Lake Hodges-Olivenhain Reservoir Water Tunnel Nears EndA water tunnel to link Lake Hodges and Olivenhain Reservoir is built by Kiewit Pacific Co. for the San Diego County Water Authority (SDCWA) in California. The tunnel will span 1,769 metres, of which 1,710 metres (or 96.7%) is completed already, and will connect to a 152 m-long tunnel that already extends below ground at the Olivenhain Reservoir. It is a 4.27 m OD tunnel (3.96 m ID). Visit www.sdcwa.org and www.kiewit.com When Lake Hodges and the Olivenhain Reservoir are connected, the project will link Lake Hodges for the first time in its 88-year history to the aqueducts that carry water from the Colorado River and Northern California. Olivenhain Dam gets nearly all its water through the aqueducts. In contrast, Lake Hodges, which is owned by the city of San Diego but serves customers of the Santa Fe Irrigation and San Dieguito Water districts, is fed by a 777 sq km watershed. Like the San Vicente pipeline (click here), the tunnel project is part of the SDCWA's emergency storage project, a system of reservoirs, pipes and other systems to provide water if a catastrophe were to cut off supply. The tunnel's purpose is to shift water between the reservoirs. The tunnel will rise 213 metres in elevation from Lake Hodges to Olivenhain Reservoir. It begins at a nearly level 0.5% grade at Lake Hodges and stays that way for about 610 metres. Then it turns and slants to a steeper 13% grade for the middle third of its length. For the final third, it tilts to a 19% grade, rising 30 cm for every 1.5 horizontal metre it advances. At the deepest point, the project will lie 122 metres below ground.The project includes the tunnel, a pump station to force water up a pipe inside the tunnel from Lake Hodges to Olivenhain Reservoir, an electricity-generating substation and power lines. Construction of the pump station began in May. During dry periods, the SDCWA will be able to refill Lake Hodges from the Olivenhain Reservoir. During wet winters when Lake Hodges fills, the authority will pump water uphill through the tunnel into the Olivenhain Reservoir. The process will take energy because the water will have to be pumped up a 213 m incline through the pipe. Moving water in the opposite direction will require only gravity, and when the water flows down the pipe, it will turn a pump turbine to produce 40 MW of hydroelectric power. The Lake Hodges tunnel project is located in the western foothills of the Peninsular Ranges geomorphic province. This province extends south from the Los Angeles basin to the southern tip of the Baja California peninsula and is characterized by northwest-trending mountain ranges that are bounded by sub parallel fault zones associated with the boundary between the North American and the Pacific plates. The province is generally composed of crystalline rocks (igneous and metamorphic rocks). The intrusive igneous rock is collectively referred as the Peninsular Ranges batholith and is characterized by northwest trending faults. The main geologic unit is the Escondido Creek leucogranodiorite. This Cretaceous-age granitic rock unit contains inclusions of Jurassic-age Santiago Peak Volcanics. Workers began to bore on Lake Hodges' north shore last September. Excavation is done by drilling and blasting, using a new Terex Reedrill two-boom electric hydraulic jumbo with 3.65 m slides, model MK35HE-PS, working at a unique drive. The explosives are Magnafrac Plus HW and the detonators are 4.9 m Exel LP, both from Orica and supplied by W.A. Murphy. Visit www.reedrill.com, www.oricaminingservices.com or www.orica.com and www.murphypowder.comThe cycle begins with drilling a pattern of 58 to 65 holes, each 4.4 cm in diameter, into the rock wall, then packing explosives into the holes before setting off electronically from outside. Crews extend the tunnel 7.3 to 11 metres every day (3.65 m production rounds per shift). Three five-man crews rotate through three eight-hour shifts throughout the day, so crews are on the job 24 hours a day, Mondays through Fridays. On weekends, they pour concrete on the tunnel floor and perform maintenance tasks.The moderatly jointed bald-headed hard rock geology does not require ground support, with the exceptions of two shear zone locations and weathered rock area at the portal where split-set bolts and chain link fence was used for ground support. Ground support utilized if necessary 1.5 m split-set bolts, split-set bolts with chain link fence and mine straps when ground was blocky in weathered rock and shear zone locations. Also, at the start of the tunnel drive at the portal, first 30.5 m horse-shoe type steel sets with 7.7 cm lagging were installed for ground support. The supplier is American Commercial. Visit www.americancommercial.comA fleet of low profile rubber tyre muckers are operated to remove the blast rock from the tunnel heading, including two Cat Eliphinstone R1600G LHDs and one Wagner ST3.5 LHD. At the portal, a Cat 966 loader loads the shot rock into a Volvo A25C rock haul truck for transport to on-site dump site. Visit www.cat.com and www.volvo.comWhen tunnelling ends, a 3 m-diameter steel pipe of varying thicknesses will be placed in the tunnel, then crews will grout between the pipe and the rock wall. The finished tunnel with steel pipe liner will have a diameter of 3.66 m. The scheduled date for breakthrough of the tunnel is August 2006.Other underground structures within the project include a 3.66 m-diameter 56.7 vertical metre surge chamber shaft. Work is in progress by subcontractor Raisebor, consisting in drilling a 4.2 m pilot hole in preparation to ream (raise bore) the surge chamber shaft using an Ingersoll Rand/Robbins raiseboring machine. Visit www.raisebor.com, www.ingersollrand.com and www.robbinstbm.com Substantial completion is scheduled for 2nd February, 2007 and final completion on 15th March, 2007. The tunnel will cost USD35 million and the full project USD104 million. Click us/82. Read E-News Weekly 12/2004. 31-32/06.