Floating Cover Replacement - City of Ogden
LOCATION: Ogden UT TIMEFRAME: August - October 2011 SCOPE OF WORK: Replace 3 towered tensioned 45 mil floating covers with a perimeter skirt upgrade PROJECT PARTNERS Owner: City of Ogden Installation: Layfield Environmental Systems Corp Engineer: Sunrise Engineering
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The City of Ogden Utah has 3 potable water reservoirs which have existing floating covers on them, comprising of 45 mil Reinforced Polypropylene with weighted tower tensioning systems around the perimeter. The floating covers were installed by CW Neal (Layfield) in 1994 and 1995. In general, the City was pleased with the performance of the covers over the years however, they did have some minor maintenance issues. As the RPP was coming close to the end of its 20 year manufacturer’s weathering warranty, the City was looking to have the existing covers removed and replaced with new covers.
As is often the case, the City faced monetary constraints in terms of having the floating covers replaced. Moreover, the City’s Public Work Dept wished to fast track this process and wanted all 3 covers replaced in the same year. There were time constraints to undertaking the task of removing and replacing 3 covers with an approximate area of 895,000 sf, as the City could not take these reservoirs out of service until after their peak demand period. This meant that the earliest that removal could begin would be late August, and if not properly managed it would mean that the installation would run into winter weather conditions adding further complications to installing the new covers. Furthermore, in order to avoid the added time and internal costs associated with a formal bidding process, the City Public Works Department was required to demonstrate to both the City Attorney’s Office and the City Council, that proceeding with a sole-source contract to Layfield was the best option in terms of technical and financial restrictions.
As to ensure all requirements for the project were understood, an onsite visit was coordinated including the City of Ogden Public Works Dept., the third party engineer that was hired for the project, as well as representatives from the Utah Dept. of Environmental Quality (DEQ).
The main concern expressed by the Dept. of Public Works was the cleaning of the debris that would accumulate around the perimeter fold of the floating cover. This was addressed by adding a skirt over the perimeter fold on the replacement covers. As this is the only fold/trough that exists on a weighted tower tensioned system, the addition of this perimeter skirt drastically minimizes any accumulation of debris in locations that are not readily visible and thereby reduces the amount of maintenance required.
The DEQ representatives were impressed with the condition of the floating covers and their performance over the 16-17 years that they were operational. With the addition of the aforementioned perimeter skirt, they had no concerns with replacing the existing floating covers with similar systems.
Once operational and DEQ concerns were satisfied, the next obstacles to overcome were to try and meet the City of Ogden’s financial and time constraints. There are many advantages to a floating cover with a weighted tower tensioned system over other types of systems. The first being that as this system does not require troughs/sumps, cleaning the floating cover is much quicker. The second advantage is that when replacing the floating cover, a majority of the hardware can be reused when installing the new cover. During the site visit conducted by Layfield, it was confirmed that a majority of the tensioning hardware could be reused when installing the new covers. This meant substantial savings for the City of Ogden.
Layfield worked closely with the City of Ogden Public Works Dept. and their third party engineer to understand their requirements and constraints when designing the floating cover throughout the process. We assisted by providing written documentation that would aid them in demonstrating to the City of Ogden Attorney’s office and City Council, that it was in the their best interest to sole source the replacement of the floating covers to Layfield. The items addressed were Layfield’s familiarity with the site, the positive performance of the existing floating covers and the savings that would be realized by the City in reusing the existing hardware.
Upon receiving the written proposal both the City Attorney and the City Council immediately approved this project to be fast tracked and to have Layfield remove the existing covers as well as fabricate and install the replacement floating covers.