18 AAC 72.035. Conventional onsite systems

(a) A person may install a septic tank if

(1) the design and construction of the septic tank, exclusive of tank capacity, meets the minimum specifications for septic tanks contained in Appendix K of the state's plumbing code as required under AS 18.60.705 and 18 AAC 72.070(b) ;

(2) a septic tank serving a single-family home or duplex has a capacity of at least 1,000 gallons, plus 250 gallons per bedroom over three served by the tank;

(3) the net minimum volume of a septic tank serving structures other than those described in (2) of this subsection is

(A) at least 1,000 gallons for systems with daily design flows up to 750 gpd;

(B) at least 1.5 times the daily design flow for systems with daily design flows between 750 and 1,500 gpd; or

(C) at least 1,125 gallons plus 0.75 times the daily design flow for systems with daily design flows exceeding 1,500 gpd;

(4) septic tank access openings have watertight covers that are

(A) bolted;

(B) padlocked;

(D) otherwise securely fastened in place; and

(5) the installation of a septic tank is completed by a person described in 18 AAC 72.015(b) , (c), or (d).

(b) Except as provided in (d) of this section and 18 AAC 72.200(b) , plans for a conventional onsite system must be approved by the department as required by 18 AAC 72.200.

(c) A conventional onsite system must have frost penetration protection that meets the requirements of Table A of this subsection, such as adequate depth of burial, mounding above grade, or insulation.

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TABLE A INSULATION REQUIREMENTS Geographical Depth of Ground Cover Area or Insulation Equivalent Southeast Alaska (east of 141УИ W. longitude) 3 feet of cover Southwest Alaska (Kodiak Island Borough and all areas southwest of Chignik, including Chignik) 2 feet of cover The area within the Valdez corporate boundary, and the coastal area south and east of Valdez to 141УИ W. longitude 3 feet of cover All remaining areas of the state 4 feet of cover For up to two feet of the required ground cover, the applicant may substitute insulation material that does not absorb water, with department approval of material type and thickness as protective of public health, public and private water systems, and the environment, except that at least two feet of ground cover must be maintained.

(d) A person may install a conventional onsite system without plan approval if

(1) the system is for a single-family home, a duplex, or a small commercial facility;

(2) the installation of the system is completed by a person described in 18 AAC 72.015(b) , (c), or (d);

(3) the installation complies with the Installer's Manual for Conventional Onsite Domestic Wastewater Treatment and Disposal Systems, adopted by reference in 18 AAC 72.070(a) (1);

(4) the design of the system conforms to standard sanitary engineering principles and practices and adequately protects public health, the environment, and public and private water systems;

(5) the system is located in soils classified as GW, GP, GM, SW, SP, or SM under the Unified Soil Classification System;

(6) the system has a minimum infiltrative area in accordance with Table B of this subsection, or the soils and the minimum infiltrative area conform to the requirements of 18 AAC 72.260(a) (4)(A) and (D);

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TABLE B ABSORPTION FIELD AREA REQUIREMENTS FOR UNIFIED SOIL CLASSIFICATION Minimum infiltrative area,* measured in Unified Class Description square feet, per bedroom GW* Well-graded gravels 85 GP* Poorly-graded gravels 115 SW Well-graded sands 125 SP Poorly-graded sands 150 GM** Silty gravels 225 SM** Silty sands 275

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*GW and GP soils are unsuitable for use in absorption areas unless a two-foot thick layer of sand, meeting the requirements of 18 AAC 72.260(a) (4)(D), Table C, Note 1, is placed between the distribution rock and the receiving soil; the department will waive this requirement if a waiver does not threaten public health, public and private water systems, or the environment, and in accordance with 18 AAC 72.060.

**Use of these soils in absorption areas requires a percolation test by a registered engineer, conducted in accordance with 18 AAC 72.265(9) . _______________________________________________________________________

(7) the system complies with the separation distances set out in 18 AAC 72.020;

(8) the ground surface slope is less than 25 percent for trenches, and less than five percent for beds;

(9) as shown in Figure 1 of this subsection, at least 50 feet separates any part of the soil absorption system from any slope greater than 25 percent, whether man-made or natural, with a drop in the surface height greater than 10 feet; and

CLICK TO VIEW FORM

(10) the system is not located in an area

(A) known or suspected to contain permafrost;

(B) where similar systems have been known to fail;

(D) where the department finds that a discharge threatens public health, public and private water systems, or the environment.

(e) Under 18 AAC 72.060, the department will, in its discretion, grant a waiver from the requirements of (d)(8) and (d)(9) of this section for a conventional onsite system if, under the waiver, the system operates in a manner protective of public health, public and private water systems, and the environment, and if existing soil types, vegetation, geologic factors, hydrologic factors, or other pertinent factors show that there is reasonable assurance that wastewater will not surface downslope, and that an unstable slope condition will not be created.

History: Eff. 4/1/99, Register 149

Authority: AS 44.46.020

Editor's note: For guidance on designs for conventional onsite systems that would satisfy the requirements of 18 AAC 72.035(d) (4), see the references listed at 18 AAC 72.070(c) (12) and (15).

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