North Carolina Surface Water Math Practice Exam - Study Guide & Practice Questions

To calculate the rate of filtration in gallons per minute per square foot (gpm/ft²), you need to divide the total flow rate of the water plant by the total area of the filters.

First, convert the flow rate from million gallons per day (MGD) to gallons per minute (gpm). Since there are 1,440 minutes in a day, you can perform the following calculation:

12 MGD × 1,000,000 gallons/MG ÷ 1,440 minutes/day = 8,333.33 gpm.

Next, calculate the total area of the filters. Each filter measures 15 feet by 25 feet, so the area of one filter is:

15 ft × 25 ft = 375 ft².

With six filters, the total area is:

6 filters × 375 ft²/filter = 2,250 ft².

Now, calculate the rate of filtration by dividing the total flow rate by the total area:

8,333.33 gpm ÷ 2,250 ft² = 3.70 gpm/ft².

Therefore, the correct rate of filtration for the water plant is 3.70 gpm/ft², which matches the provided answer