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Onsite Wastewater System Installation Manual Handout and Frequently Asked Questions

The information contained on this page is the handout that goes with the Onsite Wastewater System Installation Manual (OWSIM). (PDF)

Septic Tanks

Does the Alaska Department of Environmental Conservation (ADEC) have a list of approved prefabricated septic tanks?
No. Tanks selected must comply with ADEC regulations and the Uniform Plumbing Code.
What are some of the requirements
A partial list includes: (see regulations/standards for the full list)
  • At least 1,000 gallons plus 250 gallons per bedroom over three
  • Manufacturer certification for required bury depth
  • Two chambers
  • Watertight covers bolted, locked or covered with fill
What are the full regulations and standards governing the construction of septic tanks?
18 AAC and Appendix H of the 2012 Uniform Plumbing Code
What are the applicable quality assurance and control standards for prefabricated septic tanks?
  • Underwriters Laboratories (UL) coating for steel septic tanks
  • International Association of Plumbing and Mechanical Officials (IAPMO) and American National Standards Institute (ANSI) Z1000 (and referenced American Society for Testing and Materials (ASTM) standards) for concrete septic tanks
  • IAPMO or National Sanitation Foundation (NSF) 40 certification for plastic or composite tanks
How does ADEC approve cast-in-place or non-prefabricated septic tanks?
ADEC will review and approve engineering plans for individual tanks only under 18 AAC 72.200

Approved Pipe Materials

Pipe Type ASTM Designation Approved for Building Sewer Approved for Disposal Sewer Approved for Drainfield Pipe Approved for Cleanout and Standpipe
Schedule 40 ABS ASTM F628 Yes Yes No Yes
Schedule 40 PVC ASTM D1785 No Yes Yes Yes
Schedule 40 PVC ASTM D2665 No Yes Yes Yes
SDR 35 PVC ASTM D3034 No Yes Yes Yes

Design and Construction Frequently Asked Questions

Which systems require engineered plans?
  • Holding Tanks
  • Mound-type absorption beds
  • Other non-conventional or alternative onsite wastewater systems
  • Package treatment plants
  • Reduced separation distance
  • Sewage lift stations (except pre-approved designs such as Anchorage Tank, Greer Tank, etc.)
  • Soils with a percolation rate slower than 60 minutes per inch
  • Surface discharges & discharges to waters of the United States
  • Systems with any non-domestic wastewater
Can a certified installer install a conventional onsite system in silt (ML) soils?
  • Only with an engineer's soil log and percolation test. Based on the percolation rate, the absorption field is then sized using the application rate specified in Division 20 Article 5.4 of the OWSIM. A copy of the engineer's soil log and percolation test must be included with the Documentation of Construction
  • ADEC offices may issue region specific guidance or exceptions based on soil survey data. Contact the ADEC office where the installation will take place

Important Definitions

"small commercial facility" from 18 AAC 72.990(71) means "a single commercial building with an expected peak design flow of 500 gpd or less of domestic wastewater

"private residence" from 18 AAC 72.990(89) means "a single residential lot that is developed as a primary habitation for not more than two families and has a total maximum design flow on the lot of not more than 1,500 gpd of domestic wastewater; a private residence

  1. includes one duplex, two single-family residential structures, or a single-family home plus an apartment;
  2. may include additional support buildings, such as a workshop, home office, greenhouse, or garage, used by the residents; and
  3. does not include a commercial development;"

Sewer Materials Locations

sewer materials location

Note: This is not a complete drawing. Sewer components shown for clarity only. See the Onsite Wastewater System Installation Manual for complete drawings.

Office Contacts

If you have any questions or concerns regarding this information, please contact the Section Manager for Wastewater Engineering Support and Plan Review.

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