By Thomas R. Grubbs, PE

This is the second in a two-part series on the latest changes to U.S. drinking water regulations. In WC&P’s October-December 1998 issues, Rip Rice and Paul Overbeck presented an excellent detailed overview of the development of many of the rules discussed in these articles as part of their three-part series “Ozone and the Safe Drinking Water Act.” The rules discussed in the first article, which ran in December, are available at the U.S. Environmental Protection Agency’s online presence on the Office of Ground Water and Drinking Water website at: . The rules discussed in this second article are available at a subsection of this site which can be found at: . For more information, contact USEPA Safe Drinking Water Hotline: (800) 426‑4791.

Summary: For over 20 years, the U.S. Environmental Protection Agency (USEPA) has developed and implemented regulations to 1) control disease-causing microorganisms in drinking water with requirements for physical removal via filtration processes and inactivation through disinfection, and 2) control the by-products formed during disinfection. Since 1992, USEPA has worked with stakeholders in a series of regulatory development processes to develop protective, cost-effective, implementable rules to achieve these two objectives simultaneously.
The Stage 1 Disinfectant/Disinfection By-product (D/DBP) Rule and its companion rule, the Interim ESWTR (IESWTR), finalized in December 1998, are the first in a series of rules to be published over the next several years to control pathogens while minimizing the public health risks from disinfectants and disinfection by-products (DBPs). To address the complex issues associated with regulating pathogens and DBPs simultaneously, USEPA began a rule-making process in 1992 by convening a Regulatory Negotiation (RegNeg) Advisory Committee, representing a range of stakeholders affected by possible regulation. These new rules are a product of six years of collaboration among water suppliers; environmental, consumer and public health groups; local elected officials, and local, state and federal regulatory and public health agencies

Applicability, compliance dates
The existing 1979 Total Trihalomethane (TTHM) Rule requirements apply only to systems serving at least 10,000 people. The Stage 1 D/DBP Rule applies to all community water systems and non-transient, non-community water systems that deliver water treated with a chemical disinfectant for either primary or residual treatment. In addition, certain requirements apply to transient, non-community water systems that use chlorine dioxide.

Subpart H systems (systems that use surface water or groundwater under the direct influence of surface water—GWUDI—as a source) serving 10,000 or more people must begin to comply with the requirements of the Stage 1 D/DBP Rule no later than January 2002. Systems that need to make capital improvements to comply may apply to the state for an extension of up to 24 months. Subpart H systems that serve fewer than 10,000 people, and all affected groundwater systems, must begin to comply with the requirements no later than January 2004. Extensions are not available to these systems, since the additional 24 months have already been provided.

The IESWTR applies to subpart H systems that serve 10,000 or more people. Additionally, states are required to conduct sanitary surveys for all subpart H systems. Systems must comply with turbidity and monitoring requirements beginning in January 2002. However, systems with elevated levels of DBPs are required to develop an evaluation of their existing disinfection practices and establish a disinfection profile no later than March 2001.

D/DBP Rule requirements
The Stage 1 D/DBP Rule sets maximum contaminant level goals (MCLGs) for some of the regulated DBPs, a more stringent MCL for TTHMs and new MCLs for the five haloacetic acids (HAA5), bromate (a by-product of ozone) and chlorite (a by-product of chlorine dioxide). MCLGs are non-enforceable public health goals set at concentrations at which no known or anticipated adverse health effects are expected to occur. MCLs are enforceable standards.

Disinfectant residuals
To protect against potential health risks caused by high levels of residual disinfectants, the Stage 1 D/DBP Rule sets maximum residual disinfectant level goals (MRDLGs) and maximum residual disinfectant levels (MRDLs). Like MCLGs and MCLs, respectively—MRDLGs are non-enforceable while MRDLs are enforceable requirements.

DBPP treatment techniques
Subpart H systems using conventional filtration treatment (consisting of coagulation, flocculation, sedimentation, and filtration) must remove specified levels of organic DBPPs, measured as total organic carbon (TOC). The treatment technique was established because disinfectants can react with DBPPs to form both regulated and unregulated DBPs. By minimizing the production of all DBPs, USEPA believes risks to public health will be reduced. Systems comply by removing specified percentages of TOC using enhanced coagulation or enhanced softening. Alternatively, systems can show they meet alternative performance criteria that indicate removal of DBPPs is unnecessary or impractical.

IESWTR requirements
Subpart H systems having average annual TTHM ³ 0.064 mg/L or annual average HAA5 ³ 0.048 mg/L must develop a disinfection profile. The disinfection profile is a compilation of daily water quality and disinfection treatment measurements that demonstrate efficacy of the disinfection process over a one-year period.

This provision provides a process for a system and the state to work together to assure there’ll be no significant reduction in microbial protection as a result of disinfection practice modifications designed to meet MCLs for DBPs established in the Stage 1 D/DBP Rule. Those systems required to develop disinfection profiles that then wish to change their disinfection practices to meet the new MCLs must establish the disinfection benchmark (the lowest monthly average disinfection level) and consult with the state prior to implementing such changes. In addition, they must keep the disinfection profile on file for the state to review during sanitary surveys.

The IESWTR sets an MCLG of zero for the protozoan Cryptosporidium. It also establishes a requirement for 2-log (99 percent) removal of Cryptosporidium for systems that must currently filter under the SWTR. Systems that use conventional filtration treatment or direct filtration (consisting of coagulation, flocculation and filtration) meet this requirement if they comply with the strengthened turbidity performance standards for combined filter effluent (discussed next). Systems that use slow sand or diatomaceous earth filtration meet the 2-log removal requirement if they comply with the existing turbidity performance standards under the SWTR.

