2007/11/21 Council Agenda Packet

1€ PHASE 3 - SOUTII END INTERCEPTOR EXTENSION S"f,a'CION 186 PIPELINE PROTECTION INTRODUCTION File Cite of U.verett I)epartirrent Of' Public Works has requested that URS Corporation design the support 01'a section 01-01C South End Interceptor Extension pipeline in the vicinity of Station 186. fhc support is required to protect the pipeline from a new Burlington Northern Santa Fe (BNSF) rail track that will cross over the pipeline. The design work will be Phase 3 of the 36'x' Street Sewer Protection Project contract between the City and URS. The scope was first discussed during, a meeting between Souheil Nasr of the City and Cecil Urlich of URS on .lune 11, 2007_ The Cite provided URS .with geotechnical reports, pipeline drawings and piling records, and track design drawings, and Brian Hamilton of URS obtained track design information from James Rhodes of IINTB. A draft scope that included geotecttnical drilling was submitted by URS to the Cite on June 29, 2007 but was held pending BNSF review and approval. The [.Manned �,eotechnical work was reduced in scope because of difficulties in coordinating a drill rid and flagger. Eventually. in order to not delay the project, it was agreed during a meeting on September 27, 2007 between Nlessrs. Nasr and Urlich, Hamilton, Bob Wallace and Xiangdong [-fan ol'URS to complete the design \without drilling and to rely ort geotechnical data frorn nearby projects. It .was understood that differing site conditions may be encountered during construction. PROJECT BACKGROUND The pipeline and rail track clesign drawings show that the new track (Turkey Trail) will cross over a jog section of the pipeline in the vicinity of Stn. 186. The jog section is approximately 110 feet long and is near the east boundary of Lowell Park between 47"' and 48"' Streets. The pipeline is 36 -inch diameter steel. and 8> feet of the joy, section is imide a 60 -inch diameter steel casing. The pipeline Jog section is approximately northwest to southeast oriented. -1-11e purpose of the project is to protect the pipeline from the loads of: the new embankment and track. The track dcsi<_,n drawiugs prepared by HNTB in 2007 show that there are two existing tracks crossing over the pipeline jour, and that they will be replaced by the Turkey Trail Track. One of the existinr, tracks is active, the other is inactive. The inactive track can be removed at the start of construction, but the active track will remain operational till near the end of construction. URS understands (flat BNSF plans to raise the track three feet above the existing grade because of local flooding by rising waters from a nearby stream. BNSF plans to remove the existing active track by November 30, 2007, and build the new track by December 14. Therefore, to expedite construction, the URS desitii will phase work outside the active track to be completed first to minimize the impact of no track between when the active track is removed and new track is built. According to Mr. Rhodes, there is a fiber optic cable buried about 10 feet deep near the pipeline but the exact location of the cable is not known. The 2007 IINTB drawing Sheet 36 of 67 for the Turkey Trail Track Project shows a Tel.'Fiber line Jelus, Allstreanl, BNSF) approximately 72 inches deep in the project area, but does not provide a detailed location. The pipeline as -constructed drawings prepared by Gray & Osborne in 1992 show that the pipeline jo<, section is covered by about 5 feet of soil. and that 85 feet of the pipeline is cased in 60 -inch URS Pace I of 10 9G