Section 306.502  Alton Combined Sewer Overflow Discharges

a)         The discharge from the Piasa-State Street Sewer at Mississippi River mile 202.64 is not subject to 35 Ill. Adm. Code 304.106, 304.120, 304.121 and 304.124 during the following conditions:

1)         Before replacement of the existing Locks and Dam 26, when the tailwater elevation exceeds 415.3 Mean Sea Level (MSL); or

2)         After replacement of Locks and Dam 26, when the pool level exceeds elevation 420 MSL at Mississippi River miles 203.12 and 203.22 (Piasa and State Street Outlets relocated).

b)         Discharges from the City of Alton at Mississippi River miles 201.66 (Shields Valley), 202.24 (Central Avenue), 203.12 (Piasa Outlet), 203.22 (State Street Outlet), 203.61 (Summit Street), 203.87 (Bluff Street) and 204.30 (Turner Tract), are subject to the following conditions:

1)         The overflow structures and the associated interceptor sewer must be protected against intrusion by flood waters and be maintained operational at flood stages from Mississippi River backflow for a 25-year Mississippi River flood stage, except as follows:

2)         The City of Alton must maintain the south side interceptor sewer system in working condition to ensure that the system will flow at a maximum capacity.

3)         No later than the date of completion of Lock and Dam 26, the south side interceptor pump station must be upgraded to a design capacity of a minimum of 13.7 million gallons per day.

c)         Discharges from the combined sewer overflows designated in subsection (b) are not subject to the treatment requirements of Section 306.305(a) and (b) provided that:

1)         The City of Alton maintains the south side interceptor sewer system in working condition to ensure that the system will flow at a maximum capacity.

2)         The South Side interceptor pump station must be upgraded to a design capacity of a minimum of 13.7 million gallons per day.

(Source:  Amended at 47 Ill. Reg. 4641, effective March 23, 2023)