18 Alaska Admin. Code § 72.530

Current through October 17, 2024

Section 18 AAC 72.530 - Construction requirements for conventional wastewater systems

(a) All conventional wastewater systems installed under this chapter must meet the minimum construction requirements of this section unless the department approves a waiver under 18 AAC 72.540.

(b) Design flow for the wastewater system must be calculated based on

(1) 150 gallons per day for each bedroom in a residential dwelling; and

(2) typical daily flow rates for each unit of a specific type of facility publicly identified by the department as acceptable.

(c) Each component of a conventional wastewater system, including all sewer lines, septic tanks, and absorption areas, must have the minimum frost penetration protection that meets the requirements set out in the following table:

INSULATION REQUIREMENTS
Geographical Area	Depth of Soil Cover or Insulation Equivalent*
Southwest Alaska (Kodiak Island Borough and all areas southwest of Chignik, including Chignik)	two feet of soil cover
Southeast Alaska (east of 141° West longitude), the coastal area south and east of Valdez (to 141° West longitude), and the Valdez corporate boundary	three feet of soil cover
All remaining areas of the state	four feet of soil cover
*Up to two feet of the required soil cover may be substituted with insulation material publicly identified by the department as equivalent. Soil cover may not be reduced to less than two feet.

(d) Private and community sewer lines must meet the material specifications publicly identified by the department under 18 AAC 72.070 and applicable plumbing codes. In addition to meeting these requirements,

(1) private and community gravity flow sewer lines must have a minimum nominal diameter of four inches and must be laid at minimum and maximum slopes in accordance with the requirements set out in the following table:

MINIMUM AND MAXIMUM SEWER LINE SLOPES
Nominal Sewer Line Size*	Minimum Slope	Maximum Slope**
four-inch	two percent	20 percent
six-inch	one percent	13 percent
eight-inch	0.4 percent	eight percent
*For pipes larger than eight-inch nominal diameter, minimum and maximum slopes must be calculated using the Manning formula to maintain a minimum velocity of two feet per second and a maximum velocity of 10 feet per second when flowing full.
**Maximum slope may be exceeded for drop connections using a method publicly identified as guidance under 18 AAC 72.070 or for sewer lines located after pretreatment.

(2) the 10 feet immediately preceding the septic tank may not exceed a two percent slope;

(3) solid pipe without joints must span five feet from the inlet and outlet of the septic tank onto undisturbed earth, or the soil may be backfilled and compacted in six-inch lifts before laying the pipe;

(4) sewer lines must be connected to the inlet and outlet of the septic tank using mechanical watertight couplings;

(5) all pipe-to-pipe joints must be glued with cement appropriate for the pipe material;

(6) manholes must be installed on community sewer lines at locations identified in 18 AAC 72.270(b)(3); the department may publicly identify as guidance under 18 AAC 72.070 an approved best management practice where a cleanout may be installed instead of a manhole as protective of public health, public and private water systems, and the environment;

(7) a cleanout must be constructed using a wye, combination wye, or long-sweep wye fitting that has the same diameter of the private or community sewer line to which it is attached, and must extend at least one foot above the ground surface; a single cleanout must be installed with the sweep in the direction of flow; a double cleanout must be installed with the upstream sweep in the direction of flow and the downstream sweep against the flow; cleanouts must be capped and installed

(A) within five feet of the outside wall of the building foundation;

(B) at intervals not to exceed 100 feet in continuous runs; and

(C) before each aggregate horizontal change in direction of 45 degrees or more when the sewer line is located before the septic tank.

(e) A septic tank must be installed in accordance with manufacturer specifications, include necessary anti-floatation measures, and meet the following criteria:

(1) the design and construction of the septic tank, exclusive of tank capacity, meets the minimum specifications for septic tanks contained in the Uniform Plumbing Code adopted by reference under 8 AAC 63;

(2) the net minimum volume of a septic tank must be in accordance with requirements set out in the following table; and

Minimum Septic Tank Size
Residential Dwellings		Commercial Facilities
Number of Bedrooms	Minimum Tank Size*	Daily Design Flow	Minimum Tank Size*
0 - 3	1,000 gallons	Up to 500 gpd	1,000 gallons
4 - 8	1,000 plus 250 gallons for each bedroom over three	501 to 750 gpd	1,250 gallons
9 - 13	2,500 gallons	751 to 1,000 gpd	1,500 gallons
14 - 18	3,000 gallons	1,001 to 1,250 gpd	2,000 gallons
Greater than 18	1,125 + (0.75* design flow)	Greater than 1,250 gpd	1,125+ (0.75* design flow)
*Tanks may be used in series or in parallel to achieve the minimum septic tank volume. The installation and design of more than one tank must be by department as acceptable guidance under 18 AAC 72.070 method publicly identified by the and protective of public health. public and private water systems, and the environment.

(3) access to the septic tank for maintenance purposes must be provided; for tanks with a net volume

(A) of 2,000 gallons or less, a minimum four-inch diameter cleanout pipe must be installed using a mechanical watertight coupling and extended with a cap at least one foot above the ground surface; or

(B) greater than 2,000 gallons, manhole access openings must be extended to the ground surface using insulated, watertight, flanged, pre-manufactured manhole risers with locking lids; manhole risers must be compatible with the tank and installed in accordance with the manufacturer's recommendations.

