IL SEPTIC INSTALLERS EXAM QUESTIONS
WITH CORRECT ANSWERS 2025/2026
Public Sewer Connection - CORRECT ANSWER -Private residence must connect if w/in 300' or for
any commercial bldg. w/in 300' that has flows less than 1500 gpd. Commercial w/ flows = to or
greater than 1500 gpd must connect if sewer is w/in 1000'.
Unless physical barrier, ordinance, or cannot be done w/ individual line (4" line)-then PSD
system is OK.
Acceptable Pipe Materials - CORRECT ANSWER -Vitrified clay, ductile iron, or plastic.
Anything after the tank or from distribution box has to be vitrified clay or plastic.
Schedule 40 or Greater - CORRECT ANSWER -under roads, driveways, or parking areas
Gravity Slope - CORRECT ANSWER -Diameter: 4" pipe + min. slope of 12" per 100'
Building sewers in excess of 50' should have what? - CORRECT ANSWER -A C/O @ least every 50'
from building to tank, distribution box, or ATU
Creviced Limestone Formation - CORRECT ANSWER -SS system cannot be installed where
bottom of system is less than 4' from top of limestone
If limestone is known to be present a soil test must be done @ least 4' deeper than where the
bottom of the trench will be
How far away can quick disconnect be? - CORRECT ANSWER -no more than 50' away from the
device & w/in sight of
,Experimental Use Permits - CORRECT ANSWER -min. of 10 experimental systems installed b4
unconditional approval granted. Permit valid for 2 yrs & evaluated @ end of 2 yrs.
2 options for garbage grinders - CORRECT ANSWER -1. solids retention tank btwn WW source &
septic tk. for kitchen waste only. Needs to be 50% of the size of the designed septic tank w/ a
min. of 500 gals.
2. A septic tank receiving all flows sized as 50% of the septic tank size + septic tank size. i.e.,
septic tk = 1500 gals. /2 = 750 + 1500 = 2250 (would need 2500 gal tk)
How long should a homeowner keep maint. records for their system? - CORRECT ANSWER -the
life of the system
When should the 1st maintenance of a septic tank after installation be completed for a
residence? - CORRECT ANSWER -Prior to or within 3 yrs. After initial inspection it can be done
once every 5 yrs. Can be done by everyone + homeowner
If sludge layer /suspended solids are greater than 33% . . . - CORRECT ANSWER -Must pump tank
and perform maintenance
When should a septic system be evaluated initially after installation for a non-residential bldg? -
CORRECT ANSWER -prior to or w/in 3 yrs. After that it should be done @ least every 3 yrs.
Owner cannot do. has to be engineer, env. health practitioner, member of dept, HD, or septic
contractor
Aerobic Treatment Unit Evaluations - CORRECT ANSWER -1 every 6 mos @ least (same ppl) +
HOMEOWNER as long as they follow manufacturer's requirements & proper maintenance
What is the maint. schedule for SFs & WSPs w/ surface discharges? - CORRECT ANSWER -@ least
1 per yr. + H.O. if rules r followed. Pumped when solids & scum greater than 33%
, Can a H.O. install & maintain a septic system on his/her property? - CORRECT ANSWER -Yes
Who can perform the excavation for a septic system? - CORRECT ANSWER -A licensed installer
(employee while supervised) or the property owner.
What is the min. size tank for flows UP TO 500 gpd? - CORRECT ANSWER -750 gals.
If flows are greater than 500 gpd, how do you size the tank? - CORRECT ANSWER -Tank size
should be = to @ least 1.5x the estimated sewage flow
How do you size a tank(s) for flows greater than 1350 gpd? - CORRECT ANSWER -U must use
multiple tks. in a series or multiple compartment tks. where the 1st tank or the 1st comp. in a
multicomp. tk. is 1/2-2/3 of the total required capacity. of the tank(s)
How do you size the tank for a raised filter bed for a residence? - CORRECT ANSWER -It has to be
an NSF 40 batch treatment system. The aeration tank has to be 2x the daily flow
How do you size the tank for a RFB for a commercial bldg? - CORRECT ANSWER -The aeration tk.
has to be 3x the daily flow.
Multiple tanks in a series connected @ btm for flow equalization can be used
How are RFB sidewalls sized? - CORRECT ANSWER -3:1 ratio
How are distribution lines for RFBs? - CORRECT ANSWER -4" perforated pipe on 15" centers
Describe a RFB mantle - CORRECT ANSWER -Mantle must go in 6" deep to original soil. Torpedo
sand depth is 12" ttl. (0.5-2.0). Sand filter media depth is 30".
