Technical Manual: Conduits through Embankment Dams (FEMA 484)

Chapter 9—Inspection and Assessment of Conduit-Related Problems• Construction.—Cleaning of the existing conduit may be required as part of theselected renovation method; see chapter 12 for renovation methods requiringcleaning of the existing conduit.• Maintenance.—Cleaning may be required to improve the flow capacity within theconduit due to hard deposits, bacterial growths, sediments, or debris that mayhave collected in the conduit. Periodic operation of the conduit will flush outmany of these types of collections. However, infrequent operation ornonoperation may allow for continued buildup of these collections.1. Hard deposits.—If a conduit has not been periodically operated, certainmechanisms may develop within the conduit. In conduits experiencingseepage into the conduit through a joint, solid deposits may develop wherethe seepage water evaporates. These deposits often contain calciumcarbonate, which precipitates out of solution as the mineral calcite. Calcitewill form deposits when the calcium ion and bicarbonate ionconcentrations in the water increase to the point where they exceed thecapacity to dissolve in water. Hard deposits of calcium carbonateprecipitate may develop when the seepage water evaporates.2. Bacterial growths.—If a conduit has not been periodically operated, certainbacterial growths may develop within the conduit. Bacterial growths arecommon and can develop under a variety of conditions. Bacterial growthcan occur anaerobically (without oxygen) and aerobically (with oxygen).Most of the time, bacterial growths are soft and easy to remove, but insome situations, these growths can become hard and mineralized. Aerobicbacterial growth can also create hazardous conditions by depleting theoxygen in the air of a confined space.3. Sediments and debris.—If a conduit does not discharge water completely outof the system or if the discharge channel is adversely sloped, water maypartially or completely submerge the exit portal. If this occurs, sedimentsand debris can back up into the conduit, resulting in sediment deposits ordebris accumulation.9.6.2 Cleaning methodsThe improper use or the selection of incorrect cleaning equipment may causeadditional damage to a deteriorating conduit and further degrade its structuralintegrity. The type of conduit material (i.e., concrete, plastic, or metal) must beconsidered in selecting the appropriate cleaning method. Some conduit materials(such as CMP) are much more prone to defects. Cleaning of inaccessible conduitsshould only be considered after CCTV thoroughly inspects the conduit. If a229