There are moderate system deficiencies. Most of the system is in relatively good condition, although basement flooding is a problem in the lower part of the basin.
There are a few shallow conduits. Even with the separation of Tanner Creek underway, the amount of stormwater removed will not be sufficient to relieve the combined sewer trunk that runs along SW Canyon Road (BES, 1999). There are capacity problems in the lower part of the basin where the topography flattens out and surcharges occur around PGE Park and Lincoln High School.
Tanner also includes portions of Old Town/Chinatown and the Central Business District. Because of the age of the system - some of the pipes dating back before 1900 - a high percentage of sewers are in poor condition, there are hydraulic capacity problems and records of basement flooding. About two-thirds of the system is plagued with misaligned joints, cracks, and collapsing pipes, based on internal video inspections. Under peak flows, there is substantial surcharging due to backup from the Southwest Interceptor.
Condition problems are concentrated in southern portion of the basin west of I-405. Streets undergo surcharging with a water surface level less than 8 feet from the ground surface. Each collection pipe has its own diversion structure with a majority of structural problems occurring upstream. Shallow pipes are generally not a problem, except for the overflow pipe downstream of the NW Johnson Street diversion structure. A 12-inch collector serving the southwestern portion of the basin along NW Everett Street between NW 21st and 16th Avenues.
Sewer construction materials vary in this subwatershed and may include brick, clay, concrete, and stone. One 725 feet stretch along Burnside between NW 23rd Pl and SW Kingston Ave has numerous openings, mortar loss, and missing bricks (PFP, 1999).