New Disinfectants Rule Deadlines for Public Water Systems
This article describes the background, stages and the new deadlines for public water systems to comply with the most current disinfectants and disinfection byproducts rule.
By Dr. Harlan H. Bengtson, PE
Background on Disinfection and Disinfection Byproducts
Jersey City, NJ was the first U.S. city to routinely disinfect its municipal water supply, starting in 1908.1 Soon after, thousands of cities and towns across the country began to do the same and this dramatically decreased the prevalence of waterborne diseases such as cholera and typhoid. To demonstrate, the incidence rate of typhoid fever in the U.S. dropped from about 100 cases per 100,000 people in 1900 to 33.8 cases per 100,000 people in 1920.2 By 2006, this rate had dropped to 0.1 cases per 100,000 people.3
While the purification of drinking water has clearly been beneficial for public health, unintended byproducts may form when disinfectants react with water’s natural minerals. Indeed, some of these disinfection byproducts (DBPs) may pose serious health risks to humans. In tests on laboratory animals, some DBPs have been shown to be carcinogenic and cause adverse reproductive or developmental effects. In 1979, concerns about the potential health risks of DBPs led to the EPA setting an interim maximum contaminant level (MCL) of 0.10 mg/L for trihalomethanes. This MCL applied to the annual average contaminant level in any community water system that served more than 10,000 people and added a disinfectant to the drinking water as part of its treatment process.4
Between July 1997 and December 1998, under the Information Collection Rule, 296 public water systems (serving at least 100,000 persons each) monitored and collected data on microbial contaminants, disinfectants and disinfection byproducts. The resulting information helped lead to the creation of the Stage 1 Disinfectants and Disinfection Byproducts Rule.5
The Stage 1 Disinfectants and Disinfection Byproducts Rule
The EPA passed the interim Stage 1 Disinfectants and Disinfection Byproducts Rule in November 1998. The final EPA revisions to this rule were published on January 16, 2001. The final ruling regarding DBP levels covered all community water systems and non-transient, non-community systems that add a disinfectant to the drinking water at any part of the treatment process. This rule includes water systems serving less than 10,000 people.6
Key provisions in the final Stage 1 Disinfectants and Disinfection Byproducts Rule include maximum residual disinfectant level goals (MRDLGs), maximum residual disinfectant levels (MRDLs), maximum contaminant level goals (MCLGs) and maximum contaminant levels (MCLs). This information is summarized in Table 1.7
This regulation also contains stipulations for total organic carbon (TOC) removal based on the alkalinity of the source water as well as certain water system characteristics. The deadline for compliance with the Stage 1 Disinfectants and Disinfection Byproducts Rule was January 2002 for large water systems and January 2004 for groundwater and small surface water systems.8
Table 1: Goals and Limits in the Stage 1 Disinfectants and Disinfection Byproduct Rule
* TTHM is the sum of the concentrations of chloroform, bromodichlormethane, dibromochloromethane and bromoform.
** A zero MCLG for chloroform was removed by EPA, effective May 30, 2000, in accordance with an order of the U.S. Court of Appeals for the District of Columbia Court.
*** HAA5 is the sum of the concentrations of mono-, di-, and trichloroacetic acids and mono- and dibromoacetic acids.
The Stage 2 Disinfectants and Disinfection Byproducts Rule
Issued in January 2006, the Stage 2 Disinfectants and Disinfection Byproducts Rule applies to community and non-transient, non-community water systems that add and/or deliver water that is treated with a primary or residual disinfectant (other than ultraviolet light). The MCLGs and MCLs for the Stage 1 Rule (shown in Table 1) remain the same for the Stage 2 Rule, except that an MCLG of 0.07 mg/L for chloroform was included.9
The provisions of the Stage 2 Disinfectant and Disinfection Byproduct Rule are primarily about monitoring procedures, rather than changes in MCLGs or MCLs. Under the Stage 2 Rule, water systems will conduct an evaluation of their distribution systems, known as an Initial Distribution System Evaluation (IDSE). This evaluation is carried out to identify locations with high disinfection byproduct concentrations, which will then be used as sampling sites for Stage 2 DBP Rule compliance monitoring.
The Stage 2 Rule requires that TTHM and HAA5 levels be calculated for compliance with the MCLs for each monitoring location in the distribution system, which is known as the Locational Running Annual Average (LRAA). In contrast to the Stage 1 Rule, the LRAA is used rather than the running annual average of samples from all monitoring locations across the system.
Correction to Stage 2 Rule in 2009
A minor correction to the Stage 2 Rule went into effect on June 29, 2009. The January 4, 2009, Stage 2 Rule unintentionally allowed for less routine compliance monitoring than that intended for groundwater systems serving between 500 and 9,999 people. Based on this correction, these systems are now required to monitor for both total trihalomethanes (TTHM) and haloacetic acids (HAA5) concentrations at two locations instead of only being required to monitor for either TTHM or HAA5 at two locations as stated in the original Stage 2 Disinfectants and Disinfection Byproducts Rule.10
2010 – 2013 Deadlines for Compliance with the Stage 2 Rule
The compliance schedule for the Stage 2 Disinfectant and Disinfection Byproduct Rule includes deadlines for submitting an IDSE monitoring plan, completing the IDSE, submitting the IDSE report, and beginning compliance monitoring. Larger systems have earlier deadlines for each of these benchmarks. Smaller systems are allowed more time, which is summarized in Table 2.11 It should be noted that systems serving less than 10,000 people have IDSE deadlines in 2010, and all systems must begin compliance monitoring in either 2012 or 2013.
Table 2: Compliance Deadlines in Stage 2 Disinfectants & Disinfection Byproducts Rule
1. US Environmental Protection Agency. The history of drinking water treatment. Available at http://www.epa.gov/safewater/consumer/pdf/hist.pdf
2. Centers for Disease Control and Prevention. Achievements in public health, 1900–1999: safer and healthier foods. MMWR 1999; 48(40): 905.
3. Centers for Disease Control and Prevention. Summary of notifable diseases-United States, 2006. MMWR 2008; 55(53): 17.
4. US Environmental Protection Agency. Microbial and Disinfection Byproduct (MDBP) Rules. Available at http://pubweb.epa.gov/ogwdw/mdbp/mdbp.html#trihalomethanes
7. US Environmental Protection Agency. Stage 1 Disinfectants and Disinfection Byproducts Rule. Available at http://www.epa.gov/ogwdw000/mdbp/dbp1.html
9. US Environmental Protection Agency. Stage 2 Disinfectants and Disinfection Byproducts Rule. Available at http://www.epa.gov/safewater/disinfection/stage2/regulations.html
10. US Environmental Protection Agency. Minor Correction to Stage 2 Disinfectants and Disinfection Byproducts Rule. Available at http://www.epa.gov/fedrgstr/EPA-WATER/2009/June/Day-29/w14598.htm