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SANITARY SEWERS Recommended Standard Specification Plant Testing - Leakage Allowance Most manufacturers are willing to test sewer pipe in their yard prior to shipment to insure that the barrels of the pipe will not leak. Random vacuum testing of an assembly of two or more sections of pipe can also be performed at the place of manufacture to assure the integrity of the pipe joints. Field Testing - Leakage Allowed Infiltration should be held to a minimum in sanitary sewers since it reduces the carrying capacity of the sewer, keeps associated sewer system treatment costs at a minimum, and eliminates maintenance and operating costs arising from soil fines entering the system under infiltration situations. Acceptable infiltration limits have varied widely over the years but the trend in recent years has been to require sewers to meet low infiltration limits. Low leakage requirements can be met with well made concrete gravity sewer pipe and rubber gasket joints. It should be recognized by the engineer, however, that field performance represents the sum of the manufactured joint characteristics and the contractor’s installation practices. In making the joint on rubber gasket sewer pipe, the pipe being installed should be held by the lifting device straight to line and grade with the pipe in the ground. The pipe must not be held at an angle when entry is started to avoid the gasket being pinched between the shoulder of the spigot and bell at the bottom of the pipe. With the spigot carefully aligned at the entrance to the bell and with the pipe to be installed held in line with the previously laid pipe, the joint should be pulled home slowly. To check on whether reasonable workmanship was realized during the construction phase, maximum limits of allowable leakage in terms of water infiltration or exfiltration are usually included in project specifications. They should be stated in terms of both maximum allowable rate per test section and maximum allowable average rate for the total project. These project acceptance tests evaluate the quality of the contractor’s work. There are many opinions, but not much hard data, upon which to base infiltration requirements that are generally cost-effective. There will always be at least a small increment of infiltration which is not cost-effective to eliminate. The expense of the pipe and increases in construction and inspection costs fix the lower limit for infiltration allowance. Current information indicates that the 200 gallons/mile/inch-diameter/day can normally be achieved in manhole to manhole tests with minimum to no effect on construction cost. A higher allowable leakage limit should be used for an exfiltration test over that used for an infiltration test. This is because the exfiltration test is performed with a definite internal pressure head, and the exfiltration of clear water out of the pipe is less likely to be reduced than the infiltration of ground water mixed with soil fines into the pipe. A ready reference for information on construction leakage allowances in sewers and methods of test is provided in the EPA Manual of Practice, Sewer System Evaluation, Rehabilitation and New Construction. Protective Lining Products Present design methodology for sanitary sewers gives the designer the ability to predict the potential for hydrogen sulfide production. Available references include EPA’s "Design Manual on Odor and Corrosion Control in Sanitary Sewerage Systems and Treatment Plants" and ACPA’s "Design Manual, Sulfide and Corrosion Prediction and Control". If the potential for hydrogen sulfide production is determined to be significant, linings or coatings may be used to protect the inner pipe surface from corrosion. Available liners consist of a sheet of plasticized PVC with T-shaped keys running longitudinally along one face. The keys are cast into the concrete pipe during manufacture. PVC liners have been used very successfully for over 30 years. Available coatings may consist of coal tar/epoxy, polyethylene or polyurethane. Coal tar/epoxy coatings are applied by spraying either during or after manufacture of the concrete pipe in varying thicknesses. These coatings have proven to be effective providing adequate surface preparation is performed, adequate thickness is applied and adequate quality control procedures are followed. |Home| |About ICPA| |Meet Our Staff| |Join ICPA|
Illinois
Concrete Pipe Association |
