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CLOSURE CAP EXTENSION Pre-Approval of Materials The closure cap extension included geomembrane (low density polyethylene - LLDPE) and a ' geocomposite drainage layer overlain by a minimum two feet vegetative soil cover(see excerpted construction drawings). ' An important requirement of the project is to ensure adequate interface shear strength between the geomembrane, geocomposite, and the on-site soils to resist a seismic event that could be expected at this location. To verify adequate shear strength, three separate interfaces were tested: e On-site soils to LLDPE • LLDPE to Geocomposite • Geocomposite to on-site soils (vegetative layer). Because of possible variation between materials produced at different times from the same manufacturer, the County first tested the interface shear strength between typical materials proposed by the Contractor and on-site soils. Testing prior to installation allowed construction to begin on site in full confidence that the materials placed were acceptable. The Contractor proposed Agru 60 mil Double-Sided Microspike LLDPE, and Agru 200 mil Double-Sided Geocomposite. Samples of these materials were submitted on May 1, 2013. These materials were tested at Geo-Logic's Laboratory in accordance with Technical Specifications. Results indicated that these proposed materials would be acceptable (see Appendix). This conclusion was tentative because the tests were performed on typical samples, not the actual material manufactured for the project. ' Final Approval of Materials Finding the typical samples acceptable in the pre-qualifying tests,the Contractor then ordered the ' full amount of each of these materials from the manufacturers for the project. Samples of these materials were collected directly from the manufacturers' facilities and were tested again to verify that the project materials performed appropriately for the project. These materials were also found acceptable (see Appendix). Construction Construction began on May 20, 2013, starting with clearing and grubbing of the area and excavation of the surface to provide the grades on which the closure cap (geofabrics and ' vegetative soil) would be placed. Significant quantities of residue from open burning of refuse (a practice at this location before the County became owner of the property) were discovered during this work(Photo s 1 and 2),potentially causing glass fragments and other unsuitable components to be present on the surface on which the geomembrane was to be placed. To avoid compromise of the geomembrane,unsuitable material was removed from the construction area and replaced Brief Technical Certification Report 2 Department of Public Works/Solid Waste Corral Hollow Closure Cap Extension County of San Joaquin—September 6,2013