v>EPA United States Environmental Protection Agency The Analysis of Regulated Contaminant Occurrence Data from Public Water Systems in Support of the Third Six-Year Review of National Primary Drinking Water Regulations: Chemical Phase Rules and Radionuclides Rules ------- Office of Water (4607M) EP A-810-R-16-014 December 2016 www. epa. gov/ safewater ------- Disclaimer This report is in support of the revise/take no action decisions for EPA's Third Six-Year Review of Existing Drinking Water Standards Federal Register Notice. This report is intended to provide technical background for the third Six-Year Review. This document is not a regulation itself and it does not substitute for the Safe Drinking Water Act (SDWA) or EPA's regulations. Mention of trade names or commercial products does not constitute endorsement or recommendation for use. ------- This page intentionally left blank. ------- Executive Summary The 1996 Amendments to the Safe Drinking Water Act (SDWA) require that the U.S. Environmental Protection Agency (EPA) "shall, at least once every six years, review and revise, as appropriate, each National Primary Drinking Water Regulation (NPDWR)." The NPDWRs are often referred to as the national drinking water contaminant regulations or drinking water standards. The 'Six-Year Review' process is an assessment of new information on the health effects and national occurrence of the regulated contaminants, as well as new capabilities of treatment technologies and laboratory analytical methods. Through this process, EPA determines whether the new information and technical capabilities provide a scientific basis to support a revision of existing regulations that will improve public health protection. This report presents the national contaminant occurrence assessments conducted in support of EPA's third Six-Year Review of NPDWRs. Included are detailed descriptions of the national contaminant occurrence dataset, the data management procedures conducted to develop the national dataset and the statistical analytical methods employed to generate national estimates of regulated contaminant occurrence in public drinking water systems. Because there is no national database that receives and stores all relevant data on the occurrence of regulated contaminants in public drinking water systems, EPA conducted a voluntary data call-in from the states, territories and tribes to obtain the data. EPA worked with the states and primacy agencies to receive the states' and agencies' complete records of compliance monitoring data (public drinking water system regulated contaminant occurrence data) for 2006 through 2011. The compliance monitoring data were obtained through the Information Collection Request (ICR) process. EPA conducted data management and quality assurance (QA) evaluations on the data received for contaminants evaluated for the Third Six-Year Review to establish a high quality, national contaminant occurrence dataset consisting of data from 54 states/primacy agencies (46 states plus Washington, D.C. and the tribal data). The contaminant occurrence data for the these 54 states/primacy agencies comprise almost 13 million analytical records from approximately 139,000 public water systems (PWSs), which serve approximately 290 million people nationally. This dataset, the Third Six-Year Review (SYR3) ICR Dataset for the third Six-Year Review (or "SYR3 ICR Dataset"), is the largest and most comprehensive contaminant occurrence dataset ever compiled and analyzed by EPA's Drinking Water Program. To estimate national contaminant occurrence using the SYR3 ICR Dataset, EPA used a two- stage analytical approach. In the first stage of analysis (the "Stage 1 analysis"), the occurrence data were reviewed, quality-checked, characterized and then analyzed to generate simple, non- parametric estimates of national contaminant occurrence in PWSs. Simple counts were made of the number and percentage of systems and of the population served by systems that report at least one compliance monitoring sample result greater than a specified contaminant concentration threshold, such as the contaminant's Maximum Contaminant Level (MCL) (the contaminant's drinking water standard). This Stage 1 analysis, based on maximum sample concentration values, is inherently conservative. It is designed to ensure that contaminant occurrence is not underestimated for the consideration of public health protection. The Stage 1 analysis provides occurrence assessments that may be more reflective of potential acute exposure. Additional parametric statistical estimations (the "Stage 2 analyses") were conducted SYR3 Occurrence Support Document iii December 2016 ------- on a set of contaminants selected by EPA on the basis of the Six-Year Review Protocol. The Stage 2 analysis estimates long-term mean concentrations of contaminants in all systems nationwide, generating occurrence analyses that are less conservative than the Stage 1 analysis. The Stage 2 analysis also provides occurrence assessments that may be more reflective of potential chronic exposure. EPA used the Stage 1 analyses of approximate peak concentration measures to assess the national occurrence of 61 regulated contaminants (57 chemical and 4 radiologicals). Ten regulated chemical contaminants (lead, copper, 1,2-dichloroethane, 1,2-dichloropropane, benzene, carbon tetrachloride, dichloromethane, tetrachloroethylene, trichloroethylene and vinyl chloride), as well as disinfection byproducts (DBPs) and microbial contaminants were being reviewed or revised under other regulatory actions, or included in separate regulatory reviews. EPA also conducted additional Stage 2 analyses using mean concentration measures for 17 of the 61 regulated chemical contaminants. Several different variations of the Stage 1 and Stage 2 analyses were conducted to broadly characterize national occurrence and are described and presented in this report and its appendices. Additionally, two synthetic organic chemicals (SOCs) were assessed using a more detailed Stage 1 analysis while four inorganic chemicals (IOCs), nine SOCs and five volatile organic chemicals (VOCs) were assessed using the Stage 2 analytical approach. The Stage 2 occurrence analyses conducted in this report, based roughly on long-term, multi-year average contaminant occurrence, are not the same as the occurrence analyses formally conducted to assess compliance with contaminant drinking water standards (which for most contaminants are based on annual average contaminant occurrence; see Section 7 for details). Background information regarding the national contaminant occurrence data and data management is presented in Sections 1 through 5 of this report. The summary of the Stage 1 analytical findings is presented in Section 6, with more detailed Stage 1 analyses for two contaminants in Appendix A. The summary of the Stage 2 analytical findings for 17 select contaminants is presented in Section 7, with complete detailed Stage 2 occurrence findings for the 17 contaminants included in Appendix B. SYR3 Occurrence Support Document iv December 2016 ------- Table of Contents 1 Introduction 1-1 1.1 Purpose and Scope 1-2 1.2 Data Sources 1-2 1.3 Data Analysis 1-4 2 The National Compliance Monitoring ICR Dataset for the Third Six-Year Review 2-6 2.1 Completeness and Representativeness of the Six-Year Review ICR Dataset 2-7 3 Data Management 3-13 3.1 Dataset Consistency and Restructuring 3-13 3.2 Review of Dataset Content 3-14 3.3 Establishing Consistent Data Fields for Analytical Results 3-17 4 Data Quality Assurance/Quality Control 4-19 4.1 Quality Assurance Measures 4-19 4.2 Adjustments of Population Served by Public Water Systems 4-21 4.3 Adjustments of Source Water Type for Public Water Systems 4-22 5 Summary of the Compliance Monitoring Data 5-23 5.1 Characteristics of the Data - States, Systems and Records 5-23 5.2 Occurrence Variability Assessment 5-31 5.3 Threshold Evaluations 5-32 6 Stage 1 Analysis 6-35 6.1 Summary of Stage 1 Contaminant Occurrence Findings 6-35 6.2 Comparison of Stage 1 Analysis of First, Second and Third Six-Year Reviews 6-41 6.3 System Sample Point Level Analysis 6-44 7 Stage 2 Analysis 7-49 7.1 Preparing the Data for the Stage 2 Analysis 7-50 7.2 Summary of Stage 2 Contaminant Occurrence Estimations 7-50 8 References 8-52 SYR3 Occurrence Support Document v December 2016 ------- Exhibits Exhibit 1.1: States Compliance Monitoring Waivers 1-3 Exhibit 2.1: States with Compliance Monitoring Data Included in the SYR3 ICR Dataset 2-6 Exhibit 2.2: Comparison of the Total Number of Non-Purchased Systems and Retail Population Served in SDWIS/Fed and the SYR3 ICR Dataset, By State 2-9 Exhibit 2.3: Comparison of the Total Number of Systems and Retail Population Served in SDWIS/Fed and the SYR3 ICR Dataset, By Source Water Type and System Type 2-11 Exhibit 3.1: Summary of Compliance Monitoring Data Provided by States for the Third Six-Year Review 3-13 Exhibit 3.2: Data Elements Requested by EPA for the Third Six-Year Review 3-14 Exhibit 3.3: List of Contaminants for Which Data Were Requested from States 3-16 Exhibit 4.1: Chemical Group Monitoring Requirements 4-19 Exhibit 5.1: Number of Systems and Population Served by Systems in the SYR3 ICR Dataset, by Source Water Type 5-23 Exhibit 5.2: Number of Systems and Population Served by Systems in the SYR3 ICR Dataset, by System Size 5-24 Exhibit 5.3: Number of Systems and Retail Population Served by Systems in the SYR3 ICR Dataset, by System Type 5-25 Exhibit 5.4: An Inventory of Contaminant Occurrence Data in the SYR3 ICR Dataset, by State 5-25 Exhibit 5.5: An Inventory of the Contaminant Occurrence Data in the SYR3 ICR Dataset, by Contaminant 5-28 Exhibit 5.6: List of Contaminant Thresholds used in Stage 2 Occurrence Analysis1 5-33 Exhibit 6.1: Summary of Stage 1 Contaminant Occurrence Findings - Systems and Population Served by Systems 6-35 Exhibit 6.2: Number and Percent of Systems and Population Served by Systems with Detections Greater than the MCL Concentration 6-38 Exhibit 6.3: Comparison of Stage 1 Analyses of the First, Second and Third Six-Year Reviews based on the Percent of Systems 6-41 Exhibit 6.4: Summary of Stage 1 Contaminant Occurrence Findings - Sample Points and Population Served by Sample Points 6-46 Exhibit 7.1: Comparison of Stage 1 and Stage 2 Analytical Results - Percent of Systems and Population Served by Systems Greater than the MCL Concentration 7-51 SYR3 Occurrence Support Document vi December 2016 ------- Appendices APPENDIX A. Background Information and Detailed Stage 1 Analysis Occurrence Measures for 2 Select Regulated Chemical Contaminants APPENDIX B. Background Information and Detailed Stage 2 Analysis Occurrence Measures for 17 Select Regulated Chemical Contaminants SYR3 Occurrence Support Document vii December 2016 ------- Acronyms CAS Chemical Abstracts Service CWS Community Water System DBCP l,2-Dibromo-3-chloropropane DBP Disinfection Byproduct DBPR Disinfection Byproduct Rule DEHA Di(2-ethylhexyl)adipate DEHP Di(2-ethylhexyl)phthalate EDB Ethylene dibromide EPA Environmental Protection Agency (United States) EQL Estimated Quantitation Level FBRR Filter Backwash Recycling Rule GW Ground Water GWR Ground Water Rule GWUDI Ground Water Under Direct Influence (of Surface Water) HPC Heterotrophic Plate Count ICR Information Collection Request IOC Inorganic Chemical LCR Lead and Copper Rule MCL Maximum Contaminant Level MCLG Maximum Contaminant Level Goal MDL Method Detection Limit MFL Million Fibers per Liter mg/L Milligrams per Liter MOR Monthly Operating Report mrem/yr Millirem per year MRL Minimum Reporting Level ND Non-detect or Non-detection NPDWR National Primary Drinking Water Regulation NTNCWS Non-Transient Non-Community Water System OGWDW Office of Ground Water and Drinking Water PCBs Polychlorinated Biphenyls pCi/L Picocuries per Liter PQL Practical Quantitation Level PWS Public Water System PWSID Public Water System Identification Number QA Quality Assurance QC Quality Control RfD Reference Dose SDWA Safe Drinking Water Act SDWIS/Fed Safe Drinking Water Information System / Federal Versio SD WIS/State Safe Drinking Water Information System / State Version soc Synthetic Organic Chemical SP Sample Point sw Surface Water SWP Purchased Surface Water SWTR Surface Water Treatment Rule SYR3 Occurrence Support Document December 2016 ------- SYR3 Third Six-Year Review TCR Total Coliform Rule TNCWS Transient Non-Community Water System TOC Total Organic Carbon USEPA United States Environmental Protection Agency ^g/L Micrograms per Liter voc Volatile Organic Chemical SYR3 Occurrence Support Document ix December 2016 ------- 1 Introduction Pursuant to the 1996 Safe Drinking Water Act (SDWA) Amendments, the U.S. Environmental Protection Agency (EPA) conducts, at least every six years, a review of the National Primary Drinking Water Regulations (NPDWRs). For this "Six-Year Review" of the nation's public drinking water standards, EPA assesses the occurrence of regulated contaminants in public water systems (PWSs or "systems") in conjunction with other assessments of health effects, analytical feasibility and treatment feasibility. Assessments are conducted to determine if revisions to the existing NPDWRs (public drinking water standards) are appropriate. EPA completed and published the results of its first and second Six-Year Reviews of NPDWRs (68 FR 42908, USEPA, 2003a; 75 FR 15499, USEPA, 2010a) using a systematic approach, or protocol, for the reviews. EPA has applied the same protocol to the current, third Six-Year Review of NPDWRs ("Six-Year Review 3"). This report presents the assessments of national contaminant occurrence in PWSs in the United States in support of EPA's third Six-Year Review of NPDWRs. Because there is no national database of regulated drinking water contaminant occurrence data for public drinking water systems, EPA conducted a voluntary data call-in from the states, primacy agencies, territories and tribes ("states" throughout the remainder of the report) to obtain the data using the Information Collection Request (ICR) process. EPA worked with states to obtain their complete compliance monitoring data for 2006 through 2011; state data management staff were consulted to resolve any questions about the data submitted. EPA conducted data management and quality assurance (QA) evaluations to establish a high quality, national contaminant occurrence database consisting of data from 54 states/primacy agencies (46 states plus Washington, D.C., American Samoa and tribal data from Region 1, Region 4, Region 5, Region 8, Region 9 and Navajo Nation). This dataset, referred to as the National Compliance Monitoring ICR Dataset for the Third Six-Year Review (or "SYR3 ICR Dataset"), is the largest and most comprehensive compliance monitoring dataset ever compiled and analyzed by EPA's Drinking Water Program. Using this dataset, EPA employed a two-stage analytical approach to estimate a variety of occurrence measures to characterize the national occurrence of regulated contaminants in systems to support the third Six-Year Review process. As part of this ICR effort, EPA requested voluntary submission of States' SDWA compliance monitoring data for chemical contaminants regulated under Phase I, II, lib and V Rules; the Arsenic Rule; and the Radionuclides Rule. This report presents occurrence assessments for those contaminants with the exception of contaminants currently evaluated under other regulatory actions or included in separate regulatory reviews. Lead and copper occurrence assessments are not included in this report because of ongoing efforts on long-term revisions to the Lead and Copper Rule. Eight chemicals - 1,2-dichloroethane, 1,2-dichloropropane, benzene, carbon tetrachloride, dichloromethane, tetrachloroethylene, trichloroethylene and vinyl chloride - are not included in this review because these chemicals are being evaluated as part of the Group Regulation of Carcinogenic Volatile Organic Compound (VOCs) (USEPA, 201 la; USEPA, 2014). Acrylamide and epichlorohydrin are not included because there are currently no acceptable laboratory analytical methods for detecting these contaminants in drinking water. Additionally, no states submitted SYR3 data for these two contaminants; however, for the treatment technique review for these two contaminants, see Support Document for Third Six Year Review of Drinking Water Regulations for Acrylamide and Epichlorohydrin (USEPA, 2016a). SYR3 Occurrence Support Document 1-1 December 2016 ------- The microbial contaminant regulations covered in this Six-Year Review include: the Surface Water Treatment Rule (SWTR), the Interim Enhanced Surface Water Treatment Rule (IESWTR), the Long-Term 1 Enhanced Surface Water Treatment Rule (LT1ESWTR), the Long- Term 2 Enhanced Surface Water Treatment Rule (LT2ESWTR), the Filter Backwash Recycling Rule (FBRR) and the Ground Water Rule (GWR). Occurrence analyses related to these contaminants' data are not included in this report; for more detailed information on the microbial contaminants' occurrence analysis, refer to USEPA (2016b). Based on the Initial Review Branch, EPA excluded the revised Total Coliform Rule (RTCR) from the remaining steps in this Six-Year Review because it was promulgated on February 13, 2013. Furthermore, since most of the 1989 Total Coliform Rule (TCR) requirements are being replaced by the 2013 RTCR, the 1989 rule was excluded from review. EPA is also reviewing the Stage 1 and Stage 2 Disinfectant and Disinfection Byproducts Rules (DBPRs) (USEPA, 1998; USEPA, 2006) as part of the third Six-Year Review. For more information see the technical support document for DBPRs (USEPA, 2016c). This report describes the extensive data management and data quality checks conducted as part of the development of the SYR3 ICR Dataset; explains the analytical approach used to estimate the various measures of national contaminant occurrence for the 61 contaminants included in this report; and presents and describes the resulting national contaminant occurrence estimates for those contaminants. This report presents many different measures and estimates of national occurrence. Some of the contaminant occurrence measures are presented in this report as "preliminary exposure estimates" meaning they are not formal exposure estimates, but estimates of the population served by systems found to have some degree of contaminant occurrence in their drinking water samples. 1.1 Purpose and Scope EPA's Office of Ground Water and Drinking Water (OGWDW) is responsible for implementing the provisions of SDWA. Under SDWA, OGWDW develops both regulations to address the public health risks from contaminated drinking water and related programs to protect ground water (GW) and surface water (SW) supplies. The 1996 Amendments to SDWA require that EPA shall, at least once every six years, review and revise, as appropriate, each NPDWR promulgated by the Agency. SDWA specifies that revision of a NPDWR shall maintain, or provide for greater, protection of public health. Any revision of the regulations will be partially dependent on contaminant occurrence findings, on the reevaluation of the public's exposure to the contaminants and the potential adverse health effects from that exposure. The purpose of this report is to describe the contaminant occurrence data, data management and statistical methods used to develop the national contaminant occurrence estimations in support of EPA's Six-Year Review 3. This report presents occurrence assessments for 61 contaminants regulated under the Phase I, II, lib and V Rules, the Arsenic Rule and the Radionuclides Rule. As noted above, SDWA compliance monitoring data for some of the regulated contaminants collected under SYR3 (i.e., lead, copper, carcinogenic VOCs, microbials and DBPs) are being assessed separately under other regulatory actions or included in separate regulatory reviews. 1.2 Data Sources PWSs must meet health-based federal standards for contaminants, including performing regular monitoring and reporting. Water systems are required to sample and test their water and report SYR3 Occurrence Support Document 1-2 December 2016 ------- the results to the Agency with primacy for implementing the SDWA. These systems, which may be publicly- or privately-owned, serve at least 15 service connections or 25 persons. EPA established nine-year fixed compliance cycles to standardize monitoring requirements for the various contaminant rules. Each nine-year compliance cycle is divided into three three-year compliance periods. The first Compliance Period ran from January 1, 1993 to December 31, 1995. The second Compliance Period ran from 1996 to 1998 and the third Compliance Period ran from 1999 to 2001. Together, these nine years comprise one Compliance Cycle (Compliance Cycle 1). The second compliance cycle began January 1, 2002 and ended December 31, 2010; the third compliance cycle began January 1, 2011 and ends December 31, 2019. The SYR3 period of review (2006 through 2011) falls within the second and third compliance cycles. All non-purchased community water systems (CWSs) and non-transient non-community water systems (NTNCWSs) are required to sample for the Inorganic Contaminants (IOCs), Synthetic Organic Contaminants (SOCs) and Volatile Organic Contaminants (VOCs).1 States may grant waivers to PWSs to reduce sampling (Exhibit 1.1). Reduced monitoring requirements for contaminants are based on both a vulnerability assessment and previous analytical results. It is possible that systems that had been granted waivers may not have sampled at all during the SYR3 period of review. Exhibit 1.1: States Compliance Monitoring Waivers Contaminant Group / System Source Water Type Waiver Monitoring Frequency Waiver Renewal Frequency Notes1 Inorganic Contaminants (IOC)2 - Ground Water/Surface Water Once every nine years Every nine years Dependent on previous sample results. Volatile Organic Contaminants (VOC)3 - Ground Water Once every six years Every six years Vulnerability Assessment must be renewed every three years. Volatile Organic Contaminants (VOC)3 - Surface Water None Every three years Vulnerability Assessment must be renewed every three years. Synthetic Organic Contaminants (SOC) - Ground Water/Surface Water None Every three years Vulnerability Assessment must be renewed every three years. Source: EPA Chemical Contaminant Rules Compliance for Primacy Agencies 1 There are two bases for vulnerability assessments: (1) The PWS can prove that the contaminant has not been used in the area, or (2) the PWS can prove it is not susceptible to contamination from that contaminant. 2 There are no waivers allowed for nitrate or nitrite monitoring. Asbestos waiver conditions are different than the rest of the IOCs. 3 Vinyl chloride is an exception to this waiver policy. The Federal Safe Drinking Water Information System database (SDWIS/Fed) contains information about PWSs and their violations of EPA's drinking water regulations. However, SDWIS/Fed does not receive or store complete compliance monitoring data (called parametric data), which includes non-detections as well as detections. To estimate national occurrence of regulated contaminants in PWSs, it is necessary to have results from all contaminant occurrence samples, including samples which showed analytical detections and non-detections. These data 1 Transient non-community water systems are also required to sample for nitrate and nitrite. SYR3 Occurrence Support Document 1-3 December 2016 ------- are collected by states but are not required to be submitted to SDWIS/Fed. Therefore, to obtain the necessary compliance monitoring data to support national occurrence assessments for the Six-Year Review 3, EPA conducted the voluntary data call-in described in this report from the states and through the ICR process. For more information on the process undertaken to request the voluntary submission of compliance monitoring data by the states, see the third Six-Year Review ICR renewal (75 FR 6023, USEPA, 2010b). Through the ICR process, EPA requested that states voluntarily submit compliance monitoring data with records of all sample detections and non-detections collected between January 2006 and December 2011. Forty-six states and eight other primacy agencies provided compliance monitoring data that included contaminant monitoring records. Through extensive data management efforts and quality assurance evaluations, as well as through communications and consultations with state data management staff, EPA established a high quality contaminant occurrence dataset (the SYR3 ICR Dataset) that consists of data from 54 states/primacy agencies (46 states plus data from Washington, D.C. and the tribes). See Section 2 for additional details on states included in the SYR3 ICR Dataset. 1.3 Data Analysis EPA used a two-stage analytical approach to estimate the national contaminant occurrence using the SYR3 ICR Dataset. The first stage of analysis provides a simple, straightforward evaluation of occurrence of all contaminants. The "Stage 1 analysis" assesses the sources, quality and characteristics of the occurrence data and then uses the data to generate summary statistics of each contaminant's occurrence, as well as national estimates of occurrence that are simple, non- parametric and conservative.2 For each contaminant, analyses are conducted focusing on samples, water systems, population served by water systems and system sample point (SP) locations. A typical Stage 1 analysis is a simple count of the number or percentage of systems reporting at least one sample detection of a specific contaminant, or at least one sample detection with a concentration greater than the Maximum Contaminant Level (MCL) of the contaminant. The details of the Stage 1 analysis methods are described in Section 6. Based on the evaluation of the health effects and analytical methods as part of the Six-Year Review protocol, EPA selected a set of contaminants for which additional parametric statistical estimations were warranted (referred to as the "Stage 2 analysis"). The Stage 2 analysis estimates national contaminant occurrence by generating estimated long-term mean concentrations of contaminants for each water system. This Stage 2 long-term mean analysis is less conservative than the Stage 1 analysis, which reflects a rough approximation of peak occurrence. This fundamental difference between the two analytical approaches has a very direct implication: regardless of the contaminant concentration value assessed, the Stage 1 analysis findings will always exceed, or at most be approximately equal to, the Stage 2 analysis findings. For example, the Stage 1 analysis of the number of systems with at least one detection of toxaphene greater than the MCL concentration will always be greater than, or at most equal to, the Stage 2 analysis 2 The Stage 1 analyses are conservative in the sense that they are protective of human health (i.e., because they are based on a single, maximum sample detection value rather than an average value for each system, the Stage 1 analyses are more likely to overestimate occurrence and potential risks to human health than underestimate them). SYR3 Occurrence Support Document 1-4 December 2016 ------- showing the number of systems with a mean concentration of toxaphene greater than the MCL concentration. Because the Stage 2 analyses generate long-term (multi-year) mean concentration estimates for contaminant occurrence at systems, the analyses can support assessments of population served by water systems with detections (or "preliminary exposure" assessments) that may be more reflective of potential chronic exposure than the assessments from the Stage 1 analyses, which reflect a one-time peak. Section 7 describes the details of the Stage 2 analysis. This two-stage analytical approach was previously developed for other EPA national occurrence studies, including those conducted for the first Six-Year Review of NPDWRs (USEPA, 2003b) and the first and second Regulatory Determinations for Contaminants from the Drinking Water Contaminant Candidate List (USEPA, 2002, 2008a and 2008b). The approach was also used for the second Six-Year Review of NPDWRs and the third Regulatory Determinations for Contaminants from the Drinking Water Contaminant Candidate List. The overall data management and general two-stage occurrence analytical approach used for these OGWDW projects was peer-reviewed for use under the first Six-Year Review, which assessed regulated contaminant occurrence data collected from 1993 to 1997. The Stage 2 analysis used for this third Six-Year Review is consistent with the simplified version of the Stage 2 analysis that was used for the second Six-Year Review (USEPA, 2010c). This was possible because, similar to the second Six-Year Review, a large number of states provided contaminant occurrence data for the third Six-Year Review. See Section 7 for a complete description of the Stage 2 analysis; a selection of contaminants are presented in Appendix B. SYR3 Occurrence Support Document 1-5 December 2016 ------- 2 The National Compliance Monitoring ICR Dataset for the Third Six-Year Review Through the ICR process, EPA conducted a voluntary data call-in for states' compliance monitoring records and received data from a total of 54 states/primacy agencies: 46 states; American Samoa; Washington, D.C.; Region 1 tribes; Region 4 tribes; Region 5 tribes; Region 8 tribes; Region 9 tribes and the Navajo Nation. Through extensive data management efforts, quality assurance evaluations and communications with state data management staff, EPA established the SYR3 ICR Dataset (see Exhibit 2.1 below). Exhibit 2.1: States with Compliance Monitoring Data Included in the SYR3 ICR Dataset r*. £ i^Cvvti AmericsnSamoa jPjj District of Columbia | | Guam- | j Northern Marianalsiands | | Puerto Rica | j Virgin Islands 11 Tribes ~ Region? Tribes | | Region 2Tribes RegionBTribss | | Region 3 Tribes ¦ Region 9 Navajo Nation 14Trifoes ¦ Region 9 Tribes n S Tribes. ~ Region lOTribes | | Region 6Tribes ~ State Did Not Submit D= Stats Submitted Data The compliance monitoring contaminant occurrence data from these 54 states/primacy agencies for contaminants evaluated in this report for comprise more than 13 million analytical records from approximately 139,000 water systems. Approximately 290 million people are served by these systems nationally. Data quality, completeness and representativeness are key considerations for the dataset. Given the size, scope and variety of formats of the datasets received from the states, EPA conducted extensive data management and quality assurance/quality control (QA/QC) assessments on the data to be included in the SYR3 ICR Dataset. A review of completeness and representativeness, details of data management and details of quality assessments are presented in the following three sections. Additional details of the data management measures can be found in the report SYR3 Occurrence Support Document 2-6 December 2016 ------- titled The Data Management and Quality Assurance/Quality Control Process for the Third Six- Year Review Information Collection Rule Dataset (USEPA, 2016d). 2.1 Completeness and Representativeness of the Six-Year Review ICR Dataset The final SYR3 ICR Dataset consists of compliance monitoring data received from 54 out of 67 states/primacy agencies. It represents a very large sample and the largest compliance monitoring dataset ever compiled and analyzed by EPA's Drinking Water Program (Exhibit 2.1). The 54 states/primacy agencies that provided data for the SYR3 ICR Dataset comprise 95 percent of all PWSs and 92 percent of the total population served by PWSs nationally and are geographically representative of PWSs nationwide. The absence of data from the four states and nine primacy agencies in the final SYR3 ICR Dataset could potentially bias the dataset's representation of the national occurrence of particular contaminants. The four states, representing about five percent of PWSs and eight percent of population served by PWSs nationally, have a fairly small influence relative to the PWSs and populations represented by the states that did submit data. The four states that did not provide compliance monitoring contaminant occurrence data (Colorado, Delaware, Georgia and Mississippi) are generally geographically distributed across the United States and reflect a diverse mix of urban, agricultural and industrial areas. No regional geologic terrain, climatic or hydrologic zone, geography or socio-economic activity is unrepresented in the dataset. Although two states in the southeastern U.S., Georgia and Mississippi, did not provide data, all other southeast states did provide data, allowing for significant regional coverage, especially from a population-based perspective. All other regions had at most one state not included in the dataset. The SYR3 ICR Dataset, with 46 of the 50 states represented, is therefore considered reasonably complete and nationally representative as the basis of the contaminant occurrence estimates presented in this report. To further address the issue of potential bias, though, EPA conducted an assessment for each contaminant by comparing occurrence in the 4 states to that in the 46 states. Because a complete compliance monitoring dataset of all 50 states does not exist, it is not possible to know the true national occurrence for a particular contaminant or how occurrence rates for a particular contaminant in the 4 missing states compare to occurrence in the other 46 states. Therefore, an indicator of occurrence was developed using data available from the SDWIS/Fed database, which does not have complete compliance monitoring data but does include all 50 states. EPA compiled SDWIS/Fed records of MCL violations, used here as an indicator of contaminant occurrence, by state for the same years (2006-2011) as the SYR3 ICR Dataset.3 The MCL violation records were used to determine if the violation rate in the 4 missing states was significantly different than the violation rate in the 46 states in the dataset, or if the violation rate in the 46 states could be considered representative (from the same statistical population). EPA conducted this assessment for the IOCs, SOCs, VOCs and radionuclides evaluated under Six-Year Review 3. 3 While the SDWIS/Fed database does not store complete compliance monitoring parametric records, the database does maintain the most current and complete national and state records of contaminant MCL violations. Annual MCL data were extracted from SDWIS/Fed by EPA in March 2014. SYR3 Occurrence Support Document 2-7 December 2016 ------- The mean MCL violation rate for each contaminant (i.e., the percentage of systems with at least one MCL violation) was calculated for the 46 states in the dataset and separately for the 4 states not in the SYR3 ICR Dataset. For each contaminant, a statistical t-test was used to determine whether these two estimated mean MCL violation rates (46-state vs. 4-state) were significantly different; the t-test had an alpha (a) level of 0.05 and assumed unequal variance.4 If the p-value resulting from the t-test was less than 0.05, EPA rejected the null hypothesis that the two mean MCL violation rates were from the same population and accepted the alternative hypothesis that they were from different populations. Of the 61 contaminants evaluated, only nine contaminants had at least one MCL violation listed in the SDWIS/Fed database for the 2006-2011 time period; thus, t-tests were conducted on only these nine contaminants. For five contaminants (fluoride, nitrate, gross alpha, uranium and combined radium), the t-test resulted in a p-value > 0.05 (EPA failed to reject the null hypothesis). This suggests, but does not prove, that the mean MCL violation rates for the 46 states and the 4 states were not statistically different (were from the same population). For three additional contaminants, only one of the four states had MCL violations so the t-test could not be applied. Arsenic was the only contaminant for which the t-test resulted in a p-value < 0.05 (EPA rejected the null hypothesis); thus, the mean arsenic MCL violation rate for the 46 states appears to be statistically different (come from a different population) than the mean arsenic MCL violation rate for the four states. This suggests that the absence of system compliance monitoring data from the four states might result in some amount of over-estimation of occurrence for that contaminant. These findings, however, are most appropriately used as context or background for the quantitative occurrence findings presented in Sections 6 and 7 of this report. To further evaluate the completeness of each state's dataset, EPA used the SDWIS/Fed database as a reference and compared the number of water systems by state in the SYR3 ICR Dataset to the number of systems by state in the SDWIS/Fed database (frozen fourth quarter 2011). Only the SDWIS/Fed database records from the 46 states also in the SYR3 ICR Dataset were included. (As described in Section 4.2, systems that purchase 100 percent of their water are accounted for differently than non-purchased water system. To simplify this comparison of number of systems by state, only non-purchased systems were included in the counts.) The SDWIS/Fed version accessed to obtain this inventory data was the fourth quarter of 2011. Although the system inventory information represented in the two data sources is very similar, it is not equivalent. The main difference is that the SYR3 ICR Dataset reflects the total number of systems with compliance monitoring data in any of the six years represented in the dataset (2006-2011), while the SDWIS/Fed 2011 data freeze reflects the number of systems with compliance monitoring data in a single year (2011). Since systems open, close and consolidate over time, the number of systems in each state will understandably be somewhat different between the two data sources. Population changes in system service areas over time could also contribute to differences in population served numbers for systems between the two data sources. This comparison is presented in Exhibit 2.2. In order to be consistent with the SDWIS/Fed counts, the population 4 The t-test calculation used considered the variance, mean and sample size of each of the two groups of states to estimate the probability that the observed difference in sample means represents an actual difference in contaminant occurrence and not just a statistical inconsistency resulting from low sample sizes. SYR3 Occurrence Support Document 2-8 December 2016 ------- values listed for the SYR3 ICR Dataset include only the populations directly served by non- purchased systems (retail populations); total adjusted populations are discussed in Section 4.2. The comparison between the counts of systems in the two data sources indicate that the data in the SYR3 ICR Dataset are reasonably complete. Overall, there is an approximately 11 percent difference between the number of systems listed in a December 2011 SDWIS/Fed freeze compared to the number of systems in the third SYR3 ICR Dataset. (The percent difference is calculated by subtracting the number of systems in SDWIS/Fed from the number in SYR3 ICR and then dividing by the number of systems in the SYR3 ICR Dataset.) In Exhibit 2.2, positive values for percent difference indicate that more systems are reported in the SYR3 ICR Dataset, which negative values indicate that more systems are reported in the 2011 SDWIS/Fed Freeze. Comparing the number of systems for each state, the absolute percentage difference between SDWIS/Fed and the SYR3 ICR Dataset ranges from a zero percent difference (e.g., Region 1 Tribes and Utah) to an approximately 26 percent difference (e.g., Region 5 Tribes) in the number of systems. Based on the population served by systems, there is a three percent difference between the total population served by systems listed in SDWIS/Fed and the population served by systems listed in the SYR3 ICR Dataset. Comparing individual state population served values, the absolute percentage differences between SDWIS/Fed and the Six-Year states ranges from less than a one percent difference (e.g., Alabama and New Mexico) to approximately a 20 percent difference (e.g., Nebraska). Exhibit 2.2: Comparison of the Total Number of Non-Purchased Systems and Retail Population Served in SDWIS/Fed and the SYR3 ICR Dataset, By State State Total Number of Non-Purchased Systems1 Retail Population Served by Non- Purchased Systems 2011 SDWIS/Fed Freeze SYR3 ICR Data Percent Difference2 2011 SDWIS/Fed Freeze SYR3 ICR Data Percent Difference2 Alabama 399 415 4% 4,270,460 4,269,317 0.0% Alaska 1,429 1,403 -2% 718,776 762,190 6% American Samoa 19 17 -11% 60,958 61,309 1% Arizona 1,511 1,493 -1% 6,414,815 6,431,456 0.3% Arkansas 643 639 -1% 1,808,219 1,782,034 -1% California 7,215 7,540 5% 28,781,357 28,528,121 -1% Connecticut 2,523 2,971 18% 2,676,429 2,716,577 2% Florida 5,295 6,350 20% 16,742,435 17,383,116 4% Hawaii 108 118 9% 1,421,758 1,452,737 2% Idaho 1,936 1,907 -1% 1,315,860 1,360,791 3% Illinois 4,097 4,625 13% 8,228,681 8,296,918 1% Indiana 4,012 4,397 10% 4,886,097 4,946,190 1% Iowa 1,660 1,763 6% 2,365,619 2,380,108 1% Kansas 647 642 -1% 2,281,561 2,292,280 0.5% Kentucky 261 257 -2% 3,268,613 3,299,397 1% Louisiana 1,287 1,390 8% 4,844,307 4,868,351 0.5% Maine 1,851 2,198 19% 903,130 964,872 7% SYR3 Occurrence Support Document 2-9 December 2016 ------- State Total Number of Non-Purchased Systems1 Retail Population Served by Non- Purchased Systems 2011 SDWIS/Fed Freeze SYR3 ICR Data Percent Difference2 2011 SDWIS/Fed Freeze SYR3 ICR Data Percent Difference2 Maryland 3,390 3,886 15% 5,022,871 5,711,914 14% Massachusetts 1,545 1,674 8% 7,154,525 7,117,276 -1% Michigan 10,873 13,078 20% 4,809,937 5,087,202 6% Minnesota 6,943 7,753 12% 4,617,552 4,689,328 2% Missouri 2,458 2,768 13% 4,463,766 4,515,797 1% Montana 1,899 1,856 -2% 894,851 902,225 1% Navajo Nation 146 152 4% 131,031 140,818 7% Nebraska 1,155 1,283 11% 1,545,502 1,861,572 20% Nevada 531 584 10% 942,651 984,355 4% New Hampshire 2,394 2,610 9% 1,124,928 1,156,828 3% New Jersey 3,686 4,295 17% 7,428,858 7,534,923 1% New Mexico 1,109 1,089 -2% 1,899,344 1,896,614 -0.1% New York 8,206 8,945 9% 16,731,989 18,127,928 8% North Carolina 5,684 6,806 20% 6,945,228 7,131,934 3% North Dakota 301 279 -7% 513,800 508,028 -1% Ohio 4,543 5,363 18% 9,056,572 9,232,856 2% Oklahoma 960 1,102 15% 3,002,063 3,091,513 3% Oregon 2,484 2,705 9% 2,831,651 2,767,113 -2% Pennsylvania 8,779 10,128 15% 10,699,485 10,814,930 1% Region 1 - Tribes 5 5 0% 49,031 49,031 0.0% Region 4 - Tribes 31 32 3% 28,387 27,889 -2% Region 5 - Tribes 100 126 26% 139,916 154,489 10% Region 8 - Tribes 103 101 -2% 91,321 92,432 1% Region 9 - Tribes 284 314 11% 367,252 353,335 -4% Rhode Island 459 487 6% 775,182 778,796 0.5% South Carolina 1,104 1,064 -4% 2,681,749 2,683,477 0.1% South Dakota 447 463 4% 603,361 609,007 1% Tennessee 700 673 -4% 5,616,106 5,704,724 2% Texas 5,635 5,528 -2% 16,682,616 17,119,034 3% Utah 892 892 0% 1,443,051 1,470,928 2% Vermont 1,273 1,414 11% 489,778 503,324 3% Virginia 2,519 2,917 16% 4,769,127 5,340,030 12% Washington 3,902 4,309 10% 5,038,297 5,149,128 2% Washington, D.C. 1 1 0% 0 0 0.0% West Virginia 822 988 20% 1,292,503 1,314,496 2% Wisconsin 11,345 12,563 11% 4,468,486 4,576,227 2% SYR3 Occurrence Support Document 2-10 December 2016 ------- State Total Number of Non-Purchased Systems1 Retail Population Served by Non- Purchased Systems 2011 SDWIS/Fed Freeze SYR3 ICR Data Percent Difference2 2011 SDWIS/Fed Freeze SYR3 ICR Data Percent Difference2 Wyoming 698 682 -2% 380,269 378,901 -0.4% Total 132,299 147,040 11% 225,722,111 231,374,166 3% 1 As indicated in Exhibit 5-3, approximately 57 percent of the total number of water systems whose data were submitted by states for the third Six-Year Review are transient non-community water systems. Because only the nitrate/nitrite regulations require compliance monitoring by these transient systems (Exhibit 4.1), data from the transient systems were included only for the nitrate and nitrite occurrence analyses and were excluded for all occurrence analyses for lOCs, SOCs, VOCs and radiological contaminants. 2 The 'percent difference' was calculated by subtracting the 2011 SDWIS/Fed Freeze total number of non-purchased systems (or retail population served by systems) from the SYR3 ICR Dataset total number of non-purchased systems (or retail population served by systems). That difference was then divided by the total number of non-purchased systems (or retail population served by systems) from the SYR3 ICR Dataset. The 'percent difference' is less than zero if the SYR3 ICR Dataset indicated a smaller number of systems (or retail population served by systems). Exhibit 2.3 compares the number of systems and population served by these systems in the December 2011 SDWIS/Fed freeze and the SYR3 ICR Dataset stratified by source water type and system type. (For consistency with SDWIS/Fed data, non-purchased systems and the only the direct or retail population served are included in this comparison. See Section 4.2 for more information.) The overall national 46 state totals indicate about 11 percent more systems and a three percent greater population served is reported in the SYR3 ICR Dataset than is represented in SDWIS/Fed. For community water systems (CWSs), there is about a four percent difference based on the number of systems and a two percent difference based on the population served by systems. Percentage differences were larger for ground water systems than surface water systems. For non-transient non-community water systems (NTNCWSs), there is about a 13 percent difference based on the number of systems and an 8 percent difference based on the population served by systems. For transient non-community water systems (TNCWSs), there is about a 12 percent difference based on the number of systems and a 7 percent difference based on the population served by systems. CWSs account for approximately 93 percent of the total population served by systems in the United States. Exhibit 2.3: Comparison of the Total Number of Systems and Retail Population Served in SDWIS/Fed and the SYR3 ICR Dataset, By Source Water Type and System Type Source Water Type 2011 SDWIS/Fed Freeze SYR3 ICR Dataset CWS NTNCWS TNCWS Total CWS NTNCWS TNCWS Unknown1 Total Number of Non-Purchased Systems Ground Water (GW) 33,247 16,325 77,221 126,793 34,576 18,802 87,816 123 141,317 Surface Water (SW) 4,226 322 958 5,506 4,327 335 1,058 3 5,723 Total 37,473 16,647 78,179 132,299 38,903 19,137 88,874 126 147,040 SYR3 Occurrence Support Document 2-11 December 2016 ------- Source Water Type 2011 SDWIS/Fed Freeze SYR3 ICR Dataset CWS NTNCWS TNCWS Total CWS NTNCWS TNCWS Unknown1 Total Retail Population Served Ground Water (GW) 77,175,728 4,734,551 9,552,196 91,462,475 79,082,376 5,148,753 10,332,691 2,573 94,566,393 Surface Water (SW) 133,813,746 153,948 291,942 134,259,636 136,398,900 137,898 270,751 224 136,807,773 Total 210,989,474 4,888,499 9,844,138 225,722,111 215,481,276 5,286,651 10,603,442 2,797 231,374,166 1 Systems with unknown system type (i.e., system type not reported by the state) were included in the third Six-Year Review analyses. SYR3 Occurrence Support Document 2-12 December 2016 ------- 3 Data Management The data received from the states were in a variety of formats and data structures and required reformatting to a uniform structure to enable the national contaminant occurrence analyses. This section provides an overview of the data management efforts that were conducted to enable and facilitate the contaminant occurrence analyses. Additional details of the data management measures can be found in USEPA (2016d). 3.1 Dataset Consistency and Restructuring About 75 percent of all states currently store and manage at least portions of their compliance monitoring data in the Safe Drinking Water Information System/State Version (SDWIS/State). The majority of states using SDWIS/State that submitted data to EPA used a SDWIS Query Extract Tool, developed and provided by EPA, to extract and compile the EPA-requested compliance monitoring data. The Extract Tool enabled a streamlined effort by states to select, compile and format the requested data and generally resulted in state submission of complete datasets that were uniform in format. The states not using SDWIS/State submitted their compliance monitoring data "as is," resulting in a variety of formats of datasets submitted to EPA. Exhibit 3.1 lists the states that did and did not use the SDWIS Query Extract Tool. Thirty-three states and three tribes used the SDWIS Query Extract Tool to extract all or some of their chemical data; therefore, those datasets were all submitted in a similar format. States that did not use the SDWIS Query Extract Tool were restructured into a format similar to the data structure achieved by the EPA tool. The SDWIS Query Extract Tool pulls the SDWIS/State data into Microsoft (MS) Access. The 18 states/ primacy agencies that did not use the SDWIS Query Extract Tool submitted data in a variety of file types, including dBase, MS Access, comma delimited, tab delimited, Text and Excel. However, all of these datasets were converted to MS Access to enable a detailed QA/QC review. Exhibit 3.1: Summary of Compliance Monitoring Data Provided by States for the Third Six-Year Review State Name Alabama Maine Oregon Alaska Missouri Region 4 tribes Arizona Montana Region 5 tribes Arkansas Nebraska Region 8 tribes Connecticut Nevada Rhode Island States/Entities that DID use Idaho New Jersey1 South Carolina the SDWIS Extract Tool Illinois New Mexico Texas1 Indiana New York Utah Iowa North Carolina1 Vermont Kansas North Dakota Virginia Kentucky Ohio West Virginia Louisiana Oklahoma Wyoming SYR3 Occurrence Support Document 3-13 December 2016 ------- State Name American Samoa Michigan Region 9 tribes California Minnesota South Dakota States/Entities that DID NOT Florida Navajo Nation Tennessee use the SDWIS Extract Tool Hawaii New Hampshire Washington Maryland Pennsylvania Washington, D.C. Massachusetts Region 1 tribes Wisconsin 1 North Carolina, New Jersey and Texas submitted their SDWIS/State data in an Oracle database. EPA applied the SDWIS Query Extract Tool to their databases to extract and compile the compliance monitoring data requested by EPA for the Third Six-Year Review. 