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2020 Eugene Wastewater Master Plan Chapter 3: Existing Wastewater Systems 17 <br /> Table 3-6: Existing Wastewater System Estimated Replacement Value – Pressure System <br />Pipe diameter <br />(inches) <br />Average trench <br />depth (feet) <br />System length <br />(feet) <br />Construction <br />cost1 (per foot) <br />Total unit cost2 <br />(per foot) <br />Total cost of <br />reconstruction <br />4 4 543 $56 $70 $38,136 <br />6 4 6,214 $67 $84 $521,560 <br />8 4 5,364 $76 $96 $512,853 <br />10 4 1,031 $93 $117 $120,117 <br />12 4 4,189 $108 $135 $563,859 <br />14 4 115 $156 $196 $22,483 <br />16 5 7,876 $168 $210 $1,656,902 <br />28 5 7,871 $255 $319 $2,508,052 <br />30 6 13,018 $271 $338 $4,405,133 <br />36 7 60 $418 $522 $31,341 <br />42 7 13,118 $506 $633 $8,304,477 <br />72 10 266 $900 $1,125 $299,234 <br />Total 59,665 $18,984,148 3 <br />Note: 2019 dollars (ENR 12281) <br />1 Estimated construction costs are from Table 6-5 of this report for construction in developed areas. <br />2 Total unit costs include 25% for engineering and administration. <br />3 $18.98 million is the estimated replacement cost for the total Eugene pressure wastewater system. <br />SEISMIC ASSESSMENT OF THE WASTEWATER COLLECTION SYSTEM <br />In 2016 a seismic assessment of the wastewater collection system and locally owned pump stations was <br />conducted to evaluate the expected performance of a moment magnitude 9.0 Cascadia Subduction Zone <br />(CSZ) earthquake. The complete technical memo is included in Appendix A. <br />Permanent ground deformation (PGD) is one of the primary factors causing damage to buried pipes. <br />Mapping done by the Oregon Department of Geology and Mineral Industries (DOGAMI) indicates a low <br />probability of liquefaction along the Willamette River, and the south valley. There is a moderate <br />probability of liquefaction along the south hills but, due to the slopes, most wastewater pipes are only 8 <br />inches in diameter. The resulting damage would more likely cause infiltration in misaligned pipe joints, <br />rather than a completely blocked pipe. According to the assessment, the City has in excess of 20,000 <br />gravity wastewater line segments. The total number of line segments expected to experience some level <br />of damage is fewer than 200. <br />All of the pump stations are located in non- to low-liquefaction zones. Underground stations are <br />expected to perform well, and with the exception of the West Irwin station (which is scheduled to be <br />rebuilt), above ground stations are also expected to perform well. The primary issues associated with <br />pump stations are loss of power and the potential to misalign influent and effluent pipes. <br />Given that the majority of Eugene falls in the low probability of PGD, the current design and construction <br />specifications utilizing bell and spigot PVC are suitable for gravity wastewater pipe, and welded HDPE for <br />force mains. New pump stations should be designed to current seismic standards with special attention <br />to the influent and effluent pipe connections to the structure.