Field Office Compliance - Assistance

Assistance ID - 30267
Des Moines Water Works - 310338211
9966 Maffitt Lake Dr Cumming, IA 50061
Dallas County

FO 5

Report
File Name File Type File Date Note
Comments
3/1/2011 From: Graham, David [mailto:[email protected]] Sent: Tuesday, March 01, 2011 8:00 AM To: Gastineau, Janet [DNR] Subject: Filter Turbidity Hi Janet, One of our filters at the Fleur drive plant exceeded 1.0 NTU in two consecutive readings on 2/17/11. Between those two reading the turbidity peaked out at 1.19 NTU. This occurred 13 minutes after the filter was put on line. We typically see a similar spike in turbidity whenever a filter is put on line, but not normally anywhere near this high and the spikes normally only last a few minutes. The filter control program is supposed to shut a filter off any time the turbidity exceeds a operator entered set point. The set point is normally at .15 NTU, since that is well above what we expect to be getting from our filters. During the week that this occurred there had been considerable snow melt and the breakup of the Raccoon River ice. The turbidity of the Raccoon River had increased considerably and despite the typical steps taken to deal with the high raw water turbidity, we were experiencing slightly higher effluent turbidity from all of our filters and shorter filter run times. The typical spike in turbidity that occurs when a filter is put on line had gotten quite a bit higher in the filters, but none of them had been any higher than about .4 NTU until filter #16 was put on line. To avoid the problem of a new filter being shut off by a turbidity spike when it was put on line, we had increased the automatic filter shut down set point from the normal .15 NTU to .45 NTU. We were prepared to accept higher than normal filter turbidities in order to be able to keep enough filters on to process the flow through the plant and keep up with the increasing number of backwashes. When we noticed filter #16 had failed to take itself off line when the turbidity had exceeded .45 NTU, we looked into the programming and found that the part of the program that had been designed to ignore turbidity spikes above .15 NTU for 15 minutes a filter was on line to avoid nuisance alarms, was also ignoring the turbidity set point that was there to shut the filter down in the event the turbidity exceeded .45 NTU. That programming has been changed now to shut the filter off whenever there is a turbidity event that exceeds .45 NTU. If you have any questions or want any other information please let me know. JANET GASTINEAU
2/24/2011 ________________________________________ From: Gastineau, Janet [DNR] Sent: Thursday, February 24, 2011 2:27 PM To: Bunton, Jennifer [DNR] Subject: RE: individual filter profile Thanks Jennifer. My information should have said two consecutive IFE turbidity above 1.0 NTU. The turbidity reading was above 1.0, but not by much he said, for 19 minutes but he never gave me a value. I will be following up with Dave on this filter profile information and ask him. Usually we don’t even catch these till the MOR is submitted but Dave decided to call and said this one happened about 7 days ago. The Raccoon River turbidity has been up anyway with the snow/ice melt and he’s pretty sure what happed was the operator increased the setpoint for the filter automatically shutting off because they were getting a number of alarms and it didn’t get set back to the lower setpoint so it crept above 1.0. CFE was not affected. They will be reviewing SOP for changing setpoints and whether operators should even have access to changing these. ________________________________________ From: Bunton, Jennifer [DNR] Sent: Thursday, February 24, 2011 2:19 PM To: Gastineau, Janet [DNR]; Alt, Dennis [DNR]; Anderson, Michael [DNR]; Bunton, Jennifer [DNR]; Campbell, Bob [DNR]; Enfield, Daryl [DNR]; Evans, Eric [DNR]; Moeller, Mark [DNR]; Moles, Diane [DNR]; Montefusco, AJ [DNR]; Neleigh, Jim [DNR]; Slattenow, Skipp [DNR]; Veerabhadrappa, Taroon [DNR] Cc: Grapp, Shelli [DNR] Subject: RE: individual filter profile From IAC 567 40.2 (455B) “Filter profile” is a graphical representation of individual filter performance, based on continuous turbidity measurements or total particle counts versus time for an entire filter run, from startup to backwash inclusively, that includes an assessment of filter performance while another filter is being backwashed. I would be inquiring as to whether the SCADA is set appropriately when there are two measurements of exactly 1.0 NTU since this would be extremely unusual. They should be able to go back in the turbidimeters and see what the actual readings were to see how high they really went. ________________________________________ From: Gastineau, Janet [DNR] Sent: Thursday, February 24, 2011 2:10 PM To: DNR Water Supply Engineering Subject: individual filter profile DMWW recently had an individual filter that had two consecutive 1.0 NTU measurements. They are pretty sure they can report the obvious reason but are asking what a filter profile consists of. Is there some documentation they can turn to or a quick summary you can provide that I can forward to Dave? Thanks. JANET GASTINEAU
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