Ariz. Admin. Code § R18-9-A312 - Facility Design for Type 4 On-site Wastewater Treatment Facilities | State Regulations | US Law

A. General design requirements. An applicant shall ensure that the person designing an on-site wastewater treatment facility:

1. Signs the design documents submitted as part of the Notice of Intent to Discharge to obtain a Construction Authorization, including plans, specifications, drawings, reports, and calculations; and

2. Locates and designs the on-site wastewater treatment facility project using good design judgment and relies on appropriate design methods and calculations.

B. Design considerations and flow determination. An applicant shall ensure that the person designing the on-site wastewater treatment facility shall:

1. Design the facility to satisfy a 20-year operational life;

2. Design the facility based on the provisions of one or more of the general permits in R18-9-E302 through R18-9-E322 for facilities with a design flow of less than 3000 gallons per day, and R18-9-E323 for facilities with a design flow of 3000 gallons per day to less than 24,000 gallons per day;

3. Design the facility based on the facility's design flow and wastewater characteristics as specified in R18-9-A309(A)(7), (10) and (11) and R18-9-A309(B)(3);

4. For on-site wastewater treatment facilities permitted under R18-9-E303 through R18-9-E323, apply the following design requirements, as applicable:

a. Include the power source and power components in construction drawings if electricity or another type of power is necessary for facility operation;

b. If a hydraulic analysis is required under subsection (E), perform the analysis based on the location and dimensions of the bottom and sidewall surfaces of the disposal works that are identified in the design documentation;

c. Design components, piping, ports, seals, and appurtenances to withstand installation loads, internal and external operational loads, and buoyant forces. Design ports for resistance against movement, and cap or cover openings for protection from damage and entry by rodents, mosquitoes, flies, or other organisms capable of transporting a disease-causing organism;

d. Design tanks, liners, ports, seals, piping to and within the facility, and appurtenances for water tightness under all operational conditions;

e. Provide adequate storage capacity above high operating level to:

i. Accommodate a 24-hour power or pump outage, and

ii. Contain wastewater that is incompletely treated or cannot be released by the disposal works to the native soil;

f. If a fixed media process is used, provide in the construction drawings the media material, installation specification, media configuration, and wastewater loading rate of the media at the daily design flow;

g. Provide a fail-safe wastewater control or operational process, if required by the general permit to prevent discharge of inadequately treated wastewater; and

h. Reference design. If using a reference design on file with the Department, indicate the reference design within the information submitted with the Notice of Intent to Discharge.

C. Setbacks. The following setbacks apply unless the Department:

1. Specifies alternative setbacks under Article 3, Part E of this Chapter;

2. Approves a different setback under the procedure specified in subsection (G); or

3. Establishes a more stringent setback on a site- or area-specific basis to ensure compliance with water quality standards.

