17.2 Surface Water Treatment Rules & Revised Total Coliform Rule

Evolution of the Surface Water Treatment Rules

Surface water supplies—including rivers, lakes, reservoirs, and Ground Water Under the Direct Influence of surface water (GWUDI)—are inherently vulnerable to microbiological contamination from wild and domestic animal waste, agricultural runoff, municipal sewage discharges, and stormwater inflow. To shield the public from pathogenic protozoans, bacteria, and viruses, the EPA promulgated the Surface Water Treatment Rule (SWTR) in 1989, establishing a multi-barrier framework that has been systematically strengthened over four decades of regulatory evolution.

The 1989 Surface Water Treatment Rule (SWTR)

The 1989 SWTR established core treatment techniques that apply to all filtered surface water systems:

• Pathogen Reduction Benchmarks: Systems must achieve at least a 3-log (99.9%) removal and/or inactivation of Giardia lamblia cysts and at least a 4-log (99.99%) removal and/or inactivation of enteric viruses through a combination of physical filtration and chemical disinfection (the "CT" disinfection calculation framework).
• Disinfectant Residual at Entry Point: PWSs must maintain a continuous chemical disinfectant residual entering the distribution system. The disinfectant residual concentration entering the system cannot be less than 0.2 mg/L for more than 4 continuous hours.
• Distribution System Residual: A detectable disinfectant residual (or a Heterotrophic Plate Count [HPC] concentration below 500 CFU/mL) must be maintained in at least 95% of distribution samples collected each calendar month.
• Combined Filter Effluent (CFE) Turbidity Standards: For conventional or direct filtration facilities, the 1989 SWTR required that the turbidity of the combined filtered water be <= 0.5 NTU in at least 95% of measurements collected each month, and never exceed 5.0 NTU at any time.

The 1998 IESWTR and 2002 LT1ESWTR

Following major waterborne cryptosporidiosis outbreaks—most notably the 1993 Milwaukee disaster that sickened over 400,000 individuals and caused over 60 fatalities—the EPA recognized that Cryptosporidium oocysts are highly resistant to conventional free chlorine disinfection. Congress and the EPA enacted the Interim Enhanced Surface Water Treatment Rule (IESWTR) in 1998 for systems serving >= 10,000 persons, followed by the Long Term 1 Enhanced Surface Water Treatment Rule (LT1ESWTR) in 2002 extending identical standards to systems serving < 10,000 persons:

• Lowered CFE Turbidity Standards: Tightened the combined filter effluent turbidity benchmark to <= 0.3 NTU in at least 95% of samples collected every 4 hours each month, and lowered the maximum instantaneous peak limit to 1.0 NTU.
• Cryptosporidium Physical Removal Mandate: Mandated a minimum 2-log (99%) physical removal of Cryptosporidium for conventional and direct filtration plants satisfying the <= 0.3 NTU standard.
• Individual Filter Effluent (IFE) Turbidity Monitoring: Required continuous turbidity monitoring on each individual filter effluent stream, recorded every 15 minutes. Specific regulatory triggers were established: if an individual filter exhibits an IFE > 1.0 NTU in two consecutive 15-minute readings, the utility must prepare an exception report; if an IFE exceeds 0.5 NTU after 4 hours of operation following backwash in two consecutive readings, a filter profile is required; and if an IFE exceeds 2.0 NTU in two consecutive 15-minute readings, a formal filter assessment and comprehensive performance evaluation must be conducted.
• Prohibition on Uncovered Finished Reservoirs: Banned the construction of open, uncovered finished water storage reservoirs to prevent airborne and animal re-contamination.

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Long Term 2 Enhanced Surface Water Treatment Rule (LT2ESWTR)

Promulgated in 2006, the LT2ESWTR specifically targets Cryptosporidium by requiring public water systems to tailor their treatment intensity to the actual microbiological pathogen loading of their raw source water.

