• FAQs for Water Systems Performing Initial Distribution System Evaluation (IDSE) Standard Monitoring
• FAQs for Water Systems that Received a Very Small System (VSS) Waiver; 40/30 Certification; and Non-Transient, Non-community Water Systems that Disinfect
• Answers to Other FAQs

FAQs for Water Systems Performing Initial Distribution System Evaluation (IDSE) Standard Monitoring

• Yes, water systems are required to collect their Stage 1 compliance sample as well as conduct Stage 2 IDSE 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.

• 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.

• No. Water systems cannot start Stage 2 compliance monitoring early.

• 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.

• 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

• 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

• 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.

• 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.

• 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.

• 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.

• 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.

• 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.

• 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.

• 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.

• 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.

• 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.