C153773 Feasibility Study - Laserfiche WebLink

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I I I I I I I I I I I I I I I I I I I Option B-1: Maintain the Existing Gravity Intake This altemative plan is illustrated on Drawing III-A. Maintaining the existing gravity feed intake system is a feasible option for the Town since it would minimize the need for pumping and elirninate the need for new right-of-way easements for the intake. However, the present gravity sYstem does not have adequate capacity to supply the additional water demands of new develoPment and certain sections are in need of repair. Morrison has been reluctant to complete major repairs on the existing system until it can be shown that construction of a new intake is not a better option. The diversion dam on Bear Creek was repaireCl in 1983 after flooding damaged the original dam. The Army Corps of Engineers quickly designeCl emergency repairs to the dam so Morrison could continue diversions for municipal water use. the concrete dam does not span the entire creek, and the structure was designed to route f100Cling around the dam and over a boulder channel bypass. Although the dam appears stable and has withstood flooding in 1995, the Morrison intake remains susceptible to extreme f1oodihg. It is recommended that a more permanent structure, designed for long-term municipal-quality service, be planned for improved diversion capability and improved reliability during flooding. The probable cost of a new diversion dam is $150,000 at 1996 cost levels. Continued use of the existing point of diversiC)n on Bear Creek and the gravity intake involves removal of the old rock masonry stilling basin~ and complete replacement of the upper 800 feet of existing 10-inch steel intake pipeline with new 16-inch ductile iron pipe. A new grit chamber would also be constructed at the same time near the headgate. Plans and specifications were prepared by McLaughlin Water Engineers in 1985(11) for the new intake pipeline and new grit chamber, but the project was never constructed due to ending the agreement to serve Mount Carbon. The plans will need some modifications to match the present water rights portfolio. The cost of new pipe, grit chamber, replacement of pipe through 75 feet of rock tunnel, and aerial steel support structure around a rock slide Zone is expected to be $260,000. This project is more costly than typical pipeline construction projects due to the difficulty in accessing the site and crossing the river. The new intake pipe, removal of the stilling basins, and construction of a new grit chamber near the headgate would increase the capacity of the total 3,800 lineal feet of gravity pipeline to the treatment plant. Calculations indicate the capacity of the 12-inch lined cast iron pipe from the intake on Bear Creek to the water treatment plant would be approximately 4.5 cfs using a Hazen- 7Q..080.035:MSTR-PLN 111-7