1.3 Arizona Aquifer Protection Permit (APP) Program & BADCT

1.3 Arizona Aquifer Protection Permit (APP) Program & BADCT

[!NOTE] The Universal Drinking Water Presumption: Arizona Revised Statutes (A.R.S.) § 49-224 establishes that all aquifers in the State of Arizona are classified and protected for drinking water use. Unlike states that categorize groundwater into potable and industrial non-potable tiers based on baseline quality, Arizona law mandates that every discharging facility must protect groundwater to drinking water standards, regardless of the aquifer's depth or existing mineral content.

Because surface water supplies are volatile and heavily allocated throughout the American Southwest, groundwater serves as the bedrock of Arizona's municipal, agricultural, and industrial infrastructure. Over 40% of Arizona residents rely directly on groundwater for potable domestic supplies, and deep alluvial aquifers serve as the state's strategic reserve during prolonged Colorado River drought declarations. To protect these underground reserves, the Arizona Legislature established the Aquifer Protection Permit (APP) program as part of the Environmental Quality Act of 1986.

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Statutory Scope: The Jurisdictional Trigger for an APP

Under A.R.S. § 49-241, an Aquifer Protection Permit is legally required for any facility that "discharges." The statute broadly defines a discharge as any addition of a pollutant to an aquifer or to the land surface or vadose zone where there is a reasonable probability that the pollutant will reach an aquifer.

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|                    Facilities Requiring Aquifer Protection Permits                |
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| • Municipal & Private Wastewater Treatment Facilities (WWTPs / WRFs)              |
| • Surface Impoundments, Retention Ponds, and Evaporation Basins                   |
| • Sewage Sludge (Biosolids) Storage, Treatment, and Drying Facilities             |
| • Vadose Zone Infiltration & Managed Underground Aquifer Recharge Projects       |
| • Mining Leaching Facilities, Tailings Ponds, and Slag Residue Dumps              |
| • Commercial and Large On-Site Septic Systems (>3,000 Gallons Per Day)            |
| • Vadose Zone Stormwater Disposal Dry Wells & Class V Underground Injection Wells |
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Universal Protection vs. Reclassification

Under A.R.S. § 49-224, discharging entities cannot defend groundwater contamination by claiming that the receiving aquifer was previously unpotable or non-utilized. Reclassifying an aquifer to a non-drinking water status requires an exhaustive administrative and evidentiary proceeding demonstrating that:

1. The aquifer is completely isolated hydrogeologically from any current or future drinking water source.
2. The water is physically or economically untreatable for human consumption.
3. The reclassification will not cause a violation of Aquifer Water Quality Standards in adjacent aquifers.

Because of these stringent statutory criteria, ADEQ has rarely reclassified an aquifer in state history. Operators must design and operate treatment works under the assumption that all underlying water must be safeguarded for human consumption.

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Best Available Demonstrated Control Technology (BADCT)

The cornerstone of the APP program is the statutory mandate codified in A.R.S. § 49-243: every permitted facility must be designed, constructed, and operated using Best Available Demonstrated Control Technology (BADCT).

BADCT Definition and Mandate

BADCT requires the application of modern treatment processes, engineering containment, operating methods, and process controls that achieve the greatest degree of discharge reduction. Unlike traditional end-of-pipe regulations that only look at numeric limits, BADCT enforces preventative engineering multi-barriers:

• Source Reduction: Minimizing the concentration and mass of pollutants entering the wastewater stream.
• Advanced Secondary & Tertiary Treatment: Biological nutrient removal, physical filtration, and disinfection.
• Engineered Containment: Impermeable liners, hydraulic cut-off walls, and leak collection systems to eliminate or minimize seepage.

BADCT Requirements for Domestic Wastewater Treatment Facilities

ADEQ publishes formal BADCT guidance manuals for domestic wastewater treatment plants. Standard domestic BADCT mandates:

1. Secondary Biological Treatment: Suspended growth (activated sludge) or attached growth processes capable of reducing 5-day Biochemical Oxygen Demand (BOD₅) and Total Suspended Solids (TSS) to baseline levels (≤ 30 mg/L).
2. Total Nitrogen Reduction (Nitrification / Denitrification): Domestic wastewater contains high levels of organic nitrogen and ammonia ($30\text{--}60\text{ mg/L}$). If allowed to percolate into groundwater, ammonia is converted by soil nitrifiers into nitrate ($\text{NO}_3^-$), threatening the drinking water standard of 10 mg/L as N. BADCT requires full biological nitrification (converting ammonia to nitrate) followed by anoxic denitrification (reducing nitrate to harmless nitrogen gas, $\text{N}_2$), ensuring effluent total nitrogen remains below 10 mg/L before discharge.
3. Pathogen Reduction: Tertiary filtration (sand, cloth media, or membranes) coupled with chlorination or ultraviolet (UV) disinfection to eliminate enteric pathogens.
4. Surface Impoundment Lining: Storage basins, equalization basins, and sludge drying beds must incorporate synthetic geomembrane liners (such as 60-mil high-density polyethylene / HDPE) or composite liners with leak detection and removal systems (LDRS) designed to limit seepage to negligible statutory maximums.

