, Question 1
A site has a soil profile with a 30 cm thick A horizon, a 60 cm thick Bt horizon
(30% clay), and a C horizon with 5% clay. The seasonal high water table is at
90 cm. According to Utah on-site wastewater rules, which limiting condition
most likely dictates the required vertical separation and system type?
A. The Bt horizon restricts permeability, requiring a pressure distribution
system.
B. The seasonal high water table at 90 cm requires a minimum 60 cm
separation and may allow a standard trench system.
C. The sandy C horizon provides adequate permeability, so a
conventional system is acceptable.
D. The shallow A horizon limits depth, requiring an elevated mound
system.
Correct Answer: A - The Bt horizon restricts permeability,
requiring a pressure distribution system.
RATIONALE
The Bt horizon with 30% clay has a permeability that often limits
absorption, necessitating pressure distribution to avoid ponding. The
water table at 90 cm may require additional separation, but the
clay-rich horizon is the primary limiting factor. Options B, C, and D
misjudge the restrictive Bt layer or overstate the suitability of the
sandy C horizon.
Question 2
In a recirculating sand filter, the recirculation ratio is 4:1. If the forward flow is
1,000 L/day, what is the total hydraulic loading rate applied to the filter media?
A. 1,000 L/day
B. 4,000 L/day
C. 5,000 L/day
D. 3,000 L/day
Page 2
,Correct Answer: C - 5,000 L/day
RATIONALE
Total hydraulic loading = forward flow + recirculated flow = 1,000 +
(4 × 1,000) = 5,000 L/day. Recirculation ratio is the ratio of
recirculated flow to forward flow, so total is forward times (1 + ratio).
Options A, B, and D incorrectly apply the ratio or ignore one flow
component.
Question 3
A homeowner reports sewage surfacing in the yard after heavy rain. The
system is a conventional septic tank with a gravity-fed drainfield. Which of the
following is the most likely primary cause?
A. Hydraulic overload of the soil absorption field due to increased water
infiltration.
B. Failure of the septic tank baffle causing solids carryover.
C. Inadequate venting of the plumbing system.
D. Excessive sludge accumulation in the septic tank.
Correct Answer: A - Hydraulic overload of the soil absorption
field due to increased water infiltration.
RATIONALE
Heavy rain raises the water table and saturates the soil, reducing its
capacity to absorb effluent, leading to surfacing. Baffle failure or
sludge accumulation would cause solids to enter the field, but
surfacing after rain is classic hydraulic overload. Venting issues
typically cause indoor odors, not outdoor surfacing.
Question 4
When designing a mound system, which of the following factors is most
critical in determining the mound height above the natural ground surface?
A. Depth to the seasonal high water table or bedrock.
Page 3
, B. The slope of the site.
C. The permeability of the fill sand.
D. The daily wastewater flow rate.
Correct Answer: A - Depth to the seasonal high water table or
bedrock.
RATIONALE
Mound height is primarily set to provide the required vertical
separation between the infiltrative surface and the limiting condition
(water table, bedrock, or impermeable layer). Slope, fill permeability,
and flow rate affect mound dimensions and loading rates but not the
critical separation distance that dictates height. Thus, A is the most
critical.
Question 5
A septic tank serving a 4-bedroom home has a liquid capacity of 3,800 L. The
local health department requires a minimum retention time of 24 hours at
design flow. If the design flow is 1,500 L/day, what is the actual retention time,
and does it meet the requirement?
A. 2.5 days; meets requirement.
B. 1.5 days; meets requirement.
C. 2.5 days; does not meet requirement.
D. 1.5 days; does not meet requirement.
Correct Answer: A - 2.5 days; meets requirement.
RATIONALE
Retention time = tank volume / daily flow = 3,800 L / 1,500 L/day =
2.53 days (about 2.5 days), which exceeds the 24-hour minimum.
Therefore, it meets the requirement. Options B and D miscalculate the
retention time; C incorrectly states it does not meet the requirement.
