2.2 Surface Water Treatment Rules & Revised Total Coliform Rule (RTCR)

2.2 Surface Water Treatment Rules & Revised Total Coliform Rule (RTCR)

Microbial pathogens represent the most immediate, acute biological threats in public drinking water supplies. The EPA addressed these risks through a progressively strengthened sequence of federal regulations: the original Surface Water Treatment Rule (SWTR) of 1989, the Interim Enhanced Surface Water Treatment Rule (IESWTR) of 1998 for large systems, the Long Term 1 Enhanced Surface Water Treatment Rule (LT1ESWTR) of 2002 for small systems, the Long Term 2 Enhanced Surface Water Treatment Rule (LT2ESWTR) of 2006, and the Revised Total Coliform Rule (RTCR) enacted in 2016. In Arizona, ADEQ administers these rules across all surface water sources—including the Central Arizona Project (CAP) aqueduct, the Salt River Project (SRP) canal network, and rim lakes—as well as groundwater sources determined to be Ground Water Under the Direct Influence (GWUDI) of surface water.

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The Multi-Barrier Concept & Pathogen Inactivation Standards

The fundamental philosophy underlying surface water treatment is the multi-barrier concept, which holds that public health cannot rely on a single defensive process. Instead, multiple sequential physical and chemical barriers are established across the utility lifecycle:

1. Source Water Protection: Watershed management, stormwater diversion, canal security, and reservoir protection.
2. Chemical Coagulation & Flocculation: Destabilization of colloidal particles and microbial agglomeration.
3. Sedimentation / Clarification: Gravity settling and removal of flocculated solids.
4. Granular Media Filtration: Physical straining, depth filtration, and interception of microscopic cysts and oocysts.
5. Primary Disinfection: Chemical inactivation via chlorine, chloramines, chlorine dioxide, ozone, or ultraviolet (UV) radiation.
6. Distribution Residual Maintenance: Maintaining a protective secondary disinfectant residual to prevent biological regrowth.

Mandatory Log-Reduction Benchmarks

Under the SWTR framework, public water systems must achieve specified cumulative log-reductions (removal and/or inactivation) from the raw source water to finished customer water:

• Giardia lamblia: Minimum 3-log (99.9%) removal and/or inactivation.
• Enteric Viruses: Minimum 4-log (99.99%) removal and/or inactivation.
• Cryptosporidium oocysts: Minimum 2-log (99%) physical removal under IESWTR/LT1ESWTR baseline rules. Under the LT2ESWTR, systems monitor source water Cryptosporidium concentrations and are placed into one of four risk bins (Bins 1 through 4). Bin 1 requires no additional treatment beyond baseline, while Bins 2, 3, and 4 mandate an additional 1.0 to 2.5 logs of treatment credit using an approved "microbial toolbox" (such as membrane filtration, ozone, UV, or enhanced watershed management).

Conventional Treatment Credits & CT Architecture

A well-operated conventional filtration plant—incorporating chemical coagulation, rapid mixing, flocculation, sedimentation, and rapid granular media filtration—is granted standard physical removal credits by the EPA and ADEQ, provided finished water turbidity criteria are satisfied:

The remaining required log-inactivation for Giardia and viruses must be achieved via chemical disinfection, calculated as CT (disinfectant concentration $C$ in mg/L multiplied by effective contact time $T_{10}$ in minutes under peak hourly flow conditions).

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Turbidity Standards: Combined & Individual Filter Effluent

Turbidity serves as the principal operational surrogate for microbial removal efficiency. Suspended particulate matter shields pathogens from disinfectants and indicates potential breakthrough of microscopic parasite cysts.

Combined Filter Effluent (CFE) Compliance Limits

For systems utilizing conventional or direct filtration:

1. The 95th Percentile Limit: CFE turbidity must be less than or equal to 0.3 NTU in at least 95% of the measurements taken each calendar month. Measurements must be recorded every four hours that the plant is delivering water to the public (or sampled continuously via online analyzers).
2. The Maximum Ceiling Limit: CFE turbidity must never exceed 1.0 NTU at any point in time. Any instantaneous reading exceeding 1.0 NTU represents an immediate treatment technique violation requiring consultation with ADEQ.

Individual Filter Effluent (IFE) Continuous Monitoring Triggers

While CFE measures overall plant water, a single malfunctioning filter bed can allow breakthrough of Cryptosporidium oocysts while being diluted by compliant adjacent filters. Therefore, regulations require continuous turbidimetric monitoring recorded every 15 minutes on the effluent of every individual filter bed. Operators must log and report specific operational triggers:

• Trigger 1 (Exceedance at 4 Hours): If any individual filter exceeds 0.5 NTU after the first four hours of continuous operation post-backwash in two consecutive 15-minute readings, the utility must file an explanation of the cause in its monthly operating report (MOR).
• Trigger 2 (Filter Profile / Self-Assessment): If an individual filter exceeds 1.0 NTU in two consecutive 15-minute measurements, the operator must produce a filter profile or conduct a visual inspection within seven days to determine the mechanical or chemical cause.
• Trigger 3 (Core Self-Assessment): If an individual filter exceeds 1.0 NTU in two consecutive 15-minute readings for three consecutive months, the system must conduct a comprehensive filter self-assessment within 14 days.
• Trigger 4 (Comprehensive Performance Evaluation - CPE): If an individual filter exceeds 2.0 NTU in two consecutive 15-minute readings for two consecutive months, the utility must arrange for ADEQ or an approved third party to conduct an independent Comprehensive Performance Evaluation (CPE) within 30 days.

