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<br />6.2A <br />Page 54 <br /> <br />degradation. Because repairing. future leaks would likely require a pipeline shutdown, several <br />short pipeline segments would likely be replaced under this alternative to increase their <br />reliability. Also, ground shaking could damage BDPL Nos. 1 and 2 in the area of Pulgas Tunnel <br />Portal, where portions of the pipeline are aboveground and are supported by metal trusses. <br />Additionally, several pipeline connections in this area would need to be modified with expansion <br />joints to improve their seismic reliability. Finally, the ongoing inspection and maintenance <br />program for BDPL N.os. 1 and 2 would need to be expanded to include temporary repairs, <br />including painting, rust removal, timber and walkway repairs, and rivet, bolt, and brace <br />replacement. <br /> <br />The Northern Alignment Alternative would avoid several impacts of the proposed Project. <br />Because using the existing piers to cross a portion of San Francisco Bay would not require shafts <br />and a tunnel, this alternative would avoid the noise and vibration impacts associated with hauling <br />excavated material from the shafts and tunnel. In addition, it would avoid the traffic <br />consequences of seismically upgrading the Dumbarton Bridge to support SFPUC water <br />conveyance pipelines. However, using the piers would require extensive retrofitting of the <br />existing piers and the supporting pilings, thereby creating significant wildlife, fisheries, water <br />quality, and air quality impacts. As a result, the work needed to retrofit the piers to support the <br />weight of the pipeline would result in both an increase in the number and the severity of impacts <br />on the environment over that of the proposed Project. <br /> <br />This alternative would meet most, but not all of the SFPUC's Project objectives. While the <br />upland portions of the new pipeline would be seismically reliable, the seismic reliability of the <br />Bay crossing using the Dumbarton and Ravenswood piers is uncertain (attaining that reliability <br />could require significant retrofitting of the piers and supporting pilings), and the pipeline could <br />be more vulnerable to seismic events than the proposed Bay Tunnel because of the combined <br />pier/trench placement of the bay crossing. The new pipeline would increase capacity to meet the <br />estimated 2018 average winter month demand; however, it would not contribute effectively to <br />meeting this demand rapidly following a seismic event because it would be more difficult to <br />repair and may not be accessible during an emergency. For the aforementioned reasons, and the <br />reasons described below, the Commission rejects the Northern Alignment Alternative as <br />infeasible: <br /> <br />· The pilings on which the piers sit may not be structurally sound for purposes of <br />supporting a heavy water supply pipeline and therefore, retrofitting would likely be <br />needed. Therefore, this alternative would require extensive retrofitting of the piers and <br />the supporting pilings to support the estimated 2,300 pounds per linear foot of pipeline. <br />Such retrofitting would likely include either encasement or replacement of the existing <br />pilings supporting the piers with concrete pilings to support the pipeline, as well as the <br />installation of additional pilings to support the weight of the pipeline. Activities <br />associated with retrofitting and installation of pilings would result in numerous <br />environmental impacts including disturbance to fish and nesting birds in the area from <br />pile driving activities (e.g. vibration andsh<>.<?k..'\\'.~v~s),. ~~ r~~s.':1~p.e.~4e.~ ba.y..~l1.4...t~~t.... .... <br />. .......W6i.ild":catIseincte~fsed:..furbidit)<Retiofitting the piers would also Tequire :constructionon . <br />both sides of the bay, thereby increasing air quality and traffic impacts from additional <br />construction equipment and truck traffic. <br />· Because Caltrans removed the center span of the original bridge, SFPUC would need to <br />construct a submarine pipeline or tunnel between the two piers) potentially requiring the <br />placement of fill for supporting structures or the use of caissons to excavate tunnel shafts. <br />Otherwise, if the pipeline was placed in a trench on the bottom of the Bay, its excavation <br />would temporarily create turbid water conditions that could impact special-status species, <br />such as migrating steelhead. <br /> <br />44 <br />