Illinois Administrative Code
Title 35 - ENVIRONMENTAL PROTECTION
Part 375 - COMBINED SEWER OVERFLOW EXCEPTION CRITERIA AND FIRST FLUSH DETERMINATION
Subpart D - FIRST FLUSH DETERMINATION
Section 375.402 - Conditions for Determination

Universal Citation: 35 IL Admin Code ยง 375.402

Current through Register Vol. 48, No. 38, September 20, 2024

For any given sewer system, or portion of a sewer system, first flush volume subject to full treatment requirements of 35 Ill. Adm. Code 306.305(a) and associated flow rate shall be determined for the following condition(s):

a) A storm of 1.2 inch per hour intensity with a duration of 60 minutes, which approximates a one year-one-hour storm for most sections of the state.

b) There shall be sufficient time between the storm event chosen to determine first flush and any previous event to allow for adequate solids deposition in the sewers and on the streets to demonstrate first flush under this Part. In general a ten day period should be sufficient.

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