Texas On-Site Sewage Facility (OSSF) Installer II – TCEQ Exam
Prep questions & answers & rationale | 2025/2026 | Latest Update|
Instant download!!
1. A residential home produces an estimated 450 gallons of wastewater per day. Which size septic tank
is required according to TCEQ guidelines?
A. 500 gallons
B. 750 gallons
C. 1,000 gallons (correct answer)
D. 1,500 gallons
Rationale: TCEQ requires minimum tank sizes based on daily flow; for homes producing 400–600 GPD,
1,000 gallons is standard.
2. A drain field trench is 100 feet long and 3 feet wide. If the trench absorption rate is 0.6 GPD/sq ft,
what is the maximum daily flow it can handle?
A. 180 GPD
B. 1800 GPD
C. 180 sq ft × 0.6 GPD/sq ft = 108 GPD (correct answer)
D. 600 GPD
Rationale: Daily absorption = trench area × soil absorption rate (100 × 3 × 0.6 = 180 GPD).
(Note: In actual TCEQ calculations, you would use per-foot per-linear-foot absorption values; the principle
is illustrated here.)
3. Which type of alternative system is recommended when native soil is highly restrictive clay?
A. Conventional trench
B. Mound system (correct answer)
C. Standard septic tank only
D. Evapotranspiration system
,Rationale: Mound systems elevate the treatment zone, allowing effluent to percolate through engineered
soil above restrictive native soil.
4. An aerobic treatment unit (ATU) produces effluent with 30 mg/L BOD. What is the primary
purpose of this treatment?
A. Remove solids only
B. Reduce organic load before absorption field (correct answer)
C. Increase hydraulic flow
D. Direct discharge to stream
Rationale: ATUs provide higher treatment than conventional tanks by reducing biological oxygen demand
(BOD).
5. Which of the following is true regarding the use of pressure distribution in OSSF?
A. Only for gravity-fed systems
B. Allows uniform effluent distribution in low-permeability soils (correct answer)
C. Eliminates need for tanks
D. Not approved by TCEQ
Rationale: Pressurized systems prevent trench overloading and improve soil treatment.
6. A property requires a trench system on a sloped site. What is the maximum recommended slope for
trench installation?
A. 2%
B. 5% (correct answer)
C. 10%
D. No limit
Rationale: Excessive slope can cause uneven effluent distribution; TCEQ limits slope for gravity-fed
trenches.
, 7. In a repair scenario, effluent is surfacing at multiple points. What is the most likely cause?
A. Low water usage
B. Hydraulic overload or clogged absorption field (correct answer)
C. High percolation rate
D. Tank too large
Rationale: Surfacing effluent indicates the system cannot handle the volume or is obstructed.
8. Which of the following is true for septic tank compartmentalization in high-flow applications?
A. Not necessary
B. Multiple compartments improve solids settling and retention (correct answer)
C. Only affects flow rate
D. Reduces tank volume
Rationale: Compartments increase retention time and prevent solids from entering the field.
9. A trench absorption field is designed for 1,200 GPD. If the soil percolation rate is 0.4 GPD/sq ft,
what is the minimum trench area required?
A. 3,000 sq ft
B. 4,800 sq ft
C. 1,200 ÷ 0.4 = 3,000 sq ft (correct answer)
D. 1,500 sq ft
Rationale: Minimum area = daily flow ÷ percolation rate (1,200 ÷ 0.4 = 3,000 sq ft).
10. Which of the following is required for ATU installation?
A. Gravity-only design
B. Electrical power supply, pump, and aeration components (correct answer)
C. Direct discharge to surface
D. No permit
Rationale: ATUs rely on mechanical aeration and pumps to treat effluent effectively.
Prep questions & answers & rationale | 2025/2026 | Latest Update|
Instant download!!
1. A residential home produces an estimated 450 gallons of wastewater per day. Which size septic tank
is required according to TCEQ guidelines?
A. 500 gallons
B. 750 gallons
C. 1,000 gallons (correct answer)
D. 1,500 gallons
Rationale: TCEQ requires minimum tank sizes based on daily flow; for homes producing 400–600 GPD,
1,000 gallons is standard.
2. A drain field trench is 100 feet long and 3 feet wide. If the trench absorption rate is 0.6 GPD/sq ft,
what is the maximum daily flow it can handle?
A. 180 GPD
B. 1800 GPD
C. 180 sq ft × 0.6 GPD/sq ft = 108 GPD (correct answer)
D. 600 GPD
Rationale: Daily absorption = trench area × soil absorption rate (100 × 3 × 0.6 = 180 GPD).
(Note: In actual TCEQ calculations, you would use per-foot per-linear-foot absorption values; the principle
is illustrated here.)
3. Which type of alternative system is recommended when native soil is highly restrictive clay?
A. Conventional trench
B. Mound system (correct answer)
C. Standard septic tank only
D. Evapotranspiration system
,Rationale: Mound systems elevate the treatment zone, allowing effluent to percolate through engineered
soil above restrictive native soil.
4. An aerobic treatment unit (ATU) produces effluent with 30 mg/L BOD. What is the primary
purpose of this treatment?
A. Remove solids only
B. Reduce organic load before absorption field (correct answer)
C. Increase hydraulic flow
D. Direct discharge to stream
Rationale: ATUs provide higher treatment than conventional tanks by reducing biological oxygen demand
(BOD).
5. Which of the following is true regarding the use of pressure distribution in OSSF?
A. Only for gravity-fed systems
B. Allows uniform effluent distribution in low-permeability soils (correct answer)
C. Eliminates need for tanks
D. Not approved by TCEQ
Rationale: Pressurized systems prevent trench overloading and improve soil treatment.
6. A property requires a trench system on a sloped site. What is the maximum recommended slope for
trench installation?
A. 2%
B. 5% (correct answer)
C. 10%
D. No limit
Rationale: Excessive slope can cause uneven effluent distribution; TCEQ limits slope for gravity-fed
trenches.
, 7. In a repair scenario, effluent is surfacing at multiple points. What is the most likely cause?
A. Low water usage
B. Hydraulic overload or clogged absorption field (correct answer)
C. High percolation rate
D. Tank too large
Rationale: Surfacing effluent indicates the system cannot handle the volume or is obstructed.
8. Which of the following is true for septic tank compartmentalization in high-flow applications?
A. Not necessary
B. Multiple compartments improve solids settling and retention (correct answer)
C. Only affects flow rate
D. Reduces tank volume
Rationale: Compartments increase retention time and prevent solids from entering the field.
9. A trench absorption field is designed for 1,200 GPD. If the soil percolation rate is 0.4 GPD/sq ft,
what is the minimum trench area required?
A. 3,000 sq ft
B. 4,800 sq ft
C. 1,200 ÷ 0.4 = 3,000 sq ft (correct answer)
D. 1,500 sq ft
Rationale: Minimum area = daily flow ÷ percolation rate (1,200 ÷ 0.4 = 3,000 sq ft).
10. Which of the following is required for ATU installation?
A. Gravity-only design
B. Electrical power supply, pump, and aeration components (correct answer)
C. Direct discharge to surface
D. No permit
Rationale: ATUs rely on mechanical aeration and pumps to treat effluent effectively.
