NASCO Water Chemistry & Quality Control 5

Question 1

After a fecal accident in a pool, the CDC recommends raising free chlorine to what level (at pH 7.5) to inactivate non-Crypto pathogens?

Accepted Answer

2 ppm for 30 minutes

Answer

For a formed stool fecal accident, CDC recommends raising free chlorine to 2 ppm at pH 7.5 and maintaining it for at least 25–30 minutes before reopening.

Question 2

What does a high ORP (Oxidation-Reduction Potential) reading indicate about pool water?

Accepted Answer

Strong sanitizing ability of the water

Answer

A high ORP (ideally 650–750 mV) indicates that the water has a strong oxidizing capacity and is effective at killing pathogens.

Question 3

Muriatic acid (hydrochloric acid) is added to pool water to accomplish which goal?

Accepted Answer

Lower pH and total alkalinity

Answer

Muriatic acid lowers both pH and total alkalinity, making it the primary chemical for reducing these levels when they are too high.

Question 4

Sodium thiosulfate is used in aquatic facility management primarily to:

Accepted Answer

Neutralize excess chlorine

Answer

Sodium thiosulfate is a chlorine neutralizer used to quickly reduce dangerously high chlorine levels in pool water.

Question 5

What is the MOST accurate description of 'superchlorination'?

Accepted Answer

Adding a large dose of chlorine (typically 10 ppm or more) to oxidize contaminants

Answer

Superchlorination involves adding a large dose of chlorine (10 ppm or more) to oxidize organic contaminants, chloramines, and algae.

(NASCO) National Aquatic Safety Company Aquatic Facility Operator Certification Practice Test

(NASCO) National Aquatic Safety Company Aquatic Facility Operator Certification Practice Test

NASCO Water Chemistry & Quality Control 5