40 C.F.R. § 141.551
What strengthened combined filter effluent turbidity limits must my system meet?
Cite as 40 C.F.R. § 141.551 (2026)
Your system must meet two strengthened combined filter effluent turbidity limits. (a) The first combined filter effluent turbidity limit is a “95th percentile” turbidity limit that your system must meet in at least 95 percent of the turbidity measurements taken each month. Measurements must continue to be taken as described in § 141.74(a) and (c). Monthly reporting must be completed according to § 141.570. The following table describes the required limits for specific filtration technologies. If your system consists of * * * Your 95th percentile turbidity value is * * * (1) Conventional Filtration or Direct Filtration 0.3 NTU. (2) All other “Alternative” Filtration A value determined by the State (not to exceed 1 NTU) based on the demonstration described in § 141.552. (b) The second combined filter effluent turbidity limit is a “maximum” turbidity limit which your system may at no time exceed during the month. Measurements must continue to be taken as described in § 141.74(a) and (c). Monthly reporting must be completed according to § 141.570. The following table describes the required limits for specific filtration technologies. If your system consists of * * * Your maximum turbidity value is * * * (1) Conventional Filtration or Direct Filtration 1 NTU. (2) All other “Alternative Filtration” A value determined by the State (not to exceed 5 NTU) based on the demonstration as described in § 141.552. [67 FR 1839, Jan. 14, 2002, as amended at 69 FR 38856, June 29, 2004]
- Cross-references to the CFR
- 141.552.141.570.141.74