3.2 Review of Dataset Content One of the first reviews of the submitted data sets was to verify that all of the necessary data elements were included. Many of the states not using the SDWIS Query Extract Tool submitted datasets with more data elements than necessary. In those cases, EPA determined which data elements were and were not needed for the Six-Year Review 3 occurrence analyses. Exhibit 3.2 provides a detailed list of the data elements requested by EPA for Six-Year Review 3. Although data dictionaries were not necessary for the review of data from states that used the SDWIS Query Extract Tool, these files (or any other available supporting information provided by the states) were very useful when trying to interpret the data submitted by the states that did not use the SDWIS Query Extract Tool. Data dictionary and supporting information files were reviewed for a definition of the various data elements, field/row headings, codes and acronyms, among others. In addition, field names were standardized and data types were changed to similar formats. Data reported for each field were also standardized. Exhibit 3.2: Data Elements Requested by EPA for the Third Six-Year Review Data Category Description System-Specific Information Public Water System Identification Number (PWSID) The code used to identify each PWS. The code begins with the standard 2-character postal state abbreviation or Region code; the remaining seven numbers are unique to each PWS in the state. System Name Name of the PWS. Federal Public Water System Type Code A code to identify whether a system is: • Community Water System, • Non-transient Non-community Water System, or • Transient Non-community Water System. Population Served Highest average daily number of people served by a PWS, when in operation. Federal Source Water Type Type of water at the source. Source water type can be: • Ground water, or • Surface water, or • Ground water under the direct influence of surface water (GWUDI) (Note: Some states may not distinguish GWUDI from surface water sources. In those states, a GWUDI source should be reported as a surface water source type.) Sanitary Survey Information Site visit information for Total Coliform Rule (TCR), Ground Water Rule (GWR) and Surface Water Treatment Rules (SWTRs), including: site visit type, date completed, associated deficiencies identified, corrective actions taken. Treatment Information SYR3 Occurrence Support Document 3-14 December 2016 ------- Data Category Description Water System Facility System facility data, including: treatment plant identification number, treatment plant information, treatment unit process/objectives, facility flow, treatment train (train or flow of water through treatment units within the treatment plant). Filtration Type Information relating to system filtration, including: filtration status, types of filtration (e.g., unfiltered, conventional filtration and other permitted values) Treatment Technique Information Information pertaining to treatment processes. Types of treatment technique information including: coagulant/coagulant aid type and dose, disinfectant concentration (amounts, types, primary and secondary types of disinfection, disinfection profile/bench mark data), log of viral inactivation/removal, contact time, contact value, pH, temperature. Filter Backwash Information Information about filter backwash that is returned to the treatment plant influent (e.g., information on: recycle/schematic status, alternative return location, corrective action requirements and recycle flows and frequency). Sample-Specific Information Sampling Point Identification Code A sampling point identifier established by the state, unique within each applicable facility, for each applicable sampling location (e.g., entry point to the distribution system). This information enables occurrence assessments that address intra-system variability. Sample Identification Number Identifier assigned by state or the laboratory that uniquely identifies a sample. Sample Collection Date Date the sample is collected, including month, day and year. Sample Type Indicates why the sample is being collected (e.g., compliance, routine, repeat, confirmation, additional routine samples, duplicate, special, special duplicate, etc.). Sample Analysis Type Code Code for type of water sample collected. • Raw (Untreated) water sample, • Finished (Treated) water sample For lead and copper only: • Source, • Tap For TCR, Repeats only; indicator of sampling location relative to sample point where positive sample was originally collected: • Upstream, • Downstream, • Original Contaminant Contaminant name, 4-digit SDWIS contaminant identification number or Chemical Abstracts Service (CAS) Registry Number for which the sample is being analyzed. Sample Analytical Result - Sign The sign indicates whether the sample analytical result was: • (<) "less than" means the contaminant was not detected or was detected at a level "less than" the minimum reporting level (MRL). • (=) "equal to" means the contaminant was detected at a level "equal to" the value reported in "Sample Analytical Result - Value." (Not required for TCR data) Sample Analytical Result - Value Actual numeric (decimal) value of the analysis for the chemical results, or the MRL if the analytical result is less than the contaminant's MRL. For the TCR, results will indicate presence/absence. Sample Analytical Result - Unit of Measure Unit of measurement for the analytical results reported (usually expressed in either |jg/L or mg/L for chemicals; or pCi/L or mrem/yrfor radiological contaminants). (Not required for TCR data) Sample Analytical Method Number EPA identification number of the analytical method used to analyze the sample for a given contaminant. Minimum Reporting Level (MRL) - Value MRL refers to the lowest concentration of an analyte that may be reported. (Not required for TCR data) MRL - Unit of Measure Unit of measure to express the concentration value of a contaminant's MRL. (Not required for TCR data) Source Water Monitoring Information Total organic carbon (TOC), including percent TOC removal, TOC removal summary, pH, alkalinity, monitoring data entered as individual results or included in DBP (or monthly operating report (MOR)) summary records, alternative compliance criteria. Sample Summary Reports Sample summaries for Disinfection Byproduct Rules (DBPRs), SWTRs, TCR and Lead and Copper Rule (LCR) associated with analytical result records. Values used for compliance determination [e.g., turbidity (combined effluent/individual effluent), disinfectant residual levels in treatment plant and distribution system, treatment technique information, Heterotrophic Plate Count (HPC), etc.] SYR3 Occurrence Support Document 3-15 December 2016 ------- It was also necessary to confirm that all of the requested contaminants were included in each state dataset. EPA requested voluntary submission of compliance monitoring information for chemical contaminants regulated under Phase I, II, lib and V Rules; the Arsenic Rule; and the Radionuclides Rule. In addition, EPA requested data collected for the Ground Water Rule, Surface Water Treatment Rules, Disinfection Byproduct Rules and Filter Backwash Recycling Rule (FBRR). Exhibit 3.3 below lists the specific contaminants for which EPA requested monitoring data. Note that all contaminants whose data were requested are listed in the table, though not all were not analyzed as part of this report because they are being evaluated under other regulatory actions or included in separate regulatory reviews. The following contaminants/contaminant groups are not evaluated in this report: lead and copper, cVOCs, acrylamide and epichlorohydrin, disinfectants and their byproducts and microbial contaminants. See Section 1 for more details on the contaminants addressed in this report. Exhibit 3.3: List of Contaminants for Which Data Were Requested from States Chemical Contaminants (Phase 1, II, IIB and V Rules; Arsenic Rule; Lead and Copper Rule) Acrylamide 1,1-Dichloroethylene Methoxychlor Alachlor cis-1,2-Dichloroethylene Monochlorobenzene (Chlorobenzene) Antimony trans-1,2-Dichloroethylene Nitrate (as N) Arsenic Dichloromethane (Methylene chloride) Nitrite (as N) Asbestos 1,2-Dichloropropane Oxamyl (Vydate) Atrazine Di(2-ethylhexyl) adipate (DEHA) Pentachlorophenol Barium Di(2-ethylhexyl) phthalate (DEHP) Picloram Benzene Dinoseb Polychlorinated biphenyls (PCBs) Benzo[a]pyrene Diquat Selenium Beryllium Endothall Simazine Cadmium Endrin Styrene Carbofuran Epichlorohydrin 2,3,7,8-TCDD (Dioxin) Carbon tetrachloride Ethyl benzene Tetrachloroethylene Chlordane Ethylene dibromide (EDB) Thallium Chromium (total) Fluoride Toluene Copper Glyphosate Toxaphene Cyanide Heptachlor 2,4,5-TP (Silvex) 2,4-Dichlorophenoxyacetic acid (2,4-D) Heptachlor epoxide 1,2,4-T richlorobenzene Dalapon Hexachlorobenzene 1,1,1-Trichloroethane 1,2-Dibromo-3-chloropropane (DBCP) Hexachlorocyclopentadiene 1,1,2-T richloroethane 1,2-Dichlorobenzene (o-Dichlorobenzene) Lead Trichloroethylene 1,4-Dichlorobenzene (p-Dichlorobenzene) Lindane Vinyl chloride 1,2-Dichloroethane (Ethylene dichloride) Mercury (inorganic) Xylenes (total) Radiological Contaminants Combined Radium-226/228; and Radium-226 & Radium-228 (if available) Gross beta Tritium lodine-131 Uranium SYR3 Occurrence Support Document 3-16 December 2016 ------- Chemical Contaminants (Phase 1, II, IIB and V Rules; Arsenic Rule; Lead and Copper Rule) Gross alpha Strontium-90 Microbiological Contaminants Total coliforms Fecal coliforms Escherichia coli (E. coli) Disinfectants and Disinfection Byproducts Rules (DBPRs)1 Total Trihalomethanes (TTHMs): Haloacetic Acids (HAA5): Bromate Chloroform Monochloroacetic acid Chlorite Bromodichloromethane Dichloroacetic acid Chlorine Dibromochloromethane Trichloroacetic acid Chloramines Bromoform Bromoacetic acid Chlorine dioxide Dibromoacetic acid Ground Water Rule (GWR) Escherichia coli (E. coli) Enterococci Coliphage Surface Water Treatment Rules (SWTRs)2 Chlorine Cryptosporidium Heterotrophic Plate Count (HPC) Chloramines Giardia lamblia Filter Backwash Recycling Rule (FBRR) No specific occurrence data collected; see Exhibit 3.2 for data elements for FBRR 1 Including both Disinfection Byproducts/Treatment Rules: Stage 1 (December 1998) and Stage 2 (January 2006). 2 Including: Surface Water Treatment Rule (June 1989); Interim Enhanced SWTR (December 1998); Long-Term 1 Enhanced SWTR (January 2002); and, Long-Term 2 Enhanced SWTR (January 2006). 3.3 Establishing Consistent Data Fields for Analytical Results When preparing the data for the occurrence analysis, as well as a review for potential outliers, etc., it was essential to get the following three data elements into a consistent format: the sample analytical result (sign), sample analytical result (value) and sample analytical result (unit of measure). Many of the state datasets included analytical results signs (e.g., "<" for non- detections or "=" for detections), detection limits and analytical results data in multiple fields. A "DETECT" field was added to all of the state datasets to identify the results sign. Wherever the analytical result was greater than zero and the result sign indicated a detection, then DETECT was set equal to 1, representing a detection. When the analytical result was equal to zero and/or the result sign indicated a non-detection, then DETECT was set equal to 0 (i.e., a non-detect). Finally, data were received in a variety of units of measure. It was important that all data for each individual contaminant be expressed in a single unit in order to facilitate analysis. Chemical monitoring data were received in both milligrams per liter (mg/L) and micrograms per liter (|ig/L). For this analysis, all data for IOCs were converted to mg/L, while all data for the SOCs, VOCs and uranium were converted to |ig/L. Data for alpha particles, beta particles and combined SYR3 Occurrence Support Document 3-17 December 2016 ------- radium-226/228 were analyzed in picocuries per liter (pCi/L).5 Note that with the exception of asbestos and the radionuclides, all thresholds and concentrations in this report are expressed in Hg/L. 5 Although the MCL for beta particles, 4 mrem/yr, is in the unit of measure of millirem per year (mrem/yr), the primary unit of analytical measure is picocuries per liter (pCi/L). This unit of measure relates to screening thresholds of 15 pCi/L and 50 pCi/L that are defined in the 2000 Radionuclides Rule. More than 99 percent of all compliance monitoring data for beta particles submitted by the states to EPA were in units of pCi/L. The analyses presented here are based on compliance monitoring data represented in units of pCi/L and are conducted relative to the screening threshold of 50 pCi/L. SYR3 Occurrence Support Document 3-18 December 2016 ------- 4 Data Quality Assurance/Quality Control After the state data sets were converted into a consistent format, a significant effort was undertaken to ensure the quality of the data submitted. This QA/QC effort encountered a range of data quality across the different contaminants and different states. Included below is a summary description of the QA/QC measures that were conducted on the state datasets prior to analysis. Not all QA/QC measures described were conducted on all states, as noted below. For complete details of the data QA/QC measures, refer to USEPA (2016d). 4.1 Quality Assurance Measures Before the analyses of contaminant occurrence could begin, EPA performed an initial QA/QC review of each state's data. EPA sent emails to each state, asking general questions about their data set, if necessary. Question topics included descriptions of non-intuitive data element names, definitions of field headings, or non-standard codes that were not described in any documentation files from the state. It was also necessary to confirm that all of the requested contaminants were included in each state dataset. When a state was missing data for any of the contaminants listed in Exhibit 3.3, EPA asked the state to identify the reason for the omission, such as a statewide waiver for the contaminant(s). States were asked to provide data for all contaminants listed in Exhibit 3.3, but individual PWSs may be required to sample for a subset of those contaminants depending on the type of system. Exhibit 4.1 lists the systems that are required to monitor for the contaminants within each chemical group. All required data that passed the QA/QC process, given the type of system, were included in the third Six-Year Review analyses. Some systems provided monitoring data that were not required given their system type (e.g., SOC data from transient systems or radionuclide data from transient or non-transient non-community systems), however this data was available inconsistently. To ensure consistent monitoring and to avoid bias, this non-required data were maintained in the SY3 ICR database but were excluded from the third Six-Year Review analyses. Exhibit 4.1: Chemical Group Monitoring Requirements Chemical Group System Types Required to Sample (sample data included in analyses) System Types Not Required to Sample (sample data excluded from analyses) Inorganic Chemicals (lOCs) All non-purchased community water systems and non-transient non-community water systems are required to sample for lOCs. All purchased systems and transient non- community water systems are not required to sample for lOCs. Nitrate and Nitrite Non-purchased community water systems, non- transient non-community water systems and transient non-community water systems are all required to sample for nitrate and nitrite. All purchased systems are not required to sample for nitrate and nitrite Synthetic Organic Chemicals (SOCs) All non-purchased community water systems and non-transient non-community water systems are required to sample for SOCs. All purchased systems and transient non- community water systems are not required to sample for SOCs. Volatile Organic Chemicals (VOCs) All non-purchased community water systems and non-transient non-community water systems are required to sample for VOCs. All purchased systems and transient non- community water systems are not required to sample for VOCs. SYR3 Occurrence Support Document 4-19 December 2016 ------- Chemical Group System Types Required to Sample (sample data included in analyses) System Types Not Required to Sample (sample data excluded from analyses) Radiological Contaminants All non-purchased community water systems are required to sample for the radionuclides. All purchased systems and non-purchased non-transient non-community and non- purchased transient non-community water systems are not required to sample for radionuclides. EPA created several automated data QA checks to identify potential common data entry errors or numerical inconsistencies. These QA checks flagged records with potential data quality concerns. EPA sent out a detailed report to each state describing its flagged records, which included the counts of flagged records by category (described below) as well as specific questions for each of these categories. An attachment identified the specific records that were flagged; EPA requested that each state provide the appropriate disposition (delete, make corrections, etc.) of these flagged records. For all flagged records, input from the states was always used as the initial criteria in deciding on the appropriate action or decision to include / exclude the record from analysis. When states did not provide a response or action, EPA made a decision on what to do with the data in question. Below is a general description of the various QA measures that were used to identify records of potential data quality concerns. Of these flagged records, a number of categories addressed sampling concerns. For example, samples that were taken outside of the SYR3 date range, collected from non-public water systems, or identified as non-compliance were excluded from the occurrence analysis. All data from purchased systems were excluded from the occurrence analysis, as well as any sample types other than routine or confirmation. Non-nitrate or nitrite data collected from transient systems were excluded unless a state responded to say that the system in question was previously a CWS and NTNCWS at the time of sampling. Other categories of flagged records included reporting concerns, such as use of correct units, inclusion of duplicates and missing system inventory data. Samples with reported units that were not one of the standard units used for the particular contaminant were excluded unless there was strong evidence of the correct standard unit to use. Potential duplicates were included in the occurrence analysis for consistency with the second Six-Year Review unless the state confirmed that the records were in fact duplicates and should be excluded. Samples from systems that did not specify inventory data were supplemented by a 4th quarter 2011 SDWIS/Fed data freeze and were included in the occurrence analysis. However, all records from systems whose inventory data were still missing after filling gaps with SDWIS/Fed data were excluded from the analysis. For all samples, any detected concentrations that were greater than four times the contaminant's MCL and any that were greater than 10 times the MCL were flagged and sent to states for comment. Any changes suggested by the states were implemented for these records. For the states that did not respond, all concentrations less than or equal to 100 times the MCL were included; any greater than 100 times the MCL were excluded. Similarly, all detected SYR3 Occurrence Support Document 4-20 December 2016 ------- concentrations less than the contaminant's method detection limit (MDL)6 and all less than one tenth of the MDL were sent to states for comment and any changes suggested by the states were implemented. For states that did not respond, all detected concentrations greater than or equal to 1/100 of the MDL were included in the analysis and any with concentrations less than 1/100 of the MDL were excluded. In addition, data collected from raw water samples were considered based on corresponding finished water samples and compliance status. The review of states responses on these flagged records was a critical QA step prior to the data analysis. EPA documented all changes made to the compliance monitoring data and suggested to the states that they make corrections in their data system as well, if appropriate. To resolve data quality issues that required significant corrections to the raw data, such as identifying and deleting outliers or identifying and changing incorrect units, state data management staff were consulted when appropriate before data corrections were completed. The initial SYR3 ICR Dataset included more than 47 million analytical records from approximately 167,000 PWSs that serve approximately 290 million people nationally.7 More than two-thirds of these records (more than 33 million) were for contaminants that were not analyzed as part of this current Six-Year Review 3 effort (including lead, copper, cVOCs, total coliform, DBPs and others). More than 13 million analytical records underwent QA/QC review in order to be included in the SYR3 ICR Dataset for contaminants evaluated in this report for the Six-Year Review 3. After the QA/QC review was completed on these analytical records and a small percentage of records that did not meet quality standards were omitted from analyses, the final SYR3 ICR Dataset comprise almost 13 million analytical records from approximately 139,000 PWSs that serve approximately 290 million people nationally.8 4.2 Adjustments of Population Served by Public Water Systems "Purchased" water systems are the systems that purchase 100 percent of their water from other systems ("seller" or "wholesaler" systems). Compliance monitoring requirements are different for purchased water systems compared to non-purchased systems because purchased water systems do not have their own water sources (e.g., wells or intakes). As described above, EPA excluded from the analysis data from systems that purchase 100 percent of their water. However, EPA did adjust the population values of the wholesale systems to include the population of the systems that they sell to (the purchased water systems). The population served directly by these wholesale systems is known as the "retail population," while the population served indirectly 6 The Method Detection Limit, MDL, is defined as the minimum concentration of a substance that can be measured and reported with 99 percent confidence, based on an analyte concentration being greater than zero as determined from analysis of a sample in a given matrix containing the analyte. In other words, the MDL is the concentration at which presence or absence of an analyte can be dependably determined. This contrasts with the MRL, which is a concentration above the MDL, typically set 2 to 10 times the MDL and enables reporting at specified levels of precision and accuracy of the actual concentration of the analyte present in the sample. 7 This count of 167,000 PWSs represents all water systems that submitted any SYR3 data (including purchased water systems). In this case, 290 million is the population served directly (retail) by these purchased and non- purchased systems (see Section 4.2). 8 This count of 139,000 PWSs represents non-purchased systems only. The population served remains at 290 million; however, the number now reflects the total population served directly (retail) and indirectly (wholesale) by non-purchased systems only. SYR3 Occurrence Support Document 4-21 December 2016 ------- through the purchased systems is known as the "wholesale population." This adjustment ensured that all relevant population were included in the exposure estimates. For some systems, a slightly more complicated adjustment to the wholesalers' total population served values was required. Many purchased water systems buy water from more than one wholesaler. Because of this, their entire population should not be attributed to a single wholesale system and EPA must instead distribute the population across the wholesale systems. There are no data available on the actual relative quantities of water purchased from the different wholesalers. In the cases of multiple wholesalers, the population served by the purchased system was assumed to be uniformly distributed across the wholesalers. To make adjustments across the SYR3 ICR data, EPA compiled a list of all wholesale and purchased systems. This list of buyer-wholesaler relationships was from SDWIS/Fed, fourth quarter of 2010. EPA then created a crosswalk linking the purchased systems to the wholesale systems from which they purchased 100 percent of their water. The population served by each purchased system was then distributed evenly across the relevant wholesale system populations, according to the calculations described above. As a result, the contaminant occurrence measures are associated with the total (retail plus wholesale) population served by these non-purchased systems included in the Six-Year Review data. 4.3 Adjustments of Source Water Type for Public Water Systems For the third Six-Year Review analysis, each system must have a single source water type and population served designation to define each system in a unique source water type/population size strata. Systems using both ground water and surface water and systems using ground water under direct influence of surface water, were considered surface water systems for analysis. Systems with more than one specified value of their population served in the original data were included using their most frequently occurring population served value. An additional adjustment to source water type was necessary for a select group of systems whose water came from a mix of consecutive connections and their own sources. Specifically, these were systems that do not have their own intake or other SW facilities but do purchase some SW; however, in addition, they do have some of their own GW wells. In these cases, because the system does include some purchased surface water (SWP) sources, the federal source water type is listed as SWP in SDWIS/Fed and in the states' compliance monitoring data. This is the case even if the system only purchases a very small portion of their water and the rest of the water comes from GW wells. Based on the QA criteria described in Section 4.1, data from these systems should be excluded from the SYR3 data analyses since data from purchased water systems were excluded. However, the GW sources from these systems did provide legitimate (and required) compliance monitoring data. Thus, it was necessary in the SYR3 analyses to consider these SWP systems as GW systems as the compliance monitoring data that were provided by these systems were from GW sources. SYR3 Occurrence Support Document 4-22 December 2016 ------- 5 Summary of the Compliance Monitoring Data This section provides an overview of the data that were received, passed the QA/QC process and were analyzed for Six-Year Review 3. Also provided is information on the total number of systems in the final SYR3 ICR Dataset; characteristics of the systems such as system types, source water types, population served; the number of records from each state and the number of records for each contaminant. An assessment of contaminant occurrence variability over the six years was also conducted and is described below. 5.1 Characteristics of the Data - States, Systems and Records Exhibit 5.1 shows the number and percent of systems and population served by systems according to source water type in the SYR3 ICR Dataset. Exhibit 5.2 shows the number and percent of systems and the population served by systems according to source water type and system size. As discussed in Sections 4.1 and 4.2, purchased water systems were excluded and the populations served by these systems were accounted for in the occurrence analyses for the contaminants evaluated in this report. Population served values and occurrence estimates in all tables in Section 5, 6 and 7 were generated using the total (adjusted) population served, as is described in Section 4.2. Source water types stratified by all classifications, including GWUDI as well as GW and SW groupings, are presented in Exhibit 5.1. For analysis of these data, however, EPA followed its standard practice of treating GWUDI as surface water. Exhibit 5.1: Number of Systems and Population Served by Systems in the SYR3 ICR Dataset, by Source Water Type Source Water Type Systems Total Population Served by Systems Number Percent of Total Number Percent of Total Ground Water (GW) 133,516 96% 125,617,215 43% Ground Water Under the Direct Influence of Surface Water (GWUDI) 775 1% 2,075,138 1% Surface Water (SW) 4,769 3% 162,885,819 56% Total Number of Systems 139,060 100% 290,578,172 100% SYR3 Occurrence Support Document 5-23 December 2016 ------- Exhibit 5.2: Number of Systems and Population Served by Systems in the SYR3 ICR Dataset, by System Size System Size (Population Served by the System) Ground Water (GW) Surface Water (SW) Total Number of Systems Total Population Served by Systems Number of Systems Total Population Served by Systems Number of Systems Total Population Served by Systems <50 43,588 1,230,003 573 13,343 44,161 1,243,346 50-100 35,646 2,611,071 436 32,921 36,082 2,643,992 101 -500 36,323 8,464,729 891 235,031 37,214 8,699,760 501 -1,000 7,074 5,194,327 383 294,985 7,457 5,489,312 1,001 -3,300 6,066 11,206,423 821 1,694,222 6,887 12,900,645 3,301 -10,000 2,859 16,418,571 944 5,898,160 3,803 22,316,731 10,001 -50,000 1,600 34,484,799 969 22,454,312 2,569 56,939,111 50,001 -100,000 229 15,675,332 252 17,594,243 481 33,269,575 100,001 -1 million 127 23,968,963 255 69,329,070 382 93,298,033 > 1 million 4 6,362,997 20 47,414,670 24 53,777,667 Total 133,516 125,617,215 5,544 164,960,957 139,060 290,578,172 Exhibit 5.3 shows the number and percent of systems in the SYR3 ICR Dataset by system type. Although more than 57 percent of the systems are transient water systems they serve only 3.3 percent of the population; almost 95 percent of the population is served by CWSs. Only a small fraction of transient systems collected data for most of the contaminants requested in the SYR3 ICR data call-in, as transient systems are only required to collect nitrate and nitrite samples. SYR3 Occurrence Support Document 5-24 December 2016 ------- Exhibit 5.3: Number of Systems and Retail Population Served by Systems in the SYR3 ICR Dataset, by System Type System Type Systems Total Population Served by Systems Number Percent of Total Number Percent of Total Community Water System (CWS) 40,196 28.9% 275,436,560 94.8% Non-Transient Non-Community Water System (NTNCWS) 18,941 13.6% 5,572,922 1.9% Transient Non-Community Water System (TNCWS)1 79,804 57.4% 9,566,002 3.3% Unknown2 119 0.1% 2,688 0.0% Total Number of Systems 139,060 100% 290,578,172 100% 1 Only the nitrate/nitrite regulations require compliance monitoring by these transient systems; thus, data from the transient systems were included only for the nitrate and nitrite occurrence analyses and were excluded for all occurrence analyses for lOCs, SOCs, VOCs and radiological contaminants. 2 Systems with unknown system type were included in the Six-Year Review 3 analyses. None of the occurrence analyses conducted for the Six-Year Review 3 required specifying the system type. Exhibit 5.4 lists the total number of records, systems and population served by systems in each of the 54 state/tribal datasets used in the Six-Year Review 3 analyses. In addition, the last column of the table lists any contaminant(s) for which the state did not provide data. States might not have submitted data for certain contaminants if they have monitoring waivers for the contaminant. States may grant waivers to PWSs to reduce monitoring frequencies; thus, it is possible that no samples were collected by systems during the SYR3 period of review. See Section 1.2 for more information on compliance monitoring and waivers. States may have submitted data for these contaminants under the ICR; however, the data were not in a format compatible with the SYR3 ICR data set. See Exhibit 5.5 for the list of regulated contaminants evaluated for the third Six-Year Review. Exhibit 5.4: An Inventory of Contaminant Occurrence Data in the SYR3 ICR Dataset, by State State Number of Records for Regulated Contaminants 1 Number of Systems with Data for Regulated Contaminants Population Served by Systems with Data for Regulated Contaminants Did not submit useable data for the following regulated contaminants: Alabama 191,413 452 5,346,899 Alaska 53,315 1,365 817,479 American Samoa 5,208 11 62,196 Combined Radium-226 & -228 Arizona 332,193 1,739 6,813,243 Arkansas 141,835 517 2,643,519 Asbestos; 2,3,7,8-TCDD (Dioxin); Alpha Particles; Uranium; Combined Radium-226 &- 228 SYR3 Occurrence Support Document 5-25 December 2016 ------- State Number of Records for Regulated Contaminants 1 Number of Systems with Data for Regulated Contaminants Population Served by Systems with Data for Regulated Contaminants Did not submit useable data for the following regulated contaminants: California 2,224,544 7,728 42,332,069 Colorado 133 2 2,047 The State of Colorado did not provide data for any contaminants for the 3rd Six-Year Review. The counts in this row reflect data from two tribal systems located in Colorado. Connecticut 321,895 2,971 3,018,503 Florida 550,332 6,338 19,889,742 Hawaii 50,400 118 1,489,566 Alpha Particles; Combined Radium-226 & -228 Idaho 114,635 1,907 1,364,144 Illinois 387,634 4,500 11,448,122 2,3,7,8-TCDD (Dioxin) Indiana 132,072 4,267 5,482,894 Iowa 76,870 1,828 2,873,105 2,3,7,8-TCDD (Dioxin) Kansas 75,653 696 2,661,362 Kentucky 77,124 265 4,244,786 Louisiana 217,092 1,120 4,978,104 Asbestos Maine 109,766 2,182 978,294 Glyphosate; 2,3,7,8-TCDD (Dioxin); Beta Particles Maryland 163,019 3,695 5,421,969 Asbestos; Ethylene Dibromide (EDB) Massachusetts 259,042 1,666 9,484,435 2,3,7,8-TCDD (Dioxin); Combined Radium-226 & -228 Michigan 400,333 12,934 8,647,270 Minnesota 261,926 7,808 4,988,096 Mississippi 1,085 5 6,176 The State of Mississippi did not provide data for any contaminants for the 3rd Six-Year Review. The counts in this row reflect data from five tribal systems located in Mississippi. Missouri 230,179 2,660 5,463,242 Asbestos; 2,3,7,8-TCDD (Dioxin); Polychlorinated biphenyls (PCBs) Montana 126,612 966 873,923 2,3,7,8-TCDD (Dioxin) Nebraska 182,390 740 1,668,159 Nitrate; Nitrite; 2,3,7,8-TCDD (Dioxin); Polychlorinated biphenyls (PCBs) Nevada 143,882 615 2,725,079 SYR3 Occurrence Support Document 5-26 December 2016 ------- State Number of Records for Regulated Contaminants 1 Number of Systems with Data for Regulated Contaminants Population Served by Systems with Data for Regulated Contaminants Did not submit useable data for the following regulated contaminants: New Hampshire 243,533 2,606 1,201,039 Asbestos; 2,3,7,8-TCDD (Dioxin); Polychlorinated biphenyls (PCBs); Beta Particles New Jersey 369,861 4,337 9,757,926 Toxaphene; Dalapon; Diquat; Endothall; Glyphosate; 2,3,7,8-TCDD (Dioxin); Polychlorinated biphenyls (PCBs); Chlordane; Beta Particles New Mexico 185,680 902 2,003,572 New York 799,621 8,844 20,833,578 North Carolina 646,516 6,747 8,274,437 North Dakota 10,496 192 610,974 Asbestos; 2,3,7,8-TCDD (Dioxin); Beta Particles Ohio 265,231 5,343 10,703,302 Oklahoma 127,513 963 3,617,365 Asbestos; 2,3,7,8-TCDD (Dioxin); Di(2- ethylhexyl)phthalate (DEHP) Oregon 178,962 2,699 3,652,679 Pennsylvania 626,314 10,130 12,102,084 Combined Radium-226 & -228 Rhode Island 52,092 493 1,098,288 Diquat; Endothall; Glyphosate; 2,3,7,8-TCDD (Dioxin) South Carolina 126,052 1,092 3,719,705 Asbestos; Cyanide; Endothall; 2,3,7,8-TCDD (Dioxin); Polychlorinated biphenyls (PCBs); Beta Particles South Dakota 52,126 488 780,472 2,3,7,8-TCDD (Dioxin) Tennessee 43,478 667 6,628,308 Beta Particles; Combined Radium-226 & -228 Texas 563,231 6,011 26,068,814 Asbestos; Diquat; Glyphosate; 2,3,7,8-TCDD (Dioxin); Endothall; Polychlorinated biphenyls (PCBs) Utah 295,231 951 2,909,712 Vermont 72,624 1,360 590,755 Diquat; Endothall; Glyphosate; 2,3,7,8-TCDD (Dioxin); Beta Particles Virginia 209,608 1,860 6,964,718 Washington 342,363 4,170 5,715,708 2,3,7,8-TCDD (Dioxin) Washington, D.C. 1,335 1 761,124 Combined Radium-226 & -228 West Virginia 60,722 956 1,633,025 Wisconsin 389,849 8,708 4,732,724 Wyoming 59,384 443 493,316 2,3,7,8-TCDD (Dioxin) SYR3 Occurrence Support Document 5-27 December 2016 ------- State Number of Records for Regulated Contaminants 1 Number of Systems with Data for Regulated Contaminants Population Served by Systems with Data for Regulated Contaminants Did not submit useable data for the following regulated contaminants: Unknown 5 2 124 Total 12,552,409 139,060 290,578,172 1 Quality assurance steps were taken to identify and exclude fluoride samples from fluoridated water systems. The number of records presented in this table reflect the number of fluoride records before the exclusion of fluoridated systems. Exhibit 5.5 summarizes the SYR3 ICR Dataset by contaminant. For each contaminant, this table includes MCL concentration values, the number of states with data, total number of records, number of systems with data and the population served by systems that have data represented in the SYR3 ICR Dataset. Also presented are the modal MRL values for each contaminant, derived as the mode of state modal MRLs. See Section 7.1 for details regarding modal MRL values. Exhibit 5.5: An Inventory of the Contaminant Occurrence Data in the SYR3 ICR Dataset, by Contaminant Contaminant (MCL Concentration) Number of States with Data Total Number of Records Total Number of Systems Total Population Served by Systems MRL Inorganic Chemicals Antimony (6 Mg/L) 49 164,961 50,532 254,359,720 1 Mg/L Arsenic (10 |jg/L) 50 297,354 54,845 267,062,633 1 Mg/L Asbestos (7 MFL) 39 12,084 5,785 94,380,829 0.2 MFL Barium (2,000 Mg/L) 49 165,387 50,711 254,501,602 100 Mg/L Beryllium (4 Mg/L) 49 164,392 50,195 253,512,318 1 Mg/L Cadmium (5 Mg/L) 49 165,247 50,583 254,433,966 1 Mg/L Chromium (Total) (100 Mg/L) 49 167,251 50,597 254,405,306 1 Mg/L Cyanide (200 Mg/L) 49 119,659 36,907 210,427,981 10 Mg/L Fluoride1 (4,000 Mg/L) 49 256,237 47,227 189,186,454 100 Mg/L Mercury (Inorganic) (2 Mg/L) 49 164,558 50,552 254,397,552 0.2 Mg/L Nitrate (as N) (10,000 Mg/L) 49 1,157,522 132,176 266,378,543 100 Mg/L Nitrite (as N) (1,000 Mg/L) 49 445,544 85,742 224,146,056 100 Mg/L Selenium (50 Mg/L) 49 165,672 50,568 254,428,296 5 Mg/L SYR3 Occurrence Support Document 5-28 December 2016 ------- Contaminant (MCL Concentration) Number of States with Data Total Number of Records Total Number of Systems Total Population Served by Systems MRL Thallium (2 Mg/L) 49 164,156 50,522 254,265,115 1 Mg/L Synthetic Organic Chemicals2 Alachlor (2 Mg/L) 50 153,083 42,955 245,844,381 0.2 Mg/L Atrazine (3 Mg/L) 50 162,134 44,310 251,501,740 0.1 Mg/L Benzo(a)pyrene (0.2 ra/L) 50 131,437 34,341 220,684,857 0.02 Mg/L Carbofuran (40 Mg/L) 50 122,110 34,614 228,717,933 0.9 Mg/L Chlordane (2 Mg/L) 49 128,870 35,685 217,637,369 0.2 Mg/L Dalapon (200 Mg/L) 49 146,702 36,005 222,985,164 1 Mg/L Di(2-ethylhexyl)adipate (DEHA) (400 Mg/L) 50 133,169 34,628 221,563,794 0.6 Mg/L Di(2-ethylhexyl)phthalate (DEHP) (6 Mg/L) 49 133,523 33,923 216,841,935 0.6 Mg/L 1,2-Dibromo-3-chloropropane (DBCP) (0.2 Mg/L) 50 188,597 37,226 217,765,167 0.02 Mg/L 2,4-Dichlorophenoxyacetic acid (2,4-D) (70 Mg/L) 50 131,047 37,690 233,873,578 0.1 Mg/L Dinoseb (7 Mg/L) 50 126,014 36,701 230,831,397 0.2 Mg/L Diquat (20 Mg/L) 46 69,829 17,906 146,939,794 0.4 Mg/L Endothall (100 Mg/L) 45 61,972 15,538 136,801,729 9 Mg/L Endrin (2 Mg/L) 50 136,623 38,453 229,199,508 0.01 Mg/L Ethylene Dibromide (EDB) (0.05 Mg/L) 49 184,784 37,499 221,781,780 0.01 Mg/L Glyphosate (700 Mg/L) 45 70,016 18,502 145,203,976 6 Mg/L Heptachlor (0.4 Mg/L) 50 137,286 38,691 229,832,285 0.04 Mg/L Heptachlor Epoxide (0.2 Mg/L) 50 137,081 38,625 229,832,890 0.02 Mg/L Hexachlorobenzene (1 Mg/L) 50 137,816 38,498 230,197,968 0.04 Mg/L Hexachlorocyclopentadiene (50 Mg/L) 50 140,004 38,743 229,902,564 0.1 Mg/L Lindane (gamma- Hexachlorocyclohexane) (0.2 Mg/L) 50 139,076 39,260 231,972,432 0.02 Mg/L Methoxychlor (40 Mg/L) 50 139,744 39,187 233,030,961 0.1 Mg/L Oxamyl (Vydate) (200 Mg/L) 50 121,508 34,518 227,520,373 2 Mg/L SYR3 Occurrence Support Document 5-29 December 2016 ------- Contaminant (MCL Concentration) Number of States with Data Total Number of Records Total Number of Systems Total Population Served by Systems MRL Pentachlorophenol (1 Mg/L) 50 140,486 40,322 234,008,187 0.04 Mg/L Picloram (500 |jg/L) 50 128,401 37,445 233,036,908 0.1 Mg/L Polychlorinated biphenyls (PCBs) (0.5 Mg/L) 44 86,405 21,571 153,248,065 0.1 Mg/L Simazine (4 Mg/L) 50 156,862 43,240 247,063,728 0.07 Mg/L Toxaphene (3 pg/L) 49 127,187 37,043 223,888,971 1 Mg/L Mg/L 2,3,7,8-TCDD (Dioxin) (0.00003 Mg/L) 30 20,244 3,216 74,077,780 0.000005 Mg/L 2,4,5-Trichlorophenoxypropionic Acid (Silvex) (50 Mg/L) 50 126,887 36,897 230,214,788 0.2 Mg/L Volatile Organic Chemicals 1,2-Dichlorobenzene (600 Mg/L) 50 370,929 55,732 263,055,936 0.5 Mg/L 1,4-Dichlorobenzene (75 Mg/L) 50 371,276 55,739 263,060,364 0.5 Mg/L 1,1-Dichloroethylene (7 Mg/L) 50 379,522 55,728 263,336,047 0.5 Mg/L cis-1,2-Dichloroethylene (70 Mg/L) 50 376,300 55,734 263,344,982 0.5 Mg/L trans-1,2-Dichloroethylene (100 Mg/L) 50 371,580 55,633 263,180,210 0.5 Mg/L Ethylbenzene (700 Mg/L) 50 372,709 55,754 263,388,439 0.5 Mg/L Monochlorobenzene (100 Mg/L) 50 371,311 55,676 262,721,516 0.5 Mg/L Styrene (100 Mg/L) 50 370,368 55,731 263,371,533 0.5 Mg/L Toluene (1,000 Mg/L) 50 373,021 55,748 263,497,932 0.5 Mg/L 1,2,4-Trichlorobenzene (70 Mg/L) 50 369,032 55,725 263,373,653 0.5 Mg/L 1,1,1-Trichloroethane (200 Mg/L) 50 374,181 55,735 263,367,902 0.5 Mg/L 1,1,2-Trichloroethane (5 Mg/L) 50 371,877 55,733 263,373,568 0.5 Mg/L Xylenes (Total) (10,000 Mg/L) 50 323,477 51,074 248,916,224 0.5 Mg/L Radiological Contaminants Alpha Particles (15 pCi/L) 47 60,803 13,309 107,091,381 3 pCi/L Beta Particles (screening level = 50 pCi/L)3 41 43,278 11,531 109,503,691 4 pCi/L Combined Radium-226 & -228 (5 pCi/L) 42 73,018 15,805 120,504,165 1 pCi/L SYR3 Occurrence Support Document 5-30 December 2016 ------- Contaminant (MCL Concentration) Number of States with Data Total Number of Records Total Number of Systems Total Population Served by Systems MRL Uranium (30 Mg/L) 49 86,208 12,155 121,747,100 1 i-ig/i 1 Quality assurance steps were taken to identify and exclude fluoride samples from fluoridated water systems. 2 The reduced number of systems sampling for SOC data, as compared to lOCs and VOCs, likely relates to state waivers for pesticides and herbicides. 3 Although the MCL for beta particles, 4 millirem per year (mrem/yr), is in the unit of measure of mrem/yr, the primary unit of analytical measure is picocuries per liter (pCi/L). This unit of measure relates to screening thresholds of 15 pCi/L and 50 pCi/L that are defined in the 2000 Radionuclides Rule. More than 95 percent of all compliance monitoring data for beta particles submitted by the states to EPA were in units of pCi/L. The analyses presented here are based on compliance monitoring data represented in units of pCi/L and are conducted relative to the screening threshold of 50 pCi/L. 5.2 Occurrence Variability Assessment The six years of data collected through the SYR3 ICR were used to develop aggregate measures of occurrence (i.e., a single measure of occurrence that is based on all six years of data). For example, a typical measure is the percent of systems with at least one detection of a particular contaminant greater than its MCL concentration. This single measure would not differentiate between years, but would reflect detections in any of the six years considered. Recognizing that occurrence of a particular contaminant might vary over a six -year period, EPA conducted assessments to determine if the compliance monitoring data in the SYR3 ICR Dataset exhibit significant variability over time. To make these assessments, it was not possible to simply evaluate yearly sample detection rates for each contaminant at the national level. Monitoring schedules for a particular contaminant can differ from system-to-system and year-to-year (e.g., not all surface water systems monitor all contaminants quarterly). Therefore, a national comparison of system monitoring data from different years will likely result in a comparison of data from different subsets of systems nationally. The variation in compliance monitoring schedules generally corresponds to the assessed chance of contaminant occurrence based on historic monitoring results at each system. If a contaminant is shown not to occur at a system through a specified period of routine compliance monitoring, that system is authorized to conduct a reduced monitoring schedule for that contaminant. Some systems monitor contaminants as infrequently as once every year, every three years, or even every nine years. Because of this variability in monitoring schedules and its implications (i.e., the frequency and timing of sampling are not random), a simple year-to-year assessment of occurrence across all systems does not provide a clear, unambiguous assessment of occurrence variability. For this variability assessment, EPA identified systems that collected at least one sample in each of the six years of 2006 through 2011. This allowed the evaluation to focus on the observed variability in the occurrence measures due to changes in contaminant occurrence rather than differences or changes in monitoring schedules. There is no single measure of occurrence for assessing variability. Contaminant occurrence variability can be based on a number of different measures such as contaminant detection rates, concentration averages, or the frequency at which systems find a contaminant above some concentration threshold. Occurrence is also defined by a relatively small number of samples from each system, as expected given compliance monitoring requirements. Because of the small sample size, EPA compared detection rates in two, three-year groups rather than the detection SYR3 Occurrence Support Document 5-31 December 2016 ------- rates for each individual year. EPA quantified contaminant occurrence at the system level (i.e., calculating the detection rate at each system) for the first three years of data (2006-2008) and then the second three years of data (2009-2011). EPA then used standard statistical t-tests to determine whether system level occurrence in the first three years was significantly different from system level occurrence in the second three years. EPA conducted variability assessments on a subset of 15 contaminants. The 15 contaminants were: carbofuran; cis-l,2-dichloroethylene; cyanide; DBCP; dioxin; heptachlor; heptachlor epoxide; hexachlorocyclopentadiene; oxamyl; pentachlorophenol; selenium; thallium; toluene; toxaphene and xylenes (total). For each of these 15 select contaminants, the mean detection rate for each system (i.e., the percentage of detections for each system) for each time period was calculated. Results for ground water systems were evaluated separately from the results for surface water systems. For each contaminant, a t-test (paired two sample for means) was used with an alpha (a) level of 0.05 to determine whether these two estimated mean system detection rates were significantly different between the first time period and the second time period. (If the p-value resulting from the t-test was greater than 0.05, EPA did not reject the null hypothesis that the two time periods' mean system detection rates were from the same population.) If so, this would suggest, but does not prove, that the mean system detection rates of that contaminant for 2006-2008 and 2009-2011 were not significantly different (were from the same population). For 11 of the 15 contaminants assessed, there was no statistically significant variability in system detection rates (for ground water or surface water systems) between the 2006-2008 and 2009- 2011 time periods (i.e., the p-value was greater than 0.05 and EPA failed to reject the null hypothesis). For the other four contaminants, either the ground water or surface water systems' detection rates were found to be statistically different in the two time periods (i.e., the p-value was less than 0.05, EPA accepted the alternative hypothesis that the system detection rates were from different populations). Most of the contaminants with occurrence variability over time had a decrease in occurrence over the six-year period including DBCP in GW; xylenes (total) in GW and toluene in GW. Hexachlorocyclopentadiene in SW showed an increase in occurrence over the six-year period. For the four contaminants with at least some statistically significant measure of increasing or decreasing occurrence, these findings are most appropriately used as context or background for the quantitative occurrence findings presented in Sections 6 and 7 of this report. 5.3 Threshold Evaluations EPA assessed the occurrence of the regulated contaminants relative to several different thresholds. Stage 1 and Stage 2 assessments of occurrence were made relative to the MRL, identifying the simple presence/absence of a detection of a contaminant. A sample analytical result is defined as a "detection" if the quantified sample concentration of the contaminant is equal to or greater than that contaminant's MRL. Contaminant occurrence was also evaluated relative to multiple contaminant concentration thresholds including a contaminant's MCL concentration. For Stage 1 and Stage 2 assessments of occurrence relative to the MCL concentration, the criterion is that the sample concentration of the contaminant is greater than that contaminant's MCL. The Stage 1 analyses would identify any single result greater than the MCL concentration and the Stage 2 analyses would identify system estimated long-term (multi- year) average concentrations greater than the MCL concentration. SYR3 Occurrence Support Document 5-32 December 2016 ------- The Stage 1 and Stage 2 analyses conducted relative to the MCL concentration are not equivalent to the analyses conducted to estimate a potential MCL violation. Calculations of MCL violations from the sample data are not conducted in this report. Both these Stage 1 and Stage 2 analyses are based on sample detection and non-detection results from all years with data in the SYR3 ICR Dataset. The Stage 2 analysis (based on an estimated long-term average concentration) is similar but not identical to the calculation conducted to determine an MCL violation. For most regulated drinking water contaminants, an MCL violation occurs when the concentration threshold equal to a contaminant's MCL is exceeded by the estimated system annual average concentration, based on a limited number of consecutive quarterly compliance monitoring samples (typically four samples for surface water systems and two samples for ground water systems).9 In contrast, a "Stage 2 MCL exceedance" occurs when the concentration threshold equal to a particular contaminant's MCL is exceeded by the estimated system long-term average concentration, based on multiple years (not two or four consecutive quarters) of compliance monitoring samples. In accordance with the Six-Year Review 3 Protocol, EPA selected a set of contaminants for which an MCL revision might be feasible: the current MCL is limited by analytical capability (i.e., the MCL equals a practical quantitation level or PQL) and there is new information indicating improved analytical capability; or the current MCL is set equal to the Maximum Contaminant Level Goal (MCLG) and a new health effects assessment indicates it is possible to revise the MCLG. For the 61 contaminants considered in the third Six-Year Review, EPA identified 19 contaminants for which to derive other thresholds (in addition to the MCL). Two of the 19 chemical contaminants (oxamyl and carbofuran) have acute health effects and only the Stage 1 analysis was conducted. (For more details on the Stage 1 analysis, refer to Section 6 of this report.) The remaining 17 contaminants have chronic health effects and were analyzed using the Stage 2 occurrence analysis. (For more details on the Stage 2 analysis, refer to Section 7 of this report.) For 10 contaminants, EPA generated occurrence estimates relative to the estimated quantitation level (EQL). The EQL represents the potential quantitation capabilities below a PQL (USEPA, 2016e). For eight contaminants, EPA generated occurrence estimates relative to the potential MCLG. For one contaminant, EPA generated occurrence estimates relative to the (existing) MCLG and one other contaminant, EPA generated occurrence estimates relative to the PQL. Occurrence analyses relative to these additional thresholds are presented in Appendix A for oxamyl and carbofuran and Appendix B for the remaining 17 contaminants for which Stage 2 analysis was warranted. Exhibit 5.6 presents the list of thresholds used to conduct the Stage 2 occurrence analysis. For more information on the new potential thresholds of concern used in the SYR3 analyses, refer to USEPA (2016e) and (2016f). Exhibit 5.6: List of Contaminant Thresholds used in Stage 2 Occurrence Analysis1 Contaminant MCL Alternate Threshold Type Alternate Threshold Concentration Carbofuran1 40 |jg/L EQL 5 |jg/L Chlordane 2 pg/L EQL 1 hq/l 9 For nitrate and nitrite, if a single sample result is greater than or equal to the MCL, the system must collect a confirmation sample and average it with the original sample. If that average is greater than the MCL, then an MCL violation has occurred. SYR3 Occurrence Support Document 5-33 December 2016 ------- Contaminant MCL Alternate Threshold Type Alternate Threshold Concentration cis-1,2-Dichloroethylene 70 pg/L Potential MCLG 10 pg/L Cyanide 200 pg/L EQL 50 pg/L Endothall 100 pg/L Potential MCLG 50 pg/L Fluoride 4,000 pg/L Potential MCLG 900 pg/L Heptachlor 0.4 pg/L EQL 0.1 pg/L Heptachlor Epoxide 0.2 pg/L EQL 0.04 pg/L Hexachlorobenzene 1 pg/L EQL 0.1 pg/L Hexachlorocyclopentadiene 50 pg/L Potential MCLG 40 pg/L Methoxychlor 40 pg/L EQL 1 pg/L Oxamyl (Vydate)1 200 pg/L Potential MCLG 9, 10 pg/L Selenium 50 pg/L Potential MCLG 40 pg/L Styrene 100 pg/L EQL 0.5 pg/L 2,3,7,8-TCDD (Dioxin) 0.00003 pg/L EQL 0.000005 pg/L Toluene 1,000 pg/L Potential MCLG 600 pg/L Toxaphene 3 pg/L EQL 1 pg/L 1,1,2-Trichloroethane 5 pg/L MCLG 3 pg/L Xylenes (Total) 10,000 pg/L Potential MCLG 1,000 pg/L 1 Oxamyl and carbofuran have health endpoints that are associated with acute exposure; thus, the Stage 2 analysis was not appropriate. The thresholds presented in this table were used to conduct more detailed Stage 1 occurrence analyses presented in Appendix A. SYR3 Occurrence Support Document 5-34 December 2016 ------- 6 Stage 1 Analysis The Stage 1 statistical analysis of the SYR3 ICR Dataset consists of simple counts and descriptive statistics of the occurrence data for each of the regulated contaminants assessed. National contaminant occurrence estimates were conducted relative to contaminant MRLs and MCL concentrations and Section 6.1 presents the results by systems and population served by systems. A comparison of the summary Stage 1 analysis results from the first Six-Year Review with data from 1993-1997, the second Six-Year Review with data from 1998-2005 and the current Six-Year Review with data from 2006-2011, is presented in Section 6.2. A supplemental measure of occurrence, based on occurrence at sample point locations within each system, using the 2006-2011 data is described in Section 6.3 with summary sample point estimates presented in Exhibit 6.3. 