(a) Applicability. All public water systems that use groundwater, except public water systems that combine all of their groundwater with surface water or with groundwater under the direct influence of surface water prior to treatment as described in §290.111 of this title (relating to Surface Water Treatment), must comply with one or more of the treatment techniques and corrective actions of this section if a raw groundwater source sample collected under §290.109(d)(3)(C)(ii), (4)(B), (C), or (E) of this title (relating to Microbial Contaminants) was positive for fecal indicators, or if a significant deficiency was identified, or if the system is not required to conduct raw groundwater source monitoring because it provides at least 4-log treatment of viruses at each groundwater source. At the discretion of the executive director, a public water system not excluded under this subsection, shall comply with the requirements of this section after exceeding a treatment technique trigger as described in accordance with §290.109 of this title. A public water system shall comply with provisions of §290.109(d)(3)(C)(ii), (4)(B), (C), or (E) of this title except in cases where the executive director determines that the sample collected under §290.109(d)(1) and (2) of this title meets the executive director's criteria for invalidation as described in §290.109(e)(1) of this title. A public water system with a groundwater under the direct influence of surface water (GUI) or surface water/groundwater blended source(s), which provides disinfection and filtration, shall comply with provisions of this section except in cases where the executive director determines that the significant deficiency is in a portion of the distribution system that is served solely by surface water or groundwater under the direct influence of surface water.      
        (1) A groundwater system must provide written notification to the executive director that it is not required to meet the raw groundwater source monitoring requirements under §290.109(d)(4) of this title because it provides at least 4-log treatment of viruses for the specified groundwater source and must begin compliance monitoring in accordance with subsection (c) of this section. The notification must include engineering, operational, and other information required by the executive director to evaluate the submission. If the executive director determines and documents in writing that 4-log treatment of viruses is no longer necessary for a specified groundwater source or if the system discontinues 4-log treatment of viruses before the first connection for any groundwater source, the system must document this in writing and conduct raw groundwater source sampling as required under §290.109(d)(4) of this title. If the public water system discontinues 4-log treatment it shall receive prior approval in writing from the executive director that 4-log treatment is no longer necessary for that groundwater source.       
        (2) A groundwater system that places a groundwater source in service after November 30, 2009, that is not required to meet the raw source monitoring requirements under §290.109(d)(4) of this title because the system provides at least 4-log treatment of viruses for a specified groundwater source must begin compliance monitoring within 30 days of placing the source in service in accordance with subsection (c) of this section. The system must provide written notification to the executive director that it provides at least 4-log treatment of viruses before the first connection for the specified groundwater source. The notification must include engineering, operational, and other information required by the executive director to evaluate the submission. The system must conduct triggered source monitoring under §290.109(d)(4) of this title until the executive director provides written approval of the system's request to provide the 4-log treatment. If the system discontinues 4-log treatment of viruses before the first connection for a groundwater source, the system must conduct raw groundwater source sampling as required under §290.109(d)(4) of this title. If the public water system discontinues 4-log treatment it shall receive prior approval in writing from the executive director that 4-log treatment is no longer necessary for that groundwater source.       
      (b) Groundwater corrective action plan. All public water systems using groundwater must submit a corrective action plan and implement corrective action if a raw groundwater source sample was positive for fecal indicators or if a significant deficiency was identified.      
        (1) If a groundwater source sample was found to be fecal indicator positive or if a significant deficiency was identified, the system must consult with the executive director regarding appropriate corrective action and have an approved corrective action plan in place within 30 days of receiving written notification from a laboratory of the fecal indicator positive source sample collected under §290.109(d)(4) of this title or within 30 days of receiving written notification from the executive director of the identification of a significant deficiency.       
        (2) Within 120 days of receiving written notification from a laboratory of the fecal indicator positive source sample or receiving written notification from the executive director of a significant deficiency, the system must have completed corrective action or be in compliance with an approved corrective action plan and schedule.       
        (3) Any changes to the approved corrective action plan or schedule must be approved by the executive director.       
        (4) The executive director may require interim measures for the protection of public health pending approval of the corrective action plan. The system must comply with these interim measures as well as with any schedules specified by the executive director.       
        (5) Systems that are required to complete corrective action must implement one or more of the procedures in this paragraph and the details of the implementation must be specified in the approved corrective action plan. If subparagraph (A) or (F) of this paragraph is selected as part of the corrective action plan, then subparagraph (B), (C), (D), or (E) of this paragraph must also be selected.                  (A) The system may disinfect the groundwater source where the fecal indicator positive source sample was collected following the American Water Works Association (AWWA) standards for well disinfection and start monthly fecal indicator sampling at that source within 30 days after well disinfection. The executive director may discontinue the monthly source sampling requirement if corrective action is sufficient.                   (B) The system may eliminate the groundwater source that was found to be fecal indicator positive and provide an alternate groundwater source if necessary. Eliminated groundwater sources must be disconnected from the distribution system until the contamination is corrected and the executive director approves it for use.                   (C) The system may identify and eliminate the source of fecal contamination followed by well disinfection according to AWWA well disinfection standards and begin monthly fecal indicator sampling within 30 days after well disinfection. The executive director may allow the system to discontinue the monthly source sampling requirement after making a determination that corrective action is sufficient.                   (D) The system may provide treatment that reliably achieves at least 4-log treatment of viruses using inactivation, removal or an executive director-approved combination of inactivation and removal before the first connection of the groundwater source.                   (E) Correct all significant deficiencies.                   (F) Assessment source monitoring for a period of 12 months or a time period specified by the executive director from the raw groundwater source in accordance with §290.109(d)(4)(E) of this title.         
