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Western Dam Engineering 17 Conduit inspections are conducted in one of two ways; exterior conduit inspections and interior conduit inspections. Methods for inspecting the various features of a conduit mainly depend on accessibility. Exterior inspections are obviously the most cost- efficient, but rely primarily on secondary indicators of conduit performance and condition. Interior inspections can be difficult to conduct and sometimes require special equipment. For this reason, exterior inspections are typically used as a good screening tool for justifying more costly, but more definitive interior inspections. The following sections describe exterior inspections and interior inspections in more detail. Photo 1: Sinkhole around a spillway riser2 Exterior Inspections Exterior inspection of the areas above and surrounding the conduit can provide clues about the condition of the conduit. Depressions, sinkholes, or cavities noted along the outlet conduit alignment on the surface of the embankment are indications that internal erosion or backward erosion piping is likely occurring. Seepage areas may also be indicated by changes in vegetative color or excessive vegetative growth on the embankment dam surface. Cloudy discharge or sediment deposits at toe drains or conduit outlets are other external indicators of potential internal erosion issues of the embankment along or into the conduit. Unexplained outlet discharge unrelated to outlet operation or known leakage past the outlet gate is also an indication of potentially deteriorating conditions. If any of these indicators is observed during an exterior inspection, photographs should be taken and the areas monitored for continued changes. These exterior indicators warrant an inspection of the conduit’s interior if one has not been recently completed. 2 FEMA Technical Manual: Conduits Through Embankment Dams Interior Inspections In attempting to inspect the interior of any conduit, accessibility must be considered. Typical accessibility issues include access to the outlet, unwatering the conduit and stilling basin, poor air quality, or small diameter conduits. Confined space permitting, lockout/tagout safety procedures, and stand-by emergency response personnel are all generally required for man-entry into any accessible conduits. If the conduit cannot be unwatered, then special services such as closed circuit television (CCTV), remotely operated vehicles (ROVs), or divers should be used. As a general rule of thumb, dive inspections are 3 to 5 times more expensive than ROV inspections. Should divers be selected to perform an inspection, it is important that they are certified by the Association of Diving Contractors International. Similar to a typical man-entry inspection, a pre-dive inspection plan should be developed and the objectives of the inspection clearly defined prior to the dive, because underwater communication can be difficult with the diver once underwater. Conduit diameters smaller than 36 inches are generally inaccessible for man-entry and require the use of CCTV or ROVs. An ROV unit typically consists of a video unit, a power source for propulsion, vehicle controllers, and a display monitor. ROVs can be obtained for both dry and underwater conduit inspections. ROVs are capable of providing real-time viewing, continuous video for re- viewing, spot photography, and surveying for spatial reference during re-viewing (typically determined by the length of cable discharged into the conduit with the ROV unit). Photo 2: ROV entering a conduit for inspection. If unwatering of the conduit is not possible and the cost of diving is prohibitive, an ROV or CCTV unit can