CSM Illicit Discharge Detection & Elimination (IDDE) 2 — Questions and Answers
Question 1: During an IDDE field investigation, a field technician observes gray, sudsy water flowing from an outfall during dry weather. Which upstream source is MOST likely responsible?
- A leaking underground storage tank (UST)
- A cross-connected laundry or washing machine drain (Correct answer)
- Stormwater ponded in a nearby retention basin
- An overflowing sanitary manhole several blocks away
Correct answer: A cross-connected laundry or washing machine drain
Gray, sudsy water during dry weather is a classic sign of laundry or household washing machine wastewater cross-connected to the storm drain, due to the presence of detergents and surfactants.
Question 2: What is the recommended approach for tracing an illicit discharge upstream once flow is confirmed at an outfall during dry weather?
- Sample the outfall water and wait for laboratory results before any field work
- Walk the contributing drainage area and systematically check manholes and inlets moving upstream (Correct answer)
- Issue violation notices to all businesses in the drainage area
- Install automated samplers at the outfall and review data remotely
Correct answer: Walk the contributing drainage area and systematically check manholes and inlets moving upstream
Systematic upstream manhole and inlet investigation — walking the system from the outfall — is the standard IDDE field methodology to isolate the source of an illicit discharge.
Question 3: Which chemical tracer is commonly used by inspectors to confirm a specific building's drain is connected to the storm sewer rather than the sanitary sewer?
- Sodium chloride (table salt)
- Optical brighteners or fluorescent dye (Correct answer)
- Potassium permanganate
- Sodium hypochlorite (bleach)
Correct answer: Optical brighteners or fluorescent dye
Fluorescent dyes (such as fluorescein or rhodamine) or optical brighteners are introduced into building drains and detected downstream in the storm sewer to confirm an illicit connection.
Question 4: When an IDDE inspector discovers a confirmed illicit discharge from a commercial facility, what is the appropriate immediate response?
- Issue a warning letter and schedule a reinspection in 90 days
- Document findings, notify the appropriate regulatory authority, and require the discharger to eliminate the connection within a specified timeframe (Correct answer)
- Plug the storm drain outfall to prevent further discharge to the receiving water
- Refer the matter to the EPA Region office and take no local action
Correct answer: Document findings, notify the appropriate regulatory authority, and require the discharger to eliminate the connection within a specified timeframe
Confirmed illicit discharges require documentation, regulatory notification, and an enforcement action requiring the responsible party to eliminate the source within a permit-specified timeframe.
Question 5: Which of the following best describes a 'sanitary sewer cross-connection' in the context of an MS4 system?
- A pipe that carries both stormwater and treated wastewater to the same outfall
- A physical connection between a building's sanitary drain and the storm sewer that allows sewage to enter the storm system (Correct answer)
- A sewer manhole that is shared between the storm and sanitary systems for maintenance access
- An overflow structure on a combined sewer that diverts excess flow during storms
Correct answer: A physical connection between a building's sanitary drain and the storm sewer that allows sewage to enter the storm system
A sanitary sewer cross-connection occurs when a building's plumbing — either intentionally or by error — routes sewage into the storm sewer instead of the sanitary sewer, causing illicit discharge.
Question 6: Under most NPDES MS4 permit requirements, what is the minimum information that must be maintained in a storm sewer system map for IDDE purposes?
- Pipe material only
- The location of storm drain inlets, pipes, and outfalls, and the receiving waters to which they drain (Correct answer)
- Only outfall locations and receiving water names
- The age and condition rating of each pipe segment
Correct answer: The location of storm drain inlets, pipes, and outfalls, and the receiving waters to which they drain
NPDES MS4 permit IDDE requirements specify that the system map must show storm sewer locations, outfalls, and the receiving waters they discharge to, enabling effective field investigations.
Question 7: Which of the following outfall observations would be LEAST likely to indicate an illicit discharge during a dry-weather field screening visit?
- Bright orange or reddish staining around the outfall pipe
- A small trickle of clear, odorless water at an outfall 72 hours after a significant rain event (Correct answer)
- A persistent flow with a sewage odor and gray coloration
- Oily sheen on the water surface near the outfall
Correct answer: A small trickle of clear, odorless water at an outfall 72 hours after a significant rain event
A small trickle of clear, odorless water 72 hours after significant rainfall is likely base flow or subsurface drainage, a common allowable condition, and is the least indicative of an illicit discharge.
CSM Illicit Discharge Detection & Elimination (IDDE) 2
During an IDDE field investigation, a field technician observes gray, sudsy water flowing from an outfall during dry weather.
Which upstream source is MOST likely responsible?