1.4 AZPDES Surface Water Discharges & Arizona Reclaimed Water Standards

1.4 AZPDES Surface Water Discharges & Arizona Reclaimed Water Standards

[!NOTE] Federal Primacy Delegation: In December 2002, the U.S. Environmental Protection Agency (EPA) formally delegated National Pollutant Discharge Elimination System (NPDES) program primacy under Clean Water Act (CWA) Section 402 to the State of Arizona. Codified under A.R.S. Title 49, Chapter 2, Article 3.1 and A.A.C. Title 18, Chapter 9, Articles 9 and 10, the program operates as the Arizona Pollutant Discharge Elimination System (AZPDES).

While the Aquifer Protection Permit (APP) program safeguards subsurface groundwater, the AZPDES program regulates discharges to Arizona's surface waters. Concurrently, because treated wastewater is an indispensable water supply asset in the desert Southwest, ADEQ enforces comprehensive Reclaimed Water Quality Standards under A.A.C. Title 18, Chapter 11, Article 3. These dual frameworks govern effluent discharge and beneficial water reuse across the state.

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AZPDES Program Primacy & Surface Water Jurisdiction

AZPDES regulates all point source discharges of pollutants into "Waters of the United States" (WOTUS) and protected surface waters of Arizona. Arizona's arid hydrology creates unique regulatory classifications:

• Perennial Rivers: Watercourses that flow year-round, such as portions of the Colorado, Salt, and Verde Rivers.
• Intermittent Streams: Streams that flow during certain times of the year, driven by seasonal snowmelt or groundwater discharge.
• Ephemeral Washes: Dry desert arroyos and washes that flow strictly in response to immediate precipitation events.
• Effluent-Dependent Waters (EDWs): Surface watercourses created or sustained entirely by continuous discharges of treated municipal wastewater (such as sections of the Santa Cruz River near Tucson and the lower Salt River near Phoenix).

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Individual vs. General AZPDES Permits

ADEQ issues two classes of surface water discharge permits:

1. Individual AZPDES Permits: Tailored specifically for municipal wastewater reclamation facilities, industrial processing plants, and electrical power generation stations. These permits establish facility-specific numeric effluent limitations, comprehensive monitoring frequencies, mass loading limits, and receiving water impact assessments.
2. General AZPDES Permits: Administrative permits covering broad industrial categories with similar operational footprints:
   • Construction General Permit (CGP): Regulates stormwater runoff from construction sites disturbing 1.0 or more acres of land; mandates the creation and continuous execution of a Stormwater Pollution Prevention Plan (SWPPP).
   • Multi-Sector General Permit (MSGP): Controls industrial stormwater discharges across 29 distinct industrial sectors, requiring standard best management practices (BMPs) and visual monitoring.
   • Municipal Separate Storm Sewer Systems (MS4): Regulates urban municipal stormwater runoff networks (Phase I for large metropolitan populations, Phase II for small urbanized jurisdictions).
   • De Minimis & Dewatering General Permits: Authorizes short-term, low-threat discharges such as potable water main flushing, well development water, and utility vault dewatering.

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Effluent Limits, Mixing Zones, and WET Testing

AZPDES permits incorporate two tiers of effluent standards to ensure that discharged water does not compromise the designated uses of receiving waters:

+-----------------------------------------------------------------------------------+
|                     AZPDES Effluent Limitation Structure                          |
+-----------------------------------------------------------------------------------+
| 1. Technology-Based Effluent Limits (TBELs)                                       |
|    • Minimum federal secondary treatment baseline standards:                      |
|      - BOD₅: 30 mg/L monthly average, 45 mg/L weekly average (≥85% removal)       |
|      - TSS:  30 mg/L monthly average, 45 mg/L weekly average (≥85% removal)       |
|      - pH:   Must remain within 6.5 to 9.0 standard units                         |
|                                                                                   |
| 2. Water Quality-Based Effluent Limits (WQBELs)                                   |
|    • Derived from Arizona Surface Water Quality Standards (A.A.C. Title 18, Ch 11)|
|    • Site-specific limits for Ammonia, E. coli, Heavy Metals, and Nutrients       |
|    • Total Residual Chlorine (TRC): Non-detectable (mandatory dechlorination)     |
+-----------------------------------------------------------------------------------+

Dechlorination Requirement

Because chlorine and chloramines are acutely toxic to freshwater fish and aquatic invertebrates at extremely low concentrations, any facility utilizing chlorine disinfection for surface water discharge must install active dechlorination (typically dosing sulfur dioxide, $\text{SO}_2$, or sodium bisulfite, $\text{NaHSO}_3$) to reduce residual chlorine below analytical detection limits (typically $< 0.011\text{ mg/L}$).

Mixing Zones (A.A.C. R18-11-114)

A mixing zone is a geographically delineated portion of a receiving watercourse where initial dilution of a discharged effluent occurs. Within an authorized mixing zone, numeric water quality standards may be exceeded, provided:

• Acute aquatic life criteria are never exceeded within the mixing zone.
• The mixing zone does not form a barrier that impairs fish passage or aquatic organism migration.
• The discharge does not produce offensive odors, sludge deposits, or toxic concentrations.

