Water Quality Monitoring and Testing Flashcards

Which water quality parameter is most commonly used to assess the effectiveness of sediment controls at a construction site discharge point?

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.

What unit of measurement is most commonly used to express turbidity in stormwater monitoring?

Answer: NTU

Nephelometric Turbidity Units (NTU) is the standard unit used to measure turbidity in water quality monitoring programs.

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?

Answer: Sediment or turbidity

The CGP requires enhanced monitoring when construction sites discharge to 303(d)-listed impaired water bodies for sediment or turbidity.

A grab sample collected for turbidity monitoring at a construction site should ideally be taken:

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.

What is the typical acceptable turbidity benchmark for construction site discharges under many state NPDES permits before further action is required?

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.

Which device is most commonly used in the field to measure turbidity during stormwater monitoring?

Answer: Turbidimeter or nephelometer

A turbidimeter or nephelometer measures light scattered by particles in water and is the standard field instrument for turbidity monitoring.

When sampling stormwater at a pipe discharge point, where should the sample be collected relative to the discharge?

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.