CSM Illicit Discharge Detection & Elimination (IDDE) 1 — Questions and Answers
Question 1: Which federal regulatory program is the primary driver requiring MS4 operators to develop and implement Illicit Discharge Detection and Elimination (IDDE) programs?
- Clean Water Act Section 401
- NPDES Phase I and Phase II Stormwater Permit Program (Correct answer)
- Safe Drinking Water Act Surface Water Treatment Rule
- Resource Conservation and Recovery Act Subtitle D
Correct answer: NPDES Phase I and Phase II Stormwater Permit Program
The NPDES Phase I and Phase II Stormwater Permit Program, under the Clean Water Act, requires regulated MS4 operators to develop IDDE programs as one of six minimum control measures.
Question 2: Which of the following is correctly classified as an illicit discharge to a municipal separate storm sewer system (MS4)?
- Uncontaminated groundwater infiltration into storm pipes
- Residential car washing wastewater entering a storm drain (Correct answer)
- Stormwater runoff from a construction site with an active permit
- Irrigation return flows from agricultural operations
Correct answer: Residential car washing wastewater entering a storm drain
Residential car washing wastewater contains soaps, oils, and other pollutants that are prohibited discharges to the storm sewer; it is considered illicit because it is not stormwater.
Question 3: What is the first critical step in establishing a municipal IDDE program?
- Installing dry-weather flow monitoring equipment at all outfalls
- Creating and maintaining a complete map of the storm sewer system (Correct answer)
- Issuing fines to businesses with suspected illegal connections
- Training field staff in water quality sampling procedures
Correct answer: Creating and maintaining a complete map of the storm sewer system
A complete storm sewer system map is the foundation of any IDDE program because field staff must know where pipes go and where outfalls are located before investigating potential illicit connections.
Question 4: Which water quality indicator is most commonly used in field screening to detect the presence of sanitary sewage contamination in stormwater outfall flows?
- Total dissolved solids (TDS)
- Fecal coliform or E. coli bacteria (Correct answer)
- Turbidity (NTU)
- Total suspended solids (TSS)
Correct answer: Fecal coliform or E. coli bacteria
Fecal coliform and E. coli are reliable biological indicators of human sewage contamination and are the standard parameters used to confirm sanitary sewer cross-connections in IDDE screening.
Question 5: What is the primary purpose of conducting dry-weather screening at storm drain outfalls?
- To measure peak flow rates for hydraulic modeling
- To detect non-stormwater flows that may indicate illicit connections or discharges (Correct answer)
- To assess the structural integrity of outfall pipes
- To calculate pollutant loading from impervious surfaces
Correct answer: To detect non-stormwater flows that may indicate illicit connections or discharges
Dry-weather screening identifies outfalls with unexplained flows during periods of no recent rainfall, which is a primary indicator of potential illicit connections to sanitary lines or illegal dumping.
Question 6: Under NPDES MS4 permits, which of the following discharges is typically listed as an allowable non-stormwater discharge and is NOT considered illicit?
- Wastewater from floor drains in auto repair shops
- Lawn watering and landscape irrigation runoff (Correct answer)
- Washwater from washing out concrete mixers
- Discharge from portable toilet cleanouts
Correct answer: Lawn watering and landscape irrigation runoff
Lawn watering and landscape irrigation runoff are explicitly listed in most NPDES MS4 permits as allowable non-stormwater discharges, provided they do not cause or contribute to water quality violations.
Question 7: Which field parameter, when measured above ambient background levels at a storm drain outfall during dry weather, is a strong indicator of a sanitary sewer cross-connection?
- Dissolved oxygen below 5 mg/L
- Surfactants (detergents) above background levels (Correct answer)
- pH between 6.5 and 8.5
- Conductivity below 100 µS/cm
Correct answer: Surfactants (detergents) above background levels
Elevated surfactant levels in dry-weather outfall flow strongly suggest discharge of household or commercial wastewater containing soaps and detergents from an illicit cross-connection.
CSM Illicit Discharge Detection & Elimination (IDDE) 1
Which federal regulatory program is the primary driver requiring MS4 operators to develop and implement Illicit Discharge Detection and Elimination (IDDE) programs?