Whole Effluent Toxicity (WET) Testing

Individual AZPDES permits require routine Whole Effluent Toxicity (WET) testing. WET testing utilizes live laboratory test organisms to evaluate the aggregate, synergistic toxic impact of all chemical constituents present in the effluent:

• Acute Toxicity Bioassays: Measure short-term organism lethality over a 48-hour to 96-hour exposure window.
• Chronic Toxicity Bioassays: Measure long-term sublethal impacts on organism reproduction, growth, and survival over a 7-day test protocol.
• Standard Test Species: The freshwater water flea (Ceriodaphnia dubia) and the fathead minnow (Pimephales promelas).

If effluent fails a WET test, the operator is required to initiate an immediate Toxicity Identification Evaluation (TIE) and Toxicity Reduction Evaluation (TRE) to locate and eliminate the source of toxicity.

Compliance Reporting & Emergency Spill Notifications

AZPDES compliance requires timely, verifiable reporting through ADEQ's electronic enterprise portals.

Discharge Monitoring Reports (DMRs)

All monitoring data collected during each calendar month—including daily flows, effluent BOD₅, TSS, pH, E. coli, and nutrient concentrations—must be submitted to ADEQ electronically using the NetDMR system (accessed via ADEQ's myDEQ portal) on or before the 28th day of the month following the monitoring period.

The Mandatory 24-Hour Emergency Spill / Upset Notification

Under standard AZPDES permit conditions and state environmental enforcement rules, permittees must adhere to strict emergency notification protocols:

• 24-Hour Oral Notification: Any non-compliance that may endanger human health or the environment—including unpermitted bypasses, Sanitary Sewer Overflows (SSOs), treatment plant upsets, or toxic spills—must be reported orally to the ADEQ 24-Hour Spill Hotline within 24 hours of the operator becoming aware of the circumstance.
• 5-Day Written Submission: A comprehensive written report must be submitted to ADEQ within 5 calendar days of the initial oral notification. The report must contain:
  1. A detailed description of the non-compliance and its underlying cause.
  2. The exact dates, times, and duration of the event (or expected duration if ongoing).
  3. Estimated spill volume in gallons and whether the discharge reached a surface water body.
  4. Immediate containment and remediation steps implemented to minimize environmental impact.
  5. Long-term preventative measures established to prevent future recurrence.

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Arizona Reclaimed Water Quality Standards (A.A.C. Title 18, Chapter 11, Article 3)

In Arizona, reclaimed water is categorized into five distinct quality tiers based on the degree of pathogen reduction, filtration, and biological nutrient removal. These standards dictate what reuse applications are legally permissible.

The Plus (+) Designation: Total Nitrogen Control

Notice that the difference between Class A and Class A+, as well as between Class B and Class B+, is the plus (+) designation. The plus designation specifically requires that the facility implement biological nitrification and denitrification to achieve a Total Nitrogen concentration of less than 10 mg/L as N (evaluated as a running 5-day or monthly average). This standard protects underlying aquifers from nitrate exceedances when large volumes of reclaimed water are applied to agricultural or landscape turf.

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Cross-Connection Control & Purple Pipe Separation Standards

Because reclaimed water contains chemical and biological constituents unsuited for drinking, physical isolation between reclaimed distribution infrastructure and potable water networks is mandatory under A.A.C. Title 18, Chapter 5 and ADEQ Engineering Bulletins.

Universal Visual Identification: The Purple Standard

• Pantone Purple: All reclaimed water piping, valves, meter boxes, valve box covers, sprinkler heads, and fire hydrants must be color-coded using Pantone 512 or 522 purple (either through purple-tinted pipe resin or continuous purple polywrap).
• Bilingual Warning Text: Piping and public fixtures must be clearly stenciled with bilingual warning messages in bold block letters:

"CAUTION: RECLAIMED WATER - DO NOT DRINK"
"ATENCIÓN: AGUA RECUPERADA - NO BEBER"

Physical Separation from Potable Water Mains

To prevent contamination in the event of pipe rupture or pressure loss, reclaimed water mains must maintain strict spatial clearance from potable water pipes:

1. Horizontal Separation: Reclaimed water mains must be installed at least 6 feet horizontally from any parallel potable water main (standard municipal utility engineering typically mandates 10 feet where feasible).
2. Vertical Separation: Where reclaimed lines cross potable water mains, the reclaimed line must be installed with at least 2 feet of vertical clearance.
3. Potable Above Reclaimed: The potable water main must always be installed ABOVE the reclaimed water line. This prevents gravity drainage of reclaimed water into the potable pipe in the event of joint failure or trench collapse.
4. Structural Sleeving: If minimum vertical or horizontal clearances cannot be physically achieved due to existing subterranean infrastructure, the reclaimed main must be encased in a continuous watertight steel or PVC sleeve extending a minimum distance (typically 10 feet) on either side of the crossing.

Cross-Connection Prohibitions & Backflow Assemblies

Physical interconnections between a reclaimed water line and a potable water system are strictly prohibited under penalty of law. Where potable water is supplied as an auxiliary backup supply to an irrigation pond or storage tank filled with reclaimed water, the potable supply must discharge through an approved physical Air Gap (AG) located at least twice the internal diameter of the supply pipe above the overflow rim, or through an approved Reduced Pressure Principle Backflow Assembly (RPBA) inspected and tested annually.