Double Lined Brine Storage Pond for Natural Gas Salt Deposit Reservoir
Below ground double liner containment system to contain brine derived from creation of an underground petroleum reservoir in a salt deposit
1.4 million square feet (130,235 square meters) of 40 mil (1.0 mm) thick Enviro Liner 6040 Geomembrane, 700,000 square feet (65,120 square meters) of 220 mil (5.6 mm) Geonet, 700,000 square feet (65,120 square meters) of 10 oz (283.5 grams) non-woven Geotextile cushion
Salt storage caverns are constructed within deep salt bed deposits by circulating fluid to dissolve the salt deposit. The resulting cavern or reservoir is used to store hydrocarbons and liquefied petrochemicals within the salt deposit. A salt cavern is constructed by dissolving the salt deposits underground and extracting the resulting brine solution and placing it into a holding pond. Layfield was tasked with lining a below ground storage pond in Ontario, Canada to prevent leakage and potential contamination of underlying aquifers. The brine storage pond was lined with a double liner system that consists of a geosynthetic drainage composite encapsulated between two layers of geomembrane. The drainage composite monitors and captures any leakage through the primary or overlying geomembrane and the secondary or underlying geomembrane contains the leakage that occurs through the primary geomembrane.
There were a series of challenges during the design phase for this large brine storage pond including:
1. Selection of geosynthetics and method of fabrication, e.g., factory fabrication v. field fabrication
2. Chemical resistance of the geosynthetics to the brine
3. UV resistance of the primary geomembrane due to the long-term exposure and weathering in this exposed application.
4. Performance of the geonet within the drainage composite when subjected to high compressive stresses and the sediment in the brine solution.
5. Local weather conditions, which included higher than average rainfall, resulted in the site being completely saturated in the fall months, but the owner wanted the pond operational by early Spring of the following year.
Available data from the manufacturer shows that the transmissivity of the geonet is 20 times higher than that of a double-sided drainage composite, i.e., a geonet with two non-woven geotextiles. A drainage composite has at least one non-woven geotextile heat-bonded to the top or bottom of the geonet, which over time can intrude into the geonet causing a reduction in transmissivity. Initial designs included a double-sided drainage composite, i.e., two heat-bonded geotextiles, between the two 40 mil (1.0 mm) thick geomembranes. Layfield proposed just using a geonet to prevent geotextile intrusion and maintain the full transmissivity of the geonet over time. However, questions were raised about the possibility of a flexible 40 mil (1.0 mm) thick geomembrane deforming into the openings of the geonet and reducing its transmissivity or the geonet puncturing the geomembrane at the places where seams of the geonet overlap and create a bump. Layfield simulated this possible puncture situation in the laboratory (see Figure 1a) and the test results show that the geonet overlap did not puncture the geomembrane at the field stresses (see Figure 1b). Based on the laboratory testing, a geonet instead of a double-sided drainage geocomposite was encapsulated between the two layers of geomembrane to create a double-liner system with a leak detection zone for this brine storage pond.
HOW THE USE OF FABRICATION IMPROVED THIS PROJECT
Due to difficult site conditions, Layfield proposed using factory fabricated geomembrane panels in order to: minimize the amount of field welding, increase quality of the seams and final liner system, and meet the short project construction schedule (see Figure 3). Factory fabrication involves welding rolls of the geomembrane into large panels in a controlled environment, which increases seam quality and allows faster seaming. The seam quality is better because the welding is not affected by weather changes, dirt and other impurities in the seam area, and a constant temperature so the welding temperature does not have to be varied. This results in higher efficiency and quality of the seams in the factory than in the field (see Figure 4).
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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.
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 email@example.com. Please help us welcome Alphard Group to the FGI!!!!