SEPTIC INSTALLER TEST FOR
WASHINGTON STATE (WOSSA) EXAM
QUESTIONS AND ANSWERS 100% PASS
2026 UPDATE.
ANSI - ANS American National Standards Institute
BOD - ANS biochemical oxygen demand, typically expressed in mg/L.
CBOD - ANS Carbonaceous Biochemical Oxygen Demand, expressed in mg/L.
FC - ANS Fecal Coliform, expressed in number of colonies 100/ml.
LOSS - ANS large on-site sewage system
NSF - ANS Nation Sanitation Foundation International
O&G - ANS Oils and Grease, component of sewage typically originating from food stuffs
(animal fats of vegetable oils) expressed in mg/L.
RS&G - ANS Recommended Standards and Guidance
1 @COPYRIGHT 2025/2026 ALLRIGHTS RESERVED.
,SSAS - ANS a subsurface soil absorption system
TAC - ANS Technical Advisory Committee established in WAC 247-272A-0400
TN - ANS Total Nitrogen, expressed in mg/L.
TSS - ANS Total Suspended Solids. A measure of the total suspended solids in a given
solution, expressed in mg/L.
USEPA - ANS United States Environmental Protection Agency
Additive - ANS a commercial product added to an on-site sewage system intended to affect
the performance or aesthetics of an on-site sewage system
Approved - ANS Acceptable to the authority having jurisdiction. Local health officer or the
department
BED - ANS a soil dispersal component consisting of an excavation with a width greater than 3
feet
Building Sewer - ANS that part of the horizontal piping of a drainage system which starts from
the end of the building drain and which receives the discharge of the building drain and conveys
it to a public sewer, private sewer, individual sewage disposal system or other point of disposal.
It begins two feet outside the building wall and conveys sewage from the building drain to the
remaining portions of the on-site sewage system.
Cesspool - ANS a covered hole or pit for receiving drainage or sewage, as from a house
allowing liquid to seep into the surronding rock or soil
Conforming System - ANS an on-site sewage system of component meeting rules of: New
construction requirements
2 @COPYRIGHT 2025/2026 ALLRIGHTS RESERVED.
,Approved and installed within previous requirements
Permitted by WAC-246-272A-0420
Cover Material - ANS Soil placed over dispersal component, made up of mineral material with
no greater than 10% organic content. Cover may contain organic surface material, an organic
landscaper to help reduce and contain soil erosion.
Cuts and Banks - ANS a naturally occurring or artificially formed slope greater than one
hundred percent (forty-five degrees) and extending vertically at least five from the toe of the
slope to top of the slope.
Department - ANS Washington State Department of Health
Designer - ANS Person who matches site and soil characteristics with approved components
Design Flow - ANS Means the maximum volume of sewage a residence, structure or other
facility is estimated to generate in a twenty-four hour period. It incorporates both an operating
capacity and a surge capacity for the system during periodic heavy use events. The sizing and
design of a on-site sewage system component is based on the design flow.
Development - ANS The creation of a residence, structure, facility, subdivision, area, or
similar activity resulting in the production of sewage.
Disinfection - ANS The process of destroying pathogens in sewage through the application of
chlorination, ultra-violent light, or ozonation.
Distribution Technology - ANS any arrangement of equipment and/or material that
distributes sewage within and on-site sewage system.
Drainfield - ANS subsurface soil absorption system, and soil dispersal component
3 @COPYRIGHT 2025/2026 ALLRIGHTS RESERVED.
, Drainrock - ANS cleaned washed gravel or crushed rock ranging in size from 3/4" to 2.5", and
containing no more than two percent by weight passing a US No.8 sieve and no more than one
percent by weight passing through a US No. 200 Sieve.
Effluent - ANS liquid waste discharged to a septic tank or other on-site sewage system
Expanding Clay - ANS means a clay soil with the mineralogy of clay particles. Clay particles
expand when absorbing water
expansion - ANS a change in residence, facility or site that results in the quantity of sewage to
exceed the original design
Extremely gravely - ANS soils with 60% or more, but not less than 90% rock fragments by
volume.
Failure - ANS a condition of an on-site sewage component that threatens the public health by
inadequately treating the sewage, or creating a potential direct or indirect contact between
sewage and the public.
Fecal coliform bacteria - ANS bacteria found in the intestinal tracts of warm-blooded animals
that are cultured in standard tests. Generally expressed as colonies per 100 ml.
Gravely - ANS Soils with 15% or more, but less than 35% rock fragments by volume.
Gray Water - ANS Sewage from bathtubs, showers, bathroom sinks, kitchen sinks, washing
machines, and dishwashers.
Ground water - ANS Subsurface water in the zone of saturated soils, seasonally, permanently,
or as the result of the tides.
Holding tank sewage system - ANS an on-site sewage system that a holding tank with no
discharge outlet
4 @COPYRIGHT 2025/2026 ALLRIGHTS RESERVED.