6.1 Summary of Stage 1 Contaminant Occurrence Findings Several Stage 1 analyses were conducted to characterize national occurrence of regulated contaminants in public drinking water systems and are summarized in Exhibit 6.1 and Exhibit 6.2. Stage 1 analyses generated general system-level assessments of occurrence, for population served by systems and for a preliminary assessment of potential exposure to contaminants in drinking water. Exhibit 6.1 shows occurrence measures conducted relative to a contaminant's MRL, identifying analytical detections for a broad assessment of the rate of occurrence; Exhibit 6.2 shows occurrence measures relative to each contaminant's MCL concentration, making a preliminary estimate of occurrence and exposure at or above a contaminant's health-based drinking water standard. The percent of systems and population served by systems with at least one detection greater than the MCL concentration indicates the proportion of the number of systems or the proportion of population served by systems with any analytical results exceeding the concentration value of the MCL. Note that this does not indicate an MCL violation. An MCL violation occurs when the MCL is exceeded by the average results from four consecutive quarterly confirmation samples. These Stage 1 analytical findings are organized by contaminant group. Exhibit 6.1: Summary of Stage 1 Contaminant Occurrence Findings - Systems and Population Served by Systems Contaminant Total Number of Systems Systems With Detections > MRL Total Population Served by Systems Population Served by Systems With Detections > MRL Range of Detected Concentrations (5lh percentile - 95lh percentile) Number Percent Number Percent Inorganic Chemicals Antimony 50,532 2,243 4.44% 254,359,720 35,557,081 13.98% 0.06 - 6.4 |jg/L Arsenic 54,845 21,850 39.84% 267,062,633 142,045,436 53.19% 1.00 - 25.4 |jg/L Asbestos 5,785 214 3.70% 94,380,829 7,011,486 7.43% 0.10-6.8 MFL Barium 50,711 37,328 73.61% 254,501,602 215,824,476 84.80% 5.00- 310 |jg/L Beryllium 50,195 1,051 2.09% 253,512,318 18,768,223 7.40% 0.01 - 4.0 |jg/L SYR3 Occurrence Support Document 6-35 December 2016 ------- Contaminant Total Number of Systems Systems With Detections > MRL Total Population Served by Systems Population Served b\ Systems With Detections > MRL Range of Detected Concentrations (5lh percentile - 95lh percentile) Number Percent Number Percent Cadmium 50,583 1,826 3.61% 254,433,966 23,767,870 9.34% 0.05 -4.0 |jg/L Chromium (Total) 50,597 13,609 26.90% 254,405,306 102,850,010 40.43% 0.73 - 20.0 |jg/L Cyanide 36,907 1,580 4.28% 210,427,981 29,827,337 14.17% 1.62-150 |jg/L Fluoride 1 47,227 33,478 70.89% 189,186,454 164,918,799 87.17% 100.0-2,550 |jg/L Mercury (Inorganic) 50,552 1,610 3.18% 254,397,552 31,509,568 12.39% 0.02-1.4 |jg/L Nitrate (as N) 132,176 84,347 63.81% 266,378,543 237,542,569 89.17% 84.00 - 8,339 (jg/L Nitrite (as N) 85,742 10,064 11.74% 224,146,056 72,846,518 32.50% 2.00-1,150 Mg/L Selenium 50,568 8,754 17.31% 254,428,296 92,506,459 36.36% 0.60 - 27.0 jjg/L Thallium 50,522 1,828 3.62% 254,265,115 25,659,625 10.09% 0.01 -2.0 Mg/L Synthetic Organic Chemicals Alachlor 42,955 68 0.16% 245,844,381 2,409,101 0.98% 0.03-1.30 Mg/L Atrazine 44,310 1,144 2.58% 251,501,740 46,065,991 18.32% 0.10-1.73 Mg/L Benzo(a)pyrene 34,341 143 0.42% 220,684,857 8,066,622 3.66% 0.02 - 0.53 Mg/L Carbofuran 34,614 23 0.07% 228,717,933 83,512 0.04% 0.32-31.42 Mg/L Chlordane 35,685 61 0.17% 217,637,369 1,959,885 0.90% 0.03 - 2.00 Mg/L Dalapon 36,005 650 1.81% 222,985,164 22,843,243 10.24% 0.45 - 5.3 Mg/L Di (2-ethyl hexy l)adi pate (DEHA) 34,628 511 1.48% 221,563,794 9,960,923 4.50% 0.12-8.74 Mg/L Di(2-ethylhexyl)phthalate (DEHP) 33,923 4,042 11.92% 216,841,935 55,983,264 25.82% 0.29 - 6.84 Mg/L 1,2-Dibromo-3- chloropropane (DBCP) 37,226 379 1.02% 217,765,167 11,331,048 5.20% 0.01 - 0.22 Mg/L 2,4-Dichlorophenoxyacetic acid (2,4-D) 37,690 193 0.51% 233,873,578 8,842,605 3.78% 0.05 - 2.40 Mg/L Dinoseb 36,701 94 0.26% 230,831,397 878,035 0.38% 0.09 - 5.52 Mg/L Diquat 17,906 106 0.59% 146,939,794 2,804,725 1.91% 0.22 - 6.68 Mg/L Endothall 15,538 25 0.16% 136,801,729 210,779 0.15% 2.70 - 66.2 Mg/L Endrin 38,453 48 0.12% 229,199,508 2,093,675 0.91% 0.002 - 0.77 Mg/L Ethylene Dibromide (EDB) 37,499 155 0.41% 221,781,780 4,779,841 2.16% 0.01 -0.17 Mg/L Glyphosate 18,502 20 0.11% 145,203,976 238,876 0.16% 3.20 - 32.64 Mg/L SYR3 Occurrence Support Document 6-36 December 2016 ------- Contaminant Total Number of Systems Systems With Detections > MRL Total Population Served by Systems Population Served b\ Systems With Detections > MRL Range of Detected Concentrations (5lh percentile - 95lh percentile) Number Percent Number Percent Heptachlor 38,691 62 0.16% 229,832,285 3,729,607 1.62% 0.01 - 0.19 (jg/L Heptachlor Epoxide 38,625 135 0.35% 229,832,890 2,882,874 1.25% 0.01 -0.11 |jg/L Hexachlorobenzene 38,498 45 0.12% 230,197,968 1,071,688 0.47% 0.00 - 0.84 |jg/L Hexachlorocyclopentadiene 38,743 172 0.44% 229,902,564 9,511,658 4.14% 0.02-1.14 Mg/L Lindane (gamma- 1—la va 1 r* rr* r*\/r* 1 r* ava no \ 39,260 44 0.11% 231,972,432 3,391,071 1.46% 0.01 - 0.24 jjg/L Methoxychlor 39,187 68 0.17% 233,030,961 2,319,414 1.00% 0.01 - 0.93 Mg/L Oxamyl (Vydate) 34,518 37 0.11% 227,520,373 994,043 0.44% 0.35 - 37.00 Mg/L Pentachlorophenol 40,322 226 0.56% 234,008,187 7,810,865 3.34% 0.01 - 0.98 Mg/L Picloram 37,445 98 0.26% 233,036,908 1,773,249 0.76% 0.01 - 4.59 Mg/L Polychlorinated biphenyls (PCBs) 21,571 32 0.15% 153,248,065 216,797 0.14% 0.02-1.17 Mg/L Simazine 43,240 365 0.84% 247,063,728 24,110,287 9.76% 0.07 -1.30 Mg/L Toxaphene 37,043 28 0.08% 223,888,971 1,097,044 0.49% 0.13-6.89 Mg/L 2,3,7,8-TCDD (Dioxin) 3,216 8 0.25% 74,077,780 124,178 0.17% 0.000001 - 0.0007 Mg/L 2,4,5- T richlorophenoxypropionic Acid (Silvex) 36,897 59 0.16% 230,214,788 5,445,631 2.37% 0.04 - 4.57 Mg/L Volatile Organic Chemicals 1,2-Dichlorobenzene 55,732 145 0.26% 263,055,936 5,684,614 2.16% 0.13-9.64 Mg/L 1,4-Dichlorobenzene 55,739 644 1.16% 263,060,364 7,214,920 2.74% 0.10-4.53 Mg/L 1,1-Dichloroethylene 55,728 379 0.68% 263,336,047 15,927,038 6.05% 0.50 - 4.70 Mg/L cis-1,2-Dichloroethylene 55,734 516 0.93% 263,344,982 22,180,279 8.42% 0.50 - 11.00 Mg/L trans-1,2-Dichloroethylene 55,633 149 0.27% 263,180,210 5,567,372 2.12% 0.02-6.13 Mg/L Ethyl benzene 55,754 1,744 3.13% 263,388,439 17,798,704 6.76% 0.29 - 8.70 Mg/L Monochlorobenzene 55,676 217 0.39% 262,721,516 4,740,559 1.80% 0.04 - 2.71 Mg/L Styrene 55,731 387 0.69% 263,371,533 4,932,664 1.87% 0.01 - 6.60 Mg/L Toluene 55,748 2,485 4.46% 263,497,932 24,438,509 9.27% 0.27-10.85 Mg/L 1,2,4-Trichlorobenzene 55,725 147 0.26% 263,373,653 4,700,300 1.78% 0.02 -1.90 Mg/L 1,1,1-Trichloroethane 55,735 400 0.72% 263,367,902 12,878,782 4.89% 0.50- 11.50 Mg/L SYR3 Occurrence Support Document 6-37 December 2016 ------- Contaminant Total Number of Systems Systems With Detections > MRL Total Population Served by Systems Population Served b\ Systems With Detections > MRL Range of Detected Concentrations (5lh percentile - 95lh percentile) Number Percent Number Percent 1,1,2-Trichloroethane 55,733 116 0.21% 263,373,568 8,374,139 3.18% 0.03 - 2.36 |jg/L Xylenes (Total) 51,074 3,241 6.35% 248,916,224 34,901,941 14.02% 0.50-18.42 |jg/L Radiological Contaminants Alpha Particles 13,309 8,126 61.06% 107,091,381 77,231,268 72.12% 0.50 - 22 pCi/L Beta Particles 11,531 6,894 59.79% 109,503,691 76,615,844 69.97% 1.23-20.7 pCi/L Combined Radium-226 & - 228 15,805 11,092 70.18% 120,504,165 96,765,143 80.30% 0.20 - 8.2 pCi/L Uranium 12,155 6,785 55.82% 121,747,100 83,230,946 68.36% 0.49-41 |jg/L 1 Quality assurance steps were taken to identify and exclude fluoride samples from fluoridated water systems. Exhibit 6.2: Number and Percent of Systems and Population Served by Systems with Detections Greater than the MCL Concentration Contaminant (MCL Concentration) Systems With Detections > MCL Concentration Population Served by Systems With Detections > MCL Concentration Number Percent Number Percent Inorganic Chemicals Antimony (6 |jg/L) 93 0.184% 899,395 0.354% Arsenic (10 |jg/L) 3,478 6.342% 19,619,428 7.346% Asbestos (7 MFL) 8 0.138% 190,895 0.202% Barium (2,000 |jg/L) 62 0.122% 1,312,318 0.516% Beryllium (4 |jg/L) 33 0.066% 576,710 0.227% Cadmium (5 |jg/L) 63 0.125% 239,604 0.094% Chromium (Total) (1 oo |jg/L) 22 0.043% 106,717 0.042% Cyanide (200 |jg/L) 38 0.103% 502,135 0.239% Fluoride 1 (4,000 |jg/L) 343 0.726% 6,156,091 3.254% Mercury (Inorganic) (2 |jg/L) 50 0.099% 1,111,902 0.437% Nitrate (as N) (10,000 |jg/L) 3,016 2.282% 10,406,882 3.907% Nitrite (as N) (1,000 |jg/L) 523 0.610% 2,658,267 1.186% SYR3 Occurrence Support Document 6-38 December 2016 ------- Contaminant (MCL Concentration) Systems With Detections > MCL Concentration Population Served by Systems With Detections > MCL Concentration Number Percent Number Percent Selenium (50 Mg/L) 88 0.174% 626,607 0.246% Thallium (2 (jg/L) 98 0.194% 1,021,116 0.402% Synthetic Organic Chemicals Alachlor (2 (jg/L) 4 0.009% 12,793 0.005% Atrazine (3 pg/L) 64 0.144% 3,507,861 1.395% Benzo(a)pyrene (0.2 |Jg/L) 16 0.047% 1,322,607 0.599% Carbofuran (40 Mg/L) 0 0.000% 0 0.000% Chlordane (2 (jg/L) 6 0.017% 2,621 0.001% Dalapon (200 |jg/L) 1 0.003% 125 0.000% Di(2-ethylhexyl)adipate (DEHA) (400 |jg/L) 0 0.000% 0 0.000% Di(2-ethylhexyl)phthalate (DEHP) (6 (jg/L) 352 1.038% 9,060,445 4.178% 1,2-Dibromo-3-chloropropane (DBCP) (0.2 Mg/L) 103 0.277% 2,671,550 1.227% 2,4-Dichlorophenoxyacetic acid (2,4-D) (70 Mg/L) 1 0.003% 125 0.000% Dinoseb (7 Mg/L) 5 0.014% 68,933 0.030% Diquat (20 Mg/L) 1 0.006% 993 0.001% Endothall (100 Mg/L) 1 0.006% 993 0.001% Endrin (2 Mg/L) 1 0.003% 993 0.000% Ethylene Dibromide (EDB) (0.05 Mg/L) 40 0.107% 810,484 0.365% Glyphosate (700 Mg/L) 0 0.000% 0 0.000% Heptachlor (0.4 Mg/L) 3 0.008% 1,643 0.001% Heptachlor Epoxide (0.2 Mg/L) 7 0.018% 2,503 0.001% Hexachlorobenzene (1 Mg/L) 1 0.003% 6,916 0.003% Hexachlorocyclopentadiene (50 Mg/L) 1 0.003% 10,018 0.004% Lindane (gamma- Hexachlorocyclohexane) (0.2 Mg/L) 5 0.013% 20,440 0.009% Methoxychlor (40 Mg/L) 0 0.000% 0 0.000% SYR3 Occurrence Support Document 6-39 December 2016 ------- Contaminant (MCL Concentration) Systems With Detections > MCL Concentration Population Served by Systems With Detections > MCL Concentration Number Percent Number Percent Oxamyl (Vydate) (200 |jg/L) 0 0.000% 0 0.000% Pentachlorophenol (1 (jg/L) 11 0.027% 88,756 0.038% Picloram (500 |jg/L) 0 0.000% 0 0.000% Polychlorinated biphenyls (PCBs) (0.5 |Jg/L) 5 0.023% 36,354 0.024% Simazine (4 (jg/L) 5 0.012% 14,816 0.006% Toxaphene (3 pg/L) 5 0.013% 714,581 0.319% 2,3,7,8-TCDD (Dioxin) (0.00003 |jg/L) 1 0.031% 550 0.001% 2,4,5-T richlorophenoxypropionic Acid (Silvex) (50 |jg/L) 1 0.003% 125 0.000% Volatile Organic Chemicals 1,2-Dichlorobenzene (600 |jg/L) 0 0.000% 0 0.000% 1,4-Dichlorobenzene (75 Mg/L) 2 0.004% 4,574 0.002% 1,1-Dichloroethylene (7 |jg/L) 28 0.050% 694,929 0.264% cis-1,2-Dichloroethylene (70 Mg/L) 1 0.002% 54 0.000% trans-1,2-Dichloroethylene (100 Mg/L) 0 0.000% 0 0.000% Ethyl benzene (700 Mg/L) 2 0.004% 282 0.000% Monochlorobenzene (100 Mg/L) 0 0.000% 0 0.000% Styrene (100 Mg/L) 1 0.002% 100 0.000% Toluene (1,000 Mg/L) 2 0.004% 583 0.000% 1,2,4-Trichlorobenzene (70 Mg/L) 0 0.000% 0 0.000% 1,1,1-Trichloroethane (200 Mg/L) 2 0.004% 1,403 0.001% 1,1,2-Trichloroethane (5 Mg/L) 3 0.005% 7,839 0.003% Xylenes (Total) (10,000 Mg/L) 0 0.000% 0 0.000% Radiological Contaminants Alpha Particles (15 pCi/L) 719 5.402% 7,353,592 6.867% Beta Particles (50 pCi/L) 54 0.468% 725,062 0.662% SYR3 Occurrence Support Document 6-40 December 2016 ------- Contaminant (MCL Concentration) Systems With Detections > MCL Concentration Population Served by Systems With Detections > MCL Concentration Number Percent Number Percent Combined Radium-226 & -228 (5 pCi/L) 788 4.986% 5,023,247 4.169% Uranium (30 |Jg/L) 523 4.303% 8,462,624 6.951% 1 Quality assurance steps were taken to identify and exclude fluoride samples from fluoridated water systems. 6.2 Comparison of Stage 1 Analysis of First, Second and Third Six-Year Reviews Exhibit 6.3 presents a comparison of contaminant occurrence estimates from the first Six-Year Review (based on compliance monitoring data from 1993-1997), the second Six-Year Review (1998-2005) and the third Six-Year Review (2006-2011). Some of the contaminants assessed for the second and third Six-Year Reviews were not assessed for the first Six-Year Review (noted in Exhibit 6.3 by a hyphen in the "Six-Year 1" columns). The occurrence estimates from the three rounds of Six-Year Review appear to be broadly similar. Note, however, that comparisons or apparent occurrence changes over time must be somewhat qualified given the differences between the three datasets. The first Six-Year Review dataset consisted of data from 16 states that were assembled into a "national cross-section" that was indicative, though not statistically representative, of national occurrence. In contrast, the SYR2 and SYR3 ICR Datasets consist of data from 45 and 46 states, respectively, that serve as a very large sample that is, essentially, nationally representative. Therefore, it is possible that differences in occurrence measures between the first and second or between the first and third Six-Year Review Stage 1 findings summarized in Exhibit 6.3 reflect differences in the respective datasets rather than differences in actual occurrence. Nonetheless, each of the three datasets provide sound assessments of national contaminant occurrence in systems, so significant differences in occurrence estimates generated for the first, second and third Six-Year Reviews may provide information on changes in occurrence over time. Occurrence evaluations specifically designed to assess occurrence trends over time might assess occurrence changes for a particular contaminant only in all the systems that were included in the first, second and third Six-Year Review datasets. These temporal analyses of contaminant occurrence were not conducted for this current assessment. Exhibit 6.3: Comparison of Stage 1 Analyses of the First, Second and Third Six- Year Reviews based on the Percent of Systems Contaminant (MCL Concentration) Percent of Systems With Detections > MRL Percent of Systems With Detections > MCL Concentration Six-Year 11 Six-Year 22 Six-Year 3 Six-Year 11 Six-Year 22 Six-Year 3 Inorganic Chemicals Antimony (6 |jg/L) 14.40% 5.98% 4.44% 0.62% 0.27% 0.18% Arsenic (io |jg/L)3 13.70% 37.33% 39.84% 0.87% 0.75% 6.34% Asbestos (7 MFL) - 3.24% 3.70% - 0.17% 0.14% Barium (2,000 |jg/L) 71.20% 72.02% 73.61% 0.17% 0.13% 0.12% SYR3 Occurrence Support Document 6-41 December 2016 ------- Contaminant (MCL Concentration) Percent of Systems With Detections > MRL Percent of Systems With Detections > MCL Concentration Six-Year 11 Six-Year 22 Six-Year 3 Six-Year 11 Six-Year 22 Six-Year 3 Beryllium (4 (jg/L) 3.32% 3.12% 2.09% 0.22% 0.11% 0.07% Cadmium (5 (jg/L) 17.60% 5.61% 3.61% 0.54% 0.27% 0.12% Chromium (Total) (1 oo |jg/L) 18.30% 24.21% 26.90% 0.13% 0.09% 0.04% Cyanide (200 |jg/L) 17.00% 4.14% 4.28% 0.17% 0.14% 0.10% Fluoride 4 (4,000 |jg/L) 83.80% 79.28% 70.89% 1.28% 1.07% 0.73% Mercury (Inorganic) (2 |jg/L) 17.30% 3.96% 3.18% 0.26% 0.17% 0.10% Nitrate (as N) (10,000 |jg/L) - 69.94% 63.81% - 2.49% 2.28% Nitrite (as N) (1,000 |jg/L) - 22.32% 11.74% - 0.74% 0.61% Selenium (50 |jg/L) 22.10% 17.28% 17.31% 0.11% 0.13% 0.17% Thallium (2 kig/L) 4.22% 3.49% 3.62% 0.68% 0.26% 0.19% Synthetic Organic Chemicals Alachlor (2 kig/L) 0.67% 0.33% 0.16% 0.00% 0.02% 0.01% Atrazine (3 kig/L) 3.83% 2.39% 2.58% 0.68% 0.26% 0.14% Benzo(a)pyrene (0.2 |Jg/L) 0.44% 0.49% 0.42% 0.05% 0.05% 0.05% Carbofuran (40 |jg/L) 0.06% 0.14% 0.07% 0.00% 0.00% 0.00% Chlordane (2 kig/L) 1.19% 0.21% 0.17% 0.01% 0.01% 0.02% Dalapon (200 |jg/L) 1.10% 1.83% 1.81% 0.00% 0.00% 0.00% Di(2-ethylhexyl)adipate (DEHA) (400 Mg/L) 7.31% 1.75% 1.48% 0.01% 0.01% 0.00% Di(2-ethylhexyl)phthalate (DEHP) (6 Mg/L) 12.50% 11.20% 11.92% 2.20% 1.66% 1.04% 1,2-Dibromo-3-chloropropane (DBCP) (0.2 |Jg/L) 1.61% 1.03% 1.02% 0.91% 0.39% 0.28% 2,4-Dichlorophenoxyacetic acid (2,4- D) (70 |jg/L) 0.12% 0.90% 0.51% 0.02% 0.00% 0.00% Dinoseb (7 |jg/L) 0.24% 0.27% 0.26% 0.02% 0.02% 0.01% Diquat (20 |Jg/L) 0.49% 0.44% 0.59% 0.02% 0.00% 0.01% Endothall (100 |jg/L) 0.15% 0.23% 0.16% 0.03% 0.02% 0.01% Endrin (2 kig/L) 0.18% 0.14% 0.12% 0.02% 0.00% 0.00% SYR3 Occurrence Support Document 6-42 December 2016 ------- Contaminant (MCL Concentration) Percent of Systems With Detections > MRL Percent of Systems With Detections > MCL Concentration Six-Year 11 Six-Year 22 Six-Year 3 Six-Year 11 Six-Year 22 Six-Year 3 Ethylene Dibromide (EDB) (0.05 |jg/L) 1.06% 0.54% 0.41% 0.72% 0.24% 0.11% Glyphosate (700 |jg/L) 0.10% 0.18% 0.11% 0.00% 0.00% 0.00% Heptachlor (0.4 |Jg/L) 0.08% 0.80% 0.16% 0.01% 0.01% 0.01% Heptachlor Epoxide (0.2 |Jg/L) 0.09% 0.22% 0.35% 0.03% 0.02% 0.02% Hexachlorobenzene (1 (jg/L) 0.09% 0.34% 0.12% 0.01% 0.01% 0.00% Hexachlorocyclopentadiene (50 Mg/L) 0.89% 0.69% 0.44% 0.00% 0.00% 0.00% Lindane (gamma- Hexachlorocyclohexane) (0.2 |Jg/L) 0.16% 0.25% 0.11% 0.04% 0.01% 0.01% Methoxychlor (40 Mg/L) 0.19% 0.16% 0.17% 0.01% 0.00% 0.00% Oxamyl (Vydate) (200 |jg/L) 0.08% 0.23% 0.11% 0.00% 0.00% 0.00% Pentachlorophenol (1 (jg/L) 0.43% 0.73% 0.56% 0.03% 0.02% 0.03% Picloram (500 |jg/L) 0.41% 0.41% 0.26% 0.00% 0.00% 0.00% Polychlorinated biphenyls (PCBs) (0.5 |Jg/L) 0.09% 0.16% 0.15% 0.03% 0.01% 0.02% Simazine (4 pg/L) 1.80% 0.72% 0.84% 0.06% 0.04% 0.01% Toxaphene (3 pg/L) 0.08% 0.13% 0.08% 0.01% 0.02% 0.01% 2,3,7,8-TCDD (Dioxin) (0.00003 Mg/L) - 0.71% 0.25% - 0.04% 0.03% 2,4,5-T richlorophenoxypropionic Acid (Silvex) (50 Mg/L) 0.40% 0.24% 0.16% 0.00% 0.00% 0.00% Volatile Organic Chemicals 1,2-Dichlorobenzene (600 Mg/L) 0.61% 0.23% 0.26% 0.00% 0.00% 0.00% 1,4-Dichlorobenzene (75 Mg/L) 1.76% 1.50% 1.16% 0.00% 0.01% 0.00% 1,1-Dichloroethylene (7 Mg/L) 1.58% 0.69% 0.68% 0.24% 0.07% 0.05% cis-1,2-Dichloroethylene (70 Mg/L) 1.37% 0.96% 0.93% 0.03% 0.01% 0.00% trans-1,2-Dichloroethylene (100 Mg/L) 0.53% 0.19% 0.27% 0.00% 0.00% 0.00% Ethyl benzene (700 Mg/L) 3.62% 3.91% 3.13% 0.00% 0.00% 0.00% Monochlorobenzene (100 Mg/L) 0.75% 0.27% 0.39% 0.00% 0.00% 0.00% Styrene (100 Mg/L) 0.99% 1.05% 0.69% 0.00% 0.01% 0.00% SYR3 Occurrence Support Document 6-43 December 2016 ------- Contaminant (MCL Concentration) Percent of Systems With Detections > MRL Percent of Systems With Detections > MCL Concentration Six-Year 11 Six-Year 22 Six-Year 3 Six-Year 11 Six-Year 22 Six-Year 3 Toluene (1,000 Mg/L) 4.73% 5.76% 4.46% 0.00% 0.00% 0.00% 1,2,4-Trichlorobenzene (70 Mg/L) 0.61% 0.32% 0.26% 0.00% 0.00% 0.00% 1,1,1-Trichloroethane (200 Mg/L) 2.50% 1.07% 0.72% 0.01% 0.00% 0.00% 1,1,2-Trichloroethane (5 Mg/L) 0.62% 0.18% 0.21% 0.04% 0.01% 0.01% Xylenes (Total) (10,000 Mg/L) 4.16% 7.59% 6.35% 0.00% 0.00% 0.00% Radiological Contaminants Alpha Particles (15 pCi/L) - 68.08% 61.06% - 4.58% 5.40% Beta Particles (50 pCi/L) - 74.51% 59.79% - 0.53% 0.47% Combined Radium-226 & -228 (5 pCi/L) - 69.97% 70.18% - 11.46% 4.99% Uranium (30 Mg/L) - 69.26% 55.82% - 7.57% 4.30% 1 The first Six-Year Review occurrence estimate values presented in this table are from the report titled Occurrence Estimation Methodology and Occurrence Findings for Six-Year Review of National Primary Drinking Water Regulations. EPA Report 815-R-03- 006, Office of Water (USEPA, 2003b). 2 The second Six-Year Review occurrence estimate values presented in this table are from the report titled The Analysis of Regulated Contaminant Occurrence Data from Public Water Systems in Support of the Second Six-Year Review of National Primary Drinking Water Regulations. EPA Report 815-B-09-006, Office ofWater (USEPA, 2010c). 3 For the third Six-Year Review, there was a different MCL for arsenic (0.01 mg/L) compared to the earlier MCL (0.05 mg/L) for the first and second Six-Year Reviews. 4 For the third Six-Year Review, quality assurance steps were taken to identify and exclude fluoride samples from fluoridated water systems. 6.3 System Sample Point Level Analysis The basic Stage 1 analytical methodology is a conservative approach; occurrence measures are based on simple counts of whether or not a system has at least one monitoring sample identified with a contaminant detection greater than a specified concentration threshold. The approach includes another implicit conservative assumption; if a detection is found in a single entry point to the distribution system or other formal system sample point (SP), then the entire population served by the system is assumed to be potentially exposed to the detected contaminant at the system. For example, if a system serves a population of 30,000 and identified a detection of a contaminant in one of its two SPs, the primary Stage 1 analytical methodology would estimate that the entire population served by the system (30,000) was potentially exposed to the maximum detected levels of the contaminant found in the one SP. In this context, sample points (SPs) are defined as the authorized drinking water sample locations for compliance monitoring of regulated contaminants. SPs primarily are entry points to the distribution system, but a small number of states allow for sampling of raw, untreated ground water wells or surface water intakes as well. In reality, many systems get water from multiple water sources, such as a mix of purchased and non-purchased water, ground water wells and surface water source intakes, among others. In SYR3 Occurrence Support Document 6-44 December 2016 ------- systems with multiple SPs, such as multiple surface water intakes, multiple wells and/or multiple entry points to the distribution system, contaminant occurrence in one source or one SP does not necessarily mean contaminant occurrence in all sources or SPs that distribute water to consumers. Given this, additional Stage 1 analyses were conducted at the SP-level to provide supplementary details of contaminant occurrence. The SP analysis is a less conservative estimate of the population served by systems with contaminant detections. To derive this SP-level measure, an assumption was necessary regarding population served by individual SPs at drinking water systems. The population served by each SP and/or entry point to the distribution system is often difficult to know and is rarely, if ever, reported along with other compliance monitoring records. Therefore, EPA assumed for the analysis that the total population served by a particular system is equally distributed across all SPs at the system.10 With this assumption, the population served all SPs with a detection of a particular contaminant is calculated by dividing the system's total population served by the number of that system's SPs with a contaminant detection. For example, if a system serves a population of 30,000 and found detections of a contaminant in one of its two SPs, then a population of 15,000 (or 30,000 x V2) would be estimated to be potentially exposed to the contaminant. This the total number of entry points and/or other SPs for each system must be determined in order to calculate the proportional population potentially exposed. This was done by counting the total number of unique SPs for each system over the entire six years of data. These counts were done separately for each contaminant at every system. While conducting these counts, it appeared that some systems may have changed their sample point numbering conventions (i.e., their "SP identification codes" or formal sample point identification number) at some point over the six years of data, which would result in a higher number of apparent SPs than the number of actual SPs. If so, this approach to sample point counting could potentially overestimate the total number of SPs for a system, thereby resulting in an underestimate of the population served by each SP.11 Exhibit 6.4 presents a summary of the Stage 1 findings based on SPs and population served by SPs. 10 This "proportional population" assumption is based on the idea that for every PWS, each sample point serves an equal portion of the system's total population. How well this assumption reflects actual populations potentially exposed to contaminant occurrence at a system will depend on the distribution system and service population configurations at individual systems. 11 Another method was explored for counting the number of SPs. This other method used the maximum number of SPs that sampled in a given year as the system's "total number of SPs." This approach likely avoids the issue of changing SP numbering conventions over time. However, this method has the potential to underestimate the total number of SPs for the system and therefore overestimate the population served by each SP. For example, a system could truly have a total of three SPs but those three SPs might not all sample within the same year, so the number of actual SPs sampled over the six-year period might be underestimated. If a system is on reduced monitoring, each SP might only need to sample as often as once every three years. SYR3 Occurrence Support Document 6-45 December 2016 ------- Exhibit 6.4: Summary of Stage 1 Contaminant Occurrence Findings - Sample Points and Population Served by Sample Points Contaminant (MCL Concentration) Percent of Sample Points Percent of Population- Served by Sample Points With Detections > MRL With Detections > MCL Concentration With Detections > MRL With Detections > MCL Concentration Inorganic Chemicals Antimony (6 |jg/L) 3.397% 0.126% 5.956% 0.068% Arsenic (10 |jg/L) 38.314% 5.840% 37.218% 1.739% Asbestos (7 MFL) 2.769% 0.086% 3.423% 0.038% Barium (2,000 |jg/L) 69.377% 0.083% 76.789% 0.138% Beryllium (4 |jg/L) 1.653% 0.040% 3.045% 0.024% Cadmium (5 |jg/L) 2.561% 0.079% 3.574% 0.020% Chromium (Total) (1 oo |jg/L) 25.561% 0.026% 28.044% 0.009% Cyanide (200 |jg/L) 2.973% 0.064% 7.260% 0.209% Fluoride 1 (4,000 |jg/L) 70.639% 0.568% 78.228% 0.313% Mercury (Inorganic) (2 |jg/L) 2.521% 0.062% 4.113% 0.029% Nitrate (as N) (10,000 |jg/L) 61.987% 1.878% 81.103% 0.723% Nitrite (as N) (1,000 |jg/L) 9.622% 0.497% 16.965% 0.601% Selenium (50 |jg/L) 15.896% 0.140% 20.489% 0.059% Thallium (2 |jg/L) 2.817% 0.120% 4.656% 0.137% Synthetic Organic Chemicals Alachlor (2 |jg/L) 0.097% 0.006% 0.392% 0.005% Atrazine (3 kig/L) 2.008% 0.086% 12.350% 0.481% Benzo(a)pyrene (0.2 |Jg/L) 0.267% 0.027% 0.702% 0.122% Carbofuran (40 |jg/L) 0.038% 0.000% 0.025% 0.000% Chlordane (2 |jg/L) 0.117% 0.010% 0.337% 0.001% Dalapon (200 |jg/L) 1.475% 0.002% 3.535% 0.000% Di(2-ethylhexyl)adipate (DEHA) (400 |jg/L) 1.080% 0.000% 1.830% 0.000% SYR3 Occurrence Support Document 6-46 December 2016 ------- Contaminant (MCL Concentration) Percent of Sample Points Percent of Population- Served by Sample Points With Detections > MRL With Detections > MCL Concentration With Detections > MRL With Detections > MCL Concentration Di(2-ethylhexyl)phthalate (DEHP) (6 (jg/L) 10.209% 0.640% 12.034% 0.849% 1,2-Dibromo-3-chloropropane (DBCP) (0.2 |Jg/L) 1.426% 0.213% 1.151% 0.114% 2,4-Dichlorophenoxyacetic acid (2,4-D) (70 Mg/L) 0.352% 0.002% 1.925% 0.000% Dinoseb (7 (jg/L) 0.170% 0.008% 0.123% 0.004% Diquat (20 Mg/L) 0.400% 0.003% 0.424% 0.000% Endothall (100 |jg/L) 0.100% 0.003% 0.048% 0.000% Endrin (2 (jg/L) 0.074% 0.002% 0.122% 0.000% Ethylene Dibromide (EDB) (0.05 |jg/L) 0.317% 0.080% 0.436% 0.022% Glyphosate (700 |jg/L) 0.073% 0.000% 0.051% 0.000% Heptachlor (0.4 |Jg/L) 0.098% 0.005% 0.236% 0.000% Heptachlor Epoxide (0.2 |Jg/L) 0.264% 0.011% 0.202% 0.001% Hexachlorobenzene (1 (jg/L) 0.075% 0.002% 0.084% 0.001% Hexachlorocyclopentadiene (50 Mg/L) 0.289% 0.002% 1.292% 0.004% Lindane (gamma-Hexachlorocyclohexane) (0.2 |Jg/L) 0.067% 0.008% 0.490% 0.002% Methoxychlor (40 Mg/L) 0.104% 0.000% 0.132% 0.000% Oxamyl (Vydate) (200 |jg/L) 0.063% 0.000% 0.055% 0.000% Pentachlorophenol (1 (jg/L) 0.389% 0.016% 0.742% 0.016% Picloram (500 |jg/L) 0.174% 0.000% 0.217% 0.000% Polychlorinated biphenyls (PCBs) (0.5 |Jg/L) 0.085% 0.013% 0.060% 0.015% Simazine (4 (jg/L) 0.612% 0.007% 5.603% 0.006% Toxaphene (3 pg/L) 0.048% 0.008% 0.089% 0.048% 2,3,7,8-TCDD (Dioxin) (0.00003 |jg/L) 0.107% 0.013% 0.107% 0.001% 2,4,5-Trichlorophenoxypropionic Acid (Silvex) (50 Mg/L) 0.103% 0.002% 0.614% 0.000% Volatile Organic Chemicals 1,2-Dichlorobenzene (600 |jg/L) 0.212% 0.000% 0.472% 0.000% SYR3 Occurrence Support Document 6-47 December 2016 ------- Contaminant (MCL Concentration) Percent of Sample Points Percent of Population- Served by Sample Points With Detections > MRL With Detections > MCL Concentration With Detections > MRL With Detections > MCL Concentration 1,4-Dichlorobenzene (75 Mg/L) 0.771% 0.002% 0.900% 0.000% 1,1-Dichloroethylene (7 (jg/L) 0.737% 0.030% 1.535% 0.011% cis-1,2-Dichloroethylene (70 Mg/L) 1.083% 0.001% 2.058% 0.000% trans-1,2-Dichloroethylene (100 Mg/L) 0.181% 0.000% 0.489% 0.000% Ethyl benzene (700 Mg/L) 1.949% 0.002% 1.672% 0.000% Monochlorobenzene (100 Mg/L) 0.263% 0.000% 0.528% 0.000% Styrene (100 Mg/L) 0.408% 0.001% 0.639% 0.000% Toluene (1,000 Mg/L) 2.778% 0.002% 2.483% 0.000% 1,2,4-Trichlorobenzene (70 Mg/L) 0.154% 0.000% 0.434% 0.000% 1,1,1-Trichloroethane (200 Mg/L) 0.587% 0.002% 0.980% 0.000% 1,1,2-Trichloroethane (5 Mg/L) 0.129% 0.004% 0.425% 0.001% Xylenes (Total) (10,000 Mg/L) 4.112% 0.000% 3.586% 0.000% Radiological Contaminants Alpha Particles (15 pCi/L) 57.551% 4.248% 60.478% 2.976% Beta Particles (50 pCi/L) 54.782% 0.319% 59.160% 0.237% Combined Radium-226 & -228 (5 pCi/L) 67.174% 4.305% 69.367% 2.045% Uranium (30 Mg/L) 57.952% 3.399% 57.905% 0.971% 1 Quality assurance steps were taken to identify and exclude fluoride samples from fluoridated water systems. SYR3 Occurrence Support Document 6-48 December 2016 ------- 7 Stage 2 Analysis Based on the initial review under the Third Six-Year Review Protocol, EPA determined that 10 chemical contaminants (lead, copper, 1,2-dichloroethane, 1,2-dichloropropane, benzene, carbon tetrachloride, dichloromethane, tetrachloroethylene, trichloroethylene and vinyl chloride) were being reviewed or revised under other regulatory actions and, therefore, no further action was taken under Six-Year Review 3. EPA reviewed the remaining chemical contaminants for new health effects and analytical feasibility information and 19 chemical contaminants were identified for additional analysis. Two of the 19 chemical contaminants (oxamyl and carbofuran) have health endpoints associated with acute exposure and, therefore, did not require the Stage 2 analysis which is most appropriate for contaminants for which chronic health effects are of concern. (Detailed Stage 1 analyses for oxamyl and carbofuran are included in Appendix A of this report.) The remaining 17 contaminants have chronic health effects and were evaluated via the Stage 2 occurrence analysis. These 19 contaminants fall into two groups: (1) contaminants with analytical limitations - carbofuran; chlordane; cyanide; heptachlor; heptachlor epoxide; hexachlorobenzene; methoxychlor; styrene; 2,3,7,8-TCDD (dioxin); toxaphene; 1,1,2- trichloroethane and (2) non-carcinogens with updated health assessments - cis-1,2- dichloroethylene; endothall; fluoride; hexachlorocyclopentadiene; oxamyl; selenium; toluene and xylenes (total). The SYR3 ICR Dataset is as large and robust as the dataset used for the second Six-Year Review; thus, similar to SYR2, it was again possible for SYR3 to use a simple analytical approach to estimate system means. System means were calculated using a simple arithmetic average of all detection and non-detection records for each system. The Stage 2 analysis system contaminant long-term mean estimates provide a less conservative contaminant occurrence estimate than does the Stage 1 analysis, which is based on a single maximum sample result exceeding a certain contaminant threshold. As described above, the Stage 2 analyses also provide better occurrence estimates for contaminants for which chronic health effects are of concern. In order to calculate a contaminant arithmetic mean for each system, a numeric value was substituted for each non-detection record. This "simple substitution method" for the non- detections is a straight-forward and standard data management approach for this type of analysis (e.g., Helsel and Hirsch, 1991). PWSs use this approach for calculating annual, rolling, four- quarter average contaminant concentrations and can substitute zero for each sample non- detection record when generating average concentration values. For the third Six-Year Review, three different substitution values were applied-zero, one-half the MRL value and the full MRL value. Since the true, but unknown, concentration of a contaminant for each non-detection is theoretically between zero and the MRL, using a substitution value of zero for each non- detection generates a lower bound estimated average, substituting the full MRL generates an upper bound estimate and substituting the V2 MRL value generates a mid-range estimate. EPA calculated three arithmetic means for each contaminant at each system using the zero, one-half MRL and full MRL substitution values. For each of these three substitution values, system contaminant means were calculated for all systems with data in the SYR3 ICR Dataset, then the percent of all systems with a long-term mean concentration greater than each contaminant's MCL concentration was calculated. SYR3 Occurrence Support Document 7-49 December 2016 ------- 7.1 Preparing the Data for the Stage 2 Analysis As was described in Section 3.3, in order to conduct the Stage 1 and Stage 2 occurrence analysis, each contaminant sample analytical result must specify a sample analytical result (value) and a sample analytical result (sign) to indicate whether that result is a detection (sample analytical result greater than or equal to the MRL) or a non-detection. Sample records reported as non- detections tend to be less uniform and less complete than sample records for analytical detections. Some states reported MRL data, recording it in the analytical result field and also including a "<" in a corresponding field to identify the record as a non-detection. Other states simply included a zero or negative result in the analytical result field to signify a non-detection and did not include any MRL data. The Stage 1 analyses are not affected by how non-detections are specifically recorded. However, since the Stage 2 analyses were conducted using a "simple substitution" approach that substitutes MRL values for reported analytical non-detections, non- zero MRL numeric values needed to replace all analytical results that were reported either as zero, "non-detection," "ND," etc. A convention was established where EPA replaced any missing non-detect results with the most common modal MRL value for the state in which the system was located (derived directly from the PWS compliance monitoring data submitted to EPA in the SYR3 ICR Dataset). In some cases, though, all MRL data for a specific contaminant's data from an entire state were missing. The missing values were replaced with the national modal MRL derived as the mode of all the state modal MRL values for that contaminant. If state-modal MRL values were extremely low or high, a process was developed to identify and replace such values with more reasonable MRL values. Reported MRL values that were below the minimum MDL, greater than the national modal MRL, or missing were replaced with the national modal MRL. For complete details of the data management measures, including the methods used to identify and replace non-numeric or incorrect non-detection records, see USEPA (2016d). 7.2 Summary of Stage 2 Contaminant Occurrence Estimations The results from these Stage 2 analyses presented below in Exhibit 7.1 reflect the percentage of systems and population served by systems, with an estimated system contaminant mean exceeding the respective MCL concentration for each contaminant over the six-year period of data in the SYR3 ICR Dataset. The results using the zero substitution value are shown because they are equivalent to how states are authorized to calculate system means for compliance determinations. (For comparison, the Stage 1 results relative to the MCL concentration are also included.) Note: The results in Exhibit 7.1 do not necessarily indicate an MCL violation. The long-term mean in the Stage 2 analysis differs from compliance assessments that calculate a system mean concentration over four consecutive quarters. An MCL violation occurs, for example, when the MCL is exceeded at a sampling point by the average results from the consecutive samples at that sampling point. Please see Appendix B for additional measures of contaminant occurrence based on the Stage 2 analyses, including presentations of the numbers of systems and population served generated using the V2 MRL and full MRL substitution values, which supplement the calculations using zero substitution values presented in Exhibit 7.1. The appendix summary tables present findings separately for ground water vs. surface water and present occurrence measures that identify the total number of systems and total population served by systems with estimated system SYR3 Occurrence Support Document 7-50 December 2016 ------- contaminant means greater than the MCL concentration, as well as many other thresholds. For more information on the potential thresholds of concern used in the SYR3 Stage 2 analyses, refer to Section 5.3. Exhibit 7.1: Comparison of Stage 1 and Stage 2 Analytical Results - Percent of Systems and Population Served by Systems Greater than the MCL Concentration Contaminant (MCL Concentration) Percent of Systems > MCL Concentration Percent of Population Served by Systems > MCL Concentration Stage 11 (one detect Stage 22 (mean > MCL Stage 11 (one detect Stage 22 (mean > MCL Chlordane (2 Mg/L) 0.017% 0.003% 0.001 % 0.0005% cis-1,2-Dichloroethylene (70 Mg/L) 0.002% 0.000% 0.00002% 0.000% Cyanide (200 |jg/L) 0.103% 0.019% 0.239% 0.038% Endothall (100 |jg/L) 0.006% 0.006% 0.001 % 0.001% Fluoride 3 (4,000 jjg/L) 0.726% 0.284% 3.254% 0.032% Heptachlor (0.4 Mg/L) 0.008% 0.005% 0.001 % 0.001% Heptachlor Epoxide (0.2 Mg/L) 0.018% 0.005% 0.001 % 0.001% Hexachlorobenzene (1 Mg/L) 0.003% 0.000% 0.003% 0.000% Hexachlorocyclopentadiene (50 Mg/L) 0.003% 0.000% 0.004% 0.000% Methoxychlor (40 Mg/L) 0.000% 0.000% 0.000% 0.000% Selenium (50 Mg/L) 0.174% 0.061% 0.246% 0.008% Styrene (100 Mg/L) 0.002% 0.000% 0.00004% 0.000% 2,3,7,8-TCDD (Dioxin) (0.00003 Mg/L) 0.031 % 0.031% 0.001 % 0.001% Toluene (1,000 Mg/L) 0.004% 0.000% 0.0002% 0.000% Toxaphene (3 M9/L) 0.013% 0.005% 0.319% 0.104% 1,1,2-Trichloroethane (5 Mg/L) 0.004% 0.000% 0.001 % 0.000% Xylenes (10,000 Mg/L) 0.000% 0.000% 0.000% 0.000% 1 The Stage 1 results represent the percent of systems with at least one sample analytical result greater than a contaminant's MCL concentration. 2 The Stage 2 results represent the percent of systems with an estimated long-term mean concentration greater than a contaminant's MCL concentration. The Stage 2 results presented here are based on long-term means generated by substituting zero for each non-detection record. For the Stage 2 results based on substituting the value of the full MRL or % MRL (instead of zero), please refer to Appendix B. 3 Quality assurance steps were taken to identify and exclude fluoride samples from fluoridated water systems. SYR3 Occurrence Support Document 7-51 December 2016 ------- 8 References Helsel, D.R. and R.M. Hirsch. 1991. "Statistical Methods in Water Resources," Chapter A3, Book 4 of Techniques of Water-Resources Investigations of the United States Geologic Survey. United States Environmental Protection Agency (USEPA). 1986. National Primary and Secondary Drinking Water Regulations; Fluoride; Final Rule. 51 FR 11396. April 2, 1986. USEPA. 1991a. National Primary Drinking Water Regulations—Synthetic Organic Chemicals and Inorganic Chemicals; Monitoring for Unregulated Contaminants; National Primary Drinking Water Regulations Implementation; National Secondary Drinking Water Regulations; Final Rule. 56 FR 3526. January 30, 1991. USEPA. 1991b. Integrated Risk Information System (IRIS) - Selenium. Oral RfD. Last modified October 2016. Available online at: http://www.epa.gov/iris/subst/0472.htm USEPA. 1992. Drinking Water; National Primary Drinking Water Regulations—Synthetic Organic Chemicals and Inorganic Chemicals; National Primary Drinking Water Regulations Implementation; Final Rule. 57 FR 31776. July 17, 1992. USEPA. 1998. National Primary Drinking Water Regulations: Disinfectants and Disinfection Byproducts; Final Rule. 63 FR 69390. December 16, 1998. USEPA. 2002. Analysis of National Occurrence of the 1998 Contaminant Candidate List (CCL) Regulatory Determination Priority Contaminants in Public Water Systems. EPA Report 815-D- 01-002. May 2002. USEPA. 2003a. National Primary Drinking Water Regulations; Announcement of Completion of EPA's Review of Existing Drinking Water Standards. 68 FR 42907. July 18, 2003. USEPA. 2003b. Occurrence Estimation Methodology and Occurrence Findings for Six-Year Review of National Primary Drinking Water Regulations. EPA Report 815-R-03-006. June 2003. USEPA. 2006. National Primary Drinking Water Regulations: Stage 2 Disinfectants and Disinfection Byproducts Rule; Final Rule. 71 FR 388. January 4, 2006. USEPA. 2008a. The Analysis of Occurrence Data from the Unregulated Contaminant Monitoring (UCM) Program and National Inorganics and Radionuclides Survey (NIRS) in Support of Regulatory Determinations for the Second Drinking Water Contaminant Candidate List. EPA Report 815-R-08-014. June 2008. USEPA. 2008b. 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 Report 815-R-08-013. June 2008. USEPA. 2010a. National Primary Drinking Water Regulations; Announcement of the Results of EPA's Review of Existing Drinking Water Standards and Request for Public Comment and/or Information on Related Issues. 75 FR 15499. March 29, 2010. SYR3 Occurrence Support Document 8-52 December 2016 ------- USEPA. 2010b. Agency Information Collection Activities; Submission to OMB for Review and Approval; Contaminant Occurrence Data in Support of EPA's Third Six-Year Review of National Primary Drinking Water Regulations (Renewal). 75 FR 6023. February 5, 2010. USEPA. 2010c. The Analysis of Regulated Contaminant Occurrence Data from Public Water Systems in Support of the Second Six-Year Review of National Primary Drinking Water Regulations. EPA Report 815-B-09-006. September 2010. USEPA. 201 la. National Primary Drinking Water Regulations: Group Regulation of Carcinogenic Volatile Organic Compounds (VOCs). 40 CFR 141 40 CFR 142. USEPA. 201 lb. Exposure Factors Handbook 2011 Edition (Final). U.S. Environmental Protection Agency, Washington, DC, EPA/600/R-09/052F, 2011. USEPA. 2014. National Drinking Water Advisory Council Meeting Summary, November 6-7, 2014. USEPA. 2016a. Support Document for Third Six-Year Review of Drinking Water Regulations for Acrylamide and Epichlorohydrin. EPA- 810-R-16-019. December 2016. USEPA. 2016b. Six-Year Review 3 Technical Support Document for Microbial Contaminant Regulations. EPA-810-R16-010. December 2016. USEPA. 2016c. Six-Year Review 3 Technical Support Document for Disinfectants/Disinfection Byproducts Rules. EPA-810-R-16-012. December 2016. USEPA. 2016d. The Data Management and Quality Assurance/Quality Control Process for the Third Six- Year Review Information Collection Rule Dataset. EPA-810-R-16-015. December 2016. USEPA. 2016e. Development of Estimated Quantitation Levels for the Third Six-Year Review of National Primary Drinking Water Regulations (Chemical Phase Rules). EPA-810-R-16-002. December 2016. USEPA. 2016f. Six- Year Review 3-Health Effects Assessment for Existing Chemical and Radionuclide National Primary Drinking Water Regulations-Summary Report. December 2016. Yang, G., R. Zhou, S. Yin, L. Gu, B. Yan, Y. Liu, Y. Liu, and X. Li. 1989a. Studies of safe maximal daily dietary selenium intake in a seleniferous area in China. I. Selenium intake and tissue levels of the inhabitants. Journal of Trace Elements and Electrolytes in Health and Disease. 3(2): 77-87. Yang, G., S. Yin, R. Zhou, L. Gu, B. Yan, Y. Liu, and Y. Liu. 1989b. Studies of safe maximal daily dietary Se-intake in a seleniferous area in China. II. Relation between Se- intake and the manifestation of clinical signs and certain biochemical alterations in blood and urine. Journal of Trace Elements and Electrolytes in Health and Disease. 3(3): 123-130. SYR3 Occurrence Support Document 8-53 December 2016 ------- Appendices APPENDIX A. Background Information and Detailed Stage 1 Analysis Occurrence Measures for 2 Select Regulated Chemical Contaminants APPENDIX B. Background Information and Detailed Stage 2 Analysis Occurrence Measures for 17 Select Regulated Chemical Contaminants ------- A Background Information and Detailed Stage 1 Analysis Occurrence Measures for 2 Select Regulated Chemical Contaminants SYR3 Occurrence Support Document A-l December 2016 ------- A.l Carbofuran This chapter on carbofuran includes background information such as the regulatory history and a summary of monitoring requirements, as well as occurrence and exposure estimates in drinking water. All drinking water occurrence estimates are based on data from the National Compliance Monitoring Information Collection Request (ICR) Dataset for the Third Six-Year Review (the "SYR3 ICR Dataset"). A.l.l Background The United States Environmental Protection Agency (EPA) published the current National Primary Drinking Water Regulations (NPDWR) for carbofuran on January 30, 1991 (56 FR 3526; USEPA, 1991a). The NPDWR established a maximum contaminant level goal (MCLG) and a maximum contaminant level (MCL) of 40 |ig/L. EPA based the MCLG on a reference dose (RfD) of 5 |ig/kg-day (0.005 mg/kg-day) and a cancer classification of E, evidence of non- carcinogenicity for humans. Carbofuran is regulated as a synthetic organic chemical (SOC) in drinking water. All non- purchased community water systems (CWSs) and non-transient non-community water systems (NTNCWSs) are required to sample for SOCs. Waivers are available to all systems upon a favorable vulnerability assessment and/or prior analytical results. The maximum waiver period for SOCs is three years, but this waiver can be renewed indefinitely, if it is reconfirmed that the source is not vulnerable. All CWSs and NTNCWSs without an SOC waiver must collect four consecutive quarterly samples during the initial three-year compliance period.1 If all 4 samples are non-detections, then a system serving less than 3,300 people may reduce its collection frequency to 1 sample during each consecutive compliance period; a system serving more than 3,300 people may reduce its collection frequency to 2 quarterly samples within a 12-month period during each repeat compliance period. If a chemical is detected, the system must monitor quarterly until results are reliably and consistently below the MCL (minimum of two quarterly samples for ground water systems and four quarterly samples for surface water systems). If all quarterly samples are below the MCL, the system may return to annual sampling. If a chemical is detected at a level greater than the MCL, the system (whether ground water or surface water) must take quarterly samples until four consecutive quarters are below the MCL. If all quarterly samples are below the MCL, the system may return to annual sampling. A.1.2 Occurrence in Drinking Water The analysis of carbofuran occurrence presented in the following section is based on state compliance monitoring data from the SYR3 ICR Dataset. These data consist of 122,110 analytical results from 34,614 public water systems (PWSs) during the period from 2006 to 1 All new systems or systems using a new water source that began operation after January 22, 2004 must demonstrate compliance with the MCL within a period of time specified by the State. The system must also comply with the initial sampling frequencies specified by the State to ensure that a system can demonstrate compliance with the MCL. SYR3 Occurrence Support Document A-2 December 2016 ------- 2011. The number of sample results and systems vary by state, although the state datasets have been reviewed and checked to ensure adequacy of coverage and completeness. EPA used a two-stage analytical approach to estimate the national contaminant occurrence using the SYR3 ICR Dataset. In the "Stage 1 analysis," the occurrence data were analyzed to generate simple non-parametric estimates and descriptive statistics of national contaminant occurrence in public water systems. Simple counts were made of the number and percentage of systems and population served by systems with at least one compliance monitoring sample result greater than a specified concentration threshold. The Stage 1 analysis provides occurrence assessments that are more conservative and may be more reflective of potential acute exposure than the assessments from the Stage 2 analyses. Carbofuran has health endpoints associated with acute exposure and, therefore, did not require the Stage 2 analysis. Details on the Stage 1 analysis are presented in Section 6. For carbofuran, EPA generated additional Stage 1 occurrence estimates relative to the MCL and the estimated quantitation level (EQL). Stage 1 Occurrence Estimates Stage 1 analyses for carbofuran are summarized in this section. Occurrence estimates were generated relative to the following thresholds: 40 |ig/L (the MCL) and 5 |ig/L (the EQL). The EQL represents the potential quantitation capabilities below a practical quantitation level (PQL).2 For more information on the new potential thresholds of concern used in the SYR3 analyses for carbofuran, refer to USEPA (2016d) and (2016e). Exhibit A-l presents the system-level Stage 1 analysis of carbofuran occurrence in drinking water. Exhibit A-2 presents similar information based on population served by the systems. Based on the Stage 1 analysis, no systems had any detections greater than the MCL concentration of 40 |ig/L. Three systems, serving 24,258 people, had at least 1 detection greater than the EQL concentration of 5 |ig/L. Exhibit A-1: Carbofuran Stage 1 Analysis - Summary of Systems with a Threshold Exceedance Source Water Type (Number of Systems) Threshold Number of Systems with Detections That Are Greater Than the Threshold Percent of Systems with Detections That Are Greater Than the Threshold Ground Water > 40 |jg/L 0 0.000% (31,375) > 5 |jg/L1 1 0.003% 2 When it is not possible to measure concentrations at the MCLG level, EPA often bases the MCL on an analytical feasibility level, known as a PQL. However, analytical feasibility can improve over time. As part of the Six-Year Review process, EPA evaluates whether new information regarding quantitation shows that PQLs may be reduced. The EQL represents quantitation capabilities below a PQL (USEPA, 2016d). The EQL is the threshold used to evaluate occurrence and exposure for the Stage 1 analyses. SYR3 Occurrence Support Document A-3 December 2016 ------- Source Water Type (Number of Systems) Threshold Number of Systems with Detections That Are Greater Than the Threshold Percent of Systems with Detections That Are Greater Than the Threshold Surface Water (3,239) > 40 |jg/L 0 0.000% > 5 |jg/L1 2 0.062% Combined Ground & Surface Water (34,614) > 40 |jg/L 0 0.00% > 5 |jg/L1 3 0.009% 1 The new potential threshold of concern for this contaminant is based on the EQL. The EQL represents the potential quantitation capabilities below a PQL (USEPA, 2016d). Exhibit A-2: Carbofuran Stage 1 Analysis - Summary of Population Served by Systems with a Threshold Exceedance Source Water Type (Population Served by Systems) Threshold Population Served by Systems with Detections That Are Greater Than the Threshold Percent of Population Served by Systems with Detections That Are Greater Than the Threshold Ground Water (90,319,675) > 40 |jg/L 0 0.000% > 5 |jg/L1 993 0.001% Surface Water (138,398,258) > 40 |jg/L 0 0.000% > 5 |jg/L1 23,265 0.017% Combined Ground & Surface Water (228,717,933) > 40 |jg/L 0 0.00% > 5 |jg/L1 24,258 0.011% 1 The new potential threshold of concern for this contaminant is based on the EQL. The EQL represents the potential quantitation capabilities below a PQL (USEPA, 2016d). Data for carbofuran were available from 50 states/entities. Four states did not submit data for use in the Six-Year Review (Colorado, Delaware, Georgia and Mississippi). Although the States of Colorado and Mississippi did not provide data for any contaminants for the SYR3 ICR Dataset, these states are included in the count of 50 states because a handful of tribal water systems located within these 2 states did submit carbofuran data. Exhibit A-3 presents the total number of systems in each state that submitted data for carbofuran. In addition, the geographic distribution of carbofuran occurrence in drinking water is illustrated by showing states with systems with at least one detection greater than the EQL and the MCL concentrations. No systems had detections greater than the MCL. Three systems (one in New Mexico and two in New York) had at least one detection greater than the EQL of 5 |ig/L. SYR3 Occurrence Support Document A-4 December 2016 ------- Exhibit A-3: Carbofuran Stage 1 Analysis - Summary of Systems with Threshold Exceedances by State1 Total Number of Systems with Detections Systems with Detections Systems > 5 |ig/L2 > 40 |jg/L Number Percent Number Percent AK 9 AL 383 AR 459 AS 11 AZ 868 CA 1,320 CO 1 CT 1,136 DC 1 FL 2,088 HI 115 IA 2 ID 325 IL 1,467 IN 1,210 KS 86 KY 225 LA 1,104 MA 562 MD 882 ME 127 Ml 2,423 MN 921 MO 1,321 MS 5 MT 857 NC 2,347 ND 23 SYR3 Occurrence Support Document AS December 2016 ------- State Total Number of Systems Systems with Detections > 5 |ig/L2 Systems with Detections > 40 |jg/L Number Percent Number Percent NE 656 NH 1,146 NJ 80 NM 718 1 0.14% 0 0.00% NV 303 NY 2,115 2 0.09% 0 0.00% OH 178 OK 91 OR 1,118 PA 1,289 Rl 74 SC 497 SD 258 TN 8 TX 1,535 UT 428 VA 228 VT 382 WA 700 Wl 1,912 WV 302 WY 318 Total 34,614 3 0.009% 0 0.00% 1 Blank cells within the table indicate that there were no systems with any detections that exceeded either threshold. 2 The new potential threshold of concern for this contaminant is based on the EQL. The EQL represents the potential quantitation capabilities below a PQL (USEPA, 2016d). Exhibit A-4 presents the population served by systems with at least one detection greater than the MCL concentration by state (40 |ig/L). As described above, no systems had any detections greater than the MCL. Three systems, serving 24,258 people, had at least 1 detection greater than the EQL of 5 |ig/L. SYR3 Occurrence Support Document A-6 December 2016 ------- Exhibit A-4: Carbofuran Stage 1 Analysis - Summary of Population Served by Systems with Threshold Exceedances by State1 State Total Population Population Served by Systems with Detections > 5 jjg/L2 Population Served by Systems with Detections > 40 jjg/L Population Percent Population Percent AK 39,228 AL 5,333,035 AR 2,635,934 AS 62,196 AZ 6,473,687 CA 35,686,301 CO 2,020 CT 2,883,135 DC 761,124 FL 18,943,131 HI 1,487,191 IA 165,864 ID 885,855 IL 10,998,351 IN 4,769,597 KS 1,685,226 KY 4,225,473 LA 4,964,671 MA 9,163,574 MD 4,939,512 ME 362,333 Ml 7,218,130 MN 3,752,615 MO 5,232,592 MS 6,176 MT 845,014 NC 7,832,302 ND 66,229 NE 1,653,596 SYR3 Occurrence Support Document A-7 December 2016 ------- State Total Population Population Served by Systems with Detections > 5 jjg/L2 Population Served by Systems with Detections > 40 jjg/L Population Percent Population Percent NH 949,308 NJ 5,123,511 NM 1,940,795 993 0.05% 0 0.00% NV 2,681,118 NY 10,480,579 23,265 0.22% 0 0.00% OH 2,473,669 OK 338,082 OR 3,432,212 PA 10,891,371 Rl 1,017,507 SC 3,622,250 SD 678,171 TN 1,176,648 TX 22,373,743 UT 2,752,741 VA 5,295,906 VT 387,092 WA 3,822,877 Wl 4,236,667 WV 1,499,884 WY 469,710 Total 228,717,933 24,258 0.011% 0 0.00% 1 Blank cells within the table indicate that there were no systems with any detections that exceeded either threshold. 