CSM Inspection Monitoring & Maintenance Procedures 2 — Questions and Answers
Question 1: During a post-storm inspection of a wet detention pond, an inspector notices the outlet structure's trash rack is 60% clogged with debris. What is the most appropriate immediate action?
- Document the condition and schedule cleaning within 30 days
- Remove debris immediately to restore hydraulic function and prevent flooding risk (Correct answer)
- Notify the state regulatory agency before taking any action
- Install a secondary outlet to compensate for the blockage
Correct answer: Remove debris immediately to restore hydraulic function and prevent flooding risk
A heavily clogged trash rack significantly restricts outflow and can cause upstream flooding, so immediate debris removal is required to restore design hydraulic capacity.
Question 2: A stormwater inspector finds that sediment has accumulated to 40% of the design storage volume in a dry detention basin. According to standard CSM maintenance thresholds, what action is triggered?
- No action required until 75% capacity is lost
- Increase inspection frequency to monthly until sediment reaches 50%
- Sediment removal is required, as the threshold is typically 25–33% capacity loss (Correct answer)
- File a non-compliance report with the EPA immediately
Correct answer: Sediment removal is required, as the threshold is typically 25–33% capacity loss
Most stormwater management standards require sediment removal when accumulation reduces storage capacity by 25–33%, and 40% clearly exceeds that threshold.
Question 3: Which monitoring parameter is MOST critical to measure at the inlet and outlet of a bioretention cell to assess its pollutant removal performance?
- Dissolved oxygen concentration
- Total suspended solids (TSS) and nutrient concentrations (Correct answer)
- pH only
- Water temperature differential
Correct answer: Total suspended solids (TSS) and nutrient concentrations
TSS and nutrient (nitrogen and phosphorus) concentrations measured at inlet and outlet allow calculation of pollutant removal efficiency, the primary performance metric for bioretention.
Question 4: An inspector observes seepage emerging from the downstream face of a stormwater pond embankment two feet below the crest. This condition MOST likely indicates:
- Normal seasonal groundwater fluctuation
- Internal erosion or piping — a potentially critical structural failure mode (Correct answer)
- Harmless overtopping from the last rain event
- A properly functioning underdrain system
Correct answer: Internal erosion or piping — a potentially critical structural failure mode
Seepage on the downstream face of an embankment, especially near the crest, is a warning sign of internal erosion or piping that can lead to catastrophic embankment failure.
Question 5: When inspecting a grass-lined swale for maintenance needs, which condition would MOST warrant immediate corrective action?
- Grass height of 8 inches throughout the swale
- Isolated bare soil patches less than 1 square foot near the inlet
- Rilling and erosion channels cutting through the swale bottom longitudinally (Correct answer)
- Slight discoloration of grass from iron in runoff
Correct answer: Rilling and erosion channels cutting through the swale bottom longitudinally
Longitudinal rilling in a grass swale indicates flow velocities are exceeding the protective capacity of the vegetative cover, leading to accelerating erosion that must be corrected.
Question 6: A stormwater monitoring program requires quarterly sampling of a detention pond's discharge. Samples must be collected as 'flow-weighted composite' samples. What does this method entail?
- Collecting a single grab sample at peak flow only
- Collecting equal-volume aliquots at fixed time intervals regardless of flow
- Collecting aliquots proportional to flow rate so high-flow periods are represented proportionally (Correct answer)
- Averaging results from three grab samples taken at the beginning, middle, and end of storm
Correct answer: Collecting aliquots proportional to flow rate so high-flow periods are represented proportionally
Flow-weighted composite sampling collects aliquot volumes proportional to instantaneous flow rate, ensuring the composite sample accurately represents the pollutant load discharged.
Question 7: Under NPDES MS4 permit requirements, what is the purpose of maintaining a stormwater BMP inventory with GPS coordinates and condition ratings?
- It is required only for BMPs serving industrial facilities
- It enables systematic tracking of infrastructure condition to prioritize maintenance and demonstrate permit compliance (Correct answer)
- It is used exclusively for calculating stormwater user fees
- It satisfies FEMA floodplain mapping requirements
Correct answer: It enables systematic tracking of infrastructure condition to prioritize maintenance and demonstrate permit compliance
An asset inventory with condition ratings is a core MS4 permit requirement that supports proactive maintenance scheduling, budget planning, and regulatory compliance documentation.
CSM Inspection Monitoring & Maintenance Procedures 2
During a post-storm inspection of a wet detention pond, an inspector notices the outlet structure's trash rack is 60% clogged with debris.
What is the most appropriate immediate action?