Section 58.01.08.529 - REQUIRED DISINFECTION OF DRINKING WATER, ULTRAVIOLET LIGHT01.General. a. Ultraviolet (UV) light technology is a primary disinfectant typically used for Cryptosporidium, Giardia lamblia, and virus inactivation of both surface water and groundwater supplies. Reactor performance in terms of inactivation of any particular organism is a function of the delivered dose which is determined by validation testing. PWSs that are required to maintain a disinfectant residual in the distribution system must supplement UV disinfection with a chemical disinfectant.b. UV disinfection credit will be awarded for filtered PWSs and unfiltered PWSs if the unfiltered PWS meets the requirements in 40 CFR 141.71. PWSs will receive Cryptosporidium, Giardia lamblia, and virus treatment credits by achieving the corresponding UV dose values for the appropriate target pathogen and log reduction shown in Subsection 529.03, calculated to take into account the validation factor and reduction equivalent dose. The target pathogen and the target log inactivation is used to identify the corresponding required UV dose.c. For PWSs using UV light to meet microbial treatment requirements, at least ninety-five percent (95%) of the water delivered to the public every month must be treated by UV reactors operating within validated conditions for the required UV dose.d. When reviewing proposed UV disinfection projects, the Department will use the USEPA UV Disinfection Guidance Manual for the Final Long Term 2 Enhanced Surface Water Treatment Rule referenced in Subsection 002.02 (UV Disinfection Guidance Manual) for guidance.02.Pilot Studies and Validation.a. The Department may allow on-site pilot studies on a case-by-case basis in accordance with Subsection 501.19. Pilot studies are usually used to determine how much fouling occurs on site, to evaluate UV system reliability (e.g. UV sensors, UV transmittance (UVT) monitors, ballast reliability) and to provide operators experience running a UV system. They may also be used to assess lamp aging or impacts of power quality.b. Validation testing determines the operating conditions and monitoring algorithms that the UV system will use to define how much UV dose is being delivered by the reactor during operation. The validated dose as determined through validation testing is compared to the required dose in the UV Dose Table (Subsection 529.03) to determine inactivation credit. The validated dose is calculated by dividing the determined reduction equivalent dose by a validation factor to account for biases and experimental uncertainty. UV light treatment reactors must be validated by a third party entity approved by the Department. At a minimum, validation testing must account for the following: UV absorbance of the water; lamp fouling and aging; measurement uncertainty of on-line UV sensors; UV dose distributions arising from the velocity profiles through the reactor; failure of UV lamps and other critical system components; inlet and outlet piping configuration of the UV reactor; lamp and UV sensor locations; and other parameters required by the Department. The Department may allow alternative test microbes such as MS2 phage where the UV dose response better matches that of Cryptosporidium and Giardia lamblia to provide more accurate and efficient UV dose monitoring. Additional guidance is available in the UV Disinfection Guidance Manual, referenced in Subsection 002.02, or another validation standard as approved by the Department.c. Validation testing must be conducted on full scale testing of a reactor that conforms uniformly to the UV reactors used by the PWS and inactivation of a test microorganism whose dose response characteristics have been quantified with a low pressure mercury vapor lamp.d. Validation testing must determine and establish validated operating conditions under which the reactor delivers the required UV dose in Subsection 529.03. Validated operating conditions include:ii. UV Intensity as measured by a UV sensor;iii. UV lamp operating status.e. The Department may approve an alternative approach to validation testing.03.UV Dose Table. The treatment credits listed in the dose table are based on UV light at a wavelength of two hundred fifty-four (254) nm as produced by a low pressure mercury vapor lamp. To receive treatment credit for other lamp types, the PWS must demonstrate an equivalent germicidal dose through validation testing. UV Dose Table (millijoules per square centimeter) |
Log | Cryptosporidium | Giardia lamblia | Virus |
0.5 | 1.6 | 1.5 | 39 |
1.0 | 2.5 | 2.1 | 58 |
1.5 | 3.9 | 3.0 | 79 |
2.0 | 5.8 | 5.2 | 100 |
2.5 | 8.5 | 7.7 | 121 |
3.0 | 12 | 11 | 143 |
3.5 | 15 | 15 | 163 |
4.0 | 22 | 22 | 186 |
04.Reactor Design. Inlet and outlet conditions must ensure that UV dose delivery at the plant is equal to or exceeds that utilized during validation. At a minimum, design criteria need to address target pathogen(s), required log inactivation and UV dose, flow rate, UVT, and lamp aging and fouling factors. UVT and flow rate are to be selected to account for seasonal changes in UVT. Lamp aging and fouling factors must be supported by documentation or pilot study data. Recommended approaches of the UV Disinfection Guidance Manual, referenced in Subsection 002.02, are to be used in meeting this requirement.a. The reactor systems must be designed to monitor and record parameters to verify the operation within the validated operating conditions approved by the Department. The PWS must be equipped with facilities to monitor and record UV intensity as measured by a UV sensor, flow rate, lamp status, UVT, and other parameters designated by the Department.b. The ultraviolet treatment device must be designed to provide a UV light dose equal to or greater than that specified in the UV Dose Table for the required log reduction. The UV Disinfection Guidance Manual, referenced in Subsection 002.02, must be utilized in evaluating the appropriate dose required for the target microbe. The reactor will need to deliver the target dose while operating within the validated operating conditions for that particular unit.c. The ultraviolet treatment assemblies must be designed to