OSSF Installer 1 License Exam Questions and
Answers Already Passed 2025
1. What is the primary purpose of an on-site sewage facility (OSSF)?
To treat and dispose of domestic wastewater
An OSSF is designed to safely manage and dispose of wastewater from
homes or buildings where public sewage systems are unavailable.
2. What is the maximum number of gallons per day (GPD) that an Installer I
license holder can install systems for?
500 GPD
Installer I license holders are limited to systems that treat flows of no more
than 500 gallons per day.
3. Which type of soil has the slowest permeability?
Clay
Clay particles are very small and compact, leading to slow water infiltration
rates.
4. What is the minimum distance required between an OSSF and a private
water well?
100 feet
This separation is required to prevent contamination of the drinking water
source.
,5. Which component of a septic system removes solids from wastewater?
Septic tank
The septic tank is the first step in wastewater treatment where solids settle
and scum rises.
6. Which test is used to determine the suitability of soil for an OSSF system?
Soil percolation test
This test measures how quickly water moves through soil to assess
absorption capacity.
7. What document must be submitted before installing an OSSF system?
Permit application
A permit must be issued by the permitting authority before any installation
can begin.
8. What is the maximum allowable slope on a property for an OSSF without
requiring special design?
15%
Slopes steeper than 15% require special consideration or professional
design.
9. What is the minimum cover depth for a standard lateral line in a
conventional system?
6 inches
This depth provides protection while allowing proper aerobic soil conditions.
10.What can cause premature failure of a conventional septic system?
Excessive water use
, Overloading the system can prevent proper treatment and lead to system
failure.
11.What is required before backfilling an installed OSSF system?
Inspection by the permitting authority
The system must be inspected and approved before it is covered.
12.Which of the following is a prohibited discharge for an OSSF?
Graywater into ditches or surface waters
Discharging untreated or partially treated wastewater into the environment
is illegal.
13.What does a distribution box do in a septic system?
Distributes effluent evenly to the drain field
Ensures equal flow to all parts of the drain field, preventing overloading.
14.What is the role of the aerobic treatment unit (ATU)?
Adds oxygen to help break down waste
Oxygen supports aerobic bacteria, which are more efficient at breaking
down waste.
15.What should be done if effluent backs up into a house?
Contact a licensed installer or maintenance provider immediately
This may indicate a system failure that poses health risks and must be
addressed.
16.How often should a septic tank be pumped under normal usage?
Every 3 to 5 years
Regular pumping prevents sludge buildup, which can damage the system.
Answers Already Passed 2025
1. What is the primary purpose of an on-site sewage facility (OSSF)?
To treat and dispose of domestic wastewater
An OSSF is designed to safely manage and dispose of wastewater from
homes or buildings where public sewage systems are unavailable.
2. What is the maximum number of gallons per day (GPD) that an Installer I
license holder can install systems for?
500 GPD
Installer I license holders are limited to systems that treat flows of no more
than 500 gallons per day.
3. Which type of soil has the slowest permeability?
Clay
Clay particles are very small and compact, leading to slow water infiltration
rates.
4. What is the minimum distance required between an OSSF and a private
water well?
100 feet
This separation is required to prevent contamination of the drinking water
source.
,5. Which component of a septic system removes solids from wastewater?
Septic tank
The septic tank is the first step in wastewater treatment where solids settle
and scum rises.
6. Which test is used to determine the suitability of soil for an OSSF system?
Soil percolation test
This test measures how quickly water moves through soil to assess
absorption capacity.
7. What document must be submitted before installing an OSSF system?
Permit application
A permit must be issued by the permitting authority before any installation
can begin.
8. What is the maximum allowable slope on a property for an OSSF without
requiring special design?
15%
Slopes steeper than 15% require special consideration or professional
design.
9. What is the minimum cover depth for a standard lateral line in a
conventional system?
6 inches
This depth provides protection while allowing proper aerobic soil conditions.
10.What can cause premature failure of a conventional septic system?
Excessive water use
, Overloading the system can prevent proper treatment and lead to system
failure.
11.What is required before backfilling an installed OSSF system?
Inspection by the permitting authority
The system must be inspected and approved before it is covered.
12.Which of the following is a prohibited discharge for an OSSF?
Graywater into ditches or surface waters
Discharging untreated or partially treated wastewater into the environment
is illegal.
13.What does a distribution box do in a septic system?
Distributes effluent evenly to the drain field
Ensures equal flow to all parts of the drain field, preventing overloading.
14.What is the role of the aerobic treatment unit (ATU)?
Adds oxygen to help break down waste
Oxygen supports aerobic bacteria, which are more efficient at breaking
down waste.
15.What should be done if effluent backs up into a house?
Contact a licensed installer or maintenance provider immediately
This may indicate a system failure that poses health risks and must be
addressed.
16.How often should a septic tank be pumped under normal usage?
Every 3 to 5 years
Regular pumping prevents sludge buildup, which can damage the system.
