Wastewater New York State Practice Exam 2026 - Free Wastewater Certification Practice Questions and Study Guide

To determine the surface loading rate of a rectangular primary sedimentation tank, you'll need to calculate the area of the tank's surface and then relate that to the influent flow rate.

First, calculate the area of the tank's surface. The surface area is simply the length multiplied by the width. In this case, the tank is 60 feet long and 30 feet wide:

Surface Area = Length × Width = 60 ft × 30 ft = 1,800 sq. ft.

Next, we need to convert the influent flow rate into gallons per day per square foot. The influent flow rate is given as 9.0 million gallons per day (mgd), which means:

Influet Flow Rate = 9.0 mgd = 9,000,000 gallons per day.

Now, divide the total gallons per day by the surface area to find the surface loading rate:

Surface Loading Rate = Total Flow / Surface Area = 9,000,000 gallons per day / 1,800 sq. ft.

Calculating this gives:

Surface Loading Rate = 5,000 gpd/sq. ft.

This value indicates the amount of flow per square foot of surface area in the tank, making it clear