(f) A conventional soil absorption system must

(1) include a distribution medium meeting specifications and criteria publicly identified by the department under 18 AAC 72.070 or alternate specifications presented to and approved by the department; the distribution medium must provide adequate void space and be, as measured from the springline of the distribution pipe or height of chambers,

(A) a minimum of 12 inches thick for a bed or shallow-trench type system;

(B) greater than four feet deep but not more than 12 feet deep for a deep- trench type system;

(C) not more than two feet deeper than the bottom of the distribution tank for a seepage-pit type system; and

(D) at least 18 inches but not more than four feet deep for a 5-wide type system;

(2) be installed in an area where the original ground surface slope is

(A) less than or equal to 25 percent for a shallow-trench, deep-trench, or 5-wide type absorption field; or

(B) less than or equal to 10 percent for a bed or seepage-pit type absorption field;

(3) have the minimum absorption area, calculated from the wastewater application rates in the following table, which corresponds to the soil texture. Unified Soil Classification System, or percolation rate, whichever is most conservative; soils must be classified by digging a test hole or pit within 25 feet of the perimeter of the proposed absorption field and to a minimum of six feet below the estimated bottom of the absorption;

WASTEWATER APPLICATION RATES
Percolation Ratea (minutes/inch)	Soil Texture (Unified Soil Classification)	Application Rate in sf/bedroom	Application Rate in gpd/sf for design flows	Application Rate in gpd/sf for design flows >2,500 gpd
Faster than 1	Gravel (GW/GP)	Not Suitableb	Not Suitableb	Not Suitableb
1 - 5	Gravel (GW/GP)	125	1.2	0.79 - 0.98
1 - 15	Medium to coarse sand (SW/SP)	150	1.0	0.67 - 0.89
6 - 15	Fine sand or loamy sand (SP-SM)	190	0.8	0.61-0.74
16 - 30	Sandy loam, silty gravel (GM), silty sand (SM)	250	0.6	0.52-0.61
31 - 60c	Loam, silt loam, silt (ML)	335	0.45	0.25-0.52
61 - 120d	Silty clay loam, clay loame	Not Suitabled	Not Suitabled	Not Suitabled
a. Soils classified as silty sand (SM), silty gravel (GM), or silt (ML) must have a percolation test conducted; percolation tests must be performed in accordance with either a method publicly identified by EPA or the department as acceptable, or by an alternate method that has been presented by a registered engineer and approved by the department; a certified installer may perform the percolation test for systems installed under the certified installer's certification; Soils classified as clay (CL or CH), organic silt or clay (OL), or peat (PT) require an engineer design and prior department approval. b. Soils classified as gravel (GW or GP) for which a percolation test has not been conducted or a percolation test result is faster than one minute per inch may still be used if a shallow trench or bed system is installed with a two-foot sand liner below the distribution media and if application rates used are at least 1.0 gpd/sf or 150 sf/bedroom; sand must meet the specifications publicly identified by the department under 18 AAC 72.070; the department may waive the sand liner requirement in a manner set out in 18 AAC 72.540. c. Soils with percolation rates slower than 30 minutes per inch are unsuitable for seepage pits. d. Soils with percolation rates slower than 60 minutes per inch require an engineer design and prior department approval; soils with percolation rates slower than 120 minutes per inch are considered impermeable. e. Soils without expandable clays or soil types not listed in this table require an engineer design and prior department approval.

(4) have filter fabric placed over the distribution media before backfill that meets the specifications publicly identified by the department under 18 AAC 72.070;

(5) have an effluent distribution piping system that is laid level; and the layout must be consistent with specifications and methods publicly identified by the department as acceptable for the type of absorption field;

(6) have a vertical monitor tube, at least four inches in diameter, that is perforated within the distribution media and transitioned to solid pipe extended to at least one foot above the ground surface and capped; monitor tubes must be installed

(A) in opposite comers of a bed type absorption field;

(B) at the end of each leg of a trench or 5-wide type absorption field; or

(C) for seepage pits with a single monitor tube, as a solid pipe only attached to the distribution tank; and

(7) have a maximum length for a distribution pipe of 100 feet, measured from the point where the wastewater enters the pipe.

(g) A lift station located outside the foundation of a building must

(1) be equipped with a hardwired audible and visual high water alarm, on a separate electrical circuit from the pump, mounted in a visible location near the lift station or on the exterior of the building;

(2) if located inside a septic tank,

(A) be installed concurrently with a 250-gallon increase in septic tank volume;

(B) have the pump placed in a pump vault, manufactured for that purpose; and

(C) have access to the pump, float switches, and other hardware provided through a minimum 20-inch diameter manhole riser to the ground surface;

(3) if installed as a separate pump vault, be premanufactured as a single unit or have watertight manufactured risers extended to the ground surface with access to the pump, float switches, and other hardware provided through a minimum 24-inch diameter opening with locking lid; and

(4) if a basement sump or lift station is located before the septic tank,

(A) have the minimum septic tank size, as described in (e)(2) of this section, increased by

(i) 250 gallons for residential dwellings and commercial facilities with not more than 18 bedrooms or 1,250 gallons per day; and

(ii) at least 25 percent for residential dwellings and commercial facilities not described in (i) of this subparagraph;

(B) be equipped with a grinder pump or a pump capable of passing two-inch solids; and

(C) if serving multiple structures or dwellings, other than a private residence, be equipped with at least two pumps, each of which is capable of pumping flows equal to or greater than the design flow.

18 AAC 72.530

Eff. 10/1/2023, Register 247, October 2023

Material specifications and methods publicly identified by the department as acceptable practices for conventional wastewater systems may be obtained at a department office or on the department's website.

Authority:AS 44.46.020

AS 46.03.020

AS 46.03.050

AS 46.03.100