Section R18-9-A312. Facility Design for Type 4 On-site Wastewater Treatment Facilities

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(B)(3);

4.        For on-site wastewater treatment facilities permitted under R18-9-E303 through R18-9-E323, apply the fol- lowing 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 appur- tenances 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 watertight- ness under all operational conditions;

e.         Provide adequate storage capacity above high oper- ating level to:

i.         Accommodate a 24-hour power or pump out- age, 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 con- struction 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 Depart- ment:

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

2.        Approves a different setback under the procedure speci- fied 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 Facil- ity, Including Reserve Area (In Feet)	Special Provisions
1. Building	10	Includes porches, decks, and steps (covered or uncovered), breezeways, roofed patios, carports, covered walks, and similar structures and appur- tenances.
2. Property line shared with any adjoining lot or par- cel 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 adja- cent properties agree, as evidenced by an appropriately recorded document, to limit the location of any new well on their prop- erty 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, 24-hour 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.

7. Drinking water intake from a surface water source (includes an open water body, downslope spring or a well tapping streamside saturated alluvium)	200	Measured horizontally from the on-site waste- water treatment facility to the structure or mech- anism 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 ero- sion protection is approved by the appropriate flood plain administrator.
9. Water main or branch water line	10	None
10. Domestic service water line	5	Measured horizontally between the water line and the wastewater pipe, except that the follow- ing 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 dis- tance 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 waste- water 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 gravel- less trench with:          i.   No limiting subsurface condition speci- fied 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 indi- cate 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 Dis- charge.

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

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

Percolation Rate from Percolation Test (min- utes 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.

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 consistency 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 struc- ture 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 silty 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 struc- ture 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

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

æ

 

ö

 

é                                                                                     ù

êç             11.39                              ÷                            ú

replacement or repair and is at least as large as the follow- ing:

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

SARa = êç

êç 3

ëêè

- 1.87÷  SAR1.13 + 1úSAR

ø

 

ûú

 

TSS + BOD5                  ÷                            ú

approved configuration;

b.        For other than a dwelling, a primary area for the dis- posal works sized according to subsection (D)(1) and a reserve area of 100 percent of the primary

a.         “SARa” is the adjusted soil absorption rate for dis-

posal 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 mil- ligrams per liter, and

d.        “SAR” is the soil absorption rate for septic tank effluent determined by the subsurface characteriza- tion 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

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, 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 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 Concentra- tion, 95th Percentile, Delivered to Natural Soil by the Disposal Works (Log10 of coliform concen- tration 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 characteri- zation, 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 lat- erally 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 con- tribute 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 facil- ity meets one of the following:

a.         A zone of acceptable native soil with the following characteristics exists between the bottom of the dis- posal 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 with- out causing surfacing of the wastewater as doc- umented 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 sur- face, and

ii.        The vertical separation distance from the bot- tom 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 bot- tom 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 microorgan- isms, 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 Separa- tion Distance from the Bot- tom of the Disposal Works to the Subsurface Limiting Condition (feet)	Maximum Allowable  Total Coliform Concentra- tion, 95th 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.        If the SAR of the native soil into which the dis- posal works is placed is not more than 0.63 gal- lons per day per square foot, include a hydraulic analysis with the Notice of Intent to Discharge, based on the location and dimen- sions 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 sur- facing 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 acceler- ated downward movement of insufficiently treated waste- water. If  a  subsurface limiting condition  described in R18-9-A310(D)(2)(e) exists at the location of the pro- posed 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 dis- posal 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 gal- lons 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 wastewa- ter that meets a total coliform concentration of 1,000,000 (Log106) colony forming units per 100

milliliters, 95th percentile.

F.       Materials and manufactured system components.

1.        Materials. An applicant shall use aggregate if no specifi- cation for disposal works material is provided in this Arti- cle.

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

a.         Treatment and containment components, mechanical equipment, instrumentation, and controls have mon- itoring, inspection, access and cleanout ports or cov- ers, as appropriate, for monitoring and service;

b.        Treatment and containment components, pipe, fit- tings, pumps, and related components and controls are durable, watertight, structurally sound, and capa- ble of withstanding stress from installation and oper- ational service; and

c.         Distribution lines for disposal works are constructed of clay tile laid with open joints, perforated clay pipe, perforated high density polyethylene pipe, per- forated ABS pipe, or perforated PVC pipe if the pipe is suitable for wastewater disposal use and sufficient openings are available for distribution of the waste- water into the trench or bed area.

