Septic Installer Test – Washington State (WOSSA) | 2025/2026
Updated Exam Prep & Study Guide | 100% Pass Guarantee
ANSI - correct answerAmerican National Standards Institute
BOD - correct answerbiochemical oxygen demand, typically expressed in mg/L.
CBOD - correct answerCarbonaceous Biochemical Oxygen Demand, expressed in
mg/L.
FC - correct answerFecal Coliform, expressed in number of colonies 100/ml.
LOSS - correct answerlarge on-site sewage system
NSF - correct answerNation Sanitation Foundation International
O&G - correct answerOils and Grease, component of sewage typically originating from
food stuffs (animal fats of vegetable oils) expressed in mg/L.
RS&G - correct answerRecommended Standards and Guidance
SSAS - correct answera subsurface soil absorption system
TAC - correct answerTechnical Advisory Committee established in WAC 247-272A-
0400
TN - correct answerTotal Nitrogen, expressed in mg/L.
TSS - correct answerTotal Suspended Solids. A measure of the total suspended solids
in a given solution, expressed in mg/L.
USEPA - correct answerUnited States Environmental Protection Agency
Additive - correct answera commercial product added to an on-site sewage system
intended to affect the performance or aesthetics of an on-site sewage system
Approved - correct answerAcceptable to the authority having jurisdiction. Local health
officer or the department
BED - correct answera soil dispersal component consisting of an excavation with a
width greater than 3 feet
Building Sewer - correct answerthat 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 - correct answera 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 - correct answeran on-site sewage system of component meeting
rules of: New construction requirements
Approved and installed within previous requirements
Permitted by WAC-246-272A-0420
Cover Material - correct answerSoil 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 - correct answera 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 - correct answerWashington State Department of Health
Designer - correct answerPerson who matches site and soil characteristics with
approved components
Design Flow - correct answerMeans 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 - correct answerThe creation of a residence, structure, facility,
subdivision, area, or similar activity resulting in the production of sewage.
Disinfection - correct answerThe process of destroying pathogens in sewage through
the application of chlorination, ultra-violent light, or ozonation.
Distribution Technology - correct answerany arrangement of equipment and/or material
that distributes sewage within and on-site sewage system.
Drainfield - correct answersubsurface soil absorption system, and soil dispersal
component
,Drainrock - correct answercleaned 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 - correct answerliquid waste discharged to a septic tank or other on-site sewage
system
Expanding Clay - correct answermeans a clay soil with the mineralogy of clay particles.
Clay particles expand when absorbing water
expansion - correct answera change in residence, facility or site that results in the
quantity of sewage to exceed the original design
Extremely gravely - correct answersoils with 60% or more, but not less than 90% rock
fragments by volume.
Failure - correct answera 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 - correct answerbacteria found in the intestinal tracts of warm-
blooded animals that are cultured in standard tests. Generally expressed as colonies
per 100 ml.
Gravely - correct answerSoils with 15% or more, but less than 35% rock fragments by
volume.
Gray Water - correct answerSewage from bathtubs, showers, bathroom sinks, kitchen
sinks, washing machines, and dishwashers.
Ground water - correct answerSubsurface water in the zone of saturated soils,
seasonally, permanently, or as the result of the tides.
Holding tank sewage system - correct answeran on-site sewage system that a holding
tank with no discharge outlet
hydraulic loading rate - correct answerthe amount of effluent applied to a given
treatment step, expressed as gallons per square foot per day, (gal./sq.ft./day)
industrial waste - correct answerWaste from production of consumer goods, mining,
agriculture and petroleum extraction and refining
Infiltrative surface - correct answerSurface within a treatment component or soil
dispersal component to which effluent is applied and through which effluent moves into
original, undisturbed soil or other porous treatment media.
, Installer - correct answera person approved by the local health office to install on-site
sewage systems or components
Local Health Officer - correct answerThe provincial or municipal health officer.
Maintenance - correct answerThe actions necessary to keep the on-site sewage system
components functioning as designed
Massive structure - correct answerthe condition of a soil layer in which the layer
appears as a coherent of solid mass not separated into peds of any kind
Moderated structure - correct answerWell- formed distinct peds evident in undisturbed
soil. When disturbed, soil material parts into mixture of whole peds, broken peds, and
material that is not in peds.
Monitoring - correct answerPeriodic or continuous surveillance of on-site sewage
system, which is performed by observations and measurements, to determine if the
system is functioning as intended and if system is in need of maintenance.
On-site sewage system (OSS) - correct answerAn integrated system of components ,
located on or nearby the property it serves. that conveys, stores, treats, and/or provides
subsurface soil treatment and dispersal of sewage. It consists of a collection system, a
treatment component or treatment sequence, and a soil dispersal component.
Operating capacity - correct answerthe average daily volume of sewage an OSS can
treat and disperse on a sustained basis. The operating capacity, which is lower than
design flow, is an integral part of the design and is used as an index in OSS monitoring.
Ordinary High Water Mark - correct answerThe point on the bank or shore where water
is present often enough so that the upland begins to look different from the lake or
stream bed.
Ped - correct answera unit of soil structure such as blocks, columns, granule, plate or
prism formed by natural process
Person - correct answerAny individual, partnership, corporation, association,
government or governmental subdivision or agency or other entity:
Planned Unit Development - correct answerA planned combination of diverse land uses,
such as housing, recreation, and shopping, in one contained development or
subdivision.
Platy structure - correct answerThin, flat plates of soil that lie horizontally. Usually found
in compacted soil. This type of soil will impede the vertical movement of water.
