WALMART - STORMWATER EXAM ACTUAL AND
100% CORRECT ANSWERS
1. A large retail distribution center in a watershed with a Total Maximum Daily Load (TMDL) for
sediment is required to implement stormwater control measures (SCMs). The site has a high
percentage of impervious cover and compacted soils. Which combination of SCMs would most
effectively reduce sediment loading while also providing volume reduction for the 90th percentile
storm event?
A. Proprietary hydrodynamic separators and dry detention basins
B. Vegetated swales and rain gardens
C. Permeable pavement and bioretention cells
D. Cisterns and green roofs
Answer: C
2. Under the EPA's 2015 Effluent Limitations Guidelines and Standards for the Construction and
Development Point Source Category, what is the minimum frequency for inspecting erosion and
sediment control measures during the active construction phase when the site receives 0.5 inches of
rain in a 24-hour period?
A. Once per week
B. Within 24 hours of the rain event
C. Daily during the rain event
D. Every 7 days and within 24 hours of a 0.5-inch rain event
Answer: D
3. A stormwater management plan for a Walmart Supercenter includes a proprietary
underground detention system. The site's pre-development runoff curve number (CN) is 65, and
post-development CN is 85. Using the NRCS method, what is the approximate increase in runoff
volume for a 10-year, 24-hour storm with total rainfall of 5.0 inches? (Assume initial abstraction Ia
= 0.2S, where S = (1000/CN) - 10)
A. 0.5 inches
B. 1.2 inches
C. 2.0 inches
D. 3.1 inches
Answer: B
4. Which of the following best describes the primary purpose of a stormwater pollution prevention
plan (SWPPP) under the Clean Water Act's NPDES permit for industrial activities?
A. To eliminate all stormwater discharge from the site
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,B. To identify potential sources of pollution and describe control measures to reduce the discharge of pollutants
to the maximum extent practicable
C. To monitor groundwater quality beneath the facility
D. To provide a record of all chemical spills for regulatory reporting
Answer: B
5. A Walmart distribution center is located in a karst terrain region. The stormwater management
plan must include special provisions. Which of the following is the most critical design
consideration for stormwater detention in karst areas?
A. Maximize infiltration to reduce runoff volume
B. Ensure detention basins are lined to prevent sinkhole formation
C. Use only vegetative swales for conveyance
D. Design for the 100-year storm event with no overflow
Answer: B
6. A post-construction stormwater management plan for a Walmart store must comply with local
water quality volume (WQv) requirements. The site has 4 acres of impervious cover and 1 acre of
pervious area. The local jurisdiction requires treating the first 1 inch of runoff from the entire site.
Using the volumetric runoff coefficient (C = 0.9 for impervious, 0.2 for pervious), what is the
required WQv in acre-feet?
A. 0.25 acre-feet
B. 0.30 acre-feet
C. 0.35 acre-feet
D. 0.40 acre-feet
Answer: C
7. During a storm event, a Walmart facility's stormwater outfall is sampled and shows a pH of
10.5. The facility's NPDES permit requires pH between 6.0 and 9.0. Which of the following is the
most likely cause of this exceedance?
A. Leaching from concrete washout areas
B. Spilled diesel fuel from a delivery truck
C. Decomposition of organic matter in a detention pond
D. Acid rain mixing with alkaline soil
Answer: A
8. A Walmart store's stormwater management system includes a bioretention cell designed to treat
runoff from a 2-acre parking lot. The design infiltration rate of the native soil is 0.5 in/hr. The cell
has a surface area of 0.25 acres and a ponding depth of 12 inches. What is the maximum
drawdown time for the ponded water, assuming no underdrain? (Ignore evapotranspiration and
assume uniform infiltration)
A. 12 hours
B. 24 hours
C. 36 hours
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,D. 48 hours
Answer: B
9. A Walmart distribution center is subject to the EPA's Multi-Sector General Permit (MSGP) for
stormwater discharges associated with industrial activity. The facility performs vehicle
maintenance and has a fleet of trucks. Which of the following is a required element of the SWPPP
for this sector?
