CEPSCI Water Quality Monitoring and Testing 1 — Questions and Answers
Question 1: Which water quality parameter is most commonly used to assess the effectiveness of sediment controls at a construction site discharge point?
- Dissolved oxygen
- Turbidity (Correct answer)
- pH
- Biochemical oxygen demand
Correct answer: Turbidity
Turbidity measures the cloudiness of water caused by suspended sediment particles, making it the primary indicator of sediment control effectiveness at construction discharges.
Question 2: What unit of measurement is most commonly used to express turbidity in stormwater monitoring?
- mg/L
- NTU (Correct answer)
- ppm
- CFU/100mL
Correct answer: NTU
Nephelometric Turbidity Units (NTU) is the standard unit used to measure turbidity in water quality monitoring programs.
Question 3: Under the EPA's Construction General Permit (CGP), operators must conduct water quality monitoring when a project discharges to a water body that is impaired for which of the following?
- Nitrogen or phosphorus
- Sediment or turbidity (Correct answer)
- Chlorine or fluoride
- Bacteria or pathogens
Correct answer: Sediment or turbidity
The CGP requires enhanced monitoring when construction sites discharge to 303(d)-listed impaired water bodies for sediment or turbidity.
Question 4: A grab sample collected for turbidity monitoring at a construction site should ideally be taken:
- 24 hours after a storm event ends
- At the beginning of a rain event before discharge begins
- During a storm event when discharge is actively occurring (Correct answer)
- Only during dry weather baseflow conditions
Correct answer: During a storm event when discharge is actively occurring
Grab samples for turbidity should be collected during active storm discharge to capture representative water quality conditions at the point of discharge.
Question 5: What is the typical acceptable turbidity benchmark for construction site discharges under many state NPDES permits before further action is required?
- 500 NTU
- 250 NTU (Correct answer)
- 50 NTU
- 1000 NTU
Correct answer: 250 NTU
Many state NPDES permits and the EPA CGP use a benchmark of 250 NTU as a threshold that triggers corrective action requirements.
Question 6: Which device is most commonly used in the field to measure turbidity during stormwater monitoring?
- Conductivity meter
- Turbidimeter or nephelometer (Correct answer)
- Dissolved oxygen probe
- Spectrophotometer
Correct answer: Turbidimeter or nephelometer
A turbidimeter or nephelometer measures light scattered by particles in water and is the standard field instrument for turbidity monitoring.
Question 7: When sampling stormwater at a pipe discharge point, where should the sample be collected relative to the discharge?
- Upstream of the discharge point in the receiving water
- Directly at the pipe outlet or within the first few feet of discharge (Correct answer)
- At least 100 feet downstream in the receiving water body
- At the center of the receiving stream channel
Correct answer: Directly at the pipe outlet or within the first few feet of discharge
Samples should be collected directly at or just below the discharge pipe outlet to capture the quality of water leaving the site before dilution in the receiving water.
CEPSCI Water Quality Monitoring and Testing 1
Which water quality parameter is most commonly used to assess the effectiveness of sediment controls at a construction site discharge point?