Design Criteria for CSO in Indiana

[DCEngr1]

Waste Water Engineers,

I am investigating a sewage flooding event in small-town Indiana. This system was reportedly built in the 60's. Is, or was there, a design criteria for rainfall, such as a 10-year/one-hour rain storm event that would have been, or is, in force then or now to determine if a rainfall event has actually exceeded the capacity; it being a combined sewer system?

Thank you for your assistance.

DCEngr1

 

[bimr]

Have not seen a sewer overflow with a permit condition related to rainfall totals.

You might check the NPDES. Any conditions such as you describe will be included in the permit.

 

[zelgar]

I'd go to IDEM's webpage about Combined Sewer Overflow Program at

http://in.gov/idem/cleanwater/2455.htm

I work at IDEM (Indiana Department of Environmental Management), in the Office of Land Quality for 20 years, but worked in the Office of Water for 2 years. I still have an old reference from the State Board of Health days published in 1988 that indicated that sewage lift stations should be protected from damage dues to the 100-year flood and still be operational and accessible during the 25-year flood.

 

[bimr]

Here is an NPDES from a small town in Illinois that has maybe 70% combined sewers. They were under a consent order to provide an excess flow treatment system. Basically a system that will bypass the WWTP while providing primary treatment for the CSO.

The only information in the permit regarding storms is a special condition to record the storm information.

The Permittee shall monitor the frequency of discharge (number of discharges per month) and estimate the duration (in hours) of
each discharge from each outfall listed in this Special Condition. Estimates of storm duration and total rainfall shall be provided for each storm event.

For frequency reporting, all discharges from the same storm, or occurring within 24 hours, shall be reported as one. The date th at a discharge commences shall be recorded for each outfall. Reports shall be in the form specified by the IEPA and on forms provided by the IEPA. These forms shall be submitted to the IEPA monthly with the DMRs and covering the same reporting period as the DMRs. Parameters (other than flow frequency), if required in this Permit, shall be sampled and reported as indicated in the
transmittal letter for such report forms.

 

[bimr]

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

http://www.ipcb.state.il.us/documents/dsweb/Get/Document-12052