Glossary of Water and Wastewater Terms

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5 random terms from our glossary

Sewer Root

Any part of a root system of a plant or tree that enters a collection system.

Rain

Particles of liquid water that have become too large to be held by the atmosphere. Their diameter generally is greater than 0.02 inch (0.5 mm) and they usually fall to the earth at velocities greater than 10 fps (3 m/sec) in still air. Also see PRECIPITATION.

Flow Isolation

A procedure used to measure inflow and infiltration (I/I). A section of sewer is blocked off or isolated and the flow from the section is measured.

Time-Weighted Average (TWA)

A time-weighted average is used to calculate a workers daily exposure to a hazardous substance (such as chemicals, dusts, fumes, mists, gases, or vapors) or agent (such as occupational noise), averaged to an 8-hour workday, taking into account the average levels of the substance or agent and the time spent in the area. This is the guideline OSHA uses to determine permissible exposure limits (PELs) and is essential in assessing a worker's exposure and determining what protective measures should be taken. A time-weighted average is equal to the sum of the portion of each time period (as a decimal, such as 0.25 hour) multiplied by the levels of the substance or agent during the time period divided by the hours in the workday (usually 8 hours). Also see PERMISSIBLE EXPOSURE LIMIT (PEL).

Hydraulic Population Equivalent

A flow of 100 gallons (378 liters) per day is the hydraulic or flow equivalent to the contribution or flow from one person. Population equivalent = 100 GPCD or gallons per capita per day (378 LPCD or liters per capita per day).