WITH CORRECT ANSWERS 2025/2026
Public Sewer Connection - CORRECT ANSWER -Private residence must connect if w/in 300' or for
any commercial bldg. w/in 300' that has flows less than 1500 gpd. Commercial w/ flows = to or
greater than 1500 gpd must connect if sewer is w/in 1000'.
Unless physical barrier, ordinance, or cannot be done w/ individual line (4" line)-then PSD
system is OK.
Acceptable Pipe Materials - CORRECT ANSWER -Vitrified clay, ductile iron, or plastic.
Anything after the tank or from distribution box has to be vitrified clay or plastic.
Schedule 40 or Greater - CORRECT ANSWER -under roads, driveways, or parking areas
Gravity Slope - CORRECT ANSWER -Diameter: 4" pipe + min. slope of 12" per 100'
Building sewers in excess of 50' should have what? - CORRECT ANSWER -A C/O @ least every 50'
from building to tank, distribution box, or ATU
Creviced Limestone Formation - CORRECT ANSWER -SS system cannot be installed where
bottom of system is less than 4' from top of limestone
If limestone is known to be present a soil test must be done @ least 4' deeper than where the
bottom of the trench will be
How far away can quick disconnect be? - CORRECT ANSWER -no more than 50' away from the
device & w/in sight of
,Experimental Use Permits - CORRECT ANSWER -min. of 10 experimental systems installed b4
unconditional approval granted. Permit valid for 2 yrs & evaluated @ end of 2 yrs.
2 options for garbage grinders - CORRECT ANSWER -1. solids retention tank btwn WW source &
septic tk. for kitchen waste only. Needs to be 50% of the size of the designed septic tank w/ a
min. of 500 gals.
2. A septic tank receiving all flows sized as 50% of the septic tank size + septic tank size. i.e.,
septic tk = 1500 gals. /2 = 750 + 1500 = 2250 (would need 2500 gal tk)
How long should a homeowner keep maint. records for their system? - CORRECT ANSWER -the
life of the system
When should the 1st maintenance of a septic tank after installation be completed for a
residence? - CORRECT ANSWER -Prior to or within 3 yrs. After initial inspection it can be done
once every 5 yrs. Can be done by everyone + homeowner
If sludge layer /suspended solids are greater than 33% . . . - CORRECT ANSWER -Must pump tank
and perform maintenance
When should a septic system be evaluated initially after installation for a non-residential bldg? -
CORRECT ANSWER -prior to or w/in 3 yrs. After that it should be done @ least every 3 yrs.
Owner cannot do. has to be engineer, env. health practitioner, member of dept, HD, or septic
contractor
Aerobic Treatment Unit Evaluations - CORRECT ANSWER -1 every 6 mos @ least (same ppl) +
HOMEOWNER as long as they follow manufacturer's requirements & proper maintenance
What is the maint. schedule for SFs & WSPs w/ surface discharges? - CORRECT ANSWER -@ least
1 per yr. + H.O. if rules r followed. Pumped when solids & scum greater than 33%
, Can a H.O. install & maintain a septic system on his/her property? - CORRECT ANSWER -Yes
Who can perform the excavation for a septic system? - CORRECT ANSWER -A licensed installer
(employee while supervised) or the property owner.
What is the min. size tank for flows UP TO 500 gpd? - CORRECT ANSWER -750 gals.
If flows are greater than 500 gpd, how do you size the tank? - CORRECT ANSWER -Tank size
should be = to @ least 1.5x the estimated sewage flow
How do you size a tank(s) for flows greater than 1350 gpd? - CORRECT ANSWER -U must use
multiple tks. in a series or multiple compartment tks. where the 1st tank or the 1st comp. in a
multicomp. tk. is 1/2-2/3 of the total required capacity. of the tank(s)
How do you size the tank for a raised filter bed for a residence? - CORRECT ANSWER -It has to be
an NSF 40 batch treatment system. The aeration tank has to be 2x the daily flow
How do you size the tank for a RFB for a commercial bldg? - CORRECT ANSWER -The aeration tk.
has to be 3x the daily flow.
Multiple tanks in a series connected @ btm for flow equalization can be used
How are RFB sidewalls sized? - CORRECT ANSWER -3:1 ratio
How are distribution lines for RFBs? - CORRECT ANSWER -4" perforated pipe on 15" centers
Describe a RFB mantle - CORRECT ANSWER -Mantle must go in 6" deep to original soil. Torpedo
sand depth is 12" ttl. (0.5-2.0). Sand filter media depth is 30".