A. A spill response plan for hazardous materials that includes quarterly drills
B. A quarterly monitoring program for all outfalls during storm events
C. A narrative description of potential pollutant sources and the BMPs implemented
D. A requirement to install oil-water separators on all parking lot drains
Answer: C
10. A Walmart store's stormwater pond is designed to provide water quality treatment for the first
flush. The pond's permanent pool volume is 0.5 acre-feet, and the water quality volume (WQv) is
0.8 acre-feet. If the pond has a length-to-width ratio of 3:1 and a forebay, what is the primary
function of the forebay?
A. To increase the pond's storage capacity for flood control
B. To trap coarse sediments and reduce maintenance of the main pond
C. To promote algal growth for nutrient uptake
D. To provide habitat for aquatic species
Answer: B
11. A large retail distribution center is located in a watershed designated as a Total Maximum
Daily Load (TMDL) for sediment. The facility's stormwater pollution prevention plan (SWPPP)
includes a sediment basin designed to remove 80% of total suspended solids (TSS). During a
compliance inspection, it is discovered that the basin's outlet structure has been modified to
increase discharge rate by 50%. Which of the following is the most probable consequence of this
modification?
A. Reduced TSS removal efficiency due to decreased residence time
B. Increased groundwater recharge due to higher infiltration
C. Enhanced pollutant removal due to increased turbulence
D. No impact on TSS removal if the basin volume remains unchanged
Answer: A
12. A retail facility's stormwater outfall is sampled quarterly for compliance with a site-specific
numeric effluent limit for zinc. The last four samples show concentrations of 0.12, 0.15, 0.09, and
0.18 mg/L. The permit limit is 0.14 mg/L as an average of four consecutive samples. Which of the
following actions is most appropriate based on these data?
A. Submit a notice of non-compliance because the average exceeds the limit
B. Take no action because the last sample is below the limit
C. Report compliance because the average of the four samples is exactly 0.135 mg/L
D. Initiate a targeted source investigation for zinc
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, Answer: C
13. During a storm event, a Walmart facility's stormwater retention pond overflows into a
neighboring wetland. The SWPPP identifies the pond as designed for a 25-year, 24-hour storm.
The actual storm that caused the overflow is later determined to have a return period of 50 years.
Which of the following statements best describes the legal and operational implications?
A. The facility is in violation because the pond overflowed, regardless of storm intensity
B. The facility is not in violation because the storm exceeded the design standard
C. The facility must immediately retrofit the pond to handle a 50-year storm
D. The overflow is acceptable only if the wetland is not classified as a Waters of the U.S.
Answer: B
14. A Walmart distribution center's SWPPP requires weekly visual monitoring of stormwater
discharges. An employee notes an oily sheen on the water surface during a routine inspection. The
sheen is intermittent and appears only after light rain. The facility stores hydraulic fluids in a
covered area, but no leaks are detected. Which of the following is the most likely cause of the
sheen?
A. Natural decomposition of organic matter in the retention pond
B. Residual oil from a previous spill that was not fully cleaned
C. Biological activity from algae producing surface films
D. Leaching of petroleum hydrocarbons from asphalt parking lot sealants
Answer: D
15. A facility's stormwater permit includes a benchmark for total phosphorus of 0.1 mg/L. The
facility has implemented best management practices (BMPs) including vegetated swales and a
constructed wetland. Despite these measures, the average effluent concentration is 0.12 mg/L.
Which of the following is the most appropriate next step?
A. Apply for a permit modification to increase the benchmark to 0.12 mg/L
B. Conduct a source assessment to identify and reduce phosphorus inputs
C. Immediately cease all outdoor storage of potential phosphorus sources
D. Report the exceedance as a violation and pay the associated fine
Answer: B
16. A Walmart store is located in an area with a high groundwater table. The stormwater
management plan includes infiltration basins. During a heavy rain event, the basins fail to drain
within 72 hours as designed. Subsequent investigation reveals that the soil's hydraulic conductivity
is 0.1 cm/hr, significantly lower than the design assumption of 1.0 cm/hr. Which of the following is
the most critical flaw in the original design?
