1.5 Colorado Primary Drinking Water Regulations (Regulation 11) & Compliance

Regulatory Primacy & System Classifications

The supply of potable water across Colorado is governed by CDPHE Regulation 11 (5 CCR 1002-11), formally titled the Colorado Primary Drinking Water Regulations (CPDWR). Under the federal Safe Drinking Water Act (SDWA), the U.S. Environmental Protection Agency (EPA) granted the State of Colorado primacy (primary enforcement responsibility). Primacy authorizes the Water Quality Control Division (WQCD) to establish, monitor, and enforce drinking water standards that are at least as stringent as federal standards.

Public Water System (PWS) Definitions

A Public Water System (PWS) is defined under Regulation 11 as any system providing piped water for human consumption that has at least 15 service connections OR regularly serves an average of at least 25 individuals daily for at least 60 days per year.

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|               PUBLIC WATER SYSTEM (PWS) CLASSIFICATIONS                 |
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| 1. Community Water System (CWS):                                        |
|    Serves >= 15 service connections used by year-round residents OR      |
|    regularly serves >= 25 year-round residents (e.g., cities, towns,     |
|    mobile home parks, residential subdivisions).                         |
|                                                                         |
| 2. Non-Transient Non-Community Water System (NTNCWS):                   |
|    Regularly serves >= 25 of the SAME persons for >= 6 months per year   |
|    (e.g., schools, industrial work sites, business parks with wells).   |
|                                                                         |
| 3. Transient Non-Community Water System (TNCWS):                        |
|    Serves >= 25 individuals daily for >= 60 days per year, but does NOT |
|    serve the same people (e.g., highway rest areas, campgrounds, ski     |
|    resorts, rural gas stations).                                        |
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Contaminant Standards: MCLs, MRDLs & Treatment Techniques

Regulation 11 establishes health-based limits across several distinct regulatory categories:

1. Maximum Contaminant Level (MCL): The maximum permissible level of a contaminant delivered to any user of a public water system. MCLs are enforceable health standards.
2. Maximum Residual Disinfectant Level (MRDL): The maximum permissible concentration of a disinfectant residual (chlorine, chloramines, chlorine dioxide) allowed in the distribution network. The standard MRDL for free chlorine and total chlorine is 4.0 mg/L.
3. Minimum Residual Disinfectant Limits: A PWS must maintain a minimum free chlorine residual of 0.2 mg/L at the entry point to the distribution system and maintain a detectable disinfectant residual throughout all points in the distribution network.
4. Treatment Technique (TT): An enforceable procedure or performance standard required in place of an MCL when measuring a specific contaminant is technically or economically impractical (e.g., filtration turbidity performance, coagulant dosing for total organic carbon / TOC removal).

Surface Water Treatment Rule (SWTR) Turbidity Standards

For systems utilizing surface water or GWUDI sources with conventional or direct granular media filtration:

• 95% Compliance Standard: Filtered effluent turbidity must be $\le$ 0.3 NTU in at least 95% of measurements taken each calendar month.
• Absolute Maximum Limit: Filtered effluent turbidity must never exceed 1.0 NTU in any single sample. An exceedance of 1.0 NTU is an acute violation triggering immediate investigation and potential Tier 1 notification if uncorrected.
• Log Removal / Inactivation Mandates: Treatment must achieve at least 3-log (99.9%) removal/inactivation of Giardia lamblia, 4-log (99.99%) removal/inactivation of viruses, and 2-log (99%) removal of Cryptosporidium.

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Revised Total Coliform Rule (RTCR) Compliance

Microbiological safety is evaluated under the Revised Total Coliform Rule (RTCR). Total coliform bacteria serve as operational indicators of treatment integrity and distribution sanitary barriers.

• Routine Monitoring: Samples are collected across representative distribution points according to an approved written sample siting plan. The monthly sample volume scales with population (e.g., 25–1,000 population = 1 sample/month; 1,001–2,500 = 2 samples/month; 2,501–3,300 = 3 samples/month; major metro systems collect hundreds per month).
• Positive Sample Protocol: If any routine sample tests Total Coliform positive (TC+), the laboratory must immediately test that culture for Escherichia coli (E. coli). Furthermore, the operator must collect a set of 3 repeat samples within 24 hours: (1) at the original tap, (2) within 5 service connections upstream, and (3) within 5 service connections downstream. In addition, groundwater systems must collect triggered source water samples under the Ground Water Rule.
• Level 1 Assessment: Triggered if a system collecting $<$ 40 samples/month has 2 or more TC+ samples in a month (or if a system collecting $\ge$ 40 samples exceeds 5.0% TC+). The system conducts an internal operational investigation and submits the assessment form to CDPHE within 30 days.
• Level 2 Assessment: An in-depth comprehensive inspection triggered by an acute E. coli MCL violation (e.g., $E. coli+$ routine followed by $TC+$ repeat, or $TC+$ routine followed by $E. coli+$ repeat) OR occurrence of a second Level 1 trigger within a rolling 12-month period. Conducted by a CDPHE-approved qualified party.

