Lake Forest reservoir relining and floating cover The compiled test results showed that factory seams are about 10% stronger than field seams. Factory fabrication can typically result in about 75% fewer field seams on a project. of the geomembrane liner, cover and components resulted in substantial reduction in the amount of required field welding, construction time and installation cost. Prefabrication typically results in a major reduction of installation time and construction cost. We estimate that the prefabrication of the liner and cover system reduced field welding time by over 50% on the Lake Forest project. This was also important considering the highly inclement weather conditions typically experienced in the Seattle and Puget Sound region of western Washington. The Fabricated Geomembrane InstiFIGURE 11 Factory fabrication of CSPE panels in Lakeside, Calif. plant tute (Stark et al. [2020]) has previously compared factory and field-welded thermal geomembrane seams for a large off-stream water reservoir project. This comparison showed that factory-welded seams exhibit higher seam peel and shear strengths, less variability and more consistency than field-welded thermal seams. The compiled test results showed that factory seams are about 10% stronger than field seams. Factory fabrication can typically result in about 75% fewer field seams on a project. Material selection The material selection process was a very important factor for the geomembrane liner and floating cover portion of the project. The owner has reported leakage and the existing reinforced polypropylene (RPP) material was showing signs of stress cracking and premature degradation. This included various cracks located around folds and creases (see Figures 12 and 13). Unfortunately, the extent of damage on the geomembrane liner could not be fully determined until the reservoir was taken out of service and the floating cover system was removed. The type of cracking in the material folds is often associated with multiple factors including prolonged UV exposure, continuous exposure to chlorine used for potable water disinfection and stress concentrations at upstanding folds resulting from hydrostatic pressure. Chemicals used for disinfectants in municipal water treatment include chlorine and chloramines and can function as accelerators in breaking down or leaching out the protective antioxidant packages of protective antioxidant packages in various polyolefin and PVC geomembrane-based formulations resulting in environmental stress cracking and premature material failure (Mills 2011). After a detailed review process and consideration of available materials, the owner selected chlorosulfonated polyethylene (CSPE) for the replacement geomembrane material. CSPE is a highly flexible geomembrane that has been on the market for more than 50 years with a long-established history of proven performance in municipal water containment applications using chlorine and other disinfectants. The CSPE geomembrane material is also noted to have excellent UV resistance and is backed by a 30-year manufacturers weathering warranty. 18 Geosynthetics | August September 2023