Geosynthetic bottom liner system to prevent water migration into solutioned limestone bedrock underlying reservoir
37 million square feet (3.4 million sq m) of 40 mil (1.0 mm) fPP geomembrane and 43 million square feet (4.0 million sq m) of 10 oz (283 g) nonwoven cushion geotextile
The John R. Doutt Upground Reservoir is a 9.2 billion gallon (27.6billion liter) off-stream raw water storage containment reservoir for Columbus, Ohio. The reservoir covers a plan area of 785 acres (314 hectares) and covers primarily farmland. The reservoir area is underlain by glacial till that contains large pockets of high hydraulic conductivity sands and gravels. These permeable materials are about 6 m (20 ft) thick in some areas, which essentially brings the underlying fractured limestone bedrock in close proximity to the bottom of the reservoir. Therefore, reservoir water could seep into the underlying soil and bedrock and increase solutioning of the limestone and possibly destabilize the reservoir. As a result, the designers decided to install a geosynthetic bottom liner system across the reservoir to minimize leakage and connection with the underlying limestone bedrock. The geosynthetic liner system did not extend up to near the embankment crest because the upstream portion of the embankment consists of low hydraulic conductivity soil and could be exposed to ultraviolet light and wave action.
The use of factory fabrication allowed the project to move at a much faster rate and resulted in higher quality seams than what would have been possible with field fabrication, i.e., onsite welding. Because the geomembrane was primarily factory fabricated, 78% of all seams were performed under controlled factory conditions so only 12% of the seams were field welded. One of the biggest project challenges was the shear size of the project and the compacted clayey subgrade when it rained. The relatively flat site simply did not drain surface water, which resulted in ponding and softening of the clayey subgrade. This necessitated re-working of the subgrade and other challenges for the earthwork contractor. Luckily, most of the geosynthetics were installed during dry summer conditions so the factory fabricated geomembrane panels were able to cover a lot of prepared subgrade every day to reduce damage due to rainfall. The fine-grained particles of the clayey subgrade did create issues with the field seaming of the large fabricated panels. The clay particles were so fine that they actually embedded into the geomembrane surface and could not be physically cleaned off before field seaming. This resulted in a 25% of the field seams failing project specifications. Conversely, 100% of all of the factory seams exceeded project seam strength requirements. Therefore, having large factory fabricated geomembranes panels allowed the project to be completed on budget and well ahead of schedule. The Electric Leak Location Survey (ELLS) was also highly effective in locating hidden damage to the geomembrane.
HOW THE USE OF FABRICATION IMPROVED THIS PROJECT
Factory fabricated panels allowed the project to be completed at a much faster rate than was possible if all seaming was performed in the field, i.e., field fabrication. In the summer of 2012, factory fabricated geomembrane panels were being placed at an average rate of 12 panels per day (125’ x 250’ each, 31,250 sq ft or 38.1 m x76.3 m each, 2,907 sq m). That is an average is 375,000 square feet (34,884 sqm) per day in place, tested, and covered with a 10 ounce (283 g) nonwoven cushion geotextile every day for protection. The factory fabricated seams were higher quality, approximately 9% stronger in peel strength and over 9% stronger in shear strength, than what was possible in the field due to onsite contamination of fine-grained subgrade clay particles. For more information on this important project, please see the attached article: Stark, T.D., Hernandez, M.A., and Rohe, D.S.(2020). "Geomembrane Factory and Field Thermally Welded Geomembrane Seams Comparison,” Geotextiles and Geomembranes Journal, 48(4), August, 2020, 454-467, https://doi.org/10.1016/j.geotexmem.2020.02.004.
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The FGI Pond Leakage Calculator Geomembranes v. Compacted Clay Liners
Fresh water is a precious resource with demands rising daily and supply greatly fluctuating. Only two (2) percent of all water on Earth is fresh water with the other 98% being salt water. This 2% of fresh water is comprised of: 87% ice, 12% groundwater, and 1% rivers and lakes. Thus, only 13% of the available freshwater is readily accessible. Therefore, it is imperative that we capture and hold these limited water resources for agriculture, domestic use, and industry and also protect valuable groundwater from surface or subsurface contamination.
The FGI’s Pond Leakage Calculator is a Microsoft EXCEL spreadsheet based on Darcy's Law of Seepage and provides a comparison between leakage rates from a canal, pond, or reservoir constructed with compacted fine-grained soils and a geomembrane liner system. The Leakage Calculator allows the user to input the size of the containment basin (including length, width, depth, side slope angle and freeboard), the anticipated level of hydraulic conductivity of the compacted soil or geomembrane liner, and the relative cost of water in dollars per acre-foot of water.
The Calculator then calculates the volume of the basin in gallons, a comparison of leakage rates between the compacted soil and geomembrane liner systems in gallons, and the cost of the leakage based on the cost of water per acre-foot to replace it. This Calculator is designed to help consultants, engineers, architects, and end users decide how to line their canals, ponds, reservoirs, and basins to capture and/or protect valuable fresh water. The Calculator does not consider variances in construction quality and operational techniques on the long-term effectiveness of the chosen liner system. The FGI has additional research and publications to help with other aspects of successful water containment applications.
Types of Geomembranes Four (4) popular types of geomembranes are available for pond liner systems. These four (4) geomembranes in ALPHABETICAL order are: (1) EPDM, (2) reinforced polyethylene (RPE), (3) Polypropylene (PP), and (4) Polyvinyl Chloride (PVC). EPDM (Ethylene Propylene Diene Monomer) geomembranes are unreinforced and have been used for the construction of ponds of varying kinds. EPDM geomembranes are made from rubber and can be welded together with tape and primer. EPDM can be reinforced or unreinforced. RPE geomembranes have a high tensile strength and puncture resistance because they are reinforced. RPE geomembranes also can be welded with heat. PP geomembranes can be unreinforced or reinforced depending on the application. Reinforced PP geomembranes also have a high tensile strength and puncture resistance because they are reinforced. PVC geomembranes are also unreinforced and have been used successfully for decades in water canals, ponds, and reservoirs. PVC geomembranes can be welded with heat and/or solvents.
Please click below to access FGI’s Pond Leakage Calculator.
Panel Discussion onGeosynthetics CQC & CQA Panelists: Brian Queen ofOhio Environmental Protection Agency; Shannon Goodrich of GO2CQA; TonyaSwitalski of Titan Environmental; Ryan Kamp of Chesapeake Containment Systems Recorded on July 22, 2021
The Fabricated Geomembrane Institute (FGI) is pleased to welcome its newest Associate Member, Alphard Group (Alphard). Alphard is a Canadian consulting engineering firm specializing in industrial projects, construction management, and environmental performance. Incorporated in 2010,Alphard has built a team of engineers, environmental technicians and specialists, as well as a network of collaborators and strategic partners in the industry to offer a wide range of solutions and specialized services.
Alphard is also known for its leak location expertise participating in projects all over the world, and it has developed its own technology in-house for the past 10 years.
Their FGI liaison is Marina Villarroel, Director of International Projects, who can be reached at firstname.lastname@example.org. Please help us welcome Alphard Group to the FGI!!!!