Wastewater pathogen and vector attraction reduction practice questions
20 free practice questions from 40 CFR Part 503 Subpart D. Each answer is explained and linked to the rule it comes from.
Wastewater pathogen and vector attraction reduction
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Scope and definitions
1. Which example does the 503.31(d) definition give of land with a high potential for public exposure?
- A. Agricultural land
- B. Forest
- C. A reclamation site located in a populated area
- D. A reclamation site located in an unpopulated area
Show answer
Answer: C. A reclamation site located in a populated area
Land with a high potential for public exposure "includes, but is not limited to, a public contact site and a reclamation site located in a populated area". Agricultural land, forest and a reclamation site in an unpopulated area are the examples of land with a low potential for public exposure.
Source: eCFR: 40 CFR 503.31, Special definitions (as of Nov 4, 2026)
2. Under 503.31(j), what term names organic materials in sewage sludge that have not been treated in either an aerobic or anaerobic treatment process?
- A. Unstabilized solids
- B. Volatile solids
- C. Total solids
- D. Pathogenic organisms
Show answer
Answer: A. Unstabilized solids
"Unstabilized solids are organic materials in sewage sludge that have not been treated in either an aerobic or anaerobic treatment process." Volatile solids, by contrast, "is the amount of the total solids in sewage sludge lost when the sewage sludge is combusted at 550 degrees Celsius in the presence of excess air."
Source: eCFR: 40 CFR 503.31, Special definitions (as of Nov 4, 2026)
Class A: general rule and Alternatives 1 and 2
3. Under 503.32(a)(1), what must a sewage sludge meet to be classified Class A with respect to pathogens?
- A. All six alternatives in 503.32(a)(3) through (a)(8)
- B. Any two of the alternatives in 503.32(a)(3) through (a)(8)
- C. Only Alternative 1 in 503.32(a)(3)
- D. The requirement in 503.32(a)(2) and one of the alternatives in 503.32(a)(3) through (a)(8)
Show answer
Answer: D. The requirement in 503.32(a)(2) and one of the alternatives in 503.32(a)(3) through (a)(8)
"The requirement in § 503.32(a)(2) and the requirements in either § 503.32(a)(3), (a)(4), (a)(5), (a)(6), (a)(7), or (a)(8) shall be met for a sewage sludge to be classified Class A with respect to pathogens."
4. 503.32(a)(2) says the Class A pathogen requirements must be met either before or at the same time as the vector attraction reduction requirements. Which vector attraction reduction requirements does it except from that order?
- A. 503.33(b)(1) through (b)(3)
- B. 503.33(b)(6) through (b)(8)
- C. 503.33(b)(9) and (b)(10)
- D. 503.33(b)(11) and (b)(12)
Show answer
Answer: B. 503.33(b)(6) through (b)(8)
The Class A requirements "shall be met either prior to meeting or at the same time the vector attraction reduction requirements in § 503.33, except the vector attraction reduction requirements in § 503.33 (b)(6) through (b)(8), are met."
5. Under Class A Alternative 2, what must be done with the sewage sludge at the end of the 72 hour period during which its pH is above 12?
- A. Add more alkali so the pH stays at 11.5 or higher for an additional 22 hours
- B. Air dry it to achieve a percent solids in the sewage sludge greater than 50 percent
- C. Heat it to 70 degrees Celsius or higher for 30 minutes or longer
- D. Inject it below the land surface within one hour
Show answer
Answer: B. Air dry it to achieve a percent solids in the sewage sludge greater than 50 percent
"At the end of the 72 hour period during which the pH of the sewage sludge is above 12, the sewage sludge shall be air dried to achieve a percent solids in the sewage sludge greater than 50 percent." During that period the temperature must also be "above 52 degrees Celsius for 12 hours or longer".
6. Under Class A Alternative 1, what time period does 503.32(a)(3)(ii)(B) set when the sludge is seven percent solids or higher and small particles of sludge are heated by warmed gases or an immiscible liquid?
- A. 20 minutes or longer
- B. 30 minutes or longer
- C. 72 hours
- D. 15 seconds or longer
Show answer
Answer: D. 15 seconds or longer
In that case "the temperature of the sewage sludge shall be 50 degrees Celsius or higher; the time period shall be 15 seconds or longer; and the temperature and time period shall be determined using equation (2)." The 20-minute period in (A) applies "except when small particles of sewage sludge are heated by either warmed gases or an immiscible liquid."
Class A: Alternatives 3 to 6
7. Under Class A Alternative 3, when the enteric virus density before pathogen treatment is less than one Plaque-forming Unit per four grams of total solids, how long is the sludge Class A with respect to enteric viruses?
