Section 810.29. Basic filtration requirements.

  Public water systems that use a surface water source shall provide filtration which complies with the requirements of sub. (1) , (2) , (3) , (4) , or (5) and meets the disinfection criteria specified in s. NR 810.31 (2) . Public water systems that use a groundwater source under the direct influence of surface water shall provide filtration which complies with the specifications of sub. (1) , (2) , (3) , (4) or (5) and meets the disinfection criteria specified in s. NR 810.31 (2) within 18 months of the date that a source is determined, by the department, to be under the direct influence of surface water unless they meet the filtration avoidance criteria in s NR 810.30. Failure to meet the applicable requirements of this section is a treatment technique violation.

(1)   Conventional filtration treatment.

(a) For systems using conventional filtration treatment, the turbidity level of representative samples of a system's filtered water shall be less than or equal to 0.3 nephelometric turbidity units (NTU) in at least 95% of the measurements taken each month, measured as specified in s. NR 809.113 (1) Tables A and B.

(b) The turbidity level of representative samples of a system's filtered water may not exceed one NTU, measured as specified in s. NR 809.113 (1) Tables A and B.

(c) To determine compliance with par. (a) , turbidity measurements shall be performed on representative samples of filtered water at least every 4 hours that the system serves water to the public.

(d) In lieu of the requirements of par. (c) , turbidity measurements from a continuous reading and recording turbidity monitoring device shall be recorded at predetermined 4-hour intervals to determine compliance with par. (a) . The highest turbidity measurement recorded at any time during the day shall be reported under s. NR 809.80 (7) (a) 1.

(e) A system that uses lime softening may acidify representative samples prior to analysis if using a protocol approved by the department.

(2)   Direct filtration.

(a) For systems using direct filtration, the turbidity level of representative samples of a system's filtered water shall be less than or equal to 0.3 NTU in at least 95% of the measurements taken each month, measured as specified in s. NR 809.113 (1) , Tables A and B. The department may approve a turbidity limit up to one NTU if the water supplier provides the department with documentation which reliably indicates the system achieves at least 99.9% removal or inactivation of Giardia lamblia cysts at a turbidity level above 0.5 NTU at least 95% of the time that the system delivers water to the public.

(b) The turbidity level of representative samples of a system's filtered water may not exceed 1 NTU, measured as specified in s. NR 809.113 (1) , Tables A and B.

(3)   Slow sand filtration.

(a) For systems using slow sand filtration, the turbidity level of representative samples of a system's filtered water shall be less than or equal to 1 NTU in at least 95% of the measurements taken each month, measured as specified in s. NR 809.113 (1) , Tables A and B.

(b) The turbidity level of representative samples of a system's filtered water may not exceed 5 NTU, measured as specified in s. NR 809.113 (1) , Tables A and B.

(4)   Diatomaceous earth filtration.

(a) For systems using diatomaceous earth filtration, the turbidity level of representative samples of a system's filtered water shall be less than or equal to one NTU in at least 95% of the measurements taken each month, measured as specified in s. NR 809.113 (1) , Tables A and B.

(b) The turbidity level of representative samples of a system's filtered water may not exceed 5 NTU, measured as specified in s. NR 809.113 (1) , Tables A and B.

(5)   Other filtration technologies. A public water system may use a filtration technology not listed in subs. (1) to (4) if the water supplier for the system demonstrates to the department, using pilot studies or other means, that the alternative filtration technology, in combination with disinfection treatment that meets the requirements of s. NR 810.31 , consistently achieves 99.9% removal or inactivation of Giardia lamblia cysts and 99.99% removal or inactivation of viruses, and 99.9% removal of Cryptosporidium oocysts, and the department approves the use of the filtration technology. For each approval, the department shall set turbidity performance requirements that the water system shall meet at least 95% of the time at a level that consistently achieves 99.9% removal or inactivation of Giardia lamblia cysts, 99.99% removal or inactivation of viruses, and 99% removal of Cryptosporidium oocysts. The department may set other performance requirements to assure the integrity of the technology.

History: CR 09-073 : cr. Register November 2010 No. 659 , eff. 12-1-10.