Features Requiring Setbacks	Setback For An On-Site Wastewater Treatment Facility, Including Reserve Area (In Feet)	Special Provisions
1. Building	10	Includes porches, decks (including pool decks), and steps (covered or uncovered), breezeways, roofed patios, carports, covered walks, and similar structures and appurtenances.
2. Property line shared with any adjoining lot or parcel not served by a common drinking water system* or an existing water well	50	A person may reduce the setback to a minimum of 5 feet from the property line if: a. The owners of any affected undeveloped adjacent properties agree, as evidenced by an appropriately recorded document, to limit the location of any new well on their property to at least 100 feet from the proposed treatment works and primary and reserve disposal works; and b. The arrangements and documentation are approved by the Department.
3. All other property lines	5	None
4. Public or private water supply well	100	None
5. Perennial or intermittent stream	100	Measured horizontally from the high water line of the peak streamflow from a 10-year, 24hour rainfall event.
6. Lake, reservoir, or canal	100	Measured horizontally from the high water line from a 10-year, 24-hour rainfall event at the lake or reservoir and measured horizontally from the edge of the canal.
7. Drinking water intake from a surface water source (includes an open water body, downslope spring or a well tapping stream-side saturated alluvium)	200	Measured horizontally from the on-site waste-water treatment facility to the structure or mechanism for withdrawing raw water such as a pipe inlet, grate, pump, intake or diversion box, spring box, well, or similar structure.
8. Wash or drainage easement with a drainage area of more than 20 acres	50	Measured horizontally from the nearest edge of the defined natural channel bank or drainage easement boundary. A person may reduce the setback to 25 feet if natural or constructed erosion protection is approved by the appropriate flood plain administrator.
9. Water main or branch water line	10	None
10. Domestic service water line (including domestic water holding tanks)	5	Measured horizontally between the water line and the wastewater pipe, except that the following are allowed: a. A water line may cross above a wastewater pipe if the crossing angle is between 45 and 90 degrees and the vertical separation distance is 1 foot or more. b. A water line may parallel a wastewater pipe with a horizontal separation distance of 1 foot to 5 feet if the bottom of the water line is 1 foot or more above the top of the wastewater pipe and is in a separate trench or on a bench in the same trench.
11. Downslopes or cut banks greater than 15 percent, culverts, and ditches from: a. Treatment works components b. Trench, bed, chamber technology, or gravelless trench with: i. No limiting subsurface condition specified in R18-9-A310(D)(2) , ii. A limiting subsurface condition. c. Subsurface drip lines.	10 20 50 3	Measured horizontally from the bottom of the treatment works component to the closest point of daylighting on the surface. Measured horizontally from the bottom of the lowest point of the disposal pipe or drip lines, as applicable, to the closest point of daylighting on the surface. Measured horizontally from the bottom of the lowest point of the disposal pipe or drip lines, as applicable, to the closest point of daylighting on the surface.
12. Driveway	5	Measured horizontally to the nearest edge of an on-site wastewater treatment facility excavation. A person may place a properly reinforced and protected wastewater treatment facility, except for disposal works, at any location relative to a driveway if access openings, risers, and covers carry the design load and are protected from inflow.
13. Swimming pool excavation	5	Except if soil loading or stability concerns indicate the need for a greater separation distance.
14. Easement (except drainage easement)	5	None
15. Earth fissures	100	None
* A "common drinking water system" means a system that currently serves or is under legal obligation to serve the property and may include a drinking water utility, a well-sharing agreement, or other viable water supply agreement.

D. Soil absorption rate (SAR) and disposal works sizing.

1. An applicant shall determine the soil absorption area by dividing the design flow by the applicable soil absorption rate. If soil characterization and percolation test methods yield different SAR values or if multiple applications of the same approach yield different values, the designer of the disposal works shall use the lowest SAR value unless a higher SAR value is proposed and justified to the Department's satisfaction in the Notice of Intent to Discharge.

2. The SAR used to calculate disposal works size for systems described in R18-9-E302 is as follows:

a. The SAR by percolation testing as described in R18-9-A310(F) or (G), as applicable, is determined as follows:

Percolation Rate from Percolation Test (minutes per inch)	SAR, Trench, Chamber, and Pit (gal/day/ft²)	SAR, Bed (gal/day/ft²)
Less than 1.00	A site-specific SAR is required	A site-specific SAR is required
1.00 to less than 3.00	1.20	0.93
3.00	1.10	0.73
4.00	1.00	0.67
5.00	0.90	0.60
7.00	0.75	0.50
10.0	0.63	0.42
15.0	0.50	0.33
20.0	0.44	0.29
25.0	0.40	0.27
30.0	0.36	0.24
35.0	0.33	0.22
40.0	0.31	0.21
45.0	0.29	0.20
50.0	0.28	0.19
55.0	0.27	0.18
55.0+ to 60.0	0.25	0.17
60.0+ to 120	0.20	0.13
Greater than 120	A site-specific SAR is required	A site-specific SAR is required

b. The SAR using the soil evaluation method described in R18-9-A310(E) is determined by answering the questions in the following table. The questions are read in sequence starting with "A." The first "yes" answer determines the SAR. A seepage pit is required to determine percolation rate under the procedure described in R18-9-A310(G) and would only use this table to augment the percolation test results, if appropriate.

