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City of North Olmsted Wastewater Section Background for TPS Line Replacement Project ,_,) oc.:) -'7(, A section of the 6-inch diameter ductile iron Thickened Primary Sludge (TPS) Line ruptured on Apri126, 2002. The line was constructed in 1970 and the excavation was backfilled with foundry sand as was all other construction trenches dug during the initial 1960 WWTP construction contract and in the construction contracts for the 7.0 mgd WWTP expansion in 1970. This 1960/1970 backfill material has caused the City to entirely replace the original steel naxural gas line as well as numerous potable and nonpotable water lines throughout the WWTP side during the past ten years. The TPS line conveys thickened primary sludge from the Sludge Thickening Building (STB) to the Mixed Sludge Storage Tanks. (See Figure 1 for locations of the named buildings. See Figure 3B for the schematic of the line between the two solids stream unit processes.) The thickened primary sludge flow rate is approxitnately 6 gallons per minute (8600 gallons per day) at 4% to 6% solids (i.e. approximately the consistency of taathpaste). Presently, a temporary TPS line has been placed by the piant maintenance staff (See attached three photos). The temporary TPS line extends between the discharge side of the three TPS pumps and the top of the north Mixed Sludge Storage Tank. The TPS line is ruptured somewhere between the northwestern edge of the Low Presswe Oxidation No. 1 Building (LPO1) and the south side of the Sludge Loadout Building (SLB). From the face of the Digester Building the Mixed Sludge Storage Tanks, the TPS line was backfdled using premium backfill (i.e. sand) during the 1983 WWTP Improvements Project. The 1983 TPS line work was slightly extended during the 1991 UA Fix Up Project. The requested 200 lineal feet of replacement line will extend be placed in the driveway approximately from the west face of the LPO 1 instead of one foot off the face of the building. At its present location, both concrete slabs and asphalt would have to be removed in order to install a replacement line. The requested 2001ineal feet of replacement line will extend from the termination of the TPS line work built dwing the 1991 UA Fix Up Project to the northwest comer of the LPO1. Therefore, should the rema,ining portion of the original TPS line fail in the future, it is probably likely that the plant maintenance staff would be able to replace the remaining original TPS line in the plant driveway. For the portion under the groundfloor slab inside the TPS, the remaining original TPS line would have to be replaced by a construction contractor experienced in tunneling under existing structures. OreWhitePpr.doc Page 1 of 1 May 7, 2002