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Microbial and Disinfection
By-products (MDBP) Rules
Part 1

The Long Term 2 Enhanced Surface Water Treatment Rule (LT2) along with the Stage 2 Disinfectants and Disinfection Byproducts Rule (Stage 2 DBPR) was recently signed by the USEPA and published in the Federal Register.  Together, these two rules improve protection against microbial contaminants (LT2) while reducing the potential health risks of disinfection by-products (DBP).

LT2

Intended to protect public health against Cryptosporidium and other pathogenic microorganisms in drinking water, the LT2 will address identifying and targeting higher risk public water systems (PWSs).  It will require those systems to implement treatment techniques which provide protection beyond what is required in existing regulations.

existing regs

The LT2 supplements the following existing rules that regulate treatment of surface water for pathogenic microorganisms by PWSs:

  • Surface Water Treatment Rule (SWTR)

  • Total Coliform Rule (TCR)

  • Interim Enhanced Surface Water Treatment Rule (IESWTR)

  • Long Term 1 Enhanced Surface Water Treatment Rule (LT1ESWTR)

regulated community

The LT2 applies to all PWSs using surface water or groundwater under the direct influence of surface water (GWUDI).  It additionally targets all PWSs, regardless of population, and applies to both community and non-community PWSs and transient and non-transient PWSs.  Wholesale systems must comply with the rule requirements based on the population of the largest PWS in the combined distribution system.  Consecutive systems that purchase treated water from wholesale PWSs - in full compliance with the monitoring and treatment requirements of the rule - will not be required to provide additional treatment of that water.

DBPR

Intended to reduce DBP exposure and provide more equitable public health protection to all customers, the DBPR requires systems to evaluate their water distribution systems in order to identify locations where high DBP occur.  Systems will then use these locations for future compliance monitoring.

Stage 2 vs. Stage 1

In order to achieve rule compliance, maximum contaminant levels (MCLs) will be calculated using the four quarter running annual average of samples collected at each monitoring site, called the “locational” running annual average (LRAA), rather than using an annual average of all samples collected system-wide as the Stage 1 rule allows.  The number of distribution system monitoring sites will also be population-based rather than determined based on the number of water treatment plants in the system (as is the current situation).

These changes are intended to provide more equal protection to customers throughout the distribution system.  The rule also requires systems to evaluate operational practices to prevent future MCL violations if DBP concentrations exceed an “Operational Evaluation” level. 

who must comply?

Most water systems will be required to comply with the rule in some manner. All community water systems (CWS) and nontransient noncommunity water systems (NTCWS) that produce and/or deliver water that is treated with a primary or residual disinfectant other than ultraviolet light are regulated by the Stage 2 DBPR.

Contact Water Process Group Manager,
Bill Allis, PE, to learn more about LT2; or Process Engineer, Jamie Shambaugh, PE, to learn more about DBPR.

Tune in next issue for more on MDBP regulation compliance requirements and system schedule information.

 

Cryptosporidium is a protozoan parasite commonly found in surface waters, which are used as source water supplies by public drinking water systems.  It has been identified as the cause of numerous waterborne disease outbreaks in the U.S.  When ingested, it can cause acute gastrointestinal illness, which may be severe and sometimes fatal.  Cryptosporidium is of particular concern because of it’s resistance to traditional chemical disinfection practices, such as chlorination.

new rule requirements

LT2:

Specific LT2 regulatory requirements can be classified into three primary subsections, requiring PWSs to:

  • perform source water quality monitoring;

  • possibly provide additional treatment for Cryptosporidium based on the results of the source water monitoring; and

  • take steps to address contamination risks posed by uncovered finished water storage facilities.

Stage 2 DBPR:

For the majority of systems, compliance with the Stage 2 DBPR will include the following steps:

  • submit an Initial Distribution System Evaluation (IDSE) plan or alternative;

  • perform an IDSE;

  • determine Stage 2 monitoring locations based on the IDSE (and submit an IDSE Report); and

  • conduct Stage 2 compliance monitoring.

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