...
(a) Maximum residual disinfectant levels (MRDLs) are as follows:
| Disinfectant residual | MRDL (mg/L) |
| Chlorine | 4.0 (as Cl2) |
| Chloramines | 4.0 (as Cl2) |
| Chlorine dioxide | 0.8 (as ClO2) |
(b) Compliance dates—(1) CWSs and NTNCWSs. Subpart H systems serving 10,000 or more persons must comply with this section beginning January 1, 2002. Subpart H systems serving fewer than 10,000 persons and systems using only ground water not under the direct influence of surface water must comply with this subpart beginning January 1, 2004.
(2) Transient NCWSs. Subpart H systems serving 10,000 or more persons and using chlorine dioxide as a disinfectant or oxidant must comply with the chlorine dioxide MRDL beginning January 1, 2002. Subpart H systems serving fewer than 10,000 persons and using chlorine dioxide as a disinfectant or oxidant and systems using only ground water not under the direct influence of surface water and using chlorine dioxide as a disinfectant or oxidant must comply with the chlorine dioxide MRDL beginning January 1, 2004.
(c) The Administrator, pursuant to Section 1412 of the Act, hereby identifies the following as the best technology, treatment techniques, or other means available for achieving compliance with the maximum residual disinfectant levels identified in paragraph (a) of this section: control of treatment processes to reduce disinfectant demand and control of disinfection treatment processes to reduce disinfectant levels.
[63 FR 69465 Dec. 16, 1998; 65 FR 20309 Apr. 14, 2000 (Withdrawn June 13, 2000); 66 FR 3776 Jan. 16, 2001]