l year of monitoring.
Samples & Sampling
Per the regulations, chlorine and chloramine monitoring requirements are the same in terms of number of samples and sampling point. They require as a minimum community water supplies and nontransient, noncommunity water supplies measure for residual chlorine and chloramines at the same point in the distribution system and at the same time as total coliform samples are collected.
Coliform sampling is based on the population served; therefore, the larger the population, the more disinfectant testing that needs to take place. Systems using chlorine as the residual disinfectant and operating booster chlorination systems must take three samples within the distribution systems. The samples should be collected as follows: one as close as possible to the first customer; one that is representative of the average residence time; and one as close as possible to the end of the distribution system.
In order to comply with the MDRL, systems running an annual average of monthly averages of all samples, computed quarterly, must be less than the established MDRL listed in Table 1. The EPA has approved several methods for measuring free and total chlorine based on ASTM and Standard Methods. Some states may have approved DPD colorimetric testing kits as a method to meet compliance of this rule.
Chlorine dioxide is mostly used to control taste and odor issues, but it is also used to oxidize iron and manganese and finally as a disinfectant and algaecide. Only systems using chlorine dioxide are required to monitor for this disinfectant.
Systems that are required to monitor must take daily samples at the entrance to the distribution system. Unlike chlorine and chloramines, the MDRL for chlorine dioxide cannot be exceeded for short periods of time due to potential health effects from short-term exposure to levels of the MCL of 0.8 mg/L. If any daily sample exceeds the MCL, the system is required to take three additional samples in the distribution system the following day.
The EPA has also approved methods for analyzing chlorine dioxide samples based on EPA and Standard Methods, and some states have approved DPD colorimetric testing kits as a method to meet compliance for monitoring chlorine dioxide.
The new regulations also focus on the reduction of disinfection byproducts, and public water supplies have responded by adopting alternative treatment techniques like using chloramines instead of chlorine to reduce the levels of disinfection byproducts. Some systems are also using alternatives such as ozone and chlorine dioxide as the primary disinfectant. Other systems have tried reducing the organic matter in their sources as a way to reduce the formation of disinfection byproducts. There is not one answer for solving the disinfection byproduct formation due to the fact that every system has water with a different quality and chemistry makeup.
Testing Large Systems
In 1996, the Information Collection Rule (ICR) went into effect and requires large systems serving populations of more than 100,000 and a more limited number of systems serving between 50,000 and 100,000 to collect data with regard to the disinfectants being used, occurrence of disinfection byproducts and treatment technologies being utilized.
There were about 300 public water supplies with 500 treatment plants that participated in the study, which collected data from July 1997 to December 1998. This rule was intended to help evaluate the need for changing current treatment practices as well as determined future regulation of disinfectants and disinfection byproducts. The information collected as a result of this rule was intended to help develop the regulations for Stage 1 DDBR, but the data was not complete when the rule was being developed. It did, however, play a role in the development Stage 2 DDBR.
While current EPA regulations require monitoring of 11 disinfection byproducts, more than 500 disinfection byproducts have been identified in various drinking water sources.
The World Health Organization has established guideline levels for 14 D