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

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

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

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

d.        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 opportu- nity.

4.        If a conflict exists between this Article and the manufac- turer’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 manufac- turer’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 fea- tures. When an applicant submits a Notice of Intent to Dis- charge, 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.

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

a.         A description of the requested change;

	b.     A citation to the applicable feature or technology,		bances from grubbing, and otherwise preclude damage to
	design, setback, installation, or operational require-		the disposal area that would impair performance;
	ment for which the change is being requested; and		4.     Components are protected from damage at the construc-
	c.      Justification for the requested change, including any		tion site and installed in conformance with the manufac-
	necessary supporting documentation.		turer’s instructions if consistent with this Article;
2.	The applicant shall submit the appropriate fee specified		5.     Treatment media are placed to achieve uniform density,
	under 18 A.A.C. 14 for each requested change. For pur-		prevent differential settling, produce a level inlet surface
	poses of calculating the fee, a requested change that is		unless otherwise specified by the manufacturer, and avoid
	applied multiple times in a similar manner throughout the		introduction of construction contaminants;
	facility is considered a single request if submitted for		6.     Backfill is placed to prevent damage to geotextile, liners,
	concurrent review.		tanks, and other components;
3.	The applicant shall provide sufficient information for the		7.     Soil cover is shaped to shed rainfall away from the back-
	Department to determine that the change achieves equal		fill areas and prevent ponding of runoff; and
	or better performance compared with the general permit		8.     Anti-buoyancy measures are implemented during con-
	requirement, or addresses site or system conditions more		struction if temporary saturated backfill conditions are
	satisfactorily than the requirements of this Article.		anticipated during construction.
4.	The  Department  shall  review  and  may   approve  the	B.	Operation and maintenance. In addition to operation and main-
	request for change.		tenance requirements in the general permit or specified in the
5.	The Department shall deny the request for the change if		operation and maintenance manual, the permittee shall ensure
	the change will adversely affect other permittees or cause		that the following tasks are performed, as applicable:
	or contribute to a violation of an Aquifer Water Quality		1.     Pump accumulated residues, inspect and clean wastewa-
	Standard.		ter treatment and distribution components, and manage
6.	The Department shall deny the request for the change if		residues to protect human health and the environment;
	the change:		2.     Clean, backwash, or replace effluent filters according to
	a.      Fails to achieve equal or better performance com-		the manufacturer’s instructions, and manage residues to
	pared to the general permit requirement;		protect human health and the environment;
	b.     Fails to address site or system conditions more satis-		3.     Inspect and clean the effluent baffle screen and pump
	factorily than the general permit requirement;		tank, and properly dispose of cleaning residue;
	c.      Is insufficiently justified based on the information		4.     Clean the dosing tank effluent screen, pump switches,
	provided in the submittal;		and floats, and properly dispose of cleaning residue;
	d.     Requires excessive review time, research, or special-		5.     Flush lateral lines and return flush water to the pretreat-
	ized  expertise   by  the  Department  to  act  on   the		ment headworks;
	request; or		6.     Inspect, remove and replace, if necessary, and properly
	e.      For any other justifiable cause.		dispose of filter media;
7.	The Department may approve a reduced setback for a		7.     Rod pressurized wastewater delivery lines and secondary
	facility authorized to discharge under one or more of the		distribution lines (for dosing systems), and return clean-
	general  permits   in  R18-9-E303   through  R18-9-E322,		ing water to the pretreatment headworks;
	either separately or in combination with a septic tank sys-		8.     Inspect and clean pump inlets and controls and return
	tem  authorized   under  R18-9-E302,  if  the  applicant		cleaning water to the pretreatment headworks;
	demonstrates that:		9.     Implement corrective measures if anomalous ponding,
	a.      The  treatment  performance is  significantly  better		dryness, noise, odor, or differential settling is observed;
	than that provided under R18-9-E302(B),		10.  Inspect and monitor inspection and access ports, as appli-
	b.     The wastewater loading rate is reduced, or		cable, to verify that operation is within expected limits
	c.      Surface  or  subsurface   characteristics  ensure  that		for:

reduced setbacks are protective of human health or water quality.

Historical Note

New Section adopted by final rulemaking at 7 A.A.R. 235, effective January 1, 2001 (Supp. 00-4). Amended to correct a manifest typographical error in subsection (E)(1) (Supp. 01-1). Amended by final rulemaking at 11

A.A.R. 4544, effective November 12, 2005 (05-3).