Manholes are put in sewer systems to assist in maintenance and cleaning of the sewer pipes. They can be spaced between 100 feet and 500 feet apart. There are over 12 million manhole structures in the United States. It is possible to inspect, repair, clean, and maintain pipes or install new ones in a segment between manholes using trenchless methods. The older manhole structures were typically made of brick or concrete, and they deteriorated because of the presence of hydrogen sulfide gas. The leaks from the structure may wash away the surrounding soil and weaken the structure. Manhole structures may be fractured because of the heaving of the soil from frost in cold climates. Manholes are a significant source of unwanted water in the sewerage system because of high water tables and infiltration, or simply pouring into the structure around the cover, frame, or frame seal, or holes in the cover. The ladders then become corroded and hazardous to employees using them.
Best Practices in Repairing Ancillary Structures Pump/Lift Station
• Establish appropriate pump operations, maintenance, and emergency procedures to operate pump/lift stations in a manner which avoids damage to the adjacent pipes.
• Eliminate groundwater infiltration into pump/lift stations and waterproof as well as possible.
• Make external and internal shapes of pump/lift stations as uniform and as simple as possible, while avoiding creating sharp corners, angles, or bends when constructing them or waterproofing them.
• Slope internal supporting members and floors slightly toward the wall of the structure and provide a drainage space behind the walls and floors to reduce corrosion from standing water.
• Install an internal drain at the floor wall junction to remove leakage and dispose of it in an appropriate manner.
• Where possible when upgrading pump/lift stations, eliminate them by using new technologies involving micro-tunneling or directional drilling. (See endnote 42.)
• Since there is such a variation of structures and equipment in all ancillary units, have on call specialized work crews who can repair or replace whatever equipment structure is encountered.
• Since surface problems can be deceiving especially in concrete, use core samples to determine if an actual problem is occurring and has to be dealt with.
• Always keep complete logs of all problems and repairs. There are a series of techniques which should be used in making determinations of problems in ancillary structures. They include visual inspections, digital photography, tapping with a hammer to find damaged sections, measuring hammer rebound to determine hardness of the surface, testing of the bonding material, ultrasonic measurement of thickness of materials, tilting gauges if the structure appears to be tilting, and installation of crack gauges to monitor openings and shifting of cracks.
• Repairs can vary from patching and sealing to inserting new coats and linings. Also grouting is very important to prevent water leakage.