Pennsylvania Code
Title 25 - ENVIRONMENTAL PROTECTION
Part I - Department of Environmental Protection
Subpart C - Protection of Natural Resources
Article II - Water Resources
Chapter 109 - SAFE DRINKING WATER
Subchapter G - SYSTEM MANAGEMENT RESPONSIBILITIES
Section 109.710 - Disinfectant residual in the distribution system

Universal Citation: 25 PA Code § 109.710

Current through Register Vol. 55, No. 13, March 29, 2025

(a) Until April 28, 2019, a disinfectant residual acceptable to the Department shall be maintained throughout the distribution system of the community water system sufficient to assure compliance with the microbiological MCLs and the treatment technique requirements specified in § 109.202 (relating to State MCLs, MRDLs and treatment technique requirements). The Department will determine the acceptable residual of the disinfectant considering factors such as type and form of disinfectant, temperature and pH of the water, and other characteristics of the water system.

(b) Until April 28, 2019, a public water system that uses surface water or GUDI sources or obtains finished water from another permitted public water system using surface water or GUDI sources shall comply with the following requirements:

(1) As a minimum, a detectable residual disinfectant concentration of 0.02 mg/L measured as total chlorine, combined chlorine or chlorine dioxide shall be maintained throughout the distribution system as demonstrated by monitoring conducted under § 109.301(1) and (2) or (8)(v) (relating to general monitoring requirements).

(2) Sampling points with nondetectable disinfectant residuals which have heterotrophic plate count (HPC) measurements of less than 500/ml are deemed to be in compliance with paragraph (1).

(3) When the requirements of paragraph (1) or (2) cannot be achieved, the supplier shall initiate an investigation under the Department's direction to determine the cause, potential health risks and appropriate remedial measures.

(c) Beginning April 29, 2019, a community water system using a chemical disinfectant or that delivers water that has been treated with a chemical disinfectant shall maintain a minimum residual disinfectant concentration throughout the distribution system sufficient to assure compliance with the microbiological MCLs and the treatment technique requirements specified in § 109.202. The minimum residual disinfectant concentration is 0.2 mg/L or another level approved by the Department for systems using an alternate oxidizing disinfection treatment. The residual disinfectant concentration shall be measured as follows:

(1) Free chlorine for systems using chlorine.

(2) Total chlorine for systems using chloramines.

(3) Both free chlorine and total chlorine for sampling locations in a mixing zone as identified in the monitoring plan.

(4) Both free chlorine and total chlorine when a system using chloramines is conducting a free chlorine burn.

(d) Beginning April 29, 2019, a nontransient noncommunity water system that has installed chemical disinfection or a transient noncommunity water system that has installed chemical disinfection in accordance with § 109.202(c)(1) or § 109.1302(b) (relating to treatment technique requirements) shall maintain a minimum residual disinfectant concentration throughout the distribution system sufficient to assure compliance with the microbiological MCLs and the treatment technique requirements specified in § 109.202. The minimum residual disinfectant concentration is 0.2 mg/L or another level approved by the Department for systems using an alternate oxidizing disinfection treatment. The residual disinfectant concentration shall be measured as follows:

(1) Free chlorine for systems using chlorine.

(2) Total chlorine for systems using chloramines.

(3) Both free chlorine and total chlorine for sampling locations in a mixing zone as identified in the monitoring plan.

(4) Both free chlorine and total chlorine when a system using chloramines is conducting a free chlorine burn.

(e) Beginning April 29, 2019, compliance with the disinfectant residual treatment technique will be based on the number of samples collected each month as specified in the system distribution sample siting plan submitted to the Department under § 109.701(a)(8) (relating to reporting and recordkeeping). Compliance will be determined as follows:

(1) For a public water system that collects less than 40 samples per month and uses only groundwater or purchased groundwater sources, if no more than 1 sample collected per month is less than the minimum level specified in subsection (c) or (d) for 2 consecutive months, the system is in compliance with the treatment technique.

(2) For a public water system that collects 40 or more samples per month or that uses surface water, GUDI, purchased surface water or purchased GUDI sources, if no more than 5% of the samples collected per month are less than the minimum level specified in subsection (c) or (d) for 2 consecutive months, the system is in compliance with the treatment technique.

(3) For systems reporting both free and total chlorine residual measurements in accordance with subsections (c) and (d), compliance shall be based on the higher residual measurement.

(4) A public water system that experiences a treatment technique violation shall notify the Department within 1 hour of discovery of the violation in accordance with § 109.701(a)(3) and issue a Tier 2 public notice in accordance with § 109.409 (relating to Tier 2 public notice-categories, timing and delivery of notice).

(5) In addition to the requirements in paragraphs (1)-(4), a public water system that fails to meet the minimum level specified in subsection (c) or (d) at any sample location for 2 consecutive months or more shall conduct an investigation to determine the cause and appropriate corrective actions and shall submit a written report to the Department within 60 days.

(6) The Department may approve in writing an alternate compliance schedule if the water supplier submits a written request with supporting documentation by April 29, 2019.

(f) Public water systems may increase residual chlorine or chloramine, but not chlorine dioxide, disinfectant levels in the distribution system to a level that exceeds the MRDL for that disinfectant and for a time necessary to protect public health or 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.

The provisions of this § 109.710 amended under section 4 of the Pennsylvania Safe Drinking Water Act (35 P.S. § 721.4); and section 1920-A of The Administrative Code of 1929 (71 P.S. § 510-20).

This section cited in 25 Pa. Code § 109.202 (relating to State MCLs, MRDLs and treatment technique requirements); and 25 Pa. Code § 109.301 (relating to general monitoring requirements).

Disclaimer: These regulations may not be the most recent version. Pennsylvania may have more current or accurate information. We make no warranties or guarantees about the accuracy, completeness, or adequacy of the information contained on this site or the information linked to on the state site. Please check official sources.
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