Section 811.103  Surface Water Drainage

a)         Runoff from Disturbed Areas

1)         Runoff from disturbed areas resulting from precipitation events less than or equal to the 25-year, 24-hour precipitation event that is discharged to waters of the State must meet the requirements of 35 Ill. Adm. Code 304.

2)         All discharges of runoff from disturbed areas to waters of the State must be permitted by the Agency in accordance with 35 Ill. Adm. Code 309.

3)         All treatment facilities must be equipped with bypass outlets designed to pass the peak flow of runoff from the 100-year, 24-hour precipitation event without damage to the treatment facilities or surrounding structures.

4)         All surface water control structures must be operated until the final cover is placed and erosional stability is provided by the vegetative or other cover meeting the requirements of Section 811.205 or 811.322.

5)         All discharge structures must be designed to have flow velocities that will not cause erosion and scouring of the natural or constructed lining, i.e., bottom and sides, of the receiving stream channel.

b)         Diversion of Runoff from Undisturbed Areas

1)         Runoff from undisturbed areas must be diverted around disturbed areas, unless the operator shows that it is impractical based on site-specific conditions or unless the Agency has issued a research, development, and demonstration (RD&D) permit that provides otherwise pursuant to 35 Ill. Adm. Code 813.112(a)(1), relating to run-on control systems, and that permit is in effect.

2)         Diversion facilities must be designed to prevent runoff from the 25-year, 24-hour precipitation event from entering disturbed areas, unless the Agency has issued an RD&D permit that provides otherwise pursuant to 35 Ill. Adm. Code 813.112(a)(1), relating to run-on control systems, and that permit is in effect.

3)         Runoff from undisturbed areas that becomes commingled with runoff from disturbed areas must be handled as runoff from disturbed areas and treated in accordance with subsection (a).

4)         All diversion structures must be designed to have flow velocities that will not cause erosion and scouring of the natural or constructed lining, i.e., the bottom and sides, of the diversion channel and downstream channels.

5)         All diversion structures must be operated until the final cover is placed and erosional stability is provided by the vegetative or other cover that meets the requirements of Section 811.205 or 811.322.

BOARD NOTE:  Those segments of subsections (b)(1) and (b)(2) that relate to RD&D permits are derived from 40 CFR 258.4(a)(1) (2017).

(Source:  Amended at 42 Ill. Reg. 21330, effective November 19, 2018)