allow for cleaning and replacement of the lamp, lamp sleeves, and sensor window or lens.d. All ultraviolet treatment device designs must evaluate lamp fouling and aging issues and manufacturer's recommendations regarding fouling, aging, and replacement will be discussed in the Operation and Maintenance Manual.e. For in-situ cleaning of the lamp sleeve, the design must protect the potable water from cleaning solutions.f. When off-line chemical cleaning systems are used, the UV enclosure must be removed from service, drained, flushed with an NSF/ANSI Standard 60 certified solution, drained, and rinsed before being placed back in service.g. On-line systems that use wipers or brushes may use chemical solutions provided they are NSF/ANSI Standard 60 certified.h. An automatic shutdown valve must be installed in the water supply line from the ultraviolet treatment device such that if power is not provided to the reactor or valve, the valve will be in the closed position.i. The design of the inlet and outlet piping configuration and the locations of expansions, bends, tees and valves will assure that the UV dose delivery is equal to or greater than the required UV dose. Approach length prior to each reactor included in the credited dose calculations, downstream length following each reactor, and locations of any cleaning device/mechanism must be based on validation testing.j. For parallel trains, the flow to each reactor must be equally distributed and metered or otherwise account for uneven flows in the design to ensure that the required UV dose is delivered to each train under varying flow conditions.k. Valves must be provided to allow isolating and removing from service each UV reactor.l. Reactors will be provided with air relief and pressure control valves per manufacturer requirements.m. UVT analyzers must be provided if UVT is part of the dose monitoring strategy. It is recommended that UVT be monitored on a regular basis for all PWSs to assess UVT variability.n. A single train with a standby reactor or a sufficient number of parallel ultraviolet treatment devices must be installed to ensure that adequate disinfection is provided when one unit is out of service. The Department may approve an alternate method that provides adequate disinfection such as standby chlorination. Any PWS that produces water on an irregular schedule may provide documentation for the Department's review and approval that a single reactor is an acceptable design by demonstrating there is adequate time for maintenance and cleaning during operation shutdowns.o. No bypass of the ultraviolet treatment process may be installed unless an alternate method of providing adequate disinfection is provided.05.Controls. a. A delay mechanism must be installed to provide sufficient lamp warm-up prior to allowing water to flow from the ultraviolet treatment unit.b. An automatic shutdown must be designed to activate the shutdown valve in cases where the ultraviolet light dose falls below the approved design dose or outside of the validated specifications.06.Reliability. The PWS must be capable of producing the plant design capacity at all times. a. Unless otherwise approved by the Department and in accordance with Subsection 529.04.n., a minimum of two (2) reactors is required to maintain disinfection when one unit is taken out of service. Each reactor must be sized to deliver the required UV dose under the operating conditions of flow and UVT that occur at the plant. The conditions must fall within the validated range of the reactor as determined during validation testing.b. The quality and reliability of the power supply must be analyzed and back-up power supplies will be discussed in the contingency plan.c. If UVT is above the validated range of UVT, the UV dose monitoring algorithm must default to the maximum of the validated range. If UVT is below the validated range, the UV system operation must be recorded as outside of the validated operating conditions. When UVT falls outside of ranges identified in the validated operating conditions, the contingency plan will be enacted if UVT is part of the dose monitoring strategy.d. A contingency plan for total UV disinfection failure, loss of power, or in the event that water quality changes produce water quality unsuitable for UV disinfection must be described in the PER.07.Monitoring. PWSs using UV light must monitor for the parameters necessary to demonstrate operation within the validated conditions of the required UV dose. PWS owners must check the calibration of UV sensors and online UVT monitors and recalibrate in accordance with a protocol approved by the Department. At a minimum, the following parameters must be monitored: a. If the flow rate is below the validated range, then the UV dose monitoring algorithm must default to the validated range. If the flow rate is above the validated range, then the UV system operation will be recorded as outside of the validated operating conditions;b. UV intensity as measured by UV sensors;c. UVT if UVT is part of the dose monitoring strategy; and08.Alarms. The settings or predetermined set points for the alarms must be specified in the PER. The report must also specify the alarms that will activate the contingency plan response. At a minimum, the following alarms are required: b. High turbidity if required by the Department;09.Initial Startup. The following items must be tested and verified before UV disinfected water is distributed:a. Electrical components;c. Flow split between reactor trains if applicable;d. Controls and alarms; ande. Instrument calibration.10.Operation and Maintenance Manual. A project specific operation and maintenance manual must be provided as required in Subsection 501.12. See definition of Operation and Maintenance Manual in Section 003 for the typical contents of an operation and maintenance manual and the included operations plan. The operations plan in the operation and maintenance manual must include, but is not limited to, the following information:a. Lamp replacement intervals may be based on the degree of lamp aging as indicated by the UV sensors;b. Lamp fouling analysis and cleaning procedures;Idaho Admin. Code r. 58.01.08.529