On this page:
Question 1: What do water systems that received a Very Small System (VSS) Waiver; 40/30 Certification; and Non-transient, Non-community (NTNC) water systems that disinfect need to do before beginning Stage 2 compliance monitoring?
Question 2: If I was on Stage 1 reduced monitoring, can I continue reduced monitoring under Stage 2?
- Water systems that received a VSS Waiver, 40/30 Certification and NTNC water systems that disinfect are required to complete a Compliance Monitoring Plan (CMP) for Stage 2. Templates are available here that cover some of the common stage 2 DBPR monitoring scenarios. The CMP must identify a water system's Stage 2 compliance monitoring locations, when DBP samples will be taken, and compliance calculations. A CMP must be completed before you begin Stage 2 compliance monitoring, and it must be available for review during the water system survey.
Question 3: If I was on Stage 1 increased monitoring (e.g. because of a detection of TTHM/HAA5), do I have to stay on increased monitoring under Stage 2?
- Systems that were on Stage 1 DBPR reduced monitoring may start on Stage 2 DBPR reduced monitoring if all of the following criteria are met:
- The system received a VSS waiver or a 40/30 certification. To see if your system got a VSS or 40/30, check the IDSE Waiver Lists (MS Excel). The lists are alphabetical by water system name; there is one tab for 40/30 and one for VSS. If the system did IDSE standard monitoring, they do not meet this portion of the criteria and cannot qualify initially for reduced monitoring.
- LRAAs at all monitoring sites are ≤ 0.040 mg/l for TTHM and ≤ 0.030 mg/l for HAA5.
- Source water TOC levels are ≤ 4.0 mg/l at each treatment plant (surface water only).
- The system will be monitoring at the same locations for Stage 2 DBPR as the Stage 1 DBPR. If the system had to add, subtract or change sample sites, they do not meet this portion of the criteria and cannot qualify initially for reduced monitoring.
Question 4: What are the requirements for new water systems that add a disinfectant (other than ultraviolet light) and existing systems that begin adding a disinfectant?
- Yes. Systems that were on increased Stage 1 monitoring schedule must begin Stage 2 on an increased schedule until the requirements are met to return to a routine schedule.
Question 5: How do I determine the maximum residence site in the distribution system?
- New water systems that disinfect and existing systems that begin adding disinfectant are required to conduct IDSE standard monitoring prior to beginning Stage 2 compliance monitoring.
Question 6: My sample results indicate that the highest HAA5 readings occur at one of the average sample points (not at what one would expect to be the maximum residence site) and the hightest TTHM sample results occur at another sample point. Wouldn't I get the highest TTHM and HAA5 readings at the same site?
- The maximum residence site is typically the point in the distribution system furthest from the point of disinfection ("oldest water"). A reasonable approach would be to measure chlorine residuals at various points in the distribution system and pick the point at which the chlorine residual is the lowest.
Question 7: I have a conventional 2.5-log treatment plant; do I have to sample for TOC and alkalinity?
- Not necessarily. DBP concentration curves indicate that in many cases, HAA5 formation reaches its highest concentration earlier in the distribution system (closer to the point of disinfection) than the highest TTHM formation concentrations.
Question 8: I am a surface water system but not a conventional 2.5-log treatment plant. I am seeking a reduction in DBP monitoring; am I required to sample for TOC?
- Yes. Conventional treatment plants that are rated at 2.5 log Giardia removal must sample monthly for raw water TOC, raw water alkalinity, and post-filtration TOC (may be reduced to quarterly). If you are seeking a reduction for TTHM/HAA5 monitoring, you may be eligible when both DBP levels are ≤ to 50 percent of the MCL and source water TOC running annual average is ≤ 4.0 mg/l.
Question 9: Do I have to take the raw water TOC samples at the same time as the filtered water TOC samples?
- Yes, if seeking a reduction in DBP monitoring, surface water systems must sample for raw water TOC once per month per treatment plant (may be reduced to quarterly). In general, water systems are eligible for reduced monitoring frequency when both DBP levels are ≤ 50 percent of the MCLs and source water TOC running annual average is ≤ 4.0 mg/l.
- Yes. Raw water TOC/raw water alkalinity and the filtered water TOC samples should be considered paired samples and should be taken at the same time. The raw water TOC and the raw water alkalinity should be taken at the same time and at the same site (at the raw water inlet to the first treatment process). The finished water TOC should be taken just after the filters at the combined filter effluent.
FAQs about Initial Distribution System Evaluation (IDSE) Standard Monitoring
Question 10: Do I need to report the results of IDSE monitoring to the state?
Question 11: If a water system modifies its distribution system after completing its IDSE, is the water system required to complete a new IDSE?
- No, reporting the results is optional. The IDSE standard monitoring results are not for compliance; they are to be used by the system to determine Stage 2 compliance monitoring locations.
Question 12: What happens to a water system that does not submit an IDSE report?
- No new IDSE report is required, but the water system should work with Drinking Water Services to change their Stage 2 Compliance Monitoring Plan (CMP) to address the changes to the distribution system.
Question 13: Should the results from the IDSE standard monitoring be included in the Consumer Confidence Report (CCR)?
- The water system would be in violation if it did not conduct standard monitoring and submit an IDSE report by the compliance deadline. For violations, Drinking Water Services will determine the enforcement action to be taken.
- Results from IDSE standard monitoring must be included in the range of levels a public water system reports in its Consumer Confidence Report (CCR).
EPA's Stage 2 FAQ
For answers to additional implementation questions, visit EPA's Stage 2 DBPR Frequent Questions page.