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' 4S Collection Pond Liner <br />The collection pond liner installation was started, on November 21, 1990, after the subgade was <br />' tested for density and permeability and accepted for line and Bade. The installation was done by <br />Gundle Lining Systems using 60 mil HDPE and Gundlenet produced by them. <br />' The 60 mil HDPE secondary (bottom) liner was installed continuously over the entire prepared sub- <br />grade. The liner contractor experienced little difficulty in welding the seams using the both the <br />' double hot wedge welders and the extrusion welders. All wedge welded seams were tested by <br />pressure at the air channels. The extrusion welded seams were vacuum tested, for water tight <br />' integrity. Destructive test samples cut by Gundle and tested by SRK were taken at approximately <br />500-h intervals on the seams. Any deficiencies noted were marked and repaired with caps or <br />patches, then re-vacuum tested for water tight integity. Each panel surface, patch or other repair <br />' was inspected by SRK prior to the placement of the leak detection Gundlenet system. <br />' The Gundienet material was placed over the secondary liner continuously from anchor trench to <br />anchor trench. The seams were overlapped and tied at specified intervals with approved plastic ties. <br />The seams were smooth and even when completed. <br />' The sump rock was placed over a rough sheet in the leak detection sump along with the sump leak <br />' detection pipe and covered entirely with the geonet, prior to the deployment of the primary (top) <br />liner. <br />' The 60 mil HDPE primary (top) liner was installed continuously over the entire surface of the leak <br />detection system. The welding was performed by extrusion welders. All of the extrusion welded <br />' seams were 'vacuum tested for water tight integrity, The liner contractor experienced extreme <br />difficulty in maintaining overall integity on the seams, resulting in a greater than specified number <br />of destructive tests and re-tests where seam failure was noted. A large majority of the seams <br />' initially welded were capped then vacuum tested for water tight integity. <br />' All seams and leak detection systems were tied into the anchor trenches or channels entering the <br />collection pond. <br />Three 24-in diameter solution riser sleeves located at the sump, and housing the two water return <br />pumps, were installed on top of the sewndary liner. A rough sheet was placed between the <br />secondary liner and the pipe. After ballast (Type 3 material) was placed beneath and between the <br />three pipes, the primary liner was placed over the top of the pipe and the edges welded in place. <br />Pipe boots were welded in place azound the pipe to insure a continuous sealed liner. Geonet was <br />18 <br />1 <br /> <br />