2 The new potential threshold of concern for this contaminant is based on the EQL. The EQL represents the potential quantitation capabilities below a PQL (USEPA, 2016d). A.1.3 Summary of Data A total of 122,110 analytical results from 34,614 PWSs in 50 states/entities were available in the SYR3 ICR Dataset for carbofuran. The Stage 1 analysis of occurrence in drinking water indicated that zero systems had any detections of carbofuran greater than the MCL concentration of 40 |ig/L. Three systems (one served by ground water and two served by surface water), serving 24,258 people, had at least 1 detection greater than the EQL (5 |ig/L). SYR3 Occurrence Support Document A-8 December 2016 ------- A.2 Oxamyl This chapter on oxamyl includes background information such as the regulatory history and a summary of monitoring requirements, as well as occurrence and exposure estimates in drinking water. All drinking water occurrence estimates are based on data from the National Compliance Monitoring Information Collection Request (ICR) Dataset for the Third Six-Year Review (the "SYR3 ICR Dataset"). A.2.1 Background The United States Environmental Protection Agency (EPA) published the current National Primary Drinking Water Regulations (NPDWR) for oxamyl on July 17, 1992 (57 FR 31776; USEPA, 1992). The NPDWR established a maximum contaminant level goal (MCLG) and a maximum contaminant level (MCL) of 200 |ig/L. EPA based the MCLG on a reference dose (RfD) of 25 |ig/kg-day (0.025 mg/kg-day) and a cancer classification of E, evidence of non- carcinogenicity for humans. Oxamyl is regulated as a synthetic organic chemical (SOC) in drinking water. All non-purchased community water systems (CWSs) and non-transient non-community water systems (NTNCWSs) are required to sample for SOCs. Waivers are available to all systems upon a favorable vulnerability assessment and/or prior analytical results. The maximum waiver period for SOCs is three years, but this waiver can be renewed indefinitely, if it is reconfirmed that the source is not vulnerable. All CWSs and NTNCWSs without an SOC waiver must collect four consecutive quarterly samples during the initial three-year compliance period.3 If all 4 samples are non-detections, then a system serving less than 3,300 people may reduce its collection frequency to 1 sample during each consecutive compliance period; a system serving more than 3,300 people may reduce its collection frequency to 2 quarterly samples within a 12-month period during each repeat compliance period. If a chemical is detected (but is less than the MCL), the system must monitor quarterly until results are reliably and consistently below the MCL (minimum of two quarterly samples for ground water systems and four quarterly samples for surface water systems). If all quarterly samples are below the MCL, the system may return to annual sampling. If a chemical is detected at a level greater than the MCL, the system (whether ground water or surface water) must take quarterly samples until four consecutive quarters are below the MCL. If all quarterly samples are below the MCL, the system may return to annual sampling. A.2.2 Occurrence in Drinking Water The analysis of oxamyl occurrence presented in the following section is based on state compliance monitoring data from the SYR3 ICR Dataset. These data consist of 121,508 analytical results from 34,518 public water systems (PWSs) during the period from 2006 to 3 All new systems or systems using a new water source that began operation after January 22, 2004 must demonstrate compliance with the MCL within a period of time specified by the State. The system must also comply with the initial sampling frequencies specified by the State to ensure that a system can demonstrate compliance with the MCL. SYR3 Occurrence Support Document A-9 December 2016 ------- 2011. The number of sample results and systems vary by state, although the state datasets have been reviewed and checked to ensure adequacy of coverage and completeness. EPA used a two-stage analytical approach to estimate the national contaminant occurrence using the SYR3 ICR Dataset. In the "Stage 1 analysis," the occurrence data were analyzed to generate simple non-parametric estimates and descriptive statistics of national contaminant occurrence in public water systems. Simple counts were made of the number and percentage of systems and population served by systems with at least one compliance monitoring sample result greater than a specified concentration threshold. The Stage 1 analysis provides occurrence assessments that are more conservative and may be more reflective of potential acute exposure than the assessments from the Stage 2 analyses. Oxamyl has health endpoints associated with acute exposure and, therefore, did not require the Stage 2 analysis. Details on the Stage 1 analysis are presented in Section 6. For oxamyl, since there were no analytical method limitations at the potential MCLG, EPA generated additional Stage 1 occurrence estimates relative to the MCL and two potential MCLGs. Stage 1 Occurrence Estimates Stage 1 analyses for oxamyl are summarized in this section. Occurrence estimates were generated relative to the following thresholds: 200 |ig/L (the MCL), 10 |ig/L (one potential MCLG value) and 9 |ig/L (the other potential MCLG value).4 The potential MCLG is due to changes in the RfD based on new health effects information. For more information on the new potential thresholds of concern used in the SYR3 analyses, refer to USEPA (2016d) and (2016e). Exhibit A-5 presents the system-level estimates for oxamyl occurrence in drinking water. Exhibit A-6 presents similar information based on population served by the systems. Based on the Stage 1 analyses, no systems had any detections greater than the MCL concentration of 200 |ig/L. Three systems, serving 28,146 systems, had at least 1 detection greater than the potential MCLG of 10 |ig/L. Four systems, serving 42,662 systems, had at least 1 detection greater than the potential MCLG of 9 |ig/L. 4 The MCLG for oxamyl can be derived using a normalized drinking water intake per unit body weight from birth to less than 12 months at the 90th percentile of 0.15 L/Kg (based on Table 3-19 in USEPA (201 lb)). The alternate MCLG for children derived using the normalized exposure factors is 0.009 mg/L (0.0069 mg/kg/day x 0.2/ 0.15 = 0.009 mg/L). There was no difference in the Stage 1 occurrence analysis results between the 9 |ig/L and 10 |ig/L threshold. SYR3 Occurrence Support Document A-10 December 2016 ------- Exhibit A-5: Oxamyl Stage 1 Analysis - Summary of Systems with a Threshold Exceedance Source Water Type (Number of Systems) Threshold Systems with Detections That Are Greater Than the Threshold Systems with Detections That Are Greater Than the Threshold Ground Water (31,355) > 200 |jg/L 0 0.00% > 10 |jg/L1 2 0.01% > 9 |jg/L1 2 0.01% Surface Water (3,163) > 200 |jg/L 0 0.00% > 10 |jg/L1 1 0.03% > 9 |jg/L1 2 0.06% Combined Ground & Surface Water (34,518) > 200 |jg/L 0 0.00% > 10 |jg/L1 3 0.01% > 9 |jg/L1 4 0.01% 1 The new potential threshold of concern for this contaminant is due to changes in the RfD based on new health effects information. Exhibit A-6: Oxamyl Stage 1 Analysis - Summary of Population Served by Systems with a Threshold Exceedance Source Water Type (Population Served by Systems) Threshold Population Served by Systems with Detections That Are Greater Than the Threshold Percent of Population Served by Systems with Detections That Are Greater Than the Threshold Ground Water (90,279,553) > 200 |jg/L 0 0.00% > 10 |jg/L1 19,397 0.02% > 9 |jg/L1 19,397 0.02% Surface Water (137,240,820) > 200 |jg/L 0 0.000% > 10 |jg/L1 8,749 0.01% > 9 |jg/L1 23,265 0.02% Combined Ground & Surface Water > 200 |jg/L 0 0.000% > 10 |jg/L1 28,146 0.01% SYR3 Occurrence Support Document A-ll December 2016 ------- Source Water Type (Population Served by Systems) Threshold Population Served by Systems with Detections That Are Greater Than the Threshold Percent of Population Served by Systems with Detections That Are Greater Than the Threshold Combined Ground & Surface Water, cont. (227,520,373) > 9 |jg/L1 42,662 0.02% 1 The new potential threshold of concern for this contaminant is due to changes in the RfD based on new health effects information. Data for oxamyl were available from 50 states/entities. Four states did not submit data for use in the Six-Year Review (Colorado, Delaware, Georgia and Mississippi). Although the States of Colorado and Mississippi did not provide data for any contaminants for the SYR3 ICR Dataset, these states are included in the count of 50 states because a handful of tribal water systems located within these 2 states did submit oxamyl data. Exhibit A-7 presents the total number of systems in each state that submitted data for oxamyl. In addition, the geographic distribution of oxamyl occurrence in drinking water is illustrated by showing states with systems with any detections greater than the potential MCLG and the MCL concentrations. Detection rates of oxamyl were low; no systems had any detections greater than the MCL. Three systems in three states (Florida, New Mexico and New York) had detections greater than the potential MCLG of 10 |ig/L. Four systems in three states (Florida, New Mexico and New York) had detections greater than the potential MCLG of 9 |ig/L. Exhibit A-7: Oxamyl Stage 1 Analysis - Summary of Systems with Threshold Exceedances by State12 State Total Number of Systems Systems with Detections > 9 jjg/L3 Systems with Detections >10 jjg/L3 Systems with Detections > 200 jjg/L Number Percent Number Percent Number Percent AK 9 AL 383 AR 459 AS 11 AZ 856 CA 1,336 CO 1 CT 1,136 DC 1 FL 2,087 1 0.05% 1 0.05% 0 0.00% HI 115 IA 2 ID 323 SYR3 Occurrence Support Document A-12 December 2016 ------- State Total Number of Systems Systems with Detections > 9 jjg/L3 Systems with Detections >10 jjg/L3 Systems with Detections > 200 jjg/L Number Percent Number Percent Number Percent IL 1,459 IN 1,210 KS 3 KY 225 LA 1,104 MA 564 MD 873 ME 126 Ml 2,424 MN 921 MO 1,321 MS 5 MT 857 NC 2,346 ND 23 NE 656 NH 1,146 NJ 80 NM 718 1 0.14% 1 0.14% 0 0.00% NV 304 NY 2,115 2 0.09% 1 0.05% 0 0.00% OH 178 OK 90 OR 1,118 PA 1,290 Rl 74 SC 497 SD 258 TN 7 TX 1,535 UT 428 SYR3 Occurrence Support Document A-13 December 2016 ------- State Total Number of Systems Systems with Detections > 9 jjg/L3 Systems with Detections >10 jjg/L3 Systems with Detections > 200 jjg/L Number Percent Number Percent Number Percent VA 228 VT 382 WA 700 Wl 1,914 WV 302 WY 318 Total 34,518 4 0.01% 3 0.01% 0 0.00% 1 Results are based on setting all non-detection results equal to % the MRL values in the SYR3 ICR dataset. 2 Blank cells within the table indicate that there were no systems with a mean concentration that exceeded any of the thresholds. 3 The new potential threshold of concern for this contaminant is due to changes in the RfD based on new health effects information. Exhibit A-8 presents the population served by systems with detections greater than the MCL and MCLG concentrations by state. As described above, no systems had any detections greater than the MCL. Three systems in 3 states (Florida, New Mexico and New York), serving 28,146 people, had detections greater than the potential MCLG of 10 |ig/L. Four systems in three states (Florida, New Mexico and New York), serving 42,662 people, had detections greater than the potential MCLG of 9 |ig/L. Exhibit A-8: Oxamyl Stage 1 Analysis - Summary of Population Served by Systems with Threshold Exceedances by State12 State Total Population Population Served by Systems with Detections > 9 jjg/L3 Population Served by Systems with Detections >10 mq/l3 Population Served by Systems with Detections > 200 Mg/L Population Percent Population Percent Population Percent AK 39,228 AL 5,333,035 AR 2,635,934 AS 62,196 AZ 6,470,039 CA 35,698,949 CO 2,020 CT 2,883,135 DC 761,124 FL 18,943,101 18,404 0.10% 18,404 0.10% 0 0.00% HI 1,487,191 SYR3 Occurrence Support Document A-14 December 2016 ------- State Total Population Population Served by Systems with Detections > 9 jjg/L3 Population Served by Systems with Detections >10 mq/l3 Population Served by Systems with Detections > 200 Mg/L Population Percent Population Percent Population Percent IA 165,864 ID 884,736 IL 10,997,092 IN 4,769,597 KS 482,056 KY 4,225,473 LA 4,964,671 MA 9,163,674 MD 4,936,864 ME 362,303 Ml 7,218,255 MN 3,752,615 MO 5,232,592 MS 6,176 MT 845,014 NC 7,832,272 ND 66,229 NE 1,653,596 NH 949,308 NJ 5,123,511 NM 1,940,795 993 0.05% 993 0.05% 0 0.00% NV 2,681,738 NY 10,480,579 23,265 0.22% 8,749 0.08% 0 0.00% OH 2,473,669 OK 337,997 OR 3,432,307 PA 10,895,086 Rl 1,017,507 SC 3,622,250 SD 678,171 TN 1,173,584 SYR3 Occurrence Support Document A-15 December 2016 ------- State Total Population Population Served by Systems with Detections > 9 jjg/L3 Population Served by Systems with Detections >10 mq/l3 Population Served by Systems with Detections > 200 Mg/L Population Percent Population Percent Population Percent TX 22,373,743 UT 2,752,741 VA 5,295,906 VT 387,092 WA 3,822,877 Wl 4,236,887 WV 1,499,884 WY 469,710 Total 227,520,373 42,662 0.02% 28,146 0.01% 0 0.00% 1 Results are based on setting all non-detection results equal to % the MRL values in the SYR3 ICR dataset. 2 Blank cells within the table indicate that there were no systems with a mean concentration that exceeded any of the thresholds. 3 The new potential threshold of concern for this contaminant is due to changes in the RfD based on new health effects information. A.2.3 Summary of Data A total of 121,508 analytical results from 34,518 PWSs in 50 states/entities were available in the SYR3 ICR Dataset for oxamyl. The Stage 1 analysis of occurrence in drinking water indicated that zero systems had any detections of oxamyl greater than the MCL concentration of 200 |ig/L. Three water systems (two ground water systems and one surface water system), serving a total of 28,146 people, had at least 1 detection greater than the potential MCLG of 10 |ig/L. Four water systems (two ground water systems and two surface water systems), serving a total of 42,662 people, had at least 1 detection greater than the potential MCLG of 9 |ig/L. These four water systems were located in Florida, New Mexico and New York. SYR3 Occurrence Support Document A-16 December 2016 ------- B Background Information and Detailed Stage 2 Analysis Occurrence Measures for 17 Select Regulated Chemical Contaminants SYR3 Occurrence Support Document B-l December 2016 ------- B.l Chlordane This chapter on chlordane includes background information such as the regulatory history and a summary of monitoring requirements, as well as occurrence and exposure estimates in drinking water. All drinking water occurrence estimates are based on data from the National Compliance Monitoring Information Collection Request (ICR) Dataset for the Third Six-Year Review (the "SYR3 ICR Dataset"). B.l.l Background The United States Environmental Protection Agency (EPA) published the current National Primary Drinking Water Regulations (NPDWR) for chlordane on January 30, 1991 (56 FR 3526; USEPA, 1991a). The NPDWR established a maximum contaminant level goal (MCLG) of zero based on a cancer classification of B2, probable human carcinogen. The NPDWR also established a maximum contaminant level (MCL) of 2 |ig/L based on analytical feasibility. Chlordane is regulated as a synthetic organic chemical (SOC) in drinking water. All non- purchased community water systems (CWSs) and non-transient non-community water systems (NTNCWSs) are required to sample for SOCs. Waivers are available to all systems upon a favorable vulnerability assessment and/or prior analytical results. The maximum waiver period for SOCs is three years, but this waiver can be renewed indefinitely, if it is reconfirmed that the source is not vulnerable. All CWSs and NTNCWSs without an SOC waiver must collect four consecutive quarterly samples during the initial three-year compliance period.5 If all 4 samples are non-detections, then a system serving less than 3,300 people may reduce its collection frequency to 1 sample during each consecutive compliance period; a system serving more than 3,300 people may reduce its collection frequency to 2 quarterly samples within a 12-month period during each repeat compliance period. If a chemical is detected, the system must monitor quarterly until results are reliably and consistently below the MCL (minimum of two quarterly samples for ground water systems and four quarterly samples for surface water systems). If all quarterly samples are below the MCL, the system may return to annual sampling. If a chemical is detected at a level greater than the MCL, the system (whether ground water or surface water) must take quarterly samples until four consecutive quarters are below the MCL. If all quarterly samples are below the MCL, the system may return to annual sampling. B.1.2 Occurrence in Drinking Water The analysis of chlordane occurrence presented in the following section is based on state compliance monitoring data from the SYR3 ICR Dataset. These data consist of 128,870 analytical results from 35,685 public water systems (PWSs) during the period from 2006 to 5 All new systems or systems using a new water source that began operation after January 22, 2004 must demonstrate compliance with the MCL within a period of time specified by the State. The system must also comply with the initial sampling frequencies specified by the State to ensure that a system can demonstrate compliance with the MCL. SYR3 Occurrence Support Document B-2 December 2016 ------- 2011. The number of sample results and systems vary by state, although the state datasets have been reviewed and checked to ensure adequacy of coverage and completeness. EPA used a two-stage analytical approach to estimate the national contaminant occurrence using the SYR3 ICR Dataset. In the "Stage 1 analysis," the occurrence data were analyzed to generate simple non-parametric estimates and descriptive statistics of national contaminant occurrence in public water systems. Simple counts were made of the number and percentage of systems and population served by systems with at least one compliance monitoring sample result greater than a specified concentration threshold. The Stage 1 analysis provides occurrence assessments that are more conservative and may be more reflective of potential acute exposure than the assessments from the Stage 2 analyses. Details on the Stage 1 analysis are presented in Section 6. Based on the evaluation of the health effects and analytical methods as part of the Six-Year Review protocol, EPA selected a set of contaminants, including chlordane, for which Stage 2 analyses were warranted. The Stage 2 analysis estimates national contaminant occurrence by generating estimated long-term mean concentrations of contaminants for each system. This provides occurrence analyses that are less conservative than the Stage 1 analysis, since the Stage 2 analysis is based on estimated mean concentrations rather than on a single maximum concentration. Also, because the Stage 2 analyses generate long-term (multi-year) mean concentration estimates for contaminant occurrence at systems, the analyses can support assessments of population served by systems with detections or potential exposure assessments that may be more reflective of potential chronic exposure than the assessments from the Stage 1 analyses. For the Stage 2 analyses, system arithmetic means were calculated using all sample detection records and all non-detection records. Two different substitution values -zero and V2 the minimum reporting level (MRL) value- were used to replace each non-detection record. (The national modal MRL for chlordane in the dataset is 0.2 |ig/L.) Two arithmetic mean chlordane concentrations were calculated at each system using the zero and V2 MRL substitution values. These mean calculations were performed for all systems with chlordane data in the SYR3 ICR dataset. Then, the percentages of all systems with a mean concentration greater than each threshold were calculated. For chlordane, EPA generated Stage 2 occurrence estimates relative to the MCL and the estimated quantitation level (EQL). Stage 2 Occurrence Estimates Stage 2 analyses for chlordane are summarized in this section. Occurrence estimates were generated relative to the following thresholds: 2 |ig/L (the MCL) and 1 |ig/L (EQL). Note that the EQL is equivalent to V2 the MCL. The EQL represents the potential quantitation capabilities below a practical quantitation level (PQL).6For more information on the new potential thresholds of concern used in the SYR3 Stage 2 analyses, refer to USEPA (2016d) and (2016e). 6 When it is not possible to measure concentrations at the MCLG level, EPA often bases the MCL on an analytical feasibility level, known as a PQL. However, analytical feasibility can improve over time. As part of the Six-Year Review process, EPA evaluates whether new information regarding quantitation shows that PQLs may be reduced. The EQL represents quantitation capabilities below a PQL (USEPA, 2016d). The EQL is the threshold used to evaluate occurrence and exposure for the Stage 2 analyses. SYR3 Occurrence Support Document B-3 December 2016 ------- Exhibit B-l presents the system-level Stage 2 analysis of estimated mean concentrations for chlordane occurrence in drinking water. Exhibit B-2 presents similar information based on population served by the systems. Based on the Stage 2 analyses, 1 system (0.003 percent of all systems), serving 993 people, had an estimated system mean greater than the MCL concentration of 2 |ig/L. Three water systems (approximately 0.008 percent of all systems) had an estimated mean greater than the EQL concentration of 1 |ig/L. These 3 systems serve approximately 1,353 people. Exhibit B-1: Chlordane Stage 2 Analysis - Summary of Systems with a Mean Threshold Exceedance Source Water Type (Number of Systems) Threshold Number of Systems with Mean Concentrations That Are Greater Than the Threshold Percent of Systems with Mean Concentrations That Are Greater Than the Threshold Non-detect values = 1/2 MRL Non-detect values = 0 Non-detect values = 1/2 MRL Non-detect values = 0 Ground Water (32,472) > 2 |jg/L 1 1 0.003% 0.003% > 1 |jg/L1 3 3 0.009% 0.009% Surface Water (3,213) > 2 |jg/L 0 0 0.000% 0.000% > 1 |jg/L1 0 0 0.000% 0.000% Combined Ground & Surface Water (35,685) > 2 |jg/L 1 1 0.003% 0.003% > 1 |jg/L1 3 3 0.008% 0.008% 1 The new potential threshold of concern for this contaminant is based on the EQL. The EQL represents the potential quantitation capabilities below a PQL (USEPA, 2016d). Exhibit B-2: Chlordane Stage 2 Analysis - Summary of Population Served by Systems with a Mean Threshold Exceedance Source Water Type (Population Served by Systems) Threshold Population Served by Systems with Mean Concentrations That Are Greater Than the Threshold Percent of Population Served by Systems with Mean Concentrations That Are Greater Than the Threshold Non-detect values = 1/2 MRL Non-detect values = 0 Non-detect values = 1/2 MRL Non-detect values = 0 Ground Water > 2 |jg/L 993 993 0.001% 0.001% (89,347,451) > 1 |jg/L1 1,353 1,353 0.002% 0.002% Surface Water > 2 |jg/L 0 0 0.000% 0.000% (128,289,918) > 1 |jg/L1 0 0 0.000% 0.000% SYR3 Occurrence Support Document B-4 December 2016 ------- Source Water Type (Population Served by Systems) Threshold Population Served by Systems with Mean Concentrations That Are Greater Than the Threshold Percent of Population Served by Systems with Mean Concentrations That Are Greater Than the Threshold Non-detect values = 1/2 MRL Non-detect values = 0 Non-detect values = 1/2 MRL Non-detect values = 0 Combined Ground & Surface Water (217,637,369) > 2 |jg/L 993 993 0.000% 0.000% > 1 |jg/L1 1,353 1,353 0.001% 0.001% 1 The new potential threshold of concern for this contaminant is based on the EQL. The EQL represents the potential quantitation capabilities below a PQL (USEPA, 2016d). Data for chlordane were available from 49 states/entities. Four states did not submit data for use in the Six-Year Review (Colorado, Delaware, Georgia and Mississippi). Although the States of Colorado and Mississippi did not provide data for any contaminants for the SYR3 ICR Dataset, these states are included in the table below because a handful of tribal water systems located within these two states did submit chlordane data. New Jersey did submit Six-Year data for most contaminants. There is a statewide waiver for chlordane in New Jersey, however, so no chlordane data were available from that state. Exhibit B-3 presents the total number of systems in each state that submitted data for chlordane. In addition, the geographic distribution of chlordane occurrence in drinking water is illustrated by showing states with systems with a mean concentration greater than the EQL and MCL concentrations. (Note: Only the V2 MRL substitution results are presented in this exhibit.) Detection rates were low; only one system in New Mexico had an estimated mean concentration greater than the MCL. Three systems in three states (North Carolina, New Hampshire and New Mexico) had estimated mean concentrations greater than the EQL of 1 |ig/L. Exhibit B-3: Chlordane Stage 2 Analysis - Summary of Systems with a Mean Threshold Exceedance by State12 State Total Number of Systems Systems with a Mean Concentration > 1 mq/l3 Systems with a Mean Concentration > 2 jjg/L Number Percent Number Percent AK 12 AL 383 AR 459 AS 11 AZ 873 CA 1,243 CO 1 CT 1,136 SYR3 Occurrence Support Document B-5 December 2016 ------- State Total Number of Systems Systems with a Mean Concentration > 1 mq/l3 Systems with a Mean Concentration > 2 jjg/L Number Percent Number Percent DC 1 FL 2,087 HI 111 IA 3 ID 385 IL 1,467 IN 1,212 KS 87 KY 225 LA 946 MA 565 MD 881 ME 160 Ml 13 MN 920 MO 1,332 MS 5 MT 857 NC 2,348 1 0.04% 0 0.00% ND 157 NE 696 NH 1,146 1 0.09% 0 0.00% NJ 0 NM 718 1 0.14% 1 0.14% NV 309 NY 2,119 OH 31 OK 36 OR 1,118 PA 1,267 SYR3 Occurrence Support Document B-6 December 2016 ------- State Total Number of Systems Systems with a Mean Concentration > 1 mq/l3 Systems with a Mean Concentration > 2 jjg/L Number Percent Number Percent Rl 73 SC 497 SD 269 TN 6 TX 3,925 UT 428 VA 254 VT 380 WA 1,998 Wl 1,914 WV 303 WY 318 Total 35,685 3 0.01% 1 0.003% 1 Results are based on setting all non-detection results equal to % the MRL values in the SYR3 ICR dataset. 2 Blank cells within the table indicate that there were no systems with a mean concentration that exceeded either threshold. 3 The new potential threshold of concern for this contaminant is based on the EQL. The EQL represents the potential quantitation capabilities below a PQL (USEPA, 2016d). Exhibit B-4 presents the population served by systems with a mean concentration greater than the MCL concentration by state. The total population served by systems in each state that submitted data for chlordane is presented, as well. New Mexico was the only state with an estimated system mean concentration greater than the MCL. This system served a total population of 993 people. Three systems in 3 states, serving 1,353 people, had estimated mean concentrations greater than EQL (1 |ig/L). Exhibit B-4: Chlordane Stage 2 Analysis - Summary of Population Served by Systems with a Mean Threshold Exceedance by State12 State Total Population Population Served by Systems with a Mean Concentration> 1 H9"-3 Population Served by Systems with a Mean Concentration> 2 jjg/L Population Percent Population Percent AK 39,530 AL 5,333,035 AR 2,635,934 AS 62,196 SYR3 Occurrence Support Document B-7 December 2016 ------- State Total Population Population Served by Systems with a Mean Concentration> 1 H9"-3 Population Served by Systems with a Mean Concentration> 2 jjg/L Population Percent Population Percent AZ 6,487,524 CA 35,723,529 CO 2,020 CT 2,883,135 DC 761,124 FL 18,943,101 HI 1,479,317 IA 166,302 ID 976,042 IL 10,997,826 IN 4,969,942 KS 1,817,722 KY 4,225,473 LA 4,709,163 MA 9,163,377 MD 4,939,436 ME 356,698 Ml 34,902 MN 3,752,545 MO 5,233,314 MS 6,176 MT 845,294 NC 7,832,371 310 0.004% 0 0.00% ND 592,232 NE 1,659,899 NH 949,308 50 0.01% 0 0.00% NJ 0 NM 1,940,795 993 0.05% 993 0.05% NV 2,682,358 NY 10,481,646 SYR3 Occurrence Support Document B-8 December 2016 ------- State Total Population Population Served by Systems with a Mean Concentration> 1 H9"-3 Population Served by Systems with a Mean Concentration> 2 jjg/L Population Percent Population Percent OH 755,924 OK 130,809 OR 3,432,307 PA 10,887,488 Rl 989,530 SC 3,623,380 SD 708,340 TN 1,168,508 TX 23,277,937 UT 2,752,741 VA 5,685,070 VT 386,948 WA 4,947,604 Wl 4,236,887 WV 1,500,920 WY 469,710 Total 217,637,369 1,353 0.001% 993 0.0005% 1 Results are based on setting all non-detection results equal to % the MRL values in the SYR3 ICR dataset. 2 Blank cells within the table indicate that there were no systems with a mean concentration that exceeded either threshold. 3 The new potential threshold of concern for this contaminant is based on the EQL. The EQL represents the potential quantitation capabilities below a PQL (USEPA, 2016d). B.1.3 Summary of Data A total of 128,870 analytical results from 35,685 PWSs in 49 states/entities were available in the SYR3 ICR Dataset for chlordane. The Stage 2 analysis of occurrence in drinking water indicated that 1 ground water system in New Mexico, serving 993 people, had an estimated system mean concentration of chlordane greater than the MCL concentration of 2 |ig/L. Three ground water systems, serving 1,353 people, had an estimated mean concentration greater than the EQL of 1 jig/L. SYR3 Occurrence Support Document B-9 December 2016 ------- B.2 cis-l,2-Dichloroethylene This chapter on cis-l,2-dichloroethylene includes background information such as the regulatory history and a summary of monitoring requirements, as well as occurrence and exposure estimates in drinking water. All drinking water occurrence estimates are based on data from the National Compliance Monitoring Information Collection Request (ICR) Dataset for the Third Six-Year Review (the "SYR3 ICR Dataset"). B.2.1 Background The United States Environmental Protection Agency (EPA) published the current National Primary Drinking Water Regulations (NPDWR) for cis-l,2-dichloroethylene on January 30, 1991 (56 FR 3526; USEPA, 1991a). The NPDWR established a maximum contaminant level goal (MCLG) and maximum contaminant level (MCL) of 70 |ig/L. The Agency developed the MCLG based on a reference dose (RfD) of 10 |ig/kg-day (0.01 mg/kg-day) and a cancer classification of D, not classifiable as to human carcinogenicity. cis-l,2-Dichloroethylene is regulated as a volatile organic compound (VOC) in drinking water. All non-purchased community water systems (CWSs) and non-transient non-community water systems (NTNCWSs) are required to sample for VOCs. The maximum waiver period for VOCs is two compliance periods for ground water systems and one compliance period for surface water systems. All CWSs and NTNCWSs must collect four consecutive quarterly samples during the initial three-year compliance period.7 If all four samples are non-detections, then the system may reduce to annual sampling. After three annual samples without a detection, and upon conducting a vulnerability assessment, a system may be granted a waiver. During the waiver period, the ground water system must sample at least once, while surface water system must sample at the frequency specified by the state. If a compound is detected, the system must take one sample per quarter until results are below the MCL (minimum of two quarterly samples for ground water systems and four quarterly samples for surface water systems). If all quarterly samples are reliably and consistently below the MCL, the system may return to annual sampling. If a compound is detected at a level greater than the MCL, the system (whether ground water or surface water) must take four consecutive quarterly samples until all are below the MCL. If all quarterly samples are below the MCL, the system may return to annual sampling. If a compound is detected, the system must also monitor in a similar fashion for vinyl chloride. B.2.2 Occurrence in Drinking Water The analysis of cis-l,2-dichloroethylene occurrence presented in the following section is based on state compliance monitoring data from the SYR3 ICR Dataset. These data consist of 376,300 7 All new systems or systems using a new water source that began operation after January 22, 2004 must demonstrate compliance with the MCL within a period of time specified by the State. The system must also comply with the initial sampling frequencies specified by the State to ensure that a system can demonstrate compliance with the MCL. SYR3 Occurrence Support Document B-10 December 2016 ------- analytical results from 55,734 public water systems (PWSs) during the period from 2006 to 2011. The number of sample results and systems vary by state, although the state datasets have been reviewed and checked to ensure adequacy of coverage and completeness. EPA used a two-stage analytical approach to estimate the national contaminant occurrence using the SYR3 ICR Dataset. In the "Stage 1 analysis," the occurrence data were analyzed to generate simple non-parametric estimates and descriptive statistics of national contaminant occurrence in public water systems. Simple counts were made of the number and percentage of systems and population served by systems with at least one compliance monitoring sample result greater than a specified concentration threshold. The Stage 1 analysis provides occurrence assessments that are more conservative and may be more reflective of potential acute exposure than the assessments from the Stage 2 analyses. Details on the Stage 1 analysis are presented in Section 6. Based on the evaluation of the health effects and analytical methods as part of the Six-Year Review protocol, EPA selected a set of contaminants, including cis-l,2-dichloroethylene, for which Stage 2 analyses were warranted. The Stage 2 analysis estimates national contaminant occurrence by generating estimated long-term mean concentrations of contaminants for each system. This provides occurrence analyses that are less conservative than the Stage 1 analysis, since the Stage 2 analysis is based on estimated mean concentrations rather than on a single maximum concentration. Also, because the Stage 2 analyses generate long-term (multi-year) mean concentration estimates for contaminant occurrence at systems, the analyses can support assessments of population served by systems with detections or potential exposure assessments that may be more reflective of potential chronic exposure than the assessments from the Stage 1 analyses. For the Stage 2 analyses, system arithmetic means were calculated using all sample detection records and all non-detection records. Three different substitution values -zero, V2 the minimum reporting level (MRL) value and the full MRL value- were used to replace each non-detection record. (The national modal MRL for cis-l,2-dichloroethylene in the dataset is 0.5 |ig/L.) Three arithmetic mean cis-l,2-dichloroethylene concentrations were calculated at each system using the zero, V2 MRL and full MRL substitution values. These mean calculations were performed for all systems with cis-l,2-dichloroethylene data in the SYR3 ICR dataset. Then, the percentages of all systems with a mean concentration greater than each threshold were calculated. For cis-1,2- dichloroethylene, since there were no analytical method limitations at the potential MCLG, EPA generated Stage 2 occurrence estimates relative to the MCL and the potential MCLG. Stage 2 Occurrence Estimates Stage 2 analyses for cis-l,2-dichloroethylene are summarized in this section. Occurrence estimates were generated relative to the following thresholds: 70 |ig/L (the MCL) and 10 |ig/L (the potential MCLG). The potential MCLG is due to changes in the RfD based on new health effects information. Since the practical quantitation level (PQL) for cis-l,2-dichloroethylene is less than the possible MCLG, EPA designated the possible MCLG as the threshold for the occurrence analysis. For more information on the new potential thresholds of concern used in the SYR3 Stage 2 analyses, refer to USEPA (2016d) and (2016e). Exhibit B-5 presents the system-level Stage 2 analysis of estimated mean concentrations for cis- 1,2-dichloroethylene occurrence in drinking water. Exhibit B-6 presents similar information based on population served by the systems. Based on the Stage 2 analyses, no systems had an SYR3 Occurrence Support Document B-ll December 2016 ------- estimated system mean greater than the MCL concentration of 70 |ig/L. Four systems, serving 5,569 people, had an estimated system mean greater than the potential MCLG concentration of 10 |ig/L. Exhibit B-5: cis-1,2-Dichloroethylene Stage 2 Analysis - Summary of Systems with a Mean Threshold Exceedance Source Water Type (Number of Systems) Threshold Number of Systems with Mean Concentrations That Are Greater Than the Threshold Percent of Systems with Mean Concentrations That Are Greater Than the Threshold Non-detect values = MRL Non-detect values = 1/2 MRL Non-detect values = 0 Non-detect values = MRL Non-detect values = 1/2 MRL Non-detect values = 0 Ground Water (51,302) > 70 |jg/L 0 0 0 0.000% 0.000% 0.000% > 10 |jg/L1 4 4 4 0.008% 0.008% 0.008% Surface Water (4,432) > 70 |jg/L 0 0 0 0.000% 0.000% 0.000% > 10 |jg/L1 0 0 0 0.000% 0.000% 0.000% Combined Ground & Surface Water (55,734) > 70 |jg/L 0 0 0 0.000% 0.000% 0.000% > 10 |jg/L1 4 4 4 0.007% 0.007% 0.007% 1 The new potential threshold of concern for this contaminant is due to changes in the RfD based on new health effects information. Exhibit B-6: cis-1,2-Dichloroethylene Stage 2 Analysis - Summary of Population Served by Systems with a Mean Threshold Exceedance Source Water Type (Population Served by Systems) Threshold Population Served by Systems with Mean Concentrations That Are Greater Than the Threshold Percent of Population Served by Systems with Mean Concentrations That Are Greater Than the Threshold Non-detect values = MRL Non-detect values = 1/2 MRL Non-detect values = 0 Non-detect values = MRL Non-detect values = 1/2 MRL Non-detect values = 0 Ground Water (110,779,859) > 70 |jg/L 0 0 0 0.000% 0.000% 0.000% > 10 |jg/L1 5,569 5,569 5,569 0.005% 0.005% 0.005% Surface Water (152,565,123) > 70 |jg/L 0 0 0 0.000% 0.000% 0.000% > 10 |jg/L1 0 0 0 0.000% 0.000% 0.000% Combined Ground & Surface Water > 70 |jg/L 0 0 0 0.000% 0.000% 0.000% SYR3 Occurrence Support Document B-12 December 2016 ------- Source Water Type (Population Served by Systems) Threshold Population Served by Systems with Mean Concentrations That Are Greater Than the Threshold Percent of Population Served by Systems with Mean Concentrations That Are Greater Than the Threshold Non-detect Non-detect Non-detect Non-detect Non-detect Non-detect values values values values values values = MRL = 1/2 MRL = 0 = MRL = 1/2 MRL = 0 (263,344,982) > 10 |jg/L1 5,569 5,569 5,569 0.002% 0.002% 0.002% 1 The new potential threshold of concern for this contaminant is due to changes in the RfD based on new health effects information. Data for cis-l,2-dichloroethylene were available from 50 states/entities. Four states did not submit data for use in the Six-Year Review (Colorado, Delaware, Georgia and Mississippi). Although the States of Colorado and Mississippi did not provide data for any contaminants for the SYR3 ICR Dataset, these states are included in the count of 50 states because a handful of tribal water systems located within these 2 states did submit cis-l,2-dichloroethylene data. Exhibit B-7 presents the total number of systems in each state that submitted data for cis-1,2- dichloroethylene. In addition, the geographic distribution of cis-l,2-dichloroethylene occurrence in drinking water is illustrated by showing states with systems with a mean concentration greater than the potential MCLG and MCL concentrations. (Note: Only the V2 MRL substitution results are presented in this exhibit.) No systems had an estimated mean concentration greater than the MCL. Four systems in three states (Illinois, North Carolina and Virginia) had estimated mean concentrations greater than the potential MCLG of 10 |ig/L. Exhibit B-7: cis-1,2-Dichloroethylene Stage 2 Analysis - Summary of Systems with a Mean Threshold Exceedance by State12 State Total Number of Systems Systems with a Mean Concentration >10 H9"-3 Systems with a Mean Concentration > 70 jjg/L Number Percent Number Percent AK 595 AL 384 AR 461 AS 11 AZ 1,109 CA 3,811 CO 1 CT 1,202 DC 1 FL 2,633 HI 110 IA 1,045 SYR3 Occurrence Support Document B-13 December 2016 ------- State Total Number of Systems Systems with a Mean Concentration >10 H9"-3 Systems with a Mean Concentration > 70 jjg/L Number Percent Number Percent ID 839 IL 1,493 2 0.13% 0 0.00% IN 1,196 KS 602 KY 227 LA 1,102 MA 721 MD 1,054 ME 784 Ml 2,419 MN 1,462 MO 1,445 MS 5 MT 897 NC 2,356 1 0.04% 0 0.00% ND 160 NE 705 NH 1,185 NJ 1,434 NM 744 NV 350 NY 2,498 OH 1,922 OK 685 OR 1,132 PA 3,166 Rl 152 SC 494 SD 313 TN 366 TX 4,532 SYR3 Occurrence Support Document B-14 December 2016 ------- State Total Number of Systems Systems with a Mean Concentration >10 H9"-3 Systems with a Mean Concentration > 70 jjg/L Number Percent Number Percent UT 471 VA 1,630 1 0.06% 0 0.00% VT 634 WA 2,468 Wl 2,026 WV 385 WY 317 Total 55,734 4 0.01% 0 0.00% 1 Results are based on setting all non-detection results equal to % the MRL values in the SYR3 ICR dataset. 2 Blank cells within the table indicate that there were no systems with a mean concentration that exceeded either threshold. 3 The new potential threshold of concern for this contaminant is due to changes in the RfD based on new health effects information. Exhibit B-8 presents the population served by systems with a mean concentration greater than the MCL concentration by state. The total population served by systems in each state that submitted data for cis-l,2-dichloroethylene is presented, as well. As described above, no systems had an estimated mean concentration greater than the MCL. The 4 systems in 3 states (Illinois, North Carolina and Virginia with an estimated mean concentration greater than the potential MCLG (10 |ig/L) serve 5,569 people. Exhibit B-8: cis-1,2-Dichloroethylene Stage 2 Analysis - Summary of Population Served by Systems with a Mean Threshold Exceedance by State12 State Total Population Population Served by Systems with a Mean Concentration > 10 mq/l3 Population Served by Systems with a Mean Concentration > 70 jjg/L Population Percent Population Percent AK 719,561 AL 5,334,584 AR 2,637,712 AS 62,196 AZ 6,669,227 CA 40,601,783 CO 2,020 CT 2,937,643 DC 761,124 FL 19,280,091 SYR3 Occurrence Support Document B-15 December 2016 ------- State Total Population Population Served by Systems with a Mean Concentration > 10 mq/l3 Population Served by Systems with a Mean Concentration > 70 jjg/L Population Percent Population Percent HI 1,402,969 IA 2,743,404 ID 1,219,635 IL 11,019,196 5,490 0.05% 0 0.00% IN 4,940,108 KS 2,605,030 KY 4,225,914 LA 4,966,653 MA 9,329,953 MD 5,120,409 ME 757,984 Ml 3,470,708 MN 4,373,668 MO 5,293,851 MS 6,176 MT 856,529 NC 7,827,828 54 0.00% 0 0.00% ND 592,539 NE 1,664,802 NH 961,134 NJ 9,273,130 NM 1,962,298 NV 2,697,555 NY 10,637,039 OH 10,209,121 OK 3,588,559 OR 3,434,191 PA 11,234,684 Rl 1,040,737 SC 3,637,408 SD 757,925 SYR3 Occurrence Support Document B-16 December 2016 ------- State Total Population Population Served by Systems with a Mean Concentration > 10 mq/l3 Population Served by Systems with a Mean Concentration > 70 jjg/L Population Percent Population Percent TN 6,578,052 TX 23,863,702 UT 2,802,068 VA 6,908,704 25 0.00% 0 0.00% VT 486,604 WA 5,535,827 Wl 4,273,462 WV 1,570,171 WY 469,314 Total 263,344,982 5,569 0.00% 0 0.00% 1 Results are based on setting all non-detection results equal to % the MRL values in the SYR3 ICR dataset. 2 Blank cells within the table indicate that there were no systems with a mean concentration that exceeded either threshold. 3 The new potential threshold of concern for this contaminant is due to changes in the RfD based on new health effects information. B.2.3 Summary of Data A total of 376,300 analytical results from 55,734 PWSs in 50 states/entities were available in the SYR3 ICR Dataset for cis-l,2-dichloroethylene. The Stage 2 analysis of occurrence in drinking water indicated that zero systems had an estimated system mean concentration of cis-1,2- dichloroethylene greater than the MCL concentration of 70 |ig/L. Four ground water systems, serving 5,569 people, had an estimated mean concentration greater than the potential MCLG (10 Hg/L). SYR3 Occurrence Support Document B-17 December 2016 ------- B.3 Cyanide This chapter on cyanide includes background information such as the regulatory history and a summary of monitoring requirements, as well as occurrence and exposure estimates in drinking water. All drinking water occurrence estimates are based on data from the National Compliance Monitoring Information Collection Request (ICR) Dataset for the Third Six-Year Review (the "SYR3 ICR Dataset"). B.3.1 Background The United States Environmental Protection Agency (EPA) published the current National Primary Drinking Water Regulations (NPDWR) for cyanide on July 17, 1992 (57 FR 31776; USEPA, 1992). The NPDWR established a maximum contaminant level goal (MCLG) and maximum contaminant level (MCL) of 200 |ig/L. The MCLG was developed based on a reference dose (RfD) of 20 |ig/kg-day and a cancer classification of D, not classifiable as to human carcinogenicity. Cyanide is regulated as an inorganic chemical (IOC) in drinking water. All community water systems (CWSs) and non-transient non-community water systems (NTNCWSs) are required to sample for the IOCs. Cyanide waivers may be granted if a state determines that a system is not vulnerable to cyanide contamination due to a lack of industrial cyanide sources. The maximum waiver period for cyanide is one compliance cycle. During this cycle, the system must sample at least once. (Statewide waivers for cyanide may be granted if all systems in the state are required to chlorinate.) Ground water systems must sample once during the initial three-year compliance period. Surface water systems must sample annually during the initial three-year compliance period. If all analytical results are less than the MCL, and upon considering other factors which may affect contaminant concentration, a ground water and surface water system may be granted waiver. If the results are greater than the MCL, the public water system (PWS) must take one sample per quarter until results are below the MCL (minimum of two quarterly samples for ground water systems and four quarterly samples for surface water systems).8 If all quarterly samples are reliably and consistently below the MCL, the system may continue at initial monitoring indefinitely until the state or EPA establishes an alternate schedule. B.3.2 Occurrence in Drinking Water The analysis of cyanide occurrence presented in the following section is based on state compliance monitoring data from the SYR3 ICR Dataset. These data consist of 119,659 analytical results from 36,907 PWSs during the period from 2006 to 2011. The number of sample results and systems vary by state, although the state datasets have been reviewed and checked to ensure adequacy of coverage and completeness. 8 All new systems or systems using a new water source that began operation after January 22, 2004 must demonstrate compliance with the MCL within a period of time specified by the State. The system must also comply with the initial sampling frequencies specified by the State to ensure that a system can demonstrate compliance with the MCL. SYR3 Occurrence Support Document B-18 December 2016 ------- EPA used a two-stage analytical approach to estimate the national contaminant occurrence using the SYR3 ICR Dataset. In the "Stage 1 analysis," the occurrence data were analyzed to generate simple non-parametric estimates and descriptive statistics of national contaminant occurrence in public water systems. Simple counts were made of the number and percentage of systems and population served by systems with at least one compliance monitoring sample result greater than a specified concentration threshold. The Stage 1 analysis provides occurrence assessments that are more conservative and may be more reflective of potential acute exposure than the assessments from the Stage 2 analyses. Details on the Stage 1 analysis are presented in Section 6. Based on the evaluation of the health effects and analytical methods as part of the Six-Year Review protocol, EPA selected a set of contaminants, including cyanide, for which Stage 2 analyses were warranted. The Stage 2 analysis estimates national contaminant occurrence by generating estimated long-term mean concentrations of contaminants for each system. This provides occurrence analyses that are less conservative than the Stage 1 analysis, since the Stage 2 analysis is based on estimated mean concentrations rather than on a single maximum concentration. Also, because the Stage 2 analyses generate long-term (multi-year) mean concentration estimates for contaminant occurrence at systems, the analyses can support assessments of population served by systems with detections or potential exposure assessments that may be more reflective of potential chronic exposure than the assessments from the Stage 1 analyses. For the Stage 2 analyses, system arithmetic means were calculated using all sample detection records and all non-detection records. Three different substitution values -zero, V2 the minimum reporting level (MRL) value and the full MRL value- were used to replace each non-detection record. (The national modal MRL for cyanide in the dataset is 10 |ig/L.) Three arithmetic mean cyanide concentrations were calculated at each system using the zero, V2 MRL and full MRL substitution values. These mean calculations were performed for all systems with cyanide data in the SYR3 ICR dataset. Then, the percentages of all systems with a mean concentration greater than each threshold were calculated. For cyanide, EPA generated Stage 2 occurrence estimates relative to the MCL and the estimated quantitation level (EQL). Stage 2 Occurrence Estimates Stage 2 analyses for cyanide are summarized in this section. Occurrence estimates were generated relative to the following thresholds: 200 |ig/L (the MCL) and 50 |ig/L (the EQL). The EQL represents the potential quantitation capabilities below a practical quantitation level (PQL).9 For more information on the new potential thresholds of concern used in the SYR3 Stage 2 analyses, refer to USEPA (2016d) and (2016e). Exhibit B-9 presents the system-level Stage 2 analysis of estimated mean concentrations for cyanide occurrence in drinking water. Exhibit B-10 presents similar information based on population served by the systems. Based on the Stage 2 analyses using the V2 MRL substitution 9 When it is not possible to measure concentrations at the MCLG level, EPA often bases the MCL on an analytical feasibility level, known as a PQL. However, analytical feasibility can improve over time. As part of the Six-Year Review process, EPA evaluates whether new information regarding quantitation shows that PQLs may be reduced. The EQL represents quantitation capabilities below a PQL (USEPA, 2016d). The EQL is the threshold used to evaluate occurrence and exposure for the Stage 2 analyses. SYR3 Occurrence Support Document B-19 December 2016 ------- for non-detections, 8 systems (0.022 percent of all systems), serving 80,826 people, had an estimated system mean greater than the MCL concentration of 200 |ig/L. A total of 98 systems (0.266 percent of all systems), serving 574,038 people, had an estimated system mean greater than the EQL concentration of 50 |ig/L. Exhibit B-9: Cyanide Stage 2 Analysis - Summary of Systems with a Mean Threshold Exceedance Source Water Type (Number of Systems) Threshold Number of Systems with Mean Concentrations That Are Greater Than the Threshold Percent of Systems with Mean Concentrations That Are Greater Than the Threshold Non-detect values = MRL Non-detect values = 1/2 MRL Non-detect values = 0 Non-detect values = MRL Non-detect values = 1/2 MRL Non- detect values = 0 Ground Water (33,842) > 200 |jg/L 7 7 6 0.021% 0.021% 0.018% > 50 |jg/L1 93 91 83 0.275% 0.269% 0.245% Surface Water (3,065) > 200 |jg/L 1 1 1 0.033% 0.033% 0.033% > 50 |jg/L1 7 7 7 0.228% 0.228% 0.228% Combined Ground & Surface Water (36,907) > 200 |jg/L 8 8 7 0.022% 0.022% 0.019% > 50 |jg/L1 100 98 90 0.271% 0.266% 0.244% 1 The new potential threshold of concern for this contaminant is based on the EQL. The EQL represents the potential quantitation capabilities below a PQL (USEPA, 2016d). Exhibit B-10: Cyanide Stage 2 Analysis - Summary of Population Served by Systems with a Mean Threshold Exceedance Source Water Type (Population Served by Systems) Threshold Population Served by Systems with Mean Concentrations That Are Greater Than the Threshold Percent of Population Served by Systems with Mean Concentrations That Are Greater Than the Threshold Non-detect values = MRL Non-detect values = 1/2 MRL Non-detect values = 0 Non-detect values = MRL Non-detect values = 1/2 MRL Non-detect values = 0 Ground Water > 200 |jg/L 2,521 2,521 2,287 0.003% 0.003% 0.003% (87,768,998) > 50 |jg/L1 157,428 157,231 154,877 0.179% 0.179% 0.176% Surface Water (122,658,983) > 200 |jg/L 78,305 78,305 78,305 0.064% 0.064% 0.064% > 50 |jg/L1 416,807 416,807 416,807 0.340% 0.340% 0.340% SYR3 Occurrence Support Document B-20 December 2016 ------- Source Water Type (Population Served by Systems) Threshold Population Served by Systems with Mean Concentrations That Are Greater Than the Threshold Percent of Population Served by Systems with Mean Concentrations That Are Greater Than the Threshold Non-detect values = MRL Non-detect values = 1/2 MRL Non-detect values = 0 Non-detect values = MRL Non-detect values = 1/2 MRL Non-detect values = 0 Combined Ground & Surface Water (210,427,981) > 200 |jg/L 80,826 80,826 80,592 0.038% 0.038% 0.038% > 50 |jg/L1 574,235 574,038 571,684 0.273% 0.273% 0.272% 1 The new potential threshold of concern for this contaminant is based on the EQL. The EQL represents the potential quantitation capabilities below a PQL (USEPA, 2016d). Data for cyanide were available from 49 states/entities. Four states did not submit data for use in the Six-Year Review (Colorado, Delaware, Georgia and Mississippi). Although the States of Colorado and Mississippi did not provide data for any contaminants for the SYR3 ICR Dataset, these states are included in the table below because a handful of tribal water systems located within these two states did submit cyanide data. South Carolina did submit Six-Year data for most contaminants. There is a statewide waiver for cyanide in South Carolina, however, so no cyanide data were available from that state. Exhibit B-l 1 presents the total number of systems in each state that submitted data for cyanide. In addition, the geographic distribution of cyanide occurrence in drinking water is illustrated by showing states with systems with a mean concentration greater than the EQL and MCL concentrations. (Note: Only the V2 MRL substitution results are presented in this exhibit.) The distribution of systems with mean concentrations of cyanide is geographically dispersed. Detection rates were generally low; only four states had an estimated mean concentration greater than the MCL. (Massachusetts, Minnesota, North Carolina and Nebraska each contained a single system with a mean concentration greater than the MCL in each state.) A total of 98 systems in 23 states had estimated mean concentrations greater than the EQL of 50 |ig/L. Exhibit B-11: Cyanide Stage 2 Analysis - Summary of Systems with a Mean Threshold Exceedance by State12 State Total Number of Systems Systems with a Mean Concentration > 50 jjg/L3 Systems with a Mean Concentration > 200 jjg/L Number Percent Number Percent AK 491 AL 385 1 0.26% 0 0.00% AR 460 6 1.30% 0 0.00% AS 11 AZ 1,057 CA 1,781 6 0.34% 0 0.00% CO 1 SYR3 Occurrence Support Document B-21 December 2016 ------- State Total Number of Systems Systems with a Mean Concentration > 50 jjg/L3 Systems with a Mean Concentration > 200 jjg/L Number Percent Number Percent CT 1,173 1 0.09% 0 0.00% DC 1 FL 2,608 4 0.15% 0 0.00% HI 110 IA 10 ID 126 IL 1,358 1 0.07% 0 0.00% IN 1,128 2 0.18% 0 0.00% KS 5 KY 226 LA 1,108 MA 666 2 0.30% 1 0.15% MD 8 ME 742 Ml 1,847 1 0.05% 0 0.00% MN 1,143 27 2.36% 5 0.44% MO 832 MS 5 MT 54 NC 2,182 7 0.32% 1 0.05% ND 23 NE 689 2 0.29% 1 0.15% NH 1,155 NJ 1,401 1 0.07% 0 0.00% NM 742 4 0.54% 0 0.00% NV 294 1 0.34% 0 0.00% NY 2,514 11 0.44% 0 0.00% OH 1,893 1 0.05% 0 0.00% OK 187 OR 856 PA 1,425 SYR3 Occurrence Support Document B-22 December 2016 ------- State Total Number of Systems Systems with a Mean Concentration > 50 jjg/L3 Systems with a Mean Concentration > 200 jjg/L Number Percent Number Percent Rl 153 SC 0 SD 33 TN 242 1 0.41% 0 0.00% TX 470 13 2.77% 0 0.00% UT 479 VA 1,373 1 0.07% 0 0.00% VT 410 WA 2,198 3 0.14% 0 0.00% Wl 145 1 0.69% 0 0.00% WV 391 1 0.26% 0 0.00% WY 316 Total 36,907 98 0.27% 8 0.02% 1 Results are based on setting all non-detection results equal to % the MRL values in the SYR3 ICR dataset. 2 Blank cells within the table indicate that there were no systems with a mean concentration that exceeded either threshold. 