TCEQ Wastewater Collection
System Operator Class III Exam
Questions and Correct Answers
with Detailed Rationales |
2026/2027 Edition | Exam Prep
Study Guide PDF
1. Which condition in a wastewater collection system most
directly increases the likelihood of hydrogen sulfide
generation?
A. High dissolved oxygen concentration
B. Low organic loading
C. Anaerobic conditions with abundant organic matter
D. Excessive pipeline slope
Answer: C. Anaerobic conditions with abundant organic
matter
Hydrogen sulfide (H₂S) is commonly produced when sulfate-
reducing bacteria metabolize organic material under anaerobic
conditions. These conditions frequently develop in low-flow or
stagnant portions of collection systems, force mains, wet wells,
and other areas where oxygen is depleted. H₂S can create severe
odor problems and can be oxidized to sulfuric acid, which
contributes to corrosion of concrete and other materials.
,2. A collection system operator observes that a gravity sewer
is consistently surcharging during periods of normal dry-
weather flow. What should be investigated first?
A. Chlorine residual
B. Downstream restrictions or blockages
C. Influent wastewater temperature
D. Aeration basin dissolved oxygen
Answer: B. Downstream restrictions or blockages
Persistent surcharge in a gravity sewer indicates that the flow is
being restricted or that the downstream system cannot convey
the incoming wastewater adequately. The operator should
investigate possible blockages, collapsed pipe, excessive
sediment, root intrusion, or downstream hydraulic restrictions.
CCTV inspection, manhole observations, and flow measurements
can help identify the source.
3. What is the primary purpose of a sewer manhole?
A. Increase wastewater dissolved oxygen
B. Provide access for inspection, maintenance, and cleaning
C. Remove suspended solids from wastewater
D. Disinfect wastewater before treatment
Answer: B. Provide access for inspection, maintenance, and
cleaning
Manholes provide personnel access to portions of a collection
system for inspection, cleaning, maintenance, and other
operational activities. They may also serve as locations where
sewer alignment, grade, pipe size, or direction changes. Because
,manholes are potentially confined spaces, entry requires
appropriate safety procedures and atmospheric testing.
4. Which measurement is especially important before an
operator enters a potentially hazardous sewer manhole?
A. Barometric pressure only
B. Atmospheric oxygen concentration and toxic or combustible
gases
C. Wastewater color only
D. Pipe diameter only
Answer: B. Atmospheric oxygen concentration and toxic or
combustible gases
Wastewater collection structures can contain oxygen-deficient,
toxic, or combustible atmospheres. Before entry, atmospheric
conditions must be evaluated using properly calibrated
equipment. Oxygen concentration, combustible gases, and
relevant toxic gases such as hydrogen sulfide should be
considered. Continuous monitoring may also be required
because conditions can change while work is underway.
5. What is a major advantage of preventive sewer cleaning?
A. It eliminates the need for inspections
B. It can reduce emergency blockages and sanitary sewer
overflows
C. It eliminates infiltration and inflow completely
D. It increases wastewater strength
, Answer: B. It can reduce emergency blockages and sanitary
sewer overflows
Preventive cleaning removes accumulated grease, grit, roots, and
other materials before they create significant restrictions. A
properly designed preventive maintenance program uses
historical blockage information, inspection results, pipe
characteristics, and flow conditions to determine appropriate
cleaning frequencies. It does not eliminate all blockages, but it
can significantly reduce avoidable failures.
6. Which condition is most characteristic of infiltration?
A. Rainwater entering through a storm drain connection
B. Groundwater entering through defective joints or cracks
C. Grease entering from a restaurant
D. Wastewater discharged from a residential fixture
Answer: B. Groundwater entering through defective joints or
cracks
Infiltration is groundwater that enters a sanitary sewer through
defects such as cracked pipe, defective joints, deteriorated
manholes, or improperly sealed connections. Inflow, by contrast,
generally refers to relatively rapid entry of surface or stormwater
through sources such as roof drains, yard drains, or improper
storm connections. Both infiltration and inflow can increase
collection-system flows.
7. During CCTV inspection, an operator observes roots
extending through a pipe joint. What is the most appropriate
interpretation?