For unfiltered systems, the IESWTR extends the existing watershed control requirements to include the control of potential sources of Cryptosporidium. Such sources must be included in the public water supply’s watershed control plan.

Turbidity requirements
New turbidity requirements strengthen current SWTR requirements for combined filter effluent (CFE) turbidity and introduce continuous turbidity monitoring for individual filters. For systems using conventional filtration treatment or direct filtration, the turbidity level of the CFE must be less than or equal to 0.3 nephelometric turbidity units (NTU) in at least 95 percent of the measurements taken each month, and the CFE turbidity level must at no time exceed 1 NTU (in the SWTR, these requirements are 0.5 NTU and 5 NTU, respectively).

Additionally, these systems must conduct continuous turbidity monitoring on the effluent of each individual filter. Systems must report instances of poor filter performance to the state, and must take prescribed actions to identify and correct the cause(s).

Sanitary surveys
The state or a third party approved by the state must conduct sanitary surveys for all subpart H systems, regardless of size, no less frequently than every three years for community water systems and every five years for non-community systems. A system must respond to any significant deficiencies identified during its survey, indicating how and on what schedule the system will address the deficiencies. States must assure that systems correct deficiencies identified in the survey report.

Uncovered storage facilities
The rule prohibits construction of uncovered finished water storage facilities (reservoir, holding tank or other storage facility) after Feb. 16, 1999. USEPA has also developed guidance on how to minimize the possibility of recontamination of water in existing uncovered finished water reservoirs.

Future regulations
The Stage 1 D/DBP Rule and the IESWTR were published simultaneously to address the inherent tradeoffs between protection from microbial contamination and the potential health effects from disinfectants and their by-products. These rules are the first in a series of rules that will continue to address the public health concerns associated with pathogens and chemical disinfectants. Other rules being developed for the control of pathogens and DBPs are listed below:

While the Stage 1 D/DBP Rule applies to systems of all sizes, the IESWTR applies only to subpart H systems serving at least 10,000 people. USEPA is developing a rule, the Long Term 1 ESWTR (LT1ESWTR), to strengthen microbial protection for subpart H systems serving fewer than 10,000 that will also address the risk tradeoff issue as these systems implement the Stage 1 D/DBP Rule. The agency believes the rule will generally track the approaches in the IESWTR for improved turbidity control (including individual filter monitoring) and disinfection benchmarking and profiling.

USEPA also is required to develop standards for recycling of filter backwash. It is currently gathering data, reviewing literature, and consulting with a wide range of interested parties to identify associated cost and engineering issues for a Filter Backwash Recycling Rule (FBWRR).

LT2ESWTR/Stage 2 D/DBP Rule
In the 1996 Amendments to the Safe Drinking Water Act, USEPA is required to finalize the Stage 2 D/DBP Rule by May 2002 to further address risks from disinfection by-products, based on new health effects research, occurrence data and treatment information. The agency plans to also develop a Long Term 2 ESWTR (LT2ESWTR) to ensure microbial protection isn’t compromised and may include site-specific treatment requirements if adequate data are available. It began discussions with stakeholders on the development of these rules in December 1998 and set up an advisory committee in March 1999.

Ground Water Rule (GWR)
USEPA is also developing a rule to ensure microbial protection for groundwater systems—formerly known as the Ground Water Disinfection Rule (GWDR)—through use of disinfection and other strategies (wellhead protection, well construction codes, vulnerability assessments).

USEPA developed a series of guidance manuals to support the Stage 1 D/DBP Rule and IESWTR. The manuals will help the agency, state agencies and affected public water systems implement the two interrelated rules, and will help to ensure implementation among these groups is consistent. Manuals currently available are:

  • Guidance Manual for Enhanced Coagulation and Enhanced Precipitative Softening (EPA 815-R-99-012).
  • Alternative Disinfectants and Oxidants Guidance Manual (EPA 815-R-99-014).
  • M/DBP Simultaneous Compliance Manual (EPA 815-R-99-015).
  • Guidance Manual for Compliance with the Interim Enhanced Surface Water Treatment Rule: Turbidity Provisions (EPA 815-R-99-010).
  • Uncovered Finished Water Reservoirs Guidance Manual (EPA 815-R-99-011).
  • Disinfection Profiling and Benchmarking Guidance Manual (EPA 815-R-99-013).


  1. USEPA, “National Interim Primary Drinking Water Regulations; Control of Trihalomethane in Drinking Water; Final Rule,” Federal Register, 44 (231): 68624-68707, 1979.
  2. USEPA, “Drinking Water; National Primary Drinking Water Regulations; Filtration, Disinfection; Turbidity, Giardia lamblia, Viruses, Legionella, and Heterotrophic Bacteria; Final Rule,” Federal Register, 54 (124): 27485-27541, 1989.
  3. USEPA, “National Primary Drinking Water Regulations: Disinfectants and Disinfection By-Products; Final Rule,” Federal Register, 63 (241): 69390-69476, 1998.
  4. USEPA, “National Primary Drinking Water Regulations: Interim Enhanced Surface Water Treatment; Final Rule,” Federal Register, 63 (241): 69478-69521, 1998.

About the author
Thomas R. Grubbs, PE, is an environmental engineer in USEPA’s Office of Ground Water and Drinking Water in Washington, D.C. After nearly five years in the agency’s regional office in Atlanta, he moved to the capital in 1988 to work on drinking water regulatory development, implementation, and enforcement. He was regulation manager for the Information Collection Rule and the Stage 1 D/DBP Rule and principal author of the IESWTR regulatory language. He’s currently working on development of the next round of M/DBP rules. He is a Desert Storm veteran and retired from the U.S. Army Reserves. Grubbs can be reached at (202) 260-7270.


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