Source Water Monitoring and Bin Classification

Under LT2ESWTR, all surface water and GWUDI utilities must conduct 24 months of raw water source monitoring (analyzing raw water twice monthly for Cryptosporidium, E. coli, and turbidity). Based on the arithmetic mean concentration of Cryptosporidium oocysts discovered during the 24-month study, the utility's source water is assigned to one of four regulatory Bins:

1. Bin 1 (< 0.075 oocysts/L): Low pathogen density. Conventional filtration plants receive 3.0-log Giardia, 2.0-log Cryptosporidium, and 2.0-log virus removal credit automatically by achieving CFE <= 0.3 NTU. 0 additional log treatment required.
2. Bin 2 (0.075 to < 1.0 oocysts/L): Moderate pathogen density. Requires 1.0-log additional Cryptosporidium treatment.
3. Bin 3 (1.0 to < 3.0 oocysts/L): High pathogen density. Requires 2.0-log additional Cryptosporidium treatment.
4. Bin 4 (>= 3.0 oocysts/L): Severe pathogen density. Requires 2.5-log additional Cryptosporidium treatment.

The Microbial Toolbox

Systems placed in Bins 2, 3, or 4 cannot rely on conventional free chlorine, because the thick outer shell of the Cryptosporidium oocyst makes it virtually impervious to chemical oxidation by chlorine at municipal doses and contact times. Instead, utilities must select and implement treatment technologies from the EPA Microbial Toolbox:

• Source Protection and Management: Watershed control programs (0.5-log credit), alternative intake management, or off-stream raw water storage basins providing >= 21 days retention (0.5-log credit).
• Pre-Filtration Treatment: Presedimentation basins with continuous chemical coagulant addition (0.5-log credit) or two-stage softening clarification (0.5-log credit).
• Filtration Performance Optimization: Combined Filter Effluent performance achieving <= 0.15 NTU in 95% of monthly readings (0.5-log credit), or Individual Filter Effluent achieving <= 0.10 NTU in 95% of monthly readings (0.5-log credit).
• Advanced Membrane Separation: Microfiltration (MF) and Ultrafiltration (UF) validated through challenge testing and daily direct pressure-decay integrity testing (up to 4.0-log removal credit).
• Alternative Disinfection Technologies:
  • Ultraviolet (UV) Light Irradiation: Highly effective against both Cryptosporidium and Giardia. A UV reduction dose of 12 mJ/cm² achieves 3.0-log Cryptosporidium and 3.0-log Giardia inactivation, while a dose of 22 mJ/cm² delivers 4.0-log inactivation.
  • Ozone (O3): Effective at high water temperatures and higher CT values (requires strict monitoring of bromate formation).
  • Chlorine Dioxide (ClO2): Provides log-inactivation credit depending on water temperature and concentration (requires daily monitoring of chlorite residual).

Table 17.2.1: Surface Water Treatment Rule Turbidity Standards Evolution

Table 17.2.2: LT2ESWTR Bin Classifications and Microbial Toolbox Requirements

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Revised Total Coliform Rule (RTCR): The "Find and Fix" Framework

Promulgated in 2013 and taking full regulatory effect on April 1, 2016, the Revised Total Coliform Rule (RTCR) replaced the 1989 Total Coliform Rule (TCR). The fundamental philosophy of the RTCR represents a historic regulatory paradigm shift:

Old 1989 TCR (Enforcement / Violation Model)
       |  (Exceeding monthly coliform triggered non-acute MCL violation)
       v
2016 RTCR ("Find and Fix" Public Health Protection Model)
       |  (Total coliforms are system integrity indicators; Level 1/2 assessments find sanitary defects)
       v
Acute MCL Violation Reserved Exclusively for E. coli

Under the 1989 rule, exceeding the monthly total coliform limit triggered an immediate non-acute MCL violation and mandatory public notification. However, total coliform bacteria are widespread in nature (soil, decaying vegetation, biofilm) and are rarely pathogenic themselves. Under the RTCR, the total coliform MCL was eliminated. Instead, total coliform bacteria serve as system integrity indicators that trigger an investigative process known as "Find and Fix", designed to locate sanitary defects and repair them before pathogenic contamination occurs. An acute MCL violation is reserved exclusively for Escherichia coli (E. coli), which indicates definitive fecal contamination from warm-blooded mammals.

