CESSWI CESSWI Post-Construction BMP Maintenance and Long-Term Controls 2 — Questions and Answers
Question 1: In the context of post-construction stormwater management, what does 'hydromodification' refer to?
- The process of adding chemical treatment to stormwater
- Changes in the natural hydrologic cycle (peak flows, runoff volume, duration) caused by land development (Correct answer)
- The installation of stormwater infrastructure modifications after construction
- Modifying a hydrograph by adding riprap
Correct answer: Changes in the natural hydrologic cycle (peak flows, runoff volume, duration) caused by land development
Hydromodification describes how impervious surfaces and altered drainage increase peak flows, total runoff volume, and flow duration compared to pre-development conditions, degrading stream channels.
Question 2: A vegetated filter strip used as a post-construction BMP functions primarily by:
- Storing large volumes of runoff underground
- Slowing sheet flow and allowing settling and infiltration of runoff from adjacent impervious areas (Correct answer)
- Chemically treating heavy metals in runoff
- Preventing any stormwater from leaving the site
Correct answer: Slowing sheet flow and allowing settling and infiltration of runoff from adjacent impervious areas
Vegetated filter strips use dense grass or other vegetation to slow shallow sheet flow, promote infiltration, and physically filter out sediments and other pollutants before runoff enters a water body.
Question 3: Which maintenance activity is most critical for ensuring continued function of an underground stormwater infiltration system?
- Repainting the manhole covers annually
- Removing accumulated sediment from pretreatment devices to prevent clogging of the infiltration media (Correct answer)
- Increasing the design storm return interval
- Adding sodium hypochlorite to control biological growth
Correct answer: Removing accumulated sediment from pretreatment devices to prevent clogging of the infiltration media
Sediment accumulation in upstream pretreatment structures (catch basins, forebays) is the primary cause of infiltration system failure; regular cleanout preserves the system's ability to percolate stormwater.
Question 4: Under many MS4 (Municipal Separate Storm Sewer System) permits, what is the purpose of requiring a Stormwater Pollution Prevention Plan (SWPPP) for post-construction activities?
- To replace the need for any physical BMPs on the site
- To document long-term maintenance responsibilities, inspection schedules, and ownership of post-construction BMPs (Correct answer)
- To satisfy OSHA safety requirements for the construction crew
- To provide proof of final stabilization to the local government
Correct answer: To document long-term maintenance responsibilities, inspection schedules, and ownership of post-construction BMPs
Post-construction SWPPPs or equivalent O&M agreements create a legally binding record of who is responsible for maintaining BMPs and how often inspections and maintenance must be performed.
Question 5: Green roofs are considered a post-construction LID BMP because they primarily:
- Increase total impervious surface area on a site
- Retain rainwater in a growing media layer, reducing and delaying roof runoff to the storm sewer (Correct answer)
- Filter pollutants from groundwater
- Increase peak discharge from the building footprint
Correct answer: Retain rainwater in a growing media layer, reducing and delaying roof runoff to the storm sewer
The saturated growing medium on a green roof absorbs rainfall, which is then returned to the atmosphere through evapotranspiration, reducing the volume and peak rate of runoff from the roof.
Question 6: An inspector discovers that a post-construction wet pond outlet's trash rack is missing. The most important reason to replace it immediately is to:
- Improve the aesthetic appearance of the pond
- Prevent debris from blocking the outlet pipe, which could cause uncontrolled overflow and embankment failure (Correct answer)
- Meet local landscaping ordinance requirements
- Reduce aquatic vegetation growth inside the barrel
Correct answer: Prevent debris from blocking the outlet pipe, which could cause uncontrolled overflow and embankment failure
Trash racks keep large debris from entering and blocking the outlet barrel; without one, clogging can cause water levels to exceed the embankment and lead to erosive overtopping or structural failure.
CESSWI CESSWI Post-Construction BMP Maintenance and Long-Term Controls 2
In the context of post-construction stormwater management, what does 'hydromodification' refer to?