      (c) Microbial inactivation and removal requirements. A public water system that treats groundwater in response to a fecal indicator positive source sample or significant deficiency, instead of conducting raw groundwater source monitoring, shall meet minimum requirements demonstrating at least 4-log treatment of viruses before the water is distributed to the first connection of the specified groundwater source.      
        (1) Monitoring requirements for chemical disinfectants. Groundwater systems shall monitor the performance of the disinfection facilities to ensure that appropriate disinfectant levels are maintained every day the specified source serves the public. All monitoring conducted pursuant to the requirements of this section must be conducted at sites designated in the system's monitoring plan in accordance with §290.121 of this title (relating to Monitoring Plans).                  (A) Groundwater systems serving a population greater than 3,300 must continuously monitor the residual disinfectant concentration in accordance with the analytical methods specified in 40 Code of Federal Regulations (CFR) §141.74(a)(2) at a location approved by the executive director and must record the lowest residual disinfectant concentration every day the groundwater source serves the public.                      (i) The groundwater system must maintain the executive director-approved minimum specified disinfectant residual every day the groundwater system serves water from the specified groundwater source to the public. If there is a failure in the continuous monitoring equipment, the groundwater system must conduct grab sampling every four hours until the continuous monitoring equipment is returned to service.                       (ii) The system must resume continuous residual disinfectant monitoring within 14 days.                     (B) Groundwater systems serving a population of 3,300 or fewer must monitor the disinfectant residual in accordance with the analytical methods specified in 40 CFR §141.74(a)(2) in each disinfection zone at least once each day that water from the specified groundwater source is served to the public during either a time when peak hourly raw water flow rates are occurring or at another time specified by the executive director. The system must record and maintain the disinfectant residual every day the system serves water from the groundwater source to the public. The system must collect a daily grab sample during the hour of peak flow or at another time specified by the executive director. If any daily grab sample measurement falls below the executive director-approved minimum specified disinfectant residual, the groundwater system must collect follow-up samples every four hours until the residual disinfectant concentration is restored to the executive director-approved level. Alternatively, a groundwater system that serves 3,300 or fewer people may monitor the residual disinfectant concentration continuously and meet the requirements of subparagraph (A) of this paragraph.                   (C) Disinfection contact time will be based on tracer study data or a theoretical analysis submitted by the system owner or their designated agent and approved by the executive director.                   (D) Groundwater treatment plants that fail to demonstrate an appropriate level of treatment must repeat these tests at four-hour or shorter intervals until compliance has been reestablished.         
        (2) Monitoring and operating requirements for commission-approved alternative treatment, including ultraviolet light (UV) disinfection facilities, membrane systems, and other methods that can obtain 4-log inactivation or removal of viruses.                  (A) Public water systems shall monitor the UV intensity as measured by a UV sensor, lamp status, the flow rate through the unit, and other parameters prescribed by the executive director as specified in §290.42(g)(5) of this title (relating to Water Treatment) to ensure that the units are operating within validated conditions.                   (B) Public water systems shall monitor and record membrane system performance in accordance with executive director specified requirements.         
        (3) Analytical requirements. All monitoring required by this section must be conducted at a facility approved by the executive director and using methods that conform to the requirements of §290.119 of this title (relating to Analytical Procedures).                  (A) The pH analysis must be conducted using a pH meter with a minimum accuracy of plus or minus 0.1 pH units.                   (B) The temperature of the water must be measured using a thermometer or thermocouple with a minimum accuracy of plus or minus 0.5 degrees Celsius.                   (C) The free chlorine or chloramine residual (measured as total chlorine) must be measured to a minimum accuracy of plus or minus 0.1 milligrams per liter (mg/L). Color comparators may be used for distribution system samples only. When used, a color comparator must have current reagents, an unfaded and clear color comparator, a sample cell that is not discolored or stained, and must be properly stored in a cool, dark location where it is not subjected to conditions that would result in staining. The color comparator must be used in the correct range. If a sample reads at the top of the range, the sample must be diluted with chlorine-free water, then a reading taken and the resulting residual calculated.                   (D) The chlorine dioxide residual must be measured to a minimum accuracy of plus or minus 0.05 mg/L using one of the following methods:                      (i) Amperometric titrator with platinum-platinum electrodes; or                       (ii) Lissamine Green B.                     (E) The ozone residual must be measured to a minimum accuracy of plus or minus 0.05 mg/L using an indigo method that uses a colorimeter or spectrophotometer.                  Cont'd...