Sequence of Soil Characteristics Questions	SAR, Trench, Chamber, and Pit gal/day/ft²	SAR, Bed gal/day/ft²
A. Is the horizon gravelly coarse sand or coarser?	A site-specific SAR is required	A site-specific SAR is required
B. Is the structure of the horizon moderate or strongly platy?	A site-specific SAR is required	A site-specific SAR is required
C. Is the texture of the horizon sandy clay loam, clay loam, silty clay loam, or finer and the soil structure weak platy?	A site-specific SAR is required	A site-specific SAR is required
D. Is the moist consistence stronger than firm or any cemented class?	A site-specific SAR is required	A site-specific SAR is required
E. Is the texture sandy clay, clay, or silty clay of high clay content and the structure massive or weak?	A site-specific SAR is required	A site-specific SAR is required
F. Is the texture sandy clay loam, clay loam, silty clay loam, or silt loam and the structure massive?	A site-specific SAR is required	A site-specific SAR is required
G. Is the texture of the horizon loam or sandy loam and the structure massive?	0.20	0.13
H. Is the texture sandy clay, clay, or silty clay of low clay content and the structure moderate or strong?	0.20	0.13
I. Is the texture sandy clay loam, clay loam, or silty clay loam and the structure weak?	0.20	0.13
J. Is the texture sandy clay loam, clay loam, or silty clay loam and the structure moderate or strong?	0.40	0.27
K. Is the texture sandy loam, loam, or silty loam and the structure weak?	0.40	0.27
L. Is the texture sandy loam, loam, or silt loam and the structure moderate or strong?	0.60	0.40
M. Is the texture fine sand, very fine sand, loamy fine sand, or loamy very fine sand?	0.40	0.27
N. Is the texture loamy sand or sand?	0.80	0.53
O. Is the texture coarse sand?	1.20	A site-specific SAR is required

c. If the percolation rate determined under R18-9-A310(F) or (G), whichever is applicable, is a value that lies between two consecutive percolation rate values listed in subsection (2)(a) above, the applicant must use the higher of the two listed percolation rates to obtain the most conservative SAR.

3. For an on-site wastewater treatment facility described in a general permit other than R18-9-E302, the SAR is dependent on the ability of the facility to reduce the level of TSS and BOD₅ and is calculated using the following formula:

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a. "SAR_a" is the adjusted soil absorption rate for disposal works design in gallons per day per square foot,

b. "TSS" is the total suspended solids in wastewater delivered to the disposal works in milligrams per liter,

c. "BOD₅" is the five-day biochemical oxygen demand of wastewater delivered to the disposal works in milligrams per liter, and

d. "SAR" is the soil absorption rate for septic tank effluent determined by the subsurface characterization method described in R18-9-A310.

4. An applicant shall ensure that the facility is designed so that the area of the intended installation is large enough to allow for construction of the facility and for future replacement or repair and is at least as large as the following:

a. For a dwelling, a primary area for the disposal works sized according to subsection (D)(1) and a reserve area of 100 percent of the primary area, excluding the footprint of the treatment works. A reserve area is not required for a lot in a subdivision approved before 1974 if the lot conforms to its original approved configuration;

b. For other than a dwelling, a primary area for the disposal works sized according to subsection (D)(1) and a reserve area of 100 percent of the primary area, excluding the footprint of the treatment works.

5. An applicant shall ensure that the subsurface disposal works is designed to achieve the design flow established in R18-9-A309(B)(3) through proper hydraulic function, including conditions of seasonally cold and wet weather.

E. Vertical separation distances.

1. Minimum vertical separation to the seasonal high water table for a disposal works described in R18-9-E302 receiving septic tank effluent. For a disposal works described in R18-9-E302 receiving septic tank effluent at a facility where the septic tank and disposal system described in R18-9-E302 is the sole method of treatment and disposal of wastewater, the minimum vertical separation distance between the lowest point in the disposal works and the seasonal high water table is dependent on the soil absorption rate and is determined as follows:

Soil Absorption Rate (gallons per day per square foot)			Minimum Vertical Separation Between The Bottom Of The Disposal Works And The Seasonal High Water Table (feet)
Trench and Chamber	Bed	Seepage Pit	Trench, Chamber, and Bed	Seepage Pit
1.20+	0.93+	1.20+	Not allowed for septic tank effluent	Not Allowed
0.63+ to 1.20	0.42 to 0.93	0.63+ to 1.20	10	60
0.20 to 0.63	0.13 to 0.42	0.36 to 0.63	5	60
Less than 0.20	Less than 0.13	Less than 0.36	Not allowed for septic tank effluent	Not Allowed

2. Minimum vertical separation to the seasonal high water table for treatment and disposal works technologies described in R18-9-E303 through R18-9-E322 . If the minimum vertical separation distance to the seasonal high water table for a disposal works receiving septic tank effluent specified in subsection (E)(1) is not met, the applicant shall comply with the following:

a. Employ one or more technologies described in R18-9-E303 through R18-9-E322 to achieve a reduced concentration of harmful microorganisms, expressed as total coliform in colony forming units per 100 milliliters (cfu/100 ml) delivered to native soil at the bottom of the disposal works. The applicant shall use the following table to select works that achieve a reduced total coliform concentration corresponding to the available vertical separation distance between the bottom of the disposal works and the seasonal high water table:

