.23 Disinfection.

A. The Approving Authority shall have the right to establish minimum sampling frequencies and locations for determining disinfectant residuals for public water systems. The responsibility and cost for testing, recording, and reporting the results to the Approving Authority shall be borne by the supplier of water.

B. The Approving Authority shall have the right to establish minimum disinfectant residual concentrations in a public drinking water distribution system.

C. Sampling and Analysis of Residual Disinfectant Concentrations.

(1) Sampling and analysis of residual disinfectant concentrations shall be conducted as set forth in 40 CFR §141.74(a)(2) or 141.131(c) or with DPD colorimetric test kits using protocol approved by the Approving Authority.

(2) Consecutive systems that do not add a disinfectant but deliver water that has been treated with a primary or residual disinfectant other than ultraviolet light, shall comply with the following requirements:

(a) Analytical and monitoring requirements for chlorine and chloramines in 40 CFR §§141.131(c) and 141.132(c)(1);

(b) Compliance requirements in 40 CFR §141.133(c)(1), unless required earlier by the State; and

(c) Reporting requirements for monitoring results in accordance with 40 CFR §141.134(c).

D. Maximum Residual Disinfectant Levels.

(1) 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)

(2) CWSs and NTNCWSs. Subpart H systems serving 10,000 or more individuals shall comply with this regulation beginning January 1, 2002. Subpart H systems serving fewer than 10,000 individuals and systems using only ground water not under the direct influence of surface water shall comply with this regulation beginning January 1, 2004.

E. Control of Disinfectant Residuals. Notwithstanding the MRDLs in §D(1) of this regulation, systems may increase residual disinfectant levels in the distribution system of chlorine or chloramines, except for chlorine dioxide, to a level and for a time necessary to protect public health and to address specific microbiological contamination problems caused by circumstances such as, but not limited to, distribution line breaks, storm runoff events, source water contamination events, or cross-connection events.

F. Systems shall report disinfection profiles and benchmarks to the Approving Authority as described in 40 CFR §§141.708—141.709 and Regulation .05-2L(9) and (10) of this chapter prior to making a significant change in disinfection practice.