3 The new potential threshold of concern for this contaminant is based on the EQL. The EQL represents the potential quantitation capabilities below a PQL (USEPA, 2016d). Exhibit B-12 presents the population served by systems with a mean concentration greater than the MCL concentration by state. The total population served by systems in each state that submitted data for cyanide is presented, as well. As described above, Massachusetts, Minnesota, North Carolina and Nebraska were the only four states with an estimated mean concentration greater than the MCL. A total of 574,038 people were served by the 98 systems in 23 states that had estimated mean concentrations of cyanide greater than the EQL (50 |ig/L). Exhibit B-12: Cyanide Stage 2 Analysis - Summary of Population Served by Systems with a Mean Threshold Exceedance by State12 State Total Population Population Served by Systems with a Mean Concentration > 50 jjg/L3 Population Served by Systems with a Mean Concentration > 200 \iglL Population Percent Population Percent AK 673,570 AL 5,336,667 1,800 0.03% 0 0.00% AR 2,636,302 6,366 0.24% 0 0.00% AS 62,196 AZ 6,588,496 SYR3 Occurrence Support Document B-23 December 2016 ------- State Total Population Population Served by Systems with a Mean Concentration > 50 jjg/L3 Population Served by Systems with a Mean Concentration > 200 Mg/L Population Percent Population Percent CA 37,838,435 16,380 0.04% 0 0.00% CO 2,020 CT 2,933,337 50 0.00% 0 0.00% DC 761,124 FL 19,124,265 1,295 0.01% 0 0.00% HI 1,471,730 IA 172,941 ID 515,565 IL 10,983,267 80 0.00% 0 0.00% IN 4,555,819 898 0.02% 0 0.00% KS 627,486 KY 4,225,513 LA 4,968,920 MA 9,275,574 78,353 0.84% 78,305 0.84% MD 756 ME 749,486 Ml 982,862 350 0.04% 0 0.00% MN 3,684,296 11,510 0.31% 2,223 0.06% MO 2,941,901 MS 6,176 MT 95,088 NC 7,765,979 7,346 0.09% 64 0.00% ND 66,229 NE 1,659,463 261 0.02% 234 0.01% NH 958,187 NJ 9,150,992 65 0.00% 0 0.00% NM 1,955,107 3,160 0.16% 0 0.00% NV 2,678,248 25 0.00% 0 0.00% NY 10,465,711 107,749 1.03% 0 0.00% OH 10,202,452 50 0.00% 0 0.00% OK 592,288 SYR3 Occurrence Support Document B-24 December 2016 ------- State Total Population Population Served by Systems with a Mean Concentration > 50 jjg/L3 Population Served by Systems with a Mean Concentration > 200 Mg/L Population Percent Population Percent OR 3,141,979 PA 9,952,670 Rl 1,019,797 SC 0 SD 53,644 TN 4,734,392 34,106 0.72% 0 0.00% TX 6,343,868 301,414 4.75% 0 0.00% UT 2,816,488 VA 5,599,685 633 0.01% 0 0.00% VT 385,881 WA 5,389,854 443 0.01% 0 0.00% Wl 2,238,852 1,162 0.05% 0 0.00% WV 1,573,115 542 0.03% 0 0.00% WY 469,308 Total 210,427,981 574,038 0.27% 80,826 0.04% 1 Results are based on setting all non-detection results equal to % the MRL values in the SYR3 ICR dataset. 2 Blank cells within the table indicate that there were no systems with a mean concentration that exceeded either threshold. 3 The new potential threshold of concern for this contaminant is based on the EQL. The EQL represents the potential quantitation capabilities below a PQL (USEPA, 2016d). B.3.3 Summary of Data A total of 119,659 analytical results from 36,907 PWSs in 49 states/entities were available in the SYR3 ICR Dataset for cyanide. The Stage 2 analysis of occurrence in drinking water indicated that 8 (0.02 percent of all) systems serving 80,826 people (0.038 percent of the population) had an estimated system mean concentration of cyanide greater than the MCL concentration of 200 |ig/L. A total of 98 systems, serving 574,038 people, had an estimated mean concentration greater than the EQL (50 |ig/L). The majority of systems with mean concentrations greater than the MCL and EQL were ground water systems. SYR3 Occurrence Support Document B-25 December 2016 ------- B.4 Endothall This chapter on endothall includes background information such as the regulatory history and a summary of monitoring requirements, as well as occurrence and exposure estimates in drinking water. All drinking water occurrence estimates are based on data from the National Compliance Monitoring Information Collection Request (ICR) Dataset for the Third Six-Year Review (the "SYR3 ICR Dataset"). B.4.1 Background The United States Environmental Protection Agency (EPA) published the current National Primary Drinking Water Regulations (NPDWR) for endothall on July 17, 1992 (57 FR 31776; USEPA, 1992). The NPDWR established a maximum contaminant level goal (MCLG) and a maximum contaminant level (MCL) of 100 |ig/L. EPA developed the MCLG based on a reference dose (RfD) of 20 |ig/kg-day (0.02 mg/kg-day) and a cancer classification of D, not classifiable as to human carcinogenicity. Endothall is regulated as a synthetic organic chemical (SOC) in drinking water. All non- purchased community water systems (CWSs) and non-transient non-community water systems (NTNCWSs) are required to sample for SOCs. Waivers are available to all systems upon a favorable vulnerability assessment and/or prior analytical results. The maximum waiver period for SOCs is three years, but this waiver can be renewed indefinitely, if it is reconfirmed that the source is not vulnerable. All CWSs and NTNCWSs without an SOC waiver must collect four consecutive quarterly samples during the initial three-year compliance period.10 If all 4 samples are non-detections, then a system serving less than 3,300 people may reduce its collection frequency to 1 sample during each consecutive compliance period; a system serving more than 3,300 people may reduce its collection frequency to 2 quarterly samples within a 12-month period during each repeat compliance period. If a chemical is detected, the system must monitor quarterly until results are reliably and consistently below the MCL (minimum of two quarterly samples for ground water systems and four quarterly samples for surface water systems). If all quarterly samples are below the MCL, the system may return to annual sampling. If a chemical is detected at a level greater than the MCL, the system (whether ground water or surface water) must take quarterly samples until four consecutive quarters are below the MCL. If all quarterly samples are below the MCL, the system may return to annual sampling. B.4.2 Occurrence in Drinking Water The analysis of endothall occurrence presented in the following section is based on state compliance monitoring data from the SYR3 ICR Dataset. These data consist of 61,972 analytical results from 15,538 public water systems (PWSs) during the period from 2006 to 2011. The 10 All new systems or systems using a new water source that began operation after January 22, 2004 must demonstrate compliance with the MCL within a period of time specified by the State. The system must also comply with the initial sampling frequencies specified by the State to ensure that a system can demonstrate compliance with the MCL. SYR3 Occurrence Support Document B-26 December 2016 ------- number of sample results and systems vary by state, although the state datasets have been reviewed and checked to ensure adequacy of coverage and completeness. EPA used a two-stage analytical approach to estimate the national contaminant occurrence using the SYR3 ICR Dataset. In the "Stage 1 analysis," the occurrence data were analyzed to generate simple non-parametric estimates and descriptive statistics of national contaminant occurrence in public water systems. Simple counts were made of the number and percentage of systems and population served by systems with at least one compliance monitoring sample result greater than a specified concentration threshold. The Stage 1 analysis provides occurrence assessments that are more conservative and may be more reflective of potential acute exposure than the assessments from the Stage 2 analyses. Details on the Stage 1 analysis are presented in Section 6. Based on the evaluation of the health effects and analytical methods as part of the Six-Year Review protocol, EPA selected a set of contaminants, including endothall, for which Stage 2 analyses were warranted. The Stage 2 analysis estimates national contaminant occurrence by generating estimated long-term mean concentrations of contaminants for each system. This provides occurrence analyses that are less conservative than the Stage 1 analysis, since the Stage 2 analysis is based on estimated mean concentrations rather than on a single maximum concentration. Also, because the Stage 2 analyses generate long-term (multi-year) mean concentration estimates for contaminant occurrence at systems, the analyses can support assessments of population served by systems with detections or potential exposure assessments that may be more reflective of potential chronic exposure than the assessments from the Stage 1 analyses. For the Stage 2 analyses, system arithmetic means were calculated using all sample detection records and all non-detection records. Three different substitution values -zero, V2 the minimum reporting level (MRL) value and the full MRL value- were used to replace each non-detection record. (The national modal MRL for endothall in the dataset is 9 |ig/L.) Three arithmetic mean endothall concentrations were calculated at each system using the zero, V2 MRL and full MRL substitution values. These mean calculations were performed for all systems with endothall data in the SYR3 ICR dataset. Then, the percentages of all systems with a mean concentration greater than each threshold were calculated. For endothall, since there were no analytical method limitations at the potential MCLG, EPA generated Stage 2 occurrence estimates relative to the MCL and the potential MCLG. Stage 2 Occurrence Estimates Stage 2 analyses for endothall are summarized in this section. Occurrence estimates were generated relative to the following thresholds: 100 |ig/L (the MCL) and 50 |ig/L (the potential MCLG). The potential MCLG is due to changes in the RfD based on new health effects information. For more information on the new potential thresholds of concern used in the SYR3 Stage 2 analyses, refer to USEPA (2016d) and (2016e). Exhibit B-13 presents the system-level Stage 2 analysis of estimated mean concentrations for endothall occurrence in drinking water. Exhibit B-14 presents similar information based on population served by the systems. Based on the Stage 2 analyses, one water system (approximately 0.006 percent of all systems) had an estimated mean greater than 50 |ig/L and 100 |ig/L. This system serves 993 people. SYR3 Occurrence Support Document B-27 December 2016 ------- Exhibit B-13: Endothall Stage 2 Analysis - Summary of Systems with a Mean Threshold Exceedance Source Water Type (Number of Systems) Threshold Number of Systems with Mean Concentrations That Are Greater Than the Threshold Percent of Systems with Mean Concentrations That Are Greater Than the Threshold Non-detect values = MRL Non-detect values = 1/2 MRL Non- detect values = 0 Non-detect values = MRL Non-detect values = 1/2 MRL Non-detect values = 0 Ground Water (14,033) > 100 |jg/L 1 1 1 0.007% 0.007% 0.007% > 50 |jg/L1 1 1 1 0.007% 0.007% 0.007% Surface Water (1,505) > 100 |jg/L 0 0 0 0.000% 0.000% 0.000% > 50 |jg/L1 0 0 0 0.000% 0.000% 0.000% Combined Ground & Surface Water (15,538) > 100 |jg/L 1 1 1 0.006% 0.006% 0.006% > 50 |jg/L1 1 1 1 0.006% 0.006% 0.006% 1 The new potential threshold of concern for this contaminant is due to changes in the RfD based on new health effects information. Exhibit B-14: Endothall Stage 2 Analysis - Summary of Population Served by Systems with a Mean Threshold Exceedance Source Water Type (Population Served by Systems) Threshold Population Served by Systems with Mean Concentrations That Are Greater Than the Threshold Percent of Population Served by Systems with Mean Concentrations That Are Greater Than the Threshold Non-detect values = MRL Non-detect values = 1/2 MRL Non- detect values = 0 Non-detect values = MRL Non-detect values = 1/2 MRL Non-detect values = 0 Ground Water (61,307,038) > 100 |jg/L 993 993 993 0.002% 0.002% 0.002% > 50 |jg/L1 993 993 993 0.002% 0.002% 0.002% Surface Water (75,494,691) > 100 |jg/L 0 0 0 0.000% 0.000% 0.000% > 50 |jg/L1 0 0 0 0.000% 0.000% 0.000% Combined Ground & Surface Water (136,801,729) > 100 |jg/L 993 993 993 0.001% 0.001% 0.001% > 50 |jg/L1 993 993 993 0.001% 0.001% 0.001% 1 The new potential threshold of concern for this contaminant is due to changes in the RfD based on new health effects information. SYR3 Occurrence Support Document B-28 December 2016 ------- Data for endothall were available from 45 states/entities. Four states did not submit data for use in the Six-Year Review (Colorado, Delaware, Georgia and Mississippi). Although the States of Colorado and Mississippi did not provide data for any contaminants for the SYR3 ICR Dataset, these states are included in the table below because a handful of tribal water systems located within these two states did submit endothall data. New Jersey, Rhode Island, South Carolina, Texas and Vermont did submit Six-Year data for most contaminants. There is a statewide waiver for endothall in those states, however, so no endothall data were available from them. Exhibit B-15 presents the total number of systems in each state that submitted data for endothall. In addition, the geographic distribution of endothall occurrence in drinking water is illustrated by showing states with systems with a mean concentration greater than the potential MCLG and MCL concentrations. (Note: Only the V2 MRL substitution results are presented in this exhibit.) Only one system had an estimated mean concentration greater than the MCL and the potential MCLG. This system is located in New Mexico. Exhibit B-15: Endothall Stage 2 Analysis - Summary of Systems with a Mean Threshold Exceedance by State12 State Total Number of Systems Systems with a Mean Concentration > 50 jjg/L3 Systems with a Mean Concentration >100 jjg/L Number Percent Number Percent AK 9 AL 383 AR 459 AS 11 AZ 863 CA 1,157 CO 1 CT 29 DC 1 FL 2,091 HI 115 IA 2 ID 351 IL 1,452 IN 1,210 KS 2 KY 225 SYR3 Occurrence Support Document B-29 December 2016 ------- State Total Number of Systems Systems with a Mean Concentration > 50 jjg/L3 Systems with a Mean Concentration >100 jjg/L Number Percent Number Percent LA 1,091 MA 4 MD 11 ME 12 Ml 22 MN 27 MO 21 MS 5 MT 47 NC 5 ND 23 NE 11 NH 4 NJ 0 NM 717 1 0.14% 1 0.14% NV 301 NY 80 OH 177 OK 4 OR 1,118 PA 1,249 Rl 0 SC 0 SD 258 TN 6 TX 0 UT 13 VA 8 VT 0 WA 25 Wl 1,914 SYR3 Occurrence Support Document B-30 December 2016 ------- State Total Number of Systems Systems with a Mean Concentration > 50 jjg/L3 Systems with a Mean Concentration >100 jjg/L Number Percent Number Percent WV 18 WY 6 Total 15,538 1 0.01% 1 0.01% 1 Results are based on setting all non-detection results equal to % the MRL values in the SYR3 ICR dataset. 2 Blank cells within the table indicate that there were no systems with a mean concentration that exceeded either threshold. 3 The new potential threshold of concern for this contaminant is due to changes in the RfD based on new health effects information. Exhibit B-16 presents the population served by systems with a mean concentration greater than the MCL concentration by state. The total population served by systems in each state that submitted data for endothall is presented, as well. As described above, only 1 system in New Mexico, serving 993 people, had an estimated mean concentration and the potential MCLG. Exhibit B-16: Endothall Stage 2 Analysis - Summary of Population Served by Systems with a Mean Threshold Exceedance by State12 State Total Population Population Served by Systems with a Mean Concentration > 50 jjg/L3 Population Served by Systems with a Mean Concentration > 100 Mg/L Population Percent Population Percent AK 39,228 AL 5,333,035 AR 2,635,934 AS 62,196 AZ 6,468,762 CA 36,137,032 CO 2,020 CT 245,905 DC 761,124 FL 18,991,343 HI 1,487,191 IA 165,864 ID 903,523 IL 10,996,262 IN 4,769,597 KS 482,004 KY 4,225,473 SYR3 Occurrence Support Document B-31 December 2016 ------- State Total Population Population Served by Systems with a Mean Concentration > 50 jjg/L3 Population Served by Systems with a Mean Concentration > 100 Mg/L Population Percent Population Percent LA 4,961,515 MA 108,884 MD 1,959,910 ME 48,749 Ml 225,565 MN 25,573 MO 1,380,996 MS 6,176 MT 25,192 NC 534,572 ND 66,229 NE 933,101 NH 1,461 NJ 0 NM 1,940,555 993 0.05% 993 0.05% NV 2,681,616 NY 3,370,044 OH 2,423,043 OK 7,343 OR 3,432,307 PA 10,883,210 Rl 0 SC 0 SD 680,381 TN 1,168,508 TX 0 UT 6,459 VA 839,004 VT 0 WA 695,302 Wl 4,236,887 SYR3 Occurrence Support Document B-32 December 2016 ------- State Total Population Population Served by Systems with a Mean Concentration > 50 jjg/L3 Population Served by Systems with a Mean Concentration > 100 Mg/L Population Percent Population Percent WV 379,363 WY 73,291 Total 136,801,729 993 0.001% 993 0.001% 1 Results are based on setting all non-detection results equal to % the MRL values in the SYR3 ICR dataset. 2 Blank cells within the table indicate that there were no systems with a mean concentration that exceeded either threshold. 3 The new potential threshold of concern for this contaminant is due to changes in the RfD based on new health effects information. B.4.3 Summary of Data A total of 61,972 analytical results from 15,538 PWSs in 45 states/entities were available in the SYR3 ICR Dataset for endothall. The Stage 2 analysis of occurrence in drinking water indicated that 1 ground water system in New Mexico, serving 993 people, had an estimated system mean concentration of endothall greater than the MCL concentration of 100 |ig/L and the potential MCLG of 50 |ig/L. SYR3 Occurrence Support Document B-33 December 2016 ------- B.5 Fluoride This chapter on fluoride includes background information such as the regulatory history and a summary of monitoring requirements, as well as occurrence and exposure estimates in drinking water. All drinking water occurrence estimates are based on data from the National Compliance Monitoring Information Collection Request (ICR) Dataset for the Third Six-Year Review (the "SYR3 ICR Dataset"). B.5.1 Background The United States Environmental Protection Agency (EPA) published the current National Primary Drinking Water Regulations (NPDWR) for fluoride on April 2, 1986 (51 FR 11396; USEPA, 1986). The NPDWR established a maximum contaminant level goal (MCLG) and a maximum contaminant level (MCL) of 4,000 |ig/L. EPA based the MCLG on a reference dose (RfD) of 0.11 mg/kg-day (0.025 mg/kg-day) to avoid skeletal fluorosis; fluoride was not classified as carcinogenicity for humans. EPA also established a secondary MCL of 2,000 |ig/L to protect against severe dental fluorosis. The secondary MCL is not enforceable, but triggers a public notification requirement. Fluoride is regulated as an inorganic chemical (IOC) in drinking water. All community water systems (CWSs) and non-transient non-community water systems (NTNCWSs) must sample for the regulated IOCs. The maximum waiver period for IOCs is one compliance cycle. During this cycle, the system must sample at least once. Ground water systems must sample once during the initial three-year compliance period. Surface water systems must sample annually during the initial three-year compliance period. If all analytical results are less than the MCL, and upon considering reported concentrations, degrees of variation in reported concentration and other factors which may affect contaminant concentration, a ground water and surface water system may be granted a waiver. If the results are greater than the MCL, the public water system (PWS) must take one sample per quarter until results are below the MCL (minimum of two quarterly samples for ground water systems and four quarterly samples for surface water systems).11 If all quarterly samples are reliably and consistently below the MCL, the system may continue at initial monitoring indefinitely until the state or EPA establishes an alternate schedule. B.5.2 Occurrence in Drinking Water The analysis of fluoride occurrence presented in the following section is based on state compliance monitoring data from the SYR3 ICR Dataset. These data consist of 256,237 analytical results from regulated public water systems (PWSs) during the period from 2006 to 2011. The number of sample results and systems vary by state, although the state datasets have been reviewed and checked to ensure adequacy of coverage and completeness. 11 All new systems or systems using a new water source that began operation after January 22, 2004 must demonstrate compliance with the MCL within a period of time specified by the State. The system must also comply with the initial sampling frequencies specified by the State to ensure that a system can demonstrate compliance with the MCL. SYR3 Occurrence Support Document B-34 December 2016 ------- EPA used a two-stage analytical approach to estimate the national contaminant occurrence of fluoride in drinking water using the SYR3 ICR Dataset. The "Stage 1" analysis is a simple non- parametric analysis with accompanying descriptive statistics of national contaminant occurrence among regulated public water systems. The results are simple counts of the number and percentage of systems and population served by systems that have at least one compliance monitoring sample result exceeding a specified concentration threshold. The Stage 1 analysis provides occurrence assessments that are more conservative and may be more reflective of potential acute exposure than the assessments from the Stage 2 analyses. Section 6 provides the details for the Stage 1 analysis. Based on the evaluation of the health effects and analytical methods as part of the Six-Year Review protocol, EPA selected a set of contaminants, including fluoride, for which Stage 2 analyses were warranted. The Stage 2 analysis is an assessment of national contaminant occurrence based on estimates of long-term mean concentrations of contaminants for each system. This analysis method provides occurrence estimates that are less conservative than the Stage 1 analysis, which relies on a single maximum concentration. Also, because the Stage 2 analyses generate long-term (multi-year) mean concentration estimates for contaminant occurrence at systems, the analyses can support assessments of population served by systems that may be more reflective of potential chronic exposure than the assessments from the Stage 1 analyses. For the Stage 2 analyses, EPA calculated system arithmetic means using all sample detection records and all non-detection records, excluding samples for fluoridated water (i.e., water to which a system adds fluoride to maintain a concentration in the 700 to 1,200 |ig/L range).12 There are three different substitution values -zero, V2 the minimum reporting level (MRL) value and the full MRL value-to replace each non-detection record. (The national modal MRL for the fluoride dataset is 50 |ig/L.) Thus, there are three arithmetic mean fluoride concentrations calculated for each system using the zero, V2 MRL and full MRL substitution values. There are mean estimates for all systems with fluoride data in the SYR3 ICR dataset. There are corresponding percentages that reflect the share of all systems with a mean concentration greater than each threshold. For fluoride, since there were no analytical method limitations at the potential MCLG, EPA generated Stage 2 occurrence estimates relative to the MCL and the potential MCLG. Stage 2 Occurrence Estimates This section provides summary results of the Stage 2 analyses for fluoride. Occurrence estimates were generated relative to several thresholds: 4,000 |ig/L (the MCL), 900 |ig/L (the potential MCLG value) and four interim values - 3,000 |ig/L, 2,000 |ig/L, 1,500 |ig/L and 1,000 |ig/L. The potential MCLG is due to changes in the RfD based on new health effects information. For more information on the new potential thresholds of concern used in the SYR3 Stage 2 analyses, refer to USEPA (2016d) and (2016e). 12 The fluoridation range during the sample period was 700 to 1,200 |ig/L. but the current fluoridation target is 700 |ig/L. Thus, historical samples of fluoridated water could exceed of the fluoride concentration thresholds that overlap the fluoridation range, whereas samples that reflect the current target would not. Therefore, EPA excluded samples for fluoridated water to remove an upward bias in the occurrence estimates. SYR3 Occurrence Support Document B-35 December 2016 ------- Exhibit B-17 presents the system-level Stage 2 results of estimated mean concentrations for fluoride occurrence in drinking water relative to various thresholds. Exhibit B-18 presents similar information based on population served by the systems. Based on the Stage 2 analyses, 134 systems serving almost 60,000 people had an estimated system mean greater than the MCL concentration of 4,000 |ig/L. More than 5,000 systems, serving 13 million people, had an estimated system mean greater than the potential MCLG of 900 |ig/L. Exhibit B-17: Fluoride Stage 2 Analysis - Summary of Systems with a Mean Threshold Exceedance Source Water Type (Number of Systems) Threshold Number of Systems with Mean Concentrations That Are Greater Than the Threshold Percent of Systems with Mean Concentrations That Are Greater Than the Threshold Non-detect values = MRL Non-detect values = 1/2 MRL Non-detect values = 0 Non-detect values = MRL Non-detect values = 1/2 MRL Non-detect values = 0 Ground Water (44,033) >4,000 |jg/L 134 134 134 0.30% 0.30% 0.30% >3,000 |jg/L 330 330 330 0.75% 0.75% 0.75% >2,000 |jg/L 964 964 964 2.19% 2.19% 2.19% >1,500 |jg/L 1,952 1,951 1,950 4.43% 4.43% 4.43% >1,000 |jg/L 4,218 4,210 4,205 9.58% 9.56% 9.55% >900 |jg/L1 4,898 4,892 4,884 11.12% 11.11% 11.09% Surface Water (3,194) >4,000 |jg/L 0 0 0 0.00% 0.00% 0.00% >3,000 |jg/L 3 3 3 0.09% 0.09% 0.09% >2,000 |jg/L 8 8 8 0.25% 0.25% 0.25% >1,500 |jg/L 21 20 20 0.66% 0.63% 0.63% >1,000 |jg/L 139 138 137 4.35% 4.32% 4.29% >900 |jg/L1 163 161 160 5.10% 5.04% 5.01% Combined Ground & Surface Water (47,227) >4,000 |jg/L 134 134 134 0.28% 0.28% 0.28% >3,000 |jg/L 333 333 333 0.71% 0.71% 0.71% >2,000 |jg/L 972 972 972 2.06% 2.06% 2.06% >1,500 |jg/L 1,973 1,971 1,970 4.18% 4.17% 4.17% >1,000 |jg/L 4,357 4,348 4,342 9.23% 9.21% 9.19% >900 |jg/L1 5,061 5,053 5,044 10.72% 10.70% 10.68% 1 The new potential threshold of concern for this contaminant is due to changes in the RfD based on new health effects information. SYR3 Occurrence Support Document B-36 December 2016 ------- Exhibit B-18: Fluoride Stage 2 Analysis - Summary of Population Served by Systems with a Mean Threshold Exceedance Source Water Type (Population Served by Systems) Threshold Population Served by Systems with Mean Concentrations That Are Greater Than the Threshold Percent of Population Served by Systems with Mean Concentrations That Are Greater Than the Threshold Non-detect values = MRL Non-detect values = 1/2 MRL Non-detect values = 0 Non-detect values = MRL Non-detect values = MRL Non-detect values = 1/2 MRL Ground Water (96,498,333) >4,000 |jg/L 59,911 59,911 59,911 0.06% 0.06% 0.06% >3,000 |jg/L 582,629 582,629 582,629 0.60% 0.60% 0.60% >2,000 |jg/L 1,503,017 1,503,017 1,503,017 1.56% 1.56% 1.56% >1,500 |jg/L 2,755,639 2,743,439 2,743,029 2.86% 2.84% 2.84% >1,000 |jg/L 8,121,680 8,114,433 8,112,955 8.42% 8.41% 8.41% >900 |jg/L1 10,059,180 10,006,942 9,926,430 10.42% 10.37% 10.29% Surface Water (92,688,121) >4,000 |jg/L 0 0 0 0.00% 0.00% 0.00% >3,000 |jg/L 20,512 20,512 20,512 0.02% 0.02% 0.02% >2,000 |jg/L 33,297 33,297 33,297 0.04% 0.04% 0.04% >1,500 |jg/L 119,381 102,529 102,529 0.13% 0.11% 0.11% >1,000 |jg/L 2,223,360 2,222,803 2,219,484 2.40% 2.40% 2.39% >900 |jg/L1 3,522,836 3,397,425 3,394,742 3.80% 3.67% 3.66% Combined Ground & Surface Water (189,186,454) >4,000 |jg/L 59,911 59,911 59,911 0.03% 0.03% 0.03% >3,000 |jg/L 603,141 603,141 603,141 0.32% 0.32% 0.32% >2,000 |jg/L 1,536,314 1,536,314 1,536,314 0.81% 0.81% 0.81% >1,500 |jg/L 2,875,020 2,845,968 2,845,558 1.52% 1.50% 1.50% >1,000 |jg/L 10,345,040 10,337,236 10,332,439 5.47% 5.46% 5.46% >900 |jg/L1 13,582,016 13,404,367 13,321,172 7.18% 7.09% 7.04% 1 The new potential threshold of concern for this contaminant is due to changes in the RfD based on new health effects information. Data for fluoride were available from 49 states/entities. Four states did not submit data for use in the Six-Year Review (Colorado, Delaware, Georgia and Mississippi). Although the State of Mississippi did not provide data for any contaminants for the SYR3 ICR Dataset, this state is included in the state-level results shown below because a handful of tribal water systems located within this state submitted fluoride data. SYR3 Occurrence Support Document B-37 December 2016 ------- Exhibit B-19 presents the total number of systems in each state that submitted data for fluoride, excluding systems that only submitted data for fluoridated water. It also shows the exceedance values for the potential MCLG (900 |ig/L) and the next two highest thresholds (1,000 |ig/L and 1,500 |ig/L), (Note: These results reflect the '/2 MRL substitution case). Exhibit B-19: Fluoride Stage 2 Analysis - Summary of Systems with a Mean Threshold Exceedance by State12 State Total Number of Systems Systems with a Mean Concentration > 1,500 jjg/L Systems with a Mean Concentration > 1,000 jjg/L Systems with a Mean Concentration > 900 jjg/L3 Number Percent Number Percent Number Percent AK 489 1 0.20% 7 1.43% 7 1.43% AL 343 4 1.17% 16 4.66% 18 5.25% AR 420 7 1.67% 13 3.10% 14 3.33% AS 11 AZ 899 90 10.01% 164 18.24% 197 21.91% CA 3,902 74 1.90% 145 3.72% 176 4.51% CT 1,168 11 0.94% 25 2.14% 27 2.31% DC 1 0 0.00% 0 0.00% 1 100.00% FL 2,589 38 1.47% 88 3.40% 112 4.33% HI 113 IA 370 41 11.08% 78 21.08% 84 22.70% ID 680 18 2.65% 38 5.59% 45 6.62% IL 653 80 12.25% 223 34.15% 268 41.04% IN 942 54 5.73% 201 21.34% 251 26.65% KS 564 18 3.19% 52 9.22% 62 10.99% KY 73 6 8.22% 17 23.29% 17 23.29% LA 1,100 21 1.91% 42 3.82% 51 4.64% MA 639 9 1.41% 28 4.38% 37 5.79% MD 164 3 1.83% 9 5.49% 9 5.49% ME 755 13 1.72% 60 7.95% 75 9.93% Ml 2,259 41 1.81% 167 7.39% 204 9.03% MN 615 14 2.28% 206 33.50% 216 35.12% MO 1,386 41 2.96% 113 8.15% 133 9.60% MS 5 0 0.00% 3 60.00% 5 100.00% MT 785 39 4.97% 66 8.41% 75 9.55% SYR3 Occurrence Support Document B-38 December 2016 ------- State Total Number of Systems Systems with a Mean Concentration > 1,500 jjg/L Systems with a Mean Concentration > 1,000 jjg/L Systems with a Mean Concentration > 900 jjg/L3 Number Percent Number Percent Number Percent NC 2,121 45 2.12% 107 5.04% 130 6.13% ND 146 19 13.01% 56 38.36% 59 40.41% NE 685 3 0.44% 37 5.40% 47 6.86% NH 1,170 103 8.80% 168 14.36% 192 16.41% NJ 1,396 5 0.36% 17 1.22% 22 1.58% NM 748 78 10.43% 131 17.51% 161 21.52% NV 330 21 6.36% 39 11.82% 50 15.15% NY 2,389 15 0.63% 36 1.51% 49 2.05% OH 1,711 149 8.71% 396 23.14% 436 25.48% OK 599 26 4.34% 45 7.51% 52 8.68% OR 847 16 1.89% 25 2.95% 31 3.66% PA 1,369 3 0.22% 10 0.73% 14 1.02% Rl 151 3 1.99% 10 6.62% 11 7.28% SC 537 32 5.96% 51 9.50% 55 10.24% SD 158 21 13.29% 31 19.62% 37 23.42% TN 126 0 0.00% 12 9.52% 13 10.32% TX 4,596 507 11.03% 898 19.54% 1,011 22.00% UT 477 5 1.05% 11 2.31% 12 2.52% VA 1,524 204 13.39% 260 17.06% 273 17.91% VT 417 1 0.24% 6 1.44% 7 1.68% WA 2,196 32 1.46% 53 2.41% 65 2.96% Wl 1,997 22 1.10% 101 5.06% 138 6.91% WV 297 4 1.35% 13 4.38% 16 5.39% WY 315 34 10.79% 74 23.49% 88 27.94% Total 47,227 1,971 4.17% 4,348 9.21% 5,053 10.70% 1 Results are based on setting all non-detection results equal to % the MRL values in the SYR3 ICR dataset. 2 Blank cells within the table indicate that there were no systems with a mean concentration that exceeded the threshold. 3 The new potential threshold of concern for this contaminant is due to changes in the RfD based on new health effects information. Exhibit B-20 provides the corresponding state-level populations served by systems that have a mean concentration greater than the thresholds show above. Again, these estimates exclude population served by systems that provided only samples for fluoridated water. SYR3 Occurrence Support Document B-39 December 2016 ------- Exhibit B-20: Fluoride Stage 2 Analysis - Summary of Population Served by Systems with a Mean Threshold Exceedance by State12 State Total Population Population Served by Systems with a Mean Concentration > 1,500 jjg/L Population Served by Systems with a Mean Concentration > 1,000 jjg/L Population Served by Systems with a Mean Concentration > 900 jjg/L1 Population Percent Population Percent Population Percent AK 653,758 173 0.03% 16,978 2.60% 16,978 2.60% AL 3,951,346 22,703 0.57% 106,577 2.70% 107,762 2.73% AR 2,154,639 7,179 0.33% 25,198 1.17% 25,228 1.17% AS 62,196 AZ 6,507,196 144,530 2.22% 473,064 7.27% 663,864 10.20% CA 41,166,323 326,394 0.79% 708,080 1.72% 804,725 1.95% CT 2,848,818 1,627 0.06% 3,220 0.11% 3,405 0.12% DC 761,124 0 0.00% 0 0.00% 761,124 100.00% FL 18,078,815 15,387 0.09% 90,117 0.50% 135,945 0.75% HI 1,486,472 IA 905,648 41,299 4.56% 205,076 22.64% 222,603 24.58% ID 1,152,093 31,922 2.77% 69,957 6.07% 70,542 6.12% IL 3,702,273 173,654 4.69% 1,365,422 36.88% 1,864,804 50.37% IN 1,913,536 195,536 10.22% 701,799 36.68% 754,671 39.44% KS 1,871,086 14,295 0.76% 116,603 6.23% 129,838 6.94% KY 528,053 12,876 2.44% 184,200 34.88% 184,200 34.88% LA 4,312,127 108,424 2.51% 144,272 3.35% 155,410 3.60% MA 7,821,027 676 0.01% 117,086 1.50% 274,799 3.51% MD 35,504 260 0.73% 3,035 8.55% 3,035 8.55% ME 445,391 1,537 0.35% 135,959 30.53% 137,673 30.91% Ml 3,038,489 13,690 0.45% 219,941 7.24% 230,257 7.58% MN 788,703 5,432 0.69% 687,349 87.15% 692,644 87.82% MO 2,663,227 55,819 2.10% 285,286 10.71% 446,999 16.78% MS 6,176 0 0.00% 2,092 33.87% 6,176 100.00% MT 740,136 16,446 2.22% 25,633 3.46% 27,817 3.76% NC 3,927,168 77,947 1.98% 278,606 7.09% 315,742 8.04% ND 412,916 8,139 1.97% 317,175 76.81% 318,479 77.13% NE 1,652,769 2,138 0.13% 116,350 7.04% 163,539 9.89% SYR3 Occurrence Support Document B-40 December 2016 ------- State Total Population Population Served by Systems with a Mean Concentration > 1,500 jjg/L Population Served by Systems with a Mean Concentration > 1,000 jjg/L Population Served by Systems with a Mean Concentration > 900 jjg/L1 Population Percent Population Percent Population Percent NH 776,183 15,863 2.04% 47,122 6.07% 51,738 6.67% NJ 9,129,229 14,346 0.16% 117,773 1.29% 157,843 1.73% NM 1,974,790 127,596 6.46% 234,708 11.89% 315,293 15.97% NV 2,418,044 16,184 0.67% 89,040 3.68% 97,135 4.02% NY 4,916,027 11,627 0.24% 71,637 1.46% 77,711 1.58% OH 1,873,754 97,603 5.21% 513,809 27.42% 544,330 29.05% OK 2,418,323 23,683 0.98% 86,054 3.56% 192,024 7.94% OR 2,928,203 11,605 0.40% 13,179 0.45% 14,260 0.49% PA 5,307,038 173 0.00% 19,316 0.36% 19,837 0.37% Rl 1,019,737 1,678 0.16% 3,008 0.29% 3,931 0.39% SC 2,376,386 103,163 4.34% 135,290 5.69% 153,744 6.47% SD 107,316 15,669 14.60% 24,356 22.70% 27,900 26.00% TN 1,822,566 0 0.00% 102,634 5.63% 124,741 6.84% TX 23,510,681 928,382 3.95% 1,951,430 8.30% 2,351,648 10.00% UT 2,816,964 29,158 1.04% 31,543 1.12% 31,813 1.13% VA 2,653,609 86,467 3.26% 183,087 6.90% 241,509 9.10% VT 345,674 32 0.01% 787 0.23% 812 0.23% WA 4,094,793 27,121 0.66% 91,164 2.23% 225,593 5.51% Wl 4,251,831 43,181 1.02% 100,169 2.36% 117,987 2.77% WV 389,087 2,489 0.64% 66,177 17.01% 74,770 19.22% WY 469,210 11,865 2.53% 55,878 11.91% 61,489 13.10% Total 189,186,454 2,845,968 1.50% 10,337,236 5.46% 13,404,367 7.09% 1 Results are based on setting all non-detection results equal to % the MRL values in the SYR3 ICR dataset. 2 Blank cells within the table indicate that there were no systems with a mean concentration that exceeded the threshold. 3 The new potential threshold of concern for this contaminant is due to changes in the RfD based on new health effects information. B.5.3 Summary of Data A total of 256,237 analytical results from 47,227 PWSs in 49 states/entities were available in the SYR3 ICR Dataset for fluoride. The Stage 2 analysis of occurrence in drinking water indicated that 134 systems had an estimated system mean concentration of fluoride greater than the MCL concentration of 4,000 |ig/L. More than 5,000 water systems, serving more than 13 million people had an estimated mean concentration greater than the potential MCLGs of 900 |ig/L. These water systems are located in almost every state. SYR3 Occurrence Support Document B-41 December 2016 ------- B.6 Heptachlor This chapter on heptachlor includes background information such as the regulatory history and a summary of monitoring requirements, as well as occurrence and exposure estimates in drinking water. All drinking water occurrence estimates are based on data from the National Compliance Monitoring Information Collection Request (ICR) Dataset for the Third Six-Year Review (the "SYR3 ICR Dataset"). B.6.1 Background The United States Environmental Protection Agency (EPA) published the current National Primary Drinking Water Regulations (NPDWR) for heptachlor on January 30, 1991 (56 FR 3526; USEPA, 1991a). The NPDWR established a maximum contaminant level goal (MCLG) of zero based on a cancer classification of B2, probable human carcinogen. The NPDWR also established a maximum contaminant level (MCL) of 0.4 |ig/L based on analytical feasibility. Heptachlor is regulated as a synthetic organic chemical (SOC) in drinking water. All non- purchased community water systems (CWSs) and non-transient non-community water systems (NTNCWSs) are required to sample for SOCs. Waivers are available to all systems upon a favorable vulnerability assessment and/or prior analytical results. The maximum waiver period for SOCs is three years, but this waiver can be renewed indefinitely, if it is reconfirmed that the source is not vulnerable. All CWSs and NTNCWSs without an SOC waiver must collect four consecutive quarterly samples during the initial three-year compliance period.13 If all 4 samples are non-detections, then a system serving less than 3,300 people may reduce its collection frequency to 1 sample during each consecutive compliance period; a system serving more than 3,300 people may reduce its collection frequency to 2 quarterly samples within a 12-month period during each repeat compliance period. If a chemical is detected, the system must monitor quarterly until results are reliably and consistently below the MCL (minimum of two quarterly samples for ground water systems and four quarterly samples for surface water systems). If all quarterly samples are below the MCL, the system may return to annual sampling. If a chemical is detected at a level greater than the MCL, the system (whether ground water or surface water) must take quarterly samples until four consecutive quarters are below the MCL. If all quarterly samples are below the MCL, the system may return to annual sampling. B.6.2 Occurrence in Drinking Water The analysis of heptachlor occurrence presented in the following section is based on state compliance monitoring data from the SYR3 ICR Dataset. These data consist of 137,286 analytical results from 38,691 public water systems (PWSs) during the period from 2006 to 13 All new systems or systems using a new water source that began operation after January 22, 2004 must demonstrate compliance with the MCL within a period of time specified by the State. The system must also comply with the initial sampling frequencies specified by the State to ensure that a system can demonstrate compliance with the MCL. SYR3 Occurrence Support Document B-42 December 2016 ------- 2011. The number of sample results and systems vary by state, although the state datasets have been reviewed and checked to ensure adequacy of coverage and completeness. EPA used a two-stage analytical approach to estimate the national contaminant occurrence using the SYR3 ICR Dataset. In the "Stage 1 analysis," the occurrence data were analyzed to generate simple non-parametric estimates and descriptive statistics of national contaminant occurrence in public water systems. Simple counts were made of the number and percentage of systems and population served by systems with at least one compliance monitoring sample result greater than a specified concentration threshold. The Stage 1 analysis provides occurrence assessments that are more conservative and may be more reflective of potential acute exposure than the assessments from the Stage 2 analyses. Details on the Stage 1 analysis are presented in Section 6. Based on the evaluation of the health effects and analytical methods as part of the Six-Year Review protocol, EPA selected a set of contaminants, including heptachlor, for which Stage 2 analyses were warranted. The Stage 2 analysis estimates national contaminant occurrence by generating estimated long-term mean concentrations of contaminants for each system. This provides occurrence analyses that are less conservative than the Stage 1 analysis, since the Stage 2 analysis is based on estimated mean concentrations rather than on a single maximum concentration. Also, because the Stage 2 analyses generate long-term (multi-year) mean concentration estimates for contaminant occurrence at systems, the analyses can support assessments of population served by systems with detections or potential exposure assessments that may be more reflective of potential chronic exposure than the assessments from the Stage 1 analyses. For the Stage 2 analyses, system arithmetic means were calculated using all sample detection records and all non-detection records. Two different substitution values -zero and V2 the minimum reporting level (MRL) value- were used to replace each non-detection record. (The national modal MRL for heptachlor in the dataset is 0.04 |ig/L.) Two arithmetic mean heptachlor concentrations were calculated at each system using the zero and V2 MRL substitution values. These mean calculations were performed for all systems with heptachlor data in the SYR3 ICR dataset. Then, the percentages of all systems with a mean concentration greater than each threshold were calculated. For heptachlor, EPA generated Stage 2 occurrence estimates relative to the MCL, V2 the MCL, the estimated quantitation level (EQL) and twice the EQL. Stage 2 Occurrence Estimates Stage 2 analyses for heptachlor are summarized in this section. Occurrence estimates were generated relative to the following thresholds: 0.4 |ig/L (the MCL), 0.2 |ig/L (V2 the MCL and two times the EQL) and 0.1 |ig/L (the EQL). The EQL represents the potential quantitation capabilities below a practical quantitation level (PQL).14For more information on the new 14 When it is not possible to measure concentrations at the MCLG level, EPA often bases the MCL on an analytical feasibility level, known as a PQL. However, analytical feasibility can improve over time. As part of the Six-Year Review process, EPA evaluates whether new information regarding quantitation shows that PQLs may be reduced. The EQL represents quantitation capabilities below a PQL (USEPA, 2016d). The EQL is the threshold used to evaluate occurrence and exposure for the Stage 2 analyses. SYR3 Occurrence Support Document B-43 December 2016 ------- potential thresholds of concern used in the SYR3 Stage 2 analyses, refer to USEPA (2016d) and (2016e). Exhibit B-21 presents the system-level Stage 2 analysis of estimated mean concentrations for heptachlor occurrence in drinking water. Exhibit B-22 presents similar information based on population served by the systems. Based on the Stage 2 analyses, three water systems (approximately 0.008 percent of all systems) had an estimated mean greater than the MCL of 0.4 |ig/L, as well as the EQL of 0.1 |ig/L. These 3 systems serve approximately 1,643 people. Exhibit B-21: Heptachlor Stage 2 Analysis - Summary of Systems with a Mean Threshold Exceedance Source Water Type (Number of Systems) Threshold Number of Systems with Mean Concentrations That Are Greater Than the Threshold Percent of Systems with Mean Concentrations That Are Greater Than the Threshold Non-detect values = 1/2 MRL Non-detect values = 0 Non-detect values = 1/2 MRL Non-detect values = 0 Ground Water (35,408) > 0.4 |jg/L 3 2 0.008% 0.006% > 0.2 |jg/L1 3 3 0.008% 0.008% >0.1 |jg/L2 3 3 0.008% 0.008% Surface Water (3,283) > 0.4 |jg/L 0 0 0.000% 0.000% > 0.2 |jg/L1 0 0 0.000% 0.000% >0.1 |jg/L2 0 0 0.000% 0.000% Combined Ground & Surface Water (38,691) > 0.4 |jg/L 3 2 0.008% 0.005% > 0.2 |jg/L1 3 3 0.008% 0.008% >0.1 |jg/L2 3 3 0.008% 0.008% 1 This threshold is equal to % the MCL and two times the EQL. 2 The new potential threshold of concern for this contaminant is based on the EQL. The EQL represents the potential quantitation capabilities below a PQL (USEPA, 2016d). SYR3 Occurrence Support Document B-44 December 2016 ------- Exhibit B-22: Heptachlor Stage 2 Analysis - Summary of Population Served by Systems with a Mean Threshold Exceedance Source Water Type (Population Served by Systems) Threshold Population Served by Systems with Mean Concentrations That Are Greater Than the Threshold Percent of Population Served by Systems with Mean Concentrations That Are Greater Than the Threshold Non-detect values = 1/2 MRL Non-detect values = 0 Non-detect values = 1/2 MRL Non-detect values = 0 Ground Water (92,583,244) > 0.4 |jg/L 1,643 1,543 0.002% 0.002% > 0.2 |jg/L1 1,643 1,643 0.002% 0.002% >0.1 |jg/L2 1,643 1,643 0.002% 0.002% Surface Water (137,249,041) > 0.4 |jg/L 0 0 0.000% 0.000% > 0.2 |jg/L1 0 0 0.000% 0.000% >0.1 |jg/L2 0 0 0.000% 0.000% Combined Ground & Surface Water (229,832,285) > 0.4 |jg/L 1,643 1,543 0.001% 0.001% > 0.2 |jg/L1 1,643 1,643 0.001% 0.001% >0.1 |jg/L2 1,643 1,643 0.001% 0.001% 1 This threshold is equal to % the MCL and two times the EQL. 2 The new potential threshold of concern for this contaminant is based on the EQL. The EQL represents the potential quantitation capabilities below a PQL (USEPA, 2016d). Data for heptachlor were available from 50 states/entities. Four states did not submit data for use in the Six-Year Review (Colorado, Delaware, Georgia and Mississippi). Although the States of Colorado and Mississippi did not provide data for any contaminants for the SYR3 ICR Dataset, these states are included in the count of 50 states because a handful of tribal water systems located within these 2 states did submit heptachlor data. Exhibit B-23 presents the total number of systems in each state that submitted data for heptachlor. In addition, the geographic distribution of heptachlor occurrence in drinking water is illustrated by showing states with systems with a mean concentration greater than the EQL, V2 MCL (or two times the EQL) and MCL concentrations. (Note: Only the V2 MRL substitution results are presented in this exhibit.) Detection rates of heptachlor were low; three states each had a single system with an estimated mean concentration greater than the MCL (Maryland, New Mexico and New York). The same three systems had estimated mean concentrations greater than V2 the MCL and EQL, as well. SYR3 Occurrence Support Document B-45 December 2016 ------- Exhibit B-23: Heptachlor Stage 2 Analysis - Summary of Systems with a Mean Threshold Exceedance by State12 State Total Number of Systems Systems with a Mean Concentration >0.1 mq/l3 Systems with a Mean Concentration > 0.2 jjg/L4 Systems with a Mean Concentration > 0.4 jjg/L Number Percent Number Percent Number Percent AK 13 AL 383 AR 459 AS 11 AZ 872 CA 1,279 CO 1 CT 1,136 DC 1 FL 2,091 HI 111 IA 3 ID 390 IL 1,468 IN 1,213 KS 87 KY 225 LA 1,102 MA 566 MD 881 1 0.11% 1 0.11% 1 0.11% ME 173 Ml 2,439 MN 920 MO 1,332 MS 5 MT 857 NC 2,348 ND 157 NE 703 SYR3 Occurrence Support Document B-46 December 2016 ------- State Total Number of Systems Systems with a Mean Concentration >0.1 mq/l3 Systems with a Mean Concentration > 0.2 jjg/L4 Systems with a Mean Concentration > 0.4 jjg/L Number Percent Number Percent Number Percent NH 1,146 NJ 46 NM 718 1 0.14% 1 0.14% 1 0.14% NV 310 NY 2,121 1 0.05% 1 0.05% 1 0.05% OH 33 OK 36 OR 1,119 PA 1,048 Rl 102 SC 497 SD 269 TN 6 TX 4,422 UT 428 VA 254 VT 380 WA 1,996 Wl 1,914 WV 302 WY 318 Total 38,691 3 0.01% 3 0.01% 3 0.01% 1 Results are based on setting all non-detection results equal to % the MRL values in the SYR3 ICR dataset. 2 Blank cells within the table indicate that there were no systems with a mean concentration that exceeded any of the thresholds. 3 The new potential threshold of concern for this contaminant is based on the EQL. The EQL represents the potential quantitation capabilities below a PQL (USEPA, 2016d). 4 This threshold is equal to % the MCL and two times the EQL. Exhibit B-24 presents the population served by systems with a mean concentration greater than the MCL concentration by state. The total population served by systems in each state that submitted data for heptachlor is presented, as well. Three states (Maryland, New Mexico and New York) contained a single system with an estimated mean concentration greater than the MCL, V2 MCL and EQL. These 3 systems served a total of 1,643 people. SYR3 Occurrence Support Document B-47 December 2016 ------- Exhibit B-24: Heptachlor Stage 2 Analysis - Summary of Population Served by Systems with a Mean Threshold Exceedance by State12 State Total Population Population Served by Systems with a Mean Concentration >0.1 mq/l3 Population Served by Systems with a Mean Concentration > 0.2 jjg/L4 Population Served by Systems with a Mean Concentration > 0.4 jjg/L Population Percent Population Percent Population Percent AK 40,300 AL 5,333,035 AR 2,635,934 AS 62,196 AZ 6,484,144 CA 35,713,404 CO 2,020 CT 2,883,135 DC 761,124 FL 18,991,343 HI 1,479,317 IA 166,302 ID 980,149 IL 10,998,526 IN 5,017,598 KS 1,817,722 KY 4,225,473 LA 4,966,772 MA 9,164,737 MD 4,939,436 100 0.00% 100 0.00% 100 0.00% ME 367,408 Ml 7,221,983 MN 3,752,545 MO 5,233,314 MS 6,176 MT 845,294 NC 7,832,371 ND 592,232 SYR3 Occurrence Support Document B-48 December 2016 ------- State Total Population Population Served by Systems with a Mean Concentration >0.1 mq/l3 Population Served by Systems with a Mean Concentration > 0.2 jjg/L4 Population Served by Systems with a Mean Concentration > 0.4 jjg/L Population Percent Population Percent Population Percent NE 1,662,774 NH 949,308 NJ 4,123,518 NM 1,940,795 993 0.05% 993 0.05% 993 0.05% NV 2,682,465 NY 10,481,222 550 0.01% 550 0.01% 550 0.01% OH 756,016 OK 145,992 OR 3,432,424 PA 10,847,346 Rl 1,002,727 SC 3,623,380 SD 708,340 TN 1,168,508 TX 23,814,787 UT 2,752,741 VA 5,685,070 VT 386,948 WA 4,947,453 Wl 4,236,887 WV 1,499,884 WY 469,710 Total 229,832,285 1,643 0.00% 1,643 0.00% 1,643 0.00% 1 Results are based on setting all non-detection results equal to % the MRL values in the SYR3 ICR dataset. 2 Blank cells within the table indicate that there were no systems with a mean concentration that exceeded any of the thresholds. 3 The new potential threshold of concern for this contaminant is based on the EQL. The EQL represents the potential quantitation capabilities below a PQL (USEPA, 2016d). 