Available Vertical Separation Distance Between the Bottom of The Disposal Works and the Seasonal High Water Table (feet)		Maximum Allowable Total Coliform Concentration, 95^th Percentile, Delivered to Natural Soil by the Disposal Works (Log₁₀ of coliform concentration in cfu per 100 milliliters)
*For SAR, 0.20 to 0.63**	*For SAR, 0.63+ to 1.20**
5	10	8**
4	8	7
3.5	7	6
3	6	5
2.5	5	4
2	4	3
1.5	3	2
1	2	1
0	0	0***

* Soil absorption rate from percolation testing or soil characterization, in gallons per square foot per day.

** Nominal value for a standard septic tank and disposal field (10⁸ colony forming units per 100 ml).

*** Nominally free of coliform bacteria.

b. Include a hydraulic analysis with the Notice of Intent to Discharge, based on the dimensions of the absorption surfaces specified in R18-9-A312(B)(4)(b), showing that the soil is sufficiently permeable to conduct wastewater downward and laterally without surfacing for the site conditions at the disposal works.

3. Vertical separation from a subsurface limiting condition described in R18-9-A310(D)(2)(d) that may cause or contribute to surfacing of wastewater. If a subsurface limiting condition described in R18-9-A310(D)(2)(d) exists at the location of the disposal works, the applicant shall ensure that the design for the on-site wastewater treatment facility meets one of the following:

a. A zone of acceptable native soil with the following characteristics exists between the bottom of the disposal works and the top of the subsurface limiting condition:

i. The zone of soil is at least 4 feet thick, and

ii. The zone of soil is sufficiently permeable to conduct wastewater released from the disposal works vertically downward and laterally without causing surfacing of the wastewater as documented by a hydraulic analysis submitted with the Notice of Intent to Discharge that is based on the dimensions of the absorption surfaces specified in R18-9-A312(B)(4)(b);

b. The subsurface limiting condition is thin enough to allow placement of a disposal works into acceptable native soil beneath the subsurface limiting condition if the following criteria are met:

i. The bottom of the subsurface limiting condition is not deeper than 10 feet below the land surface, and

ii. The vertical separation distance from the bottom of the disposal works to the seasonal high water table complies with subsection (E)(1) or (2), as applicable; or

c. If the disposal works is placed above the subsurface limiting condition and the depth to the subsurface limiting condition is less than 4 feet below the bottom of the disposal works, the design for the on-site wastewater treatment facility shall comply with all of the following:

i. Employ one or more technologies described in R18-9-E303 through R18-9-E322 to achieve a reduced concentration of harmful microorganisms, expressed as total coliform in colony forming units per 100 milliliters (cfu/100 ml), delivered to acceptable native soil at the bottom of the disposal works, as follows:

Available Vertical Separation Distance from the Bottom of the Disposal Works to the Subsurface Limiting Condition (feet)	Maximum Allowable Total Coliform Concentration, 95^th Percentile, Delivered to Acceptable Native Soil by the Disposal Works (Log₁₀ of coliform concentration in cfu per 100 milliliters)
3.5	7
3	6
2.5	5
2	4
1.5	0*
1	0*
0.5	0*
0	0*

* Nominally free of coliform bacteria.

ii. Include a hydraulic analysis with the Notice of Intent to Discharge, based on the location and dimensions of the absorption surfaces specified in R18-9-A312(B)(4)(b), showing that the soil is sufficiently permeable to conduct wastewater vertically downward and laterally without surfacing for the site conditions at the disposal works; and

iii. If a disinfection device under R18-9-E320 is proposed but is not used with surface disposal of wastewater under R18-9-E321 or "Category A" drip irrigation disposal under R18-9-E322, provide a justification with the Notice of Intent to Discharge stating why the selected type of disposal works is favored over disposal under R18-9-E321 or R18-9-E322.

4. Vertical separation from a subsurface limiting condition described in R18-9-A310(D)(2)(e) that promotes accelerated downward movement of insufficiently treated wastewater. If a subsurface limiting condition described in R18-9-A310(D)(2)(e) exists at the location of the proposed disposal works, the applicant shall ensure that the design for the on-site wastewater treatment facility meets one of the following:

a. A zone of naturally occurring soil with the following characteristics exists between the bottom of the disposal works and the top of the subsurface limiting condition:

i. The zone of soil is at least 2 feet thick, and

ii. The SAR of the soil is not less than 0.20 gallons per day per square foot nor more than 1.20 gallons per day per square foot; or

b. The on-site wastewater treatment facility employs one or more technologies described in R18-9-E303 through R18-9-E322 that produces treated wastewater that meets a total coliform concentration of 1,000,000 (Log₁₀6) colony forming units per 100 milliliters, 95^th percentile.

