OSSF DR TEST PRACTICE 2025/2026 | TEXAS TCEQ OSSF DESIGNATED REPRESENTATIVE EXAM PRE –QUESTIONS AND CORRECT
ANSWERS (VERIFIED ANSWERS) PLUS RATIONALES 2026 Q&A | INSTANT DOWNLOAD PDF.
Core Domains
Texas Administrative Code (TAC) Chapter 285 Regulations
Site Evaluation and Soil Analysis Methodologies
OSSF Planning, System Selection, and Design Criteria
Permitting, Inspection Protocols, and Enforcement
Standard Treatment System Components and Operation
Advanced Treatment Technologies and Aerobic Treatment Units (ATUs)
Disposal and Utilization Methods (Standard and Proprietary)
Professional Ethics, Legal Responsibilities, and Public Health Protection
Introduction
The purpose of this comprehensive assessment is to evaluate the technical competence, regulatory knowledge, and field-readiness of
candidates seeking certification as a Texas Commission on Environmental Quality (TCEQ) On-Site Sewage Facility (OSSF) Designated
Representative (DR). This examination assesses critical skills in site evaluation, regulatory compliance, enforcement procedures, and
system design verification. Composed of objective multiple-choice questions and complex, field-relevant scenario-based problems, the
exam requires candidates to demonstrate higher-order critical thinking and practical decision-making. Emphasizing real-world
applications, it ensures that Designated Representatives can effectively protect public health and water resources by enforcing state and
local OSSF rules with absolute precision and ethical integrity.
SECTION ONE: QUESTIONS 1–100
Question 1
According to 30 TAC Chapter 285, what is the minimum separation distance required between an On-Site Sewage Facility (OSSF) disposal field and
a public water supply well?
A. 50 feet
B. 100 feet
,C. 150 feet
D. 1 dry-period crack width
🟢 C. 150 feet
🔴 RATIONALE: Under TCEQ 30 TAC Chapter 285, the mandatory minimum horizontal separation distance between any OSSF disposal
component and a public water supply well is 150 feet to mitigate the risk of biological and chemical contamination of public drinking water.
Question 2
During a routine site evaluation, a Designated Representative (DR) identifies a soil horizon with distinct redoximorphic features (mottling) at a depth
of 18 inches below the natural ground surface. How does this finding impact the design of a standard subsurface disposal system?
A. It restricts the installation depth of a standard absorptive drainfield because it indicates a seasonal high water table.
B. It has no impact on system design if the soil texture is classified as Class III.
C. It requires the immediate installation of a holding tank with no soil discharge.
D. It allows the installer to use a deeper trench design to bypass the mottled layer.
🟢 A. It restricts the installation depth of a standard absorptive drainfield because it indicates a seasonal high water table.
🔴 RATIONALE: Redoximorphic features or soil mottling signify periodic or seasonal soil saturation (a high water table). 30 TAC Chapter 285
mandates that the bottom of a standard subsurface disposal trench must maintain a minimum separation (typically 24 inches) above this restrictive
horizon or seasonal high-water mark.
Question 3
An OSSF installer submits a design for a single-family residence with 4 bedrooms and a total living area of 3,200 square feet. The design utilizes
water-saving plumbing fixtures. What is the minimum daily wastewater design flow rate required by Texas regulations?
A. 240 gallons per day
B. 300 gallons per day
C. 360 gallons per day
D. 420 gallons per day
🟢 C. 360 gallons per day
🔴 RATIONALE: According to the TCEQ design criteria tables in 30 TAC Chapter 285, a 4-bedroom residence with a living area between 2,501 and
3,500 square feet utilizing water-saving fixtures is assigned a minimum design flow of 360 gallons per day.
Question 4
,A homeowner requests a permit to install an OSSF on a 0.40-acre tract that was platted in 2010. The tract is served by a public water supply. Does
this tract meet the minimum lot size requirements for an OSSF under standard state rules?
A. Yes, because it is served by a public water supply, which requires a minimum of 0.50 acres, but grandfathering applies automatically.
B. No, because the minimum lot size for a property served by a public water supply and utilizing an OSSF is 0.50 acres.
C. Yes, because the minimum lot size for any property with an OSSF is 0.25 acres regardless of water source.
D. No, because all OSSFs require a minimum of 1.0 acre regardless of the water source or platting date.
🟢 B. No, because the minimum lot size for a property served by a public water supply and utilizing an OSSF is 0.50 acres.
🔴 RATIONALE: For lots platted after the effective date of the current rules without an authorized local order variance, TCEQ rules mandate a
minimum lot size of 0.50 acres when served by a public water supply, and 1.0 acre when served by a private well. A 0.40-acre tract platted in 2010
fails this requirement.
Question 5
While inspecting an aerobic treatment unit (ATU) utilizing surface application (spray irrigation), the DR notices that the chlorine residual in the pump
chamber is 0.0 mg/L. Which action should the DR take immediately?
A. Issue an approval for the system but note the deficiency on the final inspection report.
B. Fail the inspection, issue a non-compliance notice, and require the addition of proper chlorine tablets or liquid chlorination before re-inspection.
C. Allow the homeowner to manually pour household bleach directly into the spray field.
D. Instruct the installer to increase the pump runtime to compensate for the lack of disinfectant.
🟢 B. Fail the inspection, issue a non-compliance notice, and require the addition of proper chlorine tablets or liquid chlorination before re-
inspection.
🔴 RATIONALE: Surface application systems require continuous, effective disinfection to protect public health from aerosolized pathogens. A
chlorine residual of at least 0.1 mg/L (or 0.5 mg/L free chlorine depending on specific local order variations/testing methods) must be maintained; a
0.0 mg/L reading represents an immediate biological hazard and regulatory failure.
Question 6
Which of the following soil classes possesses the highest clay content, exhibits the lowest permeability, and is generally considered unsuitable for a
standard conventional subsurface absorptive drainfield without modification?
A. Class Ia
B. Class Ib
C. Class III
D. Class IV
, 🟢 D. Class IV
🔴 RATIONALE: Class IV soils consist of heavy clays (such as silty clay, sandy clay, and clay). These soils have very low hydraulic conductivity and
high shrink-swell potential, making them unsuitable for standard absorptive drainfields. They require alternative or advanced treatment and disposal
methods.
Question 7
A DR notices that a licensed installer is constructing an OSSF without an approved "Authorization to Construct" permit from the local Authorized
Agent. What enforcement action is most appropriate?
A. Allow construction to finish and review the plans later.
B. Verbal warning only, as long as the installer has a valid TCEQ license.
C. Issue a formal Stop Work Order and a notice of violation for installing a system without a permit.
D. Fine the homeowner directly while permitting the installer to complete work.
🟢 C. Issue a formal Stop Work Order and a notice of violation for installing a system without a permit.
🔴 RATIONALE: Under Texas law and TCEQ rules, no person may construct, alter, repair, or extend an OSSF without first obtaining an
Authorization to Construct from the permitting authority. Proceeding without this document warrants an immediate Stop Work Order and regulatory
enforcement.
Question 8
What is the primary operational objective of a two-compartment septic tank or two tanks installed in series within a conventional OSSF system?
A. To provide advanced secondary aerobic treatment of organic solids.
B. To enhance primary settling of settleable solids and separation of fats, oils, and grease (FOG) before effluent discharges to the disposal field.
C. To maximize the volatilization of volatile organic compounds through atmospheric venting.
D. To accelerate the evaporation rate of liquid wastewater.
🟢 B. To enhance primary settling of settleable solids and separation of fats, oils, and grease (FOG) before effluent discharges to the disposal field.
🔴 RATIONALE: The primary chamber facilitates the settling of heavy solids (sludge) and the flotation of lighter materials (scum/FOG). The second
chamber provides additional retention time for finer particles to settle out, protecting the downstream disposal system from clogging.
Question 9
A site evaluator performs a ribbon test on a soil sample and determines that it forms a flexible, shiny ribbon longer than 2 inches, feels sticky and
plastic when wet, and leaves a significant stain on the fingers. Which soil class does this sample belong to?
ANSWERS (VERIFIED ANSWERS) PLUS RATIONALES 2026 Q&A | INSTANT DOWNLOAD PDF.
Core Domains
Texas Administrative Code (TAC) Chapter 285 Regulations
Site Evaluation and Soil Analysis Methodologies
OSSF Planning, System Selection, and Design Criteria
Permitting, Inspection Protocols, and Enforcement
Standard Treatment System Components and Operation
Advanced Treatment Technologies and Aerobic Treatment Units (ATUs)
Disposal and Utilization Methods (Standard and Proprietary)
Professional Ethics, Legal Responsibilities, and Public Health Protection
Introduction
The purpose of this comprehensive assessment is to evaluate the technical competence, regulatory knowledge, and field-readiness of
candidates seeking certification as a Texas Commission on Environmental Quality (TCEQ) On-Site Sewage Facility (OSSF) Designated
Representative (DR). This examination assesses critical skills in site evaluation, regulatory compliance, enforcement procedures, and
system design verification. Composed of objective multiple-choice questions and complex, field-relevant scenario-based problems, the
exam requires candidates to demonstrate higher-order critical thinking and practical decision-making. Emphasizing real-world
applications, it ensures that Designated Representatives can effectively protect public health and water resources by enforcing state and
local OSSF rules with absolute precision and ethical integrity.
SECTION ONE: QUESTIONS 1–100
Question 1
According to 30 TAC Chapter 285, what is the minimum separation distance required between an On-Site Sewage Facility (OSSF) disposal field and
a public water supply well?
A. 50 feet
B. 100 feet
,C. 150 feet
D. 1 dry-period crack width
🟢 C. 150 feet
🔴 RATIONALE: Under TCEQ 30 TAC Chapter 285, the mandatory minimum horizontal separation distance between any OSSF disposal
component and a public water supply well is 150 feet to mitigate the risk of biological and chemical contamination of public drinking water.
Question 2
During a routine site evaluation, a Designated Representative (DR) identifies a soil horizon with distinct redoximorphic features (mottling) at a depth
of 18 inches below the natural ground surface. How does this finding impact the design of a standard subsurface disposal system?
A. It restricts the installation depth of a standard absorptive drainfield because it indicates a seasonal high water table.
B. It has no impact on system design if the soil texture is classified as Class III.
C. It requires the immediate installation of a holding tank with no soil discharge.
D. It allows the installer to use a deeper trench design to bypass the mottled layer.
🟢 A. It restricts the installation depth of a standard absorptive drainfield because it indicates a seasonal high water table.
🔴 RATIONALE: Redoximorphic features or soil mottling signify periodic or seasonal soil saturation (a high water table). 30 TAC Chapter 285
mandates that the bottom of a standard subsurface disposal trench must maintain a minimum separation (typically 24 inches) above this restrictive
horizon or seasonal high-water mark.
Question 3
An OSSF installer submits a design for a single-family residence with 4 bedrooms and a total living area of 3,200 square feet. The design utilizes
water-saving plumbing fixtures. What is the minimum daily wastewater design flow rate required by Texas regulations?
A. 240 gallons per day
B. 300 gallons per day
C. 360 gallons per day
D. 420 gallons per day
🟢 C. 360 gallons per day
🔴 RATIONALE: According to the TCEQ design criteria tables in 30 TAC Chapter 285, a 4-bedroom residence with a living area between 2,501 and
3,500 square feet utilizing water-saving fixtures is assigned a minimum design flow of 360 gallons per day.
Question 4
,A homeowner requests a permit to install an OSSF on a 0.40-acre tract that was platted in 2010. The tract is served by a public water supply. Does
this tract meet the minimum lot size requirements for an OSSF under standard state rules?
A. Yes, because it is served by a public water supply, which requires a minimum of 0.50 acres, but grandfathering applies automatically.
B. No, because the minimum lot size for a property served by a public water supply and utilizing an OSSF is 0.50 acres.
C. Yes, because the minimum lot size for any property with an OSSF is 0.25 acres regardless of water source.
D. No, because all OSSFs require a minimum of 1.0 acre regardless of the water source or platting date.
🟢 B. No, because the minimum lot size for a property served by a public water supply and utilizing an OSSF is 0.50 acres.
🔴 RATIONALE: For lots platted after the effective date of the current rules without an authorized local order variance, TCEQ rules mandate a
minimum lot size of 0.50 acres when served by a public water supply, and 1.0 acre when served by a private well. A 0.40-acre tract platted in 2010
fails this requirement.
Question 5
While inspecting an aerobic treatment unit (ATU) utilizing surface application (spray irrigation), the DR notices that the chlorine residual in the pump
chamber is 0.0 mg/L. Which action should the DR take immediately?
A. Issue an approval for the system but note the deficiency on the final inspection report.
B. Fail the inspection, issue a non-compliance notice, and require the addition of proper chlorine tablets or liquid chlorination before re-inspection.
C. Allow the homeowner to manually pour household bleach directly into the spray field.
D. Instruct the installer to increase the pump runtime to compensate for the lack of disinfectant.
🟢 B. Fail the inspection, issue a non-compliance notice, and require the addition of proper chlorine tablets or liquid chlorination before re-
inspection.
🔴 RATIONALE: Surface application systems require continuous, effective disinfection to protect public health from aerosolized pathogens. A
chlorine residual of at least 0.1 mg/L (or 0.5 mg/L free chlorine depending on specific local order variations/testing methods) must be maintained; a
0.0 mg/L reading represents an immediate biological hazard and regulatory failure.
Question 6
Which of the following soil classes possesses the highest clay content, exhibits the lowest permeability, and is generally considered unsuitable for a
standard conventional subsurface absorptive drainfield without modification?
A. Class Ia
B. Class Ib
C. Class III
D. Class IV
, 🟢 D. Class IV
🔴 RATIONALE: Class IV soils consist of heavy clays (such as silty clay, sandy clay, and clay). These soils have very low hydraulic conductivity and
high shrink-swell potential, making them unsuitable for standard absorptive drainfields. They require alternative or advanced treatment and disposal
methods.
Question 7
A DR notices that a licensed installer is constructing an OSSF without an approved "Authorization to Construct" permit from the local Authorized
Agent. What enforcement action is most appropriate?
A. Allow construction to finish and review the plans later.
B. Verbal warning only, as long as the installer has a valid TCEQ license.
C. Issue a formal Stop Work Order and a notice of violation for installing a system without a permit.
D. Fine the homeowner directly while permitting the installer to complete work.
🟢 C. Issue a formal Stop Work Order and a notice of violation for installing a system without a permit.
🔴 RATIONALE: Under Texas law and TCEQ rules, no person may construct, alter, repair, or extend an OSSF without first obtaining an
Authorization to Construct from the permitting authority. Proceeding without this document warrants an immediate Stop Work Order and regulatory
enforcement.
Question 8
What is the primary operational objective of a two-compartment septic tank or two tanks installed in series within a conventional OSSF system?
A. To provide advanced secondary aerobic treatment of organic solids.
B. To enhance primary settling of settleable solids and separation of fats, oils, and grease (FOG) before effluent discharges to the disposal field.
C. To maximize the volatilization of volatile organic compounds through atmospheric venting.
D. To accelerate the evaporation rate of liquid wastewater.
🟢 B. To enhance primary settling of settleable solids and separation of fats, oils, and grease (FOG) before effluent discharges to the disposal field.
🔴 RATIONALE: The primary chamber facilitates the settling of heavy solids (sludge) and the flotation of lighter materials (scum/FOG). The second
chamber provides additional retention time for finer particles to settle out, protecting the downstream disposal system from clogging.
Question 9
A site evaluator performs a ribbon test on a soil sample and determines that it forms a flexible, shiny ribbon longer than 2 inches, feels sticky and
plastic when wet, and leaves a significant stain on the fingers. Which soil class does this sample belong to?