Page 4
A site has a soil profile with a 30 cm thick A horizon, a 60 cm thick Bt horizon
(30% clay), and a C horizon with 5% clay. The seasonal high water table is at
90 cm. According to Utah on-site wastewater rules, which limiting condition
most likely dictates the required vertical separation and system type?
A. The Bt horizon restricts permeability, requiring a pressure distribution
system.
B. The seasonal high water table at 90 cm requires a minimum 60 cm
separation and may allow a standard trench system.
C. The sandy C horizon provides adequate permeability, so a
conventional system is acceptable.
D. The shallow A horizon limits depth, requiring an elevated mound
system.
Correct Answer: A - The Bt horizon restricts permeability,
requiring a pressure distribution system.
RATIONALE
The Bt horizon with 30% clay has a permeability that often limits
absorption, necessitating pressure distribution to avoid ponding. The
water table at 90 cm may require additional separation, but the
clay-rich horizon is the primary limiting factor. Options B, C, and D
misjudge the restrictive Bt layer or overstate the suitability of the
sandy C horizon.
Question 2
In a recirculating sand filter, the recirculation ratio is 4:1. If the forward flow is
1,000 L/day, what is the total hydraulic loading rate applied to the filter media?
A. 1,000 L/day
B. 4,000 L/day
C. 5,000 L/day
D. 3,000 L/day
Page 2
,Correct Answer: C - 5,000 L/day
RATIONALE
Total hydraulic loading = forward flow + recirculated flow = 1,000 +
(4 × 1,000) = 5,000 L/day. Recirculation ratio is the ratio of
recirculated flow to forward flow, so total is forward times (1 + ratio).
Options A, B, and D incorrectly apply the ratio or ignore one flow
component.
Question 3
A homeowner reports sewage surfacing in the yard after heavy rain. The
system is a conventional septic tank with a gravity-fed drainfield. Which of the
following is the most likely primary cause?
A. Hydraulic overload of the soil absorption field due to increased water
infiltration.
B. Failure of the septic tank baffle causing solids carryover.
C. Inadequate venting of the plumbing system.
D. Excessive sludge accumulation in the septic tank.
Correct Answer: A - Hydraulic overload of the soil absorption
field due to increased water infiltration.
RATIONALE
Heavy rain raises the water table and saturates the soil, reducing its
capacity to absorb effluent, leading to surfacing. Baffle failure or
sludge accumulation would cause solids to enter the field, but
surfacing after rain is classic hydraulic overload. Venting issues
typically cause indoor odors, not outdoor surfacing.
Question 4
When designing a mound system, which of the following factors is most
critical in determining the mound height above the natural ground surface?
A. Depth to the seasonal high water table or bedrock.
Page 3
, B. The slope of the site.
C. The permeability of the fill sand.
D. The daily wastewater flow rate.
Correct Answer: A - Depth to the seasonal high water table or
bedrock.
RATIONALE
Mound height is primarily set to provide the required vertical
separation between the infiltrative surface and the limiting condition
(water table, bedrock, or impermeable layer). Slope, fill permeability,
and flow rate affect mound dimensions and loading rates but not the
critical separation distance that dictates height. Thus, A is the most
critical.
Question 5
A septic tank serving a 4-bedroom home has a liquid capacity of 3,800 L. The
local health department requires a minimum retention time of 24 hours at
design flow. If the design flow is 1,500 L/day, what is the actual retention time,
and does it meet the requirement?
A. 2.5 days; meets requirement.
B. 1.5 days; meets requirement.
C. 2.5 days; does not meet requirement.
D. 1.5 days; does not meet requirement.
Correct Answer: A - 2.5 days; meets requirement.
RATIONALE
Retention time = tank volume / daily flow = 3,800 L / 1,500 L/day =
2.53 days (about 2.5 days), which exceeds the 24-hour minimum.
Therefore, it meets the requirement. Options B and D miscalculate the
retention time; C incorrectly states it does not meet the requirement.
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