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Development of hydrogen sulfide in small-diameter sewers is minimal,assuming sufficient fall or grade to provide surface turbulence, <br /> continuous venting through connected house stacks,and the absence of flooded sections.In such systems,sulfide controls may be <br /> limited to pumped STEP services connected to the sewer. <br /> ■Pressurized STEP services connected to small-diameter gravity sewers shall be back-drained between pump <br /> cycles to purge the entire service.A vacuum release valve shall be installed at the high point of the service and a <br /> baekdramage solenoid valve shall be installed on a tee at the pump in place of the check valve.Valve shall be 1", <br /> full port,explosion-proof,wired to close when the pump is on.Vacuum release valve shall be installed iu a tamper- <br /> proof vault readily accessible to OWNER's service personnel <br /> ■To assure against sulfide formation in slow-moving lines,small-diameter sewers should be sized to flow no more <br /> than half-full at average daily flow and to provide at least 0.5 fps velocity when flowing half-full.Minimum grades <br /> should be based on Maritimes n=0.013: <br /> 2"@ 0.16% <br /> 3"@ 0.08 <br /> 4"@ 0.05% <br /> 6"@ 0.03 <br /> 8"@ 0.02% <br /> Adverse grades and inverted siphons will create flooded sections,and shall be aerated as described above. <br /> ■Alternatively,the downstream conventional sewer and manholes shall be armored with approved acid-proof <br /> coatings for a sufficient distance to dissipate the hydrogen sulfide.The required distance shall be determined case- <br /> by-ease by the engineer,depending on sewer turbulence and anticipated initial sulfide strength.Normally a <br /> requirement to armor approximately 2000'should be anticipated. <br /> CONSTRUCTION <br /> 1.Construction should comply with applicable provisions of the 1990 Oregon AP WA Standard Specifications for <br /> sanitary sewer construction.All mechanical and electrical equipment should be subjected to performance tenting <br /> prior to acceptance by the OWNER.Contractors and supplier's warranties should be obtained. <br /> 2.Septic tanks shall be tested hydrostatically after installation and after all pipe penetrations have been completed. <br /> Tanks shall be filled to a marked point 4"above the base of the risers.Leakage shall not exceed 50 gallons per day. <br /> Existing building drains and vent stacks being reconnected shall be tested as described above. <br /> 3.All piping shall be pressure tested.Because of shallow burial and the strength of pressure-rated piping,there is <br /> often little potential for pipe deflection,and testing for deflection is optional.The engineer and OWNER should <br /> determine whether installed piping should be tested for deflection case-by-case,and should specify the design of <br /> mandrel to be used. <br /> CERTIFICATION <br /> The engineer(or his authorized agent per OAR 345-52-040)shall inspect the construction and,on completion,shall certify proper <br /> construction in accordance with the approved plans per OAR 340-52,including any change orders subsequently approved. <br /> INQUIRIES <br /> Inquiries about these guidelines should be directed to DEQ regional water-quality plan review,engineers, <br /> kt <br /> t <br />