Section 370.310  Design Basis

a)         Per Capita Flow

1)         New Sewers for Undeveloped Areas

New sewer systems to serve currently undeveloped areas shall be designed on the basis of a design average flow of not less than 100 gallons per capita per day which is assumed to cover normal infiltration, but an additional allowance should be made where conditions are unfavorable.

2)         New Sewers for Existing Developed Areas

For new sewers designed to serve existing developed areas, the design average flow per capita (100 gpd) shall be appropriately increased to allow for inflow/infiltration contributions from the existing buildings other than roof and foundation drains which shall be excluded in accordance with Section 370.121(a).

b)         Design Peak Flow

1)         The design peak flow for sanitary sewers shall be selected based on one of the following methods:

A)        The ratio of peak to average daily flow as determined from Appendix D, Figure No. 1.

B)        Values established from an infiltration/inflow study acceptable to the Agency.

2)         Use of other values for the design peak flow will be considered if justified on the basis of extensive documentation.

3)         Combined Sewer Interceptors

Intercepting sewers, in the case of combined sewer systems, should fulfill the above requirements for sewers and have sufficient additional capacity to transport the increment of combined sewage required by the IPCB Regulations.

c)         Alternate Methods

When deviations from subsections (a) and (b) are proposed, a description of the procedure used for sewer design shall be included in the submission of plan documents.

d)         Basis of Design and Calculations

The basis of design for all sewer projects shall accompany the plan documents.  Calculations shall be submitted to show that sewers will have sufficient hydraulic capacity to transport the design peak flows.

(Source:  Amended at 21 Ill. Reg. 12444, effective August 28, 1997)