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~I <br />' Construction of the collection pond started in mid August of 1990. The earthworks for the pond <br />were completed on November 21, 1990, and synthetic liner installation started on November 23, <br />' 1990 and was completed in March of 1491. <br />The collection pond grading was done on a cut/fill basis. The west side of the pond consisted of <br />' a fill aaoss the valley floor with a maximum depth of approximately 21.5 ft. The east side was <br />established in cut. The north and south pond slopes were established predominately in cut with <br />' small sliver fills toward the west end of slopes. The pond floor is founded on the alluvial gravels <br />and sands common to the valley floor. No unusual geologic features were enwuntered in the <br />excavation. <br />' The pond crest was raised 2-ft above the design elevation at the request of the earthmoving <br />' contractor. The pond invert was raised a proportional amount to compensate for the differential <br />volume of soils, and the pond capacity volume was held constant. Excess cut materials from the <br />excavation were used to widen the west fill (downstream) and add additional buttressing. <br />' The finish grade of the pond slopes and invert were capped with a 1-ft deep layer of Type 3 liner <br />' bedding material prior to the installation of the liner system. SRK as-built Drawing No. 14711-107, <br />108, and 109 show the fmal lines, grades, and details of the facility and special features. <br />A double lined synthetic lining system was installed on the pond finish grade. 'I~te double liner <br />system contains a primary liner leak detection system. The composite liner system consists of three <br />' separate layers of synthetic materials referred to as the secondary liner, leak detection layer, and <br />the primary liner. The secondary liner (lower layer) consists of a continuous layer of 60 mil I-IDPE <br />liner which overlays the Type 3 liner bedding material. The leak detection layer (middle layer) <br />consists of a layer of geonet which is enveloped by the primary and secondary liners. The primary <br />liner (upper layer) consists of a continuous layer of 60 mil HDPE liner which acts as the main liner <br />' far the pond invert. Details of the liner system installation are discussed in further detail in section <br />4.0 of this report. <br />' The leak detection geogrid layer is tied into a leak detection sump which is located in the southeast <br />corner of the pond invert. The leak detection sump invert is approximately 5.5-ft below the pond <br />' invert and the pond floor is graded to drain to the leak detection sump. The leak detection sump <br />is filled with approximately 1,215 CF of coarse well rounded rock. Field testing indicated that the <br />rock has a void ratio of 0.64 which indicates the pond should have a fluid holding capacity of <br />' approximately 3,545 gallons. <br />t <br />1 <br />13 <br /> <br />