Updated Exam Prep & Study Guide | 100% Pass Guarantee
ANSI - correct answerAmerican National Standards Institute
BOD - correct answerbiochemical oxygen demand, typically expressed in mg/L.
CBOD - correct answerCarbonaceous Biochemical Oxygen Demand, expressed in
mg/L.
FC - correct answerFecal Coliform, expressed in number of colonies 100/ml.
LOSS - correct answerlarge on-site sewage system
NSF - correct answerNation Sanitation Foundation International
O&G - correct answerOils and Grease, component of sewage typically originating from
food stuffs (animal fats of vegetable oils) expressed in mg/L.
RS&G - correct answerRecommended Standards and Guidance
SSAS - correct answera subsurface soil absorption system
TAC - correct answerTechnical Advisory Committee established in WAC 247-272A-
0400
TN - correct answerTotal Nitrogen, expressed in mg/L.
TSS - correct answerTotal Suspended Solids. A measure of the total suspended solids
in a given solution, expressed in mg/L.
USEPA - correct answerUnited States Environmental Protection Agency
Additive - correct answera commercial product added to an on-site sewage system
intended to affect the performance or aesthetics of an on-site sewage system
Approved - correct answerAcceptable to the authority having jurisdiction. Local health
officer or the department
BED - correct answera soil dispersal component consisting of an excavation with a
width greater than 3 feet
Building Sewer - correct answerthat 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 - correct answera 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 - correct answeran on-site sewage system of component meeting
rules of: New construction requirements
Approved and installed within previous requirements
Permitted by WAC-246-272A-0420
Cover Material - correct answerSoil 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 - correct answera 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 - correct answerWashington State Department of Health
Designer - correct answerPerson who matches site and soil characteristics with
approved components
Design Flow - correct answerMeans 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 - correct answerThe creation of a residence, structure, facility,
subdivision, area, or similar activity resulting in the production of sewage.
Disinfection - correct answerThe process of destroying pathogens in sewage through
the application of chlorination, ultra-violent light, or ozonation.
Distribution Technology - correct answerany arrangement of equipment and/or material
that distributes sewage within and on-site sewage system.
Drainfield - correct answersubsurface soil absorption system, and soil dispersal
component
,Drainrock - correct answercleaned 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 - correct answerliquid waste discharged to a septic tank or other on-site sewage
system
Expanding Clay - correct answermeans a clay soil with the mineralogy of clay particles.
Clay particles expand when absorbing water
expansion - correct answera change in residence, facility or site that results in the
quantity of sewage to exceed the original design
Extremely gravely - correct answersoils with 60% or more, but not less than 90% rock
fragments by volume.
Failure - correct answera 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 - correct answerbacteria found in the intestinal tracts of warm-
blooded animals that are cultured in standard tests. Generally expressed as colonies
per 100 ml.
Gravely - correct answerSoils with 15% or more, but less than 35% rock fragments by
volume.
Gray Water - correct answerSewage from bathtubs, showers, bathroom sinks, kitchen
sinks, washing machines, and dishwashers.
Ground water - correct answerSubsurface water in the zone of saturated soils,
seasonally, permanently, or as the result of the tides.
Holding tank sewage system - correct answeran on-site sewage system that a holding
tank with no discharge outlet
hydraulic loading rate - correct answerthe amount of effluent applied to a given
treatment step, expressed as gallons per square foot per day, (gal./sq.ft./day)
industrial waste - correct answerWaste from production of consumer goods, mining,
agriculture and petroleum extraction and refining
Infiltrative surface - correct answerSurface within a treatment component or soil
dispersal component to which effluent is applied and through which effluent moves into
original, undisturbed soil or other porous treatment media.
, Installer - correct answera person approved by the local health office to install on-site
sewage systems or components
Local Health Officer - correct answerThe provincial or municipal health officer.
Maintenance - correct answerThe actions necessary to keep the on-site sewage system
components functioning as designed
Massive structure - correct answerthe condition of a soil layer in which the layer
appears as a coherent of solid mass not separated into peds of any kind
Moderated structure - correct answerWell- formed distinct peds evident in undisturbed
soil. When disturbed, soil material parts into mixture of whole peds, broken peds, and
material that is not in peds.
Monitoring - correct answerPeriodic or continuous surveillance of on-site sewage
system, which is performed by observations and measurements, to determine if the
system is functioning as intended and if system is in need of maintenance.
On-site sewage system (OSS) - correct answerAn integrated system of components ,
located on or nearby the property it serves. that conveys, stores, treats, and/or provides
subsurface soil treatment and dispersal of sewage. It consists of a collection system, a
treatment component or treatment sequence, and a soil dispersal component.
Operating capacity - correct answerthe average daily volume of sewage an OSS can
treat and disperse on a sustained basis. The operating capacity, which is lower than
design flow, is an integral part of the design and is used as an index in OSS monitoring.
Ordinary High Water Mark - correct answerThe point on the bank or shore where water
is present often enough so that the upland begins to look different from the lake or
stream bed.
Ped - correct answera unit of soil structure such as blocks, columns, granule, plate or
prism formed by natural process
Person - correct answerAny individual, partnership, corporation, association,
government or governmental subdivision or agency or other entity:
Planned Unit Development - correct answerA planned combination of diverse land uses,
such as housing, recreation, and shopping, in one contained development or
subdivision.
Platy structure - correct answerThin, flat plates of soil that lie horizontally. Usually found
in compacted soil. This type of soil will impede the vertical movement of water.