4 This threshold is equal to % the MCL and two times the EQL. B.6.3 Summary of Data A total of 137,286 analytical results from 38,691 PWSs in 50 states/entities were available in the SYR3 ICR Dataset for heptachlor. The Stage 2 analysis of occurrence in drinking water indicated that 3 ground water systems, serving 1,643 people, had an estimated system mean SYR3 Occurrence Support Document B-49 December 2016 ------- concentration of heptachlor greater than the MCL concentration of 0.4 |ig/L. The same three systems also had an estimated mean concentration greater than V2 the MCL (0.2 |ig/L) and the EQL (0.1 |ig/L). These systems were located in Maryland, New Mexico and New York. SYR3 Occurrence Support Document B-50 December 2016 ------- B.7 Heptachlor Epoxide This chapter on heptachlor epoxide includes background information such as the regulatory history and a summary of monitoring requirements, as well as occurrence and exposure estimates in drinking water. All drinking water occurrence estimates are based on data from the National Compliance Monitoring Information Collection Request (ICR) Dataset for the Third Six-Year Review (the "SYR3 ICR Dataset"). B.7.1 Background On January 30, 1991, the United States Environmental Protection Agency (EPA) published the current National Primary Drinking Water Regulations (NPDWR) for heptachlor epoxide, a product of heptachlor degradation (56 FR 3526; USEPA, 1991a). The NPDWR established a maximum contaminant level goal (MCLG) of zero based on a cancer classification of B2, probable human carcinogen. The NPDWR also established a maximum contaminant level (MCL) of 0.2 |ig/L based on analytical feasibility. Heptachlor epoxide is regulated as a synthetic organic chemical (SOC) in drinking water. All non-purchased community water systems (CWSs) and non-transient non-community water systems (NTNCWSs) are required to sample for SOCs. Waivers are available to all systems upon a favorable vulnerability assessment and/or prior analytical results. The maximum waiver period for SOCs is three years, but this waiver can be renewed indefinitely, if it is reconfirmed that the source is not vulnerable. All CWSs and NTNCWSs without an SOC waiver must collect four consecutive quarterly samples during the initial three-year compliance period.15 If all 4 samples are non-detections, then a system serving less than 3,300 persons may reduce its collection frequency to 1 sample during each consecutive compliance period; a system serving more than 3,300 persons may reduce its collection frequency to 2 quarterly samples within a 12-month period during each repeat compliance period. If a chemical is detected, the system must monitor quarterly until results are reliably and consistently below the MCL (minimum of two quarterly samples for ground water systems and four quarterly samples for surface water systems). If all quarterly samples are below the MCL, the system may return to annual sampling. If a chemical is detected at a level greater than the MCL, the system (whether ground water or surface water) must take quarterly samples until four consecutive quarters are below the MCL. If all quarterly samples are below the MCL, the system may return to annual sampling. B.7.2 Occurrence in Drinking Water The analysis of heptachlor epoxide occurrence presented in the following section is based on state compliance monitoring data from the SYR3 ICR Dataset. These data consist of 137,081 analytical results from 38,625 public water systems (PWSs) during the period from 2006 to 2011. The number of sample results and systems vary by state, although the state datasets have 15 All new systems or systems using a new water source that began operation after January 22, 2004 must demonstrate compliance with the MCL within a period of time specified by the State. The system must also comply with the initial sampling frequencies specified by the State to ensure that a system can demonstrate compliance with the MCL. SYR3 Occurrence Support Document B-51 December 2016 ------- been reviewed and checked to ensure adequacy of coverage and completeness. The national modal minimum reporting level (MRL) for heptachlor epoxide in the dataset is 0.02 |ig/L. EPA used a two-stage analytical approach to estimate the national contaminant occurrence using the SYR3 ICR Dataset. In the "Stage 1 analysis," the occurrence data were analyzed to generate simple non-parametric estimates and descriptive statistics of national contaminant occurrence in public water systems. Simple counts were made of the number and percentage of systems and population served by systems with at least one compliance monitoring sample result greater than a specified concentration threshold. The Stage 1 analysis provides occurrence assessments that are more conservative and may be more reflective of potential acute exposure than the assessments from the Stage 2 analyses. Details on the Stage 1 analysis are presented in Section 6. Based on the evaluation of the health effects and analytical methods as part of the Six-Year Review protocol, EPA selected a set of contaminants, including heptachlor epoxide, for which Stage 2 analyses were warranted. The Stage 2 analysis estimates national contaminant occurrence by generating estimated long-term mean concentrations of contaminants for each system. This provides occurrence analyses that are less conservative than the Stage 1 analysis, since the Stage 2 analysis is based on estimated mean concentrations rather than on a single maximum concentration. Also, because the Stage 2 analyses generate long-term (multi-year) mean concentration estimates for contaminant occurrence at systems, the analyses can support assessments of population served by systems with detections or potential exposure assessments that may be more reflective of potential chronic exposure than the assessments from the Stage 1 analyses. For the Stage 2 analyses, system arithmetic means that were calculated using all sample detection records and all non-detection records. Two different substitution values -zero and V2 the MRL value- were used to replace each non-detection record. (The national modal MRL for heptachlor epoxide in the dataset is 0.02 |ig/L.) Two arithmetic mean heptachlor epoxide concentrations were calculated at each system using the zero, V2 MRL and full MRL substitution values. These mean calculations were performed for all systems with data in the SYR3 ICR dataset. Then, the percentages of all systems with a mean concentration greater than each threshold were calculated. For heptachlor epoxide, EPA generated Stage 2 occurrence estimates relative to the MCL, V2 the MCL, the estimated quantitation level (EQL) and twice the EQL. Stage 2 Occurrence Estimates Stage 2 analyses for heptachlor epoxide are summarized in this section. Occurrence estimates were generated relative to the following thresholds: 0.2 |ig/L (the MCL), 0.1 |ig/L (1/2 the MCL), 0.08 |ig/L (two times the EQL) and 0.04 |ig/L (the EQL). The EQL represents the potential quantitation capabilities below a practical quantitation level (PQL).16For more 16 When it is not possible to measure concentrations at the MCLG level, EPA often bases the MCL on an analytical feasibility level, known as a PQL. However, analytical feasibility can improve over time. As part of the Six-Year Review process, EPA evaluates whether new information regarding quantitation shows that PQLs may be reduced. The EQL represents quantitation capabilities below a PQL (USEPA, 2016d). The EQL is the threshold used to evaluate occurrence and exposure for the Stage 2 analyses. SYR3 Occurrence Support Document B-52 December 2016 ------- information on the new potential thresholds of concern used in the SYR3 Stage 2 analyses, refer to USEPA (2016d) and (2016e). Exhibit B-25 presents the system-level Stage 2 analysis of estimated mean concentrations for heptachlor epoxide occurrence in drinking water. Exhibit B-26 presents similar information based on population served by the systems. Based on the Stage 2 analyses, 2 water systems (approximately 0.005 percent of all systems) had an estimated mean greater than 0.2 |ig/L (the MCL). These 2 systems serve 1,543 people. Fourteen systems (0.036 percent of all systems), serving 11,659 persons, had an estimated system mean greater than the EQL concentration of 0.04 |ig/L. Exhibit B-25: Heptachlor Epoxide Stage 2 Analysis - Summary of Systems with a Mean Threshold Exceedance Source Water Type (Number of Systems) Threshold Number of Systems with Mean Concentrations That Are Greater Than the Threshold Percent of Systems with Mean Concentrations That Are Greater Than the Threshold Non-detect values = 1/2 MRL Non-detect values = 0 Non-detect values = 1/2 MRL Non-detect values = 0 Ground Water (35,355) > 0.2 |jg/L 2 2 0.006% 0.006% > 0.1 |jg/L 6 6 0.017% 0.017% > 0.08 |jg/L 7 7 0.020% 0.020% > 0.04 |jg/L1 14 14 0.040% 0.040% Surface Water (3,270) > 0.2 |jg/L 0 0 0.000% 0.000% > 0.1 |jg/L 0 0 0.000% 0.000% > 0.08 |jg/L 0 0 0.000% 0.000% > 0.04 |jg/L1 0 0 0.000% 0.000% Combined Ground & Surface Water (38,625) > 0.2 |jg/L 2 2 0.005% 0.005% > 0.1 |jg/L 6 6 0.016% 0.016% > 0.08 |jg/L 7 7 0.018% 0.018% > 0.04 |jg/L1 14 14 0.036% 0.036% 1 The new potential threshold of concern for this contaminant is based on the EQL. The EQL represents the potential quantitation capabilities below a PQL (USEPA, 2016d). SYR3 Occurrence Support Document B-53 December 2016 ------- Exhibit B-26: Heptachlor Epoxide Stage 2 Analysis - Summary of Population Served by Systems with a Mean Threshold Exceedance Source Water Type (Population Served by Systems) Threshold Population Served by Systems with Mean Concentrations That Are Greater Than the Threshold Percent of Population Served by Systems with Mean Concentrations That Are Greater Than the Threshold Non-detect values = 1/2 MRL Non-detect values = 0 Non-detect values = 1/2 MRL Non-detect values = 0 Ground Water (92,692,937) > 0.2 |jg/L 1,543 1,543 0.002% 0.002% > 0.1 |jg/L 2,461 2,461 0.003% 0.003% > 0.08 |jg/L 2,700 2,700 0.003% 0.003% > 0.04 |jg/L1 11,659 11,659 0.013% 0.013% Surface Water (137,139,953) > 0.2 |jg/L 0 0 0.000% 0.000% > 0.1 |jg/L 0 0 0.000% 0.000% > 0.08 |jg/L 0 0 0.000% 0.000% > 0.04 |jg/L1 0 0 0.000% 0.000% Combined Ground & Surface Water (229,832,890) > 0.2 |jg/L 1,543 1,543 0.001% 0.001% > 0.1 |jg/L 2,461 2,461 0.001% 0.001% > 0.08 |jg/L 2,700 2,700 0.001% 0.001% > 0.04 |jg/L1 11,659 11,659 0.005% 0.005% 1 The new potential threshold of concern for this contaminant is based on the EQL. The EQL represents the potential quantitation capabilities below a PQL (USEPA, 2016d). Data for heptachlor epoxide were available from 50 states/entities. Four states did not submit data for use in the Six-Year Review (Colorado, Delaware, Georgia and Mississippi). Although the States of Colorado and Mississippi did not provide data for any contaminants for the SYR3 ICR Dataset, these states are included in the count of 50 states because a handful of tribal water systems located within these 2 states did submit heptachlor epoxide data. Exhibit B-27 presents the total number of systems in each state that submitted data for heptachlor epoxide. In addition, the geographic distribution of heptachlor epoxide occurrence in drinking water is illustrated by showing states with systems with a mean concentration greater than the EQL, two times the EQL, V2 MCL and MCL concentrations. (Note: Only the V2 MRL substitution results are presented in this exhibit.) Detection rates of heptachlor epoxide were low; only two systems in states (New Mexico and New York) had an estimated mean concentration greater than the MCL. Six systems in six states had estimated mean concentrations greater than V2 the MCL. SYR3 Occurrence Support Document B-54 December 2016 ------- Exhibit B-27: Heptachlor Epoxide Stage 2 Analysis - Summary of Systems with a Mean Threshold Exceedance by State1 State Total Number of Systems Systems with a Mean Concentration > 0.04 jjg/L2 Systems with a Mean Concentration > 0.08 jjg/L Systems with a Mean Concentration > 0.1 jjg/L Systems with a Mean Concentration > 0.2 jjg/L Number Percent Number Percent Number Percent Number Percent AK 13 AL 383 1 0.26% 1 0.26% 1 0.26% 0 0.00% AR 459 AS 11 AZ 872 CA 1,280 CO 1 CT 1,136 DC 1 FL 2,090 3 0.14% 0 0.00% 0 0.00% 0 0.00% HI 111 IA 3 ID 391 IL 1,467 IN 1,214 KS 87 KY 225 LA 1,078 MA 564 MD 881 1 0.11% 1 0.11% 1 0.11% 0 0.00% ME 135 Ml 2,439 MN 920 MO 1,332 MS 5 MT 857 NC 2,348 4 0.17% 1 0.04% 0 0.00% 0 0.00% ND 157 SYR3 Occurrence Support Document B-55 December 2016 ------- State Total Number of Systems Systems with a Mean Concentration > 0.04 jjg/L2 Systems with a Mean Concentration > 0.08 jjg/L Systems with a Mean Concentration > 0.1 jjg/L Systems with a Mean Concentration > 0.2 jjg/L Number Percent Number Percent Number Percent Number Percent NE 703 2 0.28% 1 0.14% 1 0.14% 0 0.00% NH 1,146 NJ 80 NM 718 1 0.14% 1 0.14% 1 0.14% 1 0.14% NV 309 NY 2,121 1 0.05% 1 0.05% 1 0.05% 1 0.05% OH 33 OK 1 OR 1,119 PA 1,047 1 0.10% 1 0.10% 1 0.10% 0 0.00% Rl 102 SC 497 SD 269 TN 6 TX 4,422 UT 428 VA 254 VT 380 WA 1,996 Wl 1,914 WV 302 WY 318 Total 38,625 14 0.04% 7 0.02% 6 0.02% 2 0.01% 1 Results are based on setting all non-detection results equal to % the MRL values in the SYR3 ICR dataset. 2 The new potential threshold of concern for this contaminant is based on the EQL. The EQL represents the potential quantitation capabilities below a PQL (USEPA, 2016d). Exhibit B-28 presents the population served by systems with a mean concentration greater than the MCL concentration by state. The total population served by systems in each state that submitted data for heptachlor epoxide is presented, as well. As described above, New Mexico and New York were the only states with an estimated mean concentration greater than the MCL. These 2 systems served a total of 1,543 people. Six systems, serving a population of 2,461 people, had estimated mean concentrations greater than V2 the MCL. SYR3 Occurrence Support Document B-56 December 2016 ------- Exhibit B-28: Heptachlor Epoxide Stage 2 Analysis - Summary of Population Served by Systems with a Mean Threshold Exceedance by State State Total Population Population Served by Systems with a Mean Concentration > 0.04 |jg/L2 Population Served by Systems with a Mean Concentration > 0.08 jjg/L Population Served by Systems with a Mean Concentration > 0.1 |jg/L Population Served by Systems with a Mean Concentration > 0.2 jjg/L Population Percent Population Percent Population Percent Population Percent AK 40,300 AL 5,333,035 200 0.004% 200 0.004% 200 0.004% 0 0.00% AR 2,635,934 AS 62,196 AZ 6,484,144 CA 35,713,444 CO 2,020 CT 2,883,135 DC 761,124 FL 18,991,163 8,522 0.045% 0 0.00% 0 0.00% 0 0.00% HI 1,479,317 IA 166,302 ID 980,519 IL 10,998,201 IN 5,018,298 KS 1,817,722 KY 4,225,473 LA 4,901,263 MA 9,164,462 MD 4,939,436 60 0.001 % 60 0.001 % 60 0.001 % 0 0.00% ME 356,040 Ml 7,221,983 MN 3,752,545 MO 5,233,314 MS 6,176 MT 845,294 NC 7,832,371 584 0.007% 239 0.003% 0 0.00% 0 0.00% SYR3 Occurrence Support Document B-57 December 2016 ------- State Total Population Population Served by Systems with a Mean Concentration > 0.04 |jg/L2 Population Served by Systems with a Mean Concentration > 0.08 jjg/L Population Served by Systems with a Mean Concentration > 0.1 |jg/L Population Served by Systems with a Mean Concentration > 0.2 jjg/L Population Percent Population Percent Population Percent Population Percent ND 592,232 NE 1,662,774 669 0.040% 577 0.035% 577 0.035% 0 0.00% NH 949,308 NJ 4,346,209 NM 1,940,795 993 0.051 % 993 0.051 % 993 0.051 % 993 0.051 % NV 2,682,358 NY 10,481,222 550 0.005% 550 0.005% 550 0.005% 550 0.005% OH 756,016 OK 464 OR 3,432,424 PA 10,847,442 81 0.001 % 81 0.001 % 81 0.001 % 0 0.00% Rl 1,002,727 SC 3,623,380 SD 708,340 TN 1,168,508 TX 23,814,787 UT 2,752,741 VA 5,685,070 VT 386,948 WA 4,947,453 Wl 4,236,887 WV 1,499,884 WY 469,710 Total 229,832,890 11,659 0.005% 2,700 0.001% 2,461 0.001% 1,543 0.001% 1 Results are based on setting all non-detection results equal to % the MRL values in the SYR3 ICR dataset. 2 The new potential threshold of concern for this contaminant is based on the EQL. The EQL represents the potential quantitation capabilities below a PQL (USEPA, 2016d). SYR3 Occurrence Support Document B-58 December 2016 ------- B.7.3 Summary of Data A total of 137,081 analytical results from 38,625 PWSs in 50 states/entities were available for the SYR3 ICR Dataset for heptachlor epoxide. The Stage 2 analysis of occurrence in drinking water indicates that 2 (0.005 percent of all) systems (serving 0.001 percent of the population) had an estimated system mean concentration of heptachlor epoxide greater than the MCL concentration of 0.2 |ig/L. Both of the systems, serving a total of 1,543 people, with an estimated mean greater than the MCL concentration were ground water systems. Six systems, serving 2,461 people, had an estimated mean concentration greater than V2 the MCL (0.1 |ig/L). These six systems were all served by ground water. SYR3 Occurrence Support Document B-59 December 2016 ------- B.8 Hexachlorobenzene This chapter on hexachlorobenzene includes background information such as the regulatory history and a summary of monitoring requirements, as well as occurrence and exposure estimates in drinking water. All drinking water occurrence estimates are based on data from the National Compliance Monitoring Information Collection Request (ICR) Dataset for the Third Six-Year Review (the "SYR3 ICR Dataset"). B.8.1 Background The United States Environmental Protection Agency (EPA) published the current National Primary Drinking Water Regulations (NPDWR) for hexachlorobenzene on July 17, 1992 (57 FR 31776; USEPA, 1992). The NPDWR established a maximum contaminant level goal (MCLG) of zero based on a cancer classification of B2, probable human carcinogen. The NPDWR also established a maximum contaminant level (MCL) of 1 |ig/L based on analytical feasibility. Hexachlorobenzene is regulated as a synthetic organic chemical (SOC) in drinking water. All non-purchased community water systems (CWSs) and non-transient non-community water systems (NTNCWSs) are required to sample for SOCs. Waivers are available to all systems upon a favorable vulnerability assessment and/or prior analytical results. The maximum waiver period for SOCs is three years, but this waiver can be renewed indefinitely, if it is reconfirmed that the source is not vulnerable. All CWSs and NTNCWSs without an SOC waiver must collect four consecutive quarterly samples during the initial three-year compliance period.17 If all 4 samples are non-detections, then a system serving less than 3,300 persons may reduce its collection frequency to 1 sample during each consecutive compliance period; a system serving more than 3,300 persons may reduce its collection frequency to 2 quarterly samples within a 12-month period during each repeat compliance period. If a chemical is detected, the system must monitor quarterly until results are reliably and consistently below the MCL (minimum of two quarterly samples for ground water systems and four quarterly samples for surface water systems). If all quarterly samples are below the MCL, the system may return to annual sampling. If a chemical is detected at a level greater than the MCL, the system (whether ground water or surface water) must take quarterly samples until four consecutive quarters are below the MCL. If all quarterly samples are below the MCL, the system may return to annual sampling. B.8.2 Occurrence in Drinking Water The analysis of hexachlorobenzene occurrence presented in the following section is based on state compliance monitoring data from the SYR3 ICR Dataset. These data consist of 137,816 analytical results from 38,498 public water systems (PWSs) during the period from 2006 to 17 All new systems or systems using a new water source that began operation after January 22, 2004 must demonstrate compliance with the MCL within a period of time specified by the State. The system must also comply with the initial sampling frequencies specified by the State to ensure that a system can demonstrate compliance with the MCL. SYR3 Occurrence Support Document B-60 December 2016 ------- 2011. The number of sample results and systems vary by state, although the state datasets have been reviewed and checked to ensure adequacy of coverage and completeness. EPA used a two-stage analytical approach to estimate the national contaminant occurrence using the SYR3 ICR Dataset. In the "Stage 1 analysis," the occurrence data were analyzed to generate simple non-parametric estimates and descriptive statistics of national contaminant occurrence in public water systems. Simple counts were made of the number and percentage of systems and population served by systems with at least one compliance monitoring sample result greater than a specified concentration threshold. The Stage 1 analysis provides occurrence assessments that are more conservative and may be more reflective of potential acute exposure than the assessments from the Stage 2 analyses. Details on the Stage 1 analysis are presented in Section 6. Based on the evaluation of the health effects and analytical methods as part of the Six-Year Review protocol, EPA selected a set of contaminants, including hexachlorobenzene, for which Stage 2 analyses were warranted. The Stage 2 analysis estimates national contaminant occurrence by generating estimated long-term mean concentrations of contaminants for each system. This provides occurrence analyses that are less conservative than the Stage 1 analysis, since the Stage 2 analysis is based on estimated mean concentrations rather than on a single maximum concentration. Also, because the Stage 2 analyses generate long-term (multi-year) mean concentration estimates for contaminant occurrence at systems, the analyses can support assessments of population served by systems with detections or potential exposure assessments that may be more reflective of potential chronic exposure than the assessments from the Stage 1 analyses. For the Stage 2 analyses, system arithmetic means were calculated using all sample detection records and all non-detection records. Two different substitution values -zero and 1/2 the minimum reporting level (MRL) value- were used to replace each non-detection record. (The national modal MRL for hexachlorobenzene in the dataset is 0.04 |ig/L.) Two arithmetic mean hexachlorobenzene concentrations were calculated at each system using the zero, V2 MRL and full MRL substitution values. These mean calculations were performed for all systems with hexachlorobenzene data in the SYR3 ICR dataset. Then, the percentages of all systems with a mean concentration greater than each threshold were calculated. For hexachlorobenzene, EPA generated Stage 2 occurrence estimates relative to the MCL, twice the estimated quantitation level (EQL) and the EQL. Stage 2 Occurrence Estimates Stage 2 analyses for hexachlorobenzene are summarized in this section. Occurrence estimates were generated relative to the following thresholds: 1 |ig/L (the MCL), 0.2 |ig/L (two times the EQL) and 0.1 |ig/L (the EQL). The EQL represents the potential quantitation capabilities below SYR3 Occurrence Support Document B-61 December 2016 ------- a practical quantitation level (PQL).18 For more information on the new potential thresholds of concern used in the SYR3 Stage 2 analyses, refer to USEPA (2016d) and (2016e). Exhibit B-29 presents the system-level Stage 2 analysis of estimated mean concentrations for hexachlorobenzene occurrence in drinking water. Exhibit B-30 presents similar information based on population served by the systems. Based on the Stage 2 analyses, no systems had an estimated system mean greater than the MCL concentration of 1 |ig/L. Six systems, serving 8,703 people, had an estimated system mean greater than the EQL of 0.1 |ig/L. Exhibit B-29: Hexachlorobenzene Stage 2 Analysis - Summary of Systems with a Mean Threshold Exceedance Source Water Type (Number of Systems) Threshold Number of Systems with Mean Concentrations That Are Greater Than the Threshold Percent of Systems with Mean Concentrations That Are Greater Than the Threshold Non-detect values = 1/2 MRL Non-detect values = 0 Non-detect values = 1/2 MRL Non-detect values = 0 Ground Water (35,255) > 1 MQ/L 0 0 0.000% 0.000% > 0.2 |jg/L 3 3 0.009% 0.009% >0.1 |jg/L1 6 5 0.017% 0.014% Surface Water (3,243) > 1 mq/l 0 0 0.000% 0.000% > 0.2 |jg/L 0 0 0.000% 0.000% >0.1 |jg/L1 0 0 0.000% 0.000% Combined Ground & Surface Water (38,498) > 1 mq/l 0 0 0.000% 0.000% > 0.2 |jg/L 3 3 0.008% 0.008% >0.1 |jg/L1 6 5 0.016% 0.013% 1 The new potential threshold of concern for this contaminant is based on the EQL. The EQL represents the potential quantitation capabilities below a PQL (USEPA, 2016d). 18 When it is not possible to measure concentrations at the MCLG level, EPA often bases the MCL on an analytical feasibility level, known as a PQL. However, analytical feasibility can improve over time. As part of the Six-Year Review process, EPA evaluates whether new information regarding quantitation shows that PQLs may be reduced. The EQL represents quantitation capabilities below a PQL (USEPA, 2016d). The EQL is the threshold used to evaluate occurrence and exposure for the Stage 2 analyses. SYR3 Occurrence Support Document B-62 December 2016 ------- Exhibit B-30: Hexachlorobenzene Stage 2 Analysis - Summary of Population Served by Systems with a Mean Threshold Exceedance Source Water Type (Population Served by Systems) Threshold Population Served by Systems with Mean Concentrations That Are Greater Than the Threshold Percent of Population Served by Systems with Mean Concentrations That Are Greater Than the Threshold Non-detect values = 1/2 MRL Non-detect values = 0 Non-detect values = 1/2 MRL Non-detect values = 0 Ground Water (92,988,313) > 1 Mg/L 0 0 0.000% 0.000% > 0.2 |jg/L 7,546 7,546 0.008% 0.008% >0.1 |jg/L1 8,703 8,589 0.009% 0.009% Surface Water (137,209,655) > 1 mq/l 0 0 0.000% 0.000% > 0.2 |jg/L 0 0 0.000% 0.000% >0.1 |jg/L1 0 0 0.000% 0.000% Combined Ground & Surface Water (230,197,968) > 1 mq/l 0 0 0.000% 0.000% > 0.2 |jg/L 7,546 7,546 0.003% 0.003% >0.1 |jg/L1 8,703 8,589 0.004% 0.004% 1 The new potential threshold of concern for this contaminant is based on the EQL. The EQL represents the potential quantitation capabilities below a PQL (USEPA, 2016d). Data for hexachlorobenzene were available from 50 states/entities. Four states did not submit data for use in the Six-Year Review (Colorado, Delaware, Georgia and Mississippi). Although the States of Colorado and Mississippi did not provide data for any contaminants for the SYR3 ICR Dataset, these states are included in the table below because a handful of tribal water systems located within these two states did submit hexachlorobenzene data. Exhibit B-31 presents the total number of systems in each state that submitted data for hexachlorobenzene. In addition, the geographic distribution of hexachlorobenzene occurrence in drinking water is illustrated by showing states with systems with a mean concentration greater than the EQL, two times the EQL and MCL concentrations. (Note: Only the V2 MRL substitution results are presented in this exhibit.) No systems had estimated mean concentrations greater than the MCL. Six systems in five different states had an estimated mean concentration greater than the EQL of 0.1 |ig/L. Exhibit B-31: Hexachlorobenzene Stage 2 Analysis - Summary of Systems with a Mean Threshold Exceedance by State12 State Total Number of Systems Systems with a Mean Concentration > 0.1 mq/l3 Systems with a Mean Concentration > 0.2 ng/L Systems with a Mean Concentration > 1 mq/l Number Percent Number Percent Number Percent AK 10 AL 383 SYR3 Occurrence Support Document B-63 December 2016 ------- State Total Number of Systems Systems with a Mean Concentration > 0.1 mq/l3 Systems with a Mean Concentration > 0.2 Mg/L Systems with a Mean Concentration > 1 mq/l Number Percent Number Percent Number Percent AR 459 AS 11 AZ 869 CA 1,317 2 0.152% 1 0.076% 0 0.00% CO 1 CT 1,135 DC 1 FL 2,090 HI 112 IA 3 ID 522 IL 1,261 IN 1,213 KS 87 KY 225 LA 1,102 1 0.091% 1 0.091% 0 0.00% MA 565 MD 881 ME 173 Ml 2,439 MN 920 MO 1,332 MS 5 MT 857 NC 2,348 ND 23 NE 703 NH 1,146 NJ 82 NM 718 1 0.139% 0 0.00% 0 0.00% NV 312 SYR3 Occurrence Support Document B-64 December 2016 ------- State Total Number of Systems Systems with a Mean Concentration > 0.1 mq/l3 Systems with a Mean Concentration > 0.2 \iglL Systems with a Mean Concentration > 1 mq/l Number Percent Number Percent Number Percent NY 2,123 1 0.047% 1 0.047% 0 0.00% OH 34 OK 1 OR 1,120 PA 1,049 Rl 103 SC 497 SD 269 TN 6 TX 4,422 1 0.023% 0 0.000% 0 0.00% UT 428 VA 254 VT 382 WA 1,994 Wl 1,914 WV 279 WY 318 Total 38,498 6 0.016% 3 0.008% 0 0.000% 1 Results are based on setting all non-detection results equal to % the MRL values in the SYR3 ICR dataset. 2 Blank cells within the table indicate that there were no systems with a mean concentration that exceeded either threshold. 3 The new potential threshold of concern for this contaminant is based on the EQL. The EQL represents the potential quantitation capabilities below a PQL (USEPA, 2016d). Exhibit B-32 presents the population served by systems with a mean concentration greater than the MCL concentration by state. The total population served by systems in each state that submitted data for hexachlorobenzene is presented, as well. As described above, no systems had estimated mean concentrations greater than the MCL. Six systems, serving 8,703 people, had an estimated mean concentration greater than the EQL of 0.1 |ig/L. SYR3 Occurrence Support Document B-65 December 2016 ------- Exhibit B-32: Hexachlorobenzene Stage 2 Analysis - Summary of Population Served by Systems with a Mean Threshold Exceedance by State12 State Total Population Served by Systems Population Served by Systems with a Mean Concentration > 0.1 mq/l3 Population Served by Systems with a Mean Concentration > 0.2 Mg/L Population Served by Systems with a Mean Concentration > 1 mq/l Number Percent Number Percent Number Percent AK 39,878 AL 5,333,035 AR 2,635,934 AS 62,196 AZ 6,471,242 CA 36,681,076 130 0.000% 80 0.000% 0 0.000% CO 2,020 CT 2,882,395 DC 761,124 FL 18,945,034 HI 1,479,717 IA 166,302 ID 1,052,952 IL 10,925,340 IN 5,017,598 KS 1,817,722 KY 4,225,473 LA 4,966,772 6,916 0.139% 6,916 0.139% 0 0.000% MA 9,164,636 MD 4,939,436 ME 367,408 Ml 7,221,983 MN 3,752,545 MO 5,233,314 MS 6,176 MT 845,294 NC 7,832,371 ND 66,229 SYR3 Occurrence Support Document B-66 December 2016 ------- State Total Population Served by Systems Population Served by Systems with a Mean Concentration > 0.1 mq/l3 Population Served by Systems with a Mean Concentration > 0.2 \iglL Population Served by Systems with a Mean Concentration > 1 mq/l Number Percent Number Percent Number Percent NE 1,662,774 NH 949,308 NJ 4,366,309 NM 1,940,795 993 0.051% 0 0.000% 0 0.000% NV 2,688,765 NY 10,481,573 550 0.005% 550 0.005% 0 0.000% OH 758,784 OK 464 OR 3,432,479 PA 10,854,480 Rl 1,003,245 SC 3,623,380 SD 708,340 TN 1,168,508 TX 23,814,787 114 0.000% 0 0.000% 0 0.000% UT 2,752,741 VA 5,685,070 VT 387,157 WA 4,949,076 Wl 4,236,887 WV 1,368,134 WY 469,710 Total 230,197,968 8,703 0.004% 7,546 0.003% 0 0.000% 1 Results are based on setting all non-detection results equal to % the MRL values in the SYR3 ICR dataset. 2 Blank cells within the table indicate that there were no systems with a mean concentration that exceeded either threshold. 3 The new potential threshold of concern for this contaminant is based on the EQL. The EQL represents the potential quantitation capabilities below a PQL (USEPA, 2016d). B.8.3 Summary of Data A total of 137,816 analytical results from 38,498 PWSs in 50 states/entities were available in the SYR3 ICR Dataset for hexachlorobenzene. The Stage 2 analysis of occurrence in drinking water indicated that no systems had an estimated system mean concentration of hexachlorobenzene SYR3 Occurrence Support Document B-67 December 2016 ------- greater than the MCL concentration of 1 |ig/L. Six systems had an estimated mean concentration greater than the EQL of 0.1 |ig/L. SYR3 Occurrence Support Document B-68 December 2016 ------- B.9 Hexachlorocyclopentadiene This chapter on hexachlorocyclopentadiene includes background information such as the regulatory history and a summary of monitoring requirements, as well as occurrence and exposure estimates in drinking water. All drinking water occurrence estimates are based on data from the National Compliance Monitoring Information Collection Request (ICR) Dataset for the Third Six-Year Review (the "SYR3 ICR Dataset"). B.9.1 Background The United States Environmental Protection Agency (EPA) published the current National Primary Drinking Water Regulations (NPDWR) for hexachlorocyclopentadiene on July 17, 1992 (57 FR 31776; USEPA, 1992). The NPDWR established a maximum contaminant level goal (MCLG) and a maximum contaminant level (MCL) of 50 |ig/L. EPA based the MCLG on a reference dose (RfD) of 7 |ig/kg-day (0.007 mg/kg-day) and a cancer classification of D, not classifiable as to human carcinogenicity. Hexachlorocyclopentadiene is regulated as a synthetic organic chemical (SOC) in drinking water. All non-purchased community water systems (CWSs) and non-transient non-community water systems (NTNCWSs) are required to sample for SOCs. Waivers are available to all systems upon a favorable vulnerability assessment and/or prior analytical results. The maximum waiver period for SOCs is three years, but this waiver can be renewed indefinitely, if it is reconfirmed that the source is not vulnerable. All CWSs and NTNCWSs without an SOC waiver must collect four consecutive quarterly samples during the initial three-year compliance period.19 If all 4 samples are non-detections, then a system serving less than 3,300 people may reduce its collection frequency to 1 sample during each consecutive compliance period; a system serving more than 3,300 people may reduce its collection frequency to 2 quarterly samples within a 12-month period during each repeat compliance period. If a chemical is detected, the system must monitor quarterly until results are reliably and consistently below the MCL (minimum of two quarterly samples for ground water systems and four quarterly samples for surface water systems). If all quarterly samples are below the MCL, the system may return to annual sampling. If a chemical is detected at a level greater than the MCL, the system (whether ground water or surface water) must take quarterly samples until four consecutive quarters are below the MCL. If all quarterly samples are below the MCL, the system may return to annual sampling. B.9.2 Occurrence in Drinking Water The analysis of hexachlorocyclopentadiene occurrence presented in the following section is based on state compliance monitoring data from the SYR3 ICR Dataset. These data consist of 140,004 analytical results from 38,743 public water systems (PWSs) during the period from 19 All new systems or systems using a new water source that began operation after January 22, 2004 must demonstrate compliance with the MCL within a period of time specified by the State. The system must also comply with the initial sampling frequencies specified by the State to ensure that a system can demonstrate compliance with the MCL. SYR3 Occurrence Support Document B-69 December 2016 ------- 2006 to 2011. The number of sample results and systems vary by state, although the state datasets have been reviewed and checked to ensure adequacy of coverage and completeness. EPA used a two-stage analytical approach to estimate the national contaminant occurrence using the SYR3 ICR Dataset. In the "Stage 1 analysis," the occurrence data were analyzed to generate simple non-parametric estimates and descriptive statistics of national contaminant occurrence in public water systems. Simple counts were made of the number and percentage of systems and population served by systems with at least one compliance monitoring sample result greater than a specified concentration threshold. The Stage 1 analysis provides occurrence assessments that are more conservative and may be more reflective of potential acute exposure than the assessments from the Stage 2 analyses. Details on the Stage 1 analysis are presented in Section 6. Based on the evaluation of the health effects and analytical methods as part of the Six-Year Review protocol, EPA selected a set of contaminants, including hexachlorocyclopentadiene, for which Stage 2 analyses were warranted. The Stage 2 analysis estimates national contaminant occurrence by generating estimated long-term mean concentrations of contaminants for each system. This provides occurrence analyses that are less conservative than the Stage 1 analysis, since the Stage 2 analysis is based on estimated mean concentrations rather than on a single maximum concentration. Also, because the Stage 2 analyses generate long-term (multi-year) mean concentration estimates for contaminant occurrence at systems, the analyses can support assessments of population served by systems with detections or potential exposure assessments that may be more reflective of potential chronic exposure than the assessments from the Stage 1 analyses. For the Stage 2 analyses, system arithmetic means were calculated using all sample detection records and all non-detection records. Three different substitution values -zero, V2 the minimum reporting level (MRL) value and the full MRL value- were used to replace each non-detection record. (The national modal MRL for hexachlorocyclopentadiene in the dataset is 0.1 |ig/L.) Three arithmetic mean hexachlorocyclopentadiene concentrations were calculated at each system using the zero, V2 MRL and full MRL substitution values. These mean calculations were performed for all systems with hexachlorocyclopentadiene data in the SYR3 ICR dataset. Then, the percentages of all systems with a mean concentration greater than each threshold were calculated. For hexachlorocyclopentadiene, since there were no analytical method limitations at the potential MCLG, EPA generated Stage 2 occurrence estimates relative to the MCL and the potential MCLG. Stage 2 Occurrence Estimates Stage 2 analyses for hexachlorocyclopentadiene are summarized in this section. Occurrence estimates were generated relative to the following thresholds: 50 |ig/L (the MCL) and 40 |ig/L (the potential MCLG). The potential MCLG is due to changes in the RfD based on new health effects information. Since the practical quantitation level (PQL) for hexachlorocyclopentadiene is less than the possible MCLG, EPA designated the possible MCLG as the threshold for the occurrence analysis. For more information on the new potential thresholds of concern used in the SYR3 Stage 2 analyses, refer to USEPA (2016d) and (2016e). SYR3 Occurrence Support Document B-70 December 2016 ------- Exhibit B-33 presents the system-level Stage 2 analysis of estimated mean concentrations for hexachlorocyclopentadiene occurrence in drinking water. Exhibit B-34 presents similar information based on population served by the systems. Based on the Stage 2 analyses, no systems had estimated system means greater than the MCL concentration of 50 |ig/L or the potential MCLG concentration of 40 |ig/L. Exhibit B-33: Hexachlorocyclopentadiene Stage 2 Analysis - Summary of Systems with a Mean Threshold Exceedance Source Water Type (Number of Systems) Threshold Number of Systems with Mean Concentrations That Are Greater Than the Threshold Percent of Systems with Mean Concentrations That Are Greater Than the Threshold Non-detect values = MRL Non-detect values = 1/2 MRL Non-detect values = 0 Non-detect values = MRL Non-detect values = 1/2 MRL Non- detect values = 0 Ground Water (35,479) > 50 |jg/L 0 0 0 0.000% 0.000% 0.000% > 40 |jg/L1 0 0 0 0.000% 0.000% 0.000% Surface Water (3,264) > 50 |jg/L 0 0 0 0.000% 0.000% 0.000% > 40 |jg/L1 0 0 0 0.000% 0.000% 0.000% Combined Ground & Surface Water (38,743) > 50 |jg/L 0 0 0 0.000% 0.000% 0.000% > 40 |jg/L1 0 0 0 0.000% 0.000% 0.000% 1 The new potential threshold of concern for this contaminant is due to changes in the RfD based on new health effects information. Exhibit B-34: Hexachlorocyclopentadiene Stage 2 Analysis - Summary of Population Served by Systems with a Mean Threshold Exceedance Source Water Type (Population Served by Systems) Threshold Population Served by Systems with Mean Concentrations That Are Greater Than the Threshold Percent of Population Served by Systems with Mean Concentrations That Are Greater Than the Threshold Non-detect values = MRL Non-detect values = 1/2 MRL Non-detect values = 0 Non-detect values = MRL Non-detect values = 1/2 MRL Non-detect values = 0 Ground Water (92,695,520) > 50 |jg/L 0 0 0 0.000% 0.000% 0.000% > 40 |jg/L1 0 0 0 0.000% 0.000% 0.000% Surface Water (137,207,044) > 50 |jg/L 0 0 0 0.000% 0.000% 0.000% > 40 |jg/L1 0 0 0 0.000% 0.000% 0.000% SYR3 Occurrence Support Document B-71 December 2016 ------- Source Water Type (Population Served by Systems) Threshold Population Served by Systems with Mean Concentrations That Are Greater Than the Threshold Percent of Population Served by Systems with Mean Concentrations That Are Greater Than the Threshold Non-detect values = MRL Non-detect values = 1/2 MRL Non-detect values = 0 Non-detect values = MRL Non-detect values = 1/2 MRL Non-detect values = 0 Combined Ground & Surface Water (229,902,564) > 50 |jg/L 0 0 0 0.000% 0.000% 0.000% > 40 |jg/L1 0 0 0 0.000% 0.000% 0.000% 1 The new potential threshold of concern for this contaminant is due to changes in the RfD based on new health effects information. Data for hexachlorocyclopentadiene were available from 50 states/entities. Four states did not submit data for use in the Six-Year Review (Colorado, Delaware, Georgia and Mississippi). Although the States of Colorado and Mississippi did not provide data for any contaminants for the SYR3 ICR Dataset, these states are included in the count of 50 states because a handful of tribal water systems located within these 2 states did submit hexachlorocyclopentadiene data. Exhibit B-35 presents the total number of systems in each state that submitted data for hexachlorocyclopentadiene. In addition, the geographic distribution of hexachlorocyclopentadiene occurrence in drinking water is illustrated by showing states with systems with a mean concentration greater than the potential MCLG and the MCL concentrations. (Note: Only the V2 MRL substitution results are presented in this exhibit.) As is described above, no systems had estimated system means greater than the MCL concentration of 50 |ig/L or the potential MCLG concentration of 40 |ig/L. Exhibit B-35: Hexachlorocyclopentadiene Stage 2 Analysis - Summary of Systems with a Mean Threshold Exceedance by State12 State Total Number of Systems Systems with a Mean Concentration > 40 jjg/L3 Systems with a Mean Concentration > 50 jjg/L Number Percent Number Percent AK 10 AL 383 AR 459 AS 11 AZ 869 CA 1,318 CO 1 CT 1,135 DC 1 FL 2,089 HI 112 SYR3 Occurrence Support Document B-72 December 2016 ------- State Total Number of Systems Systems with a Mean Concentration > 40 jjg/L3 Systems with a Mean Concentration > 50 jjg/L Number Percent Number Percent IA 3 ID 521 IL 1,261 IN 1,214 KS 86 KY 225 LA 1,102 MA 566 MD 881 ME 173 Ml 2,439 MN 920 MO 1,332 MS 5 MT 857 NC 2,348 ND 23 NE 703 NH 1,146 NJ 38 NM 718 NV 312 NY 2,123 OH 34 OK 1 OR 1,120 PA 1,317 Rl 103 SC 497 SD 269 TN 6 SYR3 Occurrence Support Document B-73 December 2016 ------- State Total Number of Systems Systems with a Mean Concentration > 40 jjg/L3 Systems with a Mean Concentration > 50 jjg/L Number Percent Number Percent TX 4,420 UT 428 VA 254 VT 382 WA 1,994 Wl 1,914 WV 302 WY 318 Total 38,743 0 0.00% 0 0.00% 1 Results are based on setting all non-detection results equal to % the MRL values in the SYR3 ICR dataset. 2 Blank cells within the table indicate that there were no systems with a mean concentration that exceeded either threshold. 3 The new potential threshold of concern for this contaminant is due to changes in the RfD based on new health effects information. Exhibit B-36 presents the population served by systems with a mean concentration greater than the MCL concentration by state. The total population served by systems in each state that submitted data for hexachlorocyclopentadiene is presented, as well. No systems had estimated system means greater than the MCL concentration of 50 |ig/L or the potential MCLG concentration of 40 |ig/L. Exhibit B-36: Hexachlorocyclopentadiene Stage 2 Analysis - Summary of Population Served by Systems with a Mean Threshold Exceedance by State12 State Total Population Population Served by Systems with a Mean Concentration > 40 jjg/L3 Population Served by Systems with a Mean Concentration > 50 Mg/L Population Percent Population Percent AK 39,878 AL 5,333,035 AR 2,635,934 AS 62,196 AZ 6,471,242 CA 36,666,576 CO 2,020 CT 2,882,395 DC 761,124 SYR3 Occurrence Support Document B-74 December 2016 ------- State Total Population Population Served by Systems with a Mean Concentration > 40 jjg/L3 Population Served by Systems with a Mean Concentration > 50 Mg/L Population Percent Population Percent FL 18,944,969 HI 1,479,717 IA 166,302 ID 1,052,868 IL 10,925,340 IN 5,032,598 KS 1,685,226 KY 4,225,473 LA 4,966,772 MA 9,164,737 MD 4,939,436 ME 367,408 Ml 7,221,983 MN 3,752,545 MO 5,233,314 MS 6,176 MT 845,294 NC 7,832,371 ND 66,229 NE 1,662,774 NH 949,308 NJ 4,027,741 NM 1,940,795 NV 2,688,765 NY 10,481,569 OH 758,784 OK 464 OR 3,432,479 PA 10,898,082 Rl 1,003,245 SYR3 Occurrence Support Document B-75 December 2016 ------- State Total Population Population Served by Systems with a Mean Concentration > 40 jjg/L3 Population Served by Systems with a Mean Concentration > 50 Mg/L Population Percent Population Percent SC 3,623,380 SD 708,340 TN 1,168,508 TX 23,814,647 UT 2,752,741 VA 5,685,070 VT 387,157 WA 4,949,076 Wl 4,236,887 WV 1,499,884 WY 469,710 Total 229,902,564 0 0.00% 0 0.00% 1 Results are based on setting all non-detection results equal to % the MRL values in the SYR3 ICR dataset. 2 Blank cells within the table indicate that there were no systems with a mean concentration that exceeded either threshold. 3 The new potential threshold of concern for this contaminant is due to changes in the RfD based on new health effects information. B.9.3 Summary of Data A total of 140,004 analytical results from 38,743 PWSs in 50 states/entities were available in the SYR3 ICR Dataset for hexachlorocyclopentadiene. The Stage 2 analysis of occurrence in drinking water indicated that zero systems had an estimated system mean concentration of hexachlorocyclopentadiene greater than the MCL concentration (50 |ig/L) or the potential MCLG (40 |ig/L). SYR3 Occurrence Support Document B-76 December 2016 ------- B.10 Methoxychlor This chapter on methoxychlor includes background information such as the regulatory history and a summary of monitoring requirements, as well as occurrence and exposure estimates in drinking water. All drinking water occurrence estimates are based on data from the National Compliance Monitoring Information Collection Request (ICR) Dataset for the Third Six-Year Review (the "SYR3 ICR Dataset"). B.10.1 Background The United States Environmental Protection Agency (EPA) published the current National Primary Drinking Water Regulations (NPDWR) for methoxychlor on January 30, 1991 (56 FR 3526; USEPA, 1991a). The NPDWR established a maximum contaminant level goal (MCLG) and a maximum contaminant level (MCL) of 40 |ig/L. The Agency based the MCLG on a reference dose (RfD) of 5 |ig/kg-day (0.005 mg/kg-day) and a cancer classification of D, not classifiable as to human carcinogenicity. Methoxychlor is regulated as a synthetic organic chemical (SOC) in drinking water. All non- purchased community water systems (CWSs) and non-transient non-community water systems (NTNCWSs) are required to sample for SOCs. Waivers are available to all systems upon a favorable vulnerability assessment and/or prior analytical results. The maximum waiver period for SOCs is three years, but this waiver can be renewed indefinitely, if it is reconfirmed that the source is not vulnerable. All CWSs and NTNCWSs without an SOC waiver must collect four consecutive quarterly samples during the initial three-year compliance period.20 If all 4 samples are non-detections, then a system serving less than 3,300 persons may reduce its collection frequency to 1 sample during each consecutive compliance period; a system serving more than 3,300 persons may reduce its collection frequency to 2 quarterly samples within a 12-month period during each repeat compliance period. If a chemical is detected, the system must monitor quarterly until results are reliably and consistently below the MCL (minimum of two quarterly samples for ground water systems and four quarterly samples for surface water systems). If all quarterly samples are below the MCL, the system may return to annual sampling. If a chemical is detected at a level greater than the MCL, the system (whether ground water or surface water) must take quarterly samples until four consecutive quarters are below the MCL. If all quarterly samples are below the MCL, the system may return to annual sampling. B.10.2 Occurrence in Drinking Water The analysis of methoxychlor occurrence presented in the following section is based on state compliance monitoring data from the SYR3 ICR Dataset. These data consist of 139,744 analytical results from 39,187 public water systems (PWSs) during the period from 2006 to 20 All new systems or systems using a new water source that began operation after January 22, 2004 must demonstrate compliance with the MCL within a period of time specified by the State. The system must also comply with the initial sampling frequencies specified by the State to ensure that a system can demonstrate compliance with the MCL. SYR3 Occurrence Support Document B-77 December 2016 ------- 2011. The number of sample results and systems vary by state, although the state datasets have been reviewed and checked to ensure adequacy of coverage and completeness. EPA used a two-stage analytical approach to estimate the national contaminant occurrence using the SYR3 ICR Dataset. In the "Stage 1 analysis," the occurrence data were analyzed to generate simple non-parametric estimates and descriptive statistics of national contaminant occurrence in public water systems. Simple counts were made of the number and percentage of systems and population served by systems with at least one compliance monitoring sample result greater than a specified concentration threshold. The Stage 1 analysis provides occurrence assessments that are more conservative and may be more reflective of potential acute exposure than the assessments from the Stage 2 analyses. Details on the Stage 1 analysis are presented in Section 6. Based on the evaluation of the health effects and analytical methods as part of the Six-Year Review protocol, EPA selected a set of contaminants, including methoxychlor, for which Stage 2 analyses were warranted. The Stage 2 analysis estimates national contaminant occurrence by generating estimated long-term mean concentrations of contaminants for each system. This provides occurrence analyses that are less conservative than the Stage 1 analysis, since the Stage 2 analysis is based on estimated mean concentrations rather than on a single maximum concentration. Also, because the Stage 2 analyses generate long-term (multi-year) mean concentration estimates for contaminant occurrence at systems, the analyses can support assessments of population served by systems with detections or potential exposure assessments that may be more reflective of potential chronic exposure than the assessments from the Stage 1 analyses. For the Stage 2 analyses, system arithmetic means were calculated using all sample detection records and all non-detection records. Three different substitution values -zero, V2 the minimum reporting level (MRL) value and the full MRL value- were used to replace each non-detection record. (The national modal MRL for methoxychlor in the dataset is 0.1 |ig/L.) Three arithmetic mean methoxychlor concentrations were calculated at each system using the zero, V2 MRL and full MRL substitution values. These mean calculations were performed for all systems with methoxychlor data in the SYR3 ICR dataset. Then, the percentages of all systems with a mean concentration greater than each threshold were calculated. For methoxychlor, EPA generated Stage 2 occurrence estimates relative to the MCL, twice the estimated quantitation level (EQL) and the EQL. Stage 2 Occurrence Estimates Stage 2 analyses for methoxychlor are summarized in this section. Occurrence estimates were generated relative to the following thresholds: 40 |ig/L (the MCL), 2 |ig/L (two times the EQL) and 1 |ig/L (the EQL). The EQL represents the potential quantitation capabilities below a SYR3 Occurrence Support Document B-78 December 2016 ------- practical quantitation level (PQL).21 For more information on the new potential thresholds of concern used in the SYR3 Stage 2 analyses, refer to USEPA (2016d) and (2016e). Exhibit B-37 presents the system-level Stage 2 analysis of estimated mean concentrations for methoxychlor occurrence in drinking water. Exhibit B-38 presents similar information based on population served by the systems. Based on the Stage 2 analyses, no systems had an estimated system mean greater than the MCL concentration of 40 |ig/L. One system, serving 993 people, had an estimated system mean greater than the EQL of 1 |ig/L. Exhibit B-37: Methoxychlor Stage 2 Analysis - Summary of Systems with a Mean Threshold Exceedance Source Water Type (Number of Systems) Threshold Number of Systems with Mean Concentrations That Are Greater Than the Threshold Percent of Systems with Mean Concentrations That Are Greater Than the Threshold Non-detect values = MRL Non-detect values = 1/2 MRL Non-detect values = 0 Non-detect values = MRL Non-detect values = 1/2 MRL Non-detect values = 0 Ground Water (35,867) > 40 |jg/L 0 0 0 0.000% 0.000% 0.000% > 2 |jg/L 1 1 1 0.003% 0.003% 0.003% > 1 |jg/L1 1 1 1 0.003% 0.003% 0.003% Surface Water (3,320) > 40 |jg/L 0 0 0 0.000% 0.000% 0.000% > 2 |jg/L 0 0 0 0.000% 0.000% 0.000% > 1 |jg/L1 0 0 0 0.000% 0.000% 0.000% Combined Ground & Surface Water (39,187) > 40 |jg/L 0 0 0 0.000% 0.000% 0.000% > 2 |jg/L 1 1 1 0.003% 0.003% 0.003% > 1 |jg/L1 1 1 1 0.003% 0.003% 0.003% 1 The new potential threshold of concern for this contaminant is based on the EQL. The EQL represents the potential quantitation capabilities below a PQL (USEPA, 2016d). 21 When it is not possible to measure concentrations at the MCLG level, EPA often bases the MCL on an analytical feasibility level, known as a PQL. However, analytical feasibility can improve over time. As part of the Six-Year Review process, EPA evaluates whether new information regarding quantitation shows that PQLs may be reduced. The EQL represents quantitation capabilities below a PQL (USEPA, 2016d). The EQL is the threshold used to evaluate occurrence and exposure for the Stage 2 analyses. SYR3 Occurrence Support Document B-79 December 2016 ------- Exhibit B-38: Methoxychlor Stage 2 Analysis - Summary of Population Served by Systems with a Mean Threshold Exceedance Source Water Type (Population Served by Systems) Threshold Population Served by Systems with Mean Concentrations That Are Greater Than the Threshold Percent of Population Served by Systems with Mean Concentrations That Are Greater Than the Threshold Non-detect values = MRL Non-detect values = 1/2 MRL Non-detect values = 0 Non-detect values = MRL Non-detect values = 1/2 MRL Non-detect values = 0 Ground Water (92,942,500) > 40 |jg/L 0 0 0 0.000% 0.000% 0.000% > 2 |jg/L 993 993 993 0.001 % 0.001% 0.001% > 1 |jg/L1 993 993 993 0.001 % 0.001% 0.001% Surface Water (140,088,461) > 40 |jg/L 0 0 0 0.000% 0.000% 0.000% > 2 |jg/L 0 0 0 0.000% 0.000% 0.000% > 1 |jg/L1 0 0 0 0.000% 0.000% 0.000% Combined Ground & Surface Water (233,030,961) > 40 |jg/L 0 0 0 0.0000% 0.0000% 0.0000% > 2 |jg/L 993 993 993 0.0004% 0.0004% 0.0004% > 1 |jg/L1 993 993 993 0.0004% 0.0004% 0.0004% 1 The new potential threshold of concern for this contaminant is based on the EQL. The EQL represents the potential quantitation capabilities below a PQL (USEPA, 2016d). Data for methoxychlor were available from 50 states/entities. Four states did not submit data for use in the Six-Year Review (Colorado, Delaware, Georgia and Mississippi). Although the States of Colorado and Mississippi did not provide data for any contaminants for the SYR3 ICR Dataset, these states are included in the table below because a handful of tribal water systems located within these two states did submit methoxychlor data. Exhibit B-39 presents the total number of systems in each state that submitted data for methoxychlor. In addition, the geographic distribution of methoxychlor occurrence in drinking water is illustrated by showing states with systems with a mean concentration greater than the EQL, two times the EQL and MCL concentrations. (Note: Only the V2 MRL substitution results are presented in this exhibit.) No systems had estimated mean concentrations greater than the MCL. One system in New Mexico had an estimated mean concentration greater than the EQL of l^g/L. SYR3 Occurrence Support Document B-80 December 2016 ------- Exhibit B-39: Methoxychlor Stage 2 Analysis - Summary of Systems with a Mean Threshold Exceedance by State12 State Total Number of Systems Systems with a Mean Concentration > 1 |ig/L3 Systems with a Mean Concentration > 2 |jg/L Systems with a Mean Concentration > 40 |jg/L Number Percent Number Percent Number Percent AK 13 AL 383 AR 459 AS 11 AZ 872 CA 1,327 CO 1 CT 1,137 DC 1 FL 2,088 HI 111 IA 8 ID 392 IL 1,468 IN 1,214 KS 87 KY 225 LA 1,102 MA 564 MD 881 ME 173 Ml 2,439 MN 920 MO 1,332 MS 5 MT 857 NC 2,348 ND 157 NE 703 SYR3 Occurrence Support Document B-81 December 2016 ------- State Total Number of Systems Systems with a Mean Concentration > 1 |ig/L3 Systems with a Mean Concentration > 2 |jg/L Systems with a Mean Concentration > 40 |jg/L Number Percent Number Percent Number Percent NH 1,146 NJ 42 NM 718 1 0.139% 1 0.139% 0 0.000% NV 311 NY 2,121 0 0.000% 0 0.000% 0 0.000% OH 228 OK 39 OR 1,119 PA 1,320 Rl 103 SC 497 SD 269 TN 6 TX 4,422 UT 428 0 0.000% 0 0.000% 0 0.000% VA 254 VT 380 WA 1,998 Wl 1,914 WV 276 WY 318 Total 39,187 1 0.003% 1 0.003% 0 0.000% 1 Results are based on setting all non-detection results equal to % the MRL values in the SYR3 ICR dataset. 2 Blank cells within the table indicate that there were no systems with a mean concentration that exceeded either threshold. 3 The new potential threshold of concern for this contaminant is based on the EQL. The EQL represents the potential quantitation capabilities below a PQL (USEPA, 2016d). Exhibit B-40 presents the population served by systems with a mean concentration greater than the MCL concentration by state. The total population served by systems in each state that submitted data for methoxychlor is presented, as well. As described above, no systems had estimated mean concentrations greater than the MCL. One system in New Mexico, serving 993 people, had an estimated mean concentration greater than the EQL of 1 |ig/L. SYR3 Occurrence Support Document B-82 December 2016 ------- Exhibit B-40: Methoxychlor Stage 2 Analysis - Summary of Population Served by Systems with a Mean Threshold Exceedance by State12 State Total Population Served by Systems Population Served by Systems with a Mean Concentration > 1 |ig/L3 Population Served by Systems with a Mean Concentration > 2 |jg/L Population Served by Systems with a Mean Concentration > 40 |jg/L Number Percent Number Percent Number Percent AK 40,300 AL 5,333,035 AR 2,635,934 AS 62,196 AZ 6,484,144 CA 36,060,067 CO 2,020 CT 2,925,135 DC 761,124 FL 18,944,904 HI 1,479,317 IA 301,990 ID 980,589 IL 10,998,526 IN 5,032,598 KS 1,817,722 KY 4,225,473 LA 4,966,772 MA 9,164,462 MD 4,939,436 ME 367,408 Ml 7,221,983 MN 3,752,545 MO 5,233,314 MS 6,176 MT 845,294 NC 7,832,371 ND 592,232 SYR3 Occurrence Support Document B-83 December 2016 ------- State Total Population Served by Systems Population Served by Systems with a Mean Concentration > 1 |ig/L3 Population Served by Systems with a Mean Concentration > 2 |jg/L Population Served by Systems with a Mean Concentration > 40 |jg/L Number Percent Number Percent Number Percent NE 1,662,774 NH 949,308 NJ 4,006,631 NM 1,940,795 993 0.051% 993 0.051% 0 0.000% NV 2,682,815 NY 10,481,222 0 0.000% 0 0.000% 0 0.000% OH 3,536,843 OK 152,140 OR 3,432,424 PA 10,900,135 Rl 1,003,245 SC 3,623,380 SD 708,340 TN 1,168,508 TX 23,814,787 UT 2,752,741 0 0.000% 0 0.000% 0 0.000% VA 5,685,070 VT 386,948 WA 4,947,604 Wl 4,236,887 WV 1,481,587 WY 469,710 Total 233,030,961 993 0.000% 993 0.000% 0 0.000% 1 Results are based on setting all non-detection results equal to % the MRL values in the SYR3 ICR dataset. 