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~L~RIN~ &~ ~ASSO(IATFS TAU6 UOATA Memo TO: Honorable Mayor and City Council Members FROM: Lee Elfering, City Engineer DATE: August 13, 2008 RE: City of Little Canada /City of Maplewood Kohlman Lane Area Project Sanitary Sewer Extension The Contractor for the Kohlman Lane Area project has completed the directional drilling of the sanitary sewer that was included in the Maplewood project to provide for the future extension of gravity sewer service to several properties south of LaBore Road. The length of the drill was 466 feet and varied in depth from approximately 20-30 feet in depth. Televising of the line discovered a 50 foot section of the line with a 2-inch sag, which raised concerns as to the functionality of the line. In discussing the reason for the sag with the Contractor, they have indicated that there was an unknown condition prior to installation. The Contractor stated that the KSTP radio towers caused interference during drilling making it difficult if not impossible to accurately track the location of the drilling head at the time of installation. Directional drilling is completed by drilling a rod with a steering and locating head through the soil without excavation. As the line is being drilled the locating head is tracked for depth and location along the alignment. Once the initial drilling is completed a hole is reamed through the soil by pulling the drill stem back through the hole created along with the actual pipe. The interference resulted in the Contractor not being able to accurately monitor the head during drilling operations. We discussed this issue with the Maplewood Inspector that was on-site who verified that there were difficulties during installation. Staff has met with the Contractors to discuss the possible solutions to the issue that exists. Below is a summary of the options with the benefits and drawbacks of each. Excavation and Correction The sewer line is approximately 25 feet deep and is located approximately 10 feet to the west and parallel with a shallower (10 foot deep) sanitary line that serves the homes along Kohlman Lane. Private utilities including gas, telephone, TV, and electric are located in the boulevard approximately 10 feet west of the line. It is also estimated that two water and sewer services would be within the excavation area. ]t is estimated that an open cut correction would be approximately $60,000.00. Benefits: • The line would be corrected prior to curb and pavement installation. • The Contractor is still on site and at least partially liable for the correction.