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The American River Common Features Project is located in the American River Watershed in Sacramento, California. In 2005, the U. S. Army Corps of Engineers was asked to certify the Sacramento River levees south of the confluence of the American River for the FEMA 100-year protection level. During this certification process, it was discovered that the level of underseepage was much worse than previously assumed, and the levees did not provide the required protection level. Three sites were identified as critical to meeting the FEMA 100-year protection level. In August of 2006 Envirocon was awarded the Pocket Geotechnical Project which contained two of these sites (reaches). One of sites was in the Pocket Area and one was located just south of the town of Freeport. The project was completed on schedule, within budget, and with no lost time accidents.
The project included two reaches (Reaches 2 and 9) of cutoff walls in the existing left bank of the Sacramento levee. The first wall constructed in Reach 2 was a 1,750 foot-long, 110-foot deep Deep Mix Method (DMM) cutoff wall. The second wall constructed in Reach 9 was a 1,520 foot-long, 40-foot deep soil-cement-bentonite (SCB) cutoff wall which required removal of 1,650 linear feet of railroad track and the implementation of a traffic control plan on Highway 160. Envirocon also completed two large modifications to the contract, including the construction of a concrete floodwall/stoplog structure and reinstallation of the railroad tracks in Reach 9.
Envirocon was required to tie the Reach 2 DMM cutoff wall to an existing 30-foot deep slurry wall on each end, while protecting it in-place. Two monitoring wells and a utility vault were also required to be protected in-place during construction. Due to the Reach 2 DMM cutoff wall alignment being located adjacent to a residential neighborhood, Envirocon had to monitor noise and vibration levels during construction, and was restricted from disturbing the land side of the levee slope. Videotaping of the adjacent homes and backyards was performed prior to construction. Envirocon accomplished all without receiving a single complaint of damage resulting from the construction.
The design also specified cutting and replacing a 16-inch active waterline crossing the Reach 9 slurry wall alignment, however, Envirocon was able to successfully excavate around the waterline without having to cut it. The existing railroad tracks in Reach 9 were also deemed historic by the State Historic Preservation Office. Envirocon preserved all of the tracks, fasteners, and other metal components during removal, so that they could be reinstalled after completion of the cutoff wall.
Differing soil conditions were discovered in Reach 9 during construction which required Envirocon to more than double the levee degrade and still maintain the tight construction schedule. The Reach 9 cutoff wall construction was coordinated with an adjacent Marina as to minimally affect their business. Envirocon also provided traffic control for a busy highway adjacent to the project during construction.
The scope of work also included degrading the existing levee to provide a working platform for the specialty long-stick excavator. During the excavation process, differing soil conditions required redesign and implementation of more conservative measures for degrading the levee an additional 4 feet to construct the slurry wall at site Reach 9, and to prevent the potential of hydraulic fracturing. Envirocon accommodated these changes and efforts resulted in a safe and stable cutoff wall without the induction of potential embankment failures. An additional challenge included the environmental constraints which required protection of the Swainson Hawk and the Longhorn Elderberry Beetle.
Envirocon held a weekly coordination meeting to keep all parties aware of current activities, upcoming events, and to assist with prompt issue resolution. The meeting was attended by SAFCA, State Department of Water Resources (DWR) & Reclamation Board, local and county representatives, subcontractors, and safety & quality control/quality assurance representatives. This meeting assisted with maintaining excellent public relations with the local residents and businesses. Envirocon’s management team responded promptly and cordially to the public's questions and concerns allowing completion of the project without any claims or complaints.
Envirocon was able to complete construction on the Pocket Geotechnical Project prior to the flood season. With a large fleet of owned equipment and in-house expertise to construct the 110-foot-deep Reach 2 DMM wall, Envirocon met the difficult qualification and experience requirements to be considered for this contract.
The high public visibility of the project was due to the critical nature of levee work in the Sacramento area in the prevention floods and the heightened interest of the Reclamation Board and SAFCA. Envirocon’s proactive safety program resulted in 16,685 exposure hours without any lost-time accidents for this project.
Envirocon received the prestigious South Pacific Division Construction Contractor of the Year Award for Civil Works/Dredging 2006 from the U.S. Army Corps of Engineers for outstanding performance. |
