# Exam Study Guide: Backwash Rates

When faced with a licensing exam, don't struggle with test anxiety! Use the question below and others from our Exam Study Guide series to properly study and prepare for exam questions. Take a look at this sample wastewater treatment licensing question along with an explanation of the correct answer.

Sample question:

A water treatment plant has three pressure filters. Each filter has a diameter of five feet. One of these filters was backwashed using 400 gpm. What was the backwash rate in gpm/ft2?

A) 25 gpm/ft2

B) 20 gpm/ft2

C) 15 gpm/ft2

D) 10 gpm/ft2

The correct answer is B, because 2.5 feet x 2.5 feet x pi = 19.6ft2; and 400 gpm ÷ 19.6ft2 = 20.4 gpm/ft2.

About the author: Drew Hoelscher is the program director of drinking water operations at the Environmental Resources Training Center (ERTC) in Edwardsville, Illinois.

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