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FAQs for Water Systems Performing Initial Distribution System Evaluation (IDSE) Standard Monitoring
Question 1: Are those water systems conducting Stage 2 IDSE Monitoring still required to conduct Stage 1 monitoring?
Question 2: Do I need to report the results of IDSE monitoring to the state?
- Yes, water systems are required to collect their Stage 1 compliance sample as well as conduct Stage 2 IDSE monitoring.
Question 3: How should systems monitor during the interval between the end of IDSE monitoring and the beginning of Stage 2 compliance monitoring?
- No. The IDSE standard monitoring results are not for compliance; they are to be used by the system to determine Stage 2 compliance monitoring locations. You must continue to report Stage 1 compliance monitoring results as these are required for compliance with Stage 1 rule.
Question 4: Can I start Stage 2 compliance monitoring early?
- Systems should continue Stage 1 monitoring until Stage 2 compliance monitoring begins. This interval is built into Stage 2 to accommodate systems that may need to make significant changes to their distribution system to meet the requirements of Stage 2.
Question 5: If a water system modifies its distribution system after completing its IDSE, is the water system required to complete a new IDSE?
- No. Water systems cannot start Stage 2 compliance monitoring early.
Question 6: 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 7: Should the results from the IDSE standard monitoring be included in the Consumer Confidence Report?
- The water system would be in violation if it did not qualify for a VSS waiver, submit a 40/30 certification, or conduct standard monitoring by the compliance deadline. The same is true for the IDSE report for systems that conducted standard monitoring. 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).
FAQs for Water Systems that received a Very Small System (VSS) Waiver; 40/30 Certification; and Non-transient, Non-Community Water Systems that Disinfect
Question 8: Do I need to do anything before I begin Stage 2 compliance monitoring in year 2013?
- Yes. Water systems that received a VSS Waiver, 40/30 Certification and non-transient non-community water systems that disinfect are required to complete a Compliance Monitoring Plan (CMP) for Stage 2.
- 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. Your system must also continue monitoring under Stage 1 until Stage 2 compliance monitoring begins.
- Surface water and GWUDI systems (and their purchasers) with populations over 3,300 must submit their compliance monitoring plans to Drinking Water Services for review prior to beginning compliance monitoring.
Answers to Other FAQs
Question 9: If I'm on Stage 1 reduced monitoring, can I continue reduced monitoring under Stage 2?
Question 10: If I am 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?
- Yes, if you meet all of the following conditions:
- The system received a VSS waiver or a 40/30 certification.
- 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 11: 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 on an 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 12: How do I determine the maximum residence site in the distribution system?
- New water systems that disinfect are required to contact Drinking Water Services in order to determine appropriate steps.
- Water systems that begin adding disinfectant are also required to contact Drinking Water Services.
Question 13: 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 highest 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"). In some cases the maximum residence site will be located not at the end of the distribution system, but in a reservoir located in the middle of the distribution system. 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 14: I have a conventional treatment plant; however, the plant is not rated at 2.5 log Giardia removal. 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 15: Do I have to take the TTHM and HAA5 samples at the same sites and at the same time?
- No, only conventional treatment plants that are rated at least 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 are required to sample for raw water TOC only (no finished water TOC or alkalinity) 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% of the MCL and source water TOC running annual average is ≤ 4.0 mg/l.
Question 16: My water system does not have a conventional treatment plant; however, I am seeking a reduction in DBP monitoring. Am I required to sample for TOC?
- It depends. Ground water systems serving 500-9,999 on annual monitoring must take dual sample sets at each location.
- A dual sample set is a set of two samples collected at the same time and same location, with one sample analyzed for TTHM and the other sample analyzed for HAA5.
- All other systems on annual monitoring and surface water/GWUDI systems serving 500-3,300 are required to take individual TTHM and HAA5 samples (instead of a dual sample set) at the locations with the highest TTHM and HAA5 concentrations, respectively.
- Surface water/GWUDI systems serving 500-3,300 may collect one dual sample set per monitoring period if the highest TTHM and HAA5 concentrations occur at the same location.
- For systems serving fewer than 500 people, only one location with a dual sample set per monitoring period is needed if highest TTHM and HAA5 concentrations occur at the same location, and month, if monitored annually.
Question 17: Do I have to take the raw water TOC samples at the same time as the filtered water TOC samples?
- Yes, you are required to sample for raw water TOC only (no finished water TOC or alkalinity) 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% of the MCL and source water TOC running annual average is ≤ 4.0 mg/l.
Question 18: Does increased monitoring affect the entire system or only the monitoring site that exceeded the trigger value?
- 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.
For answers to additional implementation questions, visit EPA's Stage 2 DBPR Frequent Questions page.
- If a monitoring site triggers increased monitoring, the entire system must switch to increased monitoring. Increased and reduced monitoring cannot be determined on a site-by-site basis.