2025 TEXAS CLASS D WATER
OPERATOR LICENSE – COMPLETE
PRACTICA EXAM & STUDY GUIDE
PART 1: TEXAS CLASS D WATER LICENSE –
CORE KNOWLEDGE DOMAINS
Domain 1: Regulations & Reporting (2025 TCEQ Focus)
Primary Standards (enforceable MCLs - Maximum Contaminant Levels) protect
health (e.g., MCL for arsenic is 0.010 mg/L). Secondary Standards
(non-enforceable guidelines) address aesthetic effects like taste, odor, and color
(e.g., secondary MCL for iron is 0.3 mg/L). The Safe Drinking Water Act
(SDWA) is federal law, implemented in Texas by TCEQ, which sets MCLs, MCLGs
(non-enforceable health goals), and MRDLs (Maximum Residual Disinfectant
Levels). Mandatory Reporting: Monthly Operating Reports (MORs) are due by
the 10th of the following month. Non-compliance (e.g., MCL exceedance) must
be reported to TCEQ within 48 hours. Consumer Confidence Reports (CCRs)
must be completed by July 1st and distributed to all customers annually. 2025
Update: TCEQ has begun requiring monitoring for PFAS under the Unregulated
Contaminant Monitoring Rule (UCMR 5).
Domain 2: Water Sources & Characteristics
Groundwater (from wells or springs) is generally lower in turbidity and
microorganisms but can have high levels of minerals like iron, manganese, and
nitrates. Surface Water (from rivers, lakes) is higher in turbidity, organic
matter, and pathogens, requiring more extensive treatment. Key water quality
parameters: Turbidity (measured in NTU; lower is better for disinfection), pH
(must be 6.5-8.5 per secondary standards), Alkalinity (buffering capacity), and
Hardness (calcium/magnesium content). Source water protection includes
establishing Wellhead Protection Areas (WHPAs) to prevent contamination.
Domain 3: Treatment Processes – Disinfection & Corrosion
Control
Chlorination is the primary disinfection method. Forms include chlorine gas
(Cl₂), sodium hypochlorite (liquid bleach), and calcium hypochlorite (solid).
Chlorine demand is the amount of chlorine consumed by organic/inorganic
,matter before a residual is achieved. Breakpoint chlorination is the point
where chlorine demand is satisfied, and a free chlorine residual begins to form.
The CT Value (Concentration x Time) must be met to inactivate pathogens like
Giardia. The system must maintain a minimum chlorine residual of 0.2 mg/L
at the farthest point in the distribution system. Corrosion control is achieved
by adjusting pH and alkalinity to form a protective scale inside pipes.
Domain 4: Treatment Processes – Coagulation, Flocculation,
Sedimentation, Filtration
Coagulation adds chemicals (alum, ferric chloride) to neutralize particle
charges. Flocculation gently mixes water to form larger, settleable flocs.
Sedimentation allows flocs to settle out in a basin. Filtration passes water
through media (e.g., rapid sand) to remove remaining particles. Jar testing is
used to determine the optimal coagulant dose. Filters must be backwashed
when the head loss becomes too great or the effluent turbidity rises. Backwash
waste must be handled properly. Filter effluent turbidity must be continuously
monitored and kept below 0.3 NTU.
Domain 5: Distribution System Operation & Maintenance
The distribution system includes mains (pipes), valves, fire hydrants,
service lines, and storage tanks. A minimum pressure of 20 psi must be
maintained to prevent contamination. New mains or repairs must be
disinfected using a chlorine solution (slug method, typically 50-100 mg/L) and
tested with bacteriological samples before being put into service.
Cross-connection control prevents contamination via backflow. Backflow types
are backsiphonage (negative pressure) and backpressure (higher pressure in
customer system). Devices include Reduced Pressure Zone (RPZ) assemblies
for high hazards. Regular flushing programs remove sediment and maintain
water quality.
Domain 6: Safety, Mathematics, & Records
Confined Space Entry (e.g., clearwells, tanks) requires a permit, trained
attendant, atmospheric testing, and proper PPE. Chemical Safety: An SDS
(Safety Data Sheet) must be available for all chemicals, and appropriate PPE
(gloves, goggles, respirator for chlorine) must be worn. Water Math is critical:
calculating chemical dosages (e.g., lbs/day = flow (MGD) x concentration (mg/L)
x 8.34), volumes (cylindrical tank volume = πr²h), and flow rates. All operational
data, lab results, and maintenance activities must be recorded in a permanent,
legible logbook, which is a legal document subject to TCEQ inspection.
, PART 2: COMPREHENSIVE 75-QUESTION
PRACTICE EXAM
1. During routine sampling, a Class D operator collects a raw water sample that
tests positive for total coliform bacteria. According to 2025 TCEQ rules, what is
the **MANDATORY** immediate follow-up action?
A) Increase the chlorine feed at the plant and record the change in the logbook.
B) Collect a set of repeat samples from the same location and from adjacent
locations within 24 hours.
C) Notify the mayor and issue a "Boil Water Notice" to all customers
immediately.
D) Shut down the well and switch to an alternate water source.
Answer: B
*The Total Coliform Rule (TCR) requires specific follow-up actions for a positive
sample. The first mandatory step is to collect repeat samples to confirm the
result and check for contamination in the distribution system before any public
notification is considered. A Boil Water Notice is triggered by E. coli confirmation,
not total coliform alone. (30 TAC §290.109(f)(2)(A))*
2. What is the primary purpose of the Safe Drinking Water Act (SDWA)?
A) To regulate the construction of new water treatment plants
B) To protect public health by regulating public drinking water supplies
C) To ensure all Texas residents have access to water
D) To set water rates for municipal utilities
Answer: B
*The SDWA is the main federal law that ensures the safety of public drinking
water. It authorizes the EPA to set national health-based standards for drinking
water to protect against both naturally occurring and man-made contaminants.
TCEQ enforces these standards in Texas. (SDWA, 42 U.S.C. §300f et seq.)*
3. A Class D water system must submit its Monthly Operating Report (MOR) to
TCEQ by what date?
A) The last day of the month being reported
B) The 15th of the following month
C) The 10th of the following month
D) Within 30 days of the end of the quarter
Answer: C
*TCEQ requires all public water systems to submit a completed Monthly
Operating Report (MOR) on or before the 10th day of the month following the
month being reported. This is a key compliance requirement. (30 TAC
§290.39(a))*
4. Which of the following is an example of a Secondary Maximum Contaminant
Level (SMCL)?
A) Arsenic: 0.010 mg/L
B) Nitrate: 10 mg/L
C) Fluoride: 4.0 mg/L
D) Iron: 0.3 mg/L
OPERATOR LICENSE – COMPLETE
PRACTICA EXAM & STUDY GUIDE
PART 1: TEXAS CLASS D WATER LICENSE –
CORE KNOWLEDGE DOMAINS
Domain 1: Regulations & Reporting (2025 TCEQ Focus)
Primary Standards (enforceable MCLs - Maximum Contaminant Levels) protect
health (e.g., MCL for arsenic is 0.010 mg/L). Secondary Standards
(non-enforceable guidelines) address aesthetic effects like taste, odor, and color
(e.g., secondary MCL for iron is 0.3 mg/L). The Safe Drinking Water Act
(SDWA) is federal law, implemented in Texas by TCEQ, which sets MCLs, MCLGs
(non-enforceable health goals), and MRDLs (Maximum Residual Disinfectant
Levels). Mandatory Reporting: Monthly Operating Reports (MORs) are due by
the 10th of the following month. Non-compliance (e.g., MCL exceedance) must
be reported to TCEQ within 48 hours. Consumer Confidence Reports (CCRs)
must be completed by July 1st and distributed to all customers annually. 2025
Update: TCEQ has begun requiring monitoring for PFAS under the Unregulated
Contaminant Monitoring Rule (UCMR 5).
Domain 2: Water Sources & Characteristics
Groundwater (from wells or springs) is generally lower in turbidity and
microorganisms but can have high levels of minerals like iron, manganese, and
nitrates. Surface Water (from rivers, lakes) is higher in turbidity, organic
matter, and pathogens, requiring more extensive treatment. Key water quality
parameters: Turbidity (measured in NTU; lower is better for disinfection), pH
(must be 6.5-8.5 per secondary standards), Alkalinity (buffering capacity), and
Hardness (calcium/magnesium content). Source water protection includes
establishing Wellhead Protection Areas (WHPAs) to prevent contamination.
Domain 3: Treatment Processes – Disinfection & Corrosion
Control
Chlorination is the primary disinfection method. Forms include chlorine gas
(Cl₂), sodium hypochlorite (liquid bleach), and calcium hypochlorite (solid).
Chlorine demand is the amount of chlorine consumed by organic/inorganic
,matter before a residual is achieved. Breakpoint chlorination is the point
where chlorine demand is satisfied, and a free chlorine residual begins to form.
The CT Value (Concentration x Time) must be met to inactivate pathogens like
Giardia. The system must maintain a minimum chlorine residual of 0.2 mg/L
at the farthest point in the distribution system. Corrosion control is achieved
by adjusting pH and alkalinity to form a protective scale inside pipes.
Domain 4: Treatment Processes – Coagulation, Flocculation,
Sedimentation, Filtration
Coagulation adds chemicals (alum, ferric chloride) to neutralize particle
charges. Flocculation gently mixes water to form larger, settleable flocs.
Sedimentation allows flocs to settle out in a basin. Filtration passes water
through media (e.g., rapid sand) to remove remaining particles. Jar testing is
used to determine the optimal coagulant dose. Filters must be backwashed
when the head loss becomes too great or the effluent turbidity rises. Backwash
waste must be handled properly. Filter effluent turbidity must be continuously
monitored and kept below 0.3 NTU.
Domain 5: Distribution System Operation & Maintenance
The distribution system includes mains (pipes), valves, fire hydrants,
service lines, and storage tanks. A minimum pressure of 20 psi must be
maintained to prevent contamination. New mains or repairs must be
disinfected using a chlorine solution (slug method, typically 50-100 mg/L) and
tested with bacteriological samples before being put into service.
Cross-connection control prevents contamination via backflow. Backflow types
are backsiphonage (negative pressure) and backpressure (higher pressure in
customer system). Devices include Reduced Pressure Zone (RPZ) assemblies
for high hazards. Regular flushing programs remove sediment and maintain
water quality.
Domain 6: Safety, Mathematics, & Records
Confined Space Entry (e.g., clearwells, tanks) requires a permit, trained
attendant, atmospheric testing, and proper PPE. Chemical Safety: An SDS
(Safety Data Sheet) must be available for all chemicals, and appropriate PPE
(gloves, goggles, respirator for chlorine) must be worn. Water Math is critical:
calculating chemical dosages (e.g., lbs/day = flow (MGD) x concentration (mg/L)
x 8.34), volumes (cylindrical tank volume = πr²h), and flow rates. All operational
data, lab results, and maintenance activities must be recorded in a permanent,
legible logbook, which is a legal document subject to TCEQ inspection.
, PART 2: COMPREHENSIVE 75-QUESTION
PRACTICE EXAM
1. During routine sampling, a Class D operator collects a raw water sample that
tests positive for total coliform bacteria. According to 2025 TCEQ rules, what is
the **MANDATORY** immediate follow-up action?
A) Increase the chlorine feed at the plant and record the change in the logbook.
B) Collect a set of repeat samples from the same location and from adjacent
locations within 24 hours.
C) Notify the mayor and issue a "Boil Water Notice" to all customers
immediately.
D) Shut down the well and switch to an alternate water source.
Answer: B
*The Total Coliform Rule (TCR) requires specific follow-up actions for a positive
sample. The first mandatory step is to collect repeat samples to confirm the
result and check for contamination in the distribution system before any public
notification is considered. A Boil Water Notice is triggered by E. coli confirmation,
not total coliform alone. (30 TAC §290.109(f)(2)(A))*
2. What is the primary purpose of the Safe Drinking Water Act (SDWA)?
A) To regulate the construction of new water treatment plants
B) To protect public health by regulating public drinking water supplies
C) To ensure all Texas residents have access to water
D) To set water rates for municipal utilities
Answer: B
*The SDWA is the main federal law that ensures the safety of public drinking
water. It authorizes the EPA to set national health-based standards for drinking
water to protect against both naturally occurring and man-made contaminants.
TCEQ enforces these standards in Texas. (SDWA, 42 U.S.C. §300f et seq.)*
3. A Class D water system must submit its Monthly Operating Report (MOR) to
TCEQ by what date?
A) The last day of the month being reported
B) The 15th of the following month
C) The 10th of the following month
D) Within 30 days of the end of the quarter
Answer: C
*TCEQ requires all public water systems to submit a completed Monthly
Operating Report (MOR) on or before the 10th day of the month following the
month being reported. This is a key compliance requirement. (30 TAC
§290.39(a))*
4. Which of the following is an example of a Secondary Maximum Contaminant
Level (SMCL)?
A) Arsenic: 0.010 mg/L
B) Nitrate: 10 mg/L
C) Fluoride: 4.0 mg/L
D) Iron: 0.3 mg/L
