Wawona Water Storage Tanks Replacement

This project will replace two public drinking water storage tanks at the park's south entrance and at the Lower Mariposa Grove. Both tanks will be replaced with new equal capacity or smaller tanks placed in the same location. The Lower Mariposa Grove tank is a 10,500 gallon steel tank and is surface mounted on a foundation ring. The grove tank may be reduced in capacity. The system no longer feeds flush toilets so capacity reduction may be achievable. The tank capacity will be verified prior to construction and will not be less than 2,000 gallons, but may be as large as the existing tank. The tank will be a bolted steel tank and will be matte black in color to help it blend into the shadows of the forested area. At the south entrance the tank is 4,000 gallons and is sub-surface mounted. The new tank will be a matte black stainless steel 2500 gallon tank and will be mounted on a concrete pad. A small retaining wall (20' long not more than 3' high) will be installed per the attached Conceptual Design Plan. The retaining wall will allow the profile of the tank to be lowered so that it is less visible from the road. The wall will be made out of granite from native material supplied from a NPS stock piled area. All concrete shall be colored dark to reduce it visual presence. Per coordination with Yosemite's Utility Branch, Archeology Branch and History, Architecture and Landscapes Branch, the above solutions were developed and selected as the preferred alternatives.

Construction work will include minor site grading and necessary plumbing to reconnect to the existing water distribution system. The work would be done in the same foot print as the existing tanks. The disturbed area will be contained to with in 8' of the existing tanks water lines. All disturbances anticipated to be contained to previously disturbed areas. Tank delivery methods will be by track trailer. Notably, the final leg of delivery for the grove tank will be via an old road. The road will require some brushing. This is the same road that is used to install the existing tank and by utility crew to service the tank.

Work will be a combination of contracted labor and in-house labor.

The proposed project scope requires that all contract equipment coming into the park be weed free and equipment will be inspected by either park vegetation staff. It also requires submission and approval of proposed material sources to be used on the project.

The current Lower Grove tank is a bolted steel tank with numerous leaks and major deterioration. The current South Entrance tank is a series of below ground small tanks bolted together. Both tanks have major rust and leakage problems. The tanks are used for storage and allow for proper chlorine contact time. The rust inhibits adequate disinfection and the leakage shortens the contact time. The poor condition of both tanks allows for foreign matter to be introduced into the tanks decreasing water quality. Replacing the two tanks will assure better storage, increase chlorine contact time, reduce water wasted and increase the water quality for visitors and residents of Yosemite. Both water tanks have outlived their life expectancy and need replacement.