ICR for UCMR 3 Final Rule March 2012
The primary objective of the statistical methods applied in this information collection is for EPA to identify and select a sample of PWSs that is representative of PWSs nationwide. The selected sample of PWSs will conduct monitoring of contaminants identified by the UCMR program. The representativeness of this sample of systems is critical to the UCMR program because the drinking water contaminant occurrence data collected by the PWSs will be used to: estimate national occurrence and exposure, establish a baseline for health effects and economic analyses, and provide information for regulatory determinations and, as appropriate, regulatory development.
Key variables associated with selecting a nationally representative sample of PWSs include: system size, source water type, and geographical location.
Section 1445(a)(2) of SDWA (as amended in 1996) requires that the UCMR program include only a representative sample of systems serving 10,000 or fewer people. In addition to satisfying statutory requirements, selection of a sample of systems for participation in UCMR allows for significant national costs savings, as compared to monitoring by all PWSs. To estimate national occurrence and exposure, the primary UCMR program objective, the representative sample of PWSs must allow EPA to collect high quality data about contaminant occurrence.
EPA anticipates that the survey (the statistical sample) objectives are achievable given the existing time and resource constraints.
High PWS response/participation rates (>95%) during UCMR 1 and 2 have given EPA confidence that equivalent or better participation rates can be achieved during UCMR 3.
The statistical approach to this data collection requires only a fraction of small systems to conduct monitoring, resulting in much smaller cost and burden at the national level than would be incurred if all systems monitored. Small systems that are selected for UCMR 3 monitoring will incur only a few hours of labor burden. EPA will pay for all laboratory fees and shipping costs related to small system testing.
• The survey results will be completed in time to inform the next cycle of CCL regulatory determinations.
PWSs are the target population for UCMR monitoring. All PWSs that serve more than 10,000 retail customers will be subject to the Assessment Monitoring component of UCMR 3 monitoring. Eligible small PWSs (serving 10,000 or fewer people) will only be required to conduct UCMR 3 monitoring if they are part of the statistical selection for Assessment Monitoring, the Screening Survey, or if they have been selected to monitor for Pre-Screen Testing. Small PWSs will only be selected to monitor for one component of UCMR 3.
EPA will develop the sample frame for the statistical selection of UCMR systems, including the system PWSID, name, source water category, and population-served data for each UCMR-eligible PWS. Initial data will be pulled from EPA's Safe Drinking Water Information System (SDWIS/FED) inventory database, and will be adjusted to account for known anomalies in population and inventory reporting (for example, how wholesalers report their population data).
UCMR 3 monitoring will include: Assessment Monitoring conducted by all PWSs serving more than 10,000 people (“large” PWSs), and 800 representative PWSs serving 10,000 or fewer people (“small” PWSs); the Screening survey conducted by all 413 systems serving more than 100,000 people (“very large” PWSs), 320 large PWSs, and 480 small PWSs; and Pre-Screen Testing conducted by 800 undisinfected ground water systems serving 1,000 or fewer people. The Pre-Screen Testing systems will be located in areas with sensitive aquifers containing fractured or karst bedrock.
In developing the representative sample, EPA considered factors such as population served, water source, and geographic location. The sample PWSs will be stratified by population served (system size), allocating samples proportionately to each State by system size, and then by water source type. (Other provisions, presented below, ensure broad geographic coverage.)
To satisfy the specifications of SDWA section 1445(a)(2)(A), the representative sample of systems will account for different system sizes, sources of water supply, and geographic location (e.g., States). The sample will be stratified by water source type (i.e., ground or surface water) and by system size category (i.e., serves 25 to 500 people, 501 to 3,300 people, etc.). This stratification allows EPA to account for different exposure risks of contaminant occurrence that may be related to the vulnerability differences between surface and ground water sources and differing management and financial capacity that can vary across system sizes.