F. Materials and manufactured system components.

1. Materials. An applicant shall use aggregate if no specification for disposal works material is provided in this Article.

2. Manufactured components. If manufactured components are used, an applicant shall design, install, and operate the on-site wastewater treatment facility following the manufacturer's specifications. The applicant shall ensure that:

a. Treatment and containment components, mechanical equipment, instrumentation, and controls have monitoring, inspection, access and cleanout ports or covers, as appropriate, for monitoring and service;

b. Treatment and containment components, pipe, fittings, pumps, and related components and controls are durable, watertight, structurally sound, and capable of withstanding stress from installation and operational service; and

c. Distribution lines for disposal works are constructed of perforated high density polyethylene pipe, perforated ABS pipe, perforated PVC pipe, or other pipe material, if the pipe is suitable for wastewater disposal use and sufficient openings are available for distribution of the wastewater into the trench or bed area.

3. Electronic components. When electronic components are used, the applicant shall ensure that:

a. The component connections are compliant with the electrical code encompassed in the local building codes applicable in the county in which the facility is installed, except as required for a pressure distribution system under R18-9-E304(D)(2)(e);

a.b. Instructions and a wiring diagram are mounted on the inside of a control panel cover;

b.c. The control panel is equipped with a multimode operation switch, red alarm light, buzzer, and reset button;

c.d. The multimode operation switch operates in the automatic position for normal system operation; and

d.e. An anomalous condition is indicated by a glowing alarm light and sounding buzzer. The continued glowing of the alarm light after pressing the reset button shall signal the need for maintenance or repair of the system at the earliest practical opportunity.

4. If a conflict exists between this Article and the manufacturer's specifications, the requirements of this Article apply. Except for the requirements in subsection (D) and (E), which always apply, if the conflict voids a manufacturer's warranty, the applicant may submit a request under subsection (G) justifying use of the manufacturer's specifications.

G. Alternative design, setback, installation, or operational features. When an applicant submits a Notice of Intent to Discharge, the applicant may request that the Department review and approve a feature of improved or alternative technology, design, setback, installation, or operation that differs from a general permit requirement in this Article. Designs incorporating alternative features already approved in a current listing on the "proprietary and other reviewed product list" pursuant to R18-9-A309(E) do not need additional approval under this subsection for only those specific alternative features already approved in the proprietary products listing.

1. The applicant shall make the request for an improved or alternative feature of technology, design, setback, installation, or operation on a form provided by the Department and include:

a. A description of the requested change;

b. A citation to the applicable feature or technology, design, setback, installation, or operational requirement for which the change is being requested; and

c. Justification for the requested change, including any necessary supporting documentation.

2. The applicant shall submit the appropriate fee specified under 18 A.A.C. 14 for each requested change. For purposes of calculating the fee, a requested change that is applied multiple times in a similar manner throughout the facility is considered a single request if submitted for concurrent review.

3. The applicant shall provide sufficient information for the Department to determine that the change achieves equal or better performance compared with the general permit requirement, or addresses site or system conditions more satisfactorily than the requirements of this Article.

4. The Department shall review and may approve the request for change.

5. The Department shall deny the request for the change if the change will adversely affect other permittees or cause or contribute to a violation of an Aquifer Water Quality Standard.

6. The Department shall deny the request for the change if the change:

a. Fails to achieve equal or better performance compared to the general permit requirement;

b. Fails to address site or system conditions more satisfactorily than the general permit requirement;

c. Is insufficiently justified based on the information provided in the submittal;

d. Requires excessive review time, research, or specialized expertise by the Department to act on the request; or

e. For any other justifiable cause.

7. The Department may approve a reduced setback for a facility authorized to discharge under one or more of the general permits in R18-9-E302 through R18-9-E323, either separately or in combination, if the applicant additionally demonstrates at least one of the following:

a. The treatment performance is significantly better than that provided under R18-9-E302(B) ,

b. The wastewater loading rate is reduced, or

c. Surface or subsurface characteristics ensure that reduced setbacks are protective of human health or water quality.

Ariz. Admin. Code § R18-9-A312 - Facility Design for Type 4 On-site Wastewater Treatment Facilities

Notes