R 325.10720 Filtration and disinfection; filtration sampling requirements.

Rule 720. (1) Subpart H supplies shall monitor under this rule to determine compliance with R 325.10611a and R 325.10611b. (2) All of the following provisions are turbidity monitoring requirements: (a) Supplies shall collect samples and perform measurements for turbidity at locations representative of filtered water at regular intervals at least once every 4 hours while the treatment plant is in operation. (b) A public water supply may substitute continuous turbidity monitoring for grab sample monitoring if the continuous measurement is validated for accuracy on a regular basis using a protocol approved by the department. Readings taken from a continuous recording turbidimeter at regular intervals at least once every 4 hours may be used to determine compliance with the treatment technique under R 325.10611b. The turbidimeter shall be calibrated using the procedure specified by the manufacturer. (c) Supplies using conventional or direct filtration shall conduct continuous monitoring of turbidity for each individual filter and shall calibrate turbidimeters using the procedure specified by the manufacturer. Supplies shall record the results of individual filter monitoring every 15 minutes. (d) If there is a failure in the continuous turbidity monitoring equipment described in subdivision (c) of this subrule, then the supply shall conduct grab sampling every 4 hours instead of continuous monitoring, but for not more than 5 working days after the failure of the equipment for supplies serving 10,000 or more people or 14 days for supplies serving fewer than 10,000 people before a violation is incurred. (e) If the supply serves fewer than 10,000 people and consists of only 2 or fewer filters, then the supply may conduct continuous monitoring of combined filter effluent turbidity instead of individual filter effluent turbidity monitoring. Continuous monitoring shall meet the same requirements in subdivisions (c) and (d) of this subrule. (3) All of the following provisions are disinfectant residual monitoring requirements at the entry points to the distribution system: (a) Supplies serving more than 3,300 people shall monitor for residual disinfectant concentration at an entry point to the distribution system on a continuous basis and record the lowest value each day. If there is a failure in the continuous monitoring equipment, the supply may take grab samples every 4 hours instead of continuous monitoring, but for no more than 5 working days following the failure of the equipment. (b) Supplies serving fewer than 3,301 people shall monitor for residual disinfectant concentration at an entry point to the distribution system at a frequency set forth in table 1 of this rule, and, if more than 1 sample is required per day, supplies shall collect samples at times evenly spaced throughout the operational day. Table 1 Residual disinfectant concentration sampling frequencies Supply size by population Samples per day 500 or fewer people 1 501 to 1,000 people 2 1,001 to 2,500 people 3 2,501 to 3,300 people 4 (c) Under R 325.10611a, supplies shall maintain a residual disinfectant concentration entering the distribution system of not less than 0.2 milligrams per liter. If the residual disinfectant concentration drops below this level at any time, then the supply shall notify the department as soon as possible, but not later than the end of the next business day. In addition, the supply shall notify the department by the end of the next business day whether or not the residual disinfectant concentration was restored to not less than 0.2 milligrams per liter within 4 hours. (4) The residual disinfectant concentration shall be measured, at least, at the same points in the distribution system and at the same time as total coliforms are sampled, as specified in R 325.10704 to R 325.10709 until March 31, 2016 and as specified in R 325.10704d to R 325.10704h beginning April 1, 2016. The department may allow a public water supply which uses both a surface water source or a ground water source under direct influence of surface water, and a ground water source, to take disinfectant residual samples at points other than the total coliform sampling points if the department determines that those points are more representative of treated (disinfected) water quality within the distribution system. Heterotrophic bacteria, measured as heterotrophic plate count (HPC) as adopted by reference in R 325.10605, may be measured instead of residual disinfectant concentration.