System Operator Class III Exam
Questions and Correct Answers
with Detailed Rationales |
2026/2027 Edition | Exam Prep
Study Guide PDF
1. Which condition in a wastewater collection system most
directly increases the likelihood of hydrogen sulfide
generation?
A. High dissolved oxygen concentration
B. Low organic loading
C. Anaerobic conditions with abundant organic matter
D. Excessive pipeline slope
Answer: C. Anaerobic conditions with abundant organic
matter
Hydrogen sulfide (H₂S) is commonly produced when sulfate-
reducing bacteria metabolize organic material under anaerobic
conditions. These conditions frequently develop in low-flow or
stagnant portions of collection systems, force mains, wet wells,
and other areas where oxygen is depleted. H₂S can create severe
odor problems and can be oxidized to sulfuric acid, which
contributes to corrosion of concrete and other materials.
,2. A collection system operator observes that a gravity sewer
is consistently surcharging during periods of normal dry-
weather flow. What should be investigated first?
A. Chlorine residual
B. Downstream restrictions or blockages
C. Influent wastewater temperature
D. Aeration basin dissolved oxygen
Answer: B. Downstream restrictions or blockages
Persistent surcharge in a gravity sewer indicates that the flow is
being restricted or that the downstream system cannot convey
the incoming wastewater adequately. The operator should
investigate possible blockages, collapsed pipe, excessive
sediment, root intrusion, or downstream hydraulic restrictions.
CCTV inspection, manhole observations, and flow measurements
can help identify the source.
3. What is the primary purpose of a sewer manhole?
A. Increase wastewater dissolved oxygen
B. Provide access for inspection, maintenance, and cleaning
C. Remove suspended solids from wastewater
D. Disinfect wastewater before treatment
Answer: B. Provide access for inspection, maintenance, and
cleaning
Manholes provide personnel access to portions of a collection
system for inspection, cleaning, maintenance, and other
operational activities. They may also serve as locations where
sewer alignment, grade, pipe size, or direction changes. Because
,manholes are potentially confined spaces, entry requires
appropriate safety procedures and atmospheric testing.
4. Which measurement is especially important before an
operator enters a potentially hazardous sewer manhole?
A. Barometric pressure only
B. Atmospheric oxygen concentration and toxic or combustible
gases
C. Wastewater color only
D. Pipe diameter only
Answer: B. Atmospheric oxygen concentration and toxic or
combustible gases
Wastewater collection structures can contain oxygen-deficient,
toxic, or combustible atmospheres. Before entry, atmospheric
conditions must be evaluated using properly calibrated
equipment. Oxygen concentration, combustible gases, and
relevant toxic gases such as hydrogen sulfide should be
considered. Continuous monitoring may also be required
because conditions can change while work is underway.
5. What is a major advantage of preventive sewer cleaning?
A. It eliminates the need for inspections
B. It can reduce emergency blockages and sanitary sewer
overflows
C. It eliminates infiltration and inflow completely
D. It increases wastewater strength
, Answer: B. It can reduce emergency blockages and sanitary
sewer overflows
Preventive cleaning removes accumulated grease, grit, roots, and
other materials before they create significant restrictions. A
properly designed preventive maintenance program uses
historical blockage information, inspection results, pipe
characteristics, and flow conditions to determine appropriate
cleaning frequencies. It does not eliminate all blockages, but it
can significantly reduce avoidable failures.
6. Which condition is most characteristic of infiltration?
A. Rainwater entering through a storm drain connection
B. Groundwater entering through defective joints or cracks
C. Grease entering from a restaurant
D. Wastewater discharged from a residential fixture
Answer: B. Groundwater entering through defective joints or
cracks
Infiltration is groundwater that enters a sanitary sewer through
defects such as cracked pipe, defective joints, deteriorated
manholes, or improperly sealed connections. Inflow, by contrast,
generally refers to relatively rapid entry of surface or stormwater
through sources such as roof drains, yard drains, or improper
storm connections. Both infiltration and inflow can increase
collection-system flows.
7. During CCTV inspection, an operator observes roots
extending through a pipe joint. What is the most appropriate
interpretation?
