265,456 263,806 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-Dichloropropene 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 Occurrence 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-Dichloropropene 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-Dichloropropene Occurrence in Public Water Systems - 

Based on Population Served 

 Table C.3.a Round 2 Data - 1,1,2,2-Tetrachloroethane 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-Tetrachloroethane Occurrence in Public Water 

Systems - Based on Population Served 

Appendix 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 STATES1 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 minimum, 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 STATES1 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 STATES1 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 minimum, 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 minimum, 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 Occurrence 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 maximum

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 Considered During CCL 2 Regulatory Determinations

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

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

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

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

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

 Table E.4.b 1,1,2,2-Tetrachloroethane Occurrence 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 Numbers1

Total Number of Samples/Systems 989 59,440

99th

 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

99th 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-1
Appendix 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-Section1 All Reporting States2 National System & 

Population Numbers3

Total Number of Samples 33,930 42,798 --

Percent of Samples with Detections 0.57% 0.86% --

99th 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 --

99th

 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 Population 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 Extrapolation5

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 detections 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 detections 99,372 0.70% 172,839 1.10% 596,000 940,000

Pop. Served by SW PWSs with detections 5,353,244 16.31% 8,343,570 19.25% 20,769,000 24,505,000

Population served by PWSs > 1⁄2 HRL 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 HRL 0 0.00% 0 0.00% 0 0

Pop. Served by SW PWSs > 1⁄2 HRL 0 0.00% 0 0.00% 0 0

Population served by PWSs > HRL 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 > HRL 0 0.00% 0 0.00% 0 0

Pop. Served by SW PWSs > HRL 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-2
Appendix 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-Section1 All Reporting States2 National System & 

Population Numbers3

Total Number of Samples 31,104 31,973 --

Percent of Samples with Detections 0.06% 0.09% --

99th

 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 --

99th

 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 PWSs 9,164 9,307 65,030

Number of GW PWSs 8,303 8,401 59,440

Number of SW PWSs 898 947 5,590

Total Population 50,917,006 52,879,061 213,008,182

Population of GW PWSs 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 Extrapolation5

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 detections 10 0.12% 14 0.17% 72 99

SW PWSs with detections 5 0.56% 6 0.63% 31 35

PWSs > 1⁄2 HRL 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 HRL 10 0.12% 13 0.15% 72 92

SW PWSs > 1⁄2 HRL 5 0.56% 6 0.63% 31 35

PWSs > HRL 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 > HRL 10 0.12% 13 0.15% 72 92

SW PWSs > HRL 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 detections 146,155 0.59% 210,418 0.81% 508,000 691,000

Pop. Served by SW PWSs with detections 290,068 0.99% 342,118 1.15% 1,262,000 1,458,000

Population served by PWSs > 1⁄2 HRL 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 HRL 146,155 0.59% 207,178 0.79% 508,000 680,000

Pop. Served by SW PWSs > 1⁄2 HRL 290,068 0.99% 342,118 1.15% 1,262,000 1,458,000

Population served by PWSs > HRL 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 > HRL 146,155 0.59% 207,178 0.79% 508,000 680,000

Pop. Served by SW PWSs > HRL 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-3
Appendix 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-Section1 All Reporting States2 National System & 

Population Numbers3

Total Number of Samples 70,631 79,388 --

Percent of Samples with Detections 0.11% 0.10% --

99th 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 --

99th

 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 PWSs 16,787 18,944 65,030

Number of GW PWSs 15,178 17,098 59,440

Number of SW PWSs 1,609 1,846 5,590

Total Population 45,951,052 55,713,623 213,008,182

Population of GW PWSs 17,423,030 21,446,615 85,681,696

Population of SW PWSs 28,528,022 34,267,008 127,326,486

Occurrence by System Number Percentage Number Percentage National Extrapolation5

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 HRL 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 HRL 41 0.27% 41 0.24% 161 143

SW PWSs > 1⁄2 HRL 9 0.56% 10 0.54% 31 30

PWSs > HRL 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 > HRL 29 0.19% 29 0.17% 114 101

SW PWSs > HRL 9 0.56% 9 0.49% 31 27

Occurrence by Population Served

Population served by PWSs with detections 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 detections 197,066 1.13% 197,066 0.92% 969,000 787,000

Pop. Served by SW PWSs with detections 55,577 0.19% 63,091 0.18% 248,000 234,000

Population served by PWSs > 1⁄2 HRL 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 HRL 141,275 0.81% 141,275 0.66% 695,000 564,000

Pop. Served by SW PWSs > 1⁄2 HRL 51,595 0.18% 59,109 0.17% 230,000 220,000

Population served by PWSs > HRL 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 > HRL 99,958 0.57% 99,958 0.47% 492,000 399,000

Pop. Served by SW PWSs > HRL 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-4
Appendix 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-Section1 All Reporting States2 National System & 

Population Numbers3

Total Number of Samples 67,688 70,784 --

Percent of Samples with Detections 0.16% 0.16% --

99th 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 --

99th

 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 Population 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 Extrapolation5

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 detections 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 detections 1,017,630 1.82% 1,365,976 2.37% 1,564,000 2,030,000

Pop. Served by SW PWSs with detections 744,568 1.70% 753,868 1.65% 2,166,000 2,097,000

Population served by PWSs > 1⁄2 HRL 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 HRL 864,770 1.55% 1,213,116 2.10% 1,329,000 1,803,000

Pop. Served by SW PWSs > 1⁄2 HRL 732,370 1.67% 741,670 1.62% 2,131,000 2,063,000

Population served by PWSs > HRL 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 > HRL 851,641 1.53% 1,167,187 2.02% 1,309,000 1,734,000

Pop. Served by SW PWSs > HRL 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-5
Appendix 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-Section1 All Reporting States2 National System & 

Population Numbers3

Total Number of Samples 98,911 112,480 --

Percent of Samples with Detections 0.02% 0.03% --

99th 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 --

99th

 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 Population 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 Extrapolation5

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 detections 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 detections 24,115 0.09% 51,543 0.17% 80,000 142,000

Pop. Served by SW PWSs with detections 1,837,990 4.06% 1,841,307 3.43% 5,164,000 4,372,000

Population served by PWSs > 1⁄2 HRL 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 HRL 24,115 0.09% 33,990 0.11% 80,000 94,000

Pop. Served by SW PWSs > 1⁄2 HRL 337,990 0.75% 337,990 0.63% 950,000 803,000

Population served by PWSs > HRL 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 > HRL 24,115 0.09% 33,990 0.11% 80,000 94,000

Pop. Served by SW PWSs > HRL 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