[Code of Federal Regulations] [Title 40, Volume 22] [Revised as of July 1, 2007] From the U.S. Government Printing Office via GPO Access [CITE: 40CFR141.73] [Page 450-451] TITLE 40--PROTECTION OF ENVIRONMENT CHAPTER I--ENVIRONMENTAL PROTECTION AGENCY (CONTINUED) PART 141_NATIONAL PRIMARY DRINKING WATER REGULATIONS--Table of Contents Subpart H_Filtration and Disinfection Sec. 141.73 Filtration. A public water system that uses a surface water source or a ground water source under the direct influence of surface water, and does not meet all of the criteria in Sec. 141.71 (a) and (b) for avoiding filtration, must provide treatment consisting of both disinfection, as specified in Sec. 141.72(b), and filtration treatment which complies with the requirements of paragraph (a), (b), (c), (d), or (e) of this section by June 29, 1993, or within 18 months of the failure to meet any one of the criteria for avoiding filtration in Sec. 141.71 (a) and (b), whichever is later. Failure to meet any requirement of this section after the date specified in this introductory paragraph is a treatment technique violation. (a) Conventional filtration treatment or direct filtration. (1) For systems 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 0.5 NTU in at least 95 percent of the measurements taken each month, measured as specified in Sec. 141.74 (a)(1) and (c)(1), except that if the State determines that the system is capable of achieving at least 99.9 percent removal and/or inactivation of Giardia lamblia cysts at some turbidity level higher than 0.5 NTU in at least 95 percent of the measurements taken each month, the State may substitute this higher turbidity limit for that system. However, in no case may the State approve a turbidity limit that allows more than 1 NTU in more than 5 percent of the samples taken each month, measured as specified in Sec. 141.74 (a)(1) and (c)(1). (2) The turbidity level of representative samples of a system's filtered water must at no time exceed 5 NTU, measured as specified in Sec. 141.74 (a)(1) and (c)(1). (3) Beginning January 1, 2002, systems serving at least 10,000 people must meet the turbidity requirements in Sec. 141.173(a). (4) Beginning January 1, 2005, systems serving fewer than 10,000 people must meet the turbidity requirements in Sec. Sec. 141.550 through 141.553. (b) Slow sand filtration. (1) For systems using slow sand filtration, the turbidity level of representative samples of a system's filtered water must be less than or equal to 1 NTU in at least 95 percent of the measurements taken each month, measured as specified in Sec. 141.74 (a)(1) and (c)(1), except that if the State determines there is no significant interference with disinfection at a higher turbidity level, the State may substitute this higher turbidity limit for that system. (2) The turbidity level of representative samples of a system's filtered water must at no time exceed 5 NTU, measured as specified in Sec. 141.74 (a)(1) and (c)(1). (c) Diatomaceous earth filtration. (1) For systems using diatomaceous earth filtration, the turbidity level of representative samples of a system's filtered water must be less than or equal to 1 NTU in at least 95 percent of the measurements taken each month, measured as specified in Sec. 141.74 (a)(1) and (c)(1). (2) The turbidity level of representative samples of a system's filtered water must at no time exceed 5 NTU, measured as specified in Sec. 141.74 (a)(1) and (c)(1). (d) Other filtration technologies. A public water system may use a filtration technology not listed in paragraphs (a) through (c) of this section if it demonstrates to the State, using pilot plant studies or other means, that the alternative filtration technology, in combination with disinfection treatment that meets the requirements of Sec. 141.72(b), consistently achieves 99.9 percent removal and/or inactivation of Giardia lamblia cysts and 99.99 percent [[Page 451]] removal and/or inactivation of viruses. For a system that makes this demonstration, the requirements of paragraph (b) of this section apply. Beginning January 1, 2002, systems serving at least 10,000 people must meet the requirements for other filtration technologies in Sec. 141.173(b). Beginning January 14, 2005, systems serving fewer than 10,000 people must meet the requirements for other filtration technologies in Sec. 141.550 through 141.553. [54 FR 27527, June 29, 1989, as amended at 63 FR 69516, Dec. 16, 1998; 66 FR 3776, Jan. 16, 2001; 67 FR 1836, Jan. 14, 2002; 69 FR 38855, June 29, 2004]