Speedway Works On Long Term Control Plans

(updated Mar 22)

Proposed Plant Operations Explained
By HNTB Engineer Richard C. Claus, P. E. BCEE

All combined sewer flow greater than the sustained peak flow capacity of the existing WWTP (8.9 million gallons a day) will be pumped by the proposed 80 MGD pump station into two 120-foot diameter primary clarifiers. The clarifiers will store up to 3.4 million gallons. For wet weather events up to a 1-year, 1-hour design storm all of this stored flow will be returned back to the WWTP for full treatment after storm flows reside. For larger storm events, the clarifiers will begin to overflow once filled and this partially treated overflow will receive ultra-violet light (UV) disinfection prior to sampling and discharge to Big Eagle Creek. All solids removed by settling in the clarifiers will be returned back to the WWTP for full treatment during or after the storm event.

(posted Feb 20)
The EPA and Indiana Department of Environmental Management are no longer tolerating untreated combined sewer flow to bypass waste water treatment plants and directly enter the stream during and after wet weather events.
The criteria for Combined Sewer Overflow (CSO) Long Term Control Plans in 2004 limited the CSO events to four times per year. This new no tolerance policy for certain rain events has changed wastewater processing standards that were valid in 2004. The new criteria regulate the treatment of one year, one hour rain events and a ten-year, one-hour rain event. These new rulings will cost communities millions of dollars in order to comply, and Speedway is not exempted from these measures to revise its Long Term Control Plan that was submitted in 2004.
The revised plan has increased the project cost from $15 million to $21.3 million. The $21.3 million is estimated in 2007 construction cost dollars.
The Speedway Storm Water Drainage Board conducted a citizen advisory committee meeting February 8th so HNTB engineers could explain the revised plan that needs to be submitted to IDEM by March 27th. The group will meet again on March 15 at 5 p.m. to finalize the plan before submission.
Richard Claus, PE, BCEE, of HNTB Corporation explained the one-year, one hour event is equal to 1.16 inches of rain that generates 3.4 million gallons excess sewage water in about four hours. The excess water can’t be processed through the plant.
The long-term control plan is focusing on diverting the excess 3.4 million gallons of sewage water from by-passing the system into the stream. The plan calls for this excess 3.4 million gallons to be contained in two open clarifiers. The town will need two 120 feet diameter clarifiers with a depth of 18 feet at the sides and middle of 23 feet deep. The open clarifiers would allow the solids to settle and “bleed back” the water into the plant for full treatment. The solids would be captured and processed through the plant for full treatment too.
The treatment process differs for the ten-year, one-hour storm. Claus explained the ten-year, one-hour storm is equivalent to two inches of rain. This storm event produces an excess volume of 6.9 million gallons that would flow through the system in six hours. The rain event could create a peak flow of 97 million gallons per day, but the planned facilities would be equipped to process only 80 million gallons per day. This is in excess of the existing wastewater treatment plant capacity, but consistent with the capacity of the existing 72-inch sewer’s slope carrying flow to the plant. The ten-year one-hour storm flow is generating a flow rate up to 80 million gallons per day that is not required to receive full treatment, but only clarification and ultra violet disinfection before being discharged into the stream. The clarifiers will hold the first 3.4 million gallons, but as the volume increases it will eventually flow over the clarifiers’ weirs into the ultra violet channels for the disinfection process. The plan provides two channels of UV disinfection.
Norm Berry, wastewater treatment plant superintendent, said the construction of the long-term control plan is tied to receiving the town’s renewal of the National Pollutant Discharge Elimination System Permit (NPDES). This permit is required to discharge into the stream. IDEM has currently placed the town’s NPDES permit on hold to coordinate it with the mandatory long-term control plans.