Section 611.743  Filtration

A PWS must provide treatment consisting of both disinfection, as specified in Section 611.242, and filtration treatment that complies with the requirements of subsection (a) or (b) or Section 611.250(b) or (c).

a)         Conventional Filtration Treatment or Direct Filtration

1)         For a supplier using conventional filtration or direct filtration, the turbidity level of representative samples of a system's filtered water must be less than or equal to 0.3 NTU in at least 95 percent of the measurements taken each month, measured as specified in Sections 611.531 and 611.533.

2)         The turbidity level of representative samples of a supplier's filtered water must at no time exceed 1 NTU, measured as specified in Sections 611.531 and 611.533.

3)         A supplier that uses lime softening may acidify representative samples prior to analysis using a protocol approved by the Agency.

b)         Filtration Technologies Other Than Conventional Filtration Treatment, Direct Filtration, Slow Sand Filtration, or Diatomaceous Earth Filtration.  A PWS supplier may use a filtration technology not listed in subsection (a) or in Section 611.250(b) or (c) if it demonstrates to the Agency, using pilot plant studies or other means, that the alternative filtration technology, in combination with disinfection treatment that meets the requirements of Section 611.242(b), consistently achieves 99.9 percent removal or inactivation of Giardia lamblia cysts and 99.99 percent removal or inactivation of viruses, and 99 percent removal of Cryptosporidium oocysts, and the Agency approves the use of the filtration technology.  For each approval, the Agency must set turbidity performance requirements that the supplier must meet at least 95 percent of the time and that the supplier must not exceed at any time at a level that consistently achieves 99.9 percent removal or inactivation of Giardia lamblia cysts, 99.99 percent removal or inactivation of viruses, and 99 percent removal of Cryptosporidium oocysts.

BOARD NOTE:  Derived from 40 CFR 141.173.

(Source:  Amended at 44 Ill. Reg. 6996, effective April 17, 2020)