.15-5 Disinfectant Residuals.

A. Applicability. CWS and NTNCWS 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.

B. Monitoring Frequency and Location. Community and nontransient noncommunity water systems that use chlorine or chloramines shall measure the residual disinfectant level at the same points in the distribution system and at the same time that total coliforms are sampled, as specified in Regulation .11 of this chapter. Subpart H systems may use the results of residual disinfectant concentration sampling conducted under 40 CFR §141.74(b)(6)(i) for unfiltered systems or 40 CFR §141.74(c)(3)(i) for systems which filter instead of taking separate samples.

C. Additional Monitoring. On each day following a routine sample monitoring result that exceeds the MRDL, the system shall take three samples as close to the first customer as possible, at intervals of at least 6 hours. If a system uses chlorine to maintain a disinfectant residual in the distribution system, and there are one or more disinfectant addition points after the entrance to the distribution system, such as booster chlorination, the system shall take one sample at each of the following locations:

(1) As close to the first customer as possible in a location representative of average residence time; and

(2) As close to the end of the distribution system as possible to reflect maximum residence time in the distribution system.

D. Location. Each system shall monitor in accordance with a monitoring plan as set forth in 40 CFR §141.132(f).

E. Compliance Determination and Notification.

(1) All monthly analyses shall be averaged arithmetically and reported to the Approving Authority. Compliance with Regulation .23D of this chapter shall be determined based on a running annual average computed quarterly of monthly averages of all samples under the requirements of 40 CFR §§141.133 and 141.134.

(2) If a supplier of water has violated Regulation .23D of this chapter as determined by the quarterly averages of sample results covering any 4 consecutive quarters, the supplier shall notify the Approving Authority as required by Regulation .19 of this chapter and give public notice as required by Regulation .20 of this chapter.

(3) In cases where systems switch between the use of chlorine and chloramines for residual disinfection during the year, compliance shall be calculated and determined by including together all monitoring results of both chlorine and chloramines. Reports submitted to the Approving Authority shall clearly indicate which residual was analyzed for each sample.