A. Underestimation of the water table elevation
B. Inadequate pretreatment of runoff before infiltration
C. Incorrect assumption of soil permeability
D. Insufficient basin volume for the drainage area
Page 4
100% CORRECT ANSWERS
1. A large retail distribution center in a watershed with a Total Maximum Daily Load (TMDL) for
sediment is required to implement stormwater control measures (SCMs). The site has a high
percentage of impervious cover and compacted soils. Which combination of SCMs would most
effectively reduce sediment loading while also providing volume reduction for the 90th percentile
storm event?
A. Proprietary hydrodynamic separators and dry detention basins
B. Vegetated swales and rain gardens
C. Permeable pavement and bioretention cells
D. Cisterns and green roofs
Answer: C
2. Under the EPA's 2015 Effluent Limitations Guidelines and Standards for the Construction and
Development Point Source Category, what is the minimum frequency for inspecting erosion and
sediment control measures during the active construction phase when the site receives 0.5 inches of
rain in a 24-hour period?
A. Once per week
B. Within 24 hours of the rain event
C. Daily during the rain event
D. Every 7 days and within 24 hours of a 0.5-inch rain event
Answer: D
3. A stormwater management plan for a Walmart Supercenter includes a proprietary
underground detention system. The site's pre-development runoff curve number (CN) is 65, and
post-development CN is 85. Using the NRCS method, what is the approximate increase in runoff
volume for a 10-year, 24-hour storm with total rainfall of 5.0 inches? (Assume initial abstraction Ia
= 0.2S, where S = (1000/CN) - 10)
A. 0.5 inches
B. 1.2 inches
C. 2.0 inches
D. 3.1 inches
Answer: B
4. Which of the following best describes the primary purpose of a stormwater pollution prevention
plan (SWPPP) under the Clean Water Act's NPDES permit for industrial activities?
A. To eliminate all stormwater discharge from the site
Page 1
,B. To identify potential sources of pollution and describe control measures to reduce the discharge of pollutants
to the maximum extent practicable
C. To monitor groundwater quality beneath the facility
D. To provide a record of all chemical spills for regulatory reporting
Answer: B
5. A Walmart distribution center is located in a karst terrain region. The stormwater management
plan must include special provisions. Which of the following is the most critical design
consideration for stormwater detention in karst areas?
A. Maximize infiltration to reduce runoff volume
B. Ensure detention basins are lined to prevent sinkhole formation
C. Use only vegetative swales for conveyance
D. Design for the 100-year storm event with no overflow
Answer: B
6. A post-construction stormwater management plan for a Walmart store must comply with local
water quality volume (WQv) requirements. The site has 4 acres of impervious cover and 1 acre of
pervious area. The local jurisdiction requires treating the first 1 inch of runoff from the entire site.
Using the volumetric runoff coefficient (C = 0.9 for impervious, 0.2 for pervious), what is the
required WQv in acre-feet?
A. 0.25 acre-feet
B. 0.30 acre-feet
C. 0.35 acre-feet
D. 0.40 acre-feet
Answer: C
7. During a storm event, a Walmart facility's stormwater outfall is sampled and shows a pH of
10.5. The facility's NPDES permit requires pH between 6.0 and 9.0. Which of the following is the
most likely cause of this exceedance?
A. Leaching from concrete washout areas
B. Spilled diesel fuel from a delivery truck
C. Decomposition of organic matter in a detention pond
D. Acid rain mixing with alkaline soil
Answer: A
8. A Walmart store's stormwater management system includes a bioretention cell designed to treat
runoff from a 2-acre parking lot. The design infiltration rate of the native soil is 0.5 in/hr. The cell
has a surface area of 0.25 acres and a ponding depth of 12 inches. What is the maximum
drawdown time for the ponded water, assuming no underdrain? (Ignore evapotranspiration and
assume uniform infiltration)
A. 12 hours
B. 24 hours
C. 36 hours
Page 2
,D. 48 hours
Answer: B
9. A Walmart distribution center is subject to the EPA's Multi-Sector General Permit (MSGP) for
stormwater discharges associated with industrial activity. The facility performs vehicle
maintenance and has a fleet of trucks. Which of the following is a required element of the SWPPP
for this sector?