Individual vs. General Aquifer Protection Permits

ADEQ categorizes APPs into two regulatory structures based on facility scale, complexity, and potential groundwater threat:

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|                    Individual Permits vs. General Permits                         |
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| Individual APPs                | General APPs (Types 1 - 4)                       |
| • Complex, large-scale systems | • Standardized, lower-risk installations         |
| • Facility-specific conditions | • Standard rules codified in A.A.C. Title 18     |
| • Detailed hydrogeologic study | • Simplified Notice of Intent (NOI) filing       |
| • Mandatory public notice/hearings • Streamlined engineering review or rule-auth  |
| • Site-specific POC well network | • Standard prescriptive setback/design rules   |
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Individual Aquifer Protection Permits

Individual APPs are required for large municipal water reclamation facilities, mining operations, industrial chemical ponds, and complex aquifer recharge facilities. Obtaining an Individual APP is an exhaustive engineering and scientific process requiring:

• Hydrogeologic Study Report: Detailed sub-surface characterization, including pump tests, lithologic cross-sections, hydraulic conductivity calculations, and numerical groundwater solute-transport modeling.
• Discharge Impact Area (DIA) Delineation: Calculating the 3-dimensional volume of the aquifer that will be impacted by the discharge over the facility's active operating life.
• Public Participation: Mandatory publication of draft permit conditions in regional newspapers, a 30-day public comment period, and potential public hearings prior to final agency determination.

General Aquifer Protection Permits

To reduce administrative burdens for routine, lower-risk discharging operations, ADEQ codifies General Permits by rule under A.A.C. Title 18, Chapter 9. General permits establish standardized, prescriptive engineering criteria:

• Type 1 General Permits: Permitted by rule with zero paperwork or fees required (e.g., standard residential septic systems permitted prior to 2001).
• Type 2 General Permits: Requires submitting a Notice of Intent (NOI) and compliance with standard operational guidelines (e.g., small industrial sumps, temporary dewatering).
• Type 3 General Permits: Requires NOI, engineering designs, and formal ADEQ review (e.g., small reclaimed water storage ponds, vehicle wash facilities).
• Type 4 General Permits: Encompasses on-site wastewater treatment facilities (up to 24,000 gallons per day design flow), alternative residential septic systems, and commercial reclaimed water distribution systems. Type 4 permits feature pre-approved design standards that bypass the need for site-specific hydrogeologic modeling.

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Hydrogeologic Framework: DIA, POC Wells, and Alert Levels

Groundwater compliance is verified through a structured hydrogeologic monitoring network established in every Individual APP.

1. Discharge Impact Area (DIA)

The Discharge Impact Area is defined as the potential aerial and vertical extent of groundwater that will be influenced by the facility's discharge. Within the DIA, ADEQ evaluates existing wellhead protection zones, drinking water extraction wells, and potential pollutant migration pathways.

2. Point of Compliance (POC)

The Point of Compliance is the vertical plane extending downward into the aquifer at which water quality standards must not be exceeded:

• Primary POC: Typically located at the downgradient edge of the pollutant management area (the physical boundary of the ponds, basins, or plant).
• Alternative POC: An authorized monitoring location positioned further downgradient when physical barriers, property boundaries, or geologic constraints prevent placing a monitoring well at the primary boundary.

3. Aquifer Water Quality Standards (AWQS)

Arizona's numeric Aquifer Water Quality Standards (A.A.C. Title 18, Chapter 11, Article 4) mirror federal National Primary Drinking Water Regulations. Key health-based parameters include:

• Nitrate as N: $10.0\text{ mg/L}$
• Nitrite as N: $1.0\text{ mg/L}$
• Fluoride: $4.0\text{ mg/L}$
• Arsenic: $0.050\text{ mg/L}$ (historically codified in state rule, though public drinking water systems must comply with the federal SDWA limit of $0.010\text{ mg/L}$)
• Lead: $0.05\text{ mg/L}$
• Volatile Organic Compounds (VOCs): Benzene ($0.005\text{ mg/L}$), Trichloroethylene / TCE ($0.005\text{ mg/L}$)

4. Alert Levels (AL) vs. Aquifer Quality Limits (AQL)

To prevent catastrophic contamination before it reaches statutory thresholds, Individual APPs establish two distinct operational metrics for each POC monitoring well:

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Dry Wells & Class V Underground Injection Control (UIC)

Arizona's dry climate makes stormwater capture and vadose zone disposal common practice. However, vadose zone disposal carries significant groundwater contamination risks.

Dry Well Regulation (A.R.S. Title 49, Chapter 2, Article 8)

A dry well is a borehole, typically 30 to 60 feet deep, drilled into the unsaturated vadose zone above the water table to dispose of stormwater runoff. Because dry wells bypass topsoil filtration layers, any chemical spilled into an industrial yard or parking lot can drain directly into the vadose zone and migrate into the aquifer.

• Mandatory Registration: All dry wells must be officially registered with ADEQ.
• Pre-Treatment Chambers: Dry wells must feature settling chambers, oil/water separator baffles, and debris screens to capture suspended solids and hydrocarbons.
• Prohibited Discharges: Discharging industrial process wastewater, chemical washdown water, or hazardous materials into a dry well is a severe violation of state and federal law.

Class V Underground Injection Wells

Deep injection wells used for aquifer storage and recovery (ASR) or commercial stormwater management are co-regulated under ADEQ's Underground Injection Control (UIC) program and the APP framework, ensuring that injected fluids meet all primary drinking water standards.