WASHINGTON STATE (WOSSA) EXAM
QUESTIONS AND ANSWERS 100% PASS
2026 UPDATE.
ANSI - ANS American National Standards Institute
BOD - ANS biochemical oxygen demand, typically expressed in mg/L.
CBOD - ANS Carbonaceous Biochemical Oxygen Demand, expressed in mg/L.
FC - ANS Fecal Coliform, expressed in number of colonies 100/ml.
LOSS - ANS large on-site sewage system
NSF - ANS Nation Sanitation Foundation International
O&G - ANS Oils and Grease, component of sewage typically originating from food stuffs
(animal fats of vegetable oils) expressed in mg/L.
RS&G - ANS Recommended Standards and Guidance
1 @COPYRIGHT 2025/2026 ALLRIGHTS RESERVED.
,SSAS - ANS a subsurface soil absorption system
TAC - ANS Technical Advisory Committee established in WAC 247-272A-0400
TN - ANS Total Nitrogen, expressed in mg/L.
TSS - ANS Total Suspended Solids. A measure of the total suspended solids in a given
solution, expressed in mg/L.
USEPA - ANS United States Environmental Protection Agency
Additive - ANS a commercial product added to an on-site sewage system intended to affect
the performance or aesthetics of an on-site sewage system
Approved - ANS Acceptable to the authority having jurisdiction. Local health officer or the
department
BED - ANS a soil dispersal component consisting of an excavation with a width greater than 3
feet
Building Sewer - ANS that part of the horizontal piping of a drainage system which starts from
the end of the building drain and which receives the discharge of the building drain and conveys
it to a public sewer, private sewer, individual sewage disposal system or other point of disposal.
It begins two feet outside the building wall and conveys sewage from the building drain to the
remaining portions of the on-site sewage system.
Cesspool - ANS a covered hole or pit for receiving drainage or sewage, as from a house
allowing liquid to seep into the surronding rock or soil
Conforming System - ANS an on-site sewage system of component meeting rules of: New
construction requirements
2 @COPYRIGHT 2025/2026 ALLRIGHTS RESERVED.
,Approved and installed within previous requirements
Permitted by WAC-246-272A-0420
Cover Material - ANS Soil placed over dispersal component, made up of mineral material with
no greater than 10% organic content. Cover may contain organic surface material, an organic
landscaper to help reduce and contain soil erosion.
Cuts and Banks - ANS a naturally occurring or artificially formed slope greater than one
hundred percent (forty-five degrees) and extending vertically at least five from the toe of the
slope to top of the slope.
Department - ANS Washington State Department of Health
Designer - ANS Person who matches site and soil characteristics with approved components
Design Flow - ANS Means the maximum volume of sewage a residence, structure or other
facility is estimated to generate in a twenty-four hour period. It incorporates both an operating
capacity and a surge capacity for the system during periodic heavy use events. The sizing and
design of a on-site sewage system component is based on the design flow.
Development - ANS The creation of a residence, structure, facility, subdivision, area, or
similar activity resulting in the production of sewage.
Disinfection - ANS The process of destroying pathogens in sewage through the application of
chlorination, ultra-violent light, or ozonation.
Distribution Technology - ANS any arrangement of equipment and/or material that
distributes sewage within and on-site sewage system.
Drainfield - ANS subsurface soil absorption system, and soil dispersal component
3 @COPYRIGHT 2025/2026 ALLRIGHTS RESERVED.
, Drainrock - ANS cleaned washed gravel or crushed rock ranging in size from 3/4" to 2.5", and
containing no more than two percent by weight passing a US No.8 sieve and no more than one
percent by weight passing through a US No. 200 Sieve.
Effluent - ANS liquid waste discharged to a septic tank or other on-site sewage system
Expanding Clay - ANS means a clay soil with the mineralogy of clay particles. Clay particles
expand when absorbing water
expansion - ANS a change in residence, facility or site that results in the quantity of sewage to
exceed the original design
Extremely gravely - ANS soils with 60% or more, but not less than 90% rock fragments by
volume.
Failure - ANS a condition of an on-site sewage component that threatens the public health by
inadequately treating the sewage, or creating a potential direct or indirect contact between
sewage and the public.
Fecal coliform bacteria - ANS bacteria found in the intestinal tracts of warm-blooded animals
that are cultured in standard tests. Generally expressed as colonies per 100 ml.
Gravely - ANS Soils with 15% or more, but less than 35% rock fragments by volume.
Gray Water - ANS Sewage from bathtubs, showers, bathroom sinks, kitchen sinks, washing
machines, and dishwashers.
Ground water - ANS Subsurface water in the zone of saturated soils, seasonally, permanently,
or as the result of the tides.
Holding tank sewage system - ANS an on-site sewage system that a holding tank with no
discharge outlet
4 @COPYRIGHT 2025/2026 ALLRIGHTS RESERVED.
