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1 <br /> <br />Two 24-inch diameter corrugated HDPE culverts were installed in the northeast comer. These <br />inflow pipes collect mnoff from the plant site that is delivered via a trapezoidal ditch. The pipes were <br />' bedded in'/.-inch screened rock. A concrete cutoff' collar was constructed near the culvert inlets to prevent <br />water migration through the bedding material. A 12-foot wide spillway channel 1.5' in depth was <br />constructed in the southwest comer of the pond. Additional earthwork included construction of an access <br />road and surface drainage ditch to direct localized surface tvnoffaround the pond embankment <br />Stockpiled soil was screened to provide subgrade bedding material for the HDPE liner. The minus <br />' 3" screened material was placed to a minimum depth of 6-inches on the pond floor, walls, and spillway. <br />Moisture was added to the bedding using a water truck and then compacted using a smooth drttrtt roller. <br />Bedding material gradation and compaction testing was completed by HP-Geotech, of Glenwood Springs. <br />' Soil testing results are attached as Appendix B. Eighteen compaction tests indicated an average of 89.2% of <br />maximum dry density (ASTM D-1577). All compaction tests exceeded the minimum allowable amount of <br />85% identified in the specifications. Gradation tests results indicated that 20% of fines were available versus <br />the 35% required in the technical specifications. Field approval was given by Colorado River Engineering <br />' for the bedding material based on inspection of the compacted subgrade. Field observations indicated that the <br />20% of fines provided a sufficient amount of cohesive soil material to produce a well "cemented" soil <br />matrix. The compacted bedding material provided a smooth subgrade foundation for placement of the liner <br />' material. <br />Additional earthwork completed after bedding placement included the construction of the liner <br />' anchor trench around the perimeter of the pond crest and a small sump pit excavated in the northwest comer <br />of the pond Floor. The bedding material was re-rolled to eliminate disturbed material. A layer of geotextile <br />fabric was placed in the sump pit to provide a smooth subgrade. The pond subgrade was completed on <br />' March 2, 2000. <br />The earthwork was completed in accordance with the grades and elevations shown on the design <br />' drawings. Appendix-C summarizes survey data collected by Kvaetner Metals during pond construction. The <br />bottom of the pond was excavated into the natural topography with a bottom elevation varying between a <br />high of 6604' at the southern end and a low point at the northern end at the sump of 6601'. The spillway <br />invert elevation is 6611.5'. The depth from the pond spillway invert to the original ground surface elevation <br />' is less than 10 feet along the pond embankment centerline. This structure would be classified as "non- <br />jurisdictional" dam by the Colorado Division of Water Resources as defined in the "Rules and Regulations <br />for Dam Safety and Dam Construction". <br />t The lining installation contractor, Colorado Lining International, mobilized to the site and began <br />work on March 3, 2000. A 60-mil layer of HDPE liner was placed in the pond and on the pond spillway <br />t chute. The liner sheets were welded using a hot wedge fuser and an extrusion rod welder. The joint integrity <br />of all welds was verified by completing air tests on the fusion welds and vacuum box tests on all extrusion <br />welds. The liner was attached to the ADS culverts using preformed HDPE pipe boots and stainless steel <br />' clamps. A second layer of 60-mil liner was tack welded below the culvert outlets to provide splashguard <br />during runoff inflow. Following inspection of the liner installation two additional patches were placed on the <br />pond floor, the spillway liner was cut and seamed to conform to the side slopes, and the northwest comer was <br />reworked to conform to the subgrade. The liner was inspected and found to be free form defects. Attached as <br />Appendix-D is the installation report and certification letter prepared by Colorado Lining International <br />summarizing inspection sheets, material testing, and panel placement locations. Attached, as Appendix-E is <br />' the materials testing report provided by Agru America. <br />1 <br />