2 Blank cells within the table indicate that there were no systems with a mean concentration that exceeded either threshold. 3 The new potential threshold of concern for this contaminant is based on the EQL. The EQL represents the potential quantitation capabilities below a PQL (USEPA, 2016d). SYR3 Occurrence Support Document B-84 December 2016 ------- B.10.3 Summary of Data A total of 139,744 analytical results from 39,187 PWSs in 50 states/entities were available in the SYR3 ICR Dataset for methoxychlor. The Stage 2 analysis of occurrence in drinking water indicated that no systems had an estimated system mean concentration of methoxychlor greater than the MCL concentration of 40 |ig/L. The only system with an estimated mean concentration greater than the EQL of 1 |ig/L was a ground water system in New Mexico. SYR3 Occurrence Support Document B-85 December 2016 ------- B.ll Selenium This chapter on selenium includes background information such as the regulatory history and a summary of monitoring requirements, as well as occurrence and exposure estimates in drinking water. All drinking water occurrence estimates are based on data from the National Compliance Monitoring Information Collection Request (ICR) Dataset for the Third Six-Year Review (the "SYR3 ICR Dataset"). B.ll.l Background The United States Environmental Protection Agency (EPA) published the current National Primary Drinking Water Regulations (NPDWR) for selenium on January 30, 1991 (56 FR 3526; USEPA, 1991a). The NPDWR established a maximum contaminant level goal (MCLG) and a maximum contaminant level (MCL) of 50 |ig/L. EPA based the MCLG on a maximum safe intake22 of 400 |ig/person/day and a cancer classification of D, not classifiable as to human carcinogenicity. Selenium is regulated as an inorganic chemical (IOC) in drinking water. All community water systems (CWSs) and non-transient non-community water systems (NTNCWSs) are required to sample for the IOCs. The maximum waiver period for IOCs is one compliance cycle. During this cycle, the system must sample at least once. Ground water systems must sample once during the initial three-year compliance period. Surface water systems must sample annually during the initial three-year compliance period. If all analytical results are less than the MCL, and upon considering reported concentrations, degrees of variation in reported concentration and other factors which may affect contaminant concentration, a ground water and surface water system may be granted a waiver. If the results are greater than the MCL, the public water system (PWS) must take one sample per quarter until results are below the MCL (minimum of two quarterly samples for ground water systems and four quarterly samples for surface water systems).23 If all quarterly samples are reliably and consistently below the MCL, the system may continue at initial monitoring indefinitely until the state or EPA establishes an alternate schedule. B.11.2 Occurrence in Drinking Water The analysis of selenium occurrence presented in the following section is based on state compliance monitoring data from the SYR3 ICR Dataset. These data consist of 165,672 analytical results from 50,568 PWSs during the period from 2006 to 2011. The number of 22 The 400 ng/day safe level was based on data (Yang etal., 1989a and 1989b) that extrapolated from blood selenium levels to estimated dietary intake in the studied population. As described in USEPA (1991a), EPA partially considered selenium's status as a nutrient and did not use the typical procedure for deriving the MCLG. Hence, there is no specific reference to a reference dose (RiD) for selenium in the 1991 FR notice. After the publication of the regulation, IRIS (USEPA, 1991b) posted an RfD of 5 (ig/kg-day for selenium using the same data that are the basis of the regulation. 23 All new systems or systems using a new water source that began operation after January 22, 2004 must demonstrate compliance with the MCL within a period of time specified by the State. The system must also comply with the initial sampling frequencies specified by the State to ensure that a system can demonstrate compliance with the MCL. SYR3 Occurrence Support Document B-86 December 2016 ------- sample results and systems vary by state, although the state datasets have been reviewed and checked to ensure adequacy of coverage and completeness. EPA used a two-stage analytical approach to estimate the national contaminant occurrence using the SYR3 ICR Dataset. In the "Stage 1 analysis," the occurrence data were analyzed to generate simple non-parametric estimates and descriptive statistics of national contaminant occurrence in public water systems. Simple counts were made of the number and percentage of systems and population served by systems with at least one compliance monitoring sample result greater than a specified concentration threshold. The Stage 1 analysis provides occurrence assessments that are more conservative and may be more reflective of potential acute exposure than the assessments from the Stage 2 analyses. Details on the Stage 1 analysis are presented in Section 6. Based on the evaluation of the health effects and analytical methods as part of the Six-Year Review protocol, EPA selected a set of contaminants, including selenium, for which Stage 2 analyses were warranted. The Stage 2 analysis estimates national contaminant occurrence by generating estimated long-term mean concentrations of contaminants for each system. This provides occurrence analyses that are less conservative than the Stage 1 analysis, since the Stage 2 analysis is based on estimated mean concentrations rather than on a single maximum concentration. Also, because the Stage 2 analyses generate long-term (multi-year) mean concentration estimates for contaminant occurrence at systems, the analyses can support assessments of population served by systems with detections or potential exposure assessments that may be more reflective of potential chronic exposure than the assessments from the Stage 1 analyses. For the Stage 2 analyses, system arithmetic means were calculated using all sample detection records and all non-detection records. Three different substitution values -zero, V2 the minimum reporting level (MRL) value and the full MRL value- were used to replace each non-detection record. (The national modal MRL for selenium in the dataset is 5 |ig/L.) Three arithmetic mean selenium concentrations were calculated at each system using the zero, V2 MRL and full MRL substitution values. These mean calculations were performed for all systems with selenium data in the SYR3 ICR dataset. Then, the percentages of all systems with a mean concentration greater than each threshold were calculated. For selenium, since there were no analytical method limitations at the potential MCLG, EPA generated Stage 2 occurrence estimates relative to the MCL and the potential MCLG. Stage 2 Occurrence Estimates Stage 2 analyses for selenium are summarized in this section. Occurrence estimates were generated relative to the following thresholds: 50 |ig/L (the MCL) and 40 |ig/L (the potential MCLG). The potential MCLG is due to changes in the reference dose (RfD) based on new health effects information. Since the practical quantitation level (PQL) for selenium is less than the possible MCLG, EPA designated the possible MCLG as the threshold for the occurrence analysis. For more information on the new potential thresholds of concern used in the SYR3 Stage 2 analyses, refer to USEPA (2016d) and (2016e). Exhibit B-41 presents the system-level Stage 2 analysis of estimated mean concentrations for selenium occurrence in drinking water. Exhibit B-42 presents similar information based on population served by the systems. Based on the Stage 2 analyses using the V2 MRL substitution for non-detections, 31 systems (0.061 percent of all systems), serving 21,489 people, had an SYR3 Occurrence Support Document B-87 December 2016 ------- estimated system mean greater than the MCL concentration of 50 |ig/L. Forty-nine systems (0.097 percent of all systems), serving 135,685 people, had an estimated system mean greater than the potential MCLG concentration of 40 |ig/L. Exhibit B-41: Selenium Stage 2 Analysis - Summary of Systems with a Mean Threshold Exceedance Source Water Type (Number of Systems) Threshold Number of Systems with Mean Concentrations That Are Greater Than the Threshold Percent of Systems with Mean Concentrations That Are Greater Than the Threshold Non-detect values = MRL Non-detect values = 1/2 MRL Non-detect values = 0 Non-detect values = MRL Non-detect values = 1/2 MRL Non-detect values = 0 Ground Water (46,378) > 50 |jg/L 31 30 30 0.067% 0.065% 0.065% > 40 |jg/L1 49 48 48 0.106% 0.103% 0.103% Surface Water (4,190) > 50 |jg/L 1 1 1 0.024% 0.024% 0.024% > 40 |jg/L1 1 1 1 0.024% 0.024% 0.024% Combined Ground & Surface Water (50,568) > 50 |jg/L 32 31 31 0.063% 0.061 % 0.061 % > 40 |jg/L1 50 49 49 0.099% 0.097% 0.097% 1 The new potential threshold of concern for this contaminant is due to changes in the RfD based on new health effects information. Exhibit B-42: Selenium Stage 2 Analysis - Summary of Population Served by Systems with a Mean Threshold Exceedance Source Water Type (Population Served by Systems) Threshold Population Served by Systems with Mean Concentrations That Are Greater Than the Threshold Percent of Population Served by Systems with Mean Concentrations That Are Greater Than the Threshold Non- detect values = MRL Non-detect values = 1/2 MRL Non- detect values = 0 Non-detect values = MRL Non-detect values = 1/2 MRL Non- detect values = 0 Ground Water (105,367,702) > 50 |jg/L 21,101 21,039 21,039 0.020% 0.020% 0.020% > 40 |jg/L1 135,421 135,235 135,235 0.129% 0.128% 0.128% Surface Water (149,060,594) > 50 |jg/L 450 450 450 0.000% 0.000% 0.000% > 40 |jg/L1 450 450 450 0.000% 0.000% 0.000% SYR3 Occurrence Support Document B-88 December 2016 ------- Source Water Type (Population Served by Systems) Threshold Population Served by Systems with Mean Concentrations That Are Greater Than the Threshold Percent of Population Served by Systems with Mean Concentrations That Are Greater Than the Threshold Non- detect values = MRL Non-detect values = 1/2 MRL Non- detect values = 0 Non-detect values = MRL Non-detect values = 1/2 MRL Non- detect values = 0 Combined Ground & Surface Water (254,428,296) > 50 |jg/L 21,551 21,489 21,489 0.008% 0.008% 0.008% > 40 |jg/L1 135,871 135,685 135,685 0.053% 0.053% 0.053% 1 The new potential threshold of concern for this contaminant is due to changes in the RfD based on new health effects information. Data for selenium were available from 49 states/entities. Four states did not submit data for use in the Six-Year Review (Colorado, Delaware, Georgia and Mississippi). Although the State of Mississippi did not provide data for any contaminants for the SYR3 ICR Dataset, this state is included in the table below because a handful of tribal water systems located within this state did submit selenium data. There were no selenium data submitted by tribal communities in Colorado. Exhibit B-43 presents the total number of systems in each state that submitted data for selenium. In addition, the geographic distribution of selenium occurrence in drinking water is illustrated by showing states with systems with a mean concentration greater than the potential MCLG and the MCL concentrations. (Note: Only the V2 MRL substitution results are presented in this exhibit.) The distribution of systems with mean concentrations of selenium is geographically dispersed. Detection rates were generally low; only 14 states had systems with an estimated mean concentration greater than the MCL. Forty-nine systems in 15 states had estimated mean concentrations greater than the potential MCLG. Exhibit B-43: Selenium Stage 2 Analysis - Summary of Systems with a Mean Threshold Exceedance by State12 State Total Number of Systems Systems with a Mean Concentration > 40 |jg/L3 Systems with a Mean Concentration > 50 |jg/L Number Percent Number Percent AK 508 AL 385 AR 460 AS 11 AZ 1,097 1 0.09% 1 0.09% CA 3,978 5 0.13% 3 0.08% CO 0 CT 1,173 DC 1 SYR3 Occurrence Support Document B-89 December 2016 ------- State Total Number of Systems Systems with a Mean Concentration > 40 |jg/L3 Systems with a Mean Concentration > 50 |jg/L Number Percent Number Percent FL 2,605 HI 112 IA 350 ID 721 IL 1,358 IN 1,191 KS 601 4 0.67% 2 0.33% KY 226 LA 1,110 MA 665 MD 595 ME 780 Ml 2,126 MN 1,144 MO 1,444 1 0.07% 1 0.07% MS 5 MT 774 NC 2,180 2 0.09% 2 0.09% ND 181 NE 687 10 1.46% 7 1.02% NH 1,167 NJ 1,402 NM 750 4 0.53% 3 0.40% NV 307 1 0.33% 1 0.33% NY 2,528 1 0.04% 1 0.04% OH 1,893 OK 625 2 0.00% 2 0.32% OR 856 PA 1,408 Rl 153 SC 559 SYR3 Occurrence Support Document B-90 December 2016 ------- State Total Number of Systems Systems with a Mean Concentration > 40 |jg/L3 Systems with a Mean Concentration > 50 |jg/L Number Percent Number Percent SD 201 TN 242 1 0.41% 0 0.00% TX 4,580 13 0.28% 5 0.11% UT 481 1 0.21% 1 0.21% VA 1,609 1 0.06% 1 0.06% VT 429 WA 2,203 Wl 1,998 WV 394 WY 315 2 0.63% 1 0.32% Total 50,568 49 0.10% 31 0.06% 1 Results are based on setting all non-detection results equal to % the MRL values in the SYR3 ICR dataset. 2 Blank cells within the table indicate that there were no systems with a mean concentration that exceeded either threshold. 3 The new potential threshold of concern for this contaminant is due to changes in the RfD based on new health effects information. Exhibit B-44 presents the population served by systems with a mean concentration greater than the MCL concentration by state. The total population served by systems in each state that submitted data for selenium is presented, as well. As described above, 14 states had systems with an estimated mean concentration greater than the MCL. These systems served a total of 21,489 people. A total of 49 systems in 15 states, serving 135,685 people, had estimated mean concentrations greater than the potential MCLG (40 |ig/L). Exhibit B-44: Selenium Stage 2 Analysis - Summary of Population Served by Systems with a Mean Threshold Exceedance by State12 State Total Population Population Served by Systems with a Mean Concentration > 40 |Jg'L3 Population Served by Systems with a Mean Concentration > 50 |jg/L Population Percent Population Percent AK 677,666 AL 5,336,667 AR 2,636,302 AS 62,196 AZ 6,659,383 144 0.00% 144 0.00% CA 41,064,051 169 0.00% 119 0.00% CO 0 SYR3 Occurrence Support Document B-91 December 2016 ------- State Total Population Population Served by Systems with a Mean Concentration > 40 |Jg'L3 Population Served by Systems with a Mean Concentration > 50 |jg/L Population Percent Population Percent CT 2,933,337 DC 761,124 FL 19,110,546 HI 1,481,171 IA 1,320,723 ID 1,157,142 IL 10,983,227 IN 4,934,479 KS 2,605,369 1,245 0.05% 614 0.02% KY 4,225,513 LA 4,970,924 MA 9,274,922 MD 163,520 ME 757,647 Ml 6,079,096 MN 3,684,918 MO 5,278,387 145 0.00% 145 0.00% MS 6,176 MT 795,027 NC 7,759,220 6,941 0.09% 6,941 0.09% ND 582,630 NE 1,656,731 10,527 0.64% 10,178 0.61% NH 959,233 NJ 9,151,032 NM 1,973,494 777 0.04% 412 0.02% NV 2,684,168 110 0.00% 110 0.00% NY 10,481,957 450 0.00% 450 0.00% OH 10,202,691 OK 3,512,817 1,026 0.00% 1,026 0.03% OR 3,141,336 PA 9,935,296 SYR3 Occurrence Support Document B-92 December 2016 ------- State Total Population Population Served by Systems with a Mean Concentration > 40 |Jg'L3 Population Served by Systems with a Mean Concentration > 50 |jg/L Population Percent Population Percent Rl 1,019,797 SC 3,653,359 SD 406,820 TN 4,734,392 65 0.00% 0 0.00% TX 23,797,890 113,626 0.48% 990 0.00% UT 2,818,359 240 0.01% 240 0.01% VA 6,907,783 30 0.00% 30 0.00% VT 405,823 WA 5,384,657 Wl 4,256,823 WV 1,573,265 WY 469,210 190 0.04% 90 0.02% Total 254,428,296 135,685 0.05% 21,489 0.01% 1 Results are based on setting all non-detection results equal to % the MRL values in the SYR3 ICR dataset. 2 Blank cells within the table indicate that there were no systems with a mean concentration that exceeded either threshold. 3 The new potential threshold of concern for this contaminant is due to changes in the RfD based on new health effects information. B.11.3 Summary of Data A total of 165,672 analytical results from 50,568 PWSs in 49 states/entities were available in the SYR3 ICR Dataset for selenium. The Stage 2 analysis of occurrence in drinking water indicated that 31 systems, serving 21,489 people, had an estimated system mean concentration of selenium greater than the MCL concentration of 50 |ig/L. A total of 49 systems, serving 135,685 people, had an estimated mean concentration greater than the potential MCLG of 40 |ig/L. All but one of the systems with a mean concentrations exceeding the MCL and potential MCLG were ground water systems. SYR3 Occurrence Support Document B-93 December 2016 ------- B.12 Styrene This chapter on styrene includes background information such as the regulatory history and a summary of monitoring requirements, as well as occurrence and exposure estimates in drinking water. All drinking water occurrence estimates are based on data from the National Compliance Monitoring Information Collection Request (ICR) Dataset for the Third Six-Year Review (the "SYR3 ICR Dataset"). B.12.1 Background The United States Environmental Protection Agency (EPA) published the current National Primary Drinking Water Regulations (NPDWR) for styrene on January 30, 1991 (56 FR 3526; USEPA, 1991a). The NPDWR established a maximum contaminant level goal (MCLG) and a maximum contaminant level (MCL) of 100 |ig/L. The Agency based the MCLG on a reference dose (RfD) of 200 |ig/kg-day (0.2 mg/kg-day). Styrene is regulated as a volatile organic compound (VOC) in drinking water. All non-purchased community water systems (CWSs) and non-transient non-community water systems (NTNCWSs) are required to sample for VOCs. The maximum waiver period for VOCs is two compliance periods for ground water systems and one compliance period for surface water systems. All CWSs and NTNCWSs must collect four consecutive quarterly samples during the initial three-year compliance period.24 If all four samples are non-detections, then the system may reduce to annual sampling. After three annual samples without a detection, and upon conducting a vulnerability assessment, a system may be granted a waiver. During the waiver period, the ground water system must sample at least once, while surface water system must sample at the frequency specified by the state. If a compound is detected, the system must take one sample per quarter until results are below the MCL (minimum of two quarterly samples for ground water systems and four quarterly samples for surface water systems). If all quarterly samples are reliably and consistently below the MCL, the system may return to annual sampling. If a compound is detected at a level greater than the MCL, the system (whether ground water or surface water) must take four consecutive quarterly samples until all are below the MCL. If all quarterly samples are below the MCL, the system may return to annual sampling. B.12.2 Occurrence in Drinking Water The analysis of styrene occurrence presented in the following section is based on state compliance monitoring data from the SYR3 ICR Dataset. These data consist of 370,368 analytical results from 55,731 public water systems (PWSs) during the period from 2006 to 2011. The number of sample results and systems vary by state, although the state datasets have been reviewed and checked to ensure adequacy of coverage and completeness. 24 All new systems or systems using a new water source that began operation after January 22, 2004 must demonstrate compliance with the MCL within a period of time specified by the State. The system must also comply with the initial sampling frequencies specified by the State to ensure that a system can demonstrate compliance with the MCL. SYR3 Occurrence Support Document B-94 December 2016 ------- EPA used a two-stage analytical approach to estimate the national contaminant occurrence using the SYR3 ICR Dataset. In the "Stage 1 analysis," the occurrence data were analyzed to generate simple non-parametric estimates and descriptive statistics of national contaminant occurrence in public water systems. Simple counts were made of the number and percentage of systems and population served by systems with at least one compliance monitoring sample result greater than a specified concentration threshold. The Stage 1 analysis provides occurrence assessments that are more conservative and may be more reflective of potential acute exposure than the assessments from the Stage 2 analyses. Details on the Stage 1 analysis are presented in Section 6. Based on the evaluation of the health effects and analytical methods as part of the Six-Year Review protocol, EPA selected a set of contaminants, including styrene, for which Stage 2 analyses were warranted. The Stage 2 analysis estimates national contaminant occurrence by generating estimated long-term mean concentrations of contaminants for each system. This provides occurrence analyses that are less conservative than the Stage 1 analysis, since the Stage 2 analysis is based on estimated mean concentrations rather than on a single maximum concentration. Also, because the Stage 2 analyses generate long-term (multi-year) mean concentration estimates for contaminant occurrence at systems, the analyses can support assessments of population served by systems with detections or potential exposure assessments that may be more reflective of potential chronic exposure than the assessments from the Stage 1 analyses. For the Stage 2 analyses, system arithmetic means were calculated using all sample detection records and all non-detection records. Three different substitution values -zero, V2 the minimum reporting level (MRL) value and the full MRL value- were used to replace each non-detection record. (The national modal MRL for styrene in the dataset is 0.5 |ig/L.) Three arithmetic mean styrene concentrations were calculated at each system using the zero, V2 MRL and full MRL substitution values. These mean calculations were performed for all systems with styrene data in the SYR3 ICR dataset. Then, the percentages of all systems with a mean concentration greater than each threshold were calculated. For styrene, EPA generated Stage 2 occurrence estimates relative to the MCL, twice the estimated quantitation level (EQL) and the EQL. Stage 2 Occurrence Estimates Stage 2 analyses for styrene are summarized in this section. Occurrence estimates were generated relative to the following thresholds: 100 |ig/L (the MCL), 1 |ig/L (two times the EQL) and 0.5 |ig/L (the EQL). The EQL represents the potential quantitation capabilities below a practical quantitation level (PQL).25 For more information on the new potential thresholds of concern used in the SYR3 Stage 2 analyses, refer to USEPA (2016d) and (2016e). Exhibit B-45 presents the system-level Stage 2 analysis of estimated mean concentrations for styrene occurrence in drinking water. Exhibit B-46 presents similar information based on population served by the systems. Based on the Stage 2 analyses, one ground water system had 25 When it is not possible to measure concentrations at the MCLG level, EPA often bases the MCL on an analytical feasibility level, known as a PQL. However, analytical feasibility can improve over time. As part of the Six-Year Review process, EPA evaluates whether new information regarding quantitation shows that PQLs may be reduced. The EQL represents quantitation capabilities below a PQL (USEPA, 2016d). The EQL is the threshold used to evaluate occurrence and exposure for the Stage 2 analyses. SYR3 Occurrence Support Document B-95 December 2016 ------- an estimated system mean greater than the MCL concentration of 100 |ig/L. A total of 117 systems, serving 571,425 people, had an estimated system mean greater than the EQL of 0.5 Hg/L. Exhibit B-45: Styrene Stage 2 Analysis - Summary of Systems with a Mean Threshold Exceedance Source Water Type (Number of Systems) Threshold Number of Systems with Mean Concentrations That Are Greater Than the Threshold Percent of Systems with Mean Concentrations That Are Greater Than the Threshold Non-detect values = MRL Non-detect values = 1/2 MRL Non-detect values = 0 Non-detect values = MRL Non-detect values = 1/2 MRL Non-detect values = 0 Ground Water (51,299) > 100 |jg/L 1 1 0 0.002% 0.002% 0.000% > 1 |Jg/L 59 48 43 0.115% 0.094% 0.084% > 0.5 |jg/L1 235 114 84 0.458% 0.222% 0.164% Surface Water (4,432) > 100 |jg/L 0 0 0 0.000% 0.000% 0.000% > 1 |Jg/L 0 0 0 0.000% 0.000% 0.000% > 0.5 |jg/L1 19 3 0 0.429% 0.068% 0.000% Combined Ground & Surface Water (55,731) > 100 |jg/L 1 1 0 0.002% 0.002% 0.000% > 1 |Jg/L 59 48 43 0.106% 0.086% 0.077% > 0.5 |jg/L1 254 117 84 0.456% 0.210% 0.151% 1 The new potential threshold of concern for this contaminant is based on the EQL. The EQL represents the potential quantitation capabilities below a PQL (USEPA, 2016d). Exhibit B-46: Styrene Stage 2 Analysis - Summary of Population Served by Systems with a Mean Threshold Exceedance Source Water Type (Population Served by Systems) Threshold Population Served by Systems with Mean Concentrations That Are Greater Than the Threshold Percent of Population Served by Systems with Mean Concentrations That Are Greater Than the Threshold Non-detect values = MRL Non-detect values = 1/2 MRL Non-detect values = 0 Non-detect values = MRL Non-detect values = 1/2 MRL Non- detect values = 0 Ground Water (110,770,943) > 100 |jg/L 100 100 0 0.000% 0.000% 0.000% > 1 |Jg/L 26,448 20,242 17,199 0.024% 0.018% 0.016% > 0.5 |jg/L1 602,074 80,116 36,835 0.544% 0.072% 0.033% Surface Water > 100 |jg/L 0 0 0 0.000% 0.000% 0.000% SYR3 Occurrence Support Document B-96 December 2016 ------- Source Water Type (Population Served by Systems) Threshold Population Served by Systems with Mean Concentrations That Are Greater Than the Threshold Percent of Population Served by Systems with Mean Concentrations That Are Greater Than the Threshold Non-detect values = MRL Non-detect values = 1/2 MRL Non-detect values = 0 Non-detect values = MRL Non-detect values = 1/2 MRL Non- detect values = 0 Surface Water, cont. (152,600,590) > 1 |jg/L 0 0 0 0.000% 0.000% 0.000% > 0.5 |jg/L1 930,047 491,309 0 0.609% 0.322% 0.000% Combined Ground & Surface Water (263,371,533) > 100 |jg/L 100 100 0 0.000% 0.000% 0.000% > 1 |Jg/L 26,448 20,242 17,199 0.010% 0.008% 0.007% > 0.5 |jg/L1 1,532,121 571,425 36,835 0.582% 0.217% 0.014% 1 The new potential threshold of concern for this contaminant is based on the EQL. The EQL represents the potential quantitation capabilities below a PQL (USEPA, 2016d). Data for styrene were available from 50 states/entities. Four states did not submit data for use in the Six-Year Review (Colorado, Delaware, Georgia and Mississippi). Although the States of Colorado and Mississippi did not provide data for any contaminants for the SYR3 ICR Dataset, these states are included in the table below because a handful of tribal water systems located within these two states did submit styrene data. Exhibit B-47 presents the total number of systems in each state that submitted data for styrene. In addition, the geographic distribution of styrene occurrence in drinking water is illustrated by showing states with systems with a mean concentration greater than the EQL, two times the EQL and MCL concentrations. (Note: Only the V2 MRL substitution results are presented in this exhibit.) No systems had estimated mean concentrations greater than the MCL. One system in Michigan had an estimated mean concentration greater than the MCL of 100 |ig/L. A total of 117 systems had an estimated mean concentration greater than the EQL of 0.5 |ig/L. Exhibit B-47: Styrene Stage 2 Analysis - Summary of Systems with a Mean Threshold Exceedance by State12 State Total Number of Systems Systems with a Mean Concentration > 0.5 |jg/L3 Systems with a Mean Concentration > 1 Hg'L Systems with a Mean Concentration >100 |jg/L Number Percent Number Percent Number Percent AK 595 0 0.000% 0 0.000% 0 0.000% AL 384 AR 461 0 0.000% 0 0.000% 0 0.000% AS 11 AZ 1,110 2 0.180% 1 0.090% 0 0.00% CA 3,811 1 0.026% 0 0.000% 0 0.00% SYR3 Occurrence Support Document B-97 December 2016 ------- State Total Number of Systems Systems with a Mean Concentration > 0.5 |jg/L3 Systems with a Mean Concentration > 1 H9'L Systems with a Mean Concentration >100 |jg/L Number Percent Number Percent Number Percent CO 1 CT 1,202 0 0.000% 0 0.000% 0 0.00% DC 1 FL 2,633 0 0.000% 0 0.000% 0 0.00% HI 110 IA 1,043 0 0.000% 0 0.000% 0 0.00% ID 839 0 0.000% 0 0.000% 0 0.00% IL 1,493 2 0.134% 0 0.000% 0 0.00% IN 1,196 7 0.585% 4 0.334% 0 0.00% KS 602 0 0.000% 0 0.000% 0 0.000% KY 227 LA 1,102 3 0.272% 0 0.000% 0 0.00% MA 721 1 0.139% 0 0.000% 0 0.00% MD 1,054 3 0.285% 2 0.190% 0 0.00% ME 784 8 1.020% 5 0.638% 0 0.00% Ml 2,419 41 1.695% 13 0.537% 1 0.04% MN 1,463 8 0.547% 6 0.410% 0 0.00% MO 1,445 1 0.069% 0 0.000% 0 0.00% MS 5 MT 897 0 0.000% 0 0.000% 0 0.00% NC 2,356 7 0.297% 3 0.127% 0 0.00% ND 160 NE 705 1 0.142% 1 0.142% 0 0.00% NH 1,185 1 0.084% 0 0.000% 0 0.00% NJ 1,434 5 0.349% 3 0.209% 0 0.00% NM 744 1 0.134% 0 0.00% 0 0.00% NV 350 NY 2,498 2 0.080% 2 0.080% 0 0.00% OH 1,922 14 0.728% 6 0.312% 0 0.00% OK 685 0 0.000% 0 0.000% 0 0.000% SYR3 Occurrence Support Document B-98 December 2016 ------- State Total Number of Systems Systems with a Mean Concentration > 0.5 |jg/L3 Systems with a Mean Concentration > 1 H9'L Systems with a Mean Concentration >100 |jg/L Number Percent Number Percent Number Percent OR 1,132 1 0.088% 0 0.000% 0 0.00% PA 3,166 2 0.063% 0 0.000% 0 0.00% Rl 152 0 0.000% 0 0.000% 0 0.00% SC 494 0 0.000% 0 0.000% 0 0.00% SD 313 0 0.000% 0 0.000% 0 0.00% TN 366 TX 4,532 0 0.000% 0 0.000% 0 0.00% UT 468 0 0.000% 0 0.000% 0 0.00% VA 1,630 2 0.123% 0 0.000% 0 0.00% VT 634 0 0.000% 0 0.000% 0 0.00% WA 2,468 0 0.000% 0 0.000% 0 0.00% Wl 2,026 4 0.197% 2 0.099% 0 0.00% WV 385 0 0.000% 0 0.000% 0 0.00% WY 317 Total 55,731 117 0.210% 48 0.086% 1 0.002% 1 Results are based on setting all non-detection results equal to % the MRL values in the SYR3 ICR dataset. 2 Blank cells within the table indicate that there were no systems with a mean concentration that exceeded either threshold. 3 The new potential threshold of concern for this contaminant is based on the EQL. The EQL represents the potential quantitation capabilities below a PQL (USEPA, 2016d). Exhibit B-48 presents the population served by systems with a mean concentration greater than the MCL concentration by state. The total population served by systems in each state that submitted data for styrene is presented, as well. As described above, 1 system in Michigan, serving 100 people, had an estimated mean concentration greater than the MCL of 100 |ig/L. A total of 117 systems, serving 571,425, had an estimated mean concentration greater than the EQL of 0.5 |ig/L. Exhibit B-48: Styrene Stage 2 Analysis - Summary of Population Served by Systems with a Mean Threshold Exceedance by State12 State Total Population Served by Systems Population Served by Systems with a Mean Concentration > 0.5 |jg/L3 Population Served by Systems with a Mean Concentration > 1 H9'L Population Served by Systems with a Mean Concentration >100 |jg/L Number Percent Number Percent Number Percent AK 719,561 0 0.000% 0 0.000% 0 0.000% AL 5,334,584 SYR3 Occurrence Support Document B-99 December 2016 ------- State Total Population Served by Systems Population Served by Systems with a Mean Concentration > 0.5 |jg/L3 Population Served by Systems with a Mean Concentration > 1 H9'L Population Served by Systems with a Mean Concentration >100 |jg/L Number Percent Number Percent Number Percent AR 2,637,712 0 0.000% 0 0.000% 0 0.000% AS 62,196 AZ 6,669,277 398 0.006% 348 0.005% 0 0.000% CA 40,638,035 564 0.001% 0 0.000% 0 0.000% CO 2,020 CT 2,937,643 0 0.000% 0 0.000% 0 0.000% DC 761,124 FL 19,280,091 0 0.000% 0 0.000% 0 0.000% HI 1,402,969 IA 2,734,678 0 0.000% 0 0.000% 0 0.000% ID 1,219,635 0 0.000% 0 0.000% 0 0.000% IL 11,019,196 775 0.007% 0 0.000% 0 0.000% IN 4,940,108 1,452 0.029% 268 0.005% 0 0.000% KS 2,605,030 0 0.00% 0 0.00% 0 0.00% KY 4,225,914 LA 4,966,653 2,483 0.050% 0 0.000% 0 0.000% MA 9,329,953 100 0.001% 0 0.000% 0 0.000% MD 5,120,409 3,295 0.064% 2,950 0.058% 0 0.000% ME 757,984 613 0.081% 463 0.061% 0 0.000% Ml 3,470,708 102,788 2.962% 5,761 0.166% 100 0.003% MN 4,374,468 441,937 10.103% 1,226 0.028% 0 0.000% MO 5,293,851 200 0.004% 0 0.000% 0 0.000% MS 6,176 MT 856,529 0 0.000% 0 0.000% 0 0.000% NC 7,827,828 2,585 0.033% 971 0.012% 0 0.000% ND 592,539 NE 1,664,802 390 0.023% 390 0.023% 0 0.000% NH 961,134 485 0.050% 0 0.000% 0 0.000% NJ 9,273,130 1,032 0.011% 825 0.009% 0 0.000% NM 1,962,298 993 0.051% 0 0.000% 0 0.000% NV 2,697,555 SYR3 Occurrence Support Document B-100 December 2016 ------- State Total Population Served by Systems Population Served by Systems with a Mean Concentration > 0.5 |jg/L3 Population Served by Systems with a Mean Concentration > 1 H9'L Population Served by Systems with a Mean Concentration >100 |jg/L Number Percent Number Percent Number Percent NY 10,637,039 4,725 0.044% 4,725 0.044% 0 0.000% OH 10,209,121 4,641 0.045% 1,825 0.018% 0 0.000% OK 3,588,559 0 0.000% 0 0.000% 0 0.000% OR 3,434,191 90 0.003% 0 0.000% 0 0.000% PA 11,234,684 484 0.004% 0 0.000% 0 0.000% Rl 1,040,737 0 0.000% 0 0.000% 0 0.000% SC 3,637,408 0 0.000% 0 0.000% 0 0.000% SD 757,925 0 0.000% 0 0.000% 0 0.000% TN 6,578,052 TX 23,863,702 0 0.000% 0 0.000% 0 0.000% UT 2,800,243 0 0.000% 0 0.000% 0 0.000% VA 6,908,704 700 0.010% 0 0.000% 0 0.000% VT 486,604 0 0.000% 0 0.000% 0 0.000% WA 5,535,827 0 0.000% 0 0.000% 0 0.000% Wl 4,273,462 695 0.016% 490 0.011 % 0 0.000% WV 1,570,171 0 0.000% 0 0.000% 0 0.000% WY 469,314 Total 263,371,533 571,425 0.217% 20,242 0.008% 100 0.000% 1 Results are based on setting all non-detection results equal to % the MRL values in the SYR3 ICR dataset. 2 Blank cells within the table indicate that there were no systems with a mean concentration that exceeded either threshold. 3 The new potential threshold of concern for this contaminant is based on the EQL. The EQL represents the potential quantitation capabilities below a PQL (USEPA, 2016d). B.12.3 Summary of Data A total of 370,368 analytical results from 55,731 PWSs in 50 states/entities were available in the SYR3 ICR Dataset for styrene. The Stage 2 analysis of occurrence in drinking water indicated that one system in Michigan had an estimated system mean concentration of styrene greater than the MCL concentration of 100 |ig/L. A total of 117 systems, serving 571,425 people, had an estimated mean concentration greater than the EQL of 0.5 |ig/L. All but three of those systems were served by ground water. SYR3 Occurrence Support Document B-101 December 2016 ------- B.13 2,3,7,8-TCDD (Dioxin) This chapter on 2,3,7,8-TCDD (dioxin) includes background information such as the regulatory history and a summary of monitoring requirements, as well as occurrence and exposure estimates in drinking water. All drinking water occurrence estimates are based on data from the National Compliance Monitoring Information Collection Request (ICR) Dataset for the Third Six-Year Review (the "SYR3 ICR Dataset"). B.13.1 Background The United States Environmental Protection Agency (EPA) published the current National Primary Drinking Water Regulations (NPDWR) for dioxin on July 17, 1992 (57 FR 31776; USEPA, 1992). The NPDWR established a maximum contaminant level goal (MCLG) of zero based on a cancer classification of B2, probable human carcinogen. The NPDWR also established a maximum contaminant level (MCL) of 0.00003 |ig/L based on analytical feasibility. Dioxin is regulated as a synthetic organic chemical (SOC) in drinking water. All non-purchased community water systems (CWSs) and non-transient non-community water systems (NTNCWSs) are required to sample for SOCs. Waivers are available to all systems upon a favorable vulnerability assessment and/or prior analytical results. The maximum waiver period for SOCs is three years, but this waiver can be renewed indefinitely, if it is reconfirmed that the source is not vulnerable. All CWSs and NTNCWSs without an SOC waiver must collect four consecutive quarterly samples during the initial three-year compliance period.26 If all 4 samples are non-detections, then a system serving less than 3,300 people may reduce its collection frequency to 1 sample during each consecutive compliance period; a system serving more than 3,300 people may reduce its collection frequency to 2 quarterly samples within a 12-month period during each repeat compliance period. If a chemical is detected, the system must monitor quarterly until results are reliably and consistently below the MCL (minimum of two quarterly samples for ground water systems and four quarterly samples for surface water systems). If all quarterly samples are below the MCL, the system may return to annual sampling. If a chemical is detected at a level greater than the MCL, the system (whether ground water or surface water) must take quarterly samples until four consecutive quarters are below the MCL. If all quarterly samples are below the MCL, the system may return to annual sampling. B.13.2 Occurrence in Drinking Water The analysis of dioxin occurrence presented in the following section is based on state compliance monitoring data from the SYR3 ICR Dataset. These data consist of 20,244 analytical results from 3,216 public water systems (PWSs) during the period from 2006 to 2011. The number of sample 26 All new systems or systems using a new water source that began operation after January 22, 2004 must demonstrate compliance with the MCL within a period of time specified by the State. The system must also comply with the initial sampling frequencies specified by the State to ensure that a system can demonstrate compliance with the MCL. SYR3 Occurrence Support Document B-102 December 2016 ------- results and systems vary by state, although the state datasets have been reviewed and checked to ensure adequacy of coverage and completeness. EPA used a two-stage analytical approach to estimate the national contaminant occurrence using the SYR3 ICR Dataset. In the "Stage 1 analysis," the occurrence data were analyzed to generate simple non-parametric estimates and descriptive statistics of national contaminant occurrence in public water systems. Simple counts were made of the number and percentage of systems and population served by systems with at least one compliance monitoring sample result greater than a specified concentration threshold. The Stage 1 analysis provides occurrence assessments that are more conservative and may be more reflective of potential acute exposure than the assessments from the Stage 2 analyses. Details on the Stage 1 analysis are presented in Section 6. Based on the evaluation of the health effects and analytical methods as part of the Six-Year Review protocol, EPA selected a set of contaminants, including dioxin, for which Stage 2 analyses were warranted. The Stage 2 analysis estimates national contaminant occurrence by generating estimated long-term mean concentrations of contaminants for each system. This provides occurrence analyses that are less conservative than the Stage 1 analysis, since the Stage 2 analysis is based on estimated mean concentrations rather than on a single maximum concentration. Also, because the Stage 2 analyses generate long-term (multi-year) mean concentration estimates for contaminant occurrence at systems, the analyses can support assessments of population served by systems with detections or potential exposure assessments that may be more reflective of potential chronic exposure than the assessments from the Stage 1 analyses. For the Stage 2 analyses, system arithmetic means were calculated using all sample detection records and all non-detection records. Two different substitution values -zero and V2 the minimum reporting level (MRL) value- were used to replace each non-detection record. (The national modal MRL for dioxin in the dataset is 0.000005 |ig/L.) Two arithmetic mean dioxin concentrations were calculated at each system using the zero and V2 MRL substitution values. These mean calculations were performed for all systems with dioxin data in the SYR3 ICR dataset. Then, the percentages of all systems with a mean concentration greater than each threshold were calculated. For dioxin, EPA generated Stage 2 occurrence estimates relative to the MCL, V2 the MCL, the estimated quantitation level (EQL) and twice the EQL. Stage 2 Occurrence Estimates Stage 2 analyses for dioxin are summarized in this section. Occurrence estimates were generated relative to four thresholds: 0.00003 |ig/L (the MCL), 0.000015 |ig/L (V2 the MCL), 0.00001 |ig/L (two times the EQL) and 0.000005 |ig/L (the EQL). The EQL represents the potential quantitation capabilities below a practical quantitation level (PQL).27For more information on 27 When it is not possible to measure concentrations at the MCLG level, EPA often bases the MCL on an analytical feasibility level, known as a PQL. However, analytical feasibility can improve over time. As part of the Six-Year Review process, EPA evaluates whether new information regarding quantitation shows that PQLs may be reduced. The EQL represents quantitation capabilities below a PQL (USEPA, 2016d). The EQL is the threshold used to evaluate occurrence and exposure for the Stage 2 analyses. SYR3 Occurrence Support Document B-103 December 2016 ------- the new potential thresholds of concern used in the SYR3 Stage 2 analyses, refer to USEPA (2016d) and (2016e). Exhibit B-49 presents the system-level Stage 2 analysis of estimated mean concentrations for dioxin occurrence in drinking water. Exhibit B-50 presents similar information based on population served by the systems. Based on the Stage 2 analyses using the V2 MRL substitution for non-detections, one water system (approximately 0.031 percent of all systems) had an estimated mean greater than the MCL of 0.00003 |ig/L. This system serves approximately 550 people. Two water systems (approximately 0.062 percent of all systems) had estimated means greater than the EQL of 0.000005 |ig/L. These 2 systems serve approximately 1,450 people. Exhibit B-49: Dioxin Stage 2 Analysis - Summary of Systems with a Mean Threshold Exceedance Source Water Type (Number of Systems) Threshold Number of Systems with Mean Concentrations That Are Greater Than the Threshold Percent of Systems with Mean Concentrations That Are Greater Than the Threshold Non-detect values = 1/2 MRL Non-detect values = 0 Non-detect values = 1/2 MRL Non-detect values = 0 Ground Water (2,653) > 0.00003 |jg/L 1 1 0.038% 0.038% > 0.000015 |jg/L 1 1 0.038% 0.038% > 0.00001 |jg/L 1 1 0.038% 0.038% > 0.000005 |jg/L1 2 1 0.075% 0.038% Surface Water (563) > 0.00003 |jg/L 0 0 0.000% 0.000% > 0.000015 |jg/L 0 0 0.000% 0.000% > 0.00001 |jg/L 0 0 0.000% 0.000% > 0.000005 |jg/L1 0 0 0.000% 0.000% Combined Ground & Surface Water (3,216) > 0.00003 |jg/L 1 1 0.031 % 0.031 % > 0.000015 |jg/L 1 1 0.031 % 0.031 % > 0.00001 |jg/L 1 1 0.031 % 0.031 % > 0.000005 |jg/L1 2 1 0.062% 0.031 % 1 The new potential threshold of concern for this contaminant is based on the EQL. The EQL represents the potential quantitation capabilities below a PQL (USEPA, 2016d). SYR3 Occurrence Support Document B-104 December 2016 ------- Exhibit B-50: Dioxin Stage 2 Analysis - Summary of Population Served by Systems with a Threshold Exceedance Source Water Type (Population Served by Systems) Threshold Population Served by Systems with Mean Concentrations That Are Greater Than the Threshold Percent of Population Served by Systems with Mean Concentrations That Are Greater Than the Threshold Non-detect values = 1/2 MRL Non-detect values = 0 Non-detect values = 1/2 MRL Non-detect values = 0 Ground Water (27,816,835) > 0.00003 |jg/L 550 550 0.002% 0.002% > 0.000015 |jg/L 550 550 0.002% 0.002% > 0.00001 |jg/L 550 550 0.002% 0.002% > 0.000005 |jg/L1 1,450 550 0.005% 0.002% Surface Water (46,260,945) > 0.00003 |jg/L 0 0 0.000% 0.000% > 0.000015 |jg/L 0 0 0.000% 0.000% > 0.00001 |jg/L 0 0 0.000% 0.000% > 0.000005 |jg/L1 0 0 0.000% 0.000% Combined Ground & Surface Water (74,077,780) > 0.00003 |jg/L 550 550 0.001% 0.001% > 0.000015 |jg/L 550 550 0.001% 0.001% > 0.00001 |jg/L 550 550 0.001% 0.001% > 0.000005 |jg/L1 1,450 550 0.002% 0.001% 1 The new potential threshold of concern for this contaminant is based on the EQL. The EQL represents the potential quantitation capabilities below a PQL (USEPA, 2016d). Data for dioxin were available from 30 states/entities. (There were no dioxin data from 20 states/entities.) Four states did not submit data for use in the Six-Year Review (Colorado, Delaware, Georgia and Mississippi). Although the State of Mississippi did not provide data for any contaminants for the SYR3 ICR Dataset, this state is included in the table below because a handful of tribal water systems located within Mississippi did submit dioxin data. Twenty states/entities included in the table below did provide Six-Year data for most contaminants but did not submit dioxin data because waivers had been granted. Exhibit B-51 presents the total number of systems in each state that submitted data for dioxin. In addition, the geographic distribution of dioxin occurrence in drinking water is illustrated by showing states with systems with a mean concentration greater than the EQL, two times the EQL, '/2 MCL and MCL concentrations. (Note: Only the V2 MRL substitution results are presented in this exhibit.) Detection rates were low; only one system in Maryland an estimated mean concentration greater than the MCL. Two systems (one in Florida and one in Maryland) had an estimated mean concentration greater than the EQL of 0.000005 |ig/L. SYR3 Occurrence Support Document B-105 December 2016 ------- Exhibit B-51: Dioxin Stage 2 Analysis - Summary of Systems with a Mean Threshold Exceedance by State12 State Total Number of Systems Systems with a Mean Concentration > 0.000005 |jg/L3 Systems with a Mean Concentration > 0.00001 |jg/L Systems with a Mean Concentration > 0.000015 |jg/L Systems with a Mean Concentration > 0.00003 |jg/L Number Percent Number Percent Number Percent Number Percent AK 6 AL 1 AR 0 AS 11 AZ 829 CA 534 CO 0 CT 10 DC 1 FL 264 1 0.38% 0 0.00% 0 0.00% 0 0.00% HI 115 IA 0 ID 1 IL 0 IN 55 KS 2 KY 56 LA 4 MA 0 MD 2 1 50.00% 1 50.00% 1 50.00% 1 50.00% ME 0 Ml 13 MN 27 MO 0 MS 5 MT 0 NC 6 ND 0 SYR3 Occurrence Support Document B-106 December 2016 ------- State Total Number of Systems Systems with a Mean Concentration > 0.000005 |jg/L3 Systems with a Mean Concentration > 0.00001 |jg/L Systems with a Mean Concentration > 0.000015 |jg/L Systems with a Mean Concentration > 0.00003 |jg/L Number Percent Number Percent Number Percent Number Percent NE 0 NH 0 NJ 0 NM 60 NV 117 NY 60 OH 18 OK 0 OR 6 PA 895 Rl 0 SC 0 SD 0 TN 3 TX 0 UT 12 VA 4 VT 0 WA 0 Wl 98 WV 1 WY 0 Total 3,216 2 0.06% 1 0.03% 1 0.03% 1 0.03% 1 Results are based on setting all non-detection results equal to % the MRL values in the SYR3 ICR dataset. 2 Blank cells within the table indicate that there were no systems with a mean concentration that exceeded any of the thresholds. 3 The new potential threshold of concern for this contaminant is based on the EQL. The EQL represents the potential quantitation capabilities below a PQL (USEPA, 2016d). Exhibit B-52 presents the population served by systems with a mean concentration greater than the MCL concentration by state. The total population served by systems in each state that submitted data for dioxin is presented, as well. As described above, 1 system in Maryland had an estimated mean concentration greater than the MCL; this system served 550 people. Two SYR3 Occurrence Support Document B-107 December 2016 ------- systems, serving a total population of 1,450 people, had an estimated mean concentration greater than the EQL of 0.000005 |ig/L. Exhibit B-52: Dioxin Stage 2 Analysis - Summary of Population Served by Systems with a Mean Threshold Exceedance by State12 State Total Population Population Served by Systems with a Mean Concentration > 0.000005 |jg/L3 Population Served by Systems with a Mean Concentration > 0.00001 |jg/L Population Served by Systems with a Mean Concentration > 0.000015 |jg/L Population Served by Systems with a Mean Concentration > 0.00003 |jg/L Population Percent Population Percent Population Percent Population Percent AK 36,711 AL 750 AR 0 AS 62,196 AZ 6,395,030 CA 29,120,942 CO 0 CT 49,751 DC 761,124 FL 9,131,313 900 0.01% 0 0.00% 0 0.00% 0 0.00% HI 1,487,191 IA 0 ID 30 IL 0 IN 2,343,163 KS 482,004 KY 2,771,859 LA 32,844 MA 0 MD 1,800,550 550 0.03% 550 0.03% 550 0.03% 550 0.03% ME 0 Ml 34,902 MN 25,573 MO 0 MS 6,176 SYR3 Occurrence Support Document B-108 December 2016 ------- State Total Population Population Served by Systems with a Mean Concentration > 0.000005 |jg/L3 Population Served by Systems with a Mean Concentration > 0.00001 |jg/L Population Served by Systems with a Mean Concentration > 0.000015 |jg/L Population Served by Systems with a Mean Concentration > 0.00003 |jg/L Population Percent Population Percent Population Percent Population Percent MT 0 NC 15,984 ND 0 NE 0 NH 0 NJ 0 NM 82,348 NV 2,577,238 NY 1,822,971 OH 1,099,358 OK 0 OR 910,206 PA 9,393,195 Rl 0 SC 0 SD 0 TN 954,057 TX 0 UT 6,159 VA 785,888 VT 0 WA 0 Wl 1,888,147 WV 120 SYR3 Occurrence Support Document B-109 December 2016 ------- State Total Population Population Served by Systems with a Mean Concentration > 0.000005 |jg/L3 Population Served by Systems with a Mean Concentration > 0.00001 |jg/L Population Served by Systems with a Mean Concentration > 0.000015 |jg/L Population Served by Systems with a Mean Concentration > 0.00003 |jg/L Population Percent Population Percent Population Percent Population Percent WY 0 Total 74,077,780 1,450 0.002% 550 0.001% 550 0.001% 550 0.001% 1 Results are based on setting all non-detection results equal to % the MRL values in the SYR3 ICR dataset. 2 Blank cells within the table indicate that there were no systems with a mean concentration that exceeded any of the thresholds. 3 The new potential threshold of concern for this contaminant is based on the EQL. The EQL represents the potential quantitation capabilities below a PQL (USEPA, 2016d). B.13.3 Summary of Data A total of 20,244 analytical results from 3,216 PWSs in 30 states/entities were available in the SYR3 ICR Dataset for dioxin. The Stage 2 analysis of occurrence in drinking water indicated that 1 ground water system in Maryland, serving 550 people, had an estimated system mean concentration of dioxin greater than the MCL concentration of 0.00003 |ig/L. Two ground water systems, serving a total population of 1,450 people, had an estimated mean concentration greater than the EQL of 0.000005 |ig/L. These two ground water systems were located in Florida and Maryland. SYR3 Occurrence Support Document B-110 December 2016 ------- B.14 Toluene This chapter on toluene includes background information such as the regulatory history and a summary of monitoring requirements, as well as occurrence and exposure estimates in drinking water. All drinking water occurrence estimates are based on data from the National Compliance Monitoring Information Collection Request (ICR) Dataset for the Third Six-Year Review (the "SYR3 ICR Dataset"). B.14.1 Background The United States Environmental Protection Agency (EPA) published the current National Primary Drinking Water Regulations (NPDWR) for toluene on January 30, 1991 (56 FR 3526; USEPA, 1991a). The NPDWR established a maximum contaminant level goal (MCLG) and a maximum contaminant level (MCL) of 1,000 |ig/L. The Agency based the MCLG on a reference dose (RfD) of 200 |ig/kg-day (0.2 mg/kg-day) and a cancer classification of D, not classifiable as to human carcinogenicity. Toluene is regulated as a volatile organic compound (VOC) in drinking water. All non-purchased community water systems (CWSs) and non-transient non-community water systems (NTNCWSs) are required to sample for VOCs. The maximum waiver period for VOCs is two compliance periods for ground water systems and one compliance period for surface water systems. All CWSs and NTNCWSs must collect four consecutive quarterly samples during the initial three-year compliance period.28 If all four samples are non-detections, then the system may reduce to annual sampling. After three annual samples without a detection, and upon conducting a vulnerability assessment, a system may be granted a waiver. During the waiver period, the ground water system must sample at least once, while surface water system must sample at the frequency specified by the state. If a compound is detected, the system must take one sample per quarter until results are below the MCL (minimum of two quarterly samples for ground water systems and four quarterly samples for surface water systems). If all quarterly samples are reliably and consistently below the MCL, the system may return to annual sampling. If a compound is detected at a level greater than the MCL, the system (whether ground water or surface water) must take four consecutive quarterly samples until all are below the MCL. If all quarterly samples are below the MCL, the system may return to annual sampling. B.14.2 Occurrence in Drinking Water The analysis of toluene occurrence presented in the following section is based on state compliance monitoring data from the SYR3 ICR Dataset. These data consist of 373,021 analytical results from 55,748 public water systems (PWSs) during the period from 2006 to 28 All new systems or systems using a new water source that began operation after January 22, 2004 must demonstrate compliance with the MCL within a period of time specified by the State. The system must also comply with the initial sampling frequencies specified by the State to ensure that a system can demonstrate compliance with the MCL. SYR3 Occurrence Support Document B-lll December 2016 ------- 2011. The number of sample results and systems vary by state, although the state datasets have been reviewed and checked to ensure adequacy of coverage and completeness. EPA used a two-stage analytical approach to estimate the national contaminant occurrence using the SYR3 ICR Dataset. In the "Stage 1 analysis," the occurrence data were analyzed to generate simple non-parametric estimates and descriptive statistics of national contaminant occurrence in public water systems. Simple counts were made of the number and percentage of systems and population served by systems with at least one compliance monitoring sample result greater than a specified concentration threshold. The Stage 1 analysis provides occurrence assessments that are more conservative and may be more reflective of potential acute exposure than the assessments from the Stage 2 analyses. Details on the Stage 1 analysis are presented in Section 6. Based on the evaluation of the health effects and analytical methods as part of the Six-Year Review protocol, EPA selected a set of contaminants, including toluene, for which Stage 2 analyses were warranted. The Stage 2 analysis estimates national contaminant occurrence by generating estimated long-term mean concentrations of contaminants for each system. This provides occurrence analyses that are less conservative than the Stage 1 analysis, since the Stage 2 analysis is based on estimated mean concentrations rather than on a single maximum concentration. Also, because the Stage 2 analyses generate long-term (multi-year) mean concentration estimates for contaminant occurrence at systems, the analyses can support assessments of population served by systems with detections or potential exposure assessments that may be more reflective of potential chronic exposure than the assessments from the Stage 1 analyses. For the Stage 2 analyses, system arithmetic means were calculated using all sample detection records and all non-detection records. Three different substitution values -zero, V2 the minimum reporting level (MRL) value and the full MRL value- were used to replace each non-detection record. (The national modal MRL for toluene in the dataset is 0.5 |ig/L.) Three arithmetic mean toluene concentrations were calculated at each system using the zero, V2 MRL and full MRL substitution values. These mean calculations were performed for all systems with toluene data in the SYR3 ICR dataset. Then, the percentages of all systems with a mean concentration greater than each threshold were calculated. For toluene, since there were no analytical method limitations at the potential MCLG, EPA generated Stage 2 occurrence estimates relative to the MCL and the potential MCLG. Stage 2 Occurrence Estimates Stage 2 analyses for toluene are summarized in this section. Occurrence estimates were generated relative to the following thresholds: 1,000 |ig/L (the MCL) and 600 |ig/L (the potential MCLG). The potential MCLG is due to changes in the RfD based on new health effects information. Since the practical quantitation level (PQL) for toluene is less than the possible MCLG, EPA designated the possible MCLG as the threshold for the occurrence analysis. For more information on the new potential thresholds of concern used in the SYR3 Stage 2 analyses, refer to USEPA (2016d) and (2016e). Exhibit B-53 presents the system-level Stage 2 analysis of estimated mean concentrations for toluene occurrence in drinking water. Exhibit B-54 presents similar information based on population served by the systems. No systems had an estimated system mean greater than the MCL concentration of 1,000 |ig/L or the potential MCLG concentration of 600 |ig/L. SYR3 Occurrence Support Document B-112 December 2016 ------- Exhibit B-53: Toluene Stage 2 Analysis - Summary of Systems with a Mean Threshold Exceedance Source Water Type (Number of Systems) Threshold Number of Systems with Mean Concentrations That Are Greater Than the Threshold Percent of Systems with Mean Concentrations That Are Greater Than the Threshold Non-detect values = MRL Non-detect values = 1/2 MRL Non-detect values = 0 Non-detect values = MRL Non-detect values = 1/2 MRL Non-detect values = 0 Ground Water (51,316) > 1,000 |jg/L 0 0 0 0.000% 0.000% 0.000% > 600 |jg/L1 0 0 0 0.000% 0.000% 0.000% Surface Water (4,432) > 1,000 |jg/L 0 0 0 0.000% 0.000% 0.000% > 600 |jg/L1 0 0 0 0.000% 0.000% 0.000% Combined Ground & Surface Water (55,748) > 1,000 |jg/L 0 0 0 0.000% 0.000% 0.000% > 600 |jg/L1 0 0 0 0.000% 0.000% 0.000% 1 The new potential threshold of concern for this contaminant is due to changes in the RfD based on new health effects information. Exhibit B-54: Toluene Stage 2 Analysis - Summary of Population Served by Systems with a Mean Threshold Exceedance Source Water Type (Population Served by Systems) Threshold Population Served by Systems with Mean Concentrations That Are Greater Than the Threshold Percent of Population Served by Systems with Mean Concentrations That Are Greater Than the Threshold Non-detect values = MRL Non-detect values = 1/2 MRL Non-detect values = 0 Non-detect values = MRL Non-detect values = 1/2 MRL Non-detect values = 0 Ground Water (110,897,342) > 1,000 |jg/L 0 0 0 0.000% 0.000% 0.000% > 600 |jg/L1 0 0 0 0.000% 0.000% 0.000% Surface Water (152,600,590) > 1,000 |jg/L 0 0 0 0.000% 0.000% 0.000% > 600 |jg/L1 0 0 0 0.000% 0.000% 0.000% Combined Ground & Surface Water > 1,000 |jg/L 0 0 0 0.000% 0.000% 0.000% Combined Ground & Surface Water, cont. > 600 |jg/L1 0 0 0 0.000% 0.000% 0.000% SYR3 Occurrence Support Document B-113 December 2016 ------- Source Water Type (Population Served by Systems) Threshold Population Served by Systems with Mean Concentrations That Are Greater Than the Threshold Percent of Population Served by Systems with Mean Concentrations That Are Greater Than the Threshold Non-detect values = MRL Non-detect values = 1/2 MRL Non-detect values = 0 Non-detect values = MRL Non-detect values = 1/2 MRL Non-detect values = 0 (263,497,932) 1 The new potential threshold of concern for this contaminant is due to changes in the RfD based on new health effects information. Data for toluene were available from 50 states/entities. Four states did not submit data for use in the Six-Year Review (Colorado, Delaware, Georgia and Mississippi). Although the States of Colorado and Mississippi did not provide data for any contaminants for the SYR3 ICR Dataset, these states are included in the count of 50 states because a handful of tribal water systems located within these 2 states did submit toluene data. Exhibit B-55 presents the total number of systems in each state that submitted data for toluene. In addition, the geographic distribution of toluene occurrence in drinking water is illustrated by showing states with systems with a mean concentration greater than the potential MCLG and MCL concentrations. (Note: Only the V2 MRL substitution results are presented in this exhibit.) No water systems had an estimated mean greater than 1,000 |ig/L (the MCL) or the potential MCLG of 600 |ig/L. Exhibit B-55: Toluene Stage 2 Analysis - Summary of Systems with a Mean Threshold Exceedance by State12 State Total Number of Systems Systems with a Mean Concentration > 600 |jg/L3 Systems with a Mean Concentration > 1,000 |jg/L Number Percent Number Percent AK 596 AL 384 AR 461 AS 11 AZ 1,110 CA 3,814 CO 1 CT 1,202 DC 1 FL 2,633 HI 111 IA 1,048 SYR3 Occurrence Support Document B-114 December 2016 ------- State Total Number of Systems Systems with a Mean Concentration > 600 |jg/L3 Systems with a Mean Concentration > 1,000 |jg/L Number Percent Number Percent ID 839 IL 1,493 IN 1,196 KS 604 KY 227 LA 1,102 MA 721 MD 1,056 ME 784 Ml 2,419 MN 1,462 MO 1,445 MS 5 MT 897 NC 2,356 ND 160 NE 705 NH 1,186 NJ 1,434 NM 744 NV 350 NY 2,498 OH 1,922 OK 685 OR 1,131 PA 3,166 Rl 152 SC 494 SD 313 TN 366 TX 4,532 SYR3 Occurrence Support Document B-115 December 2016 ------- State Total Number of Systems Systems with a Mean Concentration > 600 |jg/L3 Systems with a Mean Concentration > 1,000 |jg/L Number Percent Number Percent UT 471 VA 1,629 VT 634 WA 2,469 Wl 2,026 WV 386 WY 317 Total 55,748 0 0.00% 0 0.00% 1 Results are based on setting all non-detection results equal to % the MRL values in the SYR3 ICR dataset. 2 Blank cells within the table indicate that there were no systems with a mean concentration that exceeded either threshold. 3 The new potential threshold of concern for this contaminant is due to changes in the RfD based on new health effects information. Exhibit B-56 presents the population served by systems with a mean concentration greater than the MCL concentration by state. As stated above, no water systems had an estimated mean greater than the MCL or the potential MCLG. Exhibit B-56: Toluene Stage 2 Analysis - Summary of Population Served by Systems with a Mean Threshold Exceedance by State12 State Total Population Population Served by Systems with a Mean Concentration > 600 |jg/L3 Population Served by Systems with a Mean Concentration > 1,000 |jg/L Population Percent Population Percent AK 719,618 AL 5,334,584 AR 2,637,712 AS 62,196 AZ 6,669,277 CA 40,642,888 CO 2,020 CT 2,937,643 DC 761,124 FL 19,280,091 HI 1,479,317 SYR3 Occurrence Support Document B-116 December 2016 ------- State Total Population Population Served by Systems with a Mean Concentration > 600 |jg/L3 Population Served by Systems with a Mean Concentration > 1,000 |jg/L Population Percent Population Percent IA 2,753,930 ID 1,219,635 IL 11,019,196 IN 4,940,108 KS 2,628,748 KY 4,225,914 LA 4,966,653 MA 9,329,953 MD 5,120,669 ME 757,984 Ml 3,470,708 MN 4,373,668 MO 5,293,851 MS 6,176 MT 856,529 NC 7,827,828 ND 592,539 NE 1,664,802 NH 962,134 NJ 9,273,130 NM 1,962,298 NV 2,697,555 NY 10,637,039 OH 10,209,121 OK 3,588,559 OR 3,434,141 PA 11,234,684 Rl 1,040,737 SC 3,637,408 SD 757,925 SYR3 Occurrence Support Document B-117 December 2016 ------- State Total Population Population Served by Systems with a Mean Concentration > 600 |jg/L3 Population Served by Systems with a Mean Concentration > 1,000 |jg/L Population Percent Population Percent TN 6,578,052 TX 23,863,702 UT 2,802,068 VA 6,908,525 VT 486,604 WA 5,535,917 Wl 4,273,462 WV 1,570,196 WY 469,314 Total 263,497,932 0 0.00% 0 0.00% 1 Results are based on setting all non-detection results equal to % the MRL values in the SYR3 ICR dataset. 2 Blank cells within the table indicate that there were no systems with a mean concentration that exceeded either threshold. 3 The new potential threshold of concern for this contaminant is due to changes in the RfD based on new health effects information. B.14.3 Summary of Data A total of 373,021 analytical results from 55,748 PWSs in 50 states/entities were available in the SYR3 ICR Dataset for toluene. The Stage 2 analysis of occurrence in drinking water indicated that zero systems had an estimated system mean concentration of toluene greater than the MCL concentration of 1,000 |ig/L or the potential MCLG of 600 |ig/L. SYR3 Occurrence Support Document B-118 December 2016 ------- B.15 Toxaphene This chapter on toxaphene includes background information such as the regulatory history and a summary of monitoring requirements, as well as occurrence and exposure estimates in drinking water. All drinking water occurrence estimates are based on data from the National Compliance Monitoring Information Collection Request (ICR) Dataset for the Third Six-Year Review (the "SYR3 ICR Dataset"). B.15.1 Background The United States Environmental Protection Agency (EPA) published the current National Primary Drinking Water Regulations (NPDWR) for toxaphene on January 30, 1991 (56 FR 3526; USEPA, 1991a). The NPDWR established a maximum contaminant level goal (MCLG) of zero based on a cancer classification of B2, probable human carcinogen. The NPDWR also established a maximum contaminant level (MCL) of 3 |ig/L based on analytical feasibility. Toxaphene is regulated as a synthetic organic chemical (SOC) in drinking water. All non- purchased community water systems (CWSs) and non-transient non-community water systems (NTNCWSs) are required to sample for SOCs. Waivers are available to all systems upon a favorable vulnerability assessment and/or prior analytical results. The maximum waiver period for SOCs is three years, but waivers can be renewed indefinitely, if it is reconfirmed that the source is not vulnerable. All CWSs and NTNCWSs without an SOC waiver must collect four consecutive quarterly samples during the initial three-year compliance period.29 If all 4 samples are non-detections, then a system serving less than 3,300 people may reduce its collection frequency to 1 sample during each consecutive compliance period; a system serving more than 3,300 people may reduce its collection frequency to 2 quarterly samples within a 12-month period during each repeat compliance period. If a contaminant is detected, the system must monitor quarterly to demonstrate that results are reliably and consistently below the MCL (minimum of two quarterly samples for ground water systems and four quarterly samples for surface water systems). If all quarterly samples are below the MCL, the system may return to annual sampling. If a contaminant is detected at a concentrations greater than the MCL, the system (whether ground water or surface water) must take quarterly samples until four consecutive quarters are below the MCL. If all quarterly samples are below the MCL, the system may return to annual sampling. B.15.2 Occurrence in Drinking Water The analysis of toxaphene occurrence presented in the following section is based on state compliance monitoring data from the SYR3 ICR Dataset. These data consist of 127,187 analytical results from 37,043 public water systems (PWSs) during the period from 2006 to 2011. The number of sample results and systems vary by state, although the state datasets have been reviewed and checked to ensure adequacy of coverage and completeness. 29 All new systems or systems using a new water source that began operation after January 22, 2004 must demonstrate compliance with the MCL within a period of time specified by the state. The system must also comply with the initial sampling frequencies specified by the state to ensure that a system can demonstrate compliance with the MCL. SYR3 Occurrence Support Document B-119 December 2016 ------- EPA used a two-stage analytical approach to estimate the national contaminant occurrence using the SYR3 ICR Dataset. In the "Stage 1 analysis," the occurrence data were analyzed to generate simple non-parametric estimates and descriptive statistics of national contaminant occurrence in public water systems. Simple counts were made of the number and percentage of systems and population served by systems with at least one compliance monitoring sample result greater than a specified concentration threshold. The Stage 1 analysis provides occurrence assessments that are more conservative and may be more reflective of potential acute exposure than the assessments from the Stage 2 analyses. Details on the Stage 1 analysis are presented in Section 6. Based on the evaluation of the health effects and analytical methods as part of the Six-Year Review protocol, EPA selected a set of contaminants, including toxaphene, for which Stage 2 analyses were warranted. The Stage 2 analysis estimates national contaminant occurrence by generating estimated long-term mean concentrations of contaminants for each system. This provides occurrence analyses that are less conservative than the Stage 1 analysis, since the Stage 2 analysis is based on estimated mean concentrations rather than on a single maximum concentration. Also, because the Stage 2 analyses generate long-term (multi-year) mean concentration estimates for contaminant occurrence at systems, the analyses can support assessments of population served by systems with detections or potential exposure assessments that may be more reflective of potential chronic exposure than the assessments from the Stage 1 analyses. For the Stage 2 analyses, system arithmetic means were calculated using all sample detection records and all non-detection records. Two different substitution values -zero and V2 the minimum reporting level (MRL) value- were used to replace each non-detection record. (The national modal MRL for toxaphene in the dataset is 1 |ig/L.) Two arithmetic mean toxaphene concentrations were calculated at each system using the zero and V2 MRL substitution values. These mean calculations were performed for all systems with toxaphene data in the SYR3 ICR dataset. Then, the percentages of all systems with a mean concentration greater than each threshold were calculated. For toxaphene, EPA generated Stage 2 occurrence estimates relative to the MCL, V2 the MCL, the estimated quantitation level (EQL) and twice the EQL. Stage 2 Occurrence Estimates Stage 2 analyses for toxaphene are summarized in this section. Occurrence estimates were generated relative to four thresholds: 3 |ig/L (the MCL), 1.5 |ig/L (1/2 the MCL), 2 |ig/L (two times the EQL) and 1 |ig/L (the EQL). The EQL represents the potential quantitation capabilities below a practical quantitation level (PQL).30For more information on the new potential thresholds of concern used in the SYR3 Stage 2 analyses, refer to USEPA (2016d) and (2016e). Exhibit B-57 presents the system-level Stage 2 analysis of estimated mean concentrations for toxaphene occurrence in drinking water. Exhibit B-58 presents similar information based on population served by the systems. Two systems (0.005 percent of all systems), serving 233,219 30 When it is not possible to measure concentrations at the MCLG level, EPA often bases the MCL on an analytical feasibility level, known as a PQL. However, analytical feasibility can improve over time. As part of the Six-Year Review process, EPA evaluates whether new information regarding quantitation shows that PQLs may be reduced. The EQL represents quantitation capabilities below a PQL (USEPA, 2016d). The EQL is the threshold used to evaluate occurrence and exposure for the Stage 2 analyses. SYR3 Occurrence Support Document B-120 December 2016 ------- people, had an estimated system mean greater than the MCL concentration of 3 |ig/L. Based on the Stage 2 analyses using the V2 MRL substitution for non-detections, six water systems (approximately 0.016 percent of all systems) had an estimated mean greater than the EQL of 1 |ig/L. These 6 systems serve 715,106 people. Exhibit B-57: Toxaphene Stage 2 Analysis - Summary of Systems with a Mean Threshold Exceedance Source Water Type (Number of Systems) Threshold Number of Systems with Mean Concentrations That Are Greater Than the Threshold Percent of Systems with Mean Concentrations That Are Greater Than the Threshold Non-detect values = 1/2 MRL Non-detect values = 0 Non-detect values = 1/2 MRL Non-detect values = 0 Ground Water (33,812) > 3 |jg/L 1 1 0.003% 0.003% > 1.5 |jg/L 2 2 0.006% 0.006% > 2 |jg/L 2 2 0.006% 0.006% > 1 |jg/L1 4 2 0.012% 0.006% Surface Water (3,231) > 3 |jg/L 1 1 0.031% 0.031% > 1.5 |jg/L 2 2 0.062% 0.062% > 2 |jg/L 2 1 0.062% 0.031% > 1 |jg/L1 2 2 0.062% 0.062% Combined Ground & Surface Water (37,043) > 3 |jg/L 2 2 0.005% 0.005% > 1.5 |jg/L 4 4 0.011% 0.011% > 2 |jg/L 4 3 0.011% 0.008% > 1 |jg/L1 6 4 0.016% 0.011% 1 The new potential threshold of concern for this contaminant is based on the EQL. The EQL represents the potential quantitation capabilities below a PQL (USEPA, 2016d). SYR3 Occurrence Support Document B-121 December 2016 ------- Exhibit B-58: Toxaphene Stage 2 Analysis - Summary of Population Served by Systems with a Mean Threshold Exceedance Source Water Type (Population Served by Systems) Threshold Population Served by Systems with Mean Concentrations That Are Greater Than the Threshold Percent of Population Served by Systems with Mean Concentrations That Are Greater Than the Threshold Non-detect values = 1/2 MRL Non-detect values = 0 Non-detect values = 1/2 MRL Non-detect values = 0 Ground Water > 3 |jg/i 993 993 0.001% 0.001% Ground Water, cont. (91,710,210) > 1.5 |jg/L 1,298 1,298 0.001% 0.001% > 2 |jg/L 1,298 1,298 0.001% 0.001% > 1 |jg/L1 8,739 1,298 0.010% 0.001% Surface Water (132,718,761) > 3 |jg/L 232,226 232,226 0.175% 0.175% > 1.5 |jg/L 706,367 706,367 0.532% 0.532% > 2 |jg/L 706,367 232,226 0.532% 0.175% > 1 |jg/L1 706,367 706,367 0.532% 0.532% Combined Ground & Surface Water (223,888,971) > 3 |jg/L 233,219 233,219 0.104% 0.104% > 1.5 |jg/L 707,665 707,665 0.316% 0.316% > 2 |jg/L 707,665 233,524 0.316% 0.104% > 1 |jg/L1 715,106 707,665 0.319% 0.316% 1 The new potential threshold of concern for this contaminant is based on the EQL. The EQL represents the potential quantitation capabilities below a PQL (USEPA, 2016d). Data for toxaphene were available from 49 states/entities. Four states did not submit data for use in the Six-Year Review (Colorado, Delaware, Georgia and Mississippi). Although the States of Colorado and Mississippi did not provide data for any contaminants for the SYR3 ICR Dataset, these states are included in the table below because a handful of tribal water systems located within these two states did submit toxaphene data. New Jersey did submit Six-Year data for most contaminants. There is a statewide waiver for toxaphene in New Jersey, however, so no toxaphene data were available from that state. Exhibit B-59 presents the total number of systems in each state that submitted data for toxaphene. In addition, the geographic distribution of toxaphene occurrence in drinking water is illustrated by showing states with systems with a mean concentration greater than the EQL, two times the EQL, V2 MCL and MCL concentrations. (Note: Only the V2 MRL substitution results are presented in this exhibit.) The distribution of systems with mean concentrations of toxaphene is geographically dispersed. Detection rates were generally low; only two states had an estimated mean concentration greater than the MCL. (New Mexico and North Carolina each contained a SYR3 Occurrence Support Document B-122 December 2016 ------- single system with a mean concentration greater than the MCL in each state.) Six systems in five states had estimated mean concentrations greater than the EQL. Exhibit B-59: Toxaphene Stage 2 Analysis - Summary of Systems with a Mean Threshold Exceedance by State12 State Total Number of Systems Systems with a Mean Concentration > 1 mq/l3 Systems with a Mean Concentration > 2 jjg/L Systems with a Mean Concentration >1.5 jjg/L Systems with a Mean Concentration > 3 jjg/L Number Percent Number Percent Number Percent Number Percent AK 12 AL 382 AR 459 AS 11 AZ 872 CA 1,271 1 0.08% 1 0.08% 1 0.08% 0 0.00% CO 1 CT 1,137 DC 1 FL 2,086 HI 111 IA 1 ID 386 IL 1,466 IN 1,212 KS 87 KY 225 LA 946 1 0.11% 0 0.00% 0 0.00% 0 0.00% MA 565 MD 45 ME 160 Ml 2,439 MN 920 MO 1,332 MS 5 MT 857 NC 2,347 2 0.09% 2 0.09% 2 0.09% 1 0.04% SYR3 Occurrence Support Document B-123 December 2016 ------- State Total Number of Systems Systems with a Mean Concentration > 1 mq/l3 Systems with a Mean Concentration > 2 jjg/L Systems with a Mean Concentration >1.5 jjg/L Systems with a Mean Concentration > 3 jjg/L Number Percent Number Percent Number Percent Number Percent ND 157 NE 639 NH 1,146 NJ 0 NM 718 1 0.14% 1 0.14% 1 0.14% 1 0.14% NV 303 NY 2,117 OH 18 OK 38 OR 1,118 PA 1,045 1 0.10% 0 0.00% 0 0.00% 0 0.00% Rl 73 SC 497 SD 269 TN 6 TX 3,981 UT 428 VA 254 VT 380 WA 1,996 Wl 1,914 WV 292 WY 318 Total 37,043 6 0.02% 4 0.01% 4 0.01% 2 0.01% 1 Results are based on setting all non-detection results equal to % the MRL values in the SYR3 ICR dataset. 2 Blank cells within the table indicate that there were no systems with a mean concentration that exceeded any of the thresholds. 3 The new potential threshold of concern for this contaminant is based on the EQL. The EQL represents the potential quantitation capabilities below a PQL (USEPA, 2016d). Exhibit B-60 presents the population served by systems with a mean concentration greater than the MCL concentration by state. The total population served by systems in each state that submitted data for toxaphene is presented, as well. As described above, North Carolina and New Mexico were the only two states with an estimated mean concentration greater than the MCL of SYR3 Occurrence Support Document B-124 December 2016 ------- 3 jug/L. Six systems in 5 states, serving 715,106 people, had estimated mean concentrations greater than the EQL of 1 |ig/L. Exhibit B-60: Toxaphene Stage 2 Analysis - Summary of Population Served by Systems with a Mean Threshold Exceedance by State12 State Total Population Population Served by Systems with a Mean Concentration > 1 |ig/L3 Population Served by Systems with a Mean Concentration > 2 |jg/L Population Served by Systems with a Mean Concentration > 1.5 |jg/L Population Served by Systems with a Mean Concentration > 3 |jg/L Population Percent Population Percent Population Percent Population Percent AK 39,530 AL 5,332,585 AR 2,635,934 AS 62,196 AZ 6,487,437 CA 35,717,333 474,141 1.33% 474,141 1.33% 474,141 1.33% 0 0.00% CO 2,020 CT 2,925,135 DC 761,124 FL 18,943,061 HI 1,479,317 IA 438 ID 976,182 IL 10,997,746 IN 4,969,942 KS 1,817,722 KY 4,225,473 LA 4,709,163 6,916 0.15% 0 0.00% 0 0.00% 0 0.00% MA 9,163,377 MD 3,991,250 ME 356,698 Ml 7,221,983 MN 3,752,545 MO 5,233,314 MS 6,176 MT 845,294 SYR3 Occurrence Support Document B-125 December 2016 ------- State Total Population Population Served by Systems with a Mean Concentration > 1 |ig/L3 Population Served by Systems with a Mean Concentration > 2 |jg/L Population Served by Systems with a Mean Concentration > 1.5 |jg/L Population Served by Systems with a Mean Concentration > 3 |jg/L Population Percent Population Percent Population Percent Population Percent NC 7,832,302 232,531 2.97% 232,531 2.97% 232,531 2.97% 232,226 2.96% ND 592,232 NE 1,646,746 NH 949,308 NJ 0 NM 1,940,795 993 0.05% 993 0.05% 993 0.05% 993 0.05% NV 2,681,668 NY 10,480,954 OH 676,533 OK 136,313 OR 3,432,307 PA 10,853,332 525 0.00% 0 0.00% 0 0.00% 0 0.00% Rl 989,530 SC 3,622,250 SD 708,340 TN 1,168,508 TX 23,671,855 UT 2,752,741 VA 5,685,070 VT 386,948 WA 4,942,339 Wl 4,236,887 WV 1,379,328 WY 469,710 Total 223,888,971 715,106 0.32% 707,665 0.32% 707,665 0.32% 233,219 0.10% 1 Results are based on setting all non-detection results equal to % the MRL values in the SYR3 ICR dataset. 2 Blank cells within the table indicate that there were no systems with a mean concentration that exceeded any of the thresholds. 3 The new potential threshold of concern for this contaminant is based on the EQL. The EQL represents the potential quantitation capabilities below a PQL (USEPA, 2016d). SYR3 Occurrence Support Document B-126 December 2016 ------- B.15.3 Summary of Data A total of 127,187 analytical results from 37,043 PWSs in 49 states/entities were available in the SYR3 ICR Dataset for toxaphene. The Stage 2 analysis of occurrence in drinking water indicated that 2 water systems (1 ground water system and 1 surface water system), serving a total population of 233,219 people, had an estimated system mean concentration of toxaphene greater than the MCL concentration of 3 |ig/L. Six water systems, serving 715,106 people, had an estimated mean concentration greater than the EQL of 1 |ig/L. SYR3 Occurrence Support Document B-127 December 2016 ------- B.16 l,l?2-Trichloroethane This chapter on 1,1,2-trichloroethane includes background information such as the regulatory history and a summary of monitoring requirements, as well as occurrence and exposure estimates in drinking water. All drinking water occurrence estimates are based on data from the National Compliance Monitoring Information Collection Request (ICR) Dataset for the Third Six-Year Review (the "SYR3 ICR Dataset"). B.16.1 Background The United States Environmental Protection Agency (EPA) published the current National Primary Drinking Water Regulations (NPDWR) for 1,1,2-trichloroethane on July 17, 1992 (57 FR 31776; USEPA, 1992). The NPDWR established a maximum contaminant level goal (MCLG) of 3 |ig/L based on a reference dose (RfD) of 4 |ig/kg-day (0.004 mg/kg-day) and a cancer classification of C, possible human carcinogen. The NPDWR also established a maximum contaminant level (MCL) of 5 |ig/L based on analytical feasibility. 1,1,2-Trichloroethane is regulated as a volatile organic compound (VOC) in drinking water. All non-purchased community water systems (CWSs) and non-transient non-community water systems (NTNCWSs) are required to sample for VOCs. The maximum waiver period for VOCs is two compliance periods for ground water systems and one compliance period for surface water systems. All CWSs and NTNCWSs must collect four consecutive quarterly samples during the initial three-year compliance period.31 If all four samples are non-detections, then the system may reduce to annual sampling. After three annual samples without a detection, and upon conducting a vulnerability assessment, a system may be granted a waiver. During the waiver period, the ground water system must sample at least once, while surface water system must sample at the frequency specified by the state. If a compound is detected, the system must take one sample per quarter until results are below the MCL (minimum of two quarterly samples for ground water systems and four quarterly samples for surface water systems). If all quarterly samples are reliably and consistently below the MCL, the system may return to annual sampling. If a compound is detected at a level greater than the MCL, the system (whether ground water or surface water) must take four consecutive quarterly samples until all are below the MCL. If all quarterly samples are below the MCL, the system may return to annual sampling. B.16.2 Occurrence in Drinking Water The analysis of 1,1,2-trichloroethane occurrence presented in the following section is based on state compliance monitoring data from the SYR3 ICR Dataset. These data consist of 371,877 analytical results from 55,733 public water systems (PWSs) during the period from 2006 to 2011. The number of sample results and systems vary by state, although the state datasets have been reviewed and checked to ensure adequacy of coverage and completeness. 31 All new systems or systems using a new water source that began operation after January 22, 2004 must demonstrate compliance with the MCL within a period of time specified by the State. The system must also comply with the initial sampling frequencies specified by the State to ensure that a system can demonstrate compliance with the MCL. SYR3 Occurrence Support Document B-128 December 2016 ------- EPA used a two-stage analytical approach to estimate the national contaminant occurrence using the SYR3 ICR Dataset. In the "Stage 1 analysis," the occurrence data were analyzed to generate simple non-parametric estimates and descriptive statistics of national contaminant occurrence in public water systems. Simple counts were made of the number and percentage of systems and population served by systems with at least one compliance monitoring sample result greater than a specified concentration threshold. The Stage 1 analysis provides occurrence assessments that are more conservative and may be more reflective of potential acute exposure than the assessments from the Stage 2 analyses. Details on the Stage 1 analysis are presented in Section 6. Based on the evaluation of the health effects and analytical methods as part of the Six-Year Review protocol, EPA selected a set of contaminants, including 1,1,2-trichloroethane, for which Stage 2 analyses were warranted. The Stage 2 analysis estimates national contaminant occurrence by generating estimated long-term mean concentrations of contaminants for each system. This provides occurrence analyses that are less conservative than the Stage 1 analysis, since the Stage 2 analysis is based on estimated mean concentrations rather than on a single maximum concentration. Also, because the Stage 2 analyses generate long-term (multi-year) mean concentration estimates for contaminant occurrence at systems, the analyses can support assessments of population served by systems with detections or potential exposure assessments that may be more reflective of potential chronic exposure than the assessments from the Stage 1 analyses. For the Stage 2 analyses, system arithmetic means that were calculated using all sample detection records and all non-detection records. Three different substitution values -zero, V2 the minimum reporting level (MRL) value and the full MRL value- were used to replace each non- detection record. Three arithmetic mean 1,1,2-trichloroethane concentrations were calculated at each system using the zero, V2 MRL and full MRL substitution values. These mean calculations were performed for all systems with data in the SYR3 ICR dataset. Then, the percentages of all systems with a mean concentration greater than each threshold were calculated. For 1,1,2- trichloroethane, EPA generated Stage 2 occurrence estimates relative to the MCL and the MCLG. Note: The national modal MRL for 1,1,2-trichloroethane in the dataset is 0.5 |ig/L. Stage 2 Occurrence Estimates Stage 2 analyses for 1,1,2-trichloroethane are summarized in this section. Occurrence estimates were generated relative to the following thresholds: 5 |ig/L (the MCL) and 3 |ig/L (the MCLG). Because the current MCLG of 3 |ig/L is lower than the PQL for 1,1,2-trichloroethane of 5 |ig/L, the threshold of interest for the occurrence analysis is the current MCLG of 3 |ig/L. For more information on the new potential thresholds of concern used in the SYR3 Stage 2 analyses, refer to USEPA (2016d) and (2016e). Exhibit B-61 presents the system-level Stage 2 analysis of estimated mean concentrations for 1,1,2-trichloroethane occurrence in drinking water. Exhibit B-62 presents similar information based on population served by the systems. Based on the Stage 2 analyses, zero water systems had an estimated system mean greater than the MCL concentration of 5 |ig/L or the MCLG of 3 Hg/L- SYR3 Occurrence Support Document B-129 December 2016 ------- Exhibit B-61: 1,1,2-Trichloroethane Stage 2 Analysis - Summary of Systems with a Mean Threshold Exceedance Source Water Type (Number of Systems) Threshold Number of Systems with Mean Concentrations That Are Greater Than the Threshold Percent of Systems with Mean Concentrations That Are Greater Than the Threshold Non-detect values = MRL Non-detect values = 1/2 MRL Non-detect values = 0 Non-detect values = MRL Non-detect values = 1/2 MRL Non-detect values = 0 Ground Water (51,300) > 5 |jg/i 0 0 0 0.000% 0.000% 0.000% > 3 |jg/L1 0 0 0 0.000% 0.000% 0.000% Surface Water (4,433) > 5 |jg/L 0 0 0 0.000% 0.000% 0.000% > 3 |jg/L1 0 0 0 0.000% 0.000% 0.000% Combined Ground & Surface Water (55,733) > 5 |jg/L 0 0 0 0.000% 0.000% 0.000% > 3 |jg/L1 0 0 0 0.000% 0.000% 0.000% 1 The threshold of interest for this contaminant is the current MCLG. Exhibit B-62: 1,1,2-Trichloroethane Stage 2 Analysis - Summary of Population Served by Systems with a Mean Threshold Exceedance Source Water Type (Population Served by Systems) Threshold Population Served by Systems with Mean Concentrations That Are Greater Than the Threshold Percent of Population Served by Systems with Mean Concentrations That Are Greater Than the Threshold Non-detect values = MRL Non-detect values = 1/2 MRL Non-detect values = 0 Non-detect values = MRL Non-detect values = 1/2 MRL Non-detect values = 0 Ground Water (110,769,873) > 5 |jg/L 0 0 0 0.000% 0.000% 0.000% > 3 |jg/L1 0 0 0 0.000% 0.000% 0.000% Surface Water (152,603,695) > 5 |jg/L 0 0 0 0.000% 0.000% 0.000% > 3 |jg/L1 0 0 0 0.000% 0.000% 0.000% Combined Ground & Surface Water (263,373,568) > 5 |jg/L 0 0 0 0.000% 0.000% 0.000% > 3 |jg/L1 0 0 0 0.000% 0.000% 0.000% 1 The threshold of interest for this contaminant is the current MCLG. SYR3 Occurrence Support Document B-130 December 2016 ------- Data for 1,1,2-trichloroethane were available from 50 states/entities. Four states did not submit data for use in the Six-Year Review (Colorado, Delaware, Georgia and Mississippi). Although the States of Colorado and Mississippi did not provide data for any contaminants for the SYR3 ICR Dataset, these states are included in the table below because a handful of tribal water systems located within these two states did submit 1,1,2-trichloroethane data. Exhibit B-63 presents the total number of systems in each state that submitted data for 1,1,2- trichloroethane. In addition, the geographic distribution of 1,1,2-trichloroethane occurrence in drinking water is illustrated by showing states with systems with a mean concentration greater than the MCLG and MCL concentrations. (Note: Only the V2 MRL substitution results are presented in this exhibit.) As is described above, no systems had an estimated mean concentration greater than the MCL or the MCLG. Exhibit B-63: 1,1,2-Trichloroethane Stage 2 Analysis - Summary of Systems with a Mean Threshold Exceedance by State12 State Total Number of Systems Systems with a Mean Concentration > 3 |ig/L3 Systems with a Mean Concentration > 5 |jg/L Number Percent Number Percent AK 595 AL 384 AR 461 AS 11 AZ 1,109 CA 3,814 CO 1 CT 1,202 DC 1 FL 2,633 HI 110 IA 1,043 ID 839 IL 1,493 IN 1,196 KS 602 KY 227 LA 1,102 MA 721 MD 1,053 SYR3 Occurrence Support Document B-131 December 2016 ------- State Total Number of Systems Systems with a Mean Concentration > 3 |ig/L3 Systems with a Mean Concentration > 5 |jg/L Number Percent Number Percent ME 784 Ml 2,419 MN 1,462 MO 1,445 MS 5 MT 897 NC 2,356 ND 160 NE 705 NH 1,185 NJ 1,434 NM 743 NV 350 NY 2,498 OH 1,922 OK 685 OR 1,132 PA 3,166 Rl 152 SC 494 SD 313 TN 366 TX 4,532 UT 471 VA 1,630 VT 634 WA 2,468 Wl 2,026 WV 385 WY 317 Total 55,733 0 0.00% 0 0.00% SYR3 Occurrence Support Document B-132 December 2016 ------- 1 Results are based on setting all non-detection results equal to % the MRL values in the SYR3 ICR dataset. 2 Blank cells within the table indicate that there were no systems with a mean concentration that exceeded either threshold. 3 The threshold of interest for this contaminant is the current MCLG. Exhibit B-64 presents the population served by systems with a mean concentration greater than the MCL concentration by state. As described above, no systems had an estimated mean concentration greater than the MCL or the MCLG. Exhibit B-64: 1,1,2-Trichloroethane Stage 2 Analysis - Summary of Population Served by Systems with a Mean Threshold Exceedance by State12 State Total Population Population Served by Systems with a Mean Concentration > 3 |ig/L3 Population Served by Systems with a Mean Concentration > 5 |jg/L Population Percent Population Percent AK 719,561 AL 5,334,584 AR 2,637,712 AS 62,196 AZ 6,669,227 CA 40,641,146 CO 2,020 CT 2,937,643 DC 761,124 FL 19,280,091 HI 1,402,969 IA 2,734,678 ID 1,219,635 IL 11,019,196 IN 4,940,108 KS 2,605,030 KY 4,225,914 LA 4,966,653 MA 9,329,953 MD 5,120,409 ME 757,984 Ml 3,470,708 MN 4,373,668 SYR3 Occurrence Support Document B-133 December 2016 ------- State Total Population Population Served by Systems with a Mean Concentration > 3 |ig/L3 Population Served by Systems with a Mean Concentration > 5 |jg/L Population Percent Population Percent MO 5,293,851 MS 6,176 MT 856,529 NC 7,827,828 ND 592,539 NE 1,664,802 NH 961,134 NJ 9,273,130 NM 1,960,247 NV 2,697,555 NY 10,637,039 OH 10,209,121 OK 3,588,559 OR 3,434,191 PA 11,234,684 Rl 1,040,737 SC 3,637,408 SD 757,925 TN 6,578,052 TX 23,863,702 UT 2,802,068 VA 6,908,704 VT 486,604 WA 5,535,827 Wl 4,273,462 WV 1,570,171 WY 469,314 Total 263,373,568 0 0.00% 0 0.00% 1 Results are based on setting all non-detection results equal to % the MRL values in the SYR3 ICR dataset. 2 Blank cells within the table indicate that there were no systems with a mean concentration that exceeded either threshold. 3 The threshold of interest for this contaminant is the current MCLG. SYR3 Occurrence Support Document B-134 December 2016 ------- B.16.3 Summary of Data A total of 371,877 analytical results from 55,733 PWSs in 50 states/entities were available in the SYR3 ICRDataset for 1,1,2-trichloroethane. The Stage 2 analysis of occurrence in drinking water indicated that zero systems had an estimated system mean concentration of 1,1,2- trichloroethane greater than the MCL concentration of 5 |ig/L or the MCLG concentration of 3 Hg/L- SYR3 Occurrence Support Document B-135 December 2016 ------- B.17 Xylenes This chapter on xylenes includes background information such as the regulatory history and a summary of monitoring requirements, as well as occurrence and exposure estimates in drinking water. All drinking water occurrence estimates are based on data from the National Compliance Monitoring Information Collection Request (ICR) Dataset for the Third Six-Year Review (the "SYR3 ICR Dataset"). B.17.1 Background The United States Environmental Protection Agency (EPA) published the current National Primary Drinking Water Regulations (NPDWR) for total xylenes on January 30, 1991 (56 FR 3526; USEPA, 1991a). The NPDWR established a maximum contaminant level goal (MCLG) and a maximum contaminant level (MCL) of 10,000 |ig/L. The Agency based the MCLG on a reference dose (RfD) of 2,000 |ig/kg-day (2 mg/kg-day) and a cancer classification of D, not classifiable as to human carcinogenicity. Xylenes are regulated as volatile organic compounds (VOCs) in drinking water. All non- purchased community water systems (CWSs) and non-transient non-community water systems (NTNCWSs) are required to sample for VOCs. The maximum waiver period for VOCs is two compliance periods for ground water systems and one compliance period for surface water systems. All CWSs and NTNCWSs must collect four consecutive quarterly samples during the initial three-year compliance period.32 If all four samples are non-detections, then the system may reduce to annual sampling. After three annual samples without a detection, and upon conducting a vulnerability assessment, a system may be granted a waiver. During the waiver period, the ground water system must sample at least once, while surface water system must sample at the frequency specified by the state. If a compound is detected, the system must take one sample per quarter until results are below the MCL (minimum of two quarterly samples for ground water systems and four quarterly samples for surface water systems). If all quarterly samples are reliably and consistently below the MCL, the system may return to annual sampling. If a compound is detected at a level greater than the MCL, the system (whether ground water or surface water) must take four consecutive quarterly samples until all are below the MCL. If all quarterly samples are below the MCL, the system may return to annual sampling. B.17.2 Occurrence in Drinking Water The analysis of xylenes occurrence presented in the following section is based on state compliance monitoring data from the SYR3 ICR Dataset. These data consist of 323,477 analytical results from 51,074 public water systems (PWSs) during the period from 2006 to 32 All new systems or systems using a new water source that began operation after January 22, 2004 must demonstrate compliance with the MCL within a period of time specified by the State. The system must also comply with the initial sampling frequencies specified by the State to ensure that a system can demonstrate compliance with the MCL. SYR3 Occurrence Support Document B-136 December 2016 ------- 2011. The number of sample results and systems vary by state, although the state datasets have been reviewed and checked to ensure adequacy of coverage and completeness. EPA used a two-stage analytical approach to estimate the national contaminant occurrence using the SYR3 ICR Dataset. In the "Stage 1 analysis," the occurrence data were analyzed to generate simple non-parametric estimates and descriptive statistics of national contaminant occurrence in public water systems. Simple counts were made of the number and percentage of systems and population served by systems with at least one compliance monitoring sample result greater than a specified concentration threshold. The Stage 1 analysis provides occurrence assessments that are more conservative and may be more reflective of potential acute exposure than the assessments from the Stage 2 analyses. Details on the Stage 1 analysis are presented in Section 6. Based on the evaluation of the health effects and analytical methods as part of the Six-Year Review protocol, EPA selected a set of contaminants, including xylenes, for which Stage 2 analyses were warranted. The Stage 2 analysis estimates national contaminant occurrence by generating estimated long-term mean concentrations of contaminants for each system. This provides occurrence analyses that are less conservative than the Stage 1 analysis, since the Stage 2 analysis is based on estimated mean concentrations rather than on a single maximum concentration. Also, because the Stage 2 analyses generate long-term (multi-year) mean concentration estimates for contaminant occurrence at systems, the analyses can support assessments of population served by systems with detections or potential exposure assessments that may be more reflective of potential chronic exposure than the assessments from the Stage 1 analyses. For the Stage 2 analyses, system arithmetic means were calculated using all sample detection records and all non-detection records. Three different substitution values -zero, V2 the minimum reporting level (MRL) value and the full MRL value- were used to replace each non-detection record. (The national modal MRL for xylenes in the dataset is 0.5 |ig/L.) Three arithmetic mean xylenes concentrations were calculated at each system using the zero, V2 MRL and full MRL substitution values. These mean calculations were performed for all systems with xylenes data in the SYR3 ICR dataset. Then, the percentages of all systems with a mean concentration greater than each threshold were calculated. For xylenes, since there were no analytical method limitations at the potential MCLG, EPA generated Stage 2 occurrence estimates relative to the MCL and the potential MCLG. Stage 2 Occurrence Estimates Stage 2 analyses for xylenes are summarized in this section. Occurrence estimates were generated relative to the following thresholds: 10,000 |ig/L (the MCL) and 1,000 |ig/L (the potential MCLG). The potential MCLG is due to changes in the RfD based on new health effects information. Since the practical quantitation level (PQL) for xylenes is less than the possible MCLG, EPA designated the possible MCLG as the threshold for the occurrence analysis. For more information on the new potential thresholds of concern used in the SYR3 Stage 2 analyses, refer to USEPA (2016d) and (2016e). SYR3 Occurrence Support Document B-137 December 2016 ------- Exhibit B-65 presents the system-level Stage 2 analysis of estimated mean concentrations for xylenes occurrence in drinking water. Exhibit B-66 presents similar information based on population served by the systems. Based on the Stage 2 analyses, no systems had an estimated system mean greater than the MCL concentration of 10,000 |ig/L. Two systems, serving 825 people, had an estimated system mean greater than the potential MCLG concentration of 1,000 Hg/L- Exhibit B-65: Xylenes Stage 2 Analysis - Summary of Systems with a Mean Threshold Exceedance Source Water Type (Number of Systems) Threshold Number of Systems with Mean Concentrations That Are Greater Than the Threshold Percent of Systems with Mean Concentrations That Are Greater Than the Threshold Non-detect values = MRL Non-detect values = 1/2 MRL Non- detect values = 0 Non- detect values = MRL Non-detect values = 1/2 MRL Non-detect values = 0 Ground Water (47,037) > 10,000 |jg/L 0 0 0 0.000% 0.000% 0.000% > 1,000 |jg/L1 2 2 2 0.004% 0.004% 0.004% Surface Water (4,037) > 10,000 |jg/L 0 0 0 0.000% 0.000% 0.000% > 1,000 |jg/L1 0 0 0 0.000% 0.000% 0.000% Combined Ground & Surface Water (51,074) > 10,000 |jg/L 0 0 0 0.000% 0.000% 0.000% > 1,000 |jg/L1 2 2 2 0.004% 0.004% 0.004% 1 The new potential threshold of concern for this contaminant is due to changes in the RfD based on new health effects information. Exhibit B-66: Xylenes Stage 2 Analysis - Summary of Population Served by Systems with a Mean Threshold Exceedance Source Water Type (Population Served by Systems) Threshold Population Served by Systems with Mean Concentrations That Are Greater Than the Threshold Percent of Population Served by Systems with Mean Concentrations That Are Greater Than the Threshold Non-detect values = MRL Non-detect values = 1/2 MRL Non- detect values = 0 Non- detect values = MRL Non-detect values = 1/2 MRL Non-detect values = 0 Ground Water > 10,000 |jg/L 0 0 0 0.000% 0.000% 0.000% (106,335,621) > 1,000 |jg/L1 825 825 825 0.0008% 0.0008% 0.0008% Surface Water > 10,000 |jg/L 0 0 0 0.000% 0.000% 0.000% > 1,000 |jg/L1 0 0 0 0.000% 0.000% 0.000% SYR3 Occurrence Support Document B-138 December 2016 ------- Source Water Type (Population Served by Systems) Threshold Population Served by Systems with Mean Concentrations That Are Greater Than the Threshold Percent of Population Served by Systems with Mean Concentrations That Are Greater Than the Threshold Non-detect values = MRL Non-detect values = 1/2 MRL Non- detect values = 0 Non- detect values = MRL Non-detect values = 1/2 MRL Non-detect values = 0 Combined Ground & Surface Water > 10,000 |jg/L 0 0 0 0.000% 0.000% 0.000% (248,916,224) > 1,000 |jg/L1 825 825 825 0.0003% 0.0003% 0.0003% 1 The new potential threshold of concern for this contaminant is due to changes in the RfD based on new health effects information. Data for xylenes were available from 50 states/entities. Four states did not submit data for use in the Six-Year Review (Colorado, Delaware, Georgia and Mississippi). Although the States of Colorado and Mississippi did not provide data for any contaminants for the SYR3 ICR Dataset, these states are included in the count of 50 states because a handful of tribal water systems located within these 2 states did submit xylenes data. Exhibit B-67 presents the total number of systems in each state that submitted data for xylenes. In addition, the geographic distribution of xylenes occurrence in drinking water is illustrated by showing states with systems with a mean concentration greater than the potential MCLG and MCL concentrations. (Note: Only the V2 MRL substitution results are presented in this exhibit.) As was stated above, no systems had an estimated mean concentration greater than the MCL. Two systems in two states (Michigan and Pennsylvania) had estimated mean concentrations greater than the potential MCLG of 1,000 |ig/L. Exhibit B-67: Xylenes Stage 2 Analysis - Summary of Systems with a Mean Threshold Exceedance by State12 State Total Number of Systems Systems with a Mean Concentration > 1,000 |jg/L3 Systems with a Mean Concentration > 10,000 |jg/L Number Percent Number Percent AK 596 AL 384 AR 461 AS 11 AZ 1,111 CA 3,790 CO 1 CT 5 SYR3 Occurrence Support Document B-139 December 2016 ------- State Total Number of Systems Systems with a Mean Concentration > 1,000 |jg/L3 Systems with a Mean Concentration > 10,000 |jg/L Number Percent Number Percent DC 1 FL 2,633 HI 18 IA 1,085 ID 839 IL 1,493 IN 1,196 KS 608 KY 227 LA 1,102 MA 721 MD 1,055 ME 749 Ml 2,419 1 0.04% 0 0.00% MN 1,466 MO 1,445 MS 5 MT 897 NC 2,356 ND 160 NE 705 NH 1,185 NJ 1,428 NM 744 NV 350 NY 20 OH 1,922 OK 685 OR 1,132 PA 3,166 1 0.03% 0 0.00% SYR3 Occurrence Support Document B-140 December 2016 ------- State Total Number of Systems Systems with a Mean Concentration > 1,000 |jg/L3 Systems with a Mean Concentration > 10,000 |jg/L Number Percent Number Percent Rl 152 SC 494 SD 313 TN 366 TX 3,826 UT 471 VA 1,629 VT 465 WA 2,458 Wl 2,026 WV 386 WY 317 Total 51,074 2 0.004% 0 0.00% 1 Results are based on setting all non-detection results equal to % the MRL values in the SYR3 ICR dataset. 2 Blank cells within the table indicate that there were no systems with a mean concentration that exceeded either threshold. 3 The new potential threshold of concern for this contaminant is due to changes in the RfD based on new health effects information. Exhibit B-68 presents the population served by systems with a mean concentration greater than the MCL concentration by state. The total population served by systems in each state that submitted data for xylenes is presented, as well. As described above, no systems had an estimated mean concentration greater than the MCL. Two systems, serving 825 people, had estimated mean concentrations greater than the potential MCLG (1,000 |ig/L). Exhibit B-68: Xylenes Stage 2 Analysis - Summary of Population Served by Systems with a Mean Threshold Exceedance by State12 State Total Population Population Served by Systems with a Mean Concentration > 1,000 |jg/L3 Population Served by Systems with a Mean Concentration > 10,000 |jg/L Population Percent Population Percent AK 719,618 AL 5,334,584 AR 2,637,712 AS 62,196 AZ 6,669,311 SYR3 Occurrence Support Document B-141 December 2016 ------- State Total Population Population Served by Systems with a Mean Concentration > 1,000 |jg/L3 Population Served by Systems with a Mean Concentration > 10,000 |jg/L Population Percent Population Percent CA 40,638,016 CO 2,020 CT 193,473 DC 761,124 FL 19,280,091 HI 1,094,345 IA 2,759,457 ID 1,219,635 IL 11,019,196 IN 4,940,108 KS 2,608,108 KY 4,225,914 LA 4,966,653 MA 9,329,953 MD 5,120,434 ME 754,554 Ml 3,470,708 25 0.001 % 0 0.00% MN 4,375,774 MO 4,975,051 MS 6,176 MT 856,529 NC 7,827,828 ND 592,539 NE 1,664,802 NH 961,134 NJ 9,272,654 NM 1,962,298 NV 2,697,555 NY 32,600 OH 10,209,121 OK 3,588,559 SYR3 Occurrence Support Document B-142 December 2016 ------- State Total Population Population Served by Systems with a Mean Concentration > 1,000 |jg/L3 Population Served by Systems with a Mean Concentration > 10,000 |jg/L Population Percent Population Percent OR 3,434,191 PA 11,234,684 800 0.01% 0 0.00% Rl 1,040,737 SC 3,637,408 SD 757,925 TN 6,578,052 TX 23,407,822 UT 2,802,068 VA 6,908,536 VT 436,629 WA 5,535,245 Wl 4,273,462 WV 1,570,321 WY 469,314 Total 248,916,224 825 0.0003% 0 0.00% 1 Results are based on setting all non-detection results equal to % the MRL values in the SYR3 ICR dataset. 2 Blank cells within the table indicate that there were no systems with a mean concentration that exceeded either threshold. 3 The new potential threshold of concern for this contaminant is due to changes in the RfD based on new health effects information. B.17.3 Summary of Data A total of 323,477 analytical results from 51,074 PWSs in 50 states/entities were available in the SYR3 ICR Dataset for xylenes. The Stage 2 analysis of occurrence in drinking water indicated that zero systems had an estimated system mean concentration of xylenes greater than the MCL concentration of 10,000 |ig/L. Two ground water systems, serving a total of 825 people, had an estimated mean concentration greater than the potential MCLG (1,000 |ig/L). These two systems were located in Michigan and Pennsylvania. SYR3 Occurrence Support Document B-143 December 2016 ------- |