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Revised Total Coliform Rule (RTCR)

The Revised Total Coliform Rule (RTCR), effective April 1, 2016, replaced the legacy 1989 rule. The RTCR shifted the regulatory paradigm from punitive non-compliance to a proactive "find-and-fix" framework designed to identify and correct sanitary defects before disease transmission occurs.

Indicator Organisms: Coliforms vs. E. coli

• Total Coliforms: A broad group of rod-shaped, Gram-negative, non-spore-forming facultative anaerobic bacteria that ferment lactose with gas and acid production within 48 hours at 35°C. Total coliforms inhabit soils, decaying vegetation, and surface waters as well as mammalian intestines. They are not typically pathogenic themselves, but serve as an indicator of treatment efficacy and distribution system integrity.
• Escherichia coli (E. coli): A specific thermotolerant coliform subgroup residing exclusively in the gastrointestinal tract of humans and warm-blooded animals. Detection of E. coli provides definitive evidence of fecal contamination, signaling the probable presence of acute waterborne pathogens (such as Salmonella, Shigella, norovirus, or hepatitis A).

Routine Monitoring & Repeat Sampling Protocol

Public water systems collect routine bacteriological samples throughout the distribution network according to a written Coliform Sample Siting Plan (CSSP) approved by ADEQ. Sampling frequency scales with population served (e.g., systems serving $\le 1,000$ collect 1 sample/month, while large metropolitan utilities collect hundreds monthly).

The 24-Hour Repeat Sampling Mandate: Whenever any routine distribution sample tests positive for total coliform (TC+), the operator must collect a set of at least three repeat samples within 24 hours of laboratory notification:

1. Original Tap: One repeat sample from the exact tap where the original positive sample was collected.
2. Upstream Tap: One repeat sample within five active service connections upstream of the original tap.
3. Downstream Tap: One repeat sample within five active service connections downstream of the original tap.

Triggered Source Water Monitoring: If the system utilizes groundwater wells, a routine distribution TC+ concurrently triggers mandatory Ground Water Rule (GWR) source water sampling. The operator must collect a raw water grab sample from every active wellhead supplying that distribution pressure zone within 24 hours to determine if fecal contamination originated in the aquifer.

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Sanitary Assessments: Level 1 vs. Level 2

The RTCR establishes two tiers of sanitary assessments based on operational triggers.

Level 1 Assessment (System-Led Find-and-Fix)

• Triggers:
  • For systems collecting $\ge 40$ samples/month: More than 5.0% of routine and repeat samples in a month are total coliform positive.
  • For systems collecting $< 40$ samples/month: Two or more routine and repeat samples in a month are total coliform positive.
  • Failure to collect every required repeat sample following a single positive routine sample.
• Conducted By: The water utility staff or certified plant operator.
• Scope: A general review of distribution system operations, looking for recent water main breaks, pressure drops below 20 psi, storage tank roof breaches, fire hydrant flushing operations, cross-connection incidents, or treatment chemical feed interruptions.
• Submission: The completed Level 1 Assessment form, detailing identified sanitary defects and corrective action schedules, must be submitted to ADEQ within 30 days of triggering the assessment.

Level 2 Assessment (Comprehensive In-Depth Investigation)

• Triggers:
  • An E. coli Maximum Contaminant Level (MCL) Violation, which occurs under any of the following four conditions:
    1. An E. coli positive routine sample followed by a total coliform positive repeat sample.
    2. An E. coli positive routine sample followed by an E. coli positive repeat sample.
    3. A total coliform positive routine sample followed by an E. coli positive repeat sample.
    4. Failure to collect all required repeat samples following an E. coli positive routine sample.
  • Occurrence of a second Level 1 Assessment trigger within a rolling 12-month period.
• Conducted By: ADEQ personnel, or a qualified third party / certified operator specifically authorized by ADEQ.
• Scope: A comprehensive engineering and microbiological forensic review of source water integrity, treatment barrier efficacy, distribution system hydraulics, dead ends, storage tank stratification, sampling protocols, and physical infrastructure.
• Submission & Public Notice: The Level 2 report must be submitted to ADEQ within 30 days. An E. coli MCL violation is an acute public health emergency requiring immediate Tier 1 Public Notification (within 24 hours) and the issuance of a Boil Water Advisory (BWA) instructing consumers to bring tap water to a rolling boil for at least one full minute before consumption.