Routine Monitoring & Sample Siting Plans

Every public water system must develop and adhere to a written Sample Siting Plan approved by the state primacy agency. Routine distribution samples must be collected at representative locations throughout the distribution network (including storage tank discharge zones, dead ends, commercial hubs, and pressure zones) at regular intervals throughout the month. The required monthly sample count is determined by population: a system serving 25 to 1,000 residents collects 1 sample/month, while a system serving 100,000 residents collects 100 samples/month.

Mandatory Repeat Sampling Protocol

Whenever a routine distribution sample tests positive for total coliform (TC+), the operator must execute a strict, legally mandated repeat sampling protocol:

• Timeframe: All repeat samples must be collected within 24 hours of laboratory notification.
• Repeat Set Size: The system must collect a set of at least 3 repeat samples for each positive routine sample:
  1. Original Tap: One sample from the exact same faucet/tap where the original positive was detected.
  2. Upstream Tap: One sample from an active customer service connection located within 5 service connections upstream of the positive tap.
  3. Downstream Tap: One sample from an active customer service connection located within 5 service connections downstream of the positive tap.
• Triggered Ground Water Rule (GWR) Sampling: If the utility utilizes groundwater wells, the operator must simultaneously collect a triggered raw source water sample from each active, running well within 24 hours to determine if aquifer contamination triggered the distribution coliform hit.
• Mandatory E. coli Testing: Every sample (routine or repeat) that tests positive for total coliform must be immediately analyzed for the presence of E. coli.

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Coliform Treatment Technique Triggers: Level 1 and Level 2 Assessments

When distribution coliform results breach established thresholds, the RTCR mandates that the utility perform an engineering audit termed an Assessment to find sanitary defects and fix them.

Level 1 Assessment

• Triggers:
  1. For systems collecting >= 40 samples per month: > 5.0% of samples (routine and repeat) are total coliform-positive (TC+) during a calendar month.
  2. For systems collecting < 40 samples per month: >= 2 samples are total coliform-positive (TC+) during a calendar month.
  3. The water system fails to collect all required repeat samples within 24 hours following a single routine total coliform-positive sample.
• Performance: A Level 1 Assessment is an internal operational review conducted by the water utility's own operators or management.
• Action & Timeline: The operator inspects sample taps, chemical disinfectant feed rates, tank levels, recent distribution pressure events, main repair sites, and backflow incidents. The operator documents findings on a standardized state form, outlines corrective actions taken or planned, and must submit the completed Level 1 Assessment form to the primacy agency within 30 calendar days of the trigger date.

Level 2 Assessment

• Triggers:
  1. An E. coli MCL violation occurs (acute public health emergency).
  2. The water system triggers a second Level 1 Assessment within a rolling 12-month period (indicating chronic, unresolved vulnerability).
  3. For small systems on annual monitoring, a Level 1 trigger in two consecutive calendar years.
• Performance: A Level 2 Assessment is a rigorous, comprehensive technical audit that cannot be conducted solely by plant operators. It must be conducted by the state primacy agency or a state-approved, certified third-party assessor.
• Action & Timeline: The assessor performs a detailed forensic evaluation of the entire system: raw water source, treatment process integrity, finished water storage security (hatches, vents), distribution hydraulics, cross-connection control, and laboratory handling. The completed Level 2 Assessment report, detailing identified sanitary defects and an enforceable schedule of corrective repairs, must be submitted to the state primacy agency within 30 calendar days of the trigger.

E. coli MCL Violation Conditions

An E. coli Maximum Contaminant Level violation is an immediate public health emergency that triggers a Tier 1 Public Notice within 24 hours. An E. coli MCL violation occurs under any of the following four specific monitoring outcomes:

1. A routine sample is E. coli positive (EC+), and any repeat sample is total coliform positive (TC+).
2. A routine sample is total coliform positive (TC+), and any repeat sample is E. coli positive (EC+).
3. A routine sample is E. coli positive (EC+), and the water system fails to collect all required repeat samples.
4. A routine sample is total coliform positive (TC+), a repeat sample is total coliform positive (TC+), and the utility fails to analyze the repeat sample for E. coli.

Table 17.2.3: RTCR Assessment Triggers, Protocols, and E. coli MCL Violation Conditions