INCIDENT REPORT
December 2001

This report is to outline some operational changes that were necessary during Storm Event # 19.

The Bloomington area received 2.35 inches of rain from 12/16/01 through 12/17/01, which increased the flow of the ICS above 3500 gpm. This storm was preceded by another storm event # 18 on 12/13/01 through 12/14/01 in which 1.24 inches ofrain fell. The facility stored approximately 600,000 gals of water in the SRS tanks. The backup operator drained as much water out of the tanks prior to Storm # 19.

Due to Storm # 18, the draining of tanks and the high flows generated by Storm # 19 made the facility run at maximum capacity for 4 days. This also did not allow the operators to backwash the GAC vessels before Storm #19. When primary operator returned on 12/17/01, he observed that the head pressures on the GAC's was high. He shut down to 200 gpm and was able to perform a shortened backwash on vessels T-105AI & T105BI. The backwash helped the pressure problem temporarily. During the day, the differential pressure on both sets of vessels started to increase. It was obvious that the GAC's needed a full backwash.

The operator contacted Jessica Fliss the IDEM PM to inform her of situation. Water treatment was slowed to 200gpm to relieve pressure and thickener #2 was decanted. Later that evening, vessels T-105AI & T105A2 were backwashed. When completed, the process was returned to full capacity. Unfortunately, the differential pressures in the set of vessels not yet backwashed was too high to run. The process was returned to 200gpm and the thickeners needed to settle for the night.

The next morning 12/18/01 the thickener was again drained. Upon completion, vessels T-105BI & T- 105B2 were backwashed. Once backwash was completed, the treatment was returned to maximum capacity.

This type of storm scenario will be common in the spring of each year and could possibly be eliminated bythe addition of another backwash waste holding tank of 50,000 gal or larger. This would allow operators to backwash all carbons during a storm event with minimal reduction in processing rates waiting for thickeners to settle and decant.