A. A spill response plan for hazardous materials that includes quarterly drills
B. A quarterly monitoring program for all outfalls during storm events
C. A narrative description of potential pollutant sources and the BMPs implemented
D. A requirement to install oil-water separators on all parking lot drains
Answer: C
10. A Walmart store's stormwater pond is designed to provide water quality treatment for the first
flush. The pond's permanent pool volume is 0.5 acre-feet, and the water quality volume (WQv) is
0.8 acre-feet. If the pond has a length-to-width ratio of 3:1 and a forebay, what is the primary
function of the forebay?
A. To increase the pond's storage capacity for flood control
B. To trap coarse sediments and reduce maintenance of the main pond
C. To promote algal growth for nutrient uptake
D. To provide habitat for aquatic species
Answer: B
11. A large retail distribution center is located in a watershed designated as a Total Maximum
Daily Load (TMDL) for sediment. The facility's stormwater pollution prevention plan (SWPPP)
includes a sediment basin designed to remove 80% of total suspended solids (TSS). During a
compliance inspection, it is discovered that the basin's outlet structure has been modified to
increase discharge rate by 50%. Which of the following is the most probable consequence of this
modification?
A. Reduced TSS removal efficiency due to decreased residence time
B. Increased groundwater recharge due to higher infiltration
C. Enhanced pollutant removal due to increased turbulence
D. No impact on TSS removal if the basin volume remains unchanged
Answer: A
12. A retail facility's stormwater outfall is sampled quarterly for compliance with a site-specific
numeric effluent limit for zinc. The last four samples show concentrations of 0.12, 0.15, 0.09, and
0.18 mg/L. The permit limit is 0.14 mg/L as an average of four consecutive samples. Which of the
following actions is most appropriate based on these data?
A. Submit a notice of non-compliance because the average exceeds the limit
B. Take no action because the last sample is below the limit
C. Report compliance because the average of the four samples is exactly 0.135 mg/L
D. Initiate a targeted source investigation for zinc
Page 3
, Answer: C
13. During a storm event, a Walmart facility's stormwater retention pond overflows into a
neighboring wetland. The SWPPP identifies the pond as designed for a 25-year, 24-hour storm.
The actual storm that caused the overflow is later determined to have a return period of 50 years.
Which of the following statements best describes the legal and operational implications?
A. The facility is in violation because the pond overflowed, regardless of storm intensity
B. The facility is not in violation because the storm exceeded the design standard
C. The facility must immediately retrofit the pond to handle a 50-year storm
D. The overflow is acceptable only if the wetland is not classified as a Waters of the U.S.
Answer: B
14. A Walmart distribution center's SWPPP requires weekly visual monitoring of stormwater
discharges. An employee notes an oily sheen on the water surface during a routine inspection. The
sheen is intermittent and appears only after light rain. The facility stores hydraulic fluids in a
covered area, but no leaks are detected. Which of the following is the most likely cause of the
sheen?
A. Natural decomposition of organic matter in the retention pond
B. Residual oil from a previous spill that was not fully cleaned
C. Biological activity from algae producing surface films
D. Leaching of petroleum hydrocarbons from asphalt parking lot sealants
Answer: D
15. A facility's stormwater permit includes a benchmark for total phosphorus of 0.1 mg/L. The
facility has implemented best management practices (BMPs) including vegetated swales and a
constructed wetland. Despite these measures, the average effluent concentration is 0.12 mg/L.
Which of the following is the most appropriate next step?
A. Apply for a permit modification to increase the benchmark to 0.12 mg/L
B. Conduct a source assessment to identify and reduce phosphorus inputs
C. Immediately cease all outdoor storage of potential phosphorus sources
D. Report the exceedance as a violation and pay the associated fine
Answer: B
16. A Walmart store is located in an area with a high groundwater table. The stormwater
management plan includes infiltration basins. During a heavy rain event, the basins fail to drain
within 72 hours as designed. Subsequent investigation reveals that the soil's hydraulic conductivity
is 0.1 cm/hr, significantly lower than the design assumption of 1.0 cm/hr. Which of the following is
the most critical flaw in the original design?
A. Underestimation of the water table elevation
B. Inadequate pretreatment of runoff before infiltration
C. Incorrect assumption of soil permeability
D. Insufficient basin volume for the drainage area
Page 4