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Sanitary Surveys & Finished Storage Tank Oversight

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|                    THE 8 SANITARY SURVEY CORE ELEMENTS                  |
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| 1. Water Source (wells, intakes, watershed protection)                  |
| 2. Treatment Processes (coagulation, filtration, disinfection)          |
| 3. Distribution System (piping, pressures, looping, flushing)           |
| 4. Finished Water Storage (tanks, standpipes, vents, screens)           |
| 5. Pumps, Pumping Facilities & Controls                                 |
| 6. Monitoring, Reporting, Laboratory & Data Verification                |
| 7. Water System Management, Staffing & Financial Operations             |
| 8. Operator Compliance & ORC Certification Standards                    |
+-------------------------------------------------------------------------+

• Sanitary Survey Frequency: Conducted by CDPHE every 3 years for Community Water Systems (can be extended to 5 years for systems with outstanding performance histories) and every 5 years for Non-Community systems.
• Significant Deficiencies: Structural, operational, or mechanical defects that pose an immediate or potential pathway for contamination (e.g., cracked storage reservoir roof, missing 24-mesh vent screen, lack of backflow program). The system must submit a written response to CDPHE within 30 days and complete corrective actions (or enter an approved schedule) within 120 days.
• Storage Tank Inspection Mandate: Regulation 11 requires periodic visual inspections (annually) and comprehensive sanitary/structural inspections (minimum every 5 years) of all finished water storage tanks, including verification of sealed access hatches, gaskets, overflow flapper valves, and 24-mesh corrosion-resistant screens.

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Backflow Prevention (Rule 11.39) & Public Notice Tiers

Backflow Prevention and Cross-Connection Control (BPCCC)

Under Regulation 11.39, public water suppliers must eliminate cross-connections and prevent backflow of pollutants or contaminants into the public distribution network through backsiphonage or backpressure. Suppliers must conduct hazard surveys on all commercial, industrial, and multi-family service connections.

• Containment Assemblies: High-hazard connections require an Approved Air Gap (AG) or a Reduced Pressure Zone (RPZ) backflow preventer. Low-hazard connections may utilize a Double Check Valve Assembly (DCVA).
• Survey Compliance Ratio: Under Rule 11.39(2)(c)(iii) the supplier must survey all non-single-family-residential connections and maintain a survey compliance ratio of 1.0 each year, unless the Department approves an alternative ratio and schedule.
• Backflow Prevention Annual Compliance Ratio: Rule 11.39(3)(d) requires assemblies to be tested annually by a Certified Cross-Connection Control Technician and methods to be inspected annually, and the supplier must achieve a backflow prevention annual compliance ratio of at least 0.90. The ratio is the sum of methods inspected plus assemblies tested during the calendar year divided by the sum of methods and assemblies installed at a cross-connection that were used during that year.
• Correction Deadlines: A discovered uncontrolled cross-connection, a failed assembly test, or an inadequate backflow method must be corrected, service suspended, or the cross-connection removed within 120 days (or an approved alternative schedule), and no assembly may go two consecutive calendar years without testing. A supplier ordered in writing by the Department must control or remove the cross-connection within 10 days.
• Annual Report: The written BPCCC program report for the prior calendar year is due to CDPHE no later than May 1. A suspected or confirmed backflow contamination event must be reported to the Department within 24 hours; treatment technique violations require notice within 48 hours plus Tier 2 public notice.

Public Notification Tiers & MOR Deadlines

• Tier 1 Notice (Immediate Public Health Threat): Acute violations including E. coli MCL exceedances, Nitrate/Nitrite violations, waterborne disease outbreaks, or SWTR turbidity exceeding 1.0 NTU where treatment is compromised. Mandatory public notice within 24 hours via broadcast media, door-to-door hand delivery, or electronic reverse-911.
• Tier 2 Notice (MCL or Treatment Technique Violations): Non-acute chemical MCL exceedances (TTHM, HAA5, Fluoride) or failure to correct significant deficiencies. Public notice required within 30 days.
• Tier 3 Notice (Monitoring & Testing Violations): Failure to take required monthly samples or submit reports. Notice required within 12 months (frequently distributed via the annual Consumer Confidence Report / CCR).
• Monthly Operating Reports (MORs): All operational logs, disinfectant residual tracking, and daily turbidity logs must be submitted to CDPHE by the 10th day of the month following the reporting period.