With contaminant exposure assessment as a primary goal, systems will be selected in proportion to the population served, as was generally done under UCMR 1 and UCMR 2. This population-weighted allocation leads to statistically valid estimates of national exposure. To ensure the sample provides equity across States for involvement in the UCMR, EPA will include at least two systems from each State. This additional PWS selection requirement will provide allocation across all the States and territories to account for differences in spatial vulnerability and contaminant occurrence, and to ensure equity in participation. Small Tribal water systems across the EPA Regions are grouped into a single category (equivalent to a “State”) for the representative sample.
Because PWS status often changes over time, EPA will also select “alternate” systems that fit the size/source water strata of the originally selected system. Through an interactive review process with the States, systems that no longer meet eligibility criteria (for example, if they are in a different size category than when originally selected, have become inactive, or do not have a retail customer base) will be replaced by an alternate system that meets the stratification criteria.
The representative sample of PWSs must be selected so that the data collected yield accurate and precise estimates of national contaminant occurrence (the fraction of systems in which a contaminant occurs) and exposure (the fraction of people exposed to a contaminant). For estimates of exposure fractions, EPA will allow a margin of error of ± 1% with 99% confidence, when the estimated exposure fraction is 1%. That is, if the estimated exposure fraction is 1%, EPA will be able to state with 99% confidence that the true exposure fraction is between 0% and 2%. Because there are uncertainties and sources of variation in this and other such sampling programs, statistical sampling theory used to derive levels of accuracy and precision may not account for all of these sources of variation. Hence, the high confidence level, low allowable error, and consequent large sample size should help ensure adequate data to meet the objectives of the UCMR program.
For those PWSs required to conduct UCMR monitoring, response is a requirement. As with any regulation, some non-compliance can be expected. However, high compliance levels (>95%) during UCMR 1 and 2 (attributable to extensive outreach and compliance assistance) give EPA confidence that the same or better compliance levels can be achieved during UCMR 3. EPA plans to continue outreach and compliance assistance efforts, as needed.
No questionnaires will be used for the UCMR. Analytical results for contaminant occurrence will be electronically reported directly by the laboratories to EPA’s electronic reporting system.
For UCMR 3, EPA will apply the same basic statistical methods that were used for the UCMR 1 and UCMR 2 national representative sample of small systems. Following sample adjustments made through communications with States, >99% of the final sample of small systems (and >95% of large systems) completed their required monitoring and reporting.
Large PWSs (those serving more than 10,000 people) are required to submit their data through EPA's electronic data reporting system. Small PWSs (those serving 10,000 or fewer people) will be working directly with an EPA-appointed UCMR Sampling Coordinator, and monitoring data from the small PWSs will be submitted directly to EPA's electronic reporting system by the laboratories conducting the analyses.
High compliance levels (>95%) during UCMR 1 and 2 have given EPA confidence that equivalent or better levels can be achieved during UCMR 3. EPA plans to continue outreach and compliance assistance efforts, as needed. Each small system will be working with a UCMR Sampling Coordinator, and will have minimal reporting requirements and one-on-one compliance assistance.
Lessons learned during UCMR 1 and UCMR 2 helped refine UCMR 3 requirements.
Sampling schedule specifications have been refined, and now clarify that sampling schedules be adjusted based on sample point availability.
UCMR 3 also modifies system applicability, i.e., the types of water systems that are required to monitor. In UCMR 1 and 2, systems that purchased 100% of their water were excluded from monitoring, making estimates of exposure more difficult because many of these purchasing systems represented high-population areas. Wholesalers that have a retail population of 10,000 or below are only required to monitor if they are selected as part of the nationally representative sample of small systems for any list of UCMR contaminants. This should greatly improve exposure estimates for UCMR 3, since exposure estimates will be based on the monitoring data collected from where the water is consumed rather than where it is sold.
In addition, EPA revised the rule language to establish a requirement of reporting zip codes for customers served by the PWS. These reporting specifications are established in §§141.35(c)(1) and (d)(1) for large and small systems, respectively. EPA believes that required reporting of customer zip codes will provide EPA with useful information for future occurrence analyses.
After PWSs or their laboratories post their UCMR 3 monitoring results and required data elements to EPA's electronic reporting system, EPA allows a specified time for quality control review by the PWSs, States, and the agency before placing the data in the NCOD for public access.
Data problems may occur, but the following efforts will be taken by EPA to reduce problems and increase the dependability and quality of the occurrence data. The UCMR electronic data reporting system and EPA QA/QC assessments will screen for the use of inappropriate measurement units and other improper data. In addition, EPA plans to have other automated QC functions in place to identify possible data quality issues such as duplicate data submissions, and data completeness. All Assessment Monitoring and Screening Survey samples will be collected by trained PWS staff (Pre-Screen Testing samples will be collected by EPA) and analytical results will be generated by laboratories that are approved for UCMR 3 drinking water analysis. Electronic data submission also avoids potential re-keying errors. As part of the data QA/QC procedures, all edits or changes made to the data will be documented.
For UCMR 1 and UCMR 2, EPA developed a two-stage analytical approach for the evaluation of the national occurrence of contaminants. EPA expects to use the same 2-tier approach to analyzing the data for UCMR 3.
The first stage of analysis, Stage 1, provides a straightforward evaluation of occurrence for simple and conservative assessments of contaminant occurrence. The Stage 1 analysis of the UCMR data consists of non-parametric, unweighted counts and simple descriptive statistics of analytical results for each of the contaminants. These occurrence analyses are conducted at the sample level, system level and population-served level. For each contaminant, occurrence measures include the number and percent of samples for each contaminant with analytical detections, and the minimum, median, maximum, and 99th percentile values of those detections. System-level occurrence measures include the number and percent of systems with one or more analytical detections, and the number and percent of systems with two or more analytical detections of a given contaminant. Population-served occurrence measures include: the number and percent of population served by systems with one or more analytical detections, and the number and percent of population served by systems with two or more analytical detections of a given contaminant. Similar measures may also be conducted for each EPTDS for each system. Since these contaminant and system level occurrence measures are based on raw occurrence data (that have not been adjusted for population-weighting and sampling), they are less accurate representations of national occurrence than occurrence measures based on adjusted occurrence data.
Based on the findings of the Stage 1 analysis, EPA can select contaminant(s) for which more detailed and sophisticated statistical evaluations – the Stage 2 analysis – may be warranted as a next step to generate national probability estimates of contaminant occurrence and exposure. Specifically, the modeling and estimation of system mean contaminant concentrations may be desired. The Stage 2 analysis uses a Bayesian-based hierarchical model to estimate the percent (and number) of systems with a mean contaminant concentration above any specified concentration threshold. The Bayesian-based Hierarchical Model also provides quantified error of estimation, and enables estimates of mean contaminant concentrations below the MRL. This statistical model was used to generate the contaminant occurrence estimates for 60 regulated contaminants for the first Six-Year Review of NPDWRs, for which it underwent a peer review.
After final review and formatting the data collected through this ICR, the data will be made available to the public through the NCOD, as was done with the data collected for UCMR 1 and UCMR 2. The analytical results from UCMR 3 monitoring will support the development of the CCL; regulatory determinations; and, as appropriate, regulation development. For contaminants with significant occurrence and health effects, EPA will use the results: to support an exposure assessment; to establish the baseline for health effects and economic analyses; to analyze contaminant co-occurrence; and to evaluate treatment technology, including contaminant source management. Further, the results may suggest that the occurrence of certain contaminants may be significant enough to initiate research on health effects and treatment technology. Finally, the data may guide future source water protection efforts.
File Type | application/vnd.openxmlformats-officedocument.wordprocessingml.document |
Author | EPA |
File Modified | 0000-00-00 |
File Created | 2021-01-30 |