WASTEWATER

By Rick Lallish

Where should manholes be located in the collection system?

A. Every intersection

B. Any change in pipe diameter

C. Elevation changes

D. Junctions

Answer: A, B, C and D. Manholes are meant to provide access to the collection system. They should be present at any changes of elevation, flow, pipe size and direction, and at any junctions. Manholes may be located over mains, trunks or interceptors and should be 300 to 500 feet apart (this recommendation may vary depending on textbook). The distance should reflect the ability of cleaning equipment (for example, the length of available jet hose). Manholes should always be considered as confined spaces. More information may be found in OWP Sacramento State, Operation and Maintenance of Wastewater Collection Systems, Volume 1, 8th Edition. 

DRINKING WATER

By Drew Hoelscher

Using the data below, calculate the volume of the basin in gallons.

Flow rate: 600 gpm

Detention time: 4 hours

A. 2,400 gallons

B. 9,000 gallons

C. 144,000 gallons

D. 17,952 gallons

Answer: C. Understanding detention time calculations can help you prevent water treatment upsets and help with troubleshooting. The formula for theoretical detention time is volume in gallons divided by flow rate. In this example, we must convert the flow rate to gallons per hour and multiply by the detention time to solve for the basin volume in gallons.

600 x 60 minutes = 36,000 gph

36,000 gph x 4 hours = 144,000 gallons

About the author(s)

Rick Lallish is water pollution control program director and Drew Hoelscher is program director of drinking water operations at the Environmental Resources Training Center of Southern Illinois University Edwardsville.