- A. Until the next monitoring episode for the sewage sludge
- B. For one year
- C. For 30 days
- D. Until the end of the 72 hour period
Show answer
Answer: A. Until the next monitoring episode for the sewage sludge
In that case "the sewage sludge is Class A with respect to enteric viruses until the next monitoring episode for the sewage sludge."
8. Under Class A Alternative 4, 503.32(a)(6)(ii) sets an enteric virus density of less than one Plaque-forming Unit per four grams of total solids (dry weight basis). Which of these is one of the times that paragraph lists for meeting it?
- A. Only before pathogen treatment
- B. Within eight hours after discharge from the pathogen treatment process
- C. At the time the sewage sludge is used or disposed
- D. At the end of the 72 hour period of high pH
Show answer
Answer: C. At the time the sewage sludge is used or disposed
"The density of enteric viruses in the sewage sludge shall be less than one Plaque-forming Unit per four grams of total solids (dry weight basis) at the time the sewage sludge is used or disposed"; the paragraph also lists the time the sludge is prepared for sale or give away in a bag or other container, and the time it is prepared to meet 503.10 (b), (c), (e), or (f).
9. Under Class A Alternative 6, who determines that a process is equivalent to a Process to Further Reduce Pathogens?
- A. The permitting authority
- B. The person who prepares the sewage sludge
- C. The person who applies the sewage sludge
- D. The owner of the land where the sludge is applied
Show answer
Answer: A. The permitting authority
The sludge "shall be treated in a process that is equivalent to a Process to Further Reduce Pathogens, as determined by the permitting authority."
Class B pathogen requirements and site restrictions
10. Under 503.32(b)(1)(ii), when must the site restrictions in 503.32(b)(5) be met?
- A. Only when the sewage sludge is placed on an active sewage sludge unit
- B. Only when the sewage sludge is sold or given away in a bag or other container
- C. Only when Class B Alternative 1 is the requirement used
- D. When sewage sludge that meets the Class B pathogen requirements in 503.32(b)(2), (b)(3), or (b)(4) is applied to the land
Show answer
Answer: D. When sewage sludge that meets the Class B pathogen requirements in 503.32(b)(2), (b)(3), or (b)(4) is applied to the land
"The site restrictions in § 503.32(b)(5) shall be met when sewage sludge that meets the Class B pathogen requirements in § 503.32(b)(2), (b)(3), or (b)(4) is applied to the land."
11. For food crops with harvested parts below the land surface, what decides whether the 20-month or the 38-month harvest restriction in 503.32(b)(5) applies?
- A. Whether the land has a high or low potential for public exposure
- B. How long the sewage sludge remains on the land surface prior to incorporation into the soil
- C. The percent solids of the sewage sludge
- D. Which Class B alternative the sewage sludge met
Show answer
Answer: B. How long the sewage sludge remains on the land surface prior to incorporation into the soil
The 20-month restriction applies "when the sewage sludge remains on the land surface for four months or longer prior to incorporation into the soil" and the 38-month restriction "when the sewage sludge remains on the land surface for less than four months prior to incorporation into the soil."
12. When does the one-year turf harvest restriction in 503.32(b)(5)(vi) apply, unless otherwise specified by the permitting authority?
- A. Whenever turf is grown on any land where sewage sludge is applied
- B. Only when animals have grazed on the land
- C. When the harvested turf is placed on either land with a high potential for public exposure or a lawn
- D. Only when the sewage sludge was injected below the land surface
Show answer
Answer: C. When the harvested turf is placed on either land with a high potential for public exposure or a lawn
Turf "shall not be harvested for one year after application of the sewage sludge when the harvested turf is placed on either land with a high potential for public exposure or a lawn, unless otherwise specified by the permitting authority."
Domestic septage
13. Domestic septage applied to agricultural land, forest, or a reclamation site meets the pH option in 503.32(c)(2). Which site restrictions must still be met?
- A. None; the pH treatment replaces the site restrictions
- B. Only the grazing restriction in 503.32(b)(5)(v)
- C. Only the public access restrictions in 503.32(b)(5)(vii) and (viii)
- D. The site restrictions in 503.32(b)(5)(i) through (b)(5)(iv)
Show answer
Answer: D. The site restrictions in 503.32(b)(5)(i) through (b)(5)(iv)
The pH must be raised to 12 or higher and remain there for 30 minutes "and the site restrictions in § 503.32 (b)(5)(i) through (b)(5)(iv) shall be met."
14. Domestic septage is applied to a forest without its pH being raised. Which pathogen requirement in 503.32(c) must then be met?
- A. The site restrictions in 503.32(b)(5)
- B. Incorporation of the septage into the soil within six hours after application
- C. Covering the septage with soil or other material at the end of each operating day
- D. None; domestic septage applied to a forest has no pathogen requirement
Show answer
Answer: A. The site restrictions in 503.32(b)(5)
Under 503.32(c)(1), "The site restrictions in § 503.32(b)(5) shall be met when domestic septage is applied to agricultural land, forest, or a reclamation site"; the other option, (c)(2), requires the pH to be raised "to 12 or higher by alkali addition".
Where each vector attraction reduction option applies
15. What range of vector attraction reduction options does 503.33(a)(2) name for bulk sewage sludge applied to a lawn or a home garden?
- A. One of 503.33(b)(1) through (b)(10)
- B. One of 503.33(b)(1) through (b)(11)
- C. One of 503.33(b)(1) through (b)(8)
- D. One of 503.33(b)(9), (b)(10), or (b)(12)
Show answer
Answer: C. One of 503.33(b)(1) through (b)(8)
"One of the vector attraction reduction requirements in § 503.33 (b)(1) through (b)(8) shall be met when bulk sewage sludge is applied to a lawn or a home garden."
Source: eCFR: 40 CFR 503.33, Vector attraction reduction (as of Nov 4, 2026)
16. Sewage sludge other than domestic septage is placed on an active sewage sludge unit. Which set of vector attraction reduction options does 503.33(a)(4) say one must be met from?
- A. One of 503.33(b)(1) through (b)(12)
- B. One of 503.33(b)(1) through (b)(11)
- C. One of 503.33(b)(9) through (b)(12)
- D. Only 503.33(b)(12)
Show answer
Answer: B. One of 503.33(b)(1) through (b)(11)
"One of the vector attraction reduction requirements in § 503.33 (b)(1) through (b)(11) shall be met when sewage sludge (other than domestic septage) is placed on an active sewage sludge unit."
Source: eCFR: 40 CFR 503.33, Vector attraction reduction (as of Nov 4, 2026)
Vector attraction reduction options
17. For the aerobic bench-scale option in 503.33(b)(3), what percent solids must the portion of previously digested sewage sludge have?
- A. Two percent or less
- B. Seven percent or higher
- C. 75 percent or more
- D. Greater than 50 percent
Show answer
Answer: A. Two percent or less
The option digests "a portion of the previously digested sewage sludge that has a percent solids of two percent or less aerobically in the laboratory in a bench-scale unit for 30 additional days at 20 degrees Celsius."
Source: eCFR: 40 CFR 503.33, Vector attraction reduction (as of Nov 4, 2026)
18. What decides whether the 75 percent solids option in 503.33(b)(7) or the 90 percent solids option in 503.33(b)(8) applies?
- A. Whether the sludge is Class A or Class B
- B. Whether the sludge was aerobically or anaerobically digested
- C. Whether the sludge will be applied to a lawn or to agricultural land
- D. Whether the sludge contains unstabilized solids generated in a primary wastewater treatment process
Show answer
Answer: D. Whether the sludge contains unstabilized solids generated in a primary wastewater treatment process
(b)(7) covers sewage sludge "that does not contain unstabilized solids generated in a primary wastewater treatment process" and (b)(8) covers sewage sludge "that contains unstabilized solids generated in a primary wastewater treatment process".
Source: eCFR: 40 CFR 503.33, Vector attraction reduction (as of Nov 4, 2026)
19. Under vector attraction reduction option 503.33(b)(9), when the sewage sludge injected below the surface of the land is Class A with respect to pathogens, it must be injected within eight hours after what event?
- A. Being sampled for fecal coliform
- B. Being discharged from the pathogen treatment process
- C. Being loaded onto the application vehicle
- D. The last rainfall on the land application site
Show answer
Answer: B. Being discharged from the pathogen treatment process
Under 503.33(b)(9)(iii), "when the sewage sludge that is injected below the surface of the land is Class A with respect to pathogens, the sewage sludge shall be injected below the land surface within eight hours after being discharged from the pathogen treatment process."
Source: eCFR: 40 CFR 503.33, Vector attraction reduction (as of Nov 4, 2026)
Appendix B pathogen treatment processes
20. Appendix B describes air drying as a Process to Significantly Reduce Pathogens. What condition must hold during two of the three months the sewage sludge dries?
- A. The sewage sludge is turned at least five times
- B. The pH of the sewage sludge stays at 12 or higher
- C. The ambient average daily temperature is above zero degrees Celsius
- D. The sewage sludge is covered with soil at the end of each operating day
Show answer
Answer: C. The ambient average daily temperature is above zero degrees Celsius
"Air drying—Sewage sludge is dried on sand beds or on paved or unpaved basins. The sewage sludge dries for a minimum of three months. During two of the three months, the ambient average daily temperature is above zero degrees Celsius."
Source: eCFR: 40 CFR